This topic is about the history, the characteristics and the usage of these engines.
Bob Truax - he wanted such engines to power his Volksrocket.
My understanding is that the XLR-101 verniers were not fed by turbopumps on Atlas or Thor. Their propellant feed appears to have come from the start tanks, which must mean that propellants were pressure fed to the engines. Please correct me if I've interpreted things incorrectly! - Ed Kyle
Flometrics used LR-101 to test their pistonless propellant pump concept.http://web.archive.org/web/20090412003555/http://www.flometrics.com/rockets/rocket_pump/rocketpumptest.htm
While the main engine is operating, these engines are fed by the main engine turbopump, as they perform roll control or other attitude control. When the main engine shuts down, the engines are fed by residual tank pressure and perform vernier function. This means that ISP for these engines in their vernier function is very low, since the main prop tanks are pretty much empty during the period of vernier performance.
Without turbopump feed, thrust must also have been lower during the pure vernier phase. - Ed Kyle