Looking for information about Napier Sabre series supercharger impellers

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Senior Master Sergeant
Apr 17, 2017
midwest USA
Hey everyone,

Does anyone have any authoritative information on the supercharger impellers used on the Sabre series?

I think that there were only 2 different impellers used - the two-sided double-entry type type on the Sabre I-IV and the single-sided(?) single-entry type used on the Sabre V-VII. Any info would be appreciated but I am particularly looking for the impeller diameters.

I have had no luck either on the internet or in the books I have access to and any info would be appreciated.
The first 60 Sabre I had ø11 1/8" impellers. The remaining Series I had ø12" impeller. I don't know about the later series.
Well, here is something from the book "Allied Aircraft Piston Engines of WW2"

Interesting they switched from a double suction impeller to a single sided. The double suction would be more efficient as an air pump and better pressure balance front to back, however the installation would be quite a bit longer longer than a single sided impeller installation.
I'd imagine that both the front and rear suction elbows would have to be short, which would cause issues similar to the Merlin X.
By switching to just having one inlet elbow, that elbow would have a larger radius and thus possibly overall less head loss for the supercharger system.
I suspect that two side versus single side had more to do with the switch from a four barrel carb to a pressure injection carb. You did not need more suction to draw the fuel in from the carb bowl when you had fuel being injected under pressure into the supercharger intake. The old "Lean Cut/Rich Cut" problem with the British built Merlins stemmed from the carb used. Americans were shocked at the fact the early Spits had that problem because we had gone to pressure carbs years before. I recall reading of a new Merlin-equipped Beaufighter being supplied to Malta, and on one of its first flights over its airfield the pilot shoved the nose down and the Merlins quit; it impacted in a Spit dispersal area killing not only the Beau crew but also Spit groundcrew.

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