How to straighten a warped flap

[Frank Egyed]

Had the second most terrifying maiden flight ever today. Mental note - do NOT fly a new model even slightly tail heavy, especially on a gusty day (it was less than 9m/s), particularly on a field closely surrounded by trees, and ESPECIALLY with the outside flap warped down towards the tip... Had to take 5 steps back to regain line-tension in one of the many memorable upwind moments. Needed a strong cuppa'tea after I somehow managed to land it in one piece.

So after seeing the top of the outside wing A LOT during the flight, I looked for a warped wing and found a warped flap.  So I'm hoping someone can offer some advice with this problem. Unfortunately it's tissue covered so I can't just bend and heat. Also, it's built up rather than solid if that makes any difference...

At this stage I'm wondering if I need to cover it with film and bend and heat?

Thanks in advance...
Frank

[Chris McMillin]

Soak a big clean towel in nearly boiling water and wrap it around the flap top and bottom with hot mitts and twist it until the heat goes down. Twist it WAY past what would be straight because it's going to return. This may take a few tries.
Chris...

[Gary Dowler]

I recently fixed a warp in a built up 1/2A wing that had taken an unfortunate warp. Inboard wing warped trailing edge up at the tip.  Steamed it to no result.
Stripped the covering off and immersed the outboard section in very hot water for about
30 seconds.  Then I took a larger piece of 1" balsa and pinned the wing to it with a shim under the leading edge to reverse the warp, hoping that it will return to a neutral point. It worked wing is flat again.

Don't know if there is something in there that will help you.

Gary

[Larry Fernandez]

This is one of the reasons I build my planes with removable flaps.
You can either remove it and twist the warp out or replace it with a straight flap. Another plus, is that with the flaps removed, you can tweek the flap horns without damage to the flaps.
In your case, its too late for that, but its something to think about in future builds.

Larry, Buttafucco Stunt Team

[Randy Cuberly]

Burt Brokaw and I successfully removed warps from the flaps of my Colossus with a heat gun and patience by working on a section of the flap starting at the root (nearest the fuselage) and continuing toward the tip in individual intervals of a few minutes each.
It took all of our hands and a couple pairs of heavy work gloves bending and holding sections of the flaps while heating.  In the end it worked amazingly well.  After treating both flaps with this process we then removed the control horn flap tweaks that I had previously applied to temporarily adjust the flight characteristics to permit flying the airplane at VSC.  I would mention that these were fairly extreme "flap tweaks" that solved the outboard wing high problem of the airplane but created other aerodynamic problems that made the airplane difficult to fly well.

I had previously unsuccessfully tried using a heat gun to adjust the wing and flaps but with only one hand and the heat gun that proved to be futile.  This is, of course a very large I-Beam wing covered with poly span.

All of this was done by "eyeball precision" which is apparently good enough with the right eyeballs!

I flew the airplane this morning and it now flies straight and normal.  There are a few normal trimming things to do to the airplane now to make it track a little better but it was very gusty and turbulent here in Tucson this morning so that will happen this coming week.

So before whacking away with an xacto knife I would strongly recommend finding a buddy with a good eye and trying the heat and twist method...it works with the right attitude and patience.

Oh yeah, I would mention that these flaps were solid wood covered with two layers of fiberglass cloth with epoxy, and silk span and dope finish.  Yes they were not an easy bend but the heat made them pliable!

As you probably know this is a large I-Beam wing airplane.

Randy Cuberly

[Randy Cuberly]

PS to above post:

Heat slowly and avoid getting the heat gun too close to the surface or the finish will bubble!  Work carefully and slowly and it will work!

Randy Cuberly

[Frank Egyed]

Larry - good point... Rather than take this thread OT, can you point me towards any info on methods to make flaps removable?

Chris, Gary, Randy - Thanks for your advice, sounds like my best bet is heat and patience...

Cheers,
Frank

[Ken Culbertson]

Larry - good point... Rather than take this thread OT, can you point me towards any info on methods to make flaps removable?

Chris, Gary, Randy - Thanks for your advice, sounds like my best bet is heat and patience...

Cheers,
Frank

I used to replace the flap hinge pins with thick straight pins cut off about 1/8 larger than the hinge. The flap horn slid into an aluminum/brass tube epoxied into the flap.  Even if you don't make them removable, the tube lets you tweak them without breaking the horn loose.  I have also used a full length wire that can be slid in and out from the tip if the flaps are full span. That was when I was young ,crazy and we didn't know to seal the flaps.  I am sure today's technology has a better way.

FYI, my motive at the time was not to make them easier to tweak, it was to make them easier to finish.

Ken

[Howard Rush]

I have also used a full length wire that can be slid in and out from the tip if the flaps are full span. That was when I was young ,crazy and we didn't know to seal the flaps.

That's what I (old and crazy) do.

[Ken Culbertson]

That's what I (old and crazy) do.

If two of us did it then it must not be crazy!  Does that work as well on nylon as it did on metal?  I last used the full wire in 1967 on some brass hinges.  Can't remember who made them.  Sort of round and about an inch long.  With the metal wire they vibrated and the plane really sounded weird in the air.  You may have just triggered the answer to how I could make Robarts embedded in a tube removable.  Thanks!

Ken

[Chris McMillin]

You're welcome,  Frank. I'd add I assumed your model was painted and new which would help this process.
Chris...

[Frank Egyed]

Chris - Painted yes, new most definitely no. I inherited it from Noel Corney who wasn't using it any more and very kindly donated it to me when I said I wanted to get back into F2B.

So this morning I took all of you Gents advice on-board and adapted it to my available resources. In the absence of another pair of hands, I figured a way to hold it in place twisted while being heated, see att pic.  I ironed only the bottom inner half figuring heat would expand the wood, and kept it clamped for a few minutes until it cooled. Voila!! One eyeball precision straight flap Took maybe half an hour including pack up And it's still straight tonight so I'm hoping it'll stick...

In the process I noticed the other flap is bowed up slightly in the middle so that's tonight's project. No wonder the poor thing was a terror to fly! She must have been wetting her pants as much as I was... 

Thanks again for your help.

Cheers,
Frank