E-4 Fire-control System

The E-4 firecontrol system E-4 scematic diagram. was develloped in 1950 by Hughes Aircraft Corporation for use on the RF-86D Sabre "Sabre Dog" jet fighter armed with "Mighty Mouse" FFAR rockets. 2.75 FFAR shooting.
It used the AN/APG-37 radar with a power of 250 Kw. In search mode the antenna sweept the horizon by +/- 65 degr., and the targets were presented as a B-display on the radar scope. The antenna had conical scanning enabling the radar to automatic track the targets.
To engage a target the E-4 system had to be locked to the target. This was done by the pilot using a joystick to point the antenna and place a range gate marker on the selected target.
Once the the E-4 was locked to the target, the following information was displayed on the radar-scope: scope pictures

1) An Artificial Horizon with roll and pitch information.
2) A Time-Circle, the size of which indicated the time left until the rockets were fired.
3) A gap in the time-circle indicating Range-Rate. The gap position on the circle indicated the magnitude of increasing or decresing range to the target.
4) A refference circle at the centre of the scope.
5) A Steering dot indicating the direction to fly.

The pilot had to keep the steering dot at the centre of the scope in order to follow the computed lead-collision cource, and hit the target.
A few seconds before reaching firing-distance the pilot would arm the firing cirquits by pulling the trigger. At the correct computed firing time the computer would lower the rocket-pod and fire the selected number of rockets.
When the rockets were fired the circles on the scope changed into a "X" and later into an "8" indicating collision warning and break away.

The electro-mecanical E-4 Fire-Control Computer calculated the lead-collision course and when to lower the rocket-pod and fire the rockets using the following inputs:
1) Range and Range-rate from the radar reciever.
2) Target direction angles and angle-rates from the radar antenna.
3) Roll, pitch, altitude, g-forces and temperature information from various external sensors.

All this was done using mekanical servos, syncro resolvers, rate-gyros and a lot of triode- and pentode vacuum tubes.