I have heard that word many times and I understand that they use this word for an aerodynamic characteristic of the wing, but I have not clear what exactly means and how affects on my planes, also is it measurable? What is the washout have to do with the elevator?
Thanks for any info.

Very simply, washout is either a physically twisted wing or an aerodynamically twisted wing.

If you look at a wing from directly behind, you expect the TEs to be straight and to see exactly the same amount of top wing as you see of the bottom wing. You expect the TE to be straight behind the wing. No part of it is above or below where you expect it to be.

That same wing would have the TE moving upward as it moved from the fuselage out toward the tips if it was washed out. That is physical washout.

The idea is to have the middle of the wing stall before the wing tips stall. Or to have the wingtips stall after the middle of the wing stalls. Since a stall comes from excessive angle of attack, if you twist the wing so the tips fly at less angle of attack than the rest of the wing, they're not going to stall when the rest of the wing starts to stall.

You can also design that into a wing using the airfoils. You use an airfoil for the tips that stalls at a larger angle of attack than the airfoil that's in the middle of the wing. If you looked at the back of that wing, it wouldn't look twisted up toward the tips. But it would have aerodynamically wash out.

Yes, the physically twisted one is measured in degrees. Some people also talk how much the twist is in inches or mm's. The inches/mm amount actually is of less value as it's means little unless the wing chord and span are known. The amount of washout in inches on one airplane really doesn't give much clue what amount to washout a different size airplane to get the same effect.

If it's an aerodynamic washout, there isn't really a convenient and easy way to describe it in a single measurement.

Little or nothing.

The wing's downwash angle will be affected if it is washed out, but that effect occurrs more to the outboard part of the wing. Since the inner part of the wing has almost no washout, and it's directly in front of the horizontal tail, the horizontal tail isn't going to care much what the downwash angle of the wingtips is.

It's effect is to reduce the total lift generated by the wing at all speeds. It might also reduce the possibility of the airplane rolling when the wing or any part of it stalls, since the stall may occur more often toward the center as opposed to the tips.

Since a wing without LE or TE taper has no tendency to stall first at the tips, it's usually a waste of time to physically twist them.

When I built a Gentle Lady glider, the building instructions called for 1/4 or 1/2 , I don't remember exactly, inches of washout at the wing tips. In addition to making sure that the center of the wing stalls first, it also reduces induced drag at cruising speed. Because the wingtips are not generating much lift at cruising speeds, they also are not generating high energy tip vortices. Too much washout can have the wing center and wing tip lifting in opposite directions at high speeds which increases drag.

Actually this is not the way it works. Induced drag is very much a direct product of the amount of lift produced. The entire wing works together to produce the amount of lift the airplane needs at any moment. Since the total lift needed doesn't lessen or increase simply because the wing is twisted, that wing is going to be called on to generate whatever lift is required. And since the tips are not generating as much lift as they would without the twist, the lift has to be generated elsewhere. Since the wing generates lift by increasing the angle of attack, it simply has to increase more. So the inner parts of the wing wind up flying at a greater AOA than they could have had there been no washout. And they generate more induced drag than they would have at the lower AOA. The lift needed doesn't change simply because the wings are washed out. The induced drag that amount of lift generation creates doesn't change either.


This doesn't always work this way either. The energy of the tip vortex is very much a function of the lift the wing is being required to produce. That isn't going to change just because the tip is twisted or generating less of the overall lift required.


Very often us modelers "overdo" simple concepts. Very often the lift required at cruise needs very little AOA from the airfoil that's in the wing. The AOA might actually be less that the angle we've twisted into the poor wing. Since we've almost always placed our wing into the fuselage with an incidence that results in the wing flying at or very near it's cruise AOA then the entire wing is carried at cruise speed at the angle that would generate the appropriate lift with the least drag. But if we've twisted the tips a couple of degrees out of whack, what are they now doing? In a lot of cases that twisted tip is actually not lifting at all or is generating negative lift. In either case, the drag being created is added cost with no return.

Twisting a wing really doesn't reduce the induced drag for the airplane. It might reduce the induced drag at the tip, but that's false economy. The reduction at the tip will be found somewhere else on the wing. And there's a good chance the twist will actually result in greater drag from the wing throughout the flight envelope.

One problem we have as modelers is that our testing often is nothing more than two flights worth. On the first flight, the airplane drops a wing on approach. Somebody tells us to twist the wing and somebody else has a monokote iron so we do. Next flight, the airplane doesn't drop a wing and we've got our proof.

And it might seem to work from then on. But we've actually screwed the overall performance of the airplane in a way that probably won't ever be very obvious to us and doesn't have a simple soundbite symptom.

The beauty of washout is to the competitor who actually understands it. He gets to tell his competition how it can help cure tip stalls and then harvest the benefits from then on.

washout: means you ain't going to get your wings --
lifting airfoils and washout and Clark Y and Davis wing .etc ., were all deep dark mysteries to me - 50 years ago.
As applies to our models - most of the specialized airfoil stuff is meaningless
We are simply dealing with sizes and speeds so far removed from the full scale versions using theses shapes, that there is little if any correlation.
for really light models , a simple flat stiff sheet as a wing, works just fine and is hard to beat - current studies and even low speed tunnel work has produced data which shows it to be true.
The washout is a bandaid from bygone days -It was used to prevent drag at the outer ends of the wing - as such, it also (as noted ) reduced it's ability to share the task of lift. As for "tip stall"- that's a real puzzle to me - it is possible.
frankly on any of our RC models even scale "warbirds" I doubt washouts ability to do any good.
The only wing planform I have seen to do the job claimed for washout -- is a very low aspect ratio sym. wing - the craft just settles evenly as spanwise flow stabilizes it.

