Nose "heavy"

ArchiveBot · December 17, 2022, 6:00am

Nose “heavy”

Posted: Sat Dec 17, 2022 6:04 pm

by Skippydiesel

My Sonex/Rotax 912 ULS requires constant back pressure (up elevator) to fly straight & level.

I have checked the aileron/flap settings and all are within factory specifications - an ability to adjust the horizontal tail, reduce angle of attack, would correct the problem but I cant see how this might be done.

Any suggestions?

Re: Nose “heavy”

Posted: Sat Dec 17, 2022 8:22 pm

by Bryan Cotton

What is your CG?

Re: Nose “heavy”

Posted: Sat Dec 17, 2022 8:42 pm

by Skippydiesel

Hi Bryan,

W & B data:

Aircraft datum - Wing leading edge
Aircraft moment index - 105935 Kg.mm (5932086.in)
Aircraft empty weight - 340 Kg (749.572 lb)
Aircraft empty weight C of G - 311.34 mm (12.258 in)

Re: Nose “heavy”

Posted: Sun Dec 18, 2022 12:29 am

by Bryan Cotton

I converted your numbers to work in my spreadsheet. The wing leading edge is 52" aft of the standard Sonex datum, the tip of the spinner. If I assume you are 150 lbs and have full fuel, that puts you at 64.38" which is within the CG range, although forward. My worst case forward CG at my weight (200 lbs) is about 65.12". I am working at getting to 170 which would put me at 64.75". At the 65.12" I’m not seeing any trim issues in cruise.

Do you have trim installed? I need to trim throughout the speed range.

Re: Nose “heavy”

Posted: Sun Dec 18, 2022 2:27 am

by Skippydiesel

Spring type longitudinal trip - Full Up for duration of test flight(s) - Stick back (& heavy) for most of flight.

Re: Nose “heavy”

Posted: Sun Dec 18, 2022 5:09 am

by sonex892.

Skippy. Your non standard fuel system of main fuel being in the leading edge close to the c of g is quite different to the normal sonex. It wont alter the c of g as much as the standard fuel tank does. That is actually probably a good thing. With the standard tank there is a significant trim change required from full to empty. Providing yours is within normal c of g range it shouldnt be a problem and you will never need as much forward trim as the normal sonex requires with a full tank.
With the spring trim, I would simply experiment and add more tension to the system by either changing or shortening the spring to get more nose up trim. Personally I prefer the trim tab and adding that could be another option. The only time I run out of trim is at low speed. On landing I always go to full aft trim, its still never quite enough but not enough to be a problem.
Steve

Re: Nose “heavy”

Posted: Sun Dec 18, 2022 7:39 am

by Skippydiesel

Hi Steve,

Trim (as in the using spring or tab methods of maintaining the position of a control surface) is, I believe, not the issue. The problem is having so much up elevator (stick back) all the time. The effect is to load the main lifting surface/wing, creating drag, using energy , slowing the aircraft. When in cruise, I would like to see the elevator level with the horizontal stabiliser, only coming into play during ground opps, take off, climb out and slow flight

Re: Nose “heavy”

Posted: Sun Dec 18, 2022 8:16 am

by GraemeSmith

Elevator anti-flutter bungee in place? It applies some back stick pressure.

Re: Nose “heavy”

Posted: Sun Dec 18, 2022 12:45 pm

by T41pilot

My “B” model nose pitches down right away if any flap at all is applied. You might check your flap rigging again just to make sure.

Re: Nose “heavy”

Posted: Sun Dec 18, 2022 2:10 pm

by Bryan Cotton

T41pilot wrote:My “B” model nose pitches down right away if any flap at all is applied. You might check your flap rigging again just to make sure.

Good point! My classic A model does the same.

Re: Nose “heavy”

Posted: Sun Dec 18, 2022 2:57 pm

by Area 51%

If you’re confident the wing incidence is correct, I would take a close look at the engine thrust line.

Re: Nose “heavy”

Posted: Sun Dec 18, 2022 5:27 pm

by Skippydiesel

T41pilot/Bryan C,

Very interesting - I have been working on the plans instructions; while keeping the control stick(s) vertical in a “jig”, placing a straight edge on the aileron and measuring the “gap” at the wing spare positions. I then adjusted the flaps to the ailerons.

By any chance do you have a flap to spare gap measurement.

Re: Nose “heavy”

Posted: Sun Dec 18, 2022 5:30 pm

by Skippydiesel

Area 51% wrote:If you’re confident the wing incidence is correct, I would take a close look at the engine thrust line.

Full disclosure; This Sonex has had its wing/horizontal stabiliser, angle of attack increased by 1.6 degrees from factory/plans specifications.

Engine thrust line is defined by Sonex (factory) engine frame, with latest Sonex/Rotax “bed” adapter - I would hope that this would be well within design parameters.

Re: Nose “heavy”

Posted: Sun Dec 18, 2022 8:12 pm

by T41pilot

Skippydiesel wrote:T41pilot/Bryan C,

Very interesting - I have been working on the plans instructions; while keeping the control stick(s) vertical in a “jig”, placing a straight edge on the aileron and measuring the “gap” at the wing spare positions. I then adjusted the flaps to the ailerons.

By any chance do you have a flap to spare gap measurement.

The “B” model plans have you rig the ailerons and flaps separately using the same process though with a straight edge and dimension above the spar to the bottom of the straight edge. I would not pick one thing and rig it and then set the trailing edge of the other thing to match. I started with ailerons with my stick centered and completed the process in the plans. Fore and aft of the stick did not apply since the elevator was not involved. Took some back and forth on each side until I thought it was right. Then rigged the flaps using the same process. I then checked to see if all trailing edges matched. It took me 2 or 3 tries through the whole process but finally got that to happen. I was confident at that point that was the best the rigging was ever going to get. A small adjustment on a given linkage would yield a significant change on the spar to straight edge measurement so hence the multiple tries.

Re: Nose “heavy”

Posted: Sun Dec 18, 2022 8:29 pm

by Skippydiesel

My method was;

Construct & install a frame to securely “lock” the control columns at 90 degrees.
Make a 74mm measure, with feet, that will reliably sit at/in the same vertical plain for each aileron over several repeat measurements/adjustments.
Using a piece of angle aluminium, as the strait edge, aligning with the same line of rivets for each aileron/wing, place 74 mm measure on edge of upper wing skin/over spar, adjust aileron to measure.
Adjust flaps to aileron.

Since the above done and aircraft flown, left flap adjusted up to reduce slight tendency to role to right. Test flight, on last adjustment, yet to be done.

[list=]I only had the one location (on each aileron) - perhaps I should have repeated along entire length.
I did not go through this procedure for the flaps, instead using the aileron to provide the correct alignment - perhaps I should have repeated repeated the procedure for the flaps.[/list]

Re: Nose “heavy”

Posted: Sun Dec 18, 2022 11:39 pm

by BRS

Skippydiesel wrote:…
Full disclosure; This Sonex has had its wing/horizontal stabiliser, angle of attack increased by 1.6 degrees from factory/plans specifications.

? Is this a common modification ? I can imagine this to be helpful for shorter takeoffs and better vsby on landing flair. What else does this accomplish?

Re: Nose “heavy”

Posted: Mon Dec 19, 2022 5:33 am

by Skippydiesel

BRS wrote:

Skippydiesel wrote:…
Full disclosure; This Sonex has had its wing/horizontal stabiliser, angle of attack increased by 1.6 degrees from factory/plans specifications.

? Is this a common modification ? I can imagine this to be helpful for shorter takeoffs and better vsby on landing flair. What else does this accomplish?

Not my doing. I purchased the very very advanced plans built aircraft from the origional builder/modifier (still took my Son & I, 12 months off fairly intense work to get it to test flight condition).

The reasoning behind the modification is;

The builder flew in a number of friends Sonex’s and found them, in cruise (straight & level) to fly slightly nose high. He measured the longitudinal attitude in flight and came to the conclusion the fuselage was tilted 1.6 degrees nose high. With this information, he modified his Sonex with intention that its fuselage would be level in cruise flight.

