Gap seal

[astjp2]

Elevator gap seals are a different animal. Still illegal, but not as dangerous from an aerodynamics perspective. There are a series of tests I want to do on my planes, but to do them legally I have to put them into an experimental category for research. The designation is TEMPORARY only for the period of the tests but is the only way to LEGALLY see if gap seals in the tail and several other mods I would like to test are legal. The first tests would be to do actual measurement of things like minimum drag angle of attack, actual ROC and stall speed and other characterization tests that were never done by the designer. Once the basic data is gathered for a baseline, OTHER aircraft need to be tested to verify the data and see how much production and modification variation exists. LOTS of Nerd stuff.
Once the baseline and variability are established, tests of various mods can be done to see how effective each one is. For someone like me, this is FUN STUFF!
Areas where theory says we can make real improvements are kind of surprising. Big drag producers are actually places like INSIDE of the cowl! Cooling drag has lots of room for improvement. Also I couldn't believe how much drag was calculated from the tail wires, stab to fuselage gap, tail wheel and spring and the above mentioned rudder and elevator gaps. Another surprise is how much drag comes from leaks around the doors.

Hank

Hank, why would you even try to go through this process? If you like pain, go find a fence post that is 48" high and bang your head into it... it will hurt less than dealing with the faa

[astjp2]

Tribe.

I have been using Gap Seals in the elevators and rudder for years, not only on the Taylorcraft but on the SuperCub and Cub. The added control at low air speeds and responsiveness to small inputs while in flight, are priceless. Regarding legality, all logs books have been dully signed at annual by the IA. Caviate: the gap seals are surgical tape and NOT a permanent fixture to the airframe. Regarding ailerons gap seals, I use a 4" tape that attaches 1" to the wing with the remaining 3" covered with the same tape under it, just floating over the aileron. Im very happy with the improvements and added controls.
I have been asked: "do you notice the difference?". I have on the elevator authority and rudder and not as much in the ailerons...but..thats just me.

Do you have VG's?

[astjp2]

Hanks testing would be valuable. I've used the seals from Post #10 for three years on my elevators. Goals were various: exclude ice and snow while parked and removable to clean if covered; not glued just inserted; better elevator and trim control feel but that's only subjective; better control of AOA in and out of the stall and while landing 3-pt. I have VG's so the underside of the rear horizontal stabilizer has them for control authority so that alone may suffice. I didn't try w or w/o the VG's before the seals as they were there previously.

One early series of study by the NACA (three total by Fred Weick and others; I can link if interested) was an examination of roll, stability, control of stall, and other performance behavior like the degree of adverse aileron yaw. Their recommendation was for Taylorcraft to add increased vertical stabilizer and rudder area [which they did after WWII along with a revised aileron-wing cove like Stinson and Piper PA-12-14]. Spins were a problem at that time and flight divergence near the envelope edges was compared with variable control deflection. Altering approved control behavior and stall has consequences so caution is still recommended.

Bellanca sealed ailerons on Citabrias via an optional kit. I heard it improved aileron authority and rate of roll. I added then and it did as advertised. Same for elevator seals which later became a factory option. But in that case a tester likely wearing a chute approved the Utility Category maneuvers and others.

Gary

I can wrap a prewar up in a spin like crazy, and recover easily...but my airplane rigging is stock.

[PA1195]

Early Micro VG's lacked the under stabilizer VG's. I flew them on a PA-18A before and after. With them installed elevator control (without gap seals) was improved at low airspeed and particularly at forward CG or slow landing on floats. Installed the plane could be flown to 28 GPS, but when it stalled there was nothing left in the wing so as they say "The cows got bigger". It's a good mod if used responsibly just like gap seals.

Gary

[PA1195]

I can wrap a prewar up in a spin like crazy, and recover easily...but my airplane rigging is stock.

Do you have VG's Tim? With them spins are resisted but can be provoked. Rudder remains to prevent or delay that mode.