The full scale spitfire had lots of washout. I duplicated this on my model but I have no idea if it matters or not. I do know I have to land pretty fast.

Sure it does. We have two VQ P-40 wings, one with washout and one without. The wing that doesn't have washout would drop a tip everytime at low speed whereas the wing that does never dropped a wingtip. However, when full flaps were used, then the wing without washout had much less tendency to drop a wingtip. All Top Flite kits call for wing washout. even the ones with Selig airfoil. On the other hand, aerobatic planes do not need washout because you want the wing to snap easily.

With inboard flaps down, the outboard wing angle of attack is reduced a LOT, which is washout.

Not true. The outboard wing still flies at the same angle of attack. With inboard flaps down, the inboard wing angle of attack is increased.

I know that the Spitfire wings have wash out I was told by an owner of a Spitfire at my Club, but in fact himself did not know a clear idea of the washout, I will build a P-47 and want to know if the wings have washout, by now I have understood that this washout is a twist of the wings, and is good to maintain the plane flying at different speeds, because the wing keep flying on some part when other part of the wing has stalled (am I right?). I also have understood that is measurable (Thanks Darock). I was told by a friend on my club that he lost his first spitfire by a wrong design from Top Flite, because (He says) that "the horizontal stabilizer has a wrong incidence because the main wings have washout" then the plane rolled. That is why I wanted to know if the washout had any thing to do with the tail section. Wel I think that this a good issue for many modelists.

thats just silly talk- the "main wings " (as opposed to the little wings on the back end?) will try to assume the position THEY want which gives lift equal to the task- To clarify - you can have wash in/ wash out - set the wing at what ever angle of attack you like - BUT to fly along in level unaccelerated flight - the ENTIRE wing will assume a position (AOA) equal to that task.
The model will climb or dive till power and the drag get equalized. The entire wing will be contributing BOTH
The reason most warbirds have washout - -in models is simply to follow a scale look -
also most "warbirds" have high wing loadings and in the model - all of the wash in is just hogwash - to resolve the problem of "tip stall) what ever that is - you either must increase speed or reduce weight - no other options
You can't reshape a given area and increase lift- --you CAN make the wing more controllable at a given speed - but thats it.
Flaps do that too The lift does not increase (tho drag does) but the descent angle is more controllable.
The comment by Tall Paul is of course correct - Add inboard flap - the entire wing (and airframe) assumes a new angle - You can't do one with out the other

What you say it not correct. Wash-out does have a big effect on tip stall! Adding washout to the wingtips will give them a smaller 'angle of incidence'. If you then slow the aircraft down and keep the same altitude you would have to pitch up. The angle of attack will gradually increase untill it reaches the stalling AOA at which you should have a pitch down effect (if not the aircraft should never be stalled since you would not be able to get out of it, real aircraft with this behaviour are fitted with a 'stick pusher' but that's another thing...)
Having wash-out will make the inner portion of the wing reach its stall AOA first (before the wingtip) so you avoid tip stall.

Other options to prevent tip stall: use aerofoils which create strong vortices, use rectangular wings, using bigger thickness and chamber at the root, leading edge slots towards the tip to give the boundary layer more energy, using stall strips at the root, place vortex generators at the tip, do not use swept wings, use wing fences to prevent the outboard movement of the airflow, vortillons, saw tooth... So you see there are many ways to prevent tip stall besides keeping the speed up.

Flaps do not increase lift???? Explain please.

Bart

Flaps do not increase lift? Why do full size planes take off with 15-deg of flaps? Why do Navy planes take off an aircraft carrier with flaps?

Like I said earlier, wash out has been proven "in practice" to reduce tip stall on a warbird. One does not have to increase speed if washout was incorporated into the wing.

One more question: If flaps do not increase lift by reshaping a given area, then why do my planes balloon way up when I deploy them?

.
Sorry, it's true. The plane's attitude is adjusted for the speed with flaps down. This lowers the angle of attack of the whole plane because of the additional Cl due to the flap deflection.
The "ballooning" with flap.

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The Willis Nye detailed drawing of the Spitfire in "Scale Aircraft Drawing, Vol II, World War II," show a 0.7 degree -washin- at the location of the pitot head near the wing tip.

Fully agree with Tall Paul.

It's the change in Cl with the flap. The Cl with flap is higher than the Cl without flap, but it occurs at a lower angle of attack.
If the alpha isn't changed, the plane falls out of the sky.
Example... Cl near stall, about 8 degrees alpha, without flap. A
60 degree flap the -same- Cl (the lift hasn't changed) is -5 degrees. B.
Lowering the nose puts the wing outboard of the flap at -5 degrees C, well below stall, and the same effect as a LOT of washout.

The reason why your plane balloons when you deploy flaps is because you don't reduce the body attitude (pitch angle, NOT the same as AOA)

L = 1/2 x Rho x V² x S x Cl

If you lower flaps, as Paul said the CL increases. As a result the total lift will increase and you will climb, this is the ballooning. The logical way to solve this is to reduce the body attitude while you extend the flaps. The opposite happens if you rectract the flaps.

Bart

What makes Nye an expert? I have 2 Spitfire books with lots of photos and scale drawings which clearly show extensive washout.

Barto--
I always see lift -- as drag -one is the other - I suspect this was NEVER tought as such in school.
IF-- one deploys flap -with no other changes - the typical effect is a ballooning and a speed reduction
so IF the flaps added lift (only) the plane would climb -and continue to climb
However as you know - there is only a momentary ballooning-- the the added "lift" results in an altitude loss --unless power is added -because drag increased more than lift increased
This is why I mention that the flap does not add lift . It just recambers the airfoil converting it to an effective higher angle of attack.
also allowing the fuselage to continue flight at a lower angle of attack.