Test flying has yet to get to the point where his theory will be proved/disproved

Re: Nose “heavy”

Posted: Mon Dec 19, 2022 9:18 am

by GraemeSmith

“horizontal stabiliser, angle of attack increased by 1.6 degrees”

Which way? Meaning - remembering the horizontal stab is an upside down airfoil - increasing the angle of attack by 1.6 degrees means the leading edge goes DOWN towards the ground. Is that what actually happened?

I wonder if this got fully thought through? The main wing has to fly with some angle of attack or it won’t generate lift. So reducing the main wing angle of attack from a design angle will reduce lift. Unless you compensate (simplistically) by flying faster. Simplistically - all the speeds increase - including stall speed (??)

And of the horizontal stab has an increased angle of attack - then as you flare - it is more likely to stall and so not apply downward force. So now the nose will drop during the flare.

–

Tell me this got really well thought through and design checked before trying to fly it.

Re: Nose “heavy”

Posted: Mon Dec 19, 2022 1:14 pm

by BRS

Graeme, I understood Skippy angle of incidence description simply as the increase of the wing AOI to better streamline the fuselage in flight (makes sense) and that the horizontal was adjusted to match the wing (makes sense) since the horizontal relationship to the wing (not the fuselage) is what matters. Should keep the control system in harmony. But…

Changing the wing & horizontal AOI (1:1) will change (slightly) the fuselage AOI (intended goal) yet since the fuselage has some aerodynamic (lifting) characteristics this could be affecting the control harmony. As a result, the relationship between the wing AOI and horizontal AOI might not be 1:1 proportional as assumed.

More to it than what meets the eye.

Re: Nose “heavy”

Posted: Mon Dec 19, 2022 7:24 pm

by Skippydiesel

Good news!

Had a test flight early this morning (near ideal conditions).
The adjustment up, of each flap, has resulted in a dramatic reduction in the need for up elevator at 135 knots. Will try for 0 or near 0 elevator by doing another flap adjustment.

Re: Nose “heavy”

Posted: Sun Dec 25, 2022 7:09 pm

by Skippydiesel

Last adjustment, of flap up, resulted in nil gain, will undo the last 1/2 turn. Still have about 100 mm up on trailing edge . I may have to consider weight redistribution (if possible) or a addition of ballast to tail.

Re: Nose “heavy”

Posted: Mon Dec 26, 2022 11:31 am

by Scott Todd

When a ‘normal’ or straight wing like ours makes lift, it creates a negative pitching (nose down). The horizontal stab produces a down force to counter this. Its simple airplane physics. Look it up. In order to create this downward force, the stab usually has a negative incidence compared to the wing. Many airplane designs don’t account for this properly so some Up elevator trim is required. Sonex’s fuselage also contributes to the pitching moment. John and Pete did a good job getting this harmony correct. Once the subject airplane wing and tail incidence changed, the overall pitch trim of the airplane changed.

The last Sonex I owned had a fixed trim tabs on the underside of elevator. So does my Little wood Biplane. Its a simple solution to a simple issue. The spring trim system in a regular Sonex does the same thing. It merely takes some of the stick force out to ‘trim’ the airplane. I adjust it to put the movable trim tab in its center for hands-off cruise flight.

I would suggest the airplane is NOT nose heavy. Look at the CG on high performance airplanes like the Glasiar and Lancair. They are in the teens and your Sonex is nowhere near that. We get concerned about nose heavy if we are running out of elevator at flare. The 5 Sonex’s I have flown were not even close to this. PLEASE don’t add tail weight without consulting with some experienced Aeronautical engineers. It can have detrimental effects including added difficulty in spin recovery.

Re: Nose “heavy”

Posted: Tue Dec 27, 2022 12:31 am

by gammaxy

Skippydiesel wrote:Still have about 100 mm up on trailing edge.

Are you saying the elevator trailing edge in cruise is raised 100mm? Is this a typo? How do you measure it in flight? Looking over your shoulder? 100mm seems extremely excessive to me. Here’s Michael Smith’s video that shows it to be negligible. https://youtu.be/mh6Ys6MwTiY if yours isn’t similar, there’s something so messed up with your airplane it should be obvious. I’d question whether the incidence was really set as described. There’s no magic to this–if the cg is in the ballpark and the theres nothing dangling off the plane creating a bunch of torque then your incidence is wrong. By the way, from your description, I assume the thrust line wasn’t adjusted along with the incidence.

Re: Nose “heavy”

Posted: Tue Dec 27, 2022 7:52 am

by GraemeSmith

As Scott Todd says - the horizontal stab provides down force. It’s an “upside down” flying wing. It 'lifts" the other way from the man wing that levitates the plane off the ground. Some of it somes from the angle of incidence. Some from “negative lift”.

Spitballing - as I don’t know. I bought a built airplane. Are the horizontal stabs actually airfoils? With one surface having more camber than the other? If yes. Anyvchance they got put on the wrong side and are “upside down” and generating “lift” the wrong way that is countering the angle of incidence? Like I say - spitballing.

–

And to reinforce what Scott said - if the plane IS in CG. It’s NOT the weight distribution that is the problem. It’s something else. Find the something else - don’t redistribute the weight - failure to spin recover is a big risk here.

Re: Nose “heavy”

Posted: Tue Dec 27, 2022 8:01 am

by Bryan Cotton

GraemeSmith wrote:Are the horizontal stabs actually airfoils? With one surface having more camber than the other? If yes. Anyvchance they got put on the wrong side and are “upside down” and generating “lift” the wrong way that is countering the angle of incidence? Like I say - spitballing.

Graeme,
Same ribs for both the left and right sides of my Waiex. I assume the pedestrian straight tail Sonexes are the same. So they are symmetrical, and not super-airfoiley. After the leading edge they are pretty flat.

Re: Nose “heavy”

Posted: Tue Dec 27, 2022 1:34 pm

by Area 51%

Skippydiesel wrote:

Area 51% wrote:If you’re confident the wing incidence is correct, I would take a close look at the engine thrust line.

Full disclosure; This Sonex has had its wing/horizontal stabiliser, angle of attack increased by 1.6 degrees from factory/plans specifications.

Engine thrust line is defined by Sonex (factory) engine frame, with latest Sonex/Rotax “bed” adapter - I would hope that this would be well within design parameters.

Back to my original thinking…The design thrust line is set according to the wing’s angle of attack. The design wing-to-fuselage incidence allows the use of the fuselage as the datum to set the thrust line. A 1.6deg. change in wing incidence also changes the thrust line by 1.6deg. In this case the thrust line is pointed down the 1.6 and must be compensated for by up elevator.

Question: Does the stick pressure relax if the throttle is retarded? If not, please ignore the above.

Re: Nose “heavy”

Posted: Tue Dec 27, 2022 4:00 pm

by Skippydiesel

My apologues not sure how an extra 0 was added to my elevator up figure (100) - it should be 10mm (well under your 1/2 in).

How was this determined? - In straight/level flight, a small piece of board was placed on the instrument panel and the position of the control stick marked on it. On landing the stick was moved to the same position, as in flight and the elevator trailing edge position, in relation to the horizontal stabilizer outer “horns,” noted (10mm up).

The same board was used to determine a further change to flap settings had no discernible benefit to elevator position.

Trim of any sort will not remove the 10 mm up - trim is used to remove (lighten) stick forces not change the position of the control surface.

Adding ballast - definitely a last resort. No one wants to carry around dead weight, but if here is no other way (eg moving the battery ) to get the elevator to a level with stabilizer position it may have to be done.

At this early stage of test flying (“tweaking”) it would seem that at 135 knots the above elevator position is constant, reduction in power/speed will inevitably result in further up elevator as the pilot ties to keep the aircraft from descending (maintaining straight & level).

Re: Nose “heavy”

Posted: Tue Dec 27, 2022 8:00 pm

by Scott Todd

As Area51 points out, the thrust line is now more down. This is why its a bad idea to change airplanes designs unless you REALLY know what you are doing. Its just going to require more nose up trim because of this. You could try shimming the stab but the net down force on the tail in flight is going to be roughly the same to compensate for the added down thrust.

You could try shimming the engine but I suspect this is a no-go because of the cowl fit. It would require some major cowl work to make it look natural again. But this of course just adds more off-design variables to the system.

