Aeroconversion brake performance?
Posted: Wed Mar 16, 2022 7:34 pm
by 13brv3
Greetings,
I can already hear a chorus of groans from people reading that subject line 
I have a Onex, and it has the Azusa mechanical drum brakes. I think Iāve read everything thatās been written about making these works, but no luck so far. Iām going to spend one more session working on them, and if there isnāt a marked improvement, Iām giving up. Note that this thread is NOT asking for tips on making these work unless you have a secret thatās never been published.
I started a Onex project years ago, but life got in the way and I sold it. On that install, I had the Aeroconversion brake upgrade, which I thought was clever, and certainly compact. Iāve read plenty of comments both good and bad. Other hydraulic brakes exist (OāKeefe, Matco, etc) but theyāre not nearly as compact, though I expect theyād have more braking force.
My question is whether the Aeroconversion brakes will hold enough to do a high power run-up? I donāt need max braking force, but I DO need to be able to do a run-up, which I canāt do now. I would likely start with a single handgrip master, but eventually would go with differential of some sort.
For anyone who didnāt like them and took them off, I might be interested in buying them.
Thanks,
Rusty
Re: Aeroconversion brake performance?
Posted: Wed Mar 16, 2022 10:18 pm
by mike.smith
Iāve had the Aeroconversion brakes on my Sonex for years, and they work great. I usually run up to around 2400 or 2500 RPM with no issues.
Re: Aeroconversion brake performance?
Posted: Thu Mar 17, 2022 12:23 am
by 13brv3
Thanks for the comments. I have a 912UL which is supposed to be run up to 4000, but I canāt make 3000. Itās quite possible the geared engine will be more of a challenge for run-ups than the direct drive engine.
Rusty
Re: Aeroconversion brake performance?
Posted: Thu Mar 17, 2022 2:26 am
by Kai
Hi,
I had the Aeroconversion hydraulic brakes in my 120HP Jab Sonex A. The total package with calipers and lever operated master was provided by Sonex. They provided holding power barely adequate for a modest static runup. Braking power on my fairly short grass strip was an experience for those especially interested in hair raising situations.
The plane has since been re-engined with the R912ULS. To nobodyās particular surprise brake efficiency has gone from hair raising to useless. Ground runup is barely 3000 rpm, which should be 4000. Roll-out braking is now even worse, as the plane put on some weight during the engine swap.
I canāt decide what to do. I like the Sonex system and its parking brake setup. Differential braking is not a neccessity. However, it has been explained by knowledgable parties to me that more pressure is needed. The culprit in the setup is the master, which is too big (3/4āā). This is the smallest that the manufacturer can supply. And a smaller master would mean longer lever travel- there goes the parking brake!
I know of one R912 Sonex which kept the original Aeroconversion calipers and went with two hand lever operated masters (1/2āā) from Matco (??) mounted centrally on a bracket (so no parking brake). It transformed the roll-out braking.
What to do??
Re: Aeroconversion brake performance?
Posted: Thu Mar 17, 2022 9:17 am
by 13brv3
What to do indeedā¦ Great info, though you arenāt making my decision easier
A smaller diameter master would be the key, and itās good to know that the Aeroconversion brakes will work if you get them enough pressure. In theory, there really shouldnāt be much travel in the master cylinder. If there is, it would mean thereās air in the lines, or the lines are expanding under pressure. There may be better tubing options to minimize expansion.
I removed the original brake handle, because I donāt have enough hands to do a run-up with a separate brake handle. I went to a stick mounted lever, which I like. Toe brakes are an option as well, and as a last resort maybe heel brakes.
Rusty
Re: Aeroconversion brake performance?
Posted: Thu Mar 17, 2022 9:59 am
by Kai
Rusty,
I think youāve got a point: a hand lever operated master mounted on the stick might be an option. Both Matco and Hegar can supply, I think. However, I am uncertain what dimension to select (1/2āā or 5/8āā).
And, youāre right. The travel on the lever down on the master is really not anything to worry about: its the huge brake lever poke Sonex suggests that really restricts practical parking brake operation: once finished it is not so easy to rebuild without starting from scratch.
