GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
The Merlin was in short supply early on - what fighter (or bomber) production do you sacrifice in order to supply a quantity of M.20s?
British escort fighter--what might it have been like? (3 Viewers)
- Thread starter BarnOwlLover
- Start date
Shortround6
Lieutenant General
And design a new wing, there is some dispute as to the performance numbers. Like if they were estimates or actual test numbers. and some of the weight do not seem to track well.
Like the Wiki figures give about 1900lbs of payload but you have around 1150lbs of fuel, the needed oil, the guns of a Hurricane with about double the ammo.
It all seems a little too good to be true.
I really like the 333mph at combat load and 350mph clean.
It didn't carry ANYTHING UNDER THE WING, it clean 100% of the time.
A 21% wing at the wing root is pretty thick.
Tom Graham
Airman
- 18
- Sep 27, 2022
I think it would be the Whitley. It seems to also have had the "Power Egg" configuration for the engine/radiator etc. The Wellington and the Beaufighter also seemed to have "Power Egg" Merlins I don't know what would be involved in upgrading from the Merlin X to the Merlin XX. I would also reduce the armament to 4 Mgs. This seems to have been adequate for the Gladiator against single engine aircraft. It might also help with the wing thickness mentioned by Shortround6. If the concept worked, I would then cut back the Hurricane and Spitfire, because the M20 could be used for Home Defence on it's days off from escort missions. The M20 had the potential to create a ""Virtuous Circle".
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GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
I still find the performance figures dubious - the first red flag would be the fixed undercarriage, which offers a major performance penalty.
It may look good in paper, but two prototypes (one for a catapult launched project) with short-lived trials does not make it promising.
The Boulton-Paul P.94 would have been a better prospect with it's performance and range options.
It may look good in paper, but two prototypes (one for a catapult launched project) with short-lived trials does not make it promising.
The Boulton-Paul P.94 would have been a better prospect with it's performance and range options.
I agree, speed figures seemed too good to be true, but ...
A&AEE trials have:
333 mph at 20,400 ft (s ratio)
324 mph at 14,000 ft (m ratio) [typo fixed]
2300 ft/min initial climb
20,000 ft in 9.63 min
7560 lb, 9 lb boost
Another big surprise -- 600 rounds of .303 for the two outboard guns and 900 for the two inboard! So much ammunition it can't carry full fuel and full ammo and stay under maximum weight.
No real standout comments in the handling trials other than:
A&AEE trials have:
333 mph at 20,400 ft (s ratio)
324 mph at 14,000 ft (m ratio) [typo fixed]
2300 ft/min initial climb
20,000 ft in 9.63 min
7560 lb, 9 lb boost
Another big surprise -- 600 rounds of .303 for the two outboard guns and 900 for the two inboard! So much ammunition it can't carry full fuel and full ammo and stay under maximum weight.
No real standout comments in the handling trials other than:
- 'exceptional' view
- 'remarkable' dive acceleration
- all controls heavy and ailerons overbalanced
- 'remarkable' dive acceleration
- all controls heavy and ailerons overbalanced
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Howard Gibson
Staff Sergeant
The Miles M.20 out-ran Hurricane_Is because it was powered by a Merlin_XX with a two-speed supercharger. The Hurricane_IIs with Merlin_XXs were just as fast as the M.20. I don't trust performance tests of prototype aircraft, especially ones that did not reach service. Was it carrying full war equipment like guns, armour and self sealing fuel tanks? Eric Brown found that it lacked manoeuverability. The M.20 was a contemporary of the Fw190.
When the Americans set to work using long range fighter escorts, they had stuff going for them that the British lacked in 1940/41. In 1943, all the American aircraft were turbocharged. The bombers cruised in at well over 20,000ft. At 30,000ft, the P-47s not only were 50mph faster than the Germans, they could equal their rate of climb.
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
Would a Merlin Mustang without all the fuel be a simpler choice for an interceptor? It is British, after all. 
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In many situations, yes.Would a Merlin Mustang without all the fuel be a simpler choice for an interceptor? It is British, after all.
