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Tapered Wing Washout

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G-JIMG21/02/2018 16:21:30
63 forum posts
7 photos

I'm designing and building a twin engine model with a total wingspan of 70 inches and a fairly tapered wing profile.

Will 2 degrees washout be enough or should I increase it because of the taper?

wing profile.jpg

Denis Watkins21/02/2018 16:40:43
2717 forum posts
137 photos

G-JIMG Beech Super King Air according to google

Did you fly it? Service it ? Or serve in it?

G-JIMG21/02/2018 16:46:11
63 forum posts
7 photos

Designed it.

Denis Watkins21/02/2018 17:27:38
2717 forum posts
137 photos

Yipes GJIMG, that is a claim to fame

As an IC man, this build would be balsa, ply and no washout, as they are very thin wings if scale built

And my own preference would be thicker build

Now it is your aeroplane, probably electric and maybe depron

As a relative lightweight, my instinct is that 2° is at least some reflex, and enough

There are builders who will arrive shortly getting home from work who will contribute

G-JIMG21/02/2018 17:46:46
63 forum posts
7 photos

Thanks Dennis.

It will be electric, balsa & ply. I've already calculated weight, wing loading, etc. and George at 4-Max has run a series of tests to determine the correct Motor/ESC/Batt combination for the scale props.

TLAR says 2 degrees is OK, I just wanted to check if anyone out there had more experience on the modelling side of things.


Tim Hooper21/02/2018 17:51:52
2821 forum posts
2346 photos

I'd add the 2 degrees just to be safe when it slows up for landing.


Timo Starkloff21/02/2018 17:52:37
231 forum posts
545 photos

As a simple rule of thumb I use the following numbers as washout, depending on the difference of length of the wing root and wing tip.

ratio root/tip = washout

1.5 = 1-1.5 deg

2 = 2 deg

2.5 = 2.5 deg

3 = 3 deg

This worked well on planes from the moderate Fairey Fulmar to the thin Junkers 87. Additionally important is the wing load and the depth of the wing and the planned air speed. Airfoils should be able to cope with that. I prefer thin and modern airfoils like SD6060 and S8052 over the traditional ClarkY or NACA. They work better on sharp wings with high wing load, even at high angle of attack they’re controllable until the stall.

Edited By Timo Starkloff on 21/02/2018 18:05:54

G-JIMG21/02/2018 18:11:46
63 forum posts
7 photos

Thanks guys.

Timo's ratio method gives 2.3 degrees washout, so 2 was pretty close.


Timo Starkloff22/02/2018 06:52:34
231 forum posts
545 photos

2 degree should be fine. Washout helps a lot to prevent or soften flipping on one side because of stall. And you can fly much slower than without. I never recognised negative characteristics, not on speed models nor on normal ones (there is the argument on the internet that washout slows you down). But I had the experience with my own models at the beginning of rc flying and have seen quiet often on other models, that planes without washout are much more difficult if not impossible to fly.

Good luck for your interesting project


Andy Blackburn22/02/2018 08:26:45
425 forum posts
482 photos
1 articles

My two penn'orth:

That's quite a lot of taper so the tip chord is quite small, even at about 70" span. It might be worth looking at the CL/alpha polars; the measured zero-lift incidence sometimes changes at lower Reynolds numbers so you might be better off with a different (possibly more cambered) tip section as well as washout. And 2 degrees of geometric and/or aerodynamic washout feels about right.

Good luck with it...

Nigel R22/02/2018 09:12:34
1212 forum posts
275 photos

I'd go with - root section thinner than tip, root LE a bit sharper than tip. No idea what exact section, however, the SD8052 that Timo suggests looks to stall a couple of degrees beyond a vanilla Clark Y, so a transition from one to other would likely work quite well.

Flaps on inboard section, presumably? You might not even need this refinement if you're using flaps.

G-JIMG22/02/2018 09:55:00
63 forum posts
7 photos

Thanks guys, 2 degrees it is.


There is a large Flap area on this aircraft, from the inboard edge of the aileron to the wing root (the nacelle splits at the back and forms part of the inboard Flap). I will have to be very careful when setting the throws.

What effect, if any, do you think the winglets will have at this scale?


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