FLYBOYJ
"THE GREAT GAZOO"
Crack out performance charts and do the math! That will be the proof in the pudding
Escort Fighter Performance Comparison
- Thread starter Zipper730
- Start date
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I'm not guessing anything, get the thing flying and learn, that's what they did with the P51 at the start, they learnt on the go not only with the plane but tactics and planning, it's better than having the things sitting on the coast with only the single 85G main tank and 175 mile radius.
FLYBOYJ
"THE GREAT GAZOO"
How lean? You know when you lean you're raising cylinder head temps? At what RPM? Can you maintain a desired cruise speed and fuel burn? Until you figure this out, you're guessing
Yes they did, that's why I say look in the pilot's manual
It is, and when you "do the math" you many not be "sitting on the coast with only the single 85G main tank and 175 mile radius."
Thumpalumpacus
Major
Not all problems submit to human ingenuity, unfortunately.
FLYBOYJ
"THE GREAT GAZOO"
No Pat - you LEAN a mixture! Or as you say, a "weak mixture" haha
Until you do the math your scenario is a guess. It's that simple just spouting out what you "think" the aircraft will do is meaningless
Food for thought - you bring this up but don't you think someone recognized this 79 years ago? If so, ask yourself why this wasn't done...
33k in the air
Staff Sergeant
- 1,354
- Jan 31, 2021
An article from the Royal Aeronautical Society published in 2017:
Escort Spitfire - a missed opportunity for longer reach?
Escort Spitfire - a missed opportunity for longer reach?
Flyboy, we are talking about two different things mate, I don't mean lean the fuel mixture, I mean learn what works once you get the thing flying, load the Spit with fuel and start flying missions, say 350 miles radius and work out real world consumption figures. Like I posted have the long ranged MkIX's escorted out the first 200 miles by MkV's and P47's so they can save fuel, your not getting to Berlin but who's cares in '42-'43, bomb the Ruhr into a waste land instead.
Spitfire to Berlin? – Making Supermarine's Finest an Escort Fighter There are some good idea's in this one too, everyone seems fixated on Berlin, leave it to the RAF at night and bomb everything else within fighter coverage.
FLYBOYJ
"THE GREAT GAZOO"
OK - but this "could have" been calculated before going on missions and relying on "trial and error." These real world fuel consumption figure "should have" been calculated at the factory wayyyy before they hit a front line unit.
Same could be said for the 109, you have to ask why they weren't fitted with DT's during the BoB, doesn't make sense either.
wuzak
Captain
Maximum cruise speed for a PR.XI (similar to a IX) with Merlin 63 was 397mph @ 31,000ft - 2,650rpm, +7psi boost. Maximum cruise speed at 38,000ft was 378mph - 2,650rpm, +1.1psi boost. These were maximum cruise settings.
@ 28,000ft, 2,350rpm, +3.5psi boost, the cruise speed was 351mph.
So, fast enough, but I don't know the fuel consumption at those settings.
Mk.IX fighter will be draggier, so will be a few mph down, Merlin 66 models will have lower critical altitudes, so lower speeds again. Merlin 70 Mk.IXs (HF.IX) would be about the same as the XI.
FLYBOYJ
"THE GREAT GAZOO"
Geoffrey Sinclair
Staff Sergeant
- 931
- Sep 30, 2021
If you make up a Spitfire VIII using the various maximum size fuel tanks ever fitted to Merlin Spitfires with the external and/or rear fuselage tanks able to refill the main tanks after take off, the theoretical combat radius comes to around 500 miles, cruising all the way at maximum weak-mixture power setting of 320 mph at 20,000 feet using 66 gallons per hour, corresponding with an engine setting of 2,400 rpm, +4 lbs boost. Which translates to much but not all of Germany when based in England, taking direct courses. The requirements for combat, reserves and the need to burn off some of the rear fuselage fuel before combat means the external fuel limit is about 90 gallons.
When the Ministry of Aircraft Production began reporting external fuel tank production in December 1943 Spitfire 90 gallon tanks were being made at about 500 per month.
The standard Spitfire VIII with a 90 gallon external tank could go about as far as the 1943 P-47, add a 33 gallon rear fuselage tank the ability to fight with it still full and it can go about as far as the 1944 P-47.