Its probably only costing a few knots. You may just have to live with it. Adding ballast is not really a last resort. It should be considered a Non resort.

Re: Nose “heavy”

Posted: Tue Dec 27, 2022 9:51 pm

by gammaxy

Skippydiesel wrote:it should be 10mm (well under your 1/2 in).

Okay, that doesn’t sound as crazy as what I was picturing I suspect most of us haven’t measured our elevator deflection to that level of precision, but it’s an interesting data point. Your measurement seems reasonable to me and I question whether you’d be able to measure the drag reduction of getting it perfectly streamlined. Do you have your wheel pants and fairings installed? Those have some affect on the pitch trim, but I don’t know how hard it is to measure. As you explore more of your CG range, it will be interesting to see what that does to your elevator deflection.

Re: Nose “heavy”

Posted: Thu Dec 29, 2022 6:24 pm

by Skippydiesel

gammaxy wrote:

Skippydiesel wrote:it should be 10mm (well under your 1/2 in).

Okay, that doesn’t sound as crazy as what I was picturing I suspect most of us haven’t measured our elevator deflection to that level of precision, but it’s an interesting data point. Your measurement seems reasonable to me and I question whether you’d be able to measure the drag reduction of getting it perfectly streamlined. Do you have your wheel pants and fairings installed? Those have some affect on the pitch trim, but I don’t know how hard it is to measure. As you explore more of your CG range, it will be interesting to see what that does to your elevator deflection.

Wheel pants & fairings installed.

I would not be so concerned about the elevator up position, if the aircraft did not have a strong tendency to nose down, when stick released.

The spring type elevator trim just doesn’t have the power to overcome the elevator pressure - when I flew yesterday I had full aft trim for almost the whole flight. The only time stick forces lightened, was on base/final with 2 stages of flap at about 60 knots. Yes I can further adjust the spring lengths (or install heavier springs) but even if I get it to “hold” in flight this will just be masking the problem.

It seems to me that in straight level, high speed cruise, when not carrying baggage, the elevator trailing edge should be level with the stabiliser trailing edge.

I am seriously considering changing the, nearly 12kg Airmaster CS, prop for lighter ground adjust or inflight adjust.

ArchiveBot · December 17, 2022, 6:01am

Re: Nose “heavy”

Posted: Fri Dec 30, 2022 12:26 am

by gammaxy

Your actual problem is the Dial-a-Trim isn’t set up correctly. There are two springs that oppose each other. The one behind the seat is probably applying too much nose down pressure. It’s been a long time since I installed mine, but the manual describes how the springs should be adjusted: http://www.aeroconversions.com/support/ … nstall.pdf

This is definitely not a “nose heavy” problem. Even if your elevator were perfectly streamlined, you would likely need to apply some pressure to hold it there since the horizontal stabilizer is rarely at 0 degrees AoA. There’s only one speed where the airplane will cruise hands-off without any trim pressure. At all other speeds, you will need to apply pressure. The trim system is supposed shift this speed around, but it sounds like it’s not been adjusted correctly. By adjusting it, you won’t be masking the problem because the way it’s adjusted is the problem.

Re: Nose “heavy”

Posted: Wed Jan 11, 2023 7:18 am

by Skippydiesel

Re adjusted both elevator trim springs.

(I describe the forward stick pressure spring as the FIXED, as it can not be adjusted by the pilot. The aft stick pressure spring is the ADJUSTABLE (by pilot in flight)

Initial testing found a small improvement (lighter stick) but full aft adjustment on the trim, in cruise, is not acceptable.

The ADJUSTABLE has run out of spring length, without correcting the tendency for the aircraft to dive when stick released. This is despite reducing the tension on the FIXED spring.

The solution I have found, is to add a second thinner spring, of the same length as the ADJUSTABLE, inside the origional, thereby increasing the strength of the ADJUSTABLE. This could be achieved by a stronger single spring but I was unable to find one. The thinner spring is a neat fit, both in length & diameter, inside the origional.

The trim system now works as expected, holding the stick in the position the pilot sets, with plenty of adjustment, in both directions, to accommodate changes in aircraft loading air speed and flap.

Thank you all for your advice and all the best for the New Year.

Re: Nose “heavy”

Posted: Thu Jan 12, 2023 11:16 am

by gammaxy

That’s great, glad you got it trimmed. Did you also consider adjusting the wire swivel location on the cable to increase tension on the ADJUSTABLE spring? The plans show a procedure for setting that.

Re: Nose “heavy”

Posted: Fri Jan 13, 2023 1:04 am

by Skippydiesel

gammaxy wrote:That’s great, glad you got it trimmed. Did you also consider adjusting the wire swivel location on the cable to increase tension on the ADJUSTABLE spring? The plans show a procedure for setting that.

Yes to the ADJUSTABLE spring - pretty much ran out of spring length and only just had the aircraft trimmed with the trim wheel all the way back.

Before you ask I also adjusted the FIXED spring to reduce as much forward pressure as seemed reasonable.

I am now working on rudder trim - see new conversation.

Re: Nose “heavy”

Posted: Sun Feb 26, 2023 1:57 am

by Skippydiesel

New “problem”

At speeds above 125 knots, I am trimming almost all the way back (up elevator).

At speeds above 130 knots I have no more aft back trim left - fortunately the stick is hands off & the aircraft straight & level, at this point. The elevator trailing edge, remains at about 10mm high, at these speeds/settings. Stick a little aft of centre.

The aircraft is capable of 135 knots indicated at 4500ft. This top end, may increase marginally with further adjustments to cowling and flap/fuselage fairings.

There is no real issue (at the moment) with having so much back trim applied BUT I wonder why I need so much.

It seems to me, the effect is of the centre of gravity is shifting forward, with higher speeds.

Other than a spare headset, my log book and a spare GPS, there is no additional weight in the baggage compartment.

Most “sorties” are conducted with little or no fuel in the centre header tank (in the same position as the standard Sonex tank).

So far all flights have been single (75kg) pilot and full or near full 30L x 2 wing tanks.

Does anyone have an thoughts/explanation/fix for this???

Re: Nose “heavy”

Posted: Sun Feb 26, 2023 10:29 am

by Bryan Cotton

My thoughts:

the CG does not shift with speed
CG will shift aft as fuel is burned.
Generally more nose down trim should be required with increasing speed.

I think this brings us back to rigging - either tail vs wing or engine thrust line. What happens if you climb up high and trim for a high speed glide? That would tell you the thrust line contribution.

Re: Nose “heavy”

Posted: Sun Feb 26, 2023 3:50 pm

by GraemeSmith

Skippydiesel wrote:full 30L x 2 wing tanks.

Sorry if I missed this before - but question - what is the “arm” from datum for these tanks?

Re: Nose “heavy”

Posted: Sun Feb 26, 2023 5:21 pm

by Skippydiesel

Bryan Cotton wrote:My thoughts:

the CG does not shift with speed

CG will shift aft as fuel is burned.

Generally more nose down trim should be required with increasing speed.

I think this brings us back to rigging - either tail vs wing or engine thrust line. What happens if you climb up high and trim for a high speed glide? That would tell you the thrust line contribution.

I should of said the effect is as if the CG is moving forward. Slow speeds, say 100 knots, the stick/trim are as I would expect.
Minimal at the moment as centre “header” tank starts (TO) empty and only receives return line fuel in flighty (have just changed return line restrictor jet, to a smaller one, so flow/hr data, yet to be collected) Wing tanks are almost on the C of G.
Hence my question

Re: Nose “heavy”

Posted: Sun Feb 26, 2023 5:23 pm

by Skippydiesel

GraemeSmith wrote:

Skippydiesel wrote:full 30L x 2 wing tanks.

Sorry if I missed this before - but question - what is the “arm” from datum for these tanks?

Wing tanks are at 180mm - almost on the C of G

Re: Nose “heavy”

Posted: Sun Feb 26, 2023 5:30 pm

by Skippydiesel

In the not too distant future, I will start using the in fuselage tank/header. This tank, in the Sonex standard tank position, is able to take 35L on ground and potentially 40 L in the air (transferred from wing tanks). This forward load will significantly change the weight distribution - it may be that high speed cruise is not usable, unless I load the baggage compartment.

