Escort Spifire

Peter Gunn said:

A question (or two) if I may. While improving the breed, I see NAA really doing some work here.

So with the B/C & D/K operational what was (or was there) an E model and what role was envisioned for it?

I assume the F led directly to the P-51H but was the XP-51G designed as an interceptor? Looking at those rather stunning numbers in your last paragraph that is what I'm thinking, she looks to be a real scorcher.

And where does the J fit in and was its intended role the same as the earlier marques or was it being looked at as an interceptor version as well?

Lastly, was a five bladed prop ever tried on any of the XP-51s? If so, results?

Thanks in advance.



A factor that has always impressed my about the Mustang and those that flew them.

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The P-51E was the original designation for the P-51D to be made at Dallas under cancelled contract NA-107 (about March, 1943). NA-107 was distributed back into NA-104 and NA-103, then parsed the remainder into NA-106 for the first two P-51D-NA.

The XP-51F was a result of Kindleberger promising a scorcher LW fighter to Arnold - who authorized the contract for the first three F's (1650-3), then two G's (Merlin R.M. 14 S.M.) , then two J's (Allison V-1710 with 'infinite speed' two stage SC). The designe team focused on stripping all excess weight from the P-51B as it existed pre-85 gallon tank -------- leading to removing 2000 pounds with same HP for F, 2200 HP for G, and same for J.

The XP-51F did test the five blade Rotol but experienced undesirable stability issues.

The F/G could have been produced in fall 1944 if AAF needed a relatively long range interceptor (approximately 375 mi w/75 gallon tanks) but not near enough for Berlin or any escort mission contemplated in mid 1943.

drgondog said:

*SNIP*

The XP-51F was a result of Kindleberger promising a scorcher LW fighter to Arnold - who authorized the contract for the first three F's (1650-3), then two G's (Merlin R.M. 14 S.M.) , then two J's (Allison V-1710 with 'infinite speed' two stage SC). The designe team focused on stripping all excess weight from the P-51B as it existed pre-85 gallon tank -------- leading to removing 2000 pounds with same HP for F, 2200 HP for G, and same for J.

*SNIP*

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Not to sound too dense but what was the Merlin R.M. 14 S.M.? I don't seem to find anything on that particular engine, but admittedly, my Google-fu is rather out of sync this morning.

Also, the J-Model with an 'infinite speed' two stage SC sounds intriguing, how far along did progress get on that idea? I'll assume the jet engine pretty much nullified the need for it, but still, it sounds like performance wouldn't suffer at any altitude for lack of engine power if I'm speculating right.

Also, thanks for your answer, it cleared up any confusion I had over the different marques.

Peter Gunn said:

Not to sound too dense but what was the Merlin R.M. 14 S.M.? I don't seem to find anything on that particular engine, but admittedly, my Google-fu is rather out of sync this morning.
.

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The Merlin R.M. 14 S.M. was the Merlin 100 series. The Packard equivalent being the V-1650-9 (and later?)

The R.M series of numbers seems to (welcome correction) cover families or groups of engines of similar performance and/or construction.
For example the Merlin R.M. 6 S.M. covered the Merlin 60 and 62 while the R.M. 8 S.M. covered the Merlin 61, 63, 63A, 72 and 73.

Shortround6 said:

The Merlin R.M. 14 S.M. was the Merlin 100 series. The Packard equivalent being the V-1650-9 (and later?)

The R.M series of numbers seems to (welcome correction) cover families or groups of engines of similar performance and/or construction.
For example the Merlin R.M. 6 S.M. covered the Merlin 60 and 62 while the R.M. 8 S.M. covered the Merlin 61, 63, 63A, 72 and 73.

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The development numbers signify the engine rating.

Rolls-Royce engine mark numbers can vary in details but still have the same rating. Things such as a different reduction ratio would mean a different mark number.

The RM.14SM was certainly a 100 series motor. The V-1650-9 was a 100 series engine too, but I have seen that described as both an RM.14SM and a RM.16SM - Lumsden says the latter.

RM.8SM was the rating for the Merlin 63/V-1650-3. The Merlin 66/V-1650-7 was rated RM.10SM. The difference between these sets of engines is the supercharger gearing and the size of the supercharger.impeller size.

The Merlin 70 had the same rotor sizes as the 66 (12.0" and 10.1"). The Merlin 66 being stronger at low altitudes and the 70 at high altitudes.

The last wartime development of the Merlin was the RM.17SM which was a "low" altitude engine with even karger supercharger impellers - the first stage being, IIRC, 12.7" and the second stage I can't recall. Rated at 2100hp in FS and 2200hp in MS.

RM = Rolls-Royce Merlin
SM = (fully) supercharged and medium supercharged (ie 2 speed)

The Griffon 100 series were rated RG.3SML, so it was a 3 speed engine.

ChrisMcD said:

This looks like a very serious look at an old debate

Escort Spitfire - a missed opportunity for longer reach? - Royal Aeronautical Society

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That was interesting.