The 109-718 (109 prefix number for the Reichsluftfahrtministerium, or RLM, designation used for all reaction-propulsion [rocket and gas turbine] aviation engine projects) was designed as an assist rocket for aircraft, for rapid takeoffs or to enable them to achieve high-speed sprints, akin to what Americans called "mixed power" postwar. It was combined with a standard BMW 003 jet engine, placed atop the rear turbine casing of the jet engine to create a new variant of it, the 003R, providing a total of 1,250 kg (2,760 lb) thrust at full power apiece; it was expected the units would be fitted in pairs. Unlike most RATO boosters,^[i] the liquid-fuelled 718 rocket engine system comprising the second propulsive source of an 003R engine remained with the airframe at all times.^[1]

The rocket motor had internal and external main chambers which were cooled by the nitric acid oxidiser, fed through a coiled spiral tube. The centrifugal fuel pumps (operating at 17,000rpm) delivered a mix of nitric acid oxidiser and hydrocarbon fuel at 735 psi (50.7 bar),^[ii] a rate of 5.5 kg (12 lb) per 1,000 kg (2,200 lb) thrust per second. The 718's fuel pumps were driven by a power take-off from the jet engine which ran at 3,000 rpm. The complete unit weighed 80 kg (180 lb).^[3]

Before war's end, a Messerschmitt Me 262C-2b Heimatschützer II (Home Defender II, one of four different planned designs of the rocket-boosted Me 262 C-series) was tested with a pair of 718s — each as a part of a pair of the BMW 003R "mixed-power" propulsion units — climbing to 9,150 m (30,020 ft) in just three minutes. The 109-718 was also tested aboard an He 162E, although records do not indicate the results of this test.^[3]

The Germans hoped the rocket might eventually rely on the same fuel as jet aircraft.^[1]

Only twenty 109-718 engines were completed by war's end, each taking some 100 hours to complete.^[2]

Data from The Race for Hitler's X-Planes: Britain's 1945 Mission to Capture Secret Luftwaffe Technology^[4]

General characteristics

• Type: Liquid-propellant rocket
• Length:
• Diameter:
• Dry weight:

Components

• Compressor:
• Combustors: Catalyst ignited or Hypergolic combustion in a single combustion chamber
• Fuel type: Diesel fuel and red fuming nitric acid (RFNA / S-Stoff) oxidiser with injected catalyst or R-stoff / SV-stoff fuel and oxidiser^[5]

Performance

• Maximum thrust: 12.2625 kN (2,756.7 lbf)
• Specific fuel consumption: 0.561 kg/kN/s (12.125 lb/lbf/s), which translates to an ISP of 181.75 (s), probably at sea level

• Christopher, John (2013). The Race for Hitler's X-Planes: Britain's 1945 Mission to Capture Secret Luftwaffe Technology. Stroud, UK: History Press. ISBN 978-0-7524-6457-2.