BMW in the Sky: The Story of BMW Aircraft Engines

This page tells the aviation side of the company. The car history, from the Dixi to electric models, is in our main BMW history.

Rapp, Friz and the high-altitude IIIa

BMW's roots lie in two Munich firms of the First World War. Karl Rapp's engine works became BMW GmbH in 1917, and its chief designer was Max Friz. Friz registered his design for a new six-cylinder aero engine on 20 May 1917. It ran on the test bench on 17 September 1917 and first flew in December.

The BMW IIIa was a water-cooled inline six with a single overhead camshaft and 19.1 litres. It gave 138 kW (185 hp) at 1,400 rpm and weighed 285 kg dry. Its trick was a high compression ratio of 6.4:1 combined with a twin-barrel carburettor that compensated for altitude. The pilot used a second lever to open the throttle fully only above about 3,500–4,000 m. Lower down, the engine ran throttled to protect itself. The result was an engine that kept its power where other engines faded.

The IIIa went into the Fokker D.VII fighter, among others. About 700 were built by BMW, and some production was transferred to Opel in Rüsselsheim. The old 1cars text quotes the fighter ace Ernst Udet, who praised it as the best aero engine of its time.

1919: the altitude flight

On 17 June 1919, test pilot Franz Zeno Diemer took off from Munich's Oberwiesenfeld airfield in a DFW F 37/III. He reached 9,760 m after 87 minutes, in temperatures as low as −50 °C. The engine was the BMW IV, a IIIa with bore and stroke enlarged by 10 mm and output raised from 185 to 230 hp (about 172 kW).

The flight was never ratified as a world record. Germany had been excluded from the international aviation federation (FAI) after the war. The old 1cars text credits the flight to the IIIa; BMW's own archive names the enlarged BMW IV. Later that year, on 13 September 1919, Diemer flew a Junkers F 13 with eight people on board to 6,750 m, this time with a IIIa.

BMW's archive also stresses economy. In throttled running, the IIIa used about 200 g of fuel per horsepower-hour. The archive says that was more than a third less than a normal engine in its class, giving a range of about 1,200 km instead of 730 km.

Brakes, motorcycles and the kitchen: life between the wars

The peace treaty of 1919 banned German aircraft production for several years. BMW had to find other work. According to the old 1cars text, it built braking systems and, after taking over the neighbouring aircraft maker, used up its stocks of plywood by making kitchen furniture. The motorcycle came next: the R32 of 1923 had a flat-twin engine and shaft drive, and the old text gives its output as 8.5 hp.

The same kitchen theme returned after 1945. BMW's West German plants were then banned from building vehicles and aircraft, so the company survived by making pots, pans and bicycles.

The BMW VI and the 132: engines sold around the world

When aero-engine work resumed, BMW built bigger engines and sold licences abroad.

BMW VI (1926–1938). This 60-degree V12 had 46.9 litres. Its take-off rating reached 552 kW (750 PS) for one minute. At least 9,200 were built. It powered the Heinkel He 51 fighter, the Dornier Do 17 and prototype and civilian versions of the Heinkel He 111. In the Soviet Union, Alexander Mikulin's team built it under licence and developed it as the M-17, which went into the Tupolev TB-3 bomber. In Japan, Kawasaki built a version as the Ha9. Wolfgang von Gronau flew two BMW VIs in an open Dornier Wal flying boat across the Atlantic from east to west in 1930.

BMW 132 (from 1933). BMW bought a licence for air-cooled radial engines from Pratt & Whitney on 3 January 1928. The resulting nine-cylinder 132 had 27.7 litres and gave 533–880 kW depending on the version. More than 21,000 were made. It became the usual engine of the Junkers Ju 52 airliner and transport. On 10 August 1938, a Focke-Wulf Fw 200 Condor with BMW 132 engines flew from Berlin to New York in 24 hours and 57 minutes.

The 801 radial, the 003 jet and forced labour

In 1939 BMW bought the Berlin engine maker Bramo and merged their radial-engine projects. The result was the BMW 801, a 41.8-litre, 14-cylinder, two-row radial. The first engines ran in April 1939.

The 801 powered the Focke-Wulf Fw 190 fighter, the Junkers Ju 88 and the Dornier Do 217. More than 61,000 were built, the most of any German radial engine of the war. Its Kommandogerät set fuel flow, propeller pitch, supercharger stage, mixture and ignition from a single lever. In that sense it was an early engine-control unit.

Bramo also brought a jet project. The BMW 003 axial-flow turbojet first ran in August 1940 and first flew under a test aircraft in mid-1941. The production 003A gave 7.83 kN of thrust. It powered the Heinkel He 162 and four-engined Arado Ar 234C versions. Sources differ on production: about 3,500 in most counts, much less in one passage of the same encyclopedia entry.

This production had a human cost. BMW built the 801 using as many as 40,000 slave labourers, most of them prisoners from Nazi concentration camps, above all Dachau. After the war, the 003 design lived on abroad: its chief engineer, Hermann Östrich, developed the French SNECMA Atar from it. A copy was also built in the Soviet Union as the RD-20.

From Dahlewitz to the exit: BMW Rolls-Royce

After 1945, BMW stayed out of aviation for decades. It came back in 1990 through BMW Rolls-Royce, a joint venture with Rolls-Royce plc. The venture bought KHD Luftfahrttechnik, whose Oberursel works had built aero engines since 1913. Its base was Dahlewitz near Berlin.

The BR700 engine family was launched in 1992 with an order for 200 engines from Gulfstream. It powered the Gulfstream G550, the Bombardier Global Express and the Boeing 717. In 2000 Rolls-Royce took full control and renamed the business Rolls-Royce Deutschland. BMW sold its remaining shares in 2006, about 90 years after the IIIa. This aero-engine Rolls-Royce is a separate company from the car maker described in our history of Rolls-Royce, which has built its cars as a BMW subsidiary since 2003.

BMW aircraft engines in numbers

By our calculation, these engines add up to at least 95,000 units. The best-known 801 version gave about nine times the power of the 1917 IIIa from just over twice the displacement. The IIIa weighed about 2.1 kg per kW of output, by our calculation, which was light for an engine of 1917. Our power converter turns the period PS and hp figures into kW, and the power-to-weight calculator does the same sum for cars.

Our view: what the aero engines left in BMW cars

The aviation years explain several BMW habits that still show in the cars. The firm learned to build light, high-compression engines that keep their output under load. It also learned to combine many controls into one system, as the Kommandogerät did. The six-cylinder inline engine, BMW's first product, is still its signature layout. Today's models are listed in the BMW catalogue, and the 1950s BMW 507 shows how quickly the company returned to building sporting cars.