Riedel made superb starter motors for the German WWII turbojets, the Junkers, BMW and Heinkel.

“Two Riedel Models”

-Due to the great starting torque necessary to start those turbines and not having other practical means at that time, this internal combustion engine was applied.

-Two types have been shown: the first with a Riedel type AK-11 reference and which had a similar version RBA/S-10.

-The AK-11 could rotate at 10,000 rpm and gave 10 CV while the RBA gave 10.5 CV at 7,500 rpm. They appeared between 1942 and 1943, both in the same style.

-While the one in the lower photograph has the reference given by the German Air Ministry RLM 9-3704A.

-We see that the starter pull ring hangs from the front. In the starting process, a person stood in front of the engine socket and pulled the ring, turning the Riedel and causing it to start.

“Installation on a German engine”

“Schematic of a Riedel engine”

-The main characteristic of the Riedels with their two horizontally opposed cylinders is that they were called “Super Flats” because the stroke was only 35 mm by 70 mm of bore. They weighed about 16.5 Kg and had a displacement of 270 cc.

They had a centrifugal clutch. After the war they were built in France and applied to the first ATAR turbines (see Atar and Snecma).

“Atar with Riedel”

-They were not installed inside the front dome as in the German engines, but by means of an articulated transmission they could be installed in another part of the fuselage or the wing.

"Possible Positions"

From Appendix 6: In the San Diego Museum (USA) there is a small Riedel starter together with its Jumo 004B engine.

“Riedel two-cylinder engine, at the foot of the Jumo”

-Below we show some new views of this engine that we just received from a collaborator.

“Riedel RBA/S10”

“Another illustration of an RBA/S10”

-As we can see in the upper illustration, it is completely faired with its anchoring plate and having the possibility of installing the group in any position of the bolts around 360°.

-And in the lower one, without fairing or air direction deflectors, thanks to which we can see an electric starter and the handle for manual start-up.

-Both systems on the same Riedel.

“Another type of Riedel” (PiP)

-We can see the mounting plate of a different type, not as universal as the previous one, and also the effective fan for this ultra-fast motor -for the time-.

-Below we show an amazing and very well cared for starter from early German turbines (including the Franco-Swiss Atar).

“Riedel resting on a cylinder” (PiP)

-The normal position is with horizontally-opposed cylinders. The engine is an RBA-S10.

-What surprises us, is the type of fan with curved fins and of course the entire fairing is missing.

-It is a very high speed piston engine, capable of “launching” a compressor-turbine+accessories rotor at minimum starting speed.