# Flying wing as cheap and simple option for basic fun flying.

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Hot Wings, May 18, 2017.

1. Aug 4, 2017

### Autodidact

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Topaz is right, and I felt a little convicted by his statements and so I went to do a little more analysis of the "campstool" (it's not even a lawn chair), and I went at it pretty much exactly like you said; I went to the 103-7 appendix and looked up the lift factor for a double surface airfoil with no flaps (since it's a tailless, can't have flaps) which was 1.6, and found the wing loading would need to be no more than ≈ 3.13 lb/ft^2, goofed up and used the wrong weight and got 121.7 ft^2 instead of 105 something ft^2, figured up an alpha of about 1.7° for a 3d Cl/Calpha which corresponded to a Cm of 0.03188 or so for the Marske XM-1D airfoil and figured up a moment (taking into account tip losses) of about 188 lb/ft at 60 mph. If the gross weight is 380 lb, then that puts the CG about 6" forward of the 1/4 chord point which I show in the sketch here, but I didn't quite get the estimated CG - based on the estimated component weights - quite forward enough which is probably OK since the wing really only needs to be 105 ft^2 and there is a cut-out at the TE for the prop so I can avoid putting the pilot way out in front of the wing a la Breezy - which should reduce the moment a little. Anyway, I approached it just as you described and found out what the moment might be at 60 mph and then tried to arrange the weights so that the CG corresponded. A few more iterations and mistake corrections and it should be ready for some basic structural calcs. I think the structural weight of the wing and the sling, minus the engine, should be 85 lb or less, hopefully. It's veerry tempting to try and build this because it's so simple (or simple looking, anyway).

As far as the faster Mitchell style wing I'd like to design, yes, it needs a lot of thought, and I'm fully prepared to find out that the symmetrical airfoils are not up to it. But I just can't get over how good some of them are; the Eppler 479 symmetric airfoil has almost the same Clmax as the NACA 2415 and a much better drag polar...

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2. Aug 4, 2017

### Hot Wings

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And this is the reason I keep thinking just tacking on a canard, while not being the 'pure' way, is very practical for a part 103. Imagine a U-2 with a canard, not for pitch control, but for trim. This lets us call the junkers elevons - eleflaperons.

3. Aug 4, 2017

### pictsidhe

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The appendix stall calcs aren't applicable to flying wings. A swept flying wing can use flaps. It might be possible to use LE flaps on a plank?

Edit, just checked the appendix and I can't see planks being excluded from the stall calcs.

Last edited: Aug 4, 2017
4. Aug 4, 2017

### Hot Wings

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But if it has a canard it is no longer a flying wing.

Per the AC we can't use the area of the canard in the calculation, but a 10 foot square canard that can't be considered is a very good trade for being able to use the higher lift factor. It also helps considerably with the CG problem that different pilot weights creates.

5. Aug 5, 2017

### Aesquire

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Autodidact, like that one! Good visibility in the directions that need it. Cushions for a lighter pilot to move him forward?

Silly question. What's the minimum non-flapped wing area for a pt. 103? By the formula.

6. Aug 5, 2017

### Aerowerx

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Assuming a 200 pound pilot, and a max CL of 1.4

24 kts is 40.5 ft/s. 254 pound empty. 200 pound pilot. 30 pounds fuel.

The formula is...

S=2*484/( 40.5^2*0.00238*1.4)

Which gives 177 square feet.

7. Aug 5, 2017

### pictsidhe

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I believe that a 170lb pilot is used for stall calculations.

8. Aug 5, 2017

### Aerowerx

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Ok, 166 square feet then. And no more donuts!

9. Aug 5, 2017

### pictsidhe

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I've shed a few doughnuts myself recently, but I really don't look good at 170...

10. Aug 5, 2017

### Aesquire

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Not even Krispy Kreme? Their signature glazed weighs near nothing.

And magically converts 3 times it's mass to fat when I eat them... Maybe I shouldn't buy the 2 dozen for the price of one?

Thanks for the formula.

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11. Aug 5, 2017

### Norman

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You're going to be very hard pressed to get that from an airfoil with a positive Cm and low drag. If you don't care about drag it's not too hard though. Here's an example:

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12. Aug 5, 2017

### Norman

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So can planks but only one obscure type. Split flaps can have Cm=0 if hinged at about 40% of the wing's chord. Farther forward they even produce Cm>0. In this position they do increase lift. Think of it this way: if you move the hinge all the way to the leading edge it would be a Kruger flap.

Last edited: Aug 5, 2017
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13. Aug 5, 2017

### Aerowerx

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I just picked that number out of the air**, Norm. 1.2 would be more realistic, I think.

-------
**Genuine pun.

14. Aug 5, 2017

### pictsidhe

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I have a paper somewhere comparing dive brakes. It is one of the very few papers I found on split flaps. Another ARC paper showed power assistance for a split flap. The back was a bellows and the chamber formed was vented forward or aft to open and close it. A droop nose flap will give +Cm, that could be combined with down elevon. Or do a SWIFT, and let it trim the aircraft for lower speed? It seems that a 1.4 Cl would be a valid appendix calculation figure for a plank.

15. Aug 5, 2017

### Autodidact

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Reality aside, the lift factor that the plank wing would be allowed to use in the the 103-7 wing loading chart is 1.6 which works out to 3.13 lb/sqrft - just divide estimated empty weight plus 200lbs (170pilot + 30fuel) by 3.13 and there's your area. No reason for a simple wing to weigh 254 lb....

Last edited: Aug 5, 2017
16. Aug 6, 2017

### pictsidhe

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With 51% dive recovery type flaps, a lift factor of 2.0 would be valid. 3.9 lb/sqft? This is rather interesting.

17. Aug 6, 2017

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