X-1 Skycycle Primary Propulsion

This is the X-1 Skycycle running chassis. The shiny round ball is an insulated titanium pressure vessel that is a STEAM ROCKET containing 200 pounds of superheated steam! It develops 1,333 pounds of thrust for a total of 6 seconds. These are not very efficient rockets, but they are relatively safe. Obviously, the fuel is cheap and presents no handling, storage, or shipping problems. It is also non-toxic - you can drink it!  Evel, the master showman and salesman, even got the Olympia Brewing Company of Tumwater, Washington to be a sponsor for the water!

STEAM ROCKETS are the patented invention of Robert C. Truax, a true rocket pioneer.  His company, Truax Engineering, was hired to design and build this special motor for the X-1 Skycycle. 

That top picture also shows the small pneumatically operated outrigger wheels (in their retracted position) used to stabilize the machine on the ground at low speeds.

TB2 Rocket.GIF (10134 bytes)

Even in 1968, we knew that this steam rocket did not contain enough power to carry the machine the entire canyon distance. Extra strap-on solid propellant rockets were planned, just like used for the Space Shuttle, which first flew in 1981. Unlike the Space Shuttle, however, we would not have ignited the solids together with the main liquid rocket at the instant of launch. We planned to wait until the machine cleared the ramp and was airborne. You cannot turn off solid rockets and abort an attempt as you accelerate and then curve up the ramp!  With steam, you can!  This is similar to aircraft that use JATO solid propellant rockets to take off with extra heavy loads.  These JATO rockets are also not ignited until almost at takeoff speed.

This is a side view drawing of the concept.  From the top picture and the pictures below you can see we had to split the steam rocket exhaust in order to clear the rear motorcycle wheel.


Insulation was added to help retain the heat energy in the steam rocket.  It consisted of several layers of fiberglass and a final layer of aluminum foil - all held to the titanium pressure vessel with aluminum tape.  My friends Bruce Williams and Rein Stolz helped with the work.  As you can see from the upper right hand photo when finished we had a beer - Olympia, of course! 

Bruce was a computer programming expert and did the software for the X-1 Skycycle flight trajectories.  Had a lot to do with available rocket thrust, aerodynamic drag, vehicle weight (which continually changed as the super heated, hot water was expelled), run up distance and initial launch angle, etc.  At each instant of time the computer would sum all the forces, compute the resulting net acceleration, then integrate that to calculate the current velocity and current height and range from the launch point. 

This software was verified for accuracy by launching three TEST ROCKETS at the actual Snake River canyon site on May 6, 1972. 

Note the small model in the foreground of these last two pictures.  This was the PR DISPLAY MODEL that Evel used in some of his sponsorship presentations. 

The following photos are from the Perkins experimental rocket test center near Sacramento, California where static firings and calibration runs were made for the special Truax Engineering built Evel Knievel X-1 Skycycle STEAM ROCKET MOTOR.  Thrust force was measured as a function of time and recorded with special data acquisition equipment for several firings to establish the average forces and duration we could expect in the real world. 

Doug Malewicki attended the tests as a technical observer.

You can see the white steam exhaust exiting both nozzles. 

or go back to