Re: Nose “heavy”

Posted: Sun Feb 26, 2023 5:33 pm

by Skippydiesel

In the not too distant future, I will start using the in fuselage tank/header. This tank, in the Sonex standard tank position, is able to take 35L on ground and potentially 40 L in the air (transferred from wing tanks). This forward load will significantly change the weight distribution - it may be that high speed cruise is not usable, unless I load the baggage compartment.

One reminder point - in an effort (successful) to correct the previous nose heavy condition, the flaps are now slightly reflexed, compared with the ailerons. This is not obvious on the ground but in flight can be seen quit clearly.

Re: Nose “heavy”

Posted: Sun Feb 26, 2023 6:02 pm

by Skippydiesel

Just had a random thought - The position of the elevator(slightly up) is remaining fairly constant (judged by stick position, slightly aft of centre) - the trim (spring) is just experiencing higher air loads (due to speed) which require more effort (spring tension) to remain in position.
I have already increased the strength of the adjustable (aft pull) spring with quit noticeable impact on stick “feel” so would be reluctant to go stronger again.
The fixed (fwd pull) lighter spring has been adjusted so as to have no pull at full aft stick. It would be impacting on the adjustable spring but not much.
My last aircraft also had spring loaded elevator trim, unlike the Sonex, both springs were adjusted by the trim mechanism - I wonder would this be a better system?
At high speed cruise & when aircraft lightly loaded, I would like the up elevator to be neutral (0 trim up/down) but this may not be possible with my Sonex. I may only get neutral elevator when the baggage compartment is loaded.

Re: Nose “heavy”

Posted: Tue Feb 28, 2023 5:35 am

by Skippydiesel

Further musings;
My flaps are slightly raised/reflexed. This was done to address the slightly nose heavy control stick and it worked, at sub 120 knot speeds.
As a consequence of the flap adjustment the ailerons are now slightly down, compared with the flaps (roughly 10-15mm) in level flight.
Might adjusting the ailerons to match the flaps be the solution to my high speed problem?
What would be the effect of such an adjustment on other areas of flight eg stall performance?

Re: Nose “heavy”

Posted: Tue Feb 28, 2023 10:48 am

by dbdevkc

I would wait for an answer from someone more experienced/intelligent than me, but… my thought is flaps add both lift and drag when deployed. You can fly slower, and your stall speed is lower. I would guess that when flying with negative flaps your stall speed will be higher/faster. I fly a sailplane that has full length flaperons and I go to -5° when flying fast - that decreases drag somewhat. A difference though is that the ailerons deflect with them so I don’t know what the characteristics of negative flaps would be in a Sonex.

Re: Nose “heavy”

Posted: Tue Feb 28, 2023 2:18 pm

by Scott Todd

We already know the root cause. The wing and tail incidence change from the original builder added effective down thrust. The more power you apply (faster), the more it pulls the nose down.

There are a few simple fixes. Trying to correct the thrust line will just add more variables at this point. Adjust the trim springs as suggested. Add a fixed trim tab to the bottom of the elevator has also been suggested. Don’t get hung up on the elevator trailing edge being up during flight. Again, this is a function of the down thrust.

Stop referring to ‘nose heavy’. The proper term is something like ‘heavy aft stick force’. Nose Heavy implies weights or static forces. This entire situation is dynamic and CG doesn’t have anything to do with it. Changing load conditions can obviously affect the trim but its NOT nose heavy.

Once you get the proper trim springs adjusted, or a fixed tab adjusted, all speeds should be trimable.

Re: Nose “heavy”

Posted: Tue Feb 28, 2023 5:43 pm

by Skippydiesel

Hi Scott,

I take your point on using the term “nose heavy” - it does however describe the symptom, which as you say, could just as well be described as stick heavy.
Dwelling on the subtle changes (I previously said 1.6 when it should have been 1.5 degrees) to the aircrafts main & tail alignment, wont get me further ahead. Nor will dwelling on semantics (although I do agree precise language is desirable).

I now have a flying Sonex - after many small adjustments it is becoming less challenging to fly, however needs further “tweaking” (scientific term) to make it into the nice flying aircraft that most pilots enjoy.

To address your suggestions ;

Thrust line - if I understand (?) what this means, I have never gone down this track, relying instead on the integrity/correctness of the Sonex design.
Trim springs - I think I have gone as far as is sensible in this area. The (pilot) adjustable spring is now much stronger than the fixed. Despite this, I am at full aft trim adjustment at 130+ knots. The aircraft is straight and level at this point but I do not consider this to be an acceptable situation. In this condition I will have insufficient rear (up elevator trim) when I fill the in fuselage 35-40 L fuel header tank . Also this need for continual tail down pressure/thrust is “loading” the main wing, creating additional drag, an undesirable situation in any aircraft.
Fixed trim tabs - will always be the last option in any adjustment that I make. As far as I am concerned, they should only be used when all other fine tuning of the flight surfaces have been considered/tried.

You have not commented on the aileron/flap relationship -

If the flaps (slightly up) have lightened the stick force, will not bringing the ailerons into line with the flaps, further improve this trend?
What might be the effect on other areas of the flight envelope?

Re: Nose “heavy”

Posted: Wed Mar 01, 2023 12:17 am

by gammaxy

Thrust line - the trouble is the builder of your airplane already went down this track by rotating the wings relative to the thrust line. Exactly how much affect, I really don’t know. I’d experiment with adjusting the throttle setting significantly at high speed to see if the nose tends to rise or lower when you increase throttle. If it lowers, that’s probably a good sign your thrust line is low. Maybe others will share what theirs does. I suspect my nose rises, but would have to do the experiment to confirm, but from memory it seems mine yaws a little and the nose pulls up a bit, but I haven’t given much thought to it in a while.

Trim springs - I’m not convinced you’ve really gone as far as sensible, but without actually seeing your installation it’s hard to speculate. I haven’t heard of anyone else with this difficulty and the stick forces in the Sonex are pretty light. I feel like I could trivially add way more up trim to mine if I wanted to. You seem to have no problem trimming it by hand and the elevator is close to centered so it’s not like there’s crazy forces involved. There may be a balance where you can’t simultaneously satisfy the highest speed and lowest speed simultaneously, but it sounds like you’re pretty close already. Curious if your installation and springs were the same as everyone else’s.

Continual tail down pressure - This is just the way things are. I feel like your emphasis on this is misplaced. My explanation is a little simplified, but the torque of the CG being ahead of the wing’s lift vector, causes the nose to drop. The tail produces negative lift to counteract this torque. As the CG moves backwards to be coincident with the lift vector, there’s no longer any torque rotating the nose, so the tail can be streamlined with zero lift. As the CG moves aft of the lift vector, it tends to rotate the nose up and the tail can counteract by providing lift as you desire, but less efficiently than the wing would have. Somewhere around here, though, you start running in to stability problems where, when disturbed upwards in pitch, the wing provides more nose up torque than the (comparatively smaller) tail immediately counteracts. There’s some window where the time constant is long enough that you can still maintain control, but this is way outside of the published CG range. If you wish to keep moving the CG aft, you need a larger and larger tail. Eventually you have tandem wings, and as you keep moving back you end up with a canard. Due to the nature of 3d fluid flow, there’s efficiency tradeoffs in all these designs. The continual down pressure “problem” you are trying to solve is simply a feature of choosing a design with a small tail in the back and operating towards the front of the CG range.

By streamlining the elevator behind the horizontal stabilizer like you really want to, you are probably slightly reducing drag, but you won’t be changing the fact that the horizontal stabilizer is still producing negative lift–it is not neutrally aligned into the relative wind. The only way to get the control surface streamlined is to change the incidence of the horizontal stabilizer, fly with the CG further aft, or drastically affect the pitching moment of the rest of the airplane to compensate, probably wasting any efficiency you’re hoping to gain. The most efficient way to produce pitching moment is at the tail (canards on the cowl would be cool though).

