Reply to post: Olympus engines Re: Costs

Take-off crash 'n' burn didn't kill the Concorde, it was just too bloody expensive to maintain

Anonymous Coward
Anonymous Coward

Olympus engines Re: Costs

@steelpillow "The main cost problem was the Olympus engines. Originally built for the 1950s Avro Vulcan bomber, they were uprated and adapted for supersonic use by Concorde. Not only are military engines traditionally far more maintenance-hungry than civil, but the tacked-on afterburner was not as efficient a solution as a clean-sheet design would have been. Had investment for a new engine been available, operating costs would have been substantially lower."

The funny thing is, when cruising at Mach 2, Concorde's engines operated more efficiently than those of all other airliners - reheat was only needed for transonic flight (acceleration through Mach 1 to Mach 1.7 according to the Haynes manual I've got here). They had to, or Concorde never would have been able to carry enough fuel to cross the Atlantic because supersonic flight is not in itself efficient.

Because Concorde had variable geometry engine intakes operating by digital control, and because the engineers who worked on that part of the design were old fashioned wizardly boffins, Concorde got an 80:1 compression ratio from engine intake entrance to engine compressor exit.

That enormous compression ratio is why the engines were so efficient: basically, the higher your compression ratio, the better your efficiency; and up until relatively recently, no gas turbine engine used on subsonic airliners came close to Concorde at cruising speed. Modern designs like the RR Trent-1000 line of engines apparently provide a 50:1 compression ratio - but the engines used on the original 747, a contemporary of Concorde, had a mere 23.4:1.

As for the Concorde engines suffering due to their military origins, well, it's not that simple. They were developed from the version of the Olympus which had been enlarged and adapted for the TSR-2 - a supersonic aircraft, unlike the Vulcan. An awful lot of work went into improving the engine after that as it moved through several design iterations, particularly with respect to reducing maintenance requirements since it was intended for a civil application. You might put up with having to do engine work of some sort after every flight of a bleeding-edge military jet (at least in the 1950s or 60s), but it's out of the question with a jet airliner. Civil jet engines have to just keep on working.

According to the Concorde Haynes manual, the Olympus 593-610, the final Concorde engine, had only its origins in common with the Vulcan power plant. Bristol Siddeley began work on Concorde's engine with the Olympus 22R (aka Olympus 591, Olympus Mk 320, or BOl.22R according to various sources) and came up with the Olympus 593D - "D" for "derivative" or "derived" - from the 22R. This used the metallurgy developed for the TSR-2 engine, since it was proven to cope with supersonic flight conditions.

During the Concorde design process, it became clear a more powerful engine was needed, so Bristol re-designed the 593D to come up with the Olympus 593B ("B" for "big") - with larger diameter and longer turbines and compressors (i.e., more stages).

Now then, this engine had a cannular combustion chamber (8 separate but interlinked combustion chambers), left over from its military roots. This was replaced with a pure annular combustion chamber in the 593-602 version: it worked much better (Concorde stopped being so smoky), but suffered problems from rapid deterioration in service (erosion, burning, and cracking) which took until 1981 to solve with improved parts.

And all the while, the design engineers were working on making the engine as efficient and reliable as they could with a myriad other changes in detail. The result was excellent, it really was, for all that better could be achieved these days.

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