In Morgan and Shacklay’s Spitfire the History, it is written that the Merlin 32 had a cropped supercharger which enabled power to be provided to the propeller instead of being used to provide more air flow for operation at high attitude. Did the Merlin 32 have a cropped supercharger or was it optimised for low altitude in a different way? If not, was the supercharger modified in a way that could be mistaken for being cropped?
By: antoni - 21st December 2008 at 11:23
The low-altitude performance compared to the Merlin 45 was acheived by having a gear ratio of 8.588:1 instead of 9.09:1
The rated altitudfe for the Merlin 32 is 2500ft.Pete
I think MerlinPete is comparing the Merlin 30/32 to the Merlin 45, not the 45 to the 45M?
By: jerryw - 21st December 2008 at 00:10
RM numbers
I think I understand. The Merlin 30 and 32 had reduced size impellers, presumably for better performance at lower altitude, but they are not called cropped because the engine was designed to have them. The Merlin 45M has a reduced size impeller which is called cropped because it is a modification to the Merlin 45.
In M&S there is a table of engine variants. One of the columns is headed MoS Experimental Nomenclature. Can you explain to me what is in this column. MoS = Ministry of Supply? The entries all begin RM for Merlins and RG for Griffons – Rolls Royce Merlin and Rolls Royce Griffon? What do the numbers that follow refer to? The size of the supercharger? Somebody told me that the cropped series 45 and 50 Merlins (M suffix) were not given RM values because they were modified engines but M&S list values for all the variants except the Merlin 66-68. Is this another mistake by M&S.
Many thanks.
The numbers after RM or RG refer to the RATINGS for the particular type of engine, eg ‘3’ means the third attempt to provide a particular performance standard for that engine.
By: jerryw - 21st December 2008 at 00:05
Merlin 45
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The low-altitude performance compared to the Merlin 45 was acheived by having a gear ratio of 8.588:1 instead of 9.09:1
The rated altitudfe for the Merlin 32 is 2500ft.
Pete[/QUOTE]
The Rolls-Royce engine data sheets disagree with the above info. They all show the Merlin 45 and the Merlin 45M to have a supercharger gear ratio of 9.09.
By: antoni - 30th November 2008 at 08:59
I think I understand. The Merlin 30 and 32 had reduced size impellers, presumably for better performance at lower altitude, but they are not called cropped because the engine was designed to have them. The Merlin 45M has a reduced size impeller which is called cropped because it is a modification to the Merlin 45.
In M&S there is a table of engine variants. One of the columns is headed MoS Experimental Nomenclature. Can you explain to me what is in this column. MoS = Ministry of Supply? The entries all begin RM for Merlins and RG for Griffons – Rolls Royce Merlin and Rolls Royce Griffon? What do the numbers that follow refer to? The size of the supercharger? Somebody told me that the cropped series 45 and 50 Merlins (M suffix) were not given RM values because they were modified engines but M&S list values for all the variants except the Merlin 66-68. Is this another mistake by M&S.
Many thanks.
By: MerlinPete - 29th November 2008 at 19:04
According to the manual, the Merlin 32 does not have a cropped impeller, although its predecessor, the Merlin 30, did have the impeller reduced from 10.2″ down to 9.75″
The low-altitude performance compared to the Merlin 45 was acheived by having a gear ratio of 8.588:1 instead of 9.09:1
The rated altitudfe for the Merlin 32 is 2500ft.
Pete
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November 29, 2008 at 4:31 pm