- Thread starter
- #369
BarnOwlLover
Staff Sergeant
If built to 7.33G loading at normal max take off weight (instead of 8G at 8000 lbs) and flying on half fuel, yes. The P-51H (built to 7.33G at 9500 lbs approx) did have a 5200+ fpm climb rate on 90" supercharger boost (basically max combat/WEP power). However, that was 1945 (and it took a while to get the boost control system on the carb/supercharger to work right consistently). However, when flown on half fuel in interceptor trim (8450 lbs TO weight), that climb got boosted to over 5800 fpm. Only the XP-51F/G (which were developed into the H as a long range escort fighter instead of exclusively an interceptor) could climb faster at the time.
Performance would depend on weight, loadings and Merlin variant.
Performance would depend on weight, loadings and Merlin variant.
Spits could certainly be modified for significantly increased range for PR use - but the pros and cons and practicality for use as an escort is an argument for the engineers. Point is, the Spitfire was designed as an interceptor rather than an escort fighter - and once Bomber Command had switched to the night offensive, the need for a long range escort fighter for the RAF had largely evaporated anyway. The long range escort fighter was a need determined by long range daylight strategic bombing and the need to escort large formations - something the RAF simply didn't do much of
The second part of your argument looks particularly questionable. What evidence makes you think that's a factual assertion? Of course ROF for 20mm cannons differed and the Hispano was steadily improved, but time and time again its been pretty comprehensively discussed and generally agreed that 20mms are preferable to to .50s on the basis of fire-to-weight, destructive power etc. The .50 cal was adequate as a fighter to fighter weapon, and the US wasn't under any particular pressure to change that until the end of the war. (though 20mm became the standard after the F86 even up to the present day).
50 cal (high rate of fire) vs 20mm cannon (hitting power) (just one of several!)
Googling our old forum friend AG Williams should also give you some useful background reading on this much discussed subject
There is no reason why the Spitfire couldn't have been made into a long range fighter the BoB and Air marshal Portal not withstanding. The MkII fuselage was fitted with rear tanks in the MkV IX and XVI and the MkIII leading edge tanks in the MkVIII and rear tanks in the MkXIV, there was also a mix and match of rear, underseat, leading edge and drop tanks with various fighter, Photo recon and Seafire models. If we started with the MkIII in 1940 it could have been fitted with rear 42G upper 33G lower tanks, the 96G main, 26G leading edge and 50G dropper and by maximising the power especially take off power via the low speed gear of the supercharger it would be able to get off the ground carrying that weight, further modifications could have been extending the leading edge tanks inwards and using the empty space there, that would easily give 26G either side lifting internal capacity to over 220G with whatever size drop tank the plane could lift, MkV's got aloft with 85G main, 30G rear and 170G ferry tanks so I couldn't see the MkIII with the two speed Merlin XX having problems with the 96G main, 75G rear, 52G leading edge and either a 75 or 90G dropper, that will give the Spitfire a combat radius of over 500 miles allowing for combat, high cruise and reserve.
- Thread starter
- #372
BarnOwlLover
Staff Sergeant
That solves the issue of where to put the fuel, not where to put the fuel and not mess with CG. Spitfires with the fuselage tanks suffered from handling problems when the fuselage tanks were filled beyond a certain point. Even the P-51B/D suffered from such CG issues if the 85 gallon fuselage tank was filled much above 60 gallons.
If you're going to pack a plane like that full of fuel and make it combat suitable, you're going to have to do probably a fairly significant redesign of certain fittings to provide at least satisfactory handling regardless of fuel capacity. That's one of the reasons why the P-51H differed from not only the B/D, but also the XP-51F/G the H was based on. The F/G didn't have a fuselage tank (why they ultimately weren't appealing to the USAAF in 1944 when they flew), the H was designed to use lessons learned from them into a long-range capable fighter. Also, the P-51H had a 50 gallon fuselage tank, which was possible due to the wing tanks holding up to 105 gallons vs 92 gallons and get similar overall fuel capacity to the B/D.
There was also a paper by NAA the proposed fitting up to a 100 gallon long range tank in the P-51H, as it was thought that even with that tank it's handling on full fuel would still be superior to the B/D.
