New (2010) Stall Recovery's @ high altitudes

[jcbmack]

I think:

PA and MFS know what they are doing!

[Pugilistic Animus]

PBL

no plane is certified for rudder reversals or any other rapid control reversals, even at or below Va

http://www.pprune.org/tech-log/37214...-jet-safe.html

[Pugilistic Animus]

New (2010) Stall Recovery's @ high altitudes

New Ideas in Aviation

[HazelNuts39]

Mach and stall AoA, cLmax

Originally Posted by Mad (Flt) Scientist

Quote:
Originally Posted by Pugilistic Animus
(p-pinfinity)/(1/2rhoV^2)/Cpi=1/[1-M^2]^.5+ [M^2/1+{1-M^2}^.5]*(cpi/2)

or maybe just 1/[1-M^2]^.5 (end of PA quote)

Actually, no, mot just the "standard" Mach effect. Stall AOA ends up being a powerful function of freestream Mach, due to transonic effects in the (very accelerated) boundary layer. As a result the freestream Mach is not the Mach directly having the effect.

What you're alluding to is fine at more 'normal' AOAs.

To illustrate this further, I would redraw the diagram as shown here:
cL_AoA_M003.jpg

The (sub-critical) Mach effect cited by PA changes the lift-curve slope below cL-max. For swept wings, one could perhaps use the component of Mach normal to the wing 1/4-chord line in these equations?

With regard to stall AoA, for Mach between M1 (M1 in my diagram is low, say M=0,15) and M2 the flow is sub-critical (or low super-critical without causing shockwaves), and cL-max changes little, if at all. Above M2 the flow at high AoA is sufficiently super-critical to cause (local) shock-induced separation, and then cL-max reduces rapidly with increasing Mach.

Vs1g speeds published for one modern wide-body would seem to indicate M2=0,275 for that airplane in clean configuration.

regards,
HN39

EDIT:: For an experimental illustration of these aspects, see:
NACA Technical Note No. 1390

[Pugilistic Animus]

HazelNuts39---nice handwriting

since that relation is used by the United States, I knew it'd be right

there also be an assumption of infinite aspect ratio so vorticity circulation, would be a factor...that alone would account for some divergence from expected, also, there will be some finite measure of slip 'eta' and other Rn effects that would need to be accounted for, let's not forget 'tunnel wall error' of course many partial solutions to this aspect of the NS equation have been published which are helpful in CFD renderings ..of the problem the total problem is so difficult that with out the airfoil ordinates dc/alpha and dalpha/dM relations it would be untenable to precisely predict any composite airfoil characteristics with high accuracy...of course aerodynamics is an experimental science and not theoretical... I mean, we can now make a pile of dog cr#p fly if we wanna

[HazelNuts39]

Pugilistic Animus;

thanks for your reply. Prandtl-Glauert for normal Mach-component resulted in satisfactory correlation of CL-AoA-Mach with Flight Simulator data.

[Gulfcapt]

Great thread guys! Speaking from the point of view of an aerodynamics user rather than expert, I sure appreciate the time many have taken to explain things.

I'm with PA on the "new training." This was an item covered during my last initial type in 2005. I think it was a special emphasis item due to that Pinnacle RJ over the US midwest.

FWIW (and it may not be worth a thing...), the Gulfstream 5 has a normalized AoA indicator. Pitch Limit Indicator (PLI) shows up at .70, shaker at .85 and pusher at 1.0. Gulfstream used to publish great LRC tables that utilized AoA, but they ceased that with the G-4.

Best,
GC

[Pugilistic Animus]

Hazelnut39:
Von Karman was Prandtl's student---both, researchers--- especially Von Karman ---with his student Hsue Tsien contributed greatly to our understanding of high speed/supersonic aerodynamics, compressibility and viscosity


Gulfcapt:
You are correct!
No new ideas in aviation

[Ask21]

Stall or Spin recovery?

FAA trained or not, it is a fact that using rudder to lift a wing is commonly taught in flying schools in Australia. Judging also by the questions that appear in the PPRuNe Instructor Forum, it happens elsewhere as well. It seems to be handed down from generation to generation of young flying instructors who in turn once they achieve Grade One instructor status teach new instructors.

It has proved impossible to completely eradicate this technique throughout many general aviation flying schools. But you would think when type rating courses are conducted this erroneous teaching would soon be discovered and rectified.

From my training in a sailplane it was common training procedure to induce both stall and spin and recover from it. Stall was induced at 1000 meters /3000 feet by pulling the stick - speed slow down - increased angle of attack. To recover simply put stick forward. To induce spin - give a strong rudder at the close to stall state. That would cause one wing to drop as a stone and give a spin (rotation) To RECOVER from spin wing stick/ailron was in neutral but strong rudder to opposite side of spin to reduce rotation - it did work. Quite a lot loss of height. Does training on jets include recovery from states of spin? Or is there a mix of procedures. Seems to me that rudder should not be used unless you have a completely stalled single wing / spin situation - in that case I don't think ailron will work anyway. If ailron works I guess it would mean that the wing was not completely stalled in the first place. On the other hand it should be known that heavy rudder at close to stall angle /incompete stall could induce a complete stall of one wing and a following spin situation.

It was also common knowledge that a good designed wing would stall from the medial side first, close to the hull. That is to preserve ailron-funcion as long as possible. The lateral part of the wing will be designed with a lower angle of attac than the medial. When stall is approached there will be a shaking due to in the plane as inner part of the wings stall and experience turbulence in stead of laminar flow.

I would recommend pilots to take a training tour in a sailplane to experience a fully stalled situation and spin and practice of its recovery.

[Pugilistic Animus]

I suppose it would be some conciliation to anyone that airplanes don't really want to stall-at all

[twochai]

Gulfstream used to publish great LRC tables that utilized AoA, but they ceased that with the G-4.

Of course, the real Grumman (until it was sold as Gulfstream) used to be a designer and manufacturer of Navy carrier borne aircraft, fighters and bombers.

The US Navy has used AoA to great effect as a primary flight reference since they started flying off carrier decks. Using approach speeds as low as 1.1Vsl, I believe, would be foolhardy without AoA info.

[Lyman]

The only time I ever used the Rudder near the Stall, was to Spin an a/c that didn't want to.

[thermostat]

AoA, Stall, Airspeed.

There were cases of fighter pilots screaming down in a dive at high speed, releasing their bombs, pulling out of the dive and STALLING !!!
So even at high speed they stalled. It wasn't the lack of speed, it was the high AoA that got them.

[Intruder]

The only time I ever used the Rudder near the Stall, was to Spin an a/c that didn't want to.

THAT is VERY airplane-specific! If you ever tried using aileron input near stall in an A-4 Skyhawk, you'd get a VERY rude wakeup call! OTOH, it would turn very nicely with rudder while in a nose-up attitude at 3000+ FPM down...

[cwatters]

There were cases of fighter pilots screaming down in a dive at high speed, releasing their bombs, pulling out of the dive and STALLING !!!
So even at high speed they stalled. It wasn't the lack of speed, it was the high AoA that got them

Easily done in a glider... Enter spin, use opposite rudder to stop the rotation and exit the spin in the normal a nose down position. The speed will build rapidly and all you have to do is pull a bit too hard while trying to recover to S&L.