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Certificated to experimental for leading edge cuffs

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Petehdgs

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Years ago I read about a Cherokee 140 owner who wanted to experiment with Vortex Generators, which at the time were a new idea. He converted his certificated airplane to experimental so he could do his research on his own plane. Now Vortex generators are available for all kinds of applications on certificated aircraft.

I find myself in a similar situation and would like to ask your advice. I have a Mooney M20E and would like to improve its slow speed and stall performance, without sacrificing cruise speed or fuel economy. Vortex Generators are available but cruise speed and economy both suffer somewhat. Harry Riblett has the answer in his book GA airfoils, a leading edge cuff to correct the shortcomings of the NACA 6x series of airfoils. (See attached) Leading edge cuffs are available for a lot of certificated airplanes for STOL applications, but not for my Mooney.

To be fair, I am not looking for true STOL performance, just better low speed and stall performance than I have now. Correcting the airfoil seems like a good idea if it is possible, which appears to be the case. I am asking your advice on the best way to proceed, if at all. Thank you for taking the time to read this post.
 

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Turd Ferguson

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You would need to develop an STC or Supplemental Type Certificate. Once your plane is modified with the wing changes, you'll need to apply for an experimental R&D certificate. They will give your a period of time (not indefinite) to test fly the plane and verify performance. Once your STC is approved by the FAA, you could apply the STC to your aircraft and return it to normal category, altered by STC and sell your STC and mod package to other Mooney owners. I would anticipate retaining an engineer for the changes. I think I would also do a market survey to determine how much interest there would be in such a product. Otherwise you may end up with one plane only STC.
 

TFF

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Experimental R&D or Experimental Exhibition. If it works, you could use the data to make an STC. One issue is it might be hard to return it to standard category. It may effect the value down the road. I believe with those categories you have to have engineering to back it up before you do it. The FAA can restrict where you fly it under their discretion.

An Experimental Amateur Built major change is only a letter to the FAA telling everybody to duck while you retest your plane. I love Mooneys, but your experimental experience will not be like a homebuilt airplane.
 

blane.c

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Well building your own is quite a different pot of beans entirely isn't it. But I learned that if you are going to buy an airplane to "buy it the way you want it" because modifications are losers financially and if you buy it with the modifications you want you ain't the one on the losing end of the stick.
 

plncraze

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In Sport Aviation on the 80's there was story about Brian Seeley's "homebuilt" Mooney. He heavily modified the aircraft. You could see how he did it. It had a homemade cowl among other things.
 

Victor Bravo

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Your first call needs to be to an aero guy. Or, perhaps one of the aero guys on this forum will answer this question... what is the (physically) smallest possible leading edge re-shape cuff that will accomplish the change you want? The smaller the cuff, the less additional load it will put on the wing leading edge skin structure, and (likely) the less pitching (torsional) moment it will put on the entire wing structure.

Then call an FAA-DER engineering designee. Ask him/her how big of a deal structurally it would be to add a (___ inch) extension on the leading edge. Then decide if it is worth all of it.
 

Bill-Higdon

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Years ago I read about a Cherokee 140 owner who wanted to experiment with Vortex Generators, which at the time were a new idea. He converted his certificated airplane to experimental so he could do his research on his own plane. Now Vortex generators are available for all kinds of applications on certificated aircraft.

I find myself in a similar situation and would like to ask your advice. I have a Mooney M20E and would like to improve its slow speed and stall performance, without sacrificing cruise speed or fuel economy. Vortex Generators are available but cruise speed and economy both suffer somewhat. Harry Riblett has the answer in his book GA airfoils, a leading edge cuff to correct the shortcomings of the NACA 6x series of airfoils. (See attached) Leading edge cuffs are available for a lot of certificated airplanes for STOL applications, but not for my Mooney.

To be fair, I am not looking for true STOL performance, just better low speed and stall performance than I have now. Correcting the airfoil seems like a good idea if it is possible, which appears to be the case. I am asking your advice on the best way to proceed, if at all. Thank you for taking the time to read this post.
As for L.E mods for the NACA6x laminar flow sections Tony B. covered changes back in the 70's in Sport Aviation, he did it to his Turner T-40 this was the result of NASA R&D on it back then long before Harry R.
 

blane.c

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You don't just put a leading edge on the wing, the wingtips have to be profiled to match (if you want it to look professional) and the trim between the wing and the fuselage as well, for a Mooney maybe not so bad but for a high wing it is past the windscreen and requires additional fit.
 

Victor Bravo

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I flew in a Cherokee once that had a big leading edge extension made out of Bondo or some kind of structural filler. I was told there was nothing else under it, no sheet metal or wood, just semi-structural filler. It was to increase cruise speed, not STOL or low speed manners. Looked like it added 50 pounds to the airplane. It may have made a small difference, I can't remember, but it was not a professional Cherokee mod like the Art Mattson stuff that is STC'ed.
 

plncraze

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NASA did reports on their Grumman with the cuffs. You could probably do most of the work yourself. Talk to your local FAA folks once you have done some basic loads. As I remember the report the cuffs do their work at the stall and are just along for the ride during all other flight regimes.
 

Dana

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Like everything in aviation, it's a compromise. Add features to reduce the stall speed and you'll reduce the cruise speed as well. If you want a big reduction in stall you'll get a big reduction in cruise, if you don't want a big reduction in cruise you'll get a small reduction in stall.

So, you design your changes and present them to the FAA. You need a "program letter" which details what you want to do and where you're going to do it. If they approve it, the plane gets moved into Experimental-R&D or Experimental-Exhibition. The former will likely be quite restrictive, probably like E-AB phase 1, and the latter requires you to present the FAA with a yearly list of all the airshows or other events you intend to "exhibit" the plane at (you don't have to go to all of them, and other "proficiency" flying is allowed). Neither give the freedom that an E-AB airworthiness certificate gives you.

The once the "testing" is done, you have to get a STC approved to make the modifications to a standard category aircraft, whether a one time thing for your own use on one specific aircraft serial number or one with wider applicability that you can sell.

Either way, it's probably more work and expense than, say, building an RV-10.
 

Victor Bravo

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IF (and I say IF) it is only a small leading edge cuff, with minimal structural considerations (like the Sportsman cuff for Cessnas), then it may be viable to do it on a one-shot field approval.

This would use the same Aero guy and DER as you would have used for an STC, but you sidestep the entire "Program Letter", "Project Specific Certification Plan", and a lot of other monkey-motion.
 

Petehdgs

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Thank you all for your replies. There is a lot of good information presented here. I will start by getting some engineering data together, then discuss with an FAA DER to see if further pursuit is warranted. Since the Mooney uses both a 63-215 and a 64-412 it looks like a good place to start is to roll a set of points for both airfoils with the cuff added, and compare their aerodynamic performance to the original NACA airfoils as installed. This should tell me how the performance changes both at stall and at cruise. Anyone out there who has a good airfoil program care to spit out a couple of tests?
 
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