Another issue: the dot 5.0 brake fluid Sonex (and the brake components manufacturer) suggests, is silicone based. Use anything based on glycol (common for cars), and whoops there goes anything made of rubber. However, the red automatic transmission fluid (formerly ATF A), now Dextron something, is also based on silicone. My brother in law uses it with great success on his aircraft with hydraulic Beringer disc brakes. It stops the thing like there is no tomorrow. I am wondering why Sonex has not suggested this option- liability?
Re: Aeroconversion brake performance?
Posted: Thu Mar 17, 2022 10:08 am
by XenosN42
Hi all,
Have you been asked what is the best modification you have made to your Sonex? My answer would be using the Sonex hydraulic brakes and the OāKeefe hand lever master cylinder. http://www.okeefeaero.com/-hydraulic-brakes.html
I fly a OneX, AeroVee & Sensenich prop. I can run the engine up to 2600 RPM without any wheel slip or creep. Thatās high enough to hear that the engine is running well and that the numbers are where they should be. My WOT for take off is ~ 3200 so 2600 is good enough for the run up.
The biggest advantage of the hand brake is that I can do short field take offs properly. Left hand on the throttle and right hand holding the brake. It also gives me a good parking brake. This is hard to describe in words; really deserves a picture but I donāt have one. When I squeeze the brake handle a gap opens up at the bottom of the handle. I stick a narrow piece of metal into that gap. I can then release my hand, but the handle doesnāt move. Simple & effective.
Re: Aeroconversion brake performance?
Posted: Thu Mar 17, 2022 11:08 am
by 13brv3
Outstanding information! That sounds like my best plan for right now- Aeroconversion brakes and Hegar 1/2" bore hand lever. At some point Iāll want to figure out how to make that differential, but I donāt need it for now, or maybe ever. Iām still committed to trying to fix the mechanical brakes one more time, probably tomorrow.
Rusty
Re: Aeroconversion brake performance?
Posted: Fri Mar 18, 2022 3:37 am
by Kai
Iām with Rusty here!
But still- OāKeefe and Hegar: are those the same? A little confusing in the two last postings.
Thx
Re: Aeroconversion brake performance?
Posted: Fri Mar 18, 2022 9:38 am
by 13brv3
Kai wrote:But still- OāKeefe and Hegar: are those the same? A little confusing in the two last postings.
Iām assuming OāKeefe is just selling the Hegar master cylinders without mentioning it, or giving any other useful info like bore size or the stick clamping size. The lack of info seems to make it cheaper though I have an email into OāKeefe, but will call them today if they donāt reply this morning.
As tempting as it is to give the mechanical brakes one more try, I had to ship my Dynon back for service, so the plane will be down for 3-4 weeks. Since I have that much time, I think Iāll just go straight to the hydraulic brakes, and get the wheel pants installed. I can still run the engine and taxi, but thereās a big hole in the panel where my EFIS/EMS should be.
Rusty (looking for a spare D180)
Re: Aeroconversion brake performance?
Posted: Fri Mar 18, 2022 9:58 am
by Onex107
In my tri gear Onex, Aerovee, I had the same problem with needing both hands to hold the brake during a runup. I added a single foot brake centered in front of the rudder pedals. Itās made of welded alum. angle and tubing with a rod connected to the bottom of the brake lever. I can do a wide open runup without a problem. If you want pictures email me at flyvfr@comcast.net.
Re: Aeroconversion brake performance?
Posted: Fri Mar 18, 2022 12:19 pm
by 13brv3
A single foot pedal would be fine for run-ups, but way less than ideal for use during roll out, particularly in a tailwheel aircraft. No word from Oākeefe yet. Spruce has no stock on the Hegar, and Hegarās web page appears to be from March 2009.
Out of curiosity, doesnāt anyone happen to know the bore of the master cyl that Sonex supplies?
Rusty
Re: Aeroconversion brake performance?
Posted: Sat Mar 19, 2022 3:13 am
by Kai
Rusty,
See my posting of March 17. The diameter of the MCP master cylinder supplied by Sonex is 3/4āā. It is a pity the manufacturer canāt supply anything smaller- it would have made life so much easier!
Kai
Re: Aeroconversion brake performance?
