For their third book in the Xplanes series, Osprey has chosen what I consider to be the ultimate X-plane. It is the last of the manned rocket planes and the first to break Mach 4, Mach 5 and Mach 6. It would have probably broken Mach 7 had the program continued. The highest altitude it reached was 348,000 feet. 380,000 feet is considered the end of Earth's atmosphere.

Prior to the development of the X-15, the x-plane market was pretty much owned by Bell and Douglas when it came to high speed flight. However, North American put in the lowest bid and the best design. Naturally, the cost of the program escalated to a lot more than planned, but that is always the case when dealing with government programs.

The challenges were considerable, the main one was developing a way to take care of the considerable heat of friction that builds up when attempting those sorts of speeds. This was aleviated to some degree by using a new metal, Inconel-X, to skin the aircraft. However, Inconel-X was extremely hard. This made it difficult to form and equally difficult to weld and to machine. North American had to learn from scratch. However, the initial plane of three was ready ahead of schedule.

The next delay was in the Reaction Motors engine. The XLR-99 was not ready on time, so the lower thrust XLR-11 had to be used for the initial tests. This worked out well and enabled the pilots to get used to flying the airplane. It is interesting to note that the X-15 did not like flying at low speeds and was a lot more stable above Mach 3.

Then there was the choice of aircraft to carry it. Initially the B-36 was the choice, but it was decided that having to jack up the plane every time the X-15 was loaded (as in the X-1 and X-2) wasn't going to work well. The B-52 was chosen due to its high wing and its ability to simply pylon the aircraft. It also had plenty of clearance for the wings. The down side is that the pilot had to be aboard the plane the entire mission. There were two early B-52s used. One was an NB-52A and the other an NB-52B. The B model operated for 40 years as a carrier aircraft and in all that time, flew only a bit over 4,000 hours, making it the king of low time B-52s.

Of course, there is a lot more to this story as the X-15 was constantly developed. It was also no stranger to crashes and other issues. All of this is covered in the book. Along with this are a superb selection of photographs as well as some great art work. It makes for a superb read and one that you really need to have on your shelves.

May 2017

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