Gary

[astjp2]

I used to do them before I got the VG's, and I have done them with. 11 rotations is my max. I have also been able to cross control the ailerons, opposite rudder, wings level and turn a 360 rotation. Windows would rattle a lot but the prewar airplane has a lot of rudder control, the post war I flew in would drop a wing.

[PA1195]

VG's best mod for a Taylorcraft if margin is your goal.

Gary

[Hank Jarrett]

Hank, why would you even try to go through this process? If you like pain, go find a fence post that is 48" high and bang your head into it... it will hurt less than dealing with the faa

It's an engineer thing. First thing we tend to think about is "Why does it do that and how can I get some numbers to describe it and provide guidance to make it better?" From the time I bought my first T in the mid 70s I was always bothered by the lack of data on performance. For me, analysis isn't pain, it is fun, but then I read tech journals for recreation..

Hank

[PA1195]

These and their bibliography cover lots of early testing of taylorcraft and airfoil:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930084982.pdf

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930083935.pdf

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930082385.pdf

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930084995.pdf

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930091603.pdf

https://apps.dtic.mil/dtic/tr/fulltext/u2/a801134.pdf

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.587.571&rep=rep1&type=pdf

Gary

[N96337]

I thought aileron reversal was when the aileron deflection was capable of twisting the rear of the wing up with down aileron, or down with a up aileron. Like at Wartime Airspeed with a weak wing structure? I doubt the Taylorcraft can go fast enough for that but structural twist at speed....wouldn't surprise me with matchstick spars.

Gary

What happened with the GeeBee was that the aileron stalled as it was deflected downward in a cross wind and in 3 point attitude, effectively reversing the controls. Luckily he is as quick as he is and he got it handled in time. He said that was the last time he ever tried to 3 point it.
I guess "aileron reversal" isn't an adequate description, but that's what he called it. Here's a page he wrote in a book about it.

https://books.google.com/books?id=X8oQCZvxYZ0C&pg=PA63&lpg=PA63&dq=gee+bee+aileron+reversal&source=bl&ots=WqVhgywWVI&sig=ACfU3U1Wf5UaEXn_X-b9x51ubI_vcD-wqg&hl=en&sa=X&ved=2ahUKEwi4r4K5qq7iAhWBtVkKHTuRAGcQ6AEwCXoECAgQAQ#v=onepage&q=gee%20bee%20aileron%20reversal&f=false

[N96337]

Tim, wasn't it you that said something about the 35B airfoil? I was wondering what the Tern did? It's been so long since I saw one I can't remember.
John

[PA1195]

What happened with the GeeBee was that the aileron stalled as it was deflected downward in a cross wind and in 3 point attitude, effectively reversing the controls. Luckily he is as quick as he is and he got it handled in time. He said that was the last time he ever tried to 3 point it.
I guess "aileron reversal" isn't an adequate description, but that's what he called it. Here's a page he wrote in a book about it

I suspect that with the elliptical wing of the GB the tip wants to stall. If so down aileron may provoke it sooner especially if there's no washout to the wing for speed. See the pics>>>>

[astjp2]

Tim, wasn't it you that said something about the 35B airfoil? I was wondering what the Tern did? It's been so long since I saw one I can't remember.
John

There was a naca test for pitching and flap design, usa35b @12% chord was acceptable

[astjp2]

It's an engineer thing. First thing we tend to think about is "Why does it do that and how can I get some numbers to describe it and provide guidance to make it better?" From the time I bought my first T in the mid 70s I was always bothered by the lack of data on performance. For me, analysis isn't pain, it is fun, but then I read tech journals for recreation..

Hank

Hank, I think you missed my point, I would do you testing and just keep your mouth shut to the powers that be...and then report your results.

[PA1195]

Tim I'm still trying to contact the Tern owner for permission to measure his flap geometry. It will happen. Or I'll buy his plane and then do it.

Gary