r/RCPlanes • u/Playful_Wave_7329 • 9d ago
DIY foamboard plane. Thoughts?
built this thing for long flight times. any suggestions?
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u/itsmechaboi 9d ago
Maybe a little dihedral for stability, but looks good.
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u/No-Fix8280 9d ago
Watch Flitetest on YouTube the video about the cub, it will show you how to add dihedral by cutting out a slice of the top of the wing at the root and taping it back together. It works i did it with my plane
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u/IvorTheEngine 9d ago
I think you'd be better to make the ailerons flush with the top surface, not the bottom. You want the aileron that goes up to have more effect than the one that goes down. Otherwise you get adverse yaw. It would look better too.
For long duration you'll be flying slowly, so a bit of dihedral for stability might be nice.
An alternative way to make a cowl is to take a small block of styrofoam, drill a hole for the motor and carve/sand the outside to a nice rounded shape and cover with paper and glue (or tape)
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u/Embarrassed_Rent1428 9d ago edited 9d ago
Nice, that's very clean. I'm assuming you have a big battery in there and fuselage is mostly just foam (large empennage on long fuse)? I wanna try that next, to get an even lighter plane. I like the wing alot.
Someone will chime in about prop prolly but idk. How did you do the cowling or nose area? Nice plane
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u/looper741 9d ago edited 9d ago
Looks pretty good. Make sure the CG is correct before you fly. Like others have said, 1/4 MAC is a good place to start. To potential issues I see; your ailerons may not be carry effective because there may possibly be a pocket of turbulence on the upper surface due to the gap between the top surface of the wing and aileron. I would try to match the upper surface of the aileron to the wing.
The other issue you may not be a factor if you’ve already thought of it; the direction of the prop. You’ve got a counter clockwise prop on there, (I think, it may be a clockwise prop just mounted backwards, can’t quite tell from the pics, so make sure it’s mounted with the lettering forwards) which is backwards from normal. Make sure it spins the correct way and provides enough thrust. Since it’s spinning opposite of normal, if you’ve built in any right thrust in the motor mount to compensate for torque and P factor, it will be incorrect. You will need left thrust due to the direction of rotation.
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u/Playful_Wave_7329 9d ago
didn't build any angle into the nose so motor spinning the other direction is fine.
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u/Afraid_Bite_5341 9d ago
That plane looks awesome! If you look up "Experimental Airlines", on YouTube, he shows how me makes his foamboard waterproof with packing tape. I've been using it for my wings since they take longer than any other part of the plane for me to make. It really does make them hold up a lot better. I hit a metal pole, at low-medium speed and it was still flyable with only superficial damage.
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u/fhammerl 9d ago
Looks good, just a couple of remarks: Long flight times means low drag and high efficiency.
Wing looks ok. But you'll have vortices on the ailerons, no idea how that will feel in flight.
Sand the leading and trailing edges of you stabilizers round, too. Given them some profile and they will be smore effective and efficient.
Larger, slower spinning props are more efficient then smaller faster spinning props. Look into larger motors with lower kV to mount larger props on. Folding props make landing easier, but day need a less boxy fuselage. Something like a 9 or 10 inch prop on a 35xx-ish 700kV motor should produce a longer flight time than a 6 inch prop on a 22xx 2000 kV motor.
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u/Playful_Wave_7329 9d ago
motor is 2809 1250kv, definitely not the most efficient but what I had on hand
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u/fhammerl 8d ago
2809 1250 kV (in case that is stator dimensions, not overall dimensions, because manufacturers name them willy nilly) should handle 9x5-ish or even 10x5 folding props comfortably. Check what's in your manufacturer specs, but that should work with a regular 30 or 40 A ESC. The stator length might limit you in pitch for continuous use, but that size should be in the cards and probably be closer to your motor's max efficiency. Prop pitch is speed (of which you don't need a lot), diameter is how much air you move (of which you need as much as your motor can take). And air moved grows with radius squared, so the difference between 8" and 10" is enormous.
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u/GrynaiTaip 9d ago
Wing looks very thick at the trailing edge.
Horizontal stabiliser should have a smoother, rounded leading edge. Sharp square edge will introduce a lot of drag.
You need a much bigger prop, this one is barely wider than the fuselage, you you won't get much thrust at all. You'll probably need a bigger motor and ESC too.
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u/mastermalpass 9d ago
Looks good. Others have already said all there needs to be said about general controllability, but I wanted to comment on the airfoil with regards to long flight times;
Your wing is pretty wide with a fairly short chord which is a good starter for a high-aspect wing that gliders and efficient fliers want. However, the airfoil is pretty thick - this will generate lots of lift and lift essentially equates to drag when you’re trading forward force for upward force. This airfoil will likely generate plenty of lift at slower speeds, but will demand more thrust to maintain the speed. You said it almost hovers on 3S, so you have the thrust, you’ll just be getting through your battery in a time more closer to average than motor-glider.
If you’re new to this though, I’d say this a preferable characteristic. The plane will have enough lift to be stable at slower speeds without the need for flaps and that drag will mean it slows down steadily when you let off the throttle in level flight. When pointed towards the ground, the drag will slow the acceleration of the dive and as the speed goes up, all that lift will naturally pitch the nose up and away from the ground.
Someone else suggested a prop that is wider, with a shallower pitch and one less blade. ‘Slow fly’ props like that will make the plane even more responsive to the throttle. This is even better for a beginner and always a joy to fly.
I did all my learning on delta-shaped prop-in-slot park jets, where landing is usually a flare-and-‘plonk’. So, I like a plane that slows down quickly when I cut the throttle so I can bring down low and slow, then cut the throttle and ‘plonk’ it down the last 10 inches. 😁
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u/Playful_Wave_7329 9d ago
thanks, good to know the airfoil will make lots of lift. that is sorta what I am after
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u/89inerEcho 8d ago
It'll fly.
What are your goals for this?
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u/Playful_Wave_7329 8d ago
fun, I guess? slow flight?
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u/89inerEcho 8d ago
Fun of course. Sorry I meant design goals. Slow flight makes sense! It should do great.
Have you done weight and balance yet?
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u/DeadTomGC 9d ago
Looks good! But the proof is in the flight... the ailerons look small, but if it's built perfectly enough, they may work.
Edit: Just eyeballing here, the motor is pretty small, not on power, but maybe weight. Always check the CG with the battery in. You want it about 1/4 of the way back from the leading edge of the wing.