Instructions for building plane without kit?

[bernard]

Should the leading edge of the wing be rounded and the trailing edge be sharp? That's what the Finny 09 plan implies. I see that on my freedom flight 2017 plane, the leading edge is sharp and the trailing edge is flat. What should the proper shapes for the edges be?

I'm convinced the sharp/tapered leading edge of the Freedom Flight kit does not noticeably improve flight times. Leading and trailing edges made from square balsa sticks are fine.

[bjt4888]

Kyle,

With all due respect to Bernard as his assistance on this wiki is very good, i will relate that my experience with the sharp LE and gurney flap TE is that there is a slight benefit. For the 2014 season, I had teams construct identical airplane designs that only differed in that one team use slightly rounded 1/16" LE and square 1/16" square TE while the other teams used a drooped and rounded LE like th Finny 09 and a gurney flap TE similar to that used on the Cezar Banks design the Leading Edge. With identical rubber motors and winding, our repeated results were about 3% better consistently with the rounded and drooped LE and the gurney flap TE.

Brian T

[bernard]

Thanks for the data, Brian. I didn't realize Kyle was asking about a Gurney flap.

Kyle, increased incidence means more lift but also more drag. A Gurney flap allows the same amount of lift at a lower incidence, thus less drag and more efficiency. I came a across a paper when I was competing that found best results with a Gurney flap 5% of wing chord. For my 7.5 cm chord plane in 2015, this meant about a 1/8" flap.

[Kyle_Guo]

Kyle,

With all due respect to Bernard as his assistance on this wiki is very good, i will relate that my experience with the sharp LE and gurney flap TE is that there is a slight benefit. For the 2014 season, I had teams construct identical airplane designs that only differed in that one team use slightly rounded 1/16" LE and square 1/16" square TE while the other teams used a drooped and rounded LE like th Finny 09 and a gurney flap TE similar to that used on the Cezar Banks design the Leading Edge. With identical rubber motors and winding, our repeated results were about 3% better consistently with the rounded and drooped LE and the gurney flap TE.

Brian T

And where can I find the design that Cezar Banks made?

[bjt4888]

Kyle,

Strange; I'm trying to find the option to attach a file to a wiki message, which I have done many times before, and I don't see it. Maybe Bernard can offer assistance here.

I'll attach the Leading Edge plan as soon as I can.

Of course, this plan is for a previous year's set of rules and is not legal for this year. Elements of the design are still useful to be adapted to the current year rules. Note that the Gurney Flap shown on this design is a little shallower than what Bernard mentions. I have built designs with more depth to the Gurney Flap and haven't seen a measurable difference. A more pronounced Gurney does sometimes require different looking decalage angle setting. If you haven't worked with this term before, decalage angle is the difference in incidence angle between the wing and the stabilizer.

Brian T.

[Kyle_Guo]

I have finished the wing and the separate pieces for tip plates and I have covered them all in mylar using a spray adhesive. Before I add the tip plates, should the wing be flexible? My wing section (44.5 cm long for this year) is very bendy. The wing is strong in its joints and ribs and doesn't bend easily horizontally or vertically but if you take opposite corners of the wing and bend diagonally, it is really flexible and can bend 2 inches high and possibly more diagonally.

[bernard]

I have finished the wing and the separate pieces for tip plates and I have covered them all in mylar using a spray adhesive. Before I add the tip plates, should the wing be flexible? My wing section (44.5 cm long for this year) is very bendy. The wing is strong in its joints and ribs and doesn't bend easily horizontally or vertically but if you take opposite corners of the wing and bend diagonally, it is really flexible and can bend 2 inches high and possibly more diagonally.

Yes, a little floppiness is normal. Wings are mounted so not a large surface area opposes the direction of movement (i.e. not much drag that would cause the wing to bend significantly).

You may notice your covered sections are very sensitive to breezes. Because wings are delicate, you'll want a large plastic container to store your plane. Never fly your planes outside or carry them outside with a case or you risk warping or breaking parts.

[Kyle_Guo]

Wait, don't Gurney flaps create MORE drag? It's perpendicular to the spar, it's flat against the wind. How does this make the plane more efficient?

[bernard]

Wait, don't Gurney flaps create MORE drag? It's perpendicular to the spar, it's flat against the wind. How does this make the plane more efficient?

Gurney flaps increase drag but also increase lift. It's the lift to to drag ratio that matters: https://en.wikipedia.org/wiki/Gurney_fl ... _operation.

[Kyle_Guo]

I have finished the wings, horizontal stabilizer, vertical fin, and motor stick. I have made a socket connector to attach the wing and horizontal stabilizer with the vertical fin. I saw that on the Finny 09 plan, the stick that connects that tail, the tail boom, is slanted down. Is there any benefit of this? I was thinking about making the tail boom flat.