Suitable engines were quite few at the time for decision. The study phase was long and the engine development was fast. Many options he could see the light of day during this time. front
by 1960, so-called turbofans with lower fuel consumption than earlier engines.
The most studied engine options were versions of Bristol Olympus (pure jet) and Rolls Royce Spey (turbo fan).
At the end of 1961 two new alternatives were added: Pratt & Whitney JT8D and Rolls-Royce RB177 Medway, both civil turbo fan engines. It was assumed that some modifications would be necessary to adapt the engine to, for example double power figure. Of course, an afterburner chamber must also be added and constructed. These two alternatives were made against Olympus.
The disadvantages of Olympus were the uncertainty what regarding the decision-making situation in the United Kingdom and the engine's higher fuel consumption. The choice became difficult.
Finally, for aircraft 37, a version of JT8D which was designated RM 8 in our Air Force. What you did was choose a civilian turbo fan motor designed for Mach 0.85 to one aircraft expected to fly Mach 2.0+.
[translator's note - SAAB really wanted the Olympus, it was the Swedish Air Force insisting on the JT8D turbofan]
The engine was equipped with a Swedish developed EBK. The result was changed fan, new combustion chamber, changed turbine and of course completely new fuel control system. Practically everyone parts in the engine must be resized because of the higher power figure. For the hunting version engine we also had to do a brand new fan, low pressure compressor and new combustion chambers. Because of completely different operating conditions for RM 8, the experience of the JT8D program could only to some extent part come RM 8 credit. But aviation engine together with P&W got a lot of development work. Surprisingly, they hesitated not at KFF or Aircraft to take one engine from an airliner and put it in a war plane.
