Corvair Engines - The Justification Series

ArchiveBot · March 20, 2018, 5:00am

Corvair Engines - The Justification Series

Posted: Tue Mar 20, 2018 10:34 pm

by daleandee

- - - - CONTENTS * * * * * * * *

Preface - http://www.sonexbuilders.net/viewtopic.php?f=9&t=4273&start=20#p32792
Introduction -http://www.sonexbuilders.net/viewtopic.php?f=9&t=4273&start=20#p32837
It’s Legal - http://www.sonexbuilders.net/viewtopic.php?f=9&t=4273&start=30#p32881
Data - http://www.sonexbuilders.net/viewtopic.php?f=9&t=4273&start=30#p32910
LSA Cleanex -http://www.sonexbuilders.net/viewtopic.php?f=9&t=4273&start=50#p32949
Structure History - http://www.sonexbuilders.net/viewtopic.php?f=9&t=4273&start=50#p32988
Design Quality - http://www.sonexbuilders.net/viewtopic.php?f=9&t=4273&start=50#p33013
Performance - http://www.sonexbuilders.net/viewtopic.php?f=9&t=4273&start=60#p33029
Safety (Engine) - http://www.sonexbuilders.net/viewtopic.php?f=9&t=4273&start=60#p33049
Parts & Service - http://www.sonexbuilders.net/viewtopic.php?f=9&t=4273&start=60#p33081
Epilogue -

I would like to begin by posting a statement from Mike when he lamented the sad way we proceed on this list sometimes:

It’s a bit of a shame that we can’t respectfully talk about Corvairs here and share information; please everyone, let’s try to keep it civil.

… and perhaps we can heed his advice and try to be a little more courteous to each other.

We have a thread that is dedicated to Corvair knowledge called “Corvair - General Info” and a lot of great information is found there. But during the course of that thread a question was asked that needs to be addressed. At first my thoughts were to just let this go on by but some off line emails from other builders, some that are considering using Corvair power, as well as those that were curious brought me to rethink that approach. You see it was suggested that my putting a Corvair on this air frame was done without much thought, consideration to the factory warnings, or any research at all.

I took a bit of offense at the unwarranted and rather abrasive way the question was put forth by suggesting that I had used “blatant disregard for the design limits” in my choice to do this and that I only did so because “It’s experimental and I can set any gross weight I want.” None of that is even remotely true.

So after consulting with a moderator for the group and the Foundation I was told that the members of this forum do have the right to post relevant information for the airplanes we fly. After much consideration I have decided that I would begin a thread that will address the question of “justification.” I have no intention of arguing or debating anyone over the information I will share over the next few days. The information I will offer only pertains to me and the aircraft I have built.

But before we get started I have a few questions for the group. Did you know:

More than one Sonex has been flown over the Light Sport Limit of 1320 lbs.?
A Sonex has been flown in excess of 250 mph?
A Sonex has flown several flights with a FWF weight almost double the factory limit?
The Sonex main wing was tested to 9 Gs positive & 4.5 Gs negative and that this information was on their website?
At least one Sonex has an empty weight of 840 lbs.?

Curious,

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 21, 2018 8:28 am

by x3 skier

I’ll be reading your series. No intention to put a Corvair in my Onex but I’m always interested in general aircraft information and Sonex designs in particular.

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 21, 2018 5:26 pm

by lutorm

daleandee wrote:But before we get started I have a few questions for the group.

This is not meant as an argument either way for the Corvair or any other modifications, but I think those questions aren’t really relevant if we’re discussing design modifications.

Let me counter-ask these questions:

How many times did the Space Shuttle fly before the Challenger blew up?
Knowing what we know after the fact, were those flights safe or not?

It’s the nature of statistics that the presence of a Sonex that has flown with twice the FWF weight of the factory limit tells us little. In contrast, the presence of a Sonex with twice the FWF weight of the factory limit that had its engine fall off would tell us a whole lot.

Just so you know where I’m coming from with this: I work at SpaceX. Since I started there, we’ve had two catastrophic failures of orbital launch vehicles. I can’t go into details, but they’ve both been traced to two failures of Helium pressure vessels. They were completely different failure modes, but what they had in common is that we had successfully flown the vehicle numerous times before these anomalies. Everything appeared to work fine, but in reality, due to larger part tolerances than we were aware of, we unknowingly had much less margin than the design aimed for. Eventually, we hit a situation where the variations stacked up against us and many hundreds of millions of $$$ went up in smoke.

The Sonex design has a certain safety margin designed into it. This is meant to account for tolerances in parts, builder technique, turbulence, pilot technique, design flaws, etc. We don’t know what that margin is. John Monnett does, but he’s not going to tell us. What we’re doing when we exceed the design limits is eat into that margin. That may work. It may work fine forever. It may also only work fine until you hit severe turbulence, or do a hard landing, or pull a few extra Gs. You have no way of knowing unless you actually test it.

I think Dick van Grunsven of Vans Aircraft put it well (from https://www.facebook.com/notes/vans-aircraft-inc/what-price-a-masterpiece-by-dick-vangrunsven/237594966250883):

Along with gross weight increases, some builders take the same liberties with horsepower increases and speed increases, betting their lives on the assumption that the airplane is designed with a huge margin of safety—it is really far stronger than in needs to be. This is not really true. Certificated aircraft, and well-designed kit aircraft, are designed to withstand limit loads at specified maximum weights. During testing, they are subjected to ultimate loads, which are higher than design limit loads by a specified margin. Yes, there is a margin between the design and ultimate strengths. But that margin belongs to the engineer. He owns the margin. It is his insurance against the things he doesn’t know or can’t plan for, and the pilot’s insurance against human error, material variations, and the ravages of time. Wise pilots respect this design safety philosophy and leave this insurance policy in effect by operating strictly within established limits. They don’t try to steal the margin from the designers.

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 21, 2018 6:20 pm

by Bryan Cotton

It’s the nature of statistics that the presence of a Sonex that has flown with twice the FWF weight of the factory limit tells us little.

I used to work at Sikorsky. I did a stint in ground test, where we do fatigue test and compare part fatigue strength against flight loads to determine component life. As part of that we assume the parts and construction are all good, and use some statistical analysis to derate the strength of the part to give margins in material properties and build quality. This makes it very improbable that there are failures in the field. But, they happen, both in the past and I am sure in the future too. That is a long winded way of saying I agree with lutorm.

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 21, 2018 8:30 pm

by NWade

Here’s the short-winded way of saying I agree with lutorm: “The plural of anecdote is not data” [Kernaghan & Kuruvilla, 1982]

That quote, BTW, is not a statement about Corvair engines in any way. It is merely the acknowledgement that just because someone has done something, doesn’t mean its smart or advisable. Plenty of people build kit airplanes without understanding aerodynamics or structural engineering; so while we can have open and honest discussions on this forum, we should also be careful not to lead future builders down the proverbial garden path and ignore the compromises and risks in exceeding the design specifications of the airframe.

–Noel

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 21, 2018 11:41 pm

by lutorm

NWade wrote:Here’s the short-winded way of saying I agree with lutorm: “The plural of anecdote is not data” [Kernaghan & Kuruvilla, 1982]

True, but I think the real point is the slightly deeper “absence of evidence is not evidence of absence,”

From a point of reliability, a system can be in one of three states: 1: “has failed”, 2: “has not yet failed, but will at some point”, and 3: “has not and will not fail”. Any amount of data does not help us distinguish between 2 and 3, it just decreases the proportion of 2s by turning them into 1s. The only thing you can firmly conclude is the 1s were not reliable, which is a good lesson but isn’t enough. All you have for the things that have not failed is an absence of evidence of failure, which is not the same as evidence of the absence of failures. This is why data must be supplemented with independent design analysis.

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 8:43 am

by x3 skier

Lutorm discussion of design margin is spot on. Having spent some 50 years in the USAF aircraft development business from the F-111 to the F-22 and F-35, (losing most of my hair and gaining a lot of scar tissue) intruding into the structural or other design margins is not something to be taken lightly.

To this day, I still recall the wing failure in the early days of the F-111 and much later the static test failure of the C-17 wing, as well as many other “oh s***” moments, all of which led to major design changes and revised design guidelines.

Experimental Aviation is wonderful with the freedom to experiment. Just always remember the design is the way it is for some very good reasons and deviating from the design has risks. The bigger the deviation, the bigger the risks may be.

I myself have made and will make some minor mods to my Onex all tempered by my past history and an engineer’s perspective on why the design is the way it is.

Cheers

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 9:43 am

by GordonTurner

…and now, back to our regularly scheduled program…

You guys are all correct, but in my opinion you are overstating the case wrt homebuilt aircraft.

We are starting with a good basic design but we are each building the plane we want. Engineering is by TLAR, construction is by “that’s about as good as I can make it”, and structural materials are hopefully somewhat controlled by taking the stuff with letters and numbers from spruce instead of home (aircraft Builder’s) Depot…

I think the basic engineering of the structure as per the plans is probably pretty well engineered and analyzed, but if you think it’s SpaceX or Boeing I think you’re deluding yourself.

Finally, what seems to kill people in homebuilts is very very few structural failures and a whole bunch of engine failures followed by stall/spin. Unfortunately Dale started off with a few not so relevant statistics, but good intentions. Let’s try and get back to that discussion.

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 10:08 am

by GordonTurner

Basic info about Corvair motors is here:

https://flycorvair.net/2013/12/24/basic … formation/

According to this source, all up flight weight of the Corvair 3.0 liter engine is 220 pounds. That’s firewall forward weight, complete motor and accessories, fluids, baffles mount and cowling. It’s not much heavier than the Jab3300 in a nosewheel configuration. It’s quite likely the same as the full up turbo VW with a nose wheel. The difference in weight is in the realm of a lead acid battery give or take. Engineer it all you want, it fits, it looks about right, and it’s in the ballpark on numbers. Won’t know until I get to the weighing part, but my “analysis “ of the weight and balance spreadsheet leads me to believe I’ll be in the 700 maybe plus a little range and with the Waiex the balance should work out pretty well. I’m thinking I’ll save the battery install until as late as possible and try to tune the balance with that.

