Originally Posted by Jovanx

No.

Wow useful post, now get back under your bridge.

Mike

Originally Posted by Fig Jam

Wow useful post, now get back under your bridge.
Mike

I replied in good faith with a simple answer to a simple question. Not everyone will agree, but I gave you my honest opinion. Peace bro.

Originally Posted by sinowace

I ask about tip stalls because my last plane would tip stall easily even though it was setup correctly. The aspect ratio was very high. Just want to know what the tendencies are for this plane before I spend money on it.

I know what you mean,,, I've had a couple of high aspect ratio winged sailplanes that would tip stall very easily too ,,, and without much warning and flying at what seemed like a normal speed,,, although in world of sailplanes I don't think I'd call the mystiques 12.5 aspect ratio particularly high. I remember a molded 100in wingspan Scale Salto that was fond of tip stalling.

Mike, my tip stall bitch was a Cularis. Don't waste your money.

Here is my take on tip stalls, and I am no authority on the subject.

All wings will tip stall under the right circumstances. Tip stalls are caused by the pilot. They result from turning too slowly or too sharply resulting in the air speed of the inside wing tip dropping below the stall speed, losing lift and thus dropping into the turn.

Sometimes people recomment you bend the tip of the wing up a bit, introducing washout, in order to make the wing more tollerant of this mistake. But ultimately this is all about airspeed and angle of attack of the tip of the wing.

In general, higher wing loaded wings might be more prone to tip stall than low wing loaded wings simply because the lower the WL the slower the glider can usually fly before it will stall.

Now, if the wing has no washout it will likely tend to stall more easily than if it does have washout. So higher WL gliders with wings with no wash-out will have a greater tendency to tip stall than other gliders.

This is all very generalized. None of this is based on strong design or engineering knowledge. It is intended to provide the basic concept in terms that can be understood by non-designers/engineers.

It is my understanding that all stalls are pilot induced, even tip stalls. Keep the speed up in turns, and don't turn too sharply or to flat and you are less likely to tip stall.


OK, let the flack commence!

Originally Posted by aeajr

Here is my take on tip stalls, and I am no authority on the subject.

All wings will tip stall under the right circumstances. Tip stalls are caused by the pilot. They result from turning too slowly or too sharply resulting in the air speed of the inside wing tip dropping below the stall speed, losing lift and thus dropping into the turn.

Sometimes people recomment you bend the tip of the wing up a bit, introducing washout, in order to make the wing more tollerant of this mistake. But ultimately this is all about airspeed and angle of attack of the tip of the wing.

In general, higher wing loaded wings might be more prone to tip stall than low wing loaded wings simply because the lower the WL the slower the glider can usually fly before it will stall.

Now, if the wing has no washout it will likely tend to stall more easily than if it does have washout. So higher WL gliders with wings with no wash-out will have a greater tendency to tip stall than other gliders.

This is all very generalized. None of this is based on strong design or engineering knowledge. It is intended to provide the basic concept in terms that can be understood by non-designers/engineers.

It is my understanding that all stalls are pilot induced, even tip stalls. Keep the speed up in turns, and don't turn too sharply or to flat and you are less likely to tip stall.


OK, let the flack commence!

Whoa!!!! Now you've gone and opened yourself up on that one!!!
Ill just sit back and watch. ;-)

I agree entirely, aeajr. To get a bit into the techniques of preventing stalls:

One common mistake is trying to fly too slowly. Almost all sailplanes can fly fairly slow but most perform better with a little extra speed. A general rule is that one wants to let the nose drop a bit and build some speed when one isn't in lift to take advantage of the best lift to drag of your sailplane. Then, when one is in lift, one can slow down a bit to remain in the lift and take advantage of the rising air. With a heavier, faster, sailplane that has a relatively high wing loading it's not always possible to make your turns in the core of the thermal. That's where this little trick comes into play.

If one looks at my crude diagram you will see how it works. The orange circle is a thermal and the black oval is the flight path. With a little experience one learns how much one can tighten the turn in the thermal but the important part is to keep the speed up above the tip stall threshold. In fact, when there are only small bubbles of lift, it might even be advantageous to merely pull the nose up a bit while flying straight through the thermal and then making a wide, flat, fast turn back to said thermal.

Originally Posted by aeajr

Sometimes people recomment you bend the tip of the wing up a bit, introducing washout, in order to make the wing more tollerant of this mistake. But ultimately this is all about airspeed and angle of attack of the tip of the wing.

My understanding is that the tip of the wing is bent down in relation to the root, not up, to give a washout and prevent tip stalling. The idea is that if the plane is in a high alpha position (prior to a stall or flaring for a landing) the bent-down tips will ensure that the tip of the wing will still be flying instead of stalling.

