Six Avionics: Settling a debate (Read 1,776 times)

Some insight into "fly-by-wire", F-16 style: When the pilot made a side stick input, the FLCS (flight control system) would go out to the various avionics and see what AOA the jet was at, the Mach no., G-load, and then (and only then) send a signal to the appropriate surface actuator. The actuators are hydraulically-powered and electrically-controlled. There are only five actuators on the whole jet; two for stabs, one rudder and two for the flaperons. The jet has leading-edge flaps but their operation is totally transparent to the pilot and he has no control over them at all. The stabilators move independently and can and do assist in roll control.

The main difference between the Six's old-technology flight control system and the Viper's is how the actuators are controlled. The Six's were controlled by the stick through the HEP and HRP valves via a mechanical connection. This is basically true for all fighters prior to the F-16. FBW is the norm for all fighters after the Viper. Nothing but wires, gyros, and computers between the stick and rudder pedals and the surface actuators. The FLCS has four independent channels, any one of which can fly the jet. One is held in reserve while the other three vote on what to do, with the oddball channel ignored. If one primary channel fails, the fourth channel jumps into the mix.

I never worked much if any AFCS on the Six, nor any MA-1. I was just an instrument weenie. I do remember that the Q-tube was for artificial feel and not for any shift in mechanical advantage in the pitch axis. I could well be wrong on this. I would have LOVED to do some of those alignments that y'all are talking about! At that time, I had no idea I'd be a lifer and was just trying to get my four years in and be done with the USAF.

Interestingly enough, the F-105 did have a mechanical advantage shifting system that was controlled by mach no. from the CPU-111 CADC. Sound familiar? Yep, the D/F model Thuds were 80% interchangeable with the Six as far as their instrument suites were concerned, including the CADC. I did work a lot of AFCS on the Thud. The Thud's MA shifter system drove a screw jack that moved the pitch control rod closer to the fulcrum of a bell crank in the link so that the same stick movement resulted in less stab movement at higher mach numbers. Pretty ingenious way to do that, if you ask me.