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 10:30 am

by kmacht

I agree that the questions posed don’t provide enough data to help with a true risk evaluation. They are interesting data points but doing something once doesn’t mean it will always work or work in every situation.

As far as the other comments, doing the stress calculations for an increase in firewall forward weight is not that difficult. Some of you on here seem to make it sound like it is beyond mere mortals. I have done the stress calculations and am comfortable with what the additional corvair weight does to the airframe and the amount of safety margin remaining. The theoretical has also been proven out by the hours that the 20+ corvair powered sonex out there have put on the airframe/ engine combination. Ideally there would be rig testing with various loads applied at different cyclic rates but that is beyond the realm and financial capability of most home builders. They call it experimental aviation for a reason.

With that being said I do not plan on increasing my gross weight. Doing so is well beyond the simple calculations needed for evaluating an increase in FWF weight. Not increasing the gross weight will limit me in the size of my passengers, baggage allowance, or possibly even fuel quantity at times. Since 90% of my flying is nothing more than hour long flights by myself around the local area this is a compromise I am willing to accept.

Nobody is going to force anyone to switch their powerplant out to a corvair. The aerovee can be made to work as shown by the few hundred out there flying. Every engine combination has tradeoffs. What is important is that you are comfortable flying behind the power plant that is keeping your airborne. For me switching to a corvair makes me the most comfortable. For others it may be the aerovee, jabiru, Rotax, or some other engine yet to be discussed.

Keith
#554

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 12:57 pm

by LarryEWaiex121

Personally, if I were in the market to change engines from, say an Aero Vee to a Corvair, I wouldn’t hesitate in the least. Its not a big design change and if the worry is that just because one hangs more pounds on the airplane, the firewall is going to depart for places unknown; I think that’s completely unfounded.
With care and reason its not something that would bother me in the least. Super Cubs mostly started out with 115 HP. That went to 150 and 180. Obviously, reasoned minds looked at the structure, did some calculations, added what was needed and wallah! No engines falling off or planes falling out of the sky.
What does bother me is this continuous ongoing string of unknown engine failures. Without and answer from the NTSB, or other persons that may or may not have information.
Corvair installs have proven to be pretty sturdy installs and holding up well. That’s completely a different feeling than I had about 5 yrs ago.
I had no confidence in the Corvair as a conversion. I know feel I was wrong on that front.
The Corvair is now a very understood platform and unlike some engines, isn’t strained to the nuts to do what it does.

Larry
Waiex121YX, Camit 3300, Dynon Skyview

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 1:33 pm

by Bryan Cotton

For the record, I like the corvair. Not too keen on some of the opening statements, like flying way past Vne, super high empty weights, double FWF weights, and so on. I wouldn’t want my kid to do any of that. That is one reason it is important to have some balanced discussion. Somebody new may read that and think it is therefore ok to have 400 lbs FWF or to fly 250 mph.

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 4:12 pm

by DCASonex

This debate may be over looking the intended mission one is building their plane for. If intending for a lot of yank and bank aerobatics, while flying over terrain that provides ample emergency landing opportunities, structural and aerodynamic considerations may be of more importance than engine reliability.
and using one of the Sonex supported engines that is within the weight limits seems advisable. However, if doing more “normal” flying, but over inhospitable terrain, best engine may be that one the builder has the most confidence in. Most would like the best of both, but may lean one way or the other depending which mission they feel is the more critical. There is not likely one simple answer to this, but the more information one has available when making a choice, the better.

David A. Sonex TD, CAMit 3300. (Hilltop airport, surrounded by deep valleys and forests.)

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 4:16 pm

by LarryEWaiex121

Bryan,

Not trying to be snippy or split hairs here. I just think that Dale was pointing out the sturdiness of the design. Not implying that he had done all the things on the list.
I’m not an engineer of any type. I went to the design school of hard knocks. Some folks can look at a mechanical project and decide a proper course of action and be very successful at their endeavor. Others can get the best advice and all the best materials and still turn it into a mess.
Countless homebuilders have done amazing builds that others openly scoffed at and condemned roundly.
I would encourage builders to keep an open mind because not everything being discussed here is going way out on a limb.
Experimental design should be responsibly encouraged. We’re getting down to a level where experimentation is frowned upon for no reason other than, “the outcome is not guaranteed”. That in my mind is a cookie cutter world. Manufacturers of kits have a vested interest in no one going off the pathway. For them its all about image and liability. I understand that. They just ask, when your done, don’t call it a Sonex, or whatever kit you started off with. Its a Whizbang 5000, or whatever.
I applaud those that think outside the box and build better mouse traps.

Larry

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 6:47 pm

by lutorm

Just so we’re clear: I’m not at all against experimentation. (The 3D-printed Aerovee intake should make that clear!

But there are facts and there are judgement calls. These are facts:

Exceeding the design limits does eat into the safety margin.
Absence of previous failures is not evidence that there will be no such failures.

If you disagree with any of those two statements, you’re deluding yourself.

Now, these are judgement calls:

What remaining safety margin am I comfortable with?
How many instances of existing modifications, that have not failed, do I need to be comfortable with it?

Everyone’s answers to those will be different, and they will determine how that individual proceeds. But in order to make those judgement calls, you gotta have some data to work with.

If people have actually done their own calculations to conclude that they’re comfortable with the extra weight, please post it for everyone’s benefit.

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 7:00 pm

by rizzz

lutorm wrote:Just so we’re clear: I’m not at all against experimentation. (The 3D-printed Aerovee intake should make that clear!

But there are facts and there are judgement calls. These are facts:

Exceeding the design limits does eat into the safety margin.

Absence of previous failures is not evidence that there will be no such failures.

If you disagree with any of those two statements, you’re deluding yourself.

Now, these are judgement calls:

What remaining safety margin am I comfortable with?

How many instances of existing modifications, that have not failed, do I need to be comfortable with it?

Everyone’s answers to those will be different, and they will determine how that individual proceeds. But in order to make those judgement calls, you gotta have some data to work with.

If people have actually done their own calculations to conclude that they’re comfortable with the extra weight, please post it for everyone’s benefit.

I agree with all of this but I question that if one decides not to allow aerobatics in their plane, is exceeding the FWF limit by lets say 20lbs still “eating into the safety margin”?
Here’s how I see this (I’m not an aeronautical engineer so if I’m looking at this the wrong way, please correct me):
In the Aerobatic Category the plane can be taken up to 6G’s so with an FWF weight of 200lbs, that’s 1200lbs hanging from the nose during those instances.
In the Utility Category the plane can be taken up to 4G’s, so with and FWF weight of 220lbs, that’s 880lbs hanging from the nose.

So are we really eating into the safety margin if we don’t allow aerobatics?
It might be as you say “a judgement call”.

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 8:07 pm

by Direct C51

Who says FWF weight was the limiting factor? When they test for ultimate load they turn the plane upside down and load the wing to 9x aerobatic gross. What does that have to do with hanging an extra 20 lbs on the nose? Did they put 9x200lbs on the engine mount and the structure failed at that point? Maybe a 200 lb artificial limit was placed to ensure the market did not have to be shared with the other auto conversion? Maybe not. I bet Pete Buck would know.

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 9:21 pm

by lutorm

rizzz wrote:So are we really eating into the safety margin if we don’t allow aerobatics?
It might be as you say “a judgement call”.

Sure you are. Then you’re getting some back by imposing more strict operating limitations.

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 9:26 pm

by lutorm

Direct C51 wrote:Maybe a 200 lb artificial limit was placed to ensure the market did not have to be shared with the other auto conversion? Maybe not.

I only know that if I was the designer, and I had decided on a 200lb FWF max weight, I would design the rest of the plane to meet that limit and nothing more, rather than make the rest of the structure artificially heavier and stronger for no purpose.

Strength isn’t free, designs are always tradeoffs.

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 10:29 pm

by rizzz

lutorm wrote:

rizzz wrote:So are we really eating into the safety margin if we don’t allow aerobatics?
It might be as you say “a judgement call”.

Sure you are. Then you’re getting some back by imposing more strict operating limitations.

That’s probably the correct way of viewing this.

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 22, 2018 10:31 pm

by rizzz

Direct C51 wrote:Who says FWF weight was the limiting factor? When they test for ultimate load they turn the plane upside down and load the wing to 9x aerobatic gross. What does that have to do with hanging an extra 20 lbs on the nose? Did they put 9x200lbs on the engine mount and the structure failed at that point? Maybe a 200 lb artificial limit was placed to ensure the market did not have to be shared with the other auto conversion? Maybe not. I bet Pete Buck would know.

Indeed it would be good to know where the 200lbs limit actually comes from.

Re: Corvair Engines - The Justification Series

Posted: Fri Mar 23, 2018 2:02 pm

by dtwolcott

Did anyone think of the fact that if you increase FWF weight that that might impart extra loads on other structural parts of the plan. i.e. elevator loads and subsequent tail cone loads in flight. There is more than structural g loads on the wings that must be taken into account when discuss max gross weight and where it is distributed through out the plane.

Re: Corvair Engines - The Justification Series

Posted: Fri Mar 23, 2018 3:05 pm

by kmacht

If CG is maintained within limits and the gross weight is not exceeded the loads at the tail will be no different that what you are flying with today.

Keith
#554

ArchiveBot · March 20, 2018, 5:00am

Re: Corvair Engines - The Justification Series

Posted: Fri Mar 23, 2018 5:22 pm

by Rynoth

kmacht wrote:If CG is maintained within limits and the gross weight is not exceeded the loads at the tail will be no different that what you are flying with today.

Keith
#554

True, but if FWF weight is exceeded the loads on, say, the fwd fuselage upper longerons, would be higher. Or, the upper/lower engine mount attach angles. Or something else that Sonex engineering keeps in reserve by saying “dont exceed this limit if using our plans”

Re: Corvair Engines - The Justification Series - Preface

Posted: Fri Mar 23, 2018 6:06 pm

by daleandee

Quite an incredible response to my first posting. I want to thank all for the very civilized responses, great thoughts and information shared.
For sure there are some things I take a bit of a different view on but overall it seems that everyone is nearly on the same page.

