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Wing Washout in Sport Jets

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Wing Washout in Sport Jets

Old 08-01-2022, 02:15 PM
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3DJunk
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Default Wing Washout in Sport Jets

Hi fellows,

Is Washout common in Aerobatic Sport Jets such as: Avanti, Rebel, Mephisto, Ares, etc?

For sure it can help in delaying the stall at the tip at high alpha. However what happens in inverted? I guess the model flies most of the time high alpha in upright. Not so many people fly inverted harriers with 3D Jets, I guess...

If you know, can you please share your experiences with Washout and Sport Jets in general?

Best regards,
N
Old 08-01-2022, 02:31 PM
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wojtek
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In pattern like sport jets ( like Flash, Rebel, bandits, etc ) you don't want much if any washout in flight and these are not the high alfa types of jets anyway for most of the flight , however washout is great for stability and higher AOA on landing. The easiest way to accomplish this is a crow set up on the ailerons (where both ailerons deflect up) . This in effect adds washout to the wing. Some elevator trim is also needed around this... I have played around out also having crow on a switch allowing both wings to "wash out" by use of ailerons... besides just playing around with this to see how it changed the flight envelope, i did not find it worth it... ultimately some airframes are better for high alfa than others

Voy
Old 08-01-2022, 02:40 PM
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Originally Posted by wojtek View Post
In pattern like sport jets ( like Flash, Rebel, bandits, etc ) you don't want much if any washout in flight and these are not the high alfa types of jets anyway for most of the flight , however washout is great for stability and higher AOA on landing. The easiest way to accomplish this is a crow set up on the ailerons (where both ailerons deflect up) . This in effect adds washout to the wing. Some elevator trim is also needed around this... I have played around out also having crow on a switch allowing both wings to "wash out" by use of ailerons... besides just playing around with this to see how it changed the flight envelope, i did not find it worth it... ultimately some airframes are better for high alfa than others

Voy
Thanks for the answer. Crow is an option for landing but not for the whole flight. I forgot to mention that after measuring both wings on my Krill AreS XL I found out that there is some washout around 0,8 degress between the wing root and the shark tooth area on both wings. The model flies nice, I just wanted to check the wing alignement as I fly with 2 clicks of AIL trim. Both wings seem parallel. During this investigation washout came up...:-)

Last edited by 3DJunk; 08-01-2022 at 02:42 PM.
Old 08-01-2022, 11:32 PM
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Originally Posted by 3DJunk View Post
Thanks for the answer. Crow is an option for landing but not for the whole flight. I forgot to mention that after measuring both wings on my Krill AreS XL I found out that there is some washout around 0,8 degress between the wing root and the shark tooth area on both wings. The model flies nice, I just wanted to check the wing alignement as I fly with 2 clicks of AIL trim. Both wings seem parallel. During this investigation washout came up...:-)
If washout is ok for the whole flight then so is crow. The former is more elegant than the latter, but aerodynamically they are the same.
Old 08-06-2022, 10:50 AM
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Originally Posted by highhorse View Post
If washout is ok for the whole flight then so is crow. The former is more elegant than the latter, but aerodynamically they are the same.
I disagree crow creates too much drag and has loads of impact on AIL differential specially on aerobatic jets. Washout is built in, have a look at Avanti S v1. The plane is a true performer. If you flew it with craw I would not be so sure performance wise.
Old 08-06-2022, 11:53 AM
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Agree with the above, crow should be used for landing only. A little reflex can be beneficial to certain jets though. It will add a little washout to the wing without the lift reduction crows adds.
Hawks and A4s respond best since the aileron goes out to the wing tip, the wing does not have as much washout. Reflex addresses this,
I will add only a very minute amount is needed 1-2mm will do.
Old 08-06-2022, 02:19 PM
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Welcome the the rabbit hole…

There has been some casual conflation here of “crow” and “reflex”, and I am guilty of having contributed to same in a post above. Crow is an aileron reflex in association with flaps, primarily aimed at increasing drag with an associated byproduct of tip AOA reduction, whereas ailerons can also be reflexed on their own with the primary function being reduction in tip AOA and an associated by product of drag.

Guys, please note when comparing washout to reflex that washout isn’t “free”. It causes lift reduction via change in the localized AOA in the portion of the wing washed out. It can not decrease tip-stall issues without also affecting adverse yaw characteristics and resultant ail differential required while also increasing net induced drag as compared to an unwashed wing, and even…and this is a big one…detrimentally INcreasing tip-stall potential during negative-G flight (which technically speaking may or may not be actually be inverted) since during negative-G flight an otherwise washed-out wing becomes a washed-IN wing as alluded to in the OP. Yes, reflex does have more profile drag than washout for the same effect, but that is minuscule at the tiny amount of reflex required to effect the desired changes, while the induced drag remains nearly the same.

Meanwhile also please note that control surface deflections of any type -and in this case ailerons- don’t do their thing without also changing the effective localized AOA and stall characteristics in the same way as does washout. Does reflex cause drag? Yeah. More drag? Sometimes, but that depends on the net flight condition(s) and essentially a reflexed (*) aileron is still the same as a washed out wing.

One could even make the argument that +/- reflex mixed with +/- elevator (such that the ailerons remain unflexed when elevator is in the middle regions of throw and are only flexed either +/- in relation to elevator inputs associated with higher +/- AOAs) would offer the best of both worlds since there’s no wash-in while inverted and there’s a net reduction in drag to boot. Incidentally, there’s an older thread here where a user describes having tamed tip stalls of his wayward F-86 with just this method where he mixed a smidge of aileron reflex with + elevator.






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