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jcomm

What happened to accelerated stalls?

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Are any of you able to enter accelerated stalls in X-Plane10? Any stall as a mater of fact as you can read ahead...

Probably the most correct behavior I have found so far was that of the MU2, and the author even programmed a nice "shake" effect in the pre-stall region, but guys, pick your preferred GA aircraft, go high enough and start a steep descent. Then, pull your yoke/manche/whatever, and try to enter an accelerated stall.... Can you? You'll probably perform a loop, but entering the supposed accelerated stall will be almost impossible!  Sometimes it reminds me of some of the MS FLIGHT aircraft, probably all but the Stearman, Maule and the Carbon Cub... All other are made not to stall (accelerated) to allow users to dive and pull by fully deflecting their yokes at top speed and still recover without any consequences...

 

Might it be due to the fact that something changed in Airfoil Maker and the aircraft need to be converted, or the wings redesigned ( in X-Plane10 )?

And, since I am stalling here... stall, not accelerated, most aircraft and, keeping your yoke pulled all the way back, and even your trim at the rearmost settings, see how they all recover peacefully... after they start pitching down and gaining speed... (notice I wrote - keep your yoke pulled all the way back!!!)

:blink:

Whazzzup?

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Not at home and can´t check right now - but remember: "Accelerated" stall has nothing to do with being at a high (accelerated) airspeed.

 

There is no difference between a slow speed and a high-speed stall. The only thing that matters is the AOA at the wing. If an aircraft is going at high speeds, a full yoke deflection will usually overstress the airframe (over-g) before the critical (stall) angle of attack is reached. It is also a matter of control rigging that will determine your maximum elevator deflection and consequently your ability to attain a high enough angle of attack to stall the plane.

 

A common misconception is also the "stalling speed". Just to illustrate - a fully loaded 747 can be flown at 50kts without being in a stall! And a Cessna could be stalled at 150kts (dependent on enough elevator authority).

 

Best regards, Jan

 

P.S: If you want to really see whats going on, display the relevant flight parameters on your screen while testing. Like elevator deflection, current g-load, angle of attack, etc. Also go to planemaker, check which airfoil your plane is using, then go to airfoil maker and check the properties of that airfoil. You will see a "lift over angle-of-attack" graph, that tells you at which angle the airfoil puts out which lift. You can even create your own airfoil that stalls very abrupt, if desired!

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Yes Janov, I am aware of all that - stall depends on AoA, irrespective of speed :-)

 

But, since hinge forces are NOT taken into account in most x-planes., and you do have unrestricted control authority, unless you use control phase-out or art stab  to try to model it, pulling the stick hard will cause that increase in AoA even at higher speeds, and the airplane should enter a stall...

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Pascal, and Janov,

 

thx for you suggestions. Andy Goldstein at another forum also helped.

 

I did try it with the stock C172, the Cirrus Jet and the glider (K21).

 

The C172 can't stall because you do not get enough elevator authority, and that is due to the fact that in Plane-Maker control phase out was set, giving 50% at 85 KIAS.

 

The Cirrus does stall, and even enters irrecoverable flat spins!

 

The K21 is the most intriguing model for me, because I fly it for real... It has no control phase out, should have max L/D around 10º AoA and be stalled at around 14º

 

The glider stalls but promptly recovers. It also exhibits very weird AoAs during normal flight, mostly negative ???

 

Well, will have to investigate further...

 

Ok: Just came  from further investigation :-)

 

So... the K21 is really weird! I had never taken the time to look more carefully into it's PM internals... I just discovered that on the MISC-WINGS section a flap is available near the root section of the wings. I had never tried to use the flap because there is no flap in the real K21... Well, I used it inflight, and the AoAs look more consistent.

 

Also stalling this K21, with it's secret flap deployed offers a more consistent behavior... well... not very, but... better than without that hidden flap. I believe the author decided to make the flap to overcome something really wrong with the behavior of the K21, even with the wings data / geometry acceptably programmed in PM... 

 

With the hidden flap deployed you sure can get very high AoAs, and your glider will continue to sink while you're pulling the manche all the way back. It will eventually enter an unrecoverable flat spin, just like the Cirrus Jet (really not realistic this one....).

 

Well, I still have a lot more to learn, that's for sure!

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:unsure:

A common misconception is also the "stalling speed". Just to illustrate - a fully loaded 747 can be flown at 50kts without being in a stall! And a Cessna could be stalled at 150kts (dependent on enough elevator authority).
 

 

 

Okay, I give. I'm sure your have something up your sleeve (like an Ace)........regarding the B747 & 50kts. I just haven't yet figured the scenario.

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:unsure:

 

 

Okay, I give. I'm sure your have something up your sleeve (like an Ace)........regarding the B747 & 50kts. I just haven't yet figured the scenario.

 

Hi Larry,

 

the "trick" here is to keep the wing "unloaded" - like on a 0g parabola flight. The wing is per definition not stalled, although it certainly won´t put out enough lift to carry the weight (as would be needed for level flight).

 

The scenario isn´t very practical (or even remotely within regulations of flying a 747), I just mentioned it to illustrate that the concept of an airfoil being stalled is not about speed, it is about airflow angle.

 

Jan

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