Why is it important for wing tips to stall last on an aircraft wing? And do all ultralights have it?

[solomon]

Anyone know why the wing tips must stall last? I was once told but i forgot the reason and also would most ultralights have this feature?

 

 

[Louis Moore]

It's usually for Aileron Control during the stall, called Washout (as in thats the name of the wing twist). Stops the disturbed, stalled air from ruining your aileron control. http://en.wikipedia.org/wiki/Washout_(aviation) Wiki can say it better than me so there you go!!!!!

 

I thought all aircraft had it, except maybe super old ones, but do not quote me on that fact!

 

 

[Guest Andys@coffs]

I agree, and add that I believed when the stall starts at or around the root next to the main fuselage that the buffet is easily felt and should be understood for what it is. Given that its happening closest to the center of gravity then in the beginings of a relatively simple stall roll control is still available (even though likely slow because of the slow speed).

 

Now.....That said, you can make a wing stall at almost any combination of attitude and an associated corresponding speed and load, and in some of those combinations (like a high speed high G (hence high load), high banking turn) the early warning, time to think and act, and ignoring that, the resulting relatively placid stall will likely be replaced by a really angy beast that provides little to no warning, no time to act and a complete (or even more than one) tumble out of the turn towardss the high wing when the stall occurs. In that example washout is unlikely to have any significant benefit once you have gone past the performance edge (it does have an effect on where the edge is, but not what follows when you push too far). Aeronatuical engineers or aerobatics trained pilots feel free to jump in :<)

 

Andy

 

 

[pylon500]

In lay terms, if the wing stalls in the middle first, then the aircraft is being supported by it's wingtips, which would be stable.

 

If the wingtips stalled first, chances are one would stall before the other, making that wing drop and roll you over on your back.

 

Not what you want close to the ground!

 

Various means are used to ensure the centre of the wing stalls before the tips;

 

1. Washout built into the wing, which is twist along the wing giving the tips less angle of attack than the centre.

 

2. Change of wing section type along the wing, where the tip section is given a higher lift coefficient than the centre, which means the centre looses lift before the tips.

 

3. Aerodynamic devices added to the wing to either maintain lift to a lower speed towards the tips (cuffs, fences, vortex generators), or other devices to actually destroy lift near the centre at low speeds (stall strips).

 

4. The use of flaps will have the same effect by changing the angle of attack between the flapped area, and the non flapped area.

 

With all this in mind remember, if you are close to the stall and/or at a high angle of attack, use of the ailerons will usually cancel the effectiveness of all these devices, and you will end up on your back again!!

 

How to create and use ailerons or flapperons at low speed is another lesson........

 

Arthur.

 

 

[XP503]

Washout also makes the a/c less likely to enter a spin, and also easier to recover from a spin, from what I've read.

 

 

[facthunter]

Washout is evident on the wings of many planes. This may also reduce wing tip vortices a little. When you are inverted the washout will have the reverse effect, so it would be undesireable on an aerobatic plane. A "strake" on the inner wing leading edge is sometimes used. VG's on the upper surface of the outer wing to as well as fixed or actuated slats and slots

 

As stated the purpose is to reduce the suddennes of a wing drop and autorotation and make the plane more docile and predictable at lower speeds. It enables the ailerons to still be effective close to the stall.

 

NOTE. This control should not be relied upon and if there is any reluctance for the wing to respond, speed should be increased or pitch the plane forward to take the dynamic load off the wing. Rudder can be used to control roll to some extent too, and if your operations involve a lot of short field or slow work get plenty of practice in at a safe height. Nev

 

 

[solomon]

Great thanks guys! So I believe having the flaps down slightly will have the same affect as a twisted wing right?

 

 

[Teckair]

Great thanks guys! So I believe having the flaps down slightly will have the same affect as a twisted wing right?