I want to clarify that my opening questions were not intended as reasons or justifications for the Corvair install (although some of that data comes up later) but rather I seen these facts as things most builders of these airplanes might like to know but most likely did not. Under no circumstances would I suggest that anyone fly a Sonex over VNE (although Jeremy did that on the Turbo video) or over 1320 lbs.

So as an opening or preface let me put a few more thoughts on the list and see what others believe.

The Sonex line of aircraft exist today because a young man built an airplane he called the Monnett Mini, a.k.a the Mini Messashidt, which was a modification of the Parker Jeanies Teenie. Not only that young man but another builder in the mid-60’s purchased a Stits Playboy and modified it by installing a larger engine. Later, he modified the aircraft by installing cantilevered aluminum wings with flaps, creating the RV-1 in 1965. Were these two men showing disregard or disrespect for the designers intent?

I would also ask if it could be said that the factory is showing “blatant disregard for the design limits” of the lowly VW engine by asking an engine designed originally to output 60 HP @ 4400 RPM to now deliver 25% more @ 3400 RPM … and even further disregard the design by adding a turbo to seek 100 HP from this engine. I understand the upgraded racing parts used to build the engine but the case is basically the same and certainly the heads have less cooling area than before with heavier chamber walls and fins removed to add a second plug. Does this work? Appears it does. Reliably so? It appears that the answer to that is not quite as clear as some would like. I try to focus on safety (as I’m certain we all do) within the limits of my budget and abilities. I have to weigh my choices very carefully and determine, what for me is best.

I did consider that in my airplane I wanted the strongest air frame in my price range along with the most reliable power that I could find in an engine that would work on the air frame I choose. I nearly built a Zenith 601 … but I digress. So here’s some initial information:

Many Cleanex pilot fly aerobatics. I don’t.
Most flights are just me, fuel, and baggage and are well under 1100 lbs gross.
Flying smoothly at 1250 lbs. has proven to have no ill effects on aircraft handling and performance is quite good with 120 HP on the nose.
Va speed was reduced.

Here is the preface from the article (please note the disclaimer):

I’ve often been asked why I used a Corvair engine on my airplane and I’ve written many replies. Recently I put on the Builder’s list a set of twenty four (24) extremely compelling reasons why this engine should be considered if you are looking in the area this falls into for power & price. This engine is absolutely, by design, heads and shoulders above anything else in its price range. From crossflow heads to canted valves and the ability to cool itself extremely well, all while being smooth in operation and quite robust by design makes it an exceptional choice for an aircraft power plant.

But the question that was asked that needs to be answered wasn’t about why I put a Corvair engine on this airframe but rather the “justification” for doing so. Many guess at a few of the reasons I did this and some paint with a very broad brush. The purpose of this article is to show clearly that this was not done with any “blatant disrespect” nor was it done in an attempt to fit an engine to an “inappropriate air frame.” There is no intent to criticize or disparage the factory!

Here is the disclaimer: The information I will share in this series is my own opinions, speculations, calculations, and conclusions. I cannot and do not recommend that anyone do as I have done. Following my example could get you injured or killed for which I assume no responsibility. You have been warned. This information is not a license for you to believe that what has worked for me will work for you. I’m not aligned with anyone, or any company. No one has asked me to do this for their profit or their promotion. I’m sharing this so that the “justification” for my personal choice will be known.

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re: Corvair Engines - The Justification Series

Posted: Fri Mar 23, 2018 9:00 pm

by kmacht

Rynoth wrote:

kmacht wrote:If CG is maintained within limits and the gross weight is not exceeded the loads at the tail will be no different that what you are flying with today.

Keith
#554

True, but if FWF weight is exceeded the loads on, say, the fwd fuselage upper longerons, would be higher. Or, the upper/lower engine mount attach angles. Or something else that Sonex engineering keeps in reserve by saying “dont exceed this limit if using our plans”

I was specifically answering dtwolcotts question regarding changes in loads on the tail. As I said in a previous post I have done my own stress calculations on the mounts and associated parts and am comfortable with the margins. I also dont plan on increasing gross weight which would have a much greater impact on the airframe and not sometjing i tried to quantify. Each person will have to make their own decisions as to if they are comfortable enough deviating from the plans.

Keith
#554

Re: Corvair Engines - The Justification Series

Posted: Sat Mar 24, 2018 12:31 am

by WaiexN143NM

hi dale,
good discussion and postings. i am like larry, waiex 121yx, i always was a skeptic of the corvair. no more. its showing good reliability, on the 20 or so mounted on in the community.
at the panther booth i was impressed with the corvair kit.
phil davis plans on having his corvair sonex up from texas this year to osh18. any others?
maybe someone could hold a forum at oshkosh on this subject.

michael.

Re: Corvair Engines - The Justification Series

Posted: Sat Mar 24, 2018 2:08 am

by daleandee

WaiexN143NM wrote:phil davis plans on having his corvair sonex up from texas this year to osh18. any others?
maybe someone could hold a forum at oshkosh on this subject.

michael.

Hi Michael,

When you’re at the Panther booth (SPA) William Wynne’s booth (Fly Corvair) should be next to it. Last year Randy Bush flew his beautiful, recently finished, Cleanex up:

Complete article here:

https://flycorvair.net/2017/08/01/3000cc-cleanex-at-oshkosh-2017/

William has lots of info either doing forums or at his booth where other Corvair powered aircraft will be parked.

I work way too much to get to Osh-Kosh or Sun-N-Fun this year. Retirement hopefully comes soon and life will be different …

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re:Corvair Engines - The Justification Series - Introduction

Posted: Sun Mar 25, 2018 10:47 pm

by daleandee

In talking with a friend over the weekend concerning the ongoing discussion here he said, “like guns, Christianity, politics, etc. you should not be surprised if you don’t change many minds.” My answer is that I’m not here to change the thoughts and beliefs of anyone. This is the same man that made me understand that nobody can make me angry … I have to allow it. Likewise I have no desire to change anyone thoughts as to what they should do. People have to persuade themselves by being willing to consider all that is presented. But my approach is not to suggest that anyone follow what I have done but simply to answer the question of why I did it for myself and how I came to the conclusion I did. So more from the article i.e. the introduction:

Introduction:

Having owned a nose roller version of this air frame with a VW conversion I learned some lessons about what I liked and didn’t like about the air frame and engine combination. I finished the build on this first one though it was mostly finished when I purchased it. The VW engine did require removal and disassembly to correct some assembly errors. I flew it for five years and 175 hours. The lessons I learned that I share here are only as they apply to me, my particular situation, and my expectations as to what I consider to be acceptable, safe, & reliable.

I adore the air frame. The elevator is lighter than the ailerons so the control harmony is not completely balanced but the controls are quite light and the airplane is a real pleasure to fly. Some have compared it to an RV series and some have labeled it “the poor man’s RV.” The rudder has gobs of authority and the airplane slips very well. Flaps are quite effective and the plane will fly rock steady to some pretty slow speeds. Stalls give ample warning. It is a sporty airplane that has to be flown most all the time unless you are using a wing leveler or auto pilot. Cruise speeds allow for cross country options.

I have concerns with the factory supplied engine and carb system. No reason to go into detail as to what I don’t care for about their system as it does work for some, but it just didn’t fit what I wanted or needed in a power plant.

The tail wheel version is my preference although the nose roller version was fun. The tail wheel tends to get more stares and respect at fly-ins and fuel stops. There was the challenge of learning to fly tail wheel that was intriguing also. Having flown in two tail wheel versions and getting a taste of what 120 horsepower would do when out on the nose of this airframe I knew what I wanted but I didn’t have Jabiru money. In retrospect I’m extremely glad the Corvair is on the nose.

The Corvair was an option that I could afford but it was not, is not, and will never be, factory supported. I read the warnings and the literature from the manufacturer and then began to dig into all the facts and data surrounding the install of a Corvair engine on this air frame that I could find. I’ve had some private & semi-private conversations with manufacturer personnel and other designers that will be kept confidential. I will share as much as I can. Most of the facts (given in question form) that were shared in my opening post are available by a thorough search of the available data from the company themselves. In doing this research I discovered multiple “justifications” for using this engine & air frame combination. These I would like to share, one at a time as I list them in the days to come and leave room for group discussions. My reason for giving these validations is to put forth a response to the question of what “justifications” I have for doing what I did. So to follow, in no particular order, are the answers.

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re: Corvair Engines - The Justification Series

Posted: Mon Mar 26, 2018 10:06 am

by Gordon

Corvair Information Justification

Dale…just to let you know there are some of us reading these posts that DO LIKE your opinions and experiences with the Corvair. More information and options are a good thing.

Since I have a Onex the Corvair is not in my future (a bit too heavy) and a 3300 Jabiru would be great but a bit too heavy in price…I have the Hummel 2400 85 hp.

Don’t let the naysayers discourage your “subject matter”…we should all be open to other options. Maybe someday some of us will take the same road as you have…never say never.

Gordon…Onex…Hummel 2400

Re: Corvair Engines - The Justification Series

Posted: Mon Mar 26, 2018 11:33 am

by LarryEWaiex121

Dale,
I’m not worried about the nay-sayers. I’m certain you got your big boy pants on and I’m prepared to hear the fun stuff.
I love hearing about experimentation in a “cookie cutter” world as I’ve previously opined. Especially when it leads to trade-offs that actually improve your safety record. I believe this engine improves the overall Sonex statistical record? Time will tell.

Larry
Waiex121YX, Camit 3300, Dynon Skyview

Re: Corvair Engines - The Justification Series

Posted: Mon Mar 26, 2018 10:07 pm

by daleandee

LarryEWaiex121 wrote:I’m not worried about the nay-sayers. I’m certain you got your big boy pants on and I’m prepared to hear the fun stuff.
I love hearing about experimentation in a “cookie cutter” world as I’ve previously opined. Especially when it leads to trade-offs that actually improve your safety record. I believe this engine improves the overall Sonex statistical record? Time will tell.

