Engine Failure

Engine Failure

Failure of rocket engines is, as a rule, the result of thrust chamber burnout. Specific information on this type engine failure is given in "Thrust Chamber Burnout" (below). If engine failure is due to malfunction of the fuel control system or improper operating technique, a start can usually be made to restore engine operation, provided time and altitude permit. However, if the failure is an obvious failure within the engine, a start should not be attempted.

Malfunction Shutdowns

Automatic malfunction shutdowns can occur during the engine  start phase or during actual engine operation. The design of the malfunction shutdown circuits is such that restart attempts can safely be made after a malfunction shutdown. This is because a restart will not be successful if the malfunction which caused the original shutdown has not been corrected.

Malfunction shutdowns which can occur during the start phase are those due to main or first stage propellant valve malfunction, stage 2 ignition malfunction, or engine turbopump overspeed. Malfunction shutdowns which can occur during engine operation are those caused by engine turbopump overspeed or excessive engine vibration.

If a malfunction shutdown occurs, attempt a restart. Refer to "Engine Restart" below.

Causes of Pump Cavitation

Failure to sufficiently prime the liquid oxygen pump discharge line to the engine, excessive heat absorption by the liquid oxygen together with excessive vapor pressure (normal liquid oxygen tank vapor pressure after tank has been filled is 20 to 24 psi), or insufficient liquid oxygen tank pressure can cause pump cavitation. When liquid oxygen pump cavitation occurs, the over­speeding turbopump is stopped by the overspeed protection system. When an engine is shut down by the turbopump overspeed protection system, the turbopump overspeed caution light is illuminated.

Indications of Pump Cavitation

Cavitation is accompanied by the following indications:

• Increase of  pitch  in whine of  turbine.

• No ignition.

• No flame from chamber.

• No noise from chamber.

• No thrust chamber pressure.

• Very  high  momentary  fuel manifold  pressure.

• Very low liquid oxygen manifold pressure .

• Turbopump stops and overspeed indicator light, in cockpit, comes on.

Engine Restart

If the engine has failed or has been shut down automatically and it is determined that a restart is feasible, proceed as follows:

1. Throttle [12, fig. 5-4] – OFF.

2. Engine reset button [62, fig. 5-1] – Push.

3. Engine prime switch [56, fig. 5-1] – PRIME. Move engine prime switch to PRIME for one second and check ignition-ready light [2a, fig. 5-1] ON. Approximately 30 seconds is required to prime, with prime valve at high-flow orifice position.

4. Throttle [12, fig. 5-4] – START, then AS DESIRED.

Thrust Chamber Burnout

Thrust chamber burnout can be determined by various engine indications which can be verified by the X-15 pilot or the chase pilots. These indications are as follows:

• Fuel manifold pressure [51, fig. 5-1] drops below oxygen manifold pressure, accompanying cylinder "groaning".

• Engine emits loud ("hog-calling") scream or howl.

• Yellow streak of flame or yellow bushy flame is evident.

• Chamber pressure [50, fig. 5-1] drops while manifold pressures are within specified range.