[Milsurplus] altimeters coupled to autopilots

[boeing377 at aol.com]

I worked on a tube autopilot that had an altitude hold function. It 
just had an aneroid pressure sensing element on the autpilot chassis, 
shock mounted to isolate it mechanically. Autopilot didnt need to know 
altitude, just pressure and could control elevators (vertical axis) to 
maintain a zero change in aneroid deflection. Slaving to a radio 
altimeter would be pretty impractical as it would be essentially 
terrain following, NOT a smooth ride unless you are over the ocean or a 
flat landscape and serves no really useful purpose if you are above 
minimum enroute altitude.