Hi Larry,

Appreciate the vote of confidence. At the end of the day i don’t believe I have much to give that isn’t already known. Those that have done some research and looked at the available data already know as much or more than I know. As far as improving the safety record … you’re getting ahead of me as some others have already done. 8~)

But here is another brave Corvair flyer that posted some remarks about his airplane on another thread and I wanted to tie them into this one. Here is a pull quote:

This is the engine the airframe needs. I fly at 150 mph on 6 gal/hr with 10 gallons additional in the wings. I licensed it at 1320lbs and have flown all the 40 hours at that weight after the first few flights. It stalls at 44 indicated with flaps. and 50 clean. I fly it out of a grass strip 2800 feet with 50 foot trees either end.

Mr. Lee’s complete post is found here:

https://sonexbuilders.net/viewtopic.php?f=21&t=4217&start=10#p32864

I have flown with him in this plane and we flew off of his strip as he describes it. No worries! I was quite impressed with the man and his machine. Here is a photo and a link to Ed’s build in Kitplanes:

https://newsline.kitplanes.com/2017/05/23/ed-lee-sonex/

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re: Corvair Engines - The Justification Series - It’s Legal

Posted: Tue Mar 27, 2018 6:21 pm

by daleandee

It is an experimental airplane! That’s not an excuse but rather a fact. While some these days are arguing over what rights the citizens have (we’ll leave all of that for another day) I thank God that I still live in a country where I have the freedom to experiment with building my own airplane. That’s why these airplanes are called “experimental.” It’s written on the wing and the Air Worthiness Certificate! As builders we have the right to use our ability to search, seek, scrounge, learn, succeed, fail, and strive by experimentation, to see what we can accomplish, and to develop the end result that we desire. We gather the things that we believe will fit the purpose for which we intend to use them. If we fail the pain is ours, if we succeed we humbly ask that others respect what we have done.

Consider that the Cub has a “Super Cub” in the family and that the RV’s have a close kin called the “Rocket.” Many true scratch built (think Pietenpol as an example) experimental aircraft designs have undergone changes due to the fact that it is allowed. With this air frame there have been numerous engines used i.e. VW, Jabiru, CAMit, Corvair, Honda, Rotax, UL Power, Continental, and others.

Some may remember when the Rotax was forbidden because it violated the factory mantra of KISS? Now it’s allowed. At one time the idea of hydraulic brakes were that they were not needed as the machined drum brakes were adequate. But now the factory sells hydraulic brakes. Electric flaps were unnecessary and added weight but they wound up on the new B model. This is not to disparage the factory but rather to make a point about the guys in the field (i.e. the customers) that like to experiment and discover things that work well for them. Sometimes the manufacturer gets it too.

Are not the designers of this air frame lifelong Experimental Aircraft Association members? Do they believe in the EAA motto of “learn, build, and fly?” Some have questioned whether the gross weight or FWF weight increase was done with “blatant disrespect” or without forethought and was simply just fitting an engine to an “inappropriate air frame.”

Those types of questions seem a bit unusual when they come from those that sell experimental aircraft to experimental builders that have the privilege, yes even the right, to build as they see fit. The air frame manufacturer themselves are still “experimenting” with making the VW engine work with a turbo on it. Should they be told that they are showing “blatant disrespect” for the designers of the little VW engines? No! It’s their right to experiment. Experimentation has gotten us where we are today. But please don’t think that some have the right and others don’t because it is also my right to experiment as I see fit. To choose what meets my standards and what does not.

The answer to these questions is “no.” I didn’t just blindly walk into this combination but after much research in many areas, searching history, comparing notes and careful consideration I decided to “experiment” by putting a Corvair engine on this air frame. Again I clearly say “no” I didn’t assemble the combination just because I could … but if that was my only reason, it should suffice as I have the “right” to do so!

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re: Corvair Engines - The Justification Series - It’s Legal

Posted: Tue Mar 27, 2018 10:24 pm

by lutorm

daleandee wrote:I didn’t assemble the combination just because I could … but if that was my only reason, it should suffice as I have the “right” to do so!

I don’t get your point. Yes, you have the right to do so. As far as I know, no one has indicated otherwise. But everyone on this board also has the right to say whether they think it’s a good idea or not.

I have the right to do many things that would be incredibly dumb to attempt, and should I ever delude myself into otherwise, I’m hoping people around me will set me straight. And if I can’t make a convincing argument to the contrary, more than "I have the right to… ", I will hopefully concede that, just maybe, I should reconsider.

As an aside, I’m also a member of the canard aviation discussion forum. We had a member who bought a Cozy and proceeded with airframe modifications that knowledgeable people told him was a bad idea. They found his body strapped into the seat floating around in the Ocean after entering a deep stall during Phase I testing. He was convinced he knew what he was doing, but it turns out he did not.

Every time a thing like that happens, we’re get closer to losing those freedoms that you hold so dear. So, apart from just being the moral thing to do, keeping people from doing stupid stuff is something that is in everyone’s interest.

Since you say you have done much research and careful consideration, how about you convince us with evidence instead? I’d love to see it.

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 28, 2018 9:40 am

by dbdevkc

I have the right to do many things that would be incredibly dumb to attempt, and should I ever delude myself into otherwise, I’m hoping people around me will set me straight. And if I can’t make a convincing argument to the contrary, more than "I have the right to… ", I will hopefully concede that, just maybe, I should reconsider.

I don’t want to minimize the impact of putting 20lbs over the factory stated limit FWF. I have noted however that it was done successfully by a designer of another kit aircraft, and he continues to this day to help others do the same by producing parts necessary for the conversion. Obviously, W&B issues can be solved, and if the pilot is a lightweight person, max gross might not be an issue either. Note that the B model has the capacity for an additional 24lbs of fuel. I am well aware of the factory gross weight advisory, and here is the key paragraph:

Additionally, operating at gross weights above our published limits degrades the aircraft’s performance (climb rate, take-off/landing distance, stall speed, etc. may be affected) and reduces the margin of safety when G-loads are experienced. Airframe components may also see increased wear or reduced service life as they are subjected to loads for which they were not designed.

So what if with the extra 20lbs you are not over 1,150lbs max gross?

There are other things being done outside of the original design and written about here that don’t seem to even raise the slightest bit of concern. Folks talk about moving the battery back to the tail, adding auxiliary fuel tanks to the wings, the baggage area, even the passenger seat. But this is the one that seems to be considered incredibly dumb to attempt.

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 28, 2018 10:09 am

by petep

Gentlemen,
I think it is high time that we put away this thread as it will only become more arguemental over time. I have been active in the home built community for over 50 years and remember watching builders all but come to blows over the use of marine grade plywood verse aircraft grade plywood on Flybaby projects. Guess what, there was no common ground found then as there will likely never be any found on the Sonex engine argument.

If you choose to put a 4,000 HP T56 turbine engine on the nose of a Sonex and can get a DAR to sign it off then it is your option and your posterior you are betting on. At the same time it is no one else’s business if I chose to put a lawn mower engine on my project. Please remember that it is a short trip between unsolicited advice and a outright argument. Put this thread to rest and proceed as gentlemen builder and respect the decisions of others no matter how much or little sense they make to you because it likely makes good sense to them.

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 28, 2018 1:18 pm

by vigilant104

Dale,
Can you share the reasoning/calculations you used and the assumptions you made as you decided to go ahead with the Corvair? You are obviously happy with it (and other Cleanex owners feel the same way), but the typical exchange of ideas on this topic could benefit a >lot< from some background on how the decisions were made. Opinions (on all sides) tend to lead to unresolveable squabbles/differences if the underlying assumptions and reasoning aren’t clear. More importantly, spelling things out is more likely to enlighten a wide audience of Sonex builders, allow them to benefit from your efforts, and help them reach their individual conclusions.

Here’s something to get us started (an easy one!): How much will increasing the weight of a Sonex increase the stall speed? That was addressed in a previous thread (https://sonexbuilders.net//viewtopic.php?f=21&t=186&p=1369&hilit=stall#p1369, which contains the math). If my numbers there are right, and if the Sonex LLC published clean stall speed of 46 MPH at 1150 lbs is correct, then a 1320 lb Sonex should stall at 49.3MPH, or 43KCAS. The LSA rules specify a clean stall speed of 45 KCAS, so even a Sonex at full LSA max weight would meet the stall requirement, by these calculations. Now, that is NOT to say that flying this heavy is a good idea, and it obviously doesn’t address important structural factors, ROC, stall/spin behavior and recovery, etc, etc. Aerodynamically, it assumes that the CG doesn’t change with the increasing weight–which may be important. If, instead, we load up the nose with weight, then the downward force required at the tail goes up, and that will increase stall speed.

I’m not sure what your plans for future installments of this thread may hold, but it would be interesting to see reasoned/reasonable discussions of:
– Engine reliability factors. The Corvair has some attributes that are significantly different from the Aerovee, and if these offer improved reliability then that is worth knowing.
– Structural considerations (local–engine mount. FWF/firewall to CG loads. Airframe-wide loads (tailcone/etc).
– Aerodynamics (esp impact on spin recovery from with higher inertial loads).
– ROC comparisons (this has a safety aspect, obviously)
etc.

Obviously, not everything can be based on hard calcs, but if we show the logic trail, lay out the assumptions specifically, and identify where we are using empirical information (i.e. “this has worked elsewhere, and here’s why it is reasonable to apply it here”) then I think we’ll all learn a lot.

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 28, 2018 2:21 pm

by lutorm

petep wrote:I think it is high time that we put away this thread as it will only become more arguemental over time.

I disagree, I think there’s been a fairly constructive exchange of views here, and I’d really like to know the details of Dale’s decision. Like I said before, I’m not at all opposed to experimentation, although I disagree with some of the arguments that have been put forth. I don’t think that’s reason to stop discussing. Even if we won’t reach agreement, having all the arguments out there can only benefit others making their own decisions.

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 28, 2018 3:46 pm

by LarryEWaiex121

When someone has “nothing” to bring to the party and continues to debate something that is real vs. something that is speculative, into perpetuity; I call that being a troll.

Larry
Waiex121YX

)

ArchiveBot · March 20, 2018, 5:00am

Re: Corvair Engines - The Justification Series - Data

Posted: Wed Mar 28, 2018 5:51 pm

by daleandee

I’d like to take a moment to thank the moderator for allowing this thread on here and to everyone of you for working to keep it civil. For certain there is a lot of passion. I get that but I do trust that everyone will show a bit of patience as we have a very long way to go. My last post wasn’t meant to offend in anyway but rather to set up the narrative that it is legal to do what I have done.

