Corvair Engines - The Justification Series

[LarryEWaiex121]

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

Larry
Waiex121YX, Camit 3300, Dynon Skyview

[daleandee]

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

Hi Larry,

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

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

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

Mr. Lee's complete post is found here:

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

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



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

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

[daleandee]

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

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

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

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

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

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


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

[lutorm]

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

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

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

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

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

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

[dbdevkc]

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

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

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

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

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

[petep]

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

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

[vigilant104]

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

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

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

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

[lutorm]

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

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

[LarryEWaiex121]

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

Larry
Waiex121YX

[daleandee]

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

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

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

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Someone pointed out the factory notes on weight increase:

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

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

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



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

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

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

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

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

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

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