Adjusting pitch trim with aileron/flaps–this is probably the least efficient way possible to change pitch trim unless you’re flying a flying wing and you have no other choice. You’re effectively rotating out a fraction of the 1.5 degrees the builder built into the wings, but you’re going to have to change the comparatively smaller control surfaces by many degrees to have a noticeable impact.

Still seems clear that the only things to do are figure out the dial-a-trim, install a small fixed trim tab on the elevator, or install the adjustable tab.

Re: Nose “heavy”

Posted: Wed Mar 01, 2023 7:20 am

by Skippydiesel

So Chris, no observations on the ailerons being slightly lower than the flaps???

AND

Might raising the ailerons, to the same level as the flaps, lift the nose slightly at above 130 knots???

If I was to do this the movement ratio up: down would change - would you care to speculate on how this might effect handling???

As things stand, the aircraft can be put into a shallow turn, without rudder, and the ball remains centered.

Re: Nose “heavy”

Posted: Wed Mar 01, 2023 10:24 am

by Bryan Cotton

I used to own a 1-35C glider. You could reflex the flaps for cruise but it lowered Vne. This is because it moves the lift outboard on the wing and gives higher gust loads at the wing root. Schweizer had an optional system that would also reflex the ailerons. Then you got your Vne back.

I’m not saying this will fix your woes. My Waiex is stock and I can trim it through the entire speed range. Stock is really the way to go in my opinion.

Re: Nose “heavy”

Posted: Wed Mar 01, 2023 10:45 am

by Scott Todd

I have over 1000 hours in Kitfox’s, most of it in Classic 4’s. The models use flaperons to trim pitch. Granted, its only 100 mph but it works. Its EXTREMELY sensitive. I have also flown them with an added trim tab to the elevator. The elevator tab is much nicer and has better resolution for higher speeds such as the ones with larger motors and all the fairings. You can do it with the ailerons and flaps but I suspect it will be less efficient than doing it at the tail as Chris points out.

You are worried about drag when its just not that much. I’m a retired Aerospace Engineer, have over 2000 hours test flying over 40 years (BTW, NOT an airline pilot), have built 3 airplanes, and done first flights on 13 including all the initial trimming. Plus I’ve helped sort out flying issues on dozens of other homebuilts. Add a trim tab and you will be much happier.

I’ll try too get out to the airport today and get some pictures.

Re: Nose “heavy”

Posted: Wed Mar 01, 2023 7:39 pm

by Skippydiesel

Hi Scott,

The trim tab you are referring too - FIXED or INFLIGHT ADJUST ?

Re: Nose “heavy”

Posted: Wed Mar 01, 2023 7:55 pm

by Skippydiesel

I still don’t seem to be able to get any comment/conversation on the aileron matter - why the reluctance?

Given the span of the ailerons, even a small change in adjustment (10-15mm up) would (I would think) have a significant impact on what I call trim (may be “attitude” is better). Any such adjustment will change the up:down movement ratio - what might this do to handling?

This Sonex is currently in its TEST FLYING phase. I would expect all manor of “tweaking” would be required and anomalies addressed. All I am trying to do here is aim for the best level of trim (flight tuning) that this Sonex can achieve (with all its idiosyncrasies) in the hope that it will be an nice (not too challenging/tiring) economical, cross country tourer.

Re: Nose “heavy”

Posted: Wed Mar 01, 2023 10:15 pm

by Dave Wolfe

Most aircraft need nose down trim at high speeds and nose up trim at low speeds. Yours seems opposite to that which raises my eyebrow.

As speeds go up, so do control surface forces. You are finding your trim springs are sufficient at lower speeds where control surface forces are lower, but at higher speeds the elevator aerodynamic centering forces are overpowering the springs.

You need to get the aerodynamic forces more in balance. You can add a fixed elevator trimtab that deflects the elevator upwards, or you can adjust the incidence of the horiz stabilizer by moving the leading edge downwards compared to the trailing edge.

Re: Nose “heavy”

Posted: Wed Mar 01, 2023 11:16 pm

by Skippydiesel

Dave Wolfe wrote:Most aircraft need nose down trim at high speeds and nose up trim at low speeds. Yours seems opposite to that which raises my eyebrow.

As speeds go up, so do control surface forces. You are finding your trim springs are sufficient at lower speeds where control surface forces are lower, but at higher speeds the elevator aerodynamic centering forces are overpowering the springs.

You need to get the aerodynamic forces more in balance. You can add a fixed elevator trimtab that deflects the elevator upwards, or you can adjust the incidence of the horiz stabilizer by moving the leading edge downwards compared to the trailing edge.

Yes Dave - it would seem that my horizontal stabiliser is generating a bit too much lift, relative to other forces acting on the aircraft, hence the need for aft stick/trim to overcome this.

If you read back on this thread, this was most pronounced when I first put the aircraft into the air. Reflexing the flaps up a little, has dramatical changed things for the better (to about 120 knots).

Some of this improvement is lost at higher speeds above 120 knots.

The ailerons trailing edges, are notably lower (10-15mm) than where the flaps are now.

I understand about putting a trim tab on the elevator but consider this to be a last resort (accepting an uncomfortable compromise).

I also understand that it may be possible to change the horizontal stabiliser angle of attack (big job) to a less lift position, by raising the trailing edge edge, thus reducing the lift forces at high speeds (may also negatively change the stall characteristics).

I am trying to find out if adjusting the ailerons to match the flap angles may (1) further reduce the aft stick/trim required ? (2) what impact this may have on flying qualities?

Can you help ?

Re: Nose “heavy”

Posted: Wed Mar 01, 2023 11:27 pm

by Onex107

I would like to add two cents to this discussion. My experience is with a Onex w/ Aerovee and a nose wheel. But, I didn’t like the way the tail moved around in straight and level. Elevator trim was not a problem using the Sonex system, but the tail did not want to stay in line. So I evened out the air flow on the rudder/vertical stab by adding a gap seal to the rudder hinge line. That calmed the tail down so well that I went ahead and added gap seals to the bottom of the horizontal stab/elevators also. On the first flight I had to turn the trim down about two turns to go back to hands off. I don’t change the trim when landing so it was set to the previous cruise setting. I have to believe that I gained a lot more down force with the gap seals. Besides, they look a lot better too. It’s very easy to do, only adds ounces of weight and if you don’t like them only two rivets holds everything in place.

Re: Nose “heavy”

Posted: Thu Mar 02, 2023 1:12 am

by Skippydiesel

Onex107 wrote:I would like to add two cents to this discussion. My experience is with a Onex w/ Aerovee and a nose wheel. But, I didn’t like the way the tail moved around in straight and level. Elevator trim was not a problem using the Sonex system, but the tail did not want to stay in line. So I evened out the air flow on the rudder/vertical stab by adding a gap seal to the rudder hinge line. That calmed the tail down so well that I went ahead and added gap seals to the bottom of the horizontal stab/elevators also. On the first flight I had to turn the trim down about two turns to go back to hands off. I don’t change the trim when landing so it was set to the previous cruise setting. I have to believe that I gained a lot more down force with the gap seals. Besides, they look a lot better too. It’s very easy to do, only adds ounces of weight and if you don’t like them only two rivets holds everything in place.

Very Interesting! Onex107

My last aircraft used, from memory, two hinge points per moving surface, with a long narrow gap between wing edge & moving surface, so the gap seals that I installed, cleaned up the air flow quit a bit, especially at low speeds/high angle of attack. She was fully controllable right through her sub 30 knot stall and could pick up her skirts to achieve 120 knots indicated at 500ft ASL all on Rotax 912ULS power/fixed pitch prop.

I would have thought that on the Sonex, the full length/width piano hing on all moving surfaces, would have acted very much like a gap seal - you say not.

Any chance you would post some photos?

Re: Nose “heavy”

Posted: Thu Mar 02, 2023 8:06 am

by Dave Wolfe

So you want you elevator to be a lifting surface like a canard rather than a traditional elevator that provides downforce?

This will kill you! I wont help you achieve this. Conventional aircraft need downforce on the elevator to achieve pitch stability.

There seems to be a fundamental misunderstanding of aerodynamics going on here. The elevator MUST provide downforce in flight, this is a fundamental part of conventional aircraft design.