At the beginning I said that it wasn’t my purpose to change anyone’s mind or to argue but rather to answer the question of what justification I had for what I did. I admitted then and again now that i might be completely wrong and that if you do what I did it could get you injured or killed. I also want to offer an apology as many both online and off line are asking for numbers. Perhaps I didn’t make clear that this would be quite a journey in going through a lot of information and that it wasn’t possible to give it all in one or two posts. I see Mark has posted some stall speed info (thanks) and while I want to look at numbers (data) this time we won’t get that far. I suspect that many of you will be able to help me better understand the information I have to share.

So please feel free to reply. You don’t have to agree and are more than welcome to disagree. I only ask that you do so in a professional manner. If you have information to share or a better way forward please share. But I ask again that we be adults and resist the temptation to snipe at someone else or show a condescending attitude. I thank you all.

Someone pointed out the factory notes on weight increase:

Additionally, operating at gross weights above our published limits degrades the aircraft’s
performance (climb rate, take-off/landing distance, stall speed, etc. may be effected) and
reduces the margin of safety when G-loads are experienced. Airframe components may
also see increased wear or reduced service life as they are subjected to loads for which
they were not designed.

This is absolutely correct. If you raise the gross WITHOUT adding power to compensate, performance will be degraded. Increasing horsepower by >30% will take care of that though! 8~) You will reduce your margin of safety. But the questions are … how much margin is there? How much am I losing? Is it still safe? Am I comfortable with the trade off?

Check the numbers! The factory has a display wing on the wall that was touted at the builder’s seminar many years ago as bending at 9 Gs. Their web site at one time had a page showing the failure test numbers for the main wing. Don’t see it on their site anymore but here is a copy from the Zenith site:

Using these numbers (+9/-4.5) as our baseline we will get +6.0/-3.0 with a safety margin of 1.5 at aerobatic weight. Keep in mind that when doing these calculations the weight of the wings is subtracted as they are “self-supporting.” IIRC the Sonex wing weighs about 70 lbs. each for a total of 140 lbs. That amount is taken from our flight load calculations. Our new aerobatic load limit weight will be (950-140=) 810 lbs. for +6.0/-3.0. What about the slight gross weight increase to 1250 lbs.? This equates to ~ 8% increase. The G-ratings for the air frame at aerobatic weight leaves abundant margins when the numbers are compared to the slightly higher gross of 1250 lbs. Using the 9-G rating attained at aerobatic weight we still have ~+6.6/-3.3 for ultimate loading at the higher gross. (Remember to subtract the weight of the wings from your calculations as they are “self-supporting”). This gives a load limit at 1250 lbs. gross of +4.3787/-2.189. The factory gives two up a load limit of +4.4/-2.2 at 1150 lbs. (although I get +4.8/-2.4) and know that even at their lower numbers the load limit would still be greater than +4.0/-2.0 load limit when the gross is increased by 100 lbs. to 1250 lbs. So the factory numbers agree, by testing, that the airframe retains acceptable margins with a modest gross weight increase to 1250 lbs. & still meets ASTM G-load rating standards for factory built sport planes (+4.0/-2.0) even though that isn’t required for experimental aircraft.

How the FWF weight increase fits in here will be looked at in another section but for now just consider the structural loads that are imparted using a 200 lbs. FWF weight at 6 Gs compared with the loads of a 250 lbs. FWF weight with 4 Gs. Which load stresses the air frame more?

The air frame is stoutly built! A recent poster showed that the FWF weight of the Jabiru 3300 fully installed was 215 pounds & the Corvair at 255 pounds. It was suggested the Corvair adds 20 lbs. to the FWF weight but it’s more like 30-35 lbs. No doubt a VW conversion with steel cylinders, turbo, 2nd oil pump, 2 oil filters, lines, air/oil separator, exhaust wrapping, heat shield, water pump, electric fan, hoses, radiator, coolant, wiring, switches, etc., is near or over the strict FWF limit while the newer/lighter Corvair conversions will be ~15-18% FWF weight increase over the Jabiru 3300. Keep in mind that some additional weight on the nose helps combat the rear CG issues some have experienced when lighter engines are used.

The factory web site has a note about how the accumulation of test data for these aircraft was done i.e. “load testing using procedures prescribed by FAR part 23.” So the wing and the air frame are good to +6/-3 Gs at aerobatic weight.
As it has already been pointed out; the small increase in gross weight has a minimal effect on the tail as long as the CG is correct for the aircraft. It is the main wing that carries the load. My inspector was quite thorough with me in all aspects regarding the numbers I had regarding gross weight W/B & C/G and how I arrived at the numbers I had.

There is so much more that can be given to this one part of the discussion. Again I ask that those that reply please do so in a polite and professional manner.

PS: Apologies for the hurried post and possible bad calculations … need more coffee!

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 28, 2018 8:15 pm

by Gordon

Regarding Dales Many Comments…

Gezz Dale…calm down my man…your getting a “bit intense”…approaching “a rant” even.

Just kidding…to be clear, you have made some good points…so I am not going to add to the “mix”.

Evidently some folks don’t agree…and that’s fine. With all the information flowing from different points of view there are always a few “nuggets” in there that we can all learn from.

Your “Corvair Justification Series” is just fine with me.

Gordon…Onex…Hummel 2400

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 28, 2018 9:17 pm

by vigilant104

Dale,
As you note, the Sonex LLC acrobatic max weight is given as 950 lbs, and you presumably take no exception to that as being appropriate. That already takes into account whatever the wings weigh. If we are flying acro and have a 180 lb pilot (that’s with clothes, headset, etc) and just 50 lbs of fuel, our maximum empty weight will be 950-180-50 = 720. So, if we build a plane that weighs more than about 720 lbs empty (regardless of engine type, etc), it is, for practical purposes, incapable of safe flight at +6/-3Gs (the FAA standard for the acrobatic category).
Unless somebody can/has built a Cleanex with an empty weight of less than 720 lbs, all of them are and will be non-aerobatic, right?
That’s fine, I know you mentioned that you didn’t fly acro in yours. Lots of people enjoy their Thatcher CX4s, Cessna 152s, RV-12s, etc and never miss flying acro. But if mounting a Corvair means that acro is off the table, then we should just specifically note that as we press ahead.

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 28, 2018 10:31 pm

by rizzz

vigilant104 wrote:Dale,
As you note, the Sonex LLC acrobatic max weight is given as 950 lbs, and you presumably take no exception to that as being appropriate. That already takes into account whatever the wings weigh. If we are flying acro and have a 180 lb pilot (that’s with clothes, headset, etc) and just 50 lbs of fuel, our maximum empty weight will be 950-180-50 = 720. So, if we build a plane that weighs more than about 720 lbs empty (regardless of engine type, etc), it is, for practical purposes, incapable of safe flight at +6/-3Gs (the FAA standard for the acrobatic category).
Unless somebody can/has built a Cleanex with an empty weight of less than 720 lbs, all of them are and will be non-aerobatic, right?
That’s fine, I know you mentioned that you didn’t fly acro in yours. Lots of people enjoy their Thatcher CX4s, Cessna 152s, RV-12s, etc and never miss flying acro. But if mounting a Corvair means that acro is off the table, then we should just specifically note that as we press ahead.

I’m not sure that staying below 720lbs with a Corvair is that unachievable based on my experience:

My Sonex weighs 665lbs empty,
It has a 2.4L VW engine and itcertainly isn’t the lightest VW you can build (it has a heavy Bendix dual magneto and a full flow oil filtering system).
My aircraft is also painted, but I’ve kept everything else as light as possible.

If I had built the exact same aircraft but with a Corvair engine, would that really have increased the weight by more than 55lbs?

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 28, 2018 10:31 pm

by daleandee

vigilant104 wrote:That’s fine, I know you mentioned that you didn’t fly acro in yours. Lots of people enjoy their Thatcher CX4s, Cessna 152s, RV-12s, etc and never miss flying acro. But if mounting a Corvair means that acro is off the table, then we should just specifically note that as we press ahead.

Hi Mark,

No, I don’t fly acro. Dan Weseman did in his but he built a very light polished tail dragger and his empty weight was listed at 699 lbs although I seem to recall that it was revised up a bit later. So in keeping the acro limit at 950 lbs you are correct that the build weight with the Corvair would have to be carefully watched. So while I wouldn’t put acro off the table with a Corvair there are two caveats, 1) a light build and 2) a pilot that is somewhere close to an FAA sized guy (< 200 lbs).

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re: Corvair Engines - The Justification Series

Posted: Wed Mar 28, 2018 11:20 pm

by vigilant104

rizzz wrote:I’m not sure that staying below 720lbs with a Corvair is that unachievable based on my experience:

My Sonex weighs 665lbs empty,
It has a 2.4L VW engine and itcertainly isn’t the lightest VW you can build (it has a heavy Bendix dual magneto and a full flow oil filtering system).
My aircraft is also painted, but I’ve kept everything else as light as possible.

If I had built the exact same aircraft but with a Corvair engine, would that really have increased the weight by more than 55lbs?

I’m not sure. 55 lbs sounds like a lot, but two more jugs, two larger heads, a longer crank, a case that is long enough for two more cylinders, two additional pistons, conrods, more oil, etc-- is surely going to weigh something.

Scott Casler’s site says his 2400cc engines max out at 167 lbs.
Here (https://sonexbuilders.net//viewtopic.php?f=9&t=4273&p=32910&hilit=pounds#p32910 ) Dale cited another builder’s Corvair FWF weight as 255 lbs, which is the highest Corvair weight I recall seeing.
255 lbs - 167 lbs (Hummel/Casler) = 88 lbs more. This is almost certainly an apples/oranges comparison.

