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Design critique request - max duration flight

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Old 02-05-2012, 08:14 AM
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themicahmachine
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Default Design critique request - max duration flight

Some friends and I have started a little design-build-fly competition to see who can fly the longest on a given battery pack. The pack is either a 2s 3300mAH or a 3s 2200mAH Gens Ace pack(both 24.42WH). The battery will be the required payload and all batteries in the contest will be weighted so they are equal. Design constraints are as follows:
    [*]Maximum wingspan 59.9"[*]Maximum wetted planar area of 4sq.ft. (576sq.in.)[*]Only one power system (motor) allowed, and power can only come from the one battery pack[*]Only balsa, spruce, and plywood are allowed for structure. No composites or foam, except for one 4" wide strip of fiberglass allowed at the center of the wing.[*]Must be covered with transparent commercially-available shrink-film of any color (transparent so the structure can be inspected for compliance with the rules)[*]No electronic components may be modified from their commercially-available state[/list]I'm using a Feigao 12mm motor with a 7:1 gearbox for power. I have built the wing already (although I'm not against building another if I determine it's worth the time). I am attaching a PDF of my plans so far for open comment. This is my first scratch build. Any advice would be greatly appreciated. Note that the final battery location and layout of servos/linkage have not been finalized, pending completion of the structural design and calculation of moments for proper CG.

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Old 02-05-2012, 08:37 AM
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Default RE: Design critique request - max duration flight

Sounds like a fun little competition! IMO the triangular gussets in the wing would not need to be used. You could save a few grams there. A narrow piece of 1/32 balsa sheet could be used on the leading and trailing edges if you you are concerned about the wing "racking". The covering should hold/keep that from happening though.

I can see you building at least several dozen of these planes trying to find the right combination. I'll bet you and your friends will have a ball with this.

Ken
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Old 02-05-2012, 09:40 AM
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Default RE: Design critique request - max duration flight

I don't think your motor is going to cut it unles your flying weight is under 20 oz. As far as the wing goes, you may want to check into what airfoils are being used in DLG sailplanes.
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Old 02-05-2012, 09:46 AM
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Default RE: Design critique request - max duration flight

Really sounds like a blast. If this competition relies on other than thermal lift, here is a FWIW suggestion. Give some thought to a wing with a crow setup, though it could still be a rudder plane to save radio equipment weight. The crow could be fixed... flaps down and ailerons up. The effect is that very few rpms are needed to sustain flight as the engine thrust is diverted off the flaps downward to compress and create lift. The ailerons turned up, prevent tip stall.

I can set this mode on my Ultra Stick Lite 10 pound plane and then fly it on rudder and throttle only and it requires very little in the way of rpms and not much control action. From my experience the only thing providing more lift is a thermal. The plane would need only two servos, rudder and throttle. It will be very miserly on energy consumption.
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Old 02-05-2012, 09:53 AM
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Default RE: Design critique request - max duration flight

I woud agree with the 1/32" sheeting in the leading edge rather then triangle gussets would add a far better mount of strength with minimal amount of weight added. The covering film will do the rest...
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Old 02-05-2012, 10:33 AM
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Default RE: Design critique request - max duration flight


ORIGINAL: speedracerntrixie

I don't think your motor is going to cut it unles your flying weight is under 20 oz. As far as the wing goes, you may want to check into what airfoils are being used in DLG sailplanes.
The battery is around 7 ounces, and figuring an average density of 6lbs/cu.ft for balsa (it's almsot all contest balsa) and 1oz for covering, plus a half ounce for glue/etc., and an ounce for servos/wires, I should be around 15-16 ounces AUW.


Also, no folding props are allowed, to prevent using thermals for lift, and the plan may only descend once. Climb, fly at one altitude, land. I'll post the full rules if anyone is interested.

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Old 02-05-2012, 05:59 PM
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Default RE: Design critique request - max duration flight

I think you might be a bit too conservative on the weight of the covering....

Would be interested in the complete rules list as well as many others. This sounds fun...

Cheers,
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