Hello Gents;
I have read that Sir Stanley Hooker helped take the Merlin from being a good engine to a great one, by altering the design of the supercharger. In fact, I have read several articles on that, and seen one or two documentaries as well.
I think his involvement included taking the early Mk III Merlin superchargers to more of a Mk XX, by changing them to a central-entry charger. (can anyone confirm that?) Which makes me ask the question, where did the air enter the supercharger on the early Merlins? Somewhere else, other than through the center? I’ve seen pictures, I’ve just never understood how the early chargers worked.
Also, I’m curious if Sir Hooker was responsible for the two-stage charger in the 60 series Merlins and beyond. I’m curious about that, because it’s my understanding that Sir Hooker didn’t stick around forever with the Merlin, and that he went on to gas turbines. And if he did not help develop the two-stage charger, who did?
Pinging Merlin Pete, and others.
Thanks, Tom.
By: MerlinPete - 27th November 2010 at 22:02
Hello Tom
The difference betwen the early one, which is called a side-entry supercharger, and the central-entry type is not easy to see. I have made the two attached diagrams to try and explain it. The side-entry is so called because the air goes through a fairly sharp 90 degree turn into the impeller through six separate openings. The central-entry employs a much more aerodynamic inlet profile which also carries all the air in the same direction rather than into a circular chamber surrounding the impeller opening. The impellers are much the same and the air enters the rotating inducer in the same manner in both designs, hence the confusion about the meaning of “side-entry”.
I`ll leave it at that because all I`ll do is confuse the issue further!
Incidentally, the bulge at the rear of the so-called Babys Bum caused by the aerodynamic curvature designed into it made the Merlin 45 engine longer than the equivalent Merlin III, so the solution was to effectively turn the entire carburettor round to move the main jet mechanisms to the front, under the supercharger.
Pete
By: Avro Avian - 25th November 2010 at 19:27
You will find all answers to your questions in his book “Not Much Of An Engineer”. 🙂
Sir Stanley Hooker was actually a mathematician by trade, specialising in fluid dynamics. IIRC, one of the first things he did at Rolls Royce was to redesign the inlet elbow into the eye of the supercharger, of which produced the Merlin 45 and the first substantial increase in power output in the Merlin series. He was also involved with the Merlin 60 series, but I can’t remember the details of matching the two superchargers, in series, to the engine. His work with superchargers led to his work with developing gas turbines. I believe the RR Dart was designed around the Griffon supercharger as its compressor.
It’s been a few years since I read his book, but I did enjoy reading it and would recommend it to anyone interested in engine developement.
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November 25, 2010 at 5:48 pm