There are plenty of reasons why a longer range Spitfire would be nice to have over and above escorting long range bombers but the need for the escort mission in 1944 can be seen from the amount of use made of RAF P-51s, I do not have the numbers but understand some but not a lot of such sorties. Certainly the USAAF would have liked more long range escorts available up to around May 1944. Probably if the RAF had offered the 8th Air Force the equivalent of 1 to 3 fighter groups of long range Spitfires in mid to late 1943 the arrangements would have continued into 1944, but you would expect with the RAF P-51 units replacing the Spitfire ones. The Spitfires then take advantage of their longer range on missions over France then from September 1944 onwards while being based in Britain able to escort Bomber Command day missions over Western Germany, Bomber Command was not going to do deep penetration day raids.
The RAF did not like the way Sidney Cotton was running the reconnaissance unit, more as a collection of civil pilots than a military unit. Also in building up the unit Cotton did what he felt he needed to do, rather than go through the slow official channels, finally a few times Cotton had done what the RAF powers that be had said was not possible, in at least one case to the Admiralty's delight. It also probably did not help he was part of the pre war spying system.
The early Spitfire PR types are a maze of fuel and camera installations, conversions would have further conversions. N3069 and N3071 were the original prototypes, arrived 13 October 1939, they were initially fitted with cameras but no extra fuel. The plans were to have a range of 1,000 miles on internal fuel. N3116 and 3117 arrived 4 February and P9307 to 9310 on 11 February 1940.
When designations were handed out Type A was for N3069 and N3071 as orginally modified, PR IB or type B short range was for them fitted with a 29 gallon under seat tank, PR IC or type C long range was for a new camera fit, along with 30 gallons under the pilot seat and 30 gallons in a fixed blister under the port wing. The type D was for the wing leading edge fuel tanks which did away with the need for the under seat tank. One census says 68 mark I and 27 mark V were converted to the PR types but that includes many of the 32 mark I officially built as PRIII. PR mark III production began in August 1940, PR mark IV in June 1941.
When the Ministry of Aircraft Production began reporting external fuel tank production in December 1943 Spitfire 90 gallon tanks were being made at about 500 per month.
The standard Spitfire VIII with a 90 gallon external tank could go about as far as the 1943 P-47, add a 33 gallon rear fuselage tank the ability to fight with it still full and it can go about as far as the 1944 P-47.
There are plenty of reasons why a longer range Spitfire would be nice to have over and above escorting long range bombers but the need for the escort mission in 1944 can be seen from the amount of use made of RAF P-51s, I do not have the numbers but understand some but not a lot of such sorties. Certainly the USAAF would have liked more long range escorts available up to around May 1944. Probably if the RAF had offered the 8th Air Force the equivalent of 1 to 3 fighter groups of long range Spitfires in mid to late 1943 the arrangements would have continued into 1944, but you would expect with the RAF P-51 units replacing the Spitfire ones. The Spitfires then take advantage of their longer range on missions over France then from September 1944 onwards while being based in Britain able to escort Bomber Command day missions over Western Germany, Bomber Command was not going to do deep penetration day raids.
The RAF did not like the way Sidney Cotton was running the reconnaissance unit, more as a collection of civil pilots than a military unit. Also in building up the unit Cotton did what he felt he needed to do, rather than go through the slow official channels, finally a few times Cotton had done what the RAF powers that be had said was not possible, in at least one case to the Admiralty's delight. It also probably did not help he was part of the pre war spying system.
The early Spitfire PR types are a maze of fuel and camera installations, conversions would have further conversions. N3069 and N3071 were the original prototypes, arrived 13 October 1939, they were initially fitted with cameras but no extra fuel. The plans were to have a range of 1,000 miles on internal fuel. N3116 and 3117 arrived 4 February and P9307 to 9310 on 11 February 1940.
When designations were handed out Type A was for N3069 and N3071 as orginally modified, PR IB or type B short range was for them fitted with a 29 gallon under seat tank, PR IC or type C long range was for a new camera fit, along with 30 gallons under the pilot seat and 30 gallons in a fixed blister under the port wing. The type D was for the wing leading edge fuel tanks which did away with the need for the under seat tank. One census says 68 mark I and 27 mark V were converted to the PR types but that includes many of the 32 mark I officially built as PRIII. PR mark III production began in August 1940, PR mark IV in June 1941.
drgondog
Major
Begging he question 'why not'?
drgondog
Major
PAT303 - If you wish, first get the RPM/Boost and fuel burn rates for warm up, take off, form into squadron, climb to cruies, cruise to RV, fight for 20 minutes, cruise back, descend, loiter reserve for 20 min at low RPM/Boost.
http://www.wwiiaircraftperformance.org/mustang/P-51D_15342_AppendixB.pdf Try this for 1650-7 recognizng that the Spit IX drag is greater and probably not able to achieve same speed for same burn, even with less Induced drag at cruise.
http://www.wwiiaircraftperformance.org/mustang/P-51D_15342_AppendixB.pdf Try this for 1650-7 recognizng that the Spit IX drag is greater and probably not able to achieve same speed for same burn, even with less Induced drag at cruise.