Posted: Sat Mar 19, 2022 10:45 am
by 13brv3
I missed that Kai. MCP seems to offer only the 3/4" and a reduced power 7/8". They seem to be mostly targeted to Kart racing, and I guess maybe they never want 1/2".
Ordered the brakes from Sonex, and a handgrip type master from Spruce. The master is a drop ship item, but Iāve ordered other Hegar masters in the past, and it only took a couple days. OāKeefe didnāt have them in stock either. Sadly, I probably have plenty of time waiting for the return of the Dynon, probably mid April.
Rusty
Re: Aeroconversion brake performance?
Posted: Sat Mar 19, 2022 11:37 am
by DCASonex
If going to all the trouble of making a special one of a kind single hydraulic actuator for the brakes, why not just make two toe pedals, each with one cylinder to operate one brake. That alone doubles the force applied to each brake by each cylinder as compared to one cylinder displacing its force over twice the piston surface area.
That may also one one of the reasons OāKeeffe brakes out perform Sonex brakes. Sonex uses two pistons pressing on one side of each brake disk (trying to push the wheel off the axle) While OāKeeffe bakes are full floating calipers with a single piston clamping the brake disk from both sides, thus the area of one piston applies same force to two pads, one on each side. The force of one cylinder operating both Sonex brakes is distributed over the surface of four pistons, while with toe brakes, one cylinderās force is applied only to only one piston. I have found the standard OāKeeffe cylinders well matched to the toe bakes on my Sonex TD with a CAMit 3300 (127HP). They can hold back a full power run-up but.ā I once had a stray air current, at our hilltop airport, lift the tail and almost invert my plane when doing a full power run-up. I now only do that with tail tied to something very secure. Holding at the 1,500 RPM recommended for mag check requires very little force.
David A.
Re: Aeroconversion brake performance?
Posted: Sat Mar 19, 2022 4:32 pm
by 13brv3
For a hydraulic system like this, you need pressure, and fluid transfer. For disc brakes with the correct tubing and no air bubbles, there is essentially no fluid transfer so that can be ignored leaving only pressure. When we push on the master, we want to minimize our force, by maximizing the pressure. This is done with a smaller piston.
Say you push with 10 lbs of force on the master cylinder. If you have a larger piston with 2 square inches of area, then you generate 5 psi of pressure (10/2). If you have a smaller piston with 1 sq in of area, now you generate 10 psi (10/1). For the master, a smaller piston gives you more pressure for a given amount of force.
Since we arenāt really displacing any significant amount of fluid with a proper brake setup, that one small piston can operate one or two brakes with the same force. Having dual masters gives you differential pressure, but no increase in brake force assuming the piston size isnāt changed.
On the caliper end, we want to maximize force with the pressure we have available. If you have 10 psi of pressure available, you want the most piston area you can get (10 x total sq inches). For the caliper, more piston area (larger pistons, or more pistons) is stronger.
Of course thereās a whole other layer of brake performance when you consider pads. Brake pad surface area and compound can make the difference between working well, and not working, even when the rest of the system stays the same. Nothing is ever simple.
Rusty
Re: Aeroconversion brake performance?
Posted: Sat Mar 19, 2022 6:42 pm
by Murray Parr
Rusty is correct. Having one master cylinder supplying each slave cylinder independantly will reduce the pressure if the master cylinder size stays the same. I went with 1/2" hegar cylinders and copied the setup and geometry of the vans toe brakes. I havenāt tried them yet however, the geometry sure feels right. Wasnāt too hard to manage as I just removed the rudder pedals and did it all on the bench.
Re: Aeroconversion brake performance?
Posted: Sun Mar 20, 2022 3:16 am
by Kai
Murray,
I might be a little slow on the uptake, and I think I understand what youāre saying- but just to make sure:
SYSTEM REBUILD:
I want to keep the existing calipers from Sonex. Presently they are both operated with the single Ćø3/4āā master from MCP (supplied by Sonex). I would like to get rid of the MCP since both holding power during runup and braking power during rollout is unsatisfactory.
SCENARIO #1:
I could replace the Ćø3/4āā MCP master with one single Ćø1/2āā stick mounted hand operated Hegar master. This will increase fluid pressure in the system and consequently also the fluid force on the Sonex puck pistons. Hence much better braking. Correct??
