Tuesday, November 21All That Matters

Snow capped mountains of Afghanistan.

Snow capped mountains of Afghanistan.

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  • TestFlyJets

    Some of the scariest nights of my military career were when I was flying over these mountains at night in a U-2 Dragon Lady aircraft.

    The turbulence and rapid temperature changes in that area would play havoc with the autopilot at 70,000+ feet. Strong winds bouncing off the very tall mountains would create unstable clear air turbulence, causing the jet to pitch up and down pretty violently and often causing the autopilot to disengage. You’d suddenly find yourself with two handfuls of airplane more or less balancing on a razor’s edge in pitch black with things bouncing around so badly you couldn’t read the flight instruments.

    We would fly a set Mach number with the autopilot, in basically a very long cruise climb as the jet burned fuel and got lighter.

    Mach is dependent on air temperature, and sudden changes of a degree or two would cause rapid changes in the indicated Mach number (IMN). Since the autopilot tries to hold a specific IMN, it would pitch up or down to try to recapture the set speed.

    When you combine turbulence with air temperature changes, things could go from cool and calm to HOLY HELL JUST TRY TO HANG ON in an instant.

    The U-2 has a very narrow window between Mach overspeed and indicated stall speed at operational altitudes, often called the “coffin corner.” An increase in air temperature would cause an increase in IMN and the aircraft would pitch up to “slow down.” Mach overspeeds cause shock waves on the horizontal tail, creating buffet and vibrations that feel just like…stalling. If the shockwaves get strong enough they can rip the tail off the jet.

    With a tiny 3-4 knot indicated airspeed range between stall and Mach buffet, often accompanied by significant turbulence, it could be really difficult to tell if you were going too fast or too slow. And this is further complicated by the fact you’re wearing a full pressure suit, helmet, and gloves, which impair your senses and “seat of the pants” flying.

    It was quite common to be pitching up, with IMN increasing, and feeling what sure seemed like stall buffet, all at once.

    Regardless, all you can really do is try to read the flight instruments, get the speed back out of the red, and hope things calm down soon. Whenever this happened it was probably the longest, most terrifying 30 seconds of my flying career, no doubt.

    One other thing to add. If the plane did come apart and I had to eject, it was always on my mind that those tall mountains were higher than the altitude at which our parachute would automatically deploy. The U-2 pilot stays attached to the ejection seat until 35,000’, and then freefalls to 15,000’ when the chute opens.

    But if the mountains below me were 20,000’+, I’d be a solid 5,000’ into the granite before my parachute would trigger. Again, at night, I wouldn’t be able to see the ground. I’d get a kick in the ass at 35,000’ as the seat-man separator did its thing. I decided I would then try to count to 60 to get a little lower before manually deploying my chute. Fortunately I never got to find out if this was actually a workable plan!

    Despite all this, flying the Deuce was tremendously challenging and rewarding. Hat tip to the women and men doing it today, all over the world.

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