More Of That

Whenever I start to feel that I'm becoming too bogged down in my own problems and the dull requirements of daily life, I like to think about things like the X-15, seen above not longer after being dropped from its NB-52 carrier airplane. The X-15 flew in the early to mid 1960s. Maybe that wasn't really such a great time, and it's probably dangerous to overly romanticize the whole thing, but there was a lot to be said for being young and innocent and living in a world where bold men flew these black aircraft to the very edge of space.

The X-15 was never meant to go into orbit. The engine lacked the power, and a combination of thermal and stability issues prevented it from re-entering safely from altitudes above about 360,000 feet (450,000 feet seems to have been the thermal limit, and 360,000 feet the safe stability limit; the X-15 tended to be divergent in yaw at high angles of attack and re-entry from above 360,000 feet would require an angle of attack so high the pilot wouldn't be able to maintain control if the stability augmentation system failed, which it often did).

It was really designed to perform basic research on the then-mysterious field of hypersonic flight, to answer questions like how does hypersonic flight differ from supersonic flight and are our theoretical predictions of heating, drag, and aerodynamic forces in hypersonic flight really accurate? Hypersonic flow is hard to achieve in a wind tunnel, and even then, shock wave interactions in the wind tunnel itself make it difficult to say anything meaningful about the behavior of the model. Nowadays we can use supercomputers and computational fluid dynamics to simulate hypersonic airflow, but even if they had had supercomputers and CFD in the 1960s, they wouldn't have known if the CFD models were valid or not.

The only way to test the theoretical projections was to actually build a plane that could fly at hypersonic speeds - to go that fast and see exactly what happened. The X-15 did a lot of research in hypersonic flight, of course, with a heavy emphasis on heating and drag studies. That was its main mission. But in the process, the program did a lot of other research on things like spacesuits, insulators, ablators, reaction control systems, cockpit instrumentation, energy management systems, inertial platforms, adaptive-gain flight control systems, hypersonic degradation of cameras, and other things.

It's dangerous to say that any one airplane was the most significant airplane ever flown. But I think it's safe to say that the X-15 program was probably one of the most fruitful aerospace research programs in human history.

But once you dispense with all the jargon and technical palaver, it speaks powerfully to me of a time when I was young and anything was possible.