OR:
SCENARIO #2:
Differential braking is a safety item. Like David suggests, I could replace the single master Ćø3/4āā MCP with two pcs Ćø1/2āā masters from Hegar, ONE DEDICATED MASTER FOR EACH CALIPER. This will also increase fluid pressure in the system. Hence better braking, but not as much as scenario #1. Correct??
And of course the the milion dollar question: will this dual Ćø1/2āā master setup provide any overall better braking than the single Ćø3/4āā setup presently in the plane???
Much obliged for any comments!
Thx
Kai
Re: Aeroconversion brake performance?
Posted: Sun Mar 20, 2022 10:30 am
by 13brv3
A smaller master cylinder bore will give more brake pressure āfor the same force on the pistonā. If MCP made a 1/2" master that was a drop in replacement for the 3/4" you have, then it would absolutely improve braking. It makes me start to wonder how hard it would really be to make a custom master cylinder.
When you start considering changing from the tall handle Sonex likes, to a stick grip, or foot pedals, you are also changing the amount of leverage you have to push on the master cylinder. Youād have to look at the geometry of the actuation to determine if you gain or lose leverage compared to what you have now. Also consider that you probably have more force available from your foot than you have in grip strength, so a toe brake may gain performance simply because of the extra force you can apply.
Rusty
Re: Aeroconversion brake performance?
Posted: Sun Mar 20, 2022 10:39 am
by lpaaruule
This is what I did, itās not perfect, but Iāve been able to keep from rolling at full throttle:
viewtopic.php?f=39&t=2961&start=30#p45973
One recent observation is that the brake pads are wearing at an angle that suggests the rotors are flexing due to the increased pressure. I still occasionally think about switching to a traditional caliper design.
Re: Aeroconversion brake performance?
Posted: Mon Mar 21, 2022 2:51 am
by Kai
All,
Further to our recent discussion, the concensus seems to be that a differential system with toe brake pedals linked up to 2 pcs Ćø1/2āā master cylinders is the preferred way to go. Next comes the single hand lever brake with 1 pcs Ćø1/2āā master on the stick.
No mention has been made of differential heel brakes. I seem to recall that in my far away younger days I accumulated some hours in a plane so equipped. As far as I can remember, they worked as advertised. Yet- nothing! Is there any paricular reason for this?
What about 2 separate Ćø1/2āā master cylinder heel brakes, one for each caliper? Hegar seems to have something particularily well suited for this. I am thinking it might be possible to manufacture some sort of solid base plate with appropriate brackets for the masters. The base plate could then be bolted to the cockpit floor for the shoe heels to comfortably control the ābuttonsā.
Comments?
Thx
Kai
Re: Aeroconversion brake performance?
Posted: Mon Mar 21, 2022 7:23 am
by GraemeSmith
Kai wrote:I seem to recall that in my far away younger days I accumulated some hours in a plane so equipped. As far as I can remember, they worked as advertised. Yet- nothing! Is there any paricular reason for this?
I believe heel brakes have fallen out of favor because they cause even more ground loops and outright nose overs than toe brakes. They are prone to accidental activation by lazy feet. Or people like me with big feet that can keep their heels on the floor and work the rudders with their toes.
I flew a Champ that had them and after an hour of pattern work my calves were aching because I was having to hold my feet up so unnaturally high in order to keep my heels away from them!
Re: Aeroconversion brake performance?
Posted: Mon Mar 21, 2022 8:21 am
by Bryan Cotton
I learned to fly with heel brakes. They are not as convenient as toe brakes. The advantage of learning to fly in an antique is that you learn to never be dependent on brakes for normal ops. But I personally think they are fine.
Re: Aeroconversion brake performance?