If you're going to pack a plane like that full of fuel and make it combat suitable, you're going to have to do probably a fairly significant redesign of certain fittings to provide at least satisfactory handling regardless of fuel capacity. That's one of the reasons why the P-51H differed from not only the B/D, but also the XP-51F/G the H was based on. The F/G didn't have a fuselage tank (why they ultimately weren't appealing to the USAAF in 1944 when they flew), the H was designed to use lessons learned from them into a long-range capable fighter. Also, the P-51H had a 50 gallon fuselage tank, which was possible due to the wing tanks holding up to 105 gallons vs 92 gallons and get similar overall fuel capacity to the B/D.
There was also a paper by NAA the proposed fitting up to a 100 gallon long range tank in the P-51H, as it was thought that even with that tank it's handling on full fuel would still be superior to the B/D.
Main tankage was increased from 85 to 95 gals on the Spit VII and VIII, plus they gained 25 gals in wing LE tanks, for total of 120 gals. All was as CoG-eutral as feasible. Another 30-40 gals can be put behind the pilot (so we don't mess with the CoG that much), feeding the main tank(s), that can be used for warming-up, taxying, taking off and climb to 20-25K + a bit of initial cruise. Leaves 120 gals of internal fuel, while a 'normal' Spitfire IX would've been left with 60-65 gals. Difference of 55-60 gals x 6 miles/gal = 330-360 miles of extra 'return range'. Obviously, a good drop tank needs to be carried, minimum of 90 galas probably.
(all gallons are of the imperial flavor)
We can recall how much of a difference additional 65 gals meant on the P-47 when it went from 305 to 370 US gals of internal fuel.
All MkXVI Spitfires had the rear 42-33G tanks fitted from the factory, all MkVIII's MkXIV's and Seafire MkIII's had the leading edge tanks from the factory.
All aircraft had handling issue's when carrying extra fuel or ordnance, both the Spitfire and Mustang required wings level flight with no maneuvering when fuel laden up until the droppers were jettisoned and the rear tanks run down to 35G in the Mustang and 33G in the Spitfire, the only fighter that could fight with aux tanks was the MkXIV when using the 90G combat type, fighter trials showed it could outfight both the 109 and 190 with it attached.
View attachment 739514 If you look at the leading edge tank there is enough room inboard to double its capacity from 13G to 26G per side.
wuzak
Captain
Always worries me when there are comparisons between American and British aircraft fuel capacities when the unit "gallons" is used, the UK gallon being 20% greater in volume than the US gallon.
Presumably the 65 gallon increase for the Spitfire was in UK Gallons, which would be 78 US gallons.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
That's a good point that is often over-looked.
An Imperial Gallon is 4.54 Litres (160 FL. oz.) and a U.S. Gallon is 3.78 Liters (128 FL. oz.) - in other words, the Imperial Gallon is 1.2 U.S. Gallons.
Geoffrey Sinclair
Staff Sergeant
- 1,271
- Sep 30, 2021
All Imperial gallons unless noted as it is a British aircraft. Revision to earlier efforts now based on better information on Spitfire VIII/IX economic cruise. The idea would be to stay with the P-47, not the P-51. The brief I assume is a Spitfire escort fighter for the 8th Air Force from mid 1943 to at the latest May 1944, after that the acute need for longer range high altitude fighters goes, the RAF had Mustangs with longer ranges even without a rear fuselage tank, the USAAF had many more fighters and from September the continental airfields are open.
As of January 1944 external tanks for Spitfires being made were 30 gallon (Metal, wood, fibre) and 45, 90 and 170 gallon metal. "relevant Spitfire VIII figures from the original sources quoting maximum weak-mixture power setting as 320 mph at 20,000 ft, consuming about 1.1 gallon per minute. This corresponds with an engine setting of 2,400 rpm, +4 lbs boost (66 gallons per hour). So this seems similar. From the same source, the RAF were allocating 23 gallons for take-off and climb to 20,000 ft, and 36 gallons for 15 minutes of combat, leaving 63 gallons for cruise. This gives an endurance of 57 minutes, or a range of 304 miles, for an escort radius of 152 miles." (no reserves)
The mark VIII was 47+49 = 96 in front of the pilot, a 14 gallon tank in each wing = 124, the early IX 48+37 = 85. Under RAF rules the early mark IX range was 434 miles versus the VIII at 660 miles, or an additional 39 gallons for 226 miles, 5.8 miles per gallon at economic cruise, 170 to 200 mph, 30 minutes reserves at economic cruise would be around 15 to 17 gallons, rounded up to 20 for current purposes, given it is unlikely all fuel tanks could be fully drained.
