LeeFXDWG

Jungle,

Again, don't really know the context the original post wanted an answer to.

In a GA aircraft with a performance envelope the size of a postage stamp or the standard FAA publications, all is true regarding KIAS and stall speed.

Shift to something with swept wings or a high performance envelope, you change the equation to provide the answer.

Everything from Re number, viscosity, etc., start to play into the equation. Exactly why AF pilot training students begin with basic aero and then step a bit farther with advanced aero covering compressibility, Mcrit, etc., etc.

The one true constant is that the aircraft will ALWAYS stall when it exceeds the critical angle of attack, the true answer. That is the key and in the case of modern aircraft such as the RJ, the displays graphically display a range of speeds directly determined from the allowable/current AOA. Whether that display is in CAS or IAS doesn't matter. The IAS for stall will change as you approach the "coffin corner" of the aircrafts allowable performance envelope.

Lee

Cubdriver

Many decent responses here already. I was on the road this week and did not see this until now.

I cannot add much at this point except that the coefficient 1/2 in the equation CL =1/2 (density)(velocity squared)(Area) is a simplification, it is rounded figure representing the Reynolds Number. It is not worth mentioning for slower aircraft. If you want to split hairs then yes, indicated stall speed goes up a little bit. In faster aircraft air data computers take into account the other things affecting stall. Many of these factors have been mentioned already.

jungle

I agree with all of that, but what I don't agree with is that you can use a simple rule of thumb to calculate stall speed for any aircraft/altitude and then blithley strap on a Mcbusbo CRJ6000ER, fly it to that altitude and expect it to stall in accordance with a simple certainty at that altitude without any attention to other factors.


This quote(by another poster) implies that:
"Long story short -> if you ever find yourself having to deviate from company profile at high altitudes, remember stall speed will be higher than what you would otherwise encounter at sea level."
The author offers a simple rule of thumb, but I suspect reliance on that would not end your day well.

My point is that may not be the right answer and it may be dangerous and it is best not to encourage ignoring stall warnings under any circumstances. You know that, but some of the other readers here may not.

ryan1234

J-dog,

I'll have to retract my statement about the CRJ200 stalling at a lower AoA than anticipated. I couldn't find any conclusive reports. The points made in this discussion some may say have been too technical, on the contrary it seems that oversimplification isn't the best approach - which I agree. The pilots in the above case were flying that jet like a 172 in slow flight tottering on the brink of a stall - not realizing the effects of low density seperation had to the engines (and that particular engine) and the loss of energy at 410 is different than s.l. Limitations exist for a reason.

P-51D

Great discussion....just wanted to point out that the AC61-67B was canceled...but was replaced with AC61-67C. It still states:

j. Altitude and Temperature. Altitude has little or no effect on an airplane's indicated stall speed. Thinner air at higher altitudes will result in decreased aircraft performance and a higher true airspeed for a given indicated airspeed. Higher than standard temperatures will also contribute to increased true airspeed for a given indicated airspeed. However, the higher true airspeed has no effect on indicated approach or stall speeds. The manufacturer's recommended indicated airspeeds should therefore be maintained during the landing approach, regardless of the elevation or the density altitude at the airport of landing.

So....you were both correct and incorrect.
Yes, this is only for GA aircraft.

Aj114

Regarding to critical angle of attack and stall...
For a given aerofoil... does the stalling angle change (provided flaps are up) ofcourse...
I know the stallin speed changes and is affected by many things sucb as weight, load factor, etx etc etc. But does the stalling angle given for a specific aerofoil change? Or is it fixed and once exceeded it will stall? Is it true in regards to larger jet aircraft?
The graph CL over AOA is given to a specific aerofoil and thus aircraft type ... but does that mean it is at that one speed ? Is that graph true for cruising speed? Or thru out the whole speed for that aircraft and weight...
I was told because CL is affected by speed and Reynolds number the stalling angle cannot be fixed for a specific aerofoil thus it is variable....

galaxy flyer

A wing will generally stall at a very narrow range of AoA, but it will stall at a lower AoA in ground effect (see G650 crash report) and at high altitudes where shock waves cause earlier flow separation. Where the shock wave appears will effect the magnitude of the reduction in stall AoA. In the case of a contaminated wing leading edge, flow separation caused by a shock wave forming on the leading edge combined with ground effect can cause very large reduction in stall AoA. See CRJ contaminated wing stall accidents.

GF

Aj114

I srikl dnt get it so will it stall at a specific aoa ? Is it fixed...

galaxy flyer

No, it’s not fixed. It will be less with compressibility effects or in ground effect. Different slat/flap configurations will also have effects, which is why I said narrow range of AoA. A 172 can be said to have a single stall AoA; gets more complicated with a wider range of configurations and conditions.

GF

Bucknut

Anyone still flying the MD-80 should know about the critical AOA and how much it changes with weight, flaps and slats. It has been a long time but if I remember correctly in that airplane it changed quite a lot. Any MD 80 pilots have input?