The way you make the elevator a lifting surface is by moving the center of gravity way aft of the approved limit. Then you have an aircraft that is unstable in pitch, unpleasant to fly, and WILL ABSOLUTELY KILL YOU AND YOUR PASSENGER!.

This is why people are hesitant to talk about aileron position with you. Because theres another huge elephant in the room not making sense.

If you suddenly stop posting here, Ill look for your tail number on kathyrns report.

Re: Nose “heavy”

Posted: Thu Mar 02, 2023 9:17 am

by Scott Todd

Dave is SO right. If readers go back thru the thread, a few of us have used the proper engineering terms to describe whats going on but I think it keeps getting missed. The horizontal stabilizer is NOT generating too much lift. Just like its NOT nose heavy. The plain simple fact is it has too much down thrust due to mods by the original builder.

In the time it takes to respond to these posts you could have turned those aileron balls a turn and tried it out. That’s what a Test Pilot/Engineer would do during Flight Testing. That’s not really my suggestion/answer but I’m just saying…And as soon as you do that, you are changing the effective airfoil of the wing so other things will change. Welcome to Aircraft Design and Test Flying

FWIW, the gap seal doesn’t really change the down force. It changes the stick free position of the elevator which changes the airplane pitch trim. Its basically doing the same thing as a fixed trim tab. It changes the elevator effectiveness, reduces drag slightly, and obviously looks better But adding them should involve going back to Phase 1 and doing some extensive testing.

I’m headed to airport this morning. I’ll take some pictures of trim tabs.

Re: Nose “heavy”

Posted: Thu Mar 02, 2023 10:54 am

by dbdevkc

I don’t recall you stating if you modified the thrust line to compensate for the modification of the wing/horizontal tail angle of incidence. If not, I could see how that by itself could cause ‘nose down’ force. And another thought although it might not have any effect, the Sonex fuselage shape could be considered a ‘lifting body’, so the builder’s mod also changed the angle of attack of that lifting body.

After all this thought, discussion, debate, and effort… I personally would have begun thinking about what it would take to make the modifications to the aircraft to return the wing and tail angle of incidence back to plans/factory spec. I would think it is fair to say that is a rather significant departure from the plans with potential unforeseen effects, despite what logical understanding of the aerodynamic forces involved might indicate.

Re: Nose “heavy”

Posted: Thu Mar 02, 2023 2:21 pm

by daleandee

Thanks to Kevin & Dave for shouting the warning that needs to be applied here. I’ve followed this thread with amazement at what I don’t see.

When I reported about the Corvair install on my Sonex I was excoriated by quite a few people as this being the way to kill myself and bring shame upon the fine line of Sonex aircraft. Even though there was much thought, engineering, & empirical evidence as to the safety of what I had done there were many voices that came and shouted the warning (even though I gave several disclaimers during the thread itself).

Where are all of those voices now?

Read the thread and see:

viewtopic.php?f=9&t=4273&hilit=justification

Larry also pointed out the concerns that many have with the Aerovee engines in the thread “Sonex High Wing”.

But here we have a Sonex that was built with admitted changes that make the airplane unstable and possibly a danger to both pilot & passenger.

Why hasn’t Sonex themselves raised their voice as to what is happening here? They sure were available when Corvairs were in the discussion!

It’s just hard to understand all the vitriol over a Corvair engine on a Sonex (which has been proven to work for many years with multiple examples flying) and no one is screaming the warning about this unstable aircraft that was built and purposely changed from the plans and now appears to be exhibiting some dangerous characteristics.

This is nothing against Skippydiesel as he seems a really good guy but builders and pilots on this forum should be forthcoming about the degree of danger that is happening here as Kevin & Dave have done …

My $00.02 and change …

Dale
3.0 Corvair/Sonex Taildragger

ArchiveBot · December 17, 2022, 6:02am

Re: Nose “heavy”

Posted: Thu Mar 02, 2023 3:46 pm

by GraemeSmith

I’ve just re-read the whole thread.

An OPINION:

At almost the outset it was stated:

Full disclosure; This Sonex has had its wing/horizontal stabiliser, angle of attack increased by 1.6 degrees from factory/plans specifications.

Engine thrust line is defined by Sonex (factory) engine frame, with latest Sonex/Rotax “bed” adapter - I would hope that this would be well within design parameters.

IMO There is the problem right there. The intended consequence of moving the 1.6 degrees has NOT had the desired effect. No amount of klutzing around this has fixed it satisfactorily. I suspect that if the 1.6 degrees was removed - all would be well. Till then it’s test piloting at its extreme.

Re: Nose “heavy”

Posted: Thu Mar 02, 2023 6:01 pm

by Skippydiesel

At last some debate - even if its hardly positive.

First; a correction - I miss quoted the change to the wing angle of attack its 1.5 degrees (not 1.6) which probably doesn’t change the negative opinions but facts are better than errors.

Second; I hade this airframe inspected by a professional aircraft engineer (I paid for his input because he has the qualifications/experience) prior to purchasing. In his opinion the changes (primarily 1.5 & wing tanks) would have little impact on the aircrafts performance & handling and may achieve the builders goal which was to correct, his perceived, error in the Sonex level flight attitude.

Third; this is an experimental aircraft - those brave soles who advocate strict adherence to doctrine/design, miss the point of this class of aircraft. Presumably they have not in any small way “personalised” their creation - in my opinion they are the poorer for it.

Those that suggest this Sonex is somehow more dangerous because of the 1.5 degree change are blowing smoke out of their nether regions - the aircraft flies and well (TO, Stall, Slow Flight & Landing all good) BUT requires some fine tuning for high speed cruise.

As a neophyte in the world of aeronautical engineering/aerodynamics I try to get some opinion on any changes I am contemplating - I ask you.

This is a completed aircraft, fundamental changes to its construction are, in my opinion, not to be contemplated ie a waste of breath.

My idea to adjust the position of the ailerons, to that of the flaps, is logical - flaps have been adjusted to trim the aircraft, at the moment ailerons are apposing/countering that adjustment. I ask your advise on the possible ramifications, not permission or approval to proceed.

Re: Nose “heavy”

Posted: Thu Mar 02, 2023 6:47 pm

by GraemeSmith

The Wing Tanks are close enough to on CG that I don’t think anyone thinks that’s a problem.

I have no idea what you paid a “professional aircraft engineer” for their services - but it’s not a trival exercise to do a complete analysis of the original design, come up with what changes may entail and then sign the aircraft off as “probably” going to be OK.

And as you then rightly point out - it’s an EXPERIMENTAL. But with EXPERIMENTAL comes a responsibility to not endanger the General Public while experimenting.

Now let’s be clear - I’m NOT accusing you of that. You have come to a body of knowledge to seek some solutions. This is good. But I wonder if you have approached the designer/factory for their input. While to some extent you might get a “liability” type “we don’t recommend you do that”. But you might also get a “we tried that and it xxxxxx…”

Proceed all you want. But don’t kill an innocent member of the public. Enough of them think we are crazy enough as it is!!

Re: Nose “heavy”

Posted: Thu Mar 02, 2023 7:46 pm

by Scott Todd

The first few flights on my Biplane (2005) took lots of forward stick to keep it level. I extended the nose during the build about 8 inches to make room for the AeroVee. I did the math and extended the aft fuselage to account for the weight shift. Here is the fixed trim tab. The other elevator has has a movable tab but I didn’t get a picture. Also you can see where I changed the stab incidence after the first few flights. None of these were enough to get it in trim. Finally after talking to some other Biplane pilots, we thought the upper wing was creating a down wash on the stab. I went flying and stuck my hand up in the airstream and it made a HUGE difference. Just breaking up the air hitting the stab worked. So I added this small tab to the upper wing. Problem solved. It looks a little goofy but it flies well,is trimable in all speed ranges, and stalls benign.

I have an adjustable tab on my Onex. Same as I had on my Sonex. It works well and I like it a lot. I forgot to get a picture but this link should get you to one.

viewtopic.php?f=5&t=6667&p=50596#p50596

You can see a fixed tab under the right aileron. My Onex was started by someone else and apparently a wingtip was installed slightly warped. I discovered it after careful analysis after noticing the hard roll after first flights. Instead of taking it apart and rebuilding it, I choose the tab for now. One day I may fix it but I got it flying straight and I’m happy with it. It tends to consistently drop that wing first in a stall which is totally understandable.

