A few days ago I accompanied a couple of jeeping friends, Jim Beller and Paul Furr of St. George, UT to the Hurricane Mesa Test Track (HMTT) Facility a few miles from where we live. It is currently owned and operated by Goodrich Corporation, Universal Propulsion Company, but was started in the mid 1950s by the US Air Force.
Located atop Hurricane Mesa, HMTF has a 12,000 ft. test track that is fully capable of handling propulsion velocities exceeding supersonic (Figure 1). It is used mostly to test aircraft ejection seat systems, escape capsules, canopies, hatches, and other subsystems that require operation/actuation at specific speeds, during change of velocity at specific G forces, or under certain pitch and yaw conditions.
To accomplish this testing, solid propellant rocket motors or turbo jet engine systems (pushers or boosters) are used to propel cockpit sleds (Figure 2) up to and beyond the speed of sound (about 770 mph at sea level).
The track elevation is at 5,100 MSL (mean sea level) with the track muzzle (end) terminating at a 500-foot vertical cliff. The sloping terrain of the mesa provides an additional drop of 1,100 ft. to the valley floor below, which permits exit from the muzzle for recovery down range in the valley below, if desired. The track rails consist of two 105 lb/linear yard steel crane rails placed 59.062 inches apart in reinforced concrete foundations. Each rail is supported every 50 inches by alignment hardware. Optical truing of the rails provides for a maximum deviation of no more than 0.010 inch. The track is steel doweled to the bedrock of the mesa – the rock mass being stable and free from fault lines (Figure 3).
Initial braking of the sled is accomplished via a 2,800 foot water brake system, with final arrestment provided by hydro-mechanical gear. The system is capable of stopping a 15,000 lb. mass traveling 200 ft/sec.
Complete photographic and telemetry coverage of each test is accomplished via control circuits and velocity pick-offs monitored and controlled by a master control instrumentation network. Master control provides for real-time read-out and data collection of each test parameter, including sled propulsion staging, experiment initiation, track-side and sled-mounted camera operation (red boxes on the sled), and velocity measurements.
With the use of up to 115 rockets, testing presents substantial noise as each of the booster stages are fired. Figure 4 shows the use of solid propellant rockets (cylindrical canisters) to propel an F15 fighter test sled to the appropriate speed. Each of the rocket stages propels the sled to an additional acceleration, with the last sled firing first, and then sequentially to the pusher stage closest to the sled. As many as 4 pusher stages can be used. A variety of sleds have been used over the years as shown in the bone yard of the facility (Figure 5). A sled in preparation for ejection seat testing is shown in Figure 6.
No information was available relative to the noise sound pressure levels (SPL) experienced by the pilot, but the photo of Figure 7 would suggest that it is fairly high with the combination of the rocket and ejection seat explosions. This also gives real meaning to being “in the hot seat.”
So, what does all this have to do with hearing? You will have to wait until Part II is published next week to find out.
Photos and historical data were obtained from Jack Reed, Manager of HMTF.
- The History of Hurricane Mesa Test Facility, Company Document, McSpadden, H.J., Higgins, R.R., Goodrich Corporation, Aircraft Interior Products, Propulsion Systems, Phoenix, AZ, 2004, published by the American Institute of Aeronautics and Astronautics, Inc., with permission.↵