Engines and Engine Integration

The  RA-5C  was powered by the General Electric  J79-GE-8A (-10 in later aircraft).  This  was an axial flow , 17 stage compressor turbojet developing 17,000 pounds of thrust in afterburner. Military rated thrust was 10,900 pounds.  Engine features include variable inlet ramps, variable stator vanes, and a three stage turbine.  The afterburner included variable thrust capability and a hydromechanically controlled converging/diverging ejector type exhaust nozzle.

Contrary to popular belief, jet engines don't directly produce thrust, but high pressure, high temperature gas that the exhaust system converts to thrust while minimizing losses.  Without a functioning nozzle, thrust would be minimal and afterburner lightoff impossible.

The air induction system is equally important.  Its task is to convert external airflow (from zero to Mach 2 relative speed) to uniform subsonic flow at the compressor face, while minimizing  energy loss.  The two-dimensional ramps used on the RA-5C were particularly efficient in this function.  Shock waves that formed in the inlets were "oblique" shocks, oriented at an angle to the airflow. 

This particular system consists of variable geometry inlets, variable secondary air bypass gaps, and an automatic control system.  This system programs ramp position based on duct static pressure, ambient pressure, and aircraft Mach number.  

There are three ramps in the induction system.  For supersonic flight, it is important to reduce airflow speed efficiently.  This 2- D ramp system achieives this by a series of low-loss oblique shocks, as opposed to lossy, normal shocks of other J-79 installations, such as the F-4.

The J-79 in full afterburner is an impressive sight (see below).  Fuel flow at Combat Rated Thrust at sea level is approximately 75,000 pounds per hour, or roughly 3 gallons per second.  The fuel pumping capacity of a dual J-79 equipped aircraft is about the same as a large gas station.