Its not going to spontaneously explode. The wings are not going to fly off. The extra downthrust is an annoyance but it can be trimmed out. Add a trim tab and enjoy your new airplane

Re: Nose “heavy”

Posted: Fri Mar 03, 2023 12:09 am

by sonex892.

I think the extra incidence is an interesting idea. Done correctly it would definitely improve the visibility in cruise and also get it closer to the stall for 3 point landings. I previously built a sonerai and always thought if I was to build another I would consider increasing the incidence. Per the plans the sonerai wings were set at 0 deg incidence, the stall angle on these like the sonex is also way higher than the 3 point stance.

I dont get your thought, that the elevator pushing down is creating more drag on the wing. I’m no aeronautical engineer but or a given weight and speed the wing the be at a given angle of attack regardless, wouldn’t it?. The only time the elevator wont be pushing down when flying in a normal condition is with a c of g that is dangerously too far aft. I too would not be messing with reflexing flaps and ailerons, apart from the previous comments on reflexing the ailerons, the aileron up travel may be restricted by the counterweight.

I would think your problem is the thrust line pulling the nose down and you just dont have enough tension either on the fixed spring or on the trim spring to overcome it.

I would check the thrust line by climbing high then whilst level hold a constant speed check the elevator position. Then go to idle and glide at the same speed to see if the stick is in the same or similar position. If the stick position is alarmingly different address the thrust line of the engine. My 3300 also pulls down but I dont have an issue with that as the trim has enough authority to be set at any c of g and speed higher that 70 kts. I only ever run out of back trim when slowed to about 70 kts.

Personally I would just add an adjustable trim tab as per the plans and move on, it is very effective.
Steve

Re: Nose “heavy”

Posted: Fri Mar 03, 2023 2:26 am

by Murray Parr

I installed the dial a trim to my Waiex B and followed the instructions precisely and found the adjustable spring wasn’t anywhere near strong enough to put the elevator in the desired position so I added a much stronger spring which acheived the specified position. I haven’t flown it yet (soon:-) but I expect to need an aditional spring for this. I wouldn’t be too worried about adding a heavier spring while stil utilising your inner spring (Bunnings has a great assortment to choose from).

I think you will struggle to get much experienced advice with your question as you are likely the pioneering test subject for this. Maybe reach out to Sonex tech support and see if they have any insite to add. I would just go ahead and adjust your ailerons in small increments and test to see if any improvements or declines in performance are made. can always adjust back if necessary.

If you have the conventional tail instead of Waiex, you could just convert to the lever operated adjustable trim tab which would give more range is another potential solution. I also don’t think your 10mm elevator position above the stabiliser is an issue, a lot of the 10mm would probably dissapear with dynamic forces that don’t show while parked, have you thought of that?

Re: Nose “heavy”

Posted: Fri Mar 03, 2023 4:55 am

by Skippydiesel

Scott Todd you are a gentleman and generous with your experience, and advice - Many thanks.

I adjusted my ailerons today - one full turn of the ball end, on each short aileron rod, has brought them exactly level with the flap trailing edges. I was going to fly but the combination of dehydration/low blood sugar (hadn’t eaten/drunk in about 8 hrs) and a gusting cross wind changed my mind.

Will fly at the next opportunity and post a report.

Re: Nose “heavy”

Posted: Fri Mar 03, 2023 6:02 am

by Skippydiesel

Hi Steve,
“…that the elevator pushing down is creating more drag on the wing…”

Okay, in essence I am a retired farmer, not an engineer or fluid dynamists, so will just mumble in the hope of being mistaken for intelligent -

The horizontal stabiliser is sized and oriented (angle of attack)
So as to counter any tendency of the aircraft to stall tail first i.e the stabiliser will still be generating lift after the main wing stalls, so when the wing stalls the aircraft will drop nose down, gain speed & the wing achieve lift/out of stall.
To accommodate varying load conditions/locations.
The attached Elevator is a pilot controlled movable aerofoil that can modify the amount of stabiliser lift required for a given load/distribution and air speed.

If the stabiliser is too effective (generating more lift than necessary) the elevator must be employed to counter this lift. The rotational force generated acts on the main lifting surface (wing) as if additional load is being added which may result in a less than optimum angle of attack, reducing efficiency/speed, requiring more energy to stay aloft.
In addition the Elevator, being deployed into the slip stream, will create additional drag.

Could all be BS!

Re: Nose “heavy”

Posted: Fri Mar 03, 2023 6:20 am

by Skippydiesel

Murray Parr wrote:I installed the dial a trim to my Waiex B and followed the instructions precisely and found the adjustable spring wasn’t anywhere near strong enough to put the elevator in the desired position so I added a much stronger spring which acheived the specified position. I haven’t flown it yet (soon:-) but I expect to need an aditional spring for this. I wouldn’t be too worried about adding a heavier spring while stil utilising your inner spring (Bunnings has a great assortment to choose from).

I think you will struggle to get much experienced advice with your question as you are likely the pioneering test subject for this. Maybe reach out to Sonex tech support and see if they have any insite to add. I would just go ahead and adjust your ailerons in small increments and test to see if any improvements or declines in performance are made. can always adjust back if necessary.

If you have the conventional tail instead of Waiex, you could just convert to the lever operated adjustable trim tab which would give more range is another potential solution. I also don’t think your 10mm elevator position above the stabiliser is an issue, a lot of the 10mm would probably dissapear with dynamic forces that don’t show while parked, have you thought of that?

Gudday Murray,

“…followed the instructions precisely and found the adjustable spring wasn’t anywhere near strong enough …”

I am perversely pleased, that there is one more Sonex pilot that has found the Sonex adjustable trim spring to be not strong enough. Like you, I sourced my additional spring (goes inside the Sonex one) from Bunnings Aerospace

“…a lot of the 10mm would probably disappear with dynamic forces that don’t show while parked, have you thought of that?..”

In short yes. In flight, I employ a very expensive highly accurate piece of plywood, to measure the stick position, relative to the bottom of the instrument panel. When on ground, I can move the stick to the position I have marked on the ply, look back and see the position of Elevator as it was in flight.

It will be interesting to see if the Elevator position changes, after the ailerons have been adjusted to the Flap position - will let you know.

I have yet to fill my fuselage tank, about 29Kg over the pilot/passenger legs - fwd of CofG. As is, I have no aft trim left at 135 knots. (I do have plenty of stick movement) If the aileron adjustment doesn’t lighten the stick loads sufficiently, I will have consider an Elevator trim tab of some description, so that I can fill this tank.

Re: Nose “heavy”

Posted: Fri Mar 03, 2023 6:30 am

by Skippydiesel

sonex892. wrote:
I would think your problem is the thrust line pulling the nose down and you just dont have enough tension either on the fixed spring or on the trim spring to overcome it.

I would check the thrust line by climbing high then whilst level hold a constant speed check the elevator position. Then go to idle and glide at the same speed to see if the stick is in the same or similar position. If the stick position is alarmingly different address the thrust line of the engine. My 3300 also pulls down but I dont have an issue with that as the trim has enough authority to be set at any c of g and speed higher that 70 kts. I only ever run out of back trim when slowed to about 70 kts.

Personally I would just add an adjustable trim tab as per the plans and move on, it is very effective.
Steve

Sorry Steve, did no fully respond to your suggestions/observations.

I will certainly try your suggestion for determining engine/prop thrust influence.

I don’t have any adjustable spring trim issues below 120 knots or at landing pattern speeds.

Before you added the Elevator trim tab, did you find that you required more aft trim as your speed increased?

Re: Nose “heavy”

Posted: Fri Mar 03, 2023 10:40 am

by Scott Todd

The Aileron trim tab on my Onex is the second one. The first was smaller and I need a bit more. I sent Skippy a PM with a suggestion.

Re: Nose “heavy”

Posted: Fri Mar 03, 2023 12:29 pm

by dbdevkc

daleandee wrote:But here we have a Sonex that was built with admitted changes that make the airplane unstable and possibly a danger to both pilot & passenger.

