Did the RAF have designs for a long range escort fighter? (1 Viewer)

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Forgive the Wall-O-Text, but: The RAF had a viable design for a long-range escort fighter: the Spitfire.

Sounds odd I know, but it's not actually that unbelievable. Hear me out.

During 1937-1940, the RAF significantly developed the Spitfire Mk I for PR work, with a range of different fuel options. The PR Mk IB had a 29 gal fuel tank behind the pilot. It was unstable when the fuel tank was full, but once most of the fuel had burned off, the handling of the aircraft was almost as good as a regular Spitfire.

There was also the PR Mk ID, which had an extra 66 gal in the wings, replacing the armament and giving a total 218 imperial gallons. No rear tank was fitted though, as the aircraft balance was affected. It also had a larger oil tank, somewhat marring the wonderful lines of the nose.

Spitfire Mk Vs shuttled to Malta were successfully flown off aircraft carriers with 29 gal and 33 gal rear fuselage tanks, although they were removed once the aircraft got to Malta. The Mk Vs also flew with 29 gal rear tanks AND the 90 or 170 gal ferry tank (for a total of 284 imperial gallons).

Later in the war (late 1944) the RAF began fitting some Spitfire XVIs and Spitfire IXs with rear fuselage tanks of 41 gal total capacity. Versions with bubbletops had 33 gal.

There was also the PR Mk ID, which had an extra 66 gal in the wings, replacing the armament and giving a total 218 imperial gallons. No rear tank was fitted though, as the aircraft balance was affected. It also had a larger oil tank, somewhat marring the wonderful lines of the nose.

When time came to improve the Spitfire