Swept wing washout?

[mcross]

Hi,
Anyone have any theories on how this wing will behave? It's a flat plate with a bend. To get washout I made the bend line slant towards the trailing edge. This gives it a nice washout but, at the tip, also moves the "thickest" part of the airfoil towards the trailing edge. Think this will work, or did I build in some undesirable behavior?
Thanks,
Mike

Wing is for this plane: http://www.rcgroups.com/forums/showthread.php?t=588126

[Ollie]

See:
http://aero.stanford.edu/WingCalc.html
Use the program. Put in your wing aspect ratio, sweep angle, taper ratio and twist (washout). Then see the lift distribution with angle of attack. If the lift is too much near the tip and too much angle of attack then the wing will tip stall and snap-roll. If the wing stalls first near the root then it will stall straight ahead. When the lift ditribution is ellipical, then the stall is uniform from root to tip.

The total twist is the sum of aerodynamic washout ( zero lift angle of attack) plus geometry washout.

A flat airfoil from leading to trailing edge has zero lift angle of attack. The rub is your airfoil zero lift data. Your airfoils, with maximum camber at chord percent, shift from root to tip. You must find the airfoils' data.

[Brandano]

Works well enough on paper planes. Good stable behavior, but you'll lose something in terms of drag. But I assume that since it's a flat plate probably drag isn't a major issue here
edit: I think it will work fine on that plane, but if you find you are sacrificing too much lift and drag for the sake of stable flight you have other options. Like making the "fold" at about 25% of the entire wing, and then just add another cut with a droop on the outboard portion of the wing. Or sand in a different leading edge along the flat wing. What you really want is to have the outboard portion of the wing to stall later than the inboard portion, so transitioning from a symmetrical airfoil at the root with a sharp leading edge to a cambered airfoil at the tip with a more rounded leading edge should give you the same result

[mcross]

Ollie, thanks for the link. Without consideration of the airfoil changing over the wings length it does show the tip producing less lift over a very large aoa change. Neat program!

Thanks Brandano, I had forgotten some of the other tricks used to delay stall at the tips. I think I'll try this wing first, a change later on won't be too hard to do. My latest motor for the edf30 is pretty strong so I'm not too worried about increasing drag.

Thanks,
Mike

[mharms]

Mike,

I've used just that sort of flate plate camber bend line in a small flying wing (15 in WS) made from 3mm depron. It works great for me.

This angled-rearward camber bend line is kind of neat in how it effectively gives you washout. It also gives you a more cambered shape at the tips, which can improve the lift near the tips. However, the extra camber can cause the tips to stall at a lower AoA. So the total washout (geometric and/or aerodynamic) better compensate for that.

I'm not sure of the effect of moving the max camber point rearward on an airfoil's stall. I guess I'll fire up Profili/XFoil.

Mark

[mcross]

Mark,
Isn't the bend the other way on a wing? Isn't it to give "reflex" or down force at the tips inplace of having a horizontal stabilizer? Or is it the same as a swept wing conventional design? (Note that my picture is the bottom of the wing, lighting made it too hard to see the bend line from the top)
Thanks,
Mike

[mharms]

Mike,

Maybe this photo makes my previous post more clear?

I was commenting how the camber bend line sweeping back, like in your photo, reduced the geometric AoA out at the tips, but it also gives you more camber out at the tips. I think you can see this in the cross-sections I drew on my photo.

I've also got an upward bend at the rear to provide reflex, but if you imagine the reflex isn't there (as in your wing), I think you can see that the tip AoA would be less than the root -- at least geometrically.

Between the geometric washout, the extra tip camber and the effect of the tip camber being more rearward, hopefully, you end up with some net washout. At least that is what I was shooting for. Maybe the effect of my reflex is what makes my case work (?).

Mark

[vintage1]

The easiest way to do all this is simply to make the reflex you need anyway, more pronounced at the tips..being swept back, that gives you more 'moment' for the reflex to work over.

Use of outboard elevons will achieve this anyway..when trimmed for stability, they will both be raised a little in normal flight. As higher AofA's are used in turns and at slow speed, they will be raised even more. Simple innit?

[mcross]

Ok, thanks Mark. I see that you did it the same way I'm trying and for the same reasons, except for your additional bend for reflex.

Hi Vintage, I don't need reflex, it's for a Mig-15. I used this simple method to get some washout and was wondering if anyone knew how it'd work.

Mike