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Certificated to experimental for leading edge cuffs

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Hephaestus

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I appreciate your thought on this, but the numbers I came up with are a little lower. There were about 7000 180 & 200 HP Mooneys made, about 5000 of those are short body Cs & Es. 1% of that is 50-70 units. That would be the number who would find value in a soft stall and speed reduction on landing, and that could pay for the cost involved in development and production.
As an f driver... I ask but why?

You're going to add to empty weight to decrease stall speed, without a corresponding increase in MTOW.

I suggest you inquire over at mooneyspace about the need... I think you'll be enlightened by the market research.
 

blane.c

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I appreciate your thought on this, but the numbers I came up with are a little lower. There were about 7000 180 & 200 HP Mooneys made, about 5000 of those are short body Cs & Es. 1% of that is 50-70 units. That would be the number who would find value in a soft stall and speed reduction on landing, and that could pay for the cost involved in development and production. My initial thinking on this was the value wasn't so much in a speed reduction, but a forgiveness of the stall that allows you to get as slow as possible and hang there while you land.

So I guess I am naieve but I really thought a computer simulator would show the change in the stall if the leading edge was modified. I looked up the Abbot & Doenhoff 63-215 for the first time in several years. I was surprised at how hard the stall is, especially with full flaps, but it is pretty hard without flaps too. The interesting part is I can feel the difference with no flaps, partial flaps, and full flaps! The curves are not that different, yet I find my bird much easier to land smoothly with 1/2-2/3 flaps or no flaps than full flaps. Imagine how smooth all the landings would be if I could stretch out the top of the stall curve by 2-3 degrees AOA.

When I pulled up the same airfoil on Designfoil, the stall curve was smooth and elongated, just like I want. That is not realistic for that airfoil and tells me the computer simulation is of no use to me. The problem going forward is it calls into question Harry Riblett's claim that his suggested modifications will work as intended. He obviously knew a lot more about airfoils than I do, but going forward it seems like a lot of effort to put out on the belief that this modification will perform as intended.

So I am at an impasse.
I don't know field conditions of where you may be landing but would better brakes be possible as an option if they are available?
 

proppastie

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I can understand the desire for "Cherokee 140 style landings" some times my landings in my E are smooth and some times the nose plops down not hard but not something I would want on grass because of the not very much prop clearance......others have said carry a little power....I do not do that. I do not land on grass which I miss,, but I do not miss the "slow" as regards my old PA28-140......I think it would be pretty remarkable if you could make it happen but I would not want to put out the bucks or do the work......no real need to land on grass.
 

edwisch

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"No aircraft is crisp handling with flaps that work." Hmm. The RV series homebuilt aircraft have very crisp handling indeed. Whether the flaps "work" or not may be hard to tell on the short wing RVs or whether it's the low aspect ratio that gives the descent.
 

Rockiedog2

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Usually the pilot adjusts to the plane rather than the other way around. For all the reasons already discussed here.
 

dougbush

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Imagine how smooth all the landings would be if I could stretch out the top of the stall curve by 2-3 degrees AOA.
If a smooth landing is your goal, I suggest you finish your flare before reaching the stall angle of attack. If you're reaching the stall AoA too early, start your flare at a lower AoA (higher airspeed) for a normal landing. The entire flare should be on the linear part of the CL curve so you can gradually finesse your rate of descent by adjusting your pull on the yoke. If you got to the back side of the curve, you would be in the awkward situation of having to push on the yoke to reduce your rate of descent. The back side of the curve is for aerobatic performers. Flaps, VGs, and cuffs may increase maximum CL, but probably let go just as abruptly.

For a short field landing, you have a lower approach speed and you start the flare at a slightly lower altitude and it's quicker, but you still don't want to reach max CL before you're an inch above the runway.

There's no way to know the exact AoA for maximum CL, because it's affected by bug splats, rain, gusts, shear, and if there's any crosswind you're uncoordinated, so the two wings are seeing different wind angles. I think you have to choose whether you want to try for a full stall landing or a slightly faster one with a better chance of being a greaser.
 
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blane.c

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Greaser landings are for showing off to spectators, A "firm" landing allows you to apply meaningful braking immediately.
 

skydawg

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petehedges- I am a former DER and have experience in moving cert to EXP and don’t be too concerned with those discouraging trying something new. If we all merely accepted what’s out there, we’d all still be piloting the Wright Flyer.

for what’s it worth, I’d suggest try getting a copy of a similar STC certification plan- this will give you an idea of what the FAA looks at for such products as you will need to get an STC if you want to keep it with standard AC. I’d try to get away with only a exhibition program, rather than R&D, which is possible if you have a good flight test plan and mods are not likely to cause flight hazard. Exhibition AC doesn’t expire, whereas R&D will expire in max a year. Remember, per regulation and FAA policy, you need a good reason for moving to exp exhibition.

however, current exhibition ops limits are about same as AB, even allow IFR, so you might just keep it in exhibition if need be. Just make sure your insurance doesn’t specifically require a standard AC.....some just say a valid AC, so check before making the swap to special AC. This wasn’t an issue with my c172 after installing a V8, and rates didn’t change.

once done with prototype, it may be worth reaching out to a similar STOL kit STC holder on about what it took them to get the STC. You could apply for a single STC only for your plane rather than a multiple STC which will have less requirements.

Find a DAR experienced with this and certified aircraft (maybe call your manufacturing inspection district office, MIDO, for a reference to a DAR if needed).

Good luck.
 

plncraze

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Skydawg, did you write about your V8 install in Contact! magazine?
 

Map

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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.

I have flown and flight tested (I used to be a DER test pilot) a number of airplanes with wing cuffs.

1. You will need an STC or go experimental (permanently).
2. The cruise speed will be reduced because they add drag.
3. Cuffs influence the airflow at the outboard wing. They delay the separation during stalls (beneficial) and may lower stall speed, but negatively influence spin recovery (becomes more difficult to impossible).

If you go the STC route, the airplane will need to be spin tested, which means for a Mooney (normal category) showing compliance with recovery from 1 turn spins. With its small rudder, a Mooney with wing cuffs may end up not passing those tests.
 
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