The flight operations handbook for the Douglas X-3 Stiletto (an experimental aircraft from the early 1950s) says that the instrument panel has instruments that indicate the thrust of the two Westinghouse J34 turbojet engines. The actual aircraft in the USAF museum has instruments as in the picture. Despite being labeled "RPM", is it so that the outer scale actually shows the estimated thrust of the engine? Presumably calculated using some simple fixed mechanical linkage directly from the RPM.
The J34 model used is indeed said to have produced around 3000 lbf thrust, so that matches. The smaller inner scale shows the RPM, which for this engine goes up to 12,500 rpm, so that also matches.
Aircraft with more modern turbojets or turbofans rarely or never have instruments that directly would show the thrust, right? Is that because such an instrument is highly unreliable anyway and the actual relationship between RPM and thrust depends on factors that a simple electromechanical instrument can't know? (A glass cockpit could calculate it more accurately and display it, but I assume there is little interest in that information?)
Cropped from nationalmuseum.af.mil