BMW 109-558 Rocket Engine and Propellant Tanks This liquid-fuel rocket engine was most commonly used as the sustainer motor for the Henschel Hs 117, an experimental German antiaircraft missile developed late in World War II. Designed by the BMW rocket engine group at Berlin-Spandau, under the direction of Helmut von Zborowski, the 109-558 used concentrated nitric as an oxidizer and a composite hydrocarbon mixture codenamed “Tonka” as fuel. Its initial thrust of 375 kilograms (825 pounds) fell to 60 kilograms (130 pounds) in the last 24 seconds of burning as a result of falling pressures in the missile’s gas-pressurized tanks. The engine’s thrust could be regulated to prevent the Hs 117 from exceeding the velocity at which it was stable. Gears on the head nozzle were mechanically linked to two flat sliding valves. The gears (missing on this artifact) were actuated by an electromotor regulated by a Mach meter. Length: 2.5 m (8 ft 1 in) Thrust, max: 3,670 N (825 lb) Propellant: Tonka, nitric acid Manufacturer: Bayerische Motorn Werke (BMW) For more info: en.wikipedia.org/wiki/Schmetterling

Friend phoned saying there was a balloon launch behind the Fox. Grabbed camera and dog, brilliant weather for it, learned that it was to be training flight, tethered. Still worth watching and getting a few pics. Several metres off the ground, and the trainee pilot works the valves to stabilise it.