Eaglewatch

Hi,

I am curious to know how others have handled a problem concerning large flap surfaces, especially simulated Fowler and split flaps.

The problem is keeping a large, relatively thin flap from warping, especially over time. I have a few aircraft which were designed and built by others, which now have the problem of the flap warping; sometimes at the side edges, but most often at the trailing edge. These flaps have been built with some type of reinforced upper surface structure (framing) which dissappears into the wing when retracted. But, by necessity of the wing design, these framing structures are not very robust, and don't always solve the problem.

I have even had flaps which had been glassed on both surfaces warp over time, despite storing aircraft in relatively dry and temperate conditions such as an unused room which is air-conditioned in summer and heated in winter (no hot attics, storage buildings, overheated vans, extremes in temperature or humidity, etc.).

Ideas are welcome . . .

Regards,

Al Parry
[email protected]

blvdbuzzard

I built a set of flaps out of styrene sheet and channel stock. I built the flaps up just like I would with balsa and ply but used the styrene. It looked real good and the power needed to push and pull was next to nothing. I had the plane for 5 plus years and they to would warp in the summer. I have no idea wht to use that would not warp at all.

Dru.

im_a_rcav8r

aluminum

Eaglewatch

im_a_rcav8r . . .

Thanks for the tip. . . never gave that a thought before, but now that you mention it, aluminum does make sense for such an application.

Regards,

Al Parry
[email protected]

Tall Paul

I have scale split flaps on my Dynaflite PT-19.
1/16" plywood surface, with scale bracing on the inside.
Haven't warped in about 8 years.

Jim B.

My Feedback: (1)

Try using any of the popular plastic laminates on the market (Melamine, Arborite, Wilsonart). I use this material to build hinges, flaps, templates for foam wings, and to reinforce trailing edges and wing tips on my giant scale birds. The local construction supply store should have half sheets available for next to nothing in cost.

LaserTank

Make composite flaps over blue foam. G10 make nice surfaces.

balsadust-3

I have used a material Dave Platt calls g10 Its sold by another name by one of the jet manuf. I think Bob Violett its a material used for circut boards comes in thickness form .010 on up and works good for base for flaps or for a trailing edge you want to bring to a very fine point

LaserTank

Do a search on G10 supplier on google or webcrawler. I believe McMaster Carr is an online dealer. Around $7 for a 12x24 sheet. Shipping is high so it is worth getting a few sheets. It is laserable if you have a local guy with a system. They supply 1/8" too which makes good hinges, landing gear, etc. I get it at a local plastics shop for less than you'll pay at BVM. On another note, my buddy did Carbon cloth over spider foam on a stunt ship elevator and I could back over it with a truck.

Johng

My Feedback: (4)

Hmm, I've built a bunch of slotted/fowler flaps - haven't had the warped flap problem. Most of my flaps were solid balsa though.
What are these flaps made of and how thick, construction type, etc.

One anti warp device would be to put in diagonal ribs if it's open bay - or lay CF diagonally along the line that has to "stretch" in order for the surface to warp.

Eaglewatch

Thanks for all the good ideas, guys! I appreciate your responses.

The flap problem has occured on two giant-scale aircraft. Both had flaps made from hard 1/8" balsa, with spruce rib structures built inside (and glued across the grain of the flap's length) to help avoid such a problem. The flaps were built by placing several strips of sheet balsa in parallel (edges glued together) to alternate the wood grain, so as to avoid warping which sometimes can happen when using a solid, single sheet of balsa.

Why this method failed to work on these models, I am not sure. Also, both inner and outer flap surfaces were glassed with 3/4 oz. cloth and epoxy resin after being constructed. Note this did not happen immediately, but after about a year had passed once the aircraft were built. They were stored away from excess moisture and heat, in two different indoor rooms.

Regards,

Al Parry
[email protected]

Flypaper 2

I built split flaps on a 1/4 scale FW 190. They are 22 long.3.5 ins wide. Flap LE spar is 1/2 carbon fibre tube. Ribs glued to this. 3/32 balsa lower sheeting. TE is 1/4 by3/32 spruce. Very light and rigid. Hasn't warped in about 6 yrs.