S.P.A.D. Aircraft - Coroplast design Discuss the growing area of S.P.A.D.S. (Simple Plastic Airplane Designs). Coroplast type aircraft, pizza box planes, etc..

Nice Flat Wing!

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Old 04-26-2010, 07:16 PM
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rcairlinerflyer
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Default Nice Flat Wing!

How might this aircraft fly with a 3 pound load? It has a flat aerodynamic wing for reduced drag. She weighs in unloaded at 1/2 a pound. The wingspan is about 40 inches without the two 6 by 1 inch 45 degree winglets. Somewhere around a 250 square inch wing area.
So, total 3 1/2 pounds on 250 square inch wing area (Not including 42 approx. square inch elevator stab).
How fast might takeoff speed be? Is it very aerodynamic? Etc.
Thanks.
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Old 04-26-2010, 11:47 PM
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Default RE: Nice Flat Wing!

I'm sorry, but "a flat wing for reduced drag" is like saying it takes steroids for your junk to get bigger. Actually, airfoiled wings will simply provide lift WAY more efficiently. The reason people go flat-plate is for simplicity.

Is it aerodynamic? Technically, yes. Is it low drag (the 'right' question)? No. You're going to be getting a TON of interference drag from all of your 90* connection points. Will it fly well? Possibly. It seems to have a pretty big tail, and that helps it fly "smoother".

How will it fly? Heavy. It's wing loading is going to be CRAZY high with a 3lb payload (over 30oz/ft2).
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Old 04-27-2010, 01:41 PM
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Default RE: Nice Flat Wing!

Moved from Aerodynamics to SPAD. The plastic benders here will have some more ideas on how to best build your design to be successful.

At that weight it will fly but not well. But more importantly I'd be worried about the wing folding up at the first bit of added G load from a turn or pulling out of even a shallow dive. It is far too thin to hold the sort of spar you need to be strong enough for the flight loads it'll see. You don't say what you made the wing from but by the looks of the graphics I'm guessing that it is corroplast sign board. The wing will not hold up to any flight loads you'll see with anything near that sort of weight. Even at a 1 lb takoff weight the wing would suffer from extreme bending and likely fold up and crash the model. The little stub of wood or whatever you used at the root isn't going to be anything like enough. Even if you ran such a strip for the full span it would not be enough. Even at a 2 lb weght the flight maneuvers will generate enough G load to fold that flat wing. It may not even survive the takeoff. A single layer of corroplast is just not structurally strong enough or rigid enough to use as an RC model wing of this size and shape.

Even with a regular airfoil 250 sq inches is not a lot of area. The takeoff, landing and stall speeds will all be quite high. It would also be suceptable to high speed stalls and snap rolls with the flat or thin airfoil and the high wing loading. If you were to redesign and build a wing with adequite strength you would still want to keep the weight down to more like 2 to 2.5 lbs at a maximum. Even then it would be a fast takeoff and landing speed. 250 sq inches is what I fly with using an .049 that weights 1.5 lbs. And that has a comfortable landing and takoff speed. Up to 2 lbs I would still find OK but not as much fun. But much over that and it becomes a "special" model that would seldome be flown for fun because keeping it within its flight parameters would become too much work for my tastes.

Now that we've pretty much ripped your dreams up I will say that it LOOKS nice for the material you are using. It's hard to make a model from corroplast that has good looks yet also works within the limitations of the material. If it were me I'd make the tip chord a little wider so that the wing area bumps up to 300 sq inches. And keep the "payload" down so the whole model weighs no more than 2 to 2.5 lbs then you would have something that would fly very well. But it sure as blazes will NOT be a trainer. Not even a second model. But as a third model and provided you're VERY capable at flying your second model which should be a fairly sporty handling type then you'll be ready to try something like your twin boomer. At 2 lbs it would fly with a lot more forgiveness than if it is heavier. At 2.5 lbs it'll take off and land at racer like speeds. At 3 lbs it'll be a handful and a half for landings and takeoffs. And in the air it'll begin to do nasty snaps out of turns and dive recoverys when you least expect it due to the wing loading. So do try to keep it under 2.5 lbs for best results.

You can use corroplast for the wing and still keep it fairly thin. By getting some thinner material and creasing the inside along a couple of corrugations you can fold the material back on itself and include a carbon fiber tube about 5/16 to 3/8 in diameter at the high point to act as a spar. Even better would be a stick of wood about 1/2 inch wide by 3/8 deep that tapers to 1/2 wide by 1/4 deep at the tip. Then glue flat carbon strips 1/2 winde by .035 thick to the top and bottom of that wood spar and then fold the corroplast over this spar. The wing will still be pretty thin but it'll now be both strong and rigid. You'll need to do separate wings with this method and then join them using a good solid method at the root. Also you'll want a really good way to bond the tail booms to the wing and the fuselage to the wing. But the folks here in the SPAD forum should be able to help you with that.

Good luck on the rebuild and I wish you success with the new and better version.
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Old 04-27-2010, 06:50 PM
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Default RE: Nice Flat Wing!

Thank you all for the information. I already had a general kind of idea on what characteristics I will most likely receive from this model. I will say, I don't anticipate the plane with a three pound load but more like a one pound load. The plane is made from all double paper layered foam core foamboard that you can get from any Hobby Lobby or any hobby store. When I tested the aircraft's wings on a one pound load the wings themselves are sturdy enough. Nothing to worry about with excessive bending in flight as long as the load is fairly light. But what I am worried about, which you also mentioned, is the wing connection points to the fuselage. Not until afterwards did I realize that my design method could have been better and simpler, but of course I wanted to glue vertically to the bottom side instead of gluing horizontally inwards against the top or bottom of the bottom foamboard piece of the fuselage so the connection point would be braced much better. The reason for doing it the way I did it was because I wanted the maximum span I could get since the two wing pieces weren't that very long to begin with.
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Old 04-27-2010, 07:11 PM
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Default RE: Nice Flat Wing!

I am also integrating a UAV system and some components that will make it easier to fly including an auto stabilization unit hooked to a gps autopilot (Ardu Pilot) and some added junk with safety features such as my opto-isolator. What you can't see on the plane are the two 6 inch winglets, but I doubt they'll add much to the performance. You can see one winglet off to the side of the wing in the two top-right pictures.
I did used to have a thick wood spar on the underneath of the plane that nearly covered the span but I removed it because I thought it contributed to much weight to the craft. Most likely what I'll do is attach a thinner carbon fiber spar on to the bottom that will be much lighter and support more performance.
The reason why I insisted the load to be higher than average is because I'm planning on putting a small laptop motherboard into the plane to control it over the internet. Of course, that's another story.
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Old 04-28-2010, 12:27 AM
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Default RE: Nice Flat Wing!

We may need to get another moderator to move this to the Scratch Build forum them. I thought it was made from Corroplast and not foam board.

My concerns over the wing's ability still hold. You MAY be able to pick it up and not have it fold up at 2 lbs but in flight G loads in turns and during pitching maneuvers greatly add to the wing's load. A simple 45 degree banked turn doubles the weight that the wing needs to support. An enthusiastic amount of up elevator to avoid a crash can easily generate 6 to 8 G's so now the wing needs to support 12 to 16 lbs. A single layer of foam board is simply not going to withstand that sort of punishment for long.
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