Bailing out at 2000 mph and other stories

The A-12 and SR-71 both had problems with compressor stalls in turns. That could lead to a violent yaw and structural damage, followed by ejection.

 

I thought I had read somewhere they had a pitch stability problem at the upper limits of their possible speed resulting in the loss of a couple of aircraft and they limited permissible speed as a result. Ring a bell? Or am I confusing it with what you just described? As I recall it was up at M3.5 or so. Had the power to do that but not the airframe.

 

Is this the beginning of some kind of joke? Like...it really hurts to skydive in the rain because you hit the pointy end of the raindrops coming down...

 

Bitzman- Anything less than about mach 15 is obeying great circle rules in the atmospheric system and is unaffected by earth rotation except for being in the atmosphere that is rotating at the same speed as the Earth. If you fly over the poles at mach 3.5, where rotation speed is zero, you see exactly the same environment (except maybe temperature) as at the equator, where rotation speed is ~1500 fps or 900 knots. Above mach 15 or ~15,000 fps, you start seeing a compromise between great circle and orbital mechanics systems present at the ~25,000 fps seen in LEO, where Earth rotation is a huge factor for anything flying in the atmosphere.

To calculate rotation velocity at the equator, take the Earth's circumference in statute miles, 24,900 miles and divide by 24 hours, giving you ~1038 mph (900 knots). Rotation velocity varies from that high to zero at the rotational poles.

Brian- As far as I know, none of the A-12s or SR-71s were lost by exceeding VNE for short periods of time.

 

Rotational poles and speed of ....HUH?

 

Translation: Earth's rotation doesn't mean squat unless you are flying very high and very fast...astronaut high and rocket fast...

 

FANKS!

 

Keep in mind that Mach 3.2 at FL800 is about 310 KIAS. Not an earth shattering dynamic pressure to bail out in.

Limit speed on the SR-71 was 500 KEAS. Normal climb was at 450 KEAS to about M2.6.
Pitch stability was not an issue at high Mach. Center of pressure was moving aft, but control surface effectiveness was also decreasing.
Yaw stability and vertical surface effectiveness was getting REAL low at higher Mach, making the "unstart" of an inlet an interesting event.
I was tasked to develop a transfer function for the flight control system to detect an unstart and begin moving the spike. Problem was that the test pilots were so perceptive that they would catch it before we could verify the dynamics. We had to tell them to let it go. Of course they didn't trust a twenty something engineer farther than they could throw me.

 

That is a cool story! Any more stories you have will find an eager audience here!!!

 

Note that 450 KEAS was not mach 2.6 until you got to a very high altitude. We climbed at 640 KCAS in the F-111 after leveling at FL 300 to accelerate to supersonic speed and 640 KCAS. But we were limited by reg to FL500. The SR was just getting started there.