I think you could be right there but you need to ask someone who really knows. Aircraft design is highly specialised and can be deadly if you get it wrong. My understanding is washout is to prevent tip stalling which means when a tip stall occurs the aircraft can roll upside down. Yes all the ultralghts I have seen have it. It would be dangerous not to have it. I think also it would be dangerous to depend on having a bit of flap down, it may be OK if the flaps are set so they cannot come right up. You really need to talk to someone who is an expert on this.

 

 

[fly_tornado]

On the Tornado you can change the flap stop blocks to increase the flap angle to improve low speed handling.

 

 

[Powerin]

Great thanks guys! So I believe having the flaps down slightly will have the same affect as a twisted wing right?

Savannah's have flaperons which are divided about half way down each wing and are offset from each other to create washout as the wings themselves don't have any. I think the inner part of the flaperon is lower than the outer which would be similar to a slightly lowered conventional flap. Savannah owners could correct me.

If my memory serves correctly, lowering a flap increases the angle of attack of a wing, which means the section of wing with a lowered flap should stall first.

 

 

[turboplanner]

A slightly lowered flap will create drag, and because it might or might not work on a STOL aircraft doesn't mean it will be satisfactory on another.

 

You guys are giving advice to someone who could well build that into an incompatible wing and attempt a high speed taxy or take off.

 

Better to study aerodynamics information written by an aviation engineer.

 

 

[Guest pookemon]

In lay terms, if the wing stalls in the middle first, then the aircraft is being supported by it's wingtips, which would be stable.If the wingtips stalled first, chances are one would stall before the other, making that wing drop and roll you over on your back.

Not what you want close to the ground!

 

Various means are used to ensure the centre of the wing stalls before the tips;

 

1. Washout built into the wing, which is twist along the wing giving the tips less angle of attack than the centre.

 

2. Change of wing section type along the wing, where the tip section is given a higher lift coefficient than the centre, which means the centre looses lift before the tips.

 

3. Aerodynamic devices added to the wing to either maintain lift to a lower speed towards the tips (cuffs, fences, vortex generators), or other devices to actually destroy lift near the centre at low speeds (stall strips).

 

4. The use of flaps will have the same effect by changing the angle of attack between the flapped area, and the non flapped area.

 

With all this in mind remember, if you are close to the stall and/or at a high angle of attack, use of the ailerons will usually cancel the effectiveness of all these devices, and you will end up on your back again!!

 

How to create and use ailerons or flapperons at low speed is another lesson........

 

Arthur.

Great answer pylon500. Despite flying the Gazelle - which has close to full aileron authority in a stall (because the ailerons are located within the prop wash - and because they are not really part of the wing) - I was taught that in a stall you NEVER use your ailerons. Rudder only! Using ailerons will increase the AoA at the wing tips - making the tip stall more likely. If you do have a tip stall, using Ailerons will actually make it worse.

 

 

[facthunter]

Flapperons are a mixed blessing and a complex subject. Consider adverse aileron drag, and differential aileron beneficial effects which you tend to lose with flapperons. You end up with no UP aileron. As to the effect of flaps, on where the wing stalls, don't make any general statements. Some flaps are slotted and wing area increasers.( Fowler flaps).and may increas the angle at which that part of the wing stalls.

 

The Gazelle system is also used on the AN-2? so can operate at above the stall angle of the wing.

 

I repeat. To rely on aileron near the stall is dangerous. Train your self away from it and review the further effect of rudder. You can pick up a dropped wing with rudder but can easily overdo it and have the plane rotate the other way, and more violently.. The way the aileron increases lift is not very efficient and the drag increases much more rapidly than lift, when aileron is applied. As well you can cause that part of the wing to stall earlier than it otherwise would have, because you have effectively increased tha angle of attack, in that area. Nev

 

 

[farri]

Anyone know why the wing tips must stall last? I was once told but i forgot the reason and also would most ultralights have this feature?

Hello Solomon, I hope your flight training is going well for you!

 

I don`t know about every Ultralight aircraft having washout in the wing but this is the aircraft I built almost 30 years ago and started my flying journey in! It has wire cables in the wing and adjusting these cables gives the degree of washout....The reason for washout has already been explained for you!

 

 

Cheers,

 

Frank.

 

 

[fly_tornado]

instructions/specifications of the amount of washout for a tornado, doesn't take much

 

http://www.titanaircraft.com/manuals/tornado/92-INS-0329-B.pdf

 

 

[farri]

I put 2 degrees washout in the above aircraft.

 

Frank.

 

 

[pylon500]

So I believe having the flaps down slightly will have the same affect as a twisted wing right?

This mainly applies to faster aircraft when flying at low speeds, like take off and landing.

While twist (washout) can have some structural problems at higher speeds, this doesn't really apply to us, so we are better off just having a bit of twist.

 

It's also lighter than flaps.

 

The Gazelle system is also used on the AN-2?

No, not really, the gazelle system is more akin to what Junkers was using back in the 30's.

The AN-2 uses a sort of Frieze/Fowler type flap and aileron, much like the Foxbat uses today.

 

For the picky, the more 'remote' the hinge point is, the more Fowler it is.

 

The real difference is more to do with the underside of the trailing edge of the wing in front of the surface, if it's square like a Cub or Spitfire, it's a Frieze.

 

If the underside is rounded to allow smooth airflow up over the surface, like the flap area on a Cessna or the Foxbat (regardless of hinge point), then it's a Fowler. (That's my view anyway..)

 

Arthur.

 

 

[facthunter]

The plane I'm referring to is an Antanov but I'm not sure of the model hence the ? mark.. The Gazelle ailerons do work well at low speeds.' and fit well with a plane that is very forgiving.

 

From a pilot point of view I find the Frieze ailerons a horrible idea because they ruin the spin entry and absorb energy, and complicates the way the controls work ( In a purist way) and. ( They create drag) I don't mind a proactive rudder application a small amount of which will counteract aileron drag more efficiently than a "frieze" aileron. Nev

 

 

[damkia]

The wingtips (outer 1/3 of wing) are usually made to stall last to allow for spin recovery via ailerons and rudder after a deep or power-on stall ("dropping a wing").

 

 

[pylon500]

As a previous glider pilot, I am also not a fan of Frieze ailerons for the drag reason, and also not a great fan of flaperons because of the adverse yaw problem ( he says while spouting praise for the Foxbat ?!?!) so we are on the same page.

 

 

[facthunter]

I do appreciate your comments in this area. The aeroplane that I would like (referring to it's flight charactistics), would not be your average thing but I think it could be sold to enthusiasts. ( The idea) less stability more control. Nev

 

 

[Mazda]

Wings are desinged to stall root first because there is a short moment arm and less chance of a wing drop. If the wings stall tip first and there is any differential lift, a wing drop will result due to the longer moment arm.

 

It is achieved through washout and inboard stall strips.

 

Buffet is a byproduct as the disturbed inboard airflow buffets the tail, depending on wing and tail design.

 

Use of the aileron in or near the stall is to be avoided.

 

 

[eightyknots]

Wings are desinged to stall root first because there is a short moment arm and less chance of a wing drop. If the wings stall tip first and there is any differential lift, a wing drop will result due to the longer moment arm.It is achieved through washout and inboard stall strips.

I wonder how the ICP Savannah does it without stall strips, etc? They appear to have completely straight wings, no dihedreal, etc.

 

 

[boingk]

Probably fine - it only takes a few degrees of washout at the tip to acheive the desired results and this may not be obvious even when eyeballing the aircraft.

 

Of course, the craft we're talking about here are lightly-loaded low-power things so really should be fairly docile no matter what you're doing in them.

 

Cheers - boingk

 

 

[turboplanner]

I wonder how the ICP Savannah does it without stall strips, etc? They appear to have completely straight wings, no dihedreal, etc.

If RAA was able to produce accident reports (as in, if they could get the police report and publish the relevant aviation facts) we would all know because one did fall out of the sky from 300' with two experienced pilots in it, who fortunately survived. If they read this, they might like to make a comment on whether (a) the wings had slats, (b) the slats had been removed, but no VG's fitted, © the slats had been removed and VG's were fitted.