I thought most of the Corvairs were coming in at about 220 lbs. 220 lbs - 167 lbs (Hummel/Casler) = 53 lbs more. That seems reasonable, and is darn close to the 55bs additional you cited. If that increase is right, then you’d still be okay to fly acro in your present aircraft --if you didn’t weigh more than 180 lbs (with clothes and gear) and you don’t have more than than 50 lbs of fuel aboard.
In these comparisons, a lot depends on what is included in the weight. Induction?? Exhaust? FWF including engine mount? Oil? At any rate, it is sure that some planes fitted with an Aerovee now will be over the aerobatic weight limit if the same plane and pilot are flying behind a Corvair that weighs 50+pounds more. OTOH, as Dale points out, the difference between the Corvair and some of the other (heavier) engines that Sonex supports will be less.

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 29, 2018 12:13 pm

by samiam

Dale - Thanks for the series. We need to have this discussion and share the information. Despite quoting me on your opening post, I’ve resisted posting again until now.

Perhaps the ONLY possible objection that everyone has to the Corvair engine is its weight, and there is very little REAL information available out there on it. All comparisons are very apples to oranges.

I’m building a top-of-the-line Corvair with all lightweight parts. I’m using the billet crank which is about 8 pounds lighter and the 3.0L displacement which is also lighter. When I finish later this year, I plan to weigh it. The “dry weight” of a Camit 3300 is 182 pounds. I don’t think the weight difference will be as dramatic as some think. However, until we have these specific numbers, everything else is just conjecture.

As for the whole argument itself: I simply ask myself what the more common risk is in aviation - airplanes falling apart in midair, or their engines failing in midair.

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 29, 2018 2:13 pm

by GordonTurner

Right on Mike.

My 3.0 with billet crank is sitting in the coffee table in the middle of the living room waiting for the rest of the project to catch up. If i had some way to weigh i would. I’ll think about that one.

Gordon

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 29, 2018 2:52 pm

by WaiexN143NM

hi all,
just for reference, we weighed our cont. O-200A this am. dry weight, at 200 lbs. slick mags and harness, ms ma3spa carb and carb heat /air box,spin on oil filter, lite wt b&c starter & 30amp alt.
so no motor mount, baffeling,oil, prop, spinner, cowling,oil cooler, battery ,muffler. another 25-30 lbs?
so estimating 230 full up fwf.
this engine we built up for our zenith cruzer.

waiexN143NM
michael

Re: Corvair Engines - The Justification Series

Posted: Thu Mar 29, 2018 5:23 pm

by daleandee

vigilant104 wrote:Dale cited another builder’s Corvair FWF weight as 255 lbs, which is the highest Corvair weight I recall seeing.

As many have now commented on the FWF weight and the differences I think I may be able to clarity this a little. My Engine (3.0) was 218 lbs. The newer ones should weigh a little less as the new starter takes off 3 lbs. and the newer billet crank is lighter also. I can’t say exactly but 210-212 might be in the ballpark. What Dan was referring to is the real honest FWF weight of the install. That’s what I was driving at when I mentioned the Turbo VW motor.

The Jabiru 3300 weighs 180 but the installed weight is 215 lbs. which is 35 lbs higher. If an older Corvair at 220 lbs. is installed the FWF weight would be somewhere about 255 lbs. Newer Corvairs will save about 10 lbs. So what we don’t know is the true FWF weight of the Turbo VW motor which includes everything forward of the firewall. It would be helpful to know that number when ALL the parts are put together and weighed. That’s what SPA did in order to get real numbers for the Corvair.

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re: Corvair Engines - The Justification Series

Posted: Fri Mar 30, 2018 6:22 am

by peter anson

The Jabiru 3300 weighs 180 but the installed weight is 215 lbs. which is 35 lbs higher.

What do you think needs to be added to a 3300 Jab that weighs 35 pounds? The engine weight is quoted with everything except oil which is probably about 7 pounds. I’m pretty sure my oil cooler doesn’t weigh 28 pounds. I remember when I did the original weight and balance thinking “Phew, that was close”. My Sonex is all painted, but if the engine had been any lighter I would have had to hang weights on the nose. The initial weight was just 666 pounds (bit of help from the devil there).

Peter

ArchiveBot · March 20, 2018, 5:01am

Re: Corvair Engines - The Justification Series

Posted: Fri Mar 30, 2018 9:37 am

by radfordc

peter anson wrote:

The Jabiru 3300 weighs 180 but the installed weight is 215 lbs. which is 35 lbs higher.

What do you think needs to be added to a 3300 Jab that weighs 35 pounds? The engine weight is quoted with everything except oil which is probably about 7 pounds. I’m pretty sure my oil cooler doesn’t weigh 28 pounds. I remember when I did the original weight and balance thinking “Phew, that was close”. My Sonex is all painted, but if the engine had been any lighter I would have had to hang weights on the nose. The initial weight was just 666 pounds (bit of help from the devil there).

Peter

I’m sure he is talking about FWF weight. Engine mount, baffles, wiring, battery, etc.

Re: Corvair Engines - The Justification Series

Posted: Fri Mar 30, 2018 4:15 pm

by Gordon

The Weight Debate…?

That one post mentioned an O-200 Continental weighing in at 200 lbs for his Zenith. Apparently Lycoming has an 0-233 (a light weight 0-235) that scales in at 199 lbs.

I would love to have either one of those engines in my Onex if somebody made an engine mount for it. There are a few 3300 Jabiru’s in Onex’s but there lies the same problem…no readily available engine mount.

I think that would be a much more reliable setup than the Turbo AeroVee in a Onex…just saying.

Gordon…Onex…Hummel 2400

Re: Corvair Engines - The Justification Series - LSA Cleanex

Posted: Fri Mar 30, 2018 8:27 pm

by daleandee

Can a Cleanex (Model C = Corvair/Sonex) be flown by a pilot with a Light Sport Certificate? Let’s look at the regulations for Light Sport compliance and see how it fits.

Maximum take-off weight less than 1320 lbs. Yes Gross @ 1250 lbs (8.7 % increase from standard).
Maximum airspeed in level flight with maximum continuous power (Vh) of not more than 120 kts (138.1 mph) CAS under standard
atmospheric conditions at sea level. Yes 138 @ 2950.

More clarification on this point - Keep in mind that as the engine builder you are allowed to limit RPM (as the factory did with the Jabiru 3300-L engines) and use a climb prop instead of a cruise prop to limit cruise speed.

Maximum stalling speed or minimum steady-flight speed without the use of lift-enhancing devices (VS1) of not more than 45 kts (51.8 mph)
CAS at the aircraft’s maximum certificated takeoff weight and most critical center of gravity. Yes Clean Stall @ 48 mph – Full Flaps 42 mph.

Because stall speed is critical for LSA compliance we need to take a closer look. Everyone agrees that the factory numbers are correct for the stall speed of the air frame. Mark has already posted the formula for computing this:
Vs new = Vs old weight x √(new weight / old weight). Using this we arrive at the higher stall speed number with a known increase in gross weight and see that a clean stall of 46 mph/CAS at 1150 lbs. will be < 48 (47.9) mph/CAS at 1250 lbs. and well under the 51.8 mph/CAS allowed for light sport compliant aircraft.

There is another rule of thumb that can be used: “If weight is reduced by 10% from MTOW then Vs will be reduced by 5%, and conversely, if weight is 10% over MTOW then Vs will be 5% higher —“
So if the weight is increased by 8.7% then Vs will increase by 4.35%. That would give us 46 X 4.35% = 2.001 + 46 for a new Vs of 48.001 and still well below the light sport limit. Both of these methods confirm Mr. Lee’s flight test numbers of stall at 1320 lbs gross being 50 mph (math gives 49.3 mph). I’m not suggesting that this is a good idea at all … just sharing some math.

Maximum seating capacity of no more than two persons, including pilot. Yes
A single, reciprocating engine, if powered. Yes
A fixed or ground-adjustable propeller if a powered aircraft other than a powered glider. Yes
A nonpressurized cabin, if equipped with a cabin. Yes
Fixed landing gear, except for an aircraft intended for operation on water or a glider. Yes

Note: It has been suggested that the higher wing loading might take a Cleanex out of Light Sport compliance. There is no FAA mandated wing loading number given for compliance of any Light Sport Aircraft. Still, if there were such a requirement, the FAA has already certified a higher wing loading LSA than found on a Cleanex at 1250 lbs.

There’s always more number crunching that can be done. What I’ve presented here is for my aircraft only with its gross weight, Corvair engine output, & climb prop installed. Your gross weight, engine choice, & prop selection will be different so your mileage may vary. My expectation is that this gives clarity to the fact that by the factory data given on their web site and flight testing, my Cleanex remains within the LSA margins.

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re:Corvair Engines - Justification Series- Structure History

Posted: Mon Apr 02, 2018 1:29 pm

by daleandee

Now that we’ve been through the data using hard numbers from the factory information we will turn to more of the empirical evidence (information by observation and documentation of patterns and behavior through experimentation).

For the basis of my own decision I sought out and continue to seek out other aircraft builders, designers, fabricators, and even engineers, to gather further information as to how well the structure can sustain the additional FWF and gross weight and maintain a high margin of safety. I am not at liberty to share any private data or other evidence that has been gathered nor will I give any names, methods, or results beyond those that are not already known and public.

Keep in mind the factory warning and heed it! If you decide to go beyond what they have set as the limits of their air frame you do that by your own choice knowing that the decision is yours and so are the consequences. The information presented now is easily found by web searching and gives evidence to support the safety of my Cleanex.

Cleanex airframe history! Dan Weseman’s Cleanex first flew on 9-11-2005 and he flew it for five years before selling it. Watch him fly his Panther through an aerobatic routine and realize he flew his Cleanex the same way. His Cleanex is with its third owner and still flying. Chris Smith built a Cleanex and flew it in 2006. It is now on its second owner and he doesn’t fly it straight and level either. Many Cleanex flying videos are available by doing a simple internet search.

Consider that for nearly 15 years there have been a number of Cleanex aircraft flying with passengers, performing aerobatics, and in some cases, passengers and aerobatics together (not recommended!). At last count there were nearly 30 (I don’t have accurate information for an exact number) of these aircraft flying. In all that time, with all these different Corvair configurations, there have been no (none, zero, zip, zilch, nada) reports of any structural failures of any kind. This includes other alternative engines that have been mounted that were above the factory recommended FWF weight limit.

