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Old Feb 07, 2011, 08:12 AM
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FPV Flying Wing, Can somebody check this over please?

I keep umming and arghhhing about which platform would be best for FPV. A normal sailplane (is that the correct terminology?) seems to make sense, but then I see different flying wings on here and youtube etc, and they look pretty cool... also if I could fly with no rudder I have a free chanel for the camera.

I quickly stuck together a flyingwing design, i looked at pictures and schematics on this forum to get ideas.

The plan is attached below. I didn't want to carry on with the design if it looks like a bad idea!

The dimensions...

Root Cord = 30cm
Wingspan = 120cm
Tip Cord = 9cm
Sweep = 31cm

The CG looked good to me, its about 16cms so pretty much in the middle. More room to balence?

I would put the motor at the back, and then use the battery and whatever to balence it.

I'm not expecting a yes or no answer, just some criticism really. I will use the simple KF2 wing, I was thinking of taking it from 50% of the root cord and matching it at 50% of the tip cord? (is that a good idea?).

Do people literally just belly land these!!?

Cheers!
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Old Feb 07, 2011, 10:14 AM
gpw
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That should work fine ... with a slight bit of dihedral , it'll be more stable ... Land on the belly ... on something soft !!! Otherwise add a skid ...
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Old Feb 07, 2011, 10:38 AM
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Cool, thanks for the advice!

When you say dihedral, do you mean on the tips? Or the entire wings?

I was thinking with the tip's I will add something at around 45degrees? \______/

Not sure which method is more effective.

I'm not too experienced with flying wings, they are a whole new area for me, so I don't know what to expect. It will hopefully at some point carry FPV gear.

Do they generally fly ok with no rudder? I don't really use the rudder much on my mini funtana thinking about it, but it is handy occasionally.

Cheers!
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Old Feb 07, 2011, 03:19 PM
treefinder
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I'm no wing expert, but by happy accident (or very careful analysis and years of research - Not!) I came up with a planform that seems to groove very well. http://www.rcgroups.com/forums/showp...&postcount=228

The OSW (OneSheetWing) is only 30" span on main wing, so would have to be scaled up a good bit, but you can check the angles, etc of your design against it and get an idea of how yours will fly (video in first post). Mine is a kfm4 - top and bottom step, and flys smoothly with no perceptable angle of attack required. Wing is flat, no dihedral, but the angled tips give a nice stabilizing help. I tried her out first without them and she flew ok, but once tips were added was even more stable in yaw and self leveling (as if I'd added more dihedral) Your sweep looks proportionately same as mine (without actually overlaying the two). To your comment about rudder, Mine (and most i expect) use elevons, so tie up two channels on the rx just as if a Rudder/elevator or aileron/elevator was present. But you still should have a channel available for the cam. Lack of a rudder prevents knife edge flying (unless someone is way better than me!) and makes crosswind landings dicey if one is landing on wheels, but few wings use wheels, so no prob.
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Old Feb 07, 2011, 03:31 PM
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Thats great!! Thanks for that! The only problem mate is that you have sent me a link on shark skins
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Old Feb 07, 2011, 04:16 PM
treefinder
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Ak! Sorry bout that, here's the right one: http://www.rcgroups.com/forums/showthread.php?t=1383516

Should have noticed that a link showing "post count" wouldn't be to a thread! The shark denticles is an interesting parallel to kfm steps, tho.....
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Old Feb 07, 2011, 04:27 PM
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Nah wouldnt go with a flat one for 50".... Just cut it out of a styrofoam, you can just get a 50" version from 1 standard size board (bout 40" x 20" around here).

Your design... I think your aspect ratio is too low for a swept wing. I would enhance the tip chord, maybe even double it. And put bigger elevons on it.
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Old Feb 07, 2011, 05:34 PM
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Quote:
Originally Posted by T0RN4D0 View Post
Nah wouldnt go with a flat one for 50".... Just cut it out of a styrofoam, you can just get a 50" version from 1 standard size board (bout 40" x 20" around here).

Your design... I think your aspect ratio is too low for a swept wing. I would enhance the tip chord, maybe even double it. And put bigger elevons on it.
Thanks for the advise, would you extend the elevons across the whole wing? Or make them stock out further? (currently 2cm). I'm used to a mini funtana which has control surfaces as big as its wing

If I was to change the tip chord so it was longer, i would have a setup which looked more like 2 longer wings (like ^ ), rather than a triangle, would that make the elevons less efficent? Is there any advantage to that?

Also, why do you feel having it flat underneath would be a problem on a larger scale model? I was going to use 6mm depron.



Cheers!
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Old Feb 08, 2011, 03:40 AM
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Quote:
Originally Posted by springer View Post
Ak! Sorry bout that, here's the right one: http://www.rcgroups.com/forums/showthread.php?t=1383516

Should have noticed that a link showing "post count" wouldn't be to a thread! The shark denticles is an interesting parallel to kfm steps, tho.....
Just looked at your model, and it inspires me!

I think theres a point where I will just have to build it and see... 6mm depron is not too expensive I guess.

Do you find the model twitcy on elevation? What would happen if you rolled it slowly?
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Old Feb 08, 2011, 02:22 PM
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Here is mk2 , I have extended the wing tip chord from 90mm to 120mm

The Elevons are now 40mm rather than 20mm in chord.
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Old Feb 08, 2011, 04:51 PM
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Leonr: No, V2 is very well behaved. Slow rolls are a bit tricky, as in order to maintain altitude, I have to flip a bit of down elevator when she's inverted, and I'm not too good about that yet. without Rudder the only point that one can point it back skyward is when inverted. a more expert flyer could do it pretty nice, I'm sure. If I try a slow roll with just ailerons she'll eventually point to the ground

Your sketch looks about right to me. full span elevons, and good sweep/taper.
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Old Feb 09, 2011, 03:06 AM
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Ok great! Thanks for that!

I was thinking of maybe dropping the wingspan down to 100cm from 120cm, this would give the trailing edge a slightly less sharp angle, but then again it may well be ok as it is.

Do I calculate the wing loading to get a rough idea of what it can carry? One reason im using a flying wing is because its robust and I can chuck it in the car. With a conventional setup I have to put the seats down and position it in a way that the elevators wont get broken off etc. Just after something I can chuck in the boot and get out and fly.

The idea will adventually be FPV. I've been watching some videos and they seem to role smoothly, but they look twitchy on elevation, up down up down up down etc, but I guess thats just what comes with this style of aircraft, it has effectivly a very short tail moment (is that the right way to descibe it?).

Thanks for your help, much appreciated!
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Old Feb 09, 2011, 10:46 AM
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If you read through the OSW thread, you noted that I did a V1 that exhibited that pitch "hunting" and was generally not fun to fly. The additional sweep (pretty much all I changed) in V2 seems to have eliminated all of it. Even at very low speeds She's exhibiting no hunting although there's some wobble/yaw issues that come from me trying to manage attitude and overcontrolling her. If I just cut power and let her glide in with some up ele, she's rock solid, it's when I try to "manage" that she's getting wobbly.

For what it's worth, the wing is 1.634 sqft and weighs 7.5oz for about 4.6 oz/sqft.
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Old Feb 09, 2011, 11:53 AM
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I see! As nobody has said anymore negative things, I think I will order some foam and some carbon rods and start building soon!

Thanks for the information, it really helps me tweak it for the better!
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Old Feb 10, 2011, 01:28 PM
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Your design is similar to my Great Planes Slinger. I converted it to FPV... it is48" wingspan. I did move my engine forward after looking at Wright wings.
It has a plywood skid in the middle ... Lands great

FPV Day one (8 min 47 sec)
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