It does doesn't it, let me ask a question, when it comes to ANY Spitfire conversation what is the first thing people say was the Spits biggest problem, lack of range, every single time, lack of range, even the RAF knew it, they even went to all the trouble of making this abomination.
drgondog
Major
That chart s wrong on so many levels. The Combat Radius for the P-47C without belly tank was 125+ mi CR. The Combat Radius of the P-47C/D with 75 gal c/l tank was 230mi (Aug 1943),with 2x150gal pylon tanks was 425mi circa March/April 1944. These values for 25K cruise zone altitude.
To be in ballpark for Spit IX and comparative, you need cruise speed without 90 gal tank (outbound), with 90 gal tank from takeoff through climb through cruise and into combat, need fuel consumtion at at least MP butAAF doctrine specfied 15min MP, 5 min WEP. Then cruise clean with reduced internal weight from fuel consumed. I suspect that optimal cruise stated in miles per gallon are less in a Mark IX than the cleaner Mustang III by at least 1/2mpg.
BUT, the MOST critical variable is Internal fuel available after extended Radius 'projection' is reached and 20 minuts of combat has burned an hour of cruise fuel in 20 minutes.
For the simple answer 'why not', consider the P-51B-7 with 85 ga fuse tank had 269gal internal fuel to the 85 gallon Spit values. AND - same basic engine and about 20% lower total Drag.
Shortround6
Major General
Fixed it for you for the nit pickers.
So even in the Summer of 1943 (July 1st 1943 date on P-51B manual) the P-51B has 150 imp gallons of internal fuel. Super Spit is going to need an extra 65 gallons of internal fuel to match plus and extra 20 imp gallons to cover the difference in drag (figuring 13.3% more for drag to be generous) or 170 imp gallons internal. P-51B had 125 imp gallons external in the drop tanks (pair of US 75 gallon).
The US later figured that a P-51 without the rear tank and with a pair of 75 US gal drop tanks was good for a 460 mile radius.
US and the RAF may have used slightly different engine limits. US used 2320rpm and 36in (3lbs ?) boost as the provisional limits (July 1943 remember) on the Merlin V1650-3 for lean mixture. The British may have used 2400rpm and 4lbs for lean mixture?
At 2600-2700rpm and 7lbs of boost (rich mixture) the engine can be burning about double the GPH that it did at max lean.
The provisional range tables in the July 1943 manual show the P-51B running right on the edge of shifting to rich mixture. 215 IAS at 25,000ft with the pair of 75 US gallon drop tanks require 2350rpm and FT and 65 US GPH.
Running at 210IAS at 25,000ft with tanks requires 2250rpm at FT but only 52 US GPH.
Now the later manuals show some restrictions on the rear fuselage tank. Like at over 1/2 capacity when doing a tight turn or pull out the airplane will under go elevator reversal. Just like it sounds the plane will go in the opposite direction the pilot intends. This tendency gets less as fuel is burned off until at about 1/2 tank it goes away. This why both the Mustang and the Spitfires with rear tanks tried to burn off a fair amount of the rear tank fuel before switching to the drop tanks.
However for the Spitfire this also means that when the drop tank is dropped you only have the remaining fuel in the internal tanks. Which at absolute best ( 96 Imp gal for the two main tanks +26 IMP gal for the wing tanks + about 30 IMP gal for the rear tank (the 2nd rear tank having been used up) and using 54 imp gal for 20 minutes combat leaves about 98 Imp gal to get home.
Now we are arguing over the exact tank fitment. And the amount of fuel the Spitfire can keep in the rear tank/s and still fight for the average pilot.
And arguing about difference the difference is between the Spitfire and the Mustang speed/fuel burn.
PR Spits were not supposed to fight, they were supposed to run.