The only reported structural failure of any Sonex aircraft was a Waiex with a 1st version tail that separated in flight. That particular Waiex had the factory VW conversion and the engine quit. The NTSB report noted that the fuel tank was not breached and it had no fuel in it. The engine type had no bearing on the cause of that crash. There has been one reported non-fatal crash of a Cleanex where the NTSB preliminary report concludes the cause to be carb ice because conditions were conducive for carb ice and the pilot admitted he did not use the installed carb heat until after the engine had quit.

Even before Dan designed and built the Cleanex there were a few builders using Corvair power on these air frames. I examined one in great detail at an early American Sonex Association gathering in Crossville Tennessee built by Danny Cash. He did quite a great job of it. Even earlier … it is believed that Del Magsam was the first to fly a Corvair on this air frame. Over all this time and the much different iterations of engine mounts and power outputs there have to date been no reported concerns with the structure of this air frame or engine mount when used with a Corvair conversion. None! Today’s conversions are lighter than early engines because of advances made and the newer, lighter, engines make more power! William’s new starter setup and Dan’s new billet cranks reduce the weight of the engine even further.

In desiring to bring more safety to my personal flying it was my conclusion that my focus must be where the real safety issue is found i.e. engine failure and loss of control in flight. Loss of control occurs many times after making bad decisions when the engine quit. So as we focus on safety let’s be honest; it is not structural failure that is killing most pilots.

So increasing engine reliability at the cost of narrowing the wide safety margin built into the air frame was a wise decision for me considering that the thing that is killing more pilots is not structural failures but power plant failures. If in doubt go and read the NTSB report (from the NTSB news release 5/22/2012) and note two of the clear conclusions they give:

• Accident analyses indicate that power plant failures and loss of control in flight are the most common E-AB aircraft accident occurrences by a large margin and that accident occurrences are similar for both new and used aircraft.

• Structural failures have not been a common occurrence among E-AB aircraft.

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
172.6 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re: Re:Corvair Engines - Justification Series- Structure His

Posted: Mon Apr 02, 2018 4:41 pm

by samiam

daleandee wrote:In desiring to bring more safety to my personal flying it was my conclusion that my focus must be where the real safety issue is found i.e. engine failure and loss of control in flight. Loss of control occurs many times after making bad decisions when the engine quit. So as we focus on safety let’s be honest; it is not structural failure that is killing most pilots.

This is the crux of it for me as well, Dale. Thanks for continuing the series.

Re: Corvair Engines - The Justification Series

Posted: Mon Apr 02, 2018 6:55 pm

by Jgibson

Great information Dale, and much appreciated by me and many others I’m sure.
As I said in a previous post: the designer’s reluctance to endorse the use of the Corvair is completely understandable as the airframe design now stands. However I didn’t then and don’t now understand the reluctance to help mitigate those vulnerable areas of the plane that installation of the Corvair supposedly exposes to failure.
IMHO the Corvair simply makes a good airplane a great airplane and if airframe changes and/or modifying the airframe safely can be achieved, then why not help the present and future builders of that airframe? What’s wrong with another option for a different powerplant?
As I said: JMHO.

Re: Corvair Engines - The Justification Series

Posted: Mon Apr 02, 2018 6:57 pm

by LarryEWaiex121

Dale,

You very eloquently put on paper what I’ve tried to say a number of times. Planes are falling out of the sky, not for using the wrong bolt, or wrong rivet. They have been coming down primarily do to power failure and loss of control due to power failure and loss of control in general.
Excellent write up.

Larry

Re: Re:Corvair Engines - Justification Series- Structure His

Posted: Mon Apr 02, 2018 11:13 pm

by MichaelFarley56

daleandee wrote:
• Accident analyses indicate that power plant failures and loss of control in flight are the most common E-AB aircraft accident occurrences by a large margin and that accident occurrences are similar for both new and used aircraft.

This is the same for both E-AB aircraft in general, as well as the Sonex specifically. In the past, the Foundation has done a lot of research as to why Sonexes have crashed, and Dale just hit the nail on the head! Aside from just a few specific cases (several have ran out of fuel for example), nearly every single Sonex accident falls into one of those categories. Engine failure which can happen any time, or loss of control which seems to happen more often as new pilots are getting used to the handling characteristics of the airplane.

Re: Corvair Engines - The Justification Series

Posted: Tue Apr 03, 2018 4:07 pm

by dcstrng

GordonTurner wrote:
My 3.0 with billet crank is sitting in the coffee table in the middle of the living room waiting for the rest of the project to catch up. If i had some way to weigh i would. I’ll think about that one.

Am rather in the same boat – my garden variety 100hp with no attempt at weight savings, came in at 229# wet (no exhaust other than the shorties), so 255# is pretty well within the upper limit I’d think (hope)

Re:Corvair Engines- The Justification Series- Design Quality

Posted: Wed Apr 04, 2018 12:23 pm

by daleandee

The Cleanex FWF platform was developed by an aircraft designer! The FWF package used on my particular Cleanex is a well thought out design by Dan Weseman. While some builders in the early years made alterations to existing VW mounts, and adopted the original cowling to make the bed mounted Corvair work on this airframe, it was Dan that took a different approach. He worked with the developer of the Corvair aircraft conversion, William Wynne, to incorporate all of the latest ground and flight tested products available in his FWF design. Dan’s mount fits the airframe perfectly and the geometry of the main landing gear and the thrust line for the engine is right on the factory specs. Information from the SPA site reads; “The tail dragger mount is well tested and designed to take the rigors of grass field operation aerobatic flight.” Dan completed his FWF Cleanex package in 2005. William has been working with Corvair engines since 1989.

As the designer, builder, and test pilot of his own aerobatic aircraft, I trust the design work of Dan Weseman. Dan would never put his reputation or business at risk selling products that were not safe, tested, & fully developed. To my knowledge there has never been any concern such as cracks, or alignment issues, with Dan’s Corvair engine mount. William Wynne was there when this package was put together and he has endorsed Dan’s FWF design. Both of these men have an abundance of understanding, education, and real experience with designing, building, and flight testing their products thoroughly before offering them to experimental aircraft builders. Dan has brought many offerings to the Corvair conversion process since then. Most notably are his 5th bearing units and new stock & stroker billet crankshafts.

Dan’s cowling is also quite unique along with the large 13” prop spinner that greatly assists with the flow of cooling air into his fence baffle design under the easy to fabricate cowling that begins with his fiberglass nose bowl assembly. Doors on the cowling open easily for routine pre-flight inspections and light maintenance. Besides the functionality of the cowling and nose bowl combination, it greatly enhances the look of the airplane and gives it quite a unique appearance!

Neither Dan nor William has any desire to cause animosity with the kit manufacturer. However, they will quietly support the efforts of builders working with this air frame and engine combination. The reason I chose to use these companies (Fly Corvair & Sport Performance Aviation) came from watching and following the developments that were painstakingly taken over many years and the honest approach these men brought to the process. I first started examining Corvair power in 2004 as I considered upgrading to a faster aircraft. At that time William Wynne had been working with Corvairs for nearly 15 years, and having built a Corvair powered Zenith 601XL as a test bed, was well ahead of anyone else in knowledge & flight testing conversion ideas. Soon afterwards I discovered Dan Weseman and the skilled work he was doing. Still it would be another 8 years before my Cleanex (Myunn) would take to the skies.

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
172.6 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re:Corvair Engines - The Justification Series - Performance

Posted: Thu Apr 05, 2018 3:27 pm

by daleandee

I would like to reiterate that this series on justification is to answer the question of why I followed the path I did by installing a Corvair engine on this air frame. Remember that the views in this series are mine. Should anyone decide to follow a similar path they must understand that the choice and consequences are theirs. What has been successful for me isn’t a guarantee for anyone else. Having said that; I did follow a well-trodden path in my journey to find and build the best experimental, light sport compliant, airplane I could afford. My airplane is a very close clone to previous Cleanex models. I tried to duplicate all the things that had been shown to be highly successful on previous builds. Not only what parts to use, but the placement and coordination of the parts and how they worked together. My engine choices were limited by my budget. This caused me to work to find the best fit, the greatest reliability, and the highest performance my budget would allow. Enter the 3.0 Corvair conversion built by Dan Weseman.

We talk about safety and that must be the number one factor in our approach to building. The key factor in safety is reliability. Regardless of money savings, visual appeal, ease of operation, no maintenance required, latest & greatest, or any other attraction … if it’s not reliable it’s not worth flying behind. One of my favorite safety reminders is a William Wynne quote; “There is no characteristic more important than reliability. Anything you could get in trade for reliability isn’t worth it.” Very close to this is consistency. A great trait for humans as well as flying machines is that they will continually do their work on a reliable, dependable, and consistent basis. Working within those parameters means that changes are a warning that something is wrong and requires an investigation. That’s why it’s important to me that my engine never stumbles on the take-off roll. If it does, something is wrong and we go back to the hangar and investigate.

Real performance! As we approach safety from a different view another ‘justification” is realized by the performance data of the Cleanex showing improved capability with the greater horsepower available from a 3.0 Corvair conversion. My earlier VW version of this air frame would climb solo at a rate of ~750 fpm, and at gross of 1100 lbs. at 350-400 fpm on warm Carolina days. A Cleanex with a 3.0, 120 HP Corvair at 1250 lbs. gross will out climb a solo piloted VW powered version quite strikingly with well over a 750 fpm climb out rate. Excess power to climb is an excellent safety feature to have on an airplane. High density altitude, hot summer days, short strips, grass fields, climbing to get over mountains, etc., all become easier with more power that doesn’t over tax the engine, isn’t limited to a couple of minutes at WOT, or overheats the engine quickly requiring “step climbing.” Whenever recovering from a balked landing or a go around needs to be executed in a hurry it is easier with extra power on the nose of the airplane.

In 2009 two Corvair powered aircraft flew alongside a Jabiru 3300 powered one from Florida to Tennessee for the ASA gathering. Comparing notes upon arrival it was discovered that the fuel burn and speeds for the two different engines installed on these air frames were remarkably close to the same.

