Gap seal

[N96337]

Hank, wasn't that you that was telling about someone that tried gap seals on the aileron and experienced aileron reversal?
John

[Hank Jarrett]

Not reversal, but really screwed up roll control. There is a good reason you aren't supposed to modify control set-ups. It is NOT allowed by the FAA and for good reason. When you close the gap you change the air flow across the aileron because higher pressure air from the bottom of the wing no longer can flow through the gap and energize the boundary layer over the aileron. This can cause flow separation on the rising wing and sudden loss of roll force on that wing. When you change things like control surface gaps you become a test pilot flying an unproven airplane. You might luck out and make things better. You might not and end up with an uncontrollable airplane is some area of flight. The FAA just says, "DON'T DO IT". There are some things you probably CAN do to clean up the airframe, but I would NOT mess with aileron gap!

Hank

[Ragwing nut]

you can do that on the friese style ailerons. Air is designed to go over the top.

[Hank Jarrett]

Mike, I think he is talking about CLOSING the gap and eliminating the air going over the top. Changing the flow on what is effectively a slotted flap is NOT a good idea! You WANT flow through the gap! Did you mean "CAN'T" instead of "can"?

Hank

[PA1195]

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

Observe the airflow over the ailerons. Note the flow discontinuity behind the aileron hinge-pushrod tube opening. Might be worth sealing some more and possibly the other openings. Post WWII wings with a more open aileron cove (like Piper did in front of Cub flaps but not their ailerons) probably have different flow pattern up and over the Taylorcraft ailerons.

For the curious try brief full down aileron deflection near the stall to convince that when they let go so can that wing. Altitude is your friend when it happens.

Gary

[Ragwing nut]

Mike, I think he is talking about CLOSING the gap and eliminating the air going over the top. Changing the flow on what is effectively a slotted flap is NOT a good idea! You WANT flow through the gap! Did you mean "CAN'T" instead of "can"?

Hank

yes I meant CAN'T

[N96337]

I wasn't trying to put any gap seals on ailerons, but I was talking to another owner of a Tcraft about flap installations on this airfoil and was remembering something someone was saying about flap gap seals, and I was wondering why they would want to put a gap seal on when it screws up the effectiveness. I guess it was Del Benjamin that I was talking to about aileron reversal, as he experienced that on the GeeBee. I remember someone saying the flap should be a USA35 airfoil? Gary, or Dick, do you remember what Alsworth used on their flaps?
John

[PA1195]

Saw one with the flap mod but never got close to look. I'd put whatever Piper did for design including the upper flap gap fairing. Taylorcraft used aileron hinges with dropped pivot points and lowered hinges on the flaps that probably started structurally as ailerons.

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

[astjp2]

I did seals for the elevators and rudder, used foam like some of the cub guys did, I didn't see a noticeable difference except it retained water.

[PA1195]

Use this solid rubber for elevator seals > https://www.aircraftspruce.com/catal...apsealtail.php

Gary

[Hank Jarrett]

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

[KewFlyer]

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.

[Mark Bowden]

Hi Ralph, would you care to please post some pictures of what you have?
Thanks

[Robert Lees]

The F22 we had based at my airfield in the UK for a while had screwed-on aluminium aileron seals. The ailerons themselves did not appear to be different in design from the BC and F19 models. It was hellish sluggish in roll, but this may have partly been because it had bigger-than-normal (and hence heavier) wing tanks for the Transatlantic flight.

[PA1195]

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