Posted: Mon Mar 21, 2022 9:38 am
by DCASonex
Kai,
A single 1/2" bore master cylinder has slightly less area than a 3/4" bore ( 0.196 Sq. in vs 0.442 Sq. in. ) and thus would result in more hydraulic pressure for a GIVEN FORCE on the master cylinder. However, there are other considerations. A 1/2" bore cylinder will have to move a bit more than twice the distance to move the brake pad cylinders a given distance than would the 3/4" bore. That makes maintaining complete fill in the cylinders more important, and less able to compensate for any air that might find its way into the system. I am not sure what size the Hegar cylinders are that I purchased from OāKeeffe (was Great Plains back then) with my toe brake setup, These cylinders do not have built in hydraulic fluid reservoirs like those of some much more expensive and bulky cylinders and over time I find a bit of air in the lines, but this only means slightly more travel of the pedals. I do bleed and top them up about twice a year before air affects operation. Another consideration is the geometry of how the master cylinders are to be operated. A long lever can greatly multiply the force applied to the cylinder while requiring longer hand travel. Foot pedals and hand grips have about same amount of travel, but two feet can usually apply a lot more force than one hand.
David A.
Re: Aeroconversion brake performance?
Posted: Mon Mar 21, 2022 10:15 am
by Scott Todd
Iāve flown a few different Sonexās with the hand brake. For operating out of long or grass runways, they were adequate. I get Johnās goal was simple and inexpensive, which he attained. However, for operating on tight ramps, short runways, strong crosswinds, nothing beats differential toe brakes. Every certified GA airplane built over the last 70 years canāt be wrong. My brakes are discussed a bit on the Onex forum. The probably cost $1000 after the custom hoses, master cylinders, reservoir, AeroConversion brakes, etc but were well worth it. They will hold a full power run-up with a bit of work but a Mag check is no problem. And when I want to stand on them to make a short field or turnoff, they really work!
Here is a nice document from Matco talking about brake geometry.
https://www.google.com/url?sa=t&rct=j&q ā¦ XkB5EXrlkU
Re: Aeroconversion brake performance?
Posted: Mon Mar 21, 2022 12:25 pm
by 13brv3
Good to see some actual numbers, even if it only relates to the Matco brakes. I can certainly verify that direct pressure on heel brakes is terrible, though good exercise Iām not a fan of heel brakes, and toe brakes never seem to fit my big feet. Itās always too easy to be on the brake when you donāt mean to be.
Re: Aeroconversion brake performance?
Posted: Mon Mar 21, 2022 1:27 pm
by Scott Todd
Its an Experiment(al) homebuilt airplane. Make those rudder pedals and brakes any way you want to fit your feet. If you canāt, someone in your local EAA chapter can weld them or modify what you already have
Re: Aeroconversion brake performance?
Posted: Mon Mar 21, 2022 1:31 pm
by 13brv3
Can they also move the fuel tank out of the way so I can make the toe brake lever taller I might end up making a small lever thatās only on the inside or outside edge of the pedal, so I can more easily avoid it. A dual hand grip style on the stick would be fine as well, but it would be overly bulky with hydraulic brakes. I made a dual handle for another plane with mechanical cables, and really liked that.
Rusty
Re: Aeroconversion brake performance?
Posted: Mon Mar 21, 2022 4:13 pm
by GraemeSmith
Just for fits and giggles - my handbrake is hand brakeS. I cut the wire and attached it to two levers and "T topped the handles so I can twist the top for differential braking.
It should be noted that Sonex donāt recommend differential brakes with the non-castoring tailwheel. I can see why - it adds side load to the setup that was perhaps never intended. And for sure you can āskidā the tailwheel if you try - not very hard.
I do like the ability to differential brake on one main to help control any potential ground loop. But I avoid using it to spin the plane around. The fasteners in the 6" machined wheel fork are not set up to take it.
Re: Aeroconversion brake performance?
Posted: Mon Mar 21, 2022 5:30 pm
by mike.smith
Kai wrote:The plane has since been re-engined with the R912ULS. To nobodyās particular surprise brake efficiency has gone from hair raising to useless. Ground runup is barely 3000 rpm, which should be 4000. Roll-out braking is now even worse, as the plane put on some weight during the engine swap.
That doesnāt seen to make sense. The ENGINE spins that fast, but with the gear reduction (2.43), the max RPM of the PROP is 2,386 rpm. Thatās according to Rotaxās info on that engine. That engine is 100 hp, vs the 120 hp of something like the Jab 3300. If the brakes hold for a Jab why not a Rotax?