Interestingly the mark VIII pilot's notes mention a 26 gallon rear fuselage tank. Morgan and Shacklady talk about an 18 gallon Mareng bag in each wing for later mark IX, plus 33 or 41 gallon rear fuselage tanks. We know 75 (high back) or 2x33 (or 1x66) (low back) gallon tanks were fitted but these tanks like that of the Mustang needed to be partly emptied to improve stability and probably further emptied before entering combat.
Fuel management, the notes say take off was using the main tank, then at 2,000 feet
a) no drop tank but rear tanks filled, switch to the rear fuselage tanks until empty.
b) drop tank, no rear tanks, switch to the drop tank until empty
c) drop and rear fuselage tanks filled, change to rear tanks until only 30 gallons left in them, then switch to drop tank until empty then back to rear tanks.
Starting with the imaginary longest range Merlin Spitfire fighter version, 96 Gallons in front of the pilot, 36 in the wings, 75 behind the pilot internal, total 207 gallons. Burn 45 gallons of the rear fuselage fuel outbound. That leaves 96+36+30 = 162 gallons on board entering combat at maximum radius, allowing 36 gallons for combat and 20 gallons for reserves leaves 106 gallons, enough for 514 miles at 320 mph at 20,000 feet, outbound fuel available 90 gallons external + 45 gallons rear fuselage = 135 gallons, less 23 for warm up and climb leaving 112 gallons. Nice theoretical balance but you would need the ability to refill the internal tanks from the external ones. And it ignores all the ways range is lost. I suggest start with subtracting about 10% from the theoretical radius for real life operations, what would be good to see is an 8th Air Force P-51 fuel load planning document compared to the official fuel consumption performance figures and then apply them to the Spitfire.
Factors causing loss of range: external tank drag, formation flying, inexperienced pilots, below average performing aircraft, the extra weight (590 pounds of fuel plus tank weights pushing that to around 650 pounds, versus the actual mark VIII, rule of thumb seems to be 1 pound of self sealing fuel tank for 1 imperial gallon of capacity, external metal tanks maybe half of that). Range gain: able to fly economic cruise for a time in and outbound, able to trade height for range inbound, the small distance covered during the climb. Overall result is more than 90 gallons of external fuel required to reach the 514 mile mark. Spitfires were later cleared to carry 1,000 pounds of bombs, 100 imperial gallons of 100 octane fuel comes in at around 711 pounds.
The third edition of the Spitfire mark IX, XI and XVI pilot's notes has rear fuselage tanks with 75 gallons (66 for "rear view" fuselages), permission from the Area Commander is needed to fill the 75 gallon tanks for special operations, while the 66 gallon tanks for "rear view" fuselages "they must not be used in any circumstances". One reason for a pair of rear fuselage tanks was to reduce fuel movement, my understanding is if the 66 gallon option = 2x33 is it was safe to enter combat after one tank was emptied but the improved elevators designed by Westland were needed to carry the rear fuselage fuel in any case. While the extra forward weight of the Merlin 60 series also helped.
Standard Spitfire VIII, 124 gallons internal minus 36 combat gallons and 20 reserve gallons leaves 68 gallons, 330 miles at fast cruise, the standard 90 gallon external fuel tank would be about adequate (23 gallons for warm up and climb, leaving 67 for range). Turning to what if territory, adding a 33 gallon tank to the rear fuselage of the mark VIII means 101 gallons available for range after combat, 160 miles to the possible radius, pushing it to 480 miles, another 33 gallons internal plus the 90 gallon external tank is 123 gallons, less 23 gallons for climb and warm up, leaving 100 gallons for range, not as adequate. It would require 100 to 120 gallons of external fuel to properly exploit the internal fuel.
