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Define long range in regards to what?
The ability to fly 400 miles from base to point in Europe, fight for 20 minutes and return?
The ability to actually escort bombers over that distance, even using several relays?
What altitude?
How big a formation? As in how long to get xx number of planes off the ground, get them to desired altitude and the proper order/tactical formation. Radius is determined by first plane to go wheels up.
Nothing comes to mind immediately - but I do have an anecdote from an RCAF Squadron (Spitfire IX, Merlin 61) escorting B-17s to Amiens.
The B-17s were 20 minutes late for the rendezvous and had many diversions along the way. As a result the Spitfires were running very short of fuel on the way back. While over the Somme Estuary a young Sergeant panicked and exclaimed that he only had seven gallons left. The Section Leader (author) instructed him to disregard formation and set his engine to +4 boost, 2650 rpm and lean mixture - as well as descend at 100 feet per minute.
This leads me to believe that at that stage of the mission (essentially over enemy territory) they were using higher engine settings.
I'll keep my eye open for any mentions.
There is a further appendix to that note. It lists speeds (both ASI and true) at different heights with the boost/RPM and fuel consumption. It has been reprinted in at least one of Alfred Prices books.
It goes some thing like this for 20,000ft
ASI.............TAS...............Boost..............RPM.............GPH.
283.............368................+9.................3000............88
268.............350................+6.................2650............70
258.............300..............+3 3/4..............2650.............65
240.............310...............+3 3/4.............2400............50
230.............300...............+1 1/2.............2400............46*
" ".............." ".................+1..................2650...........48
200.............263...............-1 3/4..............2200............36*
" ".............." ".................-2 1/4..............2650............40
It is for both Merlin 45s and 46s.
The 300 TAS I made red was listed that way in Price's book (300TAS not red) , Typo in the book or original document I have no idea so take any other numbers with a grain of salt if you wish.
Now please note that a P-51D could cruise at 20,000ft at 316mph true using 57 US gallons (47.5 Imp gal ?) of fuel per hour according to the charts or 346mph true using 67 US gallons (55.8 Imp gal).
Also try to figure out out fuel used to climb to 20-25,000ft after take off. A Clean Mustang using 2700rpm and 46 in (8lbs boost ?) needed 7 minutes to climb form 15,000ft to 25,000ft, used 12 US gallons doing it and covered 21 miles of ground.
A MK V Spitfire could fly at 200ASI/225TAS at 10,000ft and burn only 29IMP gallons an hour but that is a suicidal speed and altitude to fly over German held territory even if perfectly reasonable over the last part of the Channel on the homeward flight or while looking for the home airfield.
And there you have the difference. Flying over water in the Pacific could and was done at lower speeds and altitudes until the target area was reached and throttling back for the cruise home was also possible.
The raid on La Pallice was was done around two months after D-Day and depending on starting point, could have flown either over or close to the Normandy beaches. In fact a fairly large portion of the flight could be done over allied controlled parts of France and German air strength in the area might be described as "light".
Trying to fly a 690 mile round trip in 1943 into Germany might have been a whole different story.
Your actual combat radius is determined by how much fuel is in the internal tank/s at the furthest point from home, after the drop tanks are gone.
Using US standards you would have:
5 minutes at 16lbs boost was 12.5 gallons gone.
15 minutes at 9lbs and 3000rpm was 22 gallons gone.
Using a 30 minute reserve would be around 13-14 gallons.
47 gallons accounted for leaving ??? fuel in the internal tanks?
Egress over the channel might not have to be done at at the same speed as egress over land. 12 gallons will see you almost 90 miles at 200ASI at 20,000ft. 59 gallons used?
Now the problem is IF you are escorting the bombers back or simply leaving them after combat and depending on a second relay of fighters to do the return escort? If you are weaving over/around them you are burning the fuel at the 300TAS rate but only covering ground at around a 200 TAS rate. Or say around 50 imp gallons to "escort" 200 miles. If you want to keep the speed up it gets worse.
Sticking 50-60 IMP gallons inside a MK V gets a little tricky. You can find room but what does it do to the climb, the sustained turn rate and the allowable "G" loading? This ignores any change in the handling of the aircraft due to change in the CG. Please remember that the MK IX had several hundred pounds of engine and propeller stuffed in the nose to help balance those rear fuselage tank/s.
Photo recon Spitfires weren't expected to dog fight but pretty much run in a straight line (or gentle curve) at high speed for evasion when loaded.