The Mammoth Book of Space Exploration and Disasters

On the approach and landing, I had a control problem that really turned out to have a very simple solution. But the airplane, for all intents and purposes, appeared to be unstable and pitched to me, which meant that it was very difficult to control it. The pitching oscillations got very high and I had to figure out a way to get the airplane on the ground at the bottom of the pitching oscillation so that it would not wrap up in a ball of metal.

As it turned out, I succeeded. However, I landed at 140 knots instead of my anticipated 174 knots.

Crossfield described how they adapted the controls to enable the pilot to handle the aircraft when it was in violent motion:

With the X-15 we anticipated that there could be some rather violent motions on re-entry or in some of its maneuvers. One of the difficulties with flying the high speed jet aircraft with the powerful flight control systems is that the man’s arm gets into the thing. The weight of his arm feeds the action of the airplane. That is the so-called “JC Maneuver.”

For the X-15 to preclude that possibility, we made a control system such that [the pilot] could put his arm into a rest that would resist all of these external forces and control the airplane only with the movement of his wrist. With the axis of control being in this manner – with the roll control – we made it so that it could roll on the armrest… So we took all of this spring and mass system – [the pilot’s] arm out of the control system – to make it a very precise control system. It was part of the design of that system that [caused] the problem I had on the first landing. And it was easily correctable.

Crossfield commented on the distinction between pilots and “test pilots”:

Well, we keep talking about test pilots but there is no such thing as a “test pilot.” There are all kinds of people. There are tall people, small people. Some of them are functionally illiterate and some are intellectual. Some are moral. Some are immoral. They are all just people who incidentally do flight tests. It is a profession just like anything else. There is not, to my mind, any common thing called a test pilot.

The opportunity to be a test pilot… is there for all – and probably within the grasp of most. In my mind, we should divest ourselves of this idea of special people [being] heroes, if you please, because really they do not exist.

Crossfield described how his experience has been applied to contemporary aircraft:

At one end of the jet airplane era – with very powerful control systems – we found that the [pilot’s] arm began to become an important part of the inertia. As we got into the jet era and high-speed flight – the very powerful control system that we had – we began to see the effects of a man’s arm on the control stick having an effect on the airplane as the forces on his arm varied.

With the X-15, we anticipated… some of the violent maneuvers [on re-entry] that could probably cause us some problems. So what we did was design a sidearm controller to preclude any input from his arms. It consisted of an armrest that you could hold your arm down on so that the only thing that was involved in the control of the airplane was the rotation of the wrist, with the pitch axis being… through that point and rolling your arm on the armrest. As a consequence then we could take all of that spring and mass system out of the control system. This proved to be a very useful development that we now find very often in our current-day fighters which would have had the same problems if they didn’t go to something of this nature.

Also, that sidearm control was a contributor to the problem that I had on the first landing and we corrected that quite easily.

Crossfield described what happened with the ground test on the first XLR99 engine. He explained why he was in the cockpit when the engine exploded and what happened to him:

When we installed the large engine on the X-15, [because of] our flight test plan we were going to demonstrate that the engine could be started. It could be throttled from 50 to 100 percent as designed on the first flight. The way that we were flying, I was limited to the speeds that I could allow the airplane to get so it took a very precise engine-on-off and thrust program to stay within that flight plan. To make sure that all of the systems would respond to this plan we made the last test of the engine on the airplane on the ground.