According to Roger Freeman P-47 radius with relevant external fuel, nominal tank capacity / actual capacity (US Gallons)
75/84 280 miles. In use August 1943
200/205 275 miles. (part filled) In use July 1943.
108/108 325 miles. In use September 1943.
150/165 375 miles. In use March 1944
2x150/165 550 miles. This arrangement "made handling difficult"
200/215 480 miles. In use November? 1944, project initiated in October, took 34 days to deliver the first tanks.
A Spitfire VIII with a 33 gallon rear fuselage tank and a 90 gallon external would have about 350 miles combat radius (theory 407 miles less all the deductions), it would have the range to cover actual Spitfire operations in Europe, like Britain based squadrons escorting raids on the Ruhr area. If the wing tanks could be increased to add another 12 gallons per side that would push the radius towards 400 miles.
Cumulative mark VIII production to end June 1943 was 252, halve that to account for reserves, training and losses and you have 125, around 6 or 7 squadrons, 2 wings, of Spitfires able to reach around 300 miles radius under European conditions in a force able to sustain operations.
Of course first comes convincing the British that after 3 or more years of everyone wants the Spitfire, latest version, never enough, things would change so much in 1943, the P-47 would be effective, the Luftwaffe fighter force would largely pull back, the P-51 would be delayed but then take over from the Spitfire as the everyone wants aircraft, that the loss of production changing Castle Bromwich over to mark VIII was very acceptable as would any slight delay caused by fitting a rear fuselage tank.
As of January 1944 external tanks for Spitfires being made were 30 gallon (Metal, wood, fibre) and 45, 90 and 170 gallon metal. "relevant Spitfire VIII figures from the original sources quoting maximum weak-mixture power setting as 320 mph at 20,000 ft, consuming about 1.1 gallon per minute. This corresponds with an engine setting of 2,400 rpm, +4 lbs boost (66 gallons per hour). So this seems similar. From the same source, the RAF were allocating 23 gallons for take-off and climb to 20,000 ft, and 36 gallons for 15 minutes of combat, leaving 63 gallons for cruise. This gives an endurance of 57 minutes, or a range of 304 miles, for an escort radius of 152 miles." (no reserves)
The mark VIII was 47+49 = 96 in front of the pilot, a 14 gallon tank in each wing = 124, the early IX 48+37 = 85. Under RAF rules the early mark IX range was 434 miles versus the VIII at 660 miles, or an additional 39 gallons for 226 miles, 5.8 miles per gallon at economic cruise, 170 to 200 mph, 30 minutes reserves at economic cruise would be around 15 to 17 gallons, rounded up to 20 for current purposes, given it is unlikely all fuel tanks could be fully drained.
Interestingly the mark VIII pilot's notes mention a 26 gallon rear fuselage tank. Morgan and Shacklady talk about an 18 gallon Mareng bag in each wing for later mark IX, plus 33 or 41 gallon rear fuselage tanks. We know 75 (high back) or 2x33 (or 1x66) (low back) gallon tanks were fitted but these tanks like that of the Mustang needed to be partly emptied to improve stability and probably further emptied before entering combat.
Fuel management, the notes say take off was using the main tank, then at 2,000 feet
a) no drop tank but rear tanks filled, switch to the rear fuselage tanks until empty.
b) drop tank, no rear tanks, switch to the drop tank until empty
c) drop and rear fuselage tanks filled, change to rear tanks until only 30 gallons left in them, then switch to drop tank until empty then back to rear tanks.
Starting with the imaginary longest range Merlin Spitfire fighter version, 96 Gallons in front of the pilot, 36 in the wings, 75 behind the pilot internal, total 207 gallons. Burn 45 gallons of the rear fuselage fuel outbound. That leaves 96+36+30 = 162 gallons on board entering combat at maximum radius, allowing 36 gallons for combat and 20 gallons for reserves leaves 106 gallons, enough for 514 miles at 320 mph at 20,000 feet, outbound fuel available 90 gallons external + 45 gallons rear fuselage = 135 gallons, less 23 for warm up and climb leaving 112 gallons. Nice theoretical balance but you would need the ability to refill the internal tanks from the external ones. And it ignores all the ways range is lost. I suggest start with subtracting about 10% from the theoretical radius for real life operations, what would be good to see is an 8th Air Force P-51 fuel load planning document compared to the official fuel consumption performance figures and then apply them to the Spitfire.
