At 30,000 feet, the CL vs Angle of Attack table compresses and so the airplane flies at much lower angles of attack than it does at the same weight and airspeed at sea level; while still stalling at the same point on the compressed scale. The stall angle of attack reduces by roughly half, thus reducing drag for any given AoA.
I've been busy on other things, but those statements kept nagging at me.
As everyone knows I'm a duffer when it comes to big airplanes, but for the types I deal with the statements are not borne out by the performance data.
I looked at two types the F-4 and the Mirage F-1.
The F-4 at 1g and 37500 lBS AUW has the following Calibrated Airspeed (CAS) when climbed at 7° AOA.
Sea level and 250 CAS/0.378M
20K 290CAS/0.631M. If at 250CAS AOA should be 8 at 1g
30K 285CAS/0.754M. If at 250CAS AOA should be 8.7 at 1g
40K 280CAS/0.909M. If at 250CAS AOA should be 8 at 1g
These numbers imply a slight increase in AOA when flying at the same CAS as at SL but at altitude. The statement said the opposite
Mach effects on AOA begin at around 0.75M but are relatively flat until well supersonic.
Stall AOA 20° and 1g is at:
Sea Level and 150CAS
20K and 150CAS
30K and 155CAS
40K and 165CAS
These numbers imply little change in stall speed or AOA. The statement said AOA would be halved
The Mirage F-1 at 1g and 10000 Kg AUW has the following characteristics when climbed at 5° AOA.
Sea level and 271 CAS/0.41M
20K 290CAS/0.63M
36K 288CAS/0.86M
40K 280CAS/0.91M
Mach effects on AOA begin at around 0.85M but are relatively flat until well supersonic.
Stall AOA 16° and 1g is at:
Sea Level and 145CAS
20K and 154CAS
36K and 167CAS
40K and 164CAS
In general the same value trends as the F-4 and opposite to the statements.
The amount of g that can be pulled at limiting AOA decreases with altitude because of reduced density.
The F-4 can pull 8.5g at 440CAS and SL
The F-4 can pull 7.0g at 440CAS and 20K
The F-4 can pull 6.5g at 440CAS and 30K which is the structural limit
The F-4 can pull 5.4g at 440CAS and 40K
In all cases these occur with 20°AOA.which is a constant stall AOA irrespective of altitude.
Given the fact that airliners generally have relatively high Mach wing sections similar the the F-4 and F-1 I can not see how the statements would be valid. But then I am a duffer at big airplanes
Roy