It has been suggested that a heavier Cleanex would suffer in take-off & climb performance. Take a moment to consider power loading numbers at gross for a few engines (realizing that the lower the number the better):

80 HP VW @ 1100 lbs. – 13.75
85 HP Jabiru 2200 @ 1100 lbs – 12.94
100 HP O-200 Continental @ 1250 – 12.5
100 HP VW Turbo @ 1150 – 11.5
120 HP Jabiru 3300 @ 1150 lbs. – 9.58
120 HP Corvair 3.0 @ 1250 lbs. – 10.41
110 HP Viking 110 @ 1250 – 11.36

Better numbers are available for some if using a lower gross. A 700 lbs empty weight, polished, Cleanex with a 3.0 and using 1150 lbs for gross would give a 450 lbs. useful load and the exact same numbers as the Jabiru 3300 for power loading. So when considering performance note that the 80 HP engine with the lower gross actually has the poorest power loading number while the 120 HP Corvair @ 1250 lbs. gross falls only behind the 120 HP Jabiru 3300 at 1150. That’s performance!

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
172.6 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re: Corvair Engines - The Justification Series

Posted: Fri Apr 06, 2018 8:26 am

by DCASonex

Dale, One minor clarification. The Jabiru and CAMit 3300s maximum continuous RPM is 3300. With the L series Jabiru limited by name plate change to 2,850 so that Sonex can still qualify for light sport.

David A.

Re: Corvair Engines - The Justification Series

Posted: Fri Apr 06, 2018 10:00 am

by daleandee

DCASonex wrote:Dale, One minor clarification. The Jabiru and CAMit 3300s maximum continuous RPM is 3300. With the L series Jabiru limited by name plate change to 2,850 so that Sonex can still qualify for light sport.

Hi David,

Thanks for the catch! I went back and deleted that line. I did find the 3300-L limitations in their install manual i.e. “The 3300L engine has a maximum continuous RPM rating of 2850RPM. The engine may be operated at engine speeds above 2850RPM for up to 10 minutes.”

As you pointed out & is seen in the manual, there is no difference at all in the engines so the RPM limit is strictly for light sport compliance. For any wanting a reference, that information is here, under section 3.1.1 - http://jabiru.net.au/Manuals/Engine/JEM3304-9_IM.pdf

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
172.6 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re:Corvair Engine- The Justification Series- Safety (engine)

Posted: Sat Apr 07, 2018 2:41 pm

by daleandee

Safest engine available in my price range! Scanning the NTSB site gives accident data for various engines that were available to me for this air frame in the price range I could afford. There are various ways to slice and dice the numbers so absolutes as far as true reliability are hard to measure. At the end of the day the Corvair came out ahead of any of the competitors in the price range that I was working with. From 2001-2017 the NTSB site list 14 accidents when the word “Corvair” is used in the word string box with all others blank (one was for a certified aircraft using a Corvair fuel pump). Remember that Corvair engines are used on many different types of air frames including Zenith 601, 650, 701, 750, KR’s, Peitenpols, Dragonfly, Panthers, Cleanex, and countless other aircraft since 1960 when a Corvair first flew on a Pietenpol.

As there have been many versions of flying VW, Subaru & Honda engines so there have been variations of the Corvair conversion process. Nevertheless my goal was to find out the reliability and failure rate of the particular conversion I was interested in as opposed to all other choices I could afford at the time. One of the biggest advantages I had was my previous experience with a factory VW conversion on this air frame for a number of years. It isn’t my purpose to criticize the factory offering so I’ll focus on what makes this particular Corvair conversion and its reliability so attractive for me:

• Simplicity! No need for a radiator, water hoses, water pump, cooling fan, gearbox, turbo, fuel pump, or oil cooler lines.

• It doesn’t overheat. CHTs are less than 300ºF in cruise. Oil Temps (using the stock GM cooler) are 180-220ºF.

• The Marvel Schebler aircraft carb is excellent in operation. It doesn’t hesitate, stumble, bumble, or burp.

• It does not use or leak oil. Viton seals on the pushrod tubes seal tightly and are very resistant to heat.

• It has an oil fed front bearing (5th bearing) attached to the case for prop loads.

• The hydraulic valves stay adjusted after the initial setting during the engine build.

• No head retorquing required.

• Dual ignition based on the original GM designed distributor system that advances the timing as needed for flight.

• Ignition coils that are mounted away from the engine and don’t suffer from exposure to extreme heat.

• Ignition timing is set and checked at condition inspection with an automotive timing light using factory timing marks.

• Dual fuel piston design allows the use of 100LL or 93 octane auto fuel. Ethanol free is preferred but not required.

Modern Corvair engine conversions have proven themselves to be reliable, provide good smooth power, and are quite robust. The simplicity of this well-designed, air-cooled, direct drive, naturally aspired conversion is a major part of the reason that it is as dependable as it has proven to be. Another builder makes a valid point when he insists, “If it’s not there, it cost nothing, weighs nothing, and is 100% reliable.”

Like any engine it requires regular maintenance. But with hydraulic lifters, Viton pushrod seals (no oil leaks), iridium plugs, dual ignition, certified aircraft carb, and the use of K&N high quality oil & air filters, maintenance mostly consist of oil & filter changes at 25 hours and new spark plugs during the condition inspection if needed.

Corvair reliability is a safety factor that should not be dismissed. Many things make it reliable but one of the most notable is that it is not being strained to put out an amount of power it was never designed for. In its original role the later engines were rated up to 180 HP at 5600 RPM. To ask a modern updated & de-rated version of this engine to now give 90 HP at 2800 RPM falls well within the original design specifications and greatly enhances the reliability factor.

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
172.6 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

ArchiveBot · March 20, 2018, 5:02am

Re:Corvair Engines-The Justification Series- Parts & Service

Posted: Mon Apr 09, 2018 6:04 pm

by daleandee

As I close out the list of justifications I have for using the Corvair engine on my Cleanex one of the most important, yet often overlooked factors, is not only the quality of the build, but the availability of parts and service. Even were it possible for me to spend more money on a certified engine for my aircraft the ongoing maintenance cost could be substantial. Not only the cost of replacement parts but the ability to find them and receive them quickly was high on my priority list.

Respect for where my Corvair was designed (GM) and assembled (USA), the quality of the original build (SPA), access to high quality replacement parts, easily obtained service manuals, and knowledgeable personnel if needed was extremely important to me. Installing a certified aircraft engine could get quite expensive when the time came for serious replacement parts. Depending on where on earth an engine or engine kit is made can cause delays in obtaining parts.

If the builder/owner will be the mechanic in charge (the one responsible for engine repair/maintenance) they will need proper reference manuals and materials. Corvairs are well covered using the GM shop manual, Fly Corvair conversion manual, and the newest highly detailed and illustrated manual from SPA. The more complex the FWF package is the more knowledge the mechanic in charge must have available to him. Many other FWF offerings have quite complex systems that cannot be serviced in house so they would have to be shipped out for repair or replaced. Examples may include, Electronic Fuel Injection parts, Electronic control computers, turbo units, FADEC controllers, gearbox drives, and the list goes on. The beauty of the Corvair conversion is in it’s simplicity! Gravity fed aircraft carb, simple electronic & point ignition.

Because of the massive amount of Corvair engines that GM produced, core parts are easily attainable. The engine is converted using high quality parts that are “made in USA” (with a few exceptions for ignition components) and are readily available. Parts that are design specific to my conversion have come from either William Wynne (Fly Corvair) or Dan Weseman (Sport Performance Aviation). These two companies are rock solid in the aviation business. William Wynne has been teaching, converting, upgrading, producing, and selling parts for nearly 30 years. For over 12 years Dan Weseman has been successfully designing Corvair upgrades, building engines, and now has sold quite a few kits for his own Panther design aerobatic aircraft that used the Corvair engine on the prototype.

As an example with parts; the recommended carburetor for these engines is a standard and reliable aircraft carb by Marvel Schebler or Stromberg. My particular Cleanex uses a Marvel Schebler carb that has been produced by the tens of thousands and used on O-200 Continental equipped Cessna 150 training aircraft for many years. Easily obtainable and they work! No changes in carb jetting or set-up are required.

Most all of the standard maintenance parts like spark plugs, wires, distributor cap, rotor, coils, oil, filters, gaskets, O-rings, etc., are readily available and found at most any nearby auto parts store. Other internal engine parts can be sourced through many online Corvair vendors as these vendors also support Corvair car clubs and racing teams.

Dale Williams
N319WF @ 6J2
Myunn - “daughter of Cleanex”
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
172.6 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

Re: Corvair Engines - The Justification Series

Posted: Fri May 04, 2018 7:20 pm

by dbdevkc

Just a personal note to add on here. I had been evaluating my potential use of a Corvair conversion engine long before this string of posts started. I looked into all the potential downsides of this choice (including potential dangers), and what I personally consider the upsides.

My current thought is to move ahead and go completely off the farm. I have a core motor that I am disassembling and cleaning up in the hopes to get some useful donor pieces.

I hope to be able to continue to participate in this forum and continue to get great info and tips. I guess I will just not be talking powerplants publicly.

Re: Re:Corvair Engines-The Justification Series- Parts & Ser

Posted: Sat May 05, 2018 11:37 am

by vigilant104

daleandee wrote:Parts that are design specific to my conversion have come from either William Wynne (Fly Corvair) or Dan Weseman (Sport Performance Aviation). These two companies are rock solid in the aviation business. William Wynne has been teaching, converting, upgrading, producing, and selling parts for nearly 30 years. For over 12 years Dan Weseman has been successfully designing Corvair upgrades, building engines, and now has sold quite a few kits for his own Panther design aerobatic aircraft that used the Corvair engine on the prototype.

And, just for completeness, it should be mentioned that those interested in a Corvair-based aircraft engine can also look to the Spyder engine from Azalea Aviation http://www.azaleaaviation.com/products/Spyderengines.html. Bill Clapp has a reputation for quality work and good customer service.
The existence of several sources for Corvair-based aero engines, parts, and assistance is, IMO, a positive factor that anyone considering these engines should consider. Also, it has been my observation that opinions are strong in the Corvair community (VW community, too!), and that there are “tribes” which have some amazingly deep-seated animus towards each other in the Corvair world. That part is unfortunate.