Why hasn’t Sonex themselves raised their voice as to what is happening here?

I am a little surprised about that as well. I can see why people would be a bit concerned about putting an engine on the front that is over the weight limit set by the factory, for more than just W&B issues. Although I’m not quite as concerned as I have a 3.0 sitting on my coffee table waiting and ready to go - lol.

“Those that suggest this Sonex is somehow more dangerous because of the 1.5 degree change are blowing smoke out of their nether regions - the aircraft flies and well (TO, Stall, Slow Flight & Landing all good) BUT requires some fine tuning for high speed cruise.”

Maybe. But maybe not. Has the factory given their opinion of the change and what they would recommend? Has the angle of thrust been changed such that it remains in alignment with the wing angle of attack? 1.5° does not seem like much of a change - but it does seem to be giving you fits trying to adjust flight characteristics for that change.

Re: Nose “heavy”

Posted: Fri Mar 03, 2023 12:59 pm

by Dave Wolfe

Naah.. whats giving him fits is not using an aerodynamic fix for an elevator trim problem.

The waiex elev trim springs are a v tail bandaid because its difficult to rig up two elevator trim tabs. The adjustable standard sonex straight tail trim tab seems to work well by all accounts.

Im sure all the prop planes I flew had 1.5 degrees of engine mount sag.

Re: Nose “heavy”

Posted: Fri Mar 03, 2023 3:16 pm

by Scott Todd

I don’t mean to throw Murray under the bus but his observation the spring isn’t strong enough may be invalid. He notes he hasn’t flown it yet. The spring isn’t intended to take the static weight of the elevator on the ground. Its meant to balance the aerodynamic loads.

Also, Skippy’s 10mm up position is in flight. This much elevator deflection is required to offset the added down thrust. Its not a big deal but is definitely costing him speed. He could be losing an entire knot or two A small fixed trim tab on the underside of the elevator will solve his stick force problems and he can get it adjusted so the Sonex spring system works as designed. It will still fly with the elevator trailing edge up slightly unless he monkeys with the aileron and flap positions more. Changing this rigging is not really advised as it deviates further from the original design and could have other consequences.

For review, and those who have not read the entire thread, his airplane was built with different wing and tail incidences. This resulted in added down thrust. He has been trying to find a solution to take the added stick forces out at higher speeds. Raising the flaps was suggested. He did that and it helped. Raising the ailerons was also suggested. He has done that but has yet to fly it again. Adding an elevator fixed trim tab was suggested. This requires some minor fabrication and installation and he has not tried that yet.

Re: Nose “heavy”

Posted: Fri Mar 03, 2023 11:47 pm

by Skippydiesel

Flight Test Report;

Unfortunately low cloud base about 2500-3000ft - airfield 900ft & some rain showers around. Air, not what I would call turbulent, just a little lumpy (typical Sydney Basin weather).

Aileron adjustment has worked beyond my expectations, stick forces much lighter. Trim no longer all the way aback, at 135 knots indicated. May have picked up a knot or two, hard to say due to lumpy air.

Ailerons adjusted level with flap, on ground - During high speed cruise noticed ailerons still slightly down, probably due to air load on flap - have adjusted ailerons another 1/2 turn up (will report any change).

Tried Steve’s suggestion for diagnosing thrust issues - didn’t realy have sufficient altitude (balls) to dive steep enough/long enough to get the same air speed, as in cruise. The little I did did not seem to change the, already improved, stick forces - will try again another day, from above 5500ft.

Re: Nose “heavy”

Posted: Sat Mar 04, 2023 8:19 am

by Skippydiesel

Scott Todd wrote:…
For review, and those who have not read the entire thread, his airplane was built with different wing and tail incidences. This resulted in added down thrust. He has been trying to find a solution to take the added stick forces out at higher speeds. Raising the flaps was suggested. He did that and it helped. Raising the ailerons was also suggested. He has done that but has yet to fly it again. Adding an elevator fixed trim tab was suggested. This requires some minor fabrication and installation and he has not tried that yet.

Scott - I think you are leaping to a conclusion with this statement.
It is correct that the aircraft has been built with a deliberate 1.5 degree (up) change in flight surface angle of attack.
As for the consequences of that change - it is more likely that my attempt to adhere to the Sonex rigging instructions, designed for a standard aircraft, is where the heavy stick forces have their origin.
I had to start with the Sonex specifications (I had no other) which have clearly not resulted in the handling characteristics (especially at high speed) that most builders seem to experience from the first (?) flight.
The latest adjustments have put a huge smile on my face & spring in my step. I may be straying somewhat from doctrine but it seems the girl & I may be developing some simpatico.

Re: Nose “heavy”

Posted: Sat Mar 04, 2023 10:05 am

by Scott Todd

Its not leaping to conclusions. Its geometry. The engine now has 1.5 degrees more down thrust compared to the wing and stab center lines. This will require more nose-up trim and be exaggerated as speeds increase.

Re: Nose “heavy”

Posted: Sat Mar 04, 2023 6:37 pm

by Skippydiesel

Scott Todd wrote:Its not leaping to conclusions. Its geometry. The engine now has 1.5 degrees more down thrust compared to the wing and stab center lines. This will require more nose-up trim and be exaggerated as speeds increase.

Fair comment!

Re: Nose “heavy”

Posted: Sun Mar 05, 2023 2:15 am

by Skippydiesel

Flight Test Report; .9 hrs, 6500ft, OAT 16C

Plus 1/2 additional turn (1 1/2 turns since start of adjustments) UP for both ailerons.

On ground, the ailerons are now 2-3mm above the flap position. In the air still slightly down, relative to the flap - I think I will leave it at that (for the moment)

In high speed cruise, 144 Kn TAS, Sonex is now very well behaved. Stick forces have lightened up considerably. Trim indicator has moved from full aft to about neutral. Couldn’t be happier.

Now that I have a reasonably predictable aircraft, that I am no longer fighting with & engine temps are tolerable, I will focus on the RAA Test Flying Program.

After Test flying completed (& signed off) I plan to return the Sonex to the workshop to revise cowling/engine lay out, with a view to achieving better cooling.

My thank to one & all for your advice/observations - I hope I can call on you again, to “shoot the breeze” or solve a niggling aircraft problem.

Re: Nose “heavy”

Posted: Sun Mar 05, 2023 3:33 pm

by Bryan Cotton

Nice! Glad you got it figured out.

Re: Nose “heavy”

Posted: Tue Mar 14, 2023 3:25 am

by Skippydiesel

Have decided to fit Peter Anson’s Flap Stops - have ordered - will be with me later this week.

Have been persuaded by commentary on this Forum and my recent(flap/aileron adjustment) experience - The aerodynamic force/up pressure on the flaps is considerable and the only thing holding them against moving up (in high speed cruise) is the actuating linkage on the inboard end. The multiplier effect of having the linkage at one end and the rest of the flap, unsupported against movement seems illogical - hence placing an adjustable stop/support at about mid flap span (have yet to see the detailed installation instructions).

I will let you know how it all pans out.

Re: Nose “heavy”

Posted: Tue Mar 14, 2023 9:49 am

by DCASonex

On an A series Sonex with flap lever on left side, those stops will make a very noticeable improvement and well worth the investment.

Once you get the stops adjusted where you want them, might consider using the final dimensions to make solid stops that contact a broader area near the top edge of the flaps. The small bolt heads of the adjustable stops contact a relatively soft area on the flap and I was concerned about possible cracking of the aluminum. Solid stops can be made from firm plastic or even wood.

David A.

Re: Nose “heavy”

Posted: Wed Mar 15, 2023 6:04 am

by Skippydiesel

DCASonex wrote:On an A series Sonex with flap lever on left side, those stops will make a very noticeable improvement and well worth the investment.

Once you get the stops adjusted where you want them, might consider using the final dimensions to make solid stops that contact a broader area near the top edge of the flaps. The small bolt heads of the adjustable stops contact a relatively soft area on the flap and I was concerned about possible cracking of the aluminum. Solid stops can be made from firm plastic or even wood.

David A.

For this very reason, I had intended to fit two stops per flap but Peter has advised that this is unnecessarily - so one each for now.