Converting rubber FF kits to RC (weight reducing tricks)

[davidchoate]

I'm glad you mentioned that because right now I'm selecting a radio for my 1:15 Aeronca Champ (kit #301), and I want something rock solid reliable.

To prevent warping, you can switch to contest balsa and increase the thickness of the parts. For example, if 3/32" is too flimsy, go up to 1/8" and reduce balsa density by 25%. It will weigh the same but be 78% stiffer because bending stiffness is proportional to the square of the thickness. (For simplicity, I'm assuming the elastic modulus of balsa is invariant with respect to density.)

[davidchoate]

David Lewis Quoted

"To prevent warping, you can switch to contest balsa and increase the thickness of the parts. For example, if 3/32" is too flimsy, go up to 1/8" and reduce balsa density by 25%. It will weigh the same but be 78% stiffer because bending stiffness is proportional to the square of the thickness. (For simplicity, I'm assuming the elastic modulus of balsa is invariant with respect to density.)" I personally found that rather xpensive, 1/64" spruce ply is as light and God knows how many times stronger than Balsa. It's close to $10.00 a sq. ft. But in certain instances its worth every cent. Even 1/32" ply isnt much heavier. I use it on LG hard points, and It bends so easy. I hope they dont stop using Spruce in that as well. I stocked up on whatever Spruce they had at the local hobby shop. It seems the older kits have stronger wood. I saw on a old plan even grains per inch to use on certain balsa parts. Now adays you get (in alot of kits )that light tan sponge like stringers, that may bend easy, but are not even strong as foam.The darker balsa seems better, although iy leaves rough edges that must be sanded, but I dont care. I havent built a Laser Cut kit in so long I forget what it's like.

[davidchoate]

I got a Aeronca 30" WS kit in stock by dumas. Electric Flight Magazine recently had a 5 part build on how to convert it to RC. Thats where I decided to use tail lightening, and scalloping,but I learned from this old timer that no matter if its FF or RC always scallop. Nothing looks worse than B formers showing through the finish. Also I often go back and read my M.A. News from the 80's,because they would have at least 3 builds in each a month. now its just test fly review of foamies, and RTF planes.I like building as much as flying. To know I put it together, and understand WHY it flies is what interests me. I still have'nt mastered the FF trimming , turns out the FF I ignored because I thouht it was boringly easy, is the hardest thing in modelling. Why can I build a FF that glides perfect, but under power is all over. In the older MAN they exp;ain Slow flight and higher speed flight differences, and It helpes. I noticed all my micro (24" or less WS) foamies use alot of washout and under cambered airfoil. I havent finished the article on undercamber in dec 1985 Man, but im sure its enlightening.

[David Lewis]

Konrad wrote: "I also lower the stabilizer incidence (decalage) as they often don't need or I want the added pitch stability with an R/C model that a negative (up) stabilizer affords."

Wouldn't elevator trim allow you to set the decalage anywhere you want it?

[Konrad]

Konrad wrote: "I also lower the stabilizer incidence (decalage) as they often don't need or I want the added pitch stability with an R/C model that a negative (up) stabilizer affords."

Wouldn't elevator trim allow you to set the decalage anywhere you want it?

Yes, but at the cost of trim drag. Also down trim is adding camber to the stab in the wrong direction. Planes seem to fly in better trim with a flat stab.

As drawn the Guillow models are generally set up with free flight force arrangements. R/C flight does not need or often want this kind of trim.

All the best,
Konrad