Factors causing loss of range: external tank drag, formation flying, inexperienced pilots, below average performing aircraft, the extra weight (590 pounds of fuel plus tank weights pushing that to around 650 pounds, versus the actual mark VIII, rule of thumb seems to be 1 pound of self sealing fuel tank for 1 imperial gallon of capacity, external metal tanks maybe half of that). Range gain: able to fly economic cruise for a time in and outbound, able to trade height for range inbound, the small distance covered during the climb. Overall result is more than 90 gallons of external fuel required to reach the 514 mile mark. Spitfires were later cleared to carry 1,000 pounds of bombs, 100 imperial gallons of 100 octane fuel comes in at around 711 pounds.
The third edition of the Spitfire mark IX, XI and XVI pilot's notes has rear fuselage tanks with 75 gallons (66 for "rear view" fuselages), permission from the Area Commander is needed to fill the 75 gallon tanks for special operations, while the 66 gallon tanks for "rear view" fuselages "they must not be used in any circumstances". One reason for a pair of rear fuselage tanks was to reduce fuel movement, my understanding is if the 66 gallon option = 2x33 is it was safe to enter combat after one tank was emptied but the improved elevators designed by Westland were needed to carry the rear fuselage fuel in any case. While the extra forward weight of the Merlin 60 series also helped.
Standard Spitfire VIII, 124 gallons internal minus 36 combat gallons and 20 reserve gallons leaves 68 gallons, 330 miles at fast cruise, the standard 90 gallon external fuel tank would be about adequate (23 gallons for warm up and climb, leaving 67 for range). Turning to what if territory, adding a 33 gallon tank to the rear fuselage of the mark VIII means 101 gallons available for range after combat, 160 miles to the possible radius, pushing it to 480 miles, another 33 gallons internal plus the 90 gallon external tank is 123 gallons, less 23 gallons for climb and warm up, leaving 100 gallons for range, not as adequate. It would require 100 to 120 gallons of external fuel to properly exploit the internal fuel.
According to Roger Freeman P-47 radius with relevant external fuel, nominal tank capacity / actual capacity (US Gallons)
75/84 280 miles. In use August 1943
200/205 275 miles. (part filled) In use July 1943.
108/108 325 miles. In use September 1943.
150/165 375 miles. In use March 1944
2x150/165 550 miles. This arrangement "made handling difficult"
200/215 480 miles. In use November? 1944, project initiated in October, took 34 days to deliver the first tanks.
A Spitfire VIII with a 33 gallon rear fuselage tank and a 90 gallon external would have about 350 miles combat radius (theory 407 miles less all the deductions), it would have the range to cover actual Spitfire operations in Europe, like Britain based squadrons escorting raids on the Ruhr area. If the wing tanks could be increased to add another 12 gallons per side that would push the radius towards 400 miles.
Cumulative mark VIII production to end June 1943 was 252, halve that to account for reserves, training and losses and you have 125, around 6 or 7 squadrons, 2 wings, of Spitfires able to reach around 300 miles radius under European conditions in a force able to sustain operations.
Of course first comes convincing the British that after 3 or more years of everyone wants the Spitfire, latest version, never enough, things would change so much in 1943, the P-47 would be effective, the Luftwaffe fighter force would largely pull back, the P-51 would be delayed but then take over from the Spitfire as the everyone wants aircraft, that the loss of production changing Castle Bromwich over to mark VIII was very acceptable as would any slight delay caused by fitting a rear fuselage tank.
I found this to be an interesting document especially the analysis of the Mustang with long range tanks.
The question for me is: "How would a fuel heavy Spitfire performed in combat?" Personally, I'm not convinced that a long range escort Spitfire would have been technically feasible. Not that you couldn't add range, but that the result would be very useful.
The question for me is: "How would a fuel heavy Spitfire performed in combat?" Personally, I'm not convinced that a long range escort Spitfire would have been technically feasible. Not that you couldn't add range, but that the result would be very useful.
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