BiG Gyroc, how to make non wood fins ?

[Dale Saukerson]

A couple decades ago, I built a 3.01x Gyroc (BT-70). The motor tube slides rearward on ejection to deploys the flaps and retain the motor (nothing freefalls).
It boosts good on E-F motors having only 2 fin sets. Descent speed is OK not unsafely fast. Landing on sod is great, hard packed dirt usually OK.

I've not build much in the past 2 decades (sidetracked by antique radios.).

Now I want to build a 5.43x version (4 inch LOC airframe). I've not build much in the past 20 years (other hobbies got in the way).. I want to use 3 or 4 fin sets unlike the original model. It should not be too difficult to get good boost performance on G and H motors. Vehicle weight, especially the fins, will be key to descent speed and fin damage on landing.

I've done a moderate amount of scratch building but my fin construction has been either G10 type fiberglass or balsa/bass/plywood no thicker then 1/4 inch.
Each fin/flap/rudder set will be about 232 inches square. Openrocket suggests even balsa/fiberglass sheet or cloth will be too heavy.
I've never worked with sheet foam or carbon fiber. Nor have I done any vacuum bagging.

Should I try sheet foam and carbon fiber ?
Any suggestions or techniques, or links to same?

 

[aerostadt]

I can make two suggestions.

I don't know if this is strong enough, but I have used it for an F-powered model with large fin area (gliders). I have used 1/8" balsa with stationery paper (24 pound weight) bonded to both sides with Elmer's White Glue. The glue is spread uniformly and then weighted down with books to keep the wood from warping. There may be some warping after bonding one side, but after turning it over and doing the other side, the warping is almost all gone. This material is strong and light.

Another approach is to take 1/4" balsa and bond 1/64" plywood bond with epoxy to both sides in a manner similar to the first approach. This is stronger than the first method, but heavier. I have used it on large parasite gliders that were J-powered.

 

[Dale Saukerson]

Back then, I briefly played with a composite made of 1/4 inch balsa + 015 fiberglass + cyano to bond it.
It was plenty strong but I stopped before dealing with the leading and trailing edges....(cyano fumes).


I've never used foam nor carbon fiber, thus my query on this in my original post.
Anyone have comments towards those materials ?

 

[mikemech]

Have you tried using balsa plywood? 1/32 or thinner sheets of balsa glued together with the grain of alternating sheets at right angles. I read this , probably on TRF, but I haven't tried it myself. Yet.

Mike

 

[Sooner Boomer]

I was looking at what it would take to make a 2.6" (BT80) Gyroc. I was thinking of using a foam core board with either balsa formed leading edge or just a hardwood dowel (there are several thicknesses and rigidity (quality) of foam board - avoid the cheap stuff for this project). Trailing edge would be a wide strip of balsa for hinge attachment, as would be the trailing edge flap. Foam board is already "skinned", so except for leading/trailing edge transitions, I don't think it needs any extras (at least in the size I was thinking of...)

One concern was how to attach to the body tube. I think you will need to play with the wing/flap dimensions a bit, to keep them from getting ripped off. Laying down a glassed fillet might work.

A second worry was how to actuate and "latch" the trailing edge flap. If I recall correctly, the "rudders", which also act as mounting points for the elastic and "stops" for the actuated flaps, are located towards the ends of the wings. I think I would move them closer to the center of the wing span, and possibly use small rare earth magnets to latch the flaps in place when actuated.

 

[qquake2k]

Sounds like a fun project. I'll be watching with interest.