If the tips were bent up, that would be wash-in. I don't know what that is used for.

"Washout" is a twist of the wing rather than a bend. One raises the trialling edge at the tip to reduce the angle of attack relative to the root. Ideally, the leading edge will be straight. I was able to add some washout to my foam ASW 28 by careful shaping of the balsa ailerons I made for it. It made a very big difference. With a built up wing it can be as simple as holding a twist while hitting the covering with a heat gun.

Originally Posted by peterlngh

"Washout" is a twist of the wing rather than a bend. One raises the trialling edge at the tip to reduce the angle of attack relative to the root. Ideally, the leading edge will be straight. I was able to add some washout to my foam ASW 28 by careful shaping of the balsa ailerons I made for it. It made a very big difference. With a built up wing it can be as simple as holding a twist while hitting the covering with a heat gun.

+1 that is what I meant by bending the wing down in relation to the root, but your explanation is more clear. It is a twist.

BTW. Differential aileron throw, with more up travel than down, and learning to coordinate rudder and aileron can both help prevent tip stalls. I am not a big fan of mixing rudder and aileron though.

Also. Spoilerons, with or without flaps, will generally eliminate a tendency to tip stall on landing approaches. Both ailerons up effectively adds a bunch of washout. Of course, flaps alone accomplish pretty much the same thing even if the angle of incidence at the tip is unchanged.

Originally Posted by peterlngh

"Washout" is a twist of the wing rather than a bend. One raises the trialling edge at the tip to reduce the angle of attack relative to the root. Ideally, the leading edge will be straight. I was able to add some washout to my foam ASW 28 by careful shaping of the balsa ailerons I made for it. It made a very big difference. With a built up wing it can be as simple as holding a twist while hitting the covering with a heat gun.

Thank you peterlngh. This is a better explaination of what I was refering to in my post.

Usually an appropriate amount of washout is designed into the wing at the time of build. So, if the Mystique wings would benefit from washout, I would expect it was designed into the building jigs used to build the wings.

The more sheeting on the wing the harder it is to introduce washout after the wing is completed. In any case I doubt this will be a major concern for the Mystique.


What will be a concern to the pilot is getting to know his glider, how it turns, what speed it flies and what is the best and most appropriate speed and turning radius.

Most often I have read about people facing tip stalls on landing approach. This often happens in the down wind to cross wind turn or cross wind to up wind turn going onto final approach. This is where this usually rears its ugly head. You are often near the ground, slowing dow, perhaps with some flap out and you get it going too slowly and .... you drop a wing.

You hear the pilot scream out, "The #$&% thing tip stalled!"

What he means is he got it going too slow or tried to turn too tight and HE tip stalled it.

Practice your landing pattern up high so, if you do drop a wing, if you do "tip stall", you will do it with plenty of height to recover and live to try it again.


In fact most gliders can be stood on a wing tip in a turn. Try it!

Get your glider up high. With a little speed on simply go into a very tight turn and apply some elevatator. You can get the wings almost verticle and maintain it for seveal turns. This is like a crazy tight loop, but with the wings up and down. The glider will go up on a wing tip and be able to turn almost within the length from nose to tail.

I often do this when I am getting to know my glider so see what it will do. I have put my Supras, Ava, Spirit "up on a wing tip" at udner 50 feet when working a very small thermal. If the thermal is strong enough, the glider will go up.

But you have to practice this up high because if you are NOT in lift and have to transition out of this position ... well it takes a bit of practice which is best done up high so you can recover from your mistakes.


Also you might want to let your friends know you are doing this. They may assume you have lost control and are about to go into a spiral and crash.

I like your explanation and diagram Peter
The folks at HH at the AMA expo told me the mystique has washout built in
And has very benign stall charcteristics

Another trick that some designers employ is using transitioning airfoils so that airfoil out near tips has less camber than at root sorta creating built in washout

Tip stalls occur more rarely than people generally think. I do not care for the term, in my opinion it's overused. Just because one wing drops doesn't necessarily mean the tip randomly stalled. Many times the wing on that side may have stalled, or some other portions of the entire wing.

Stall progression of a wing has a lot to do with planform. Washout (geometric and/or aerodynamic) is often applied so that the stall progresses from root to tip so as to preserve aileron effectiveness. If a wing drops and you can pick up the tip with aileron then the tip is obviously not stalled. The problem with using aileron to pick up a wing at low speeds or high angles of attack is that the downgoing aileron increases local AoA and can then stall the tip. Rudder is your friend when maneuvering at low speeds, using an aileron to rudder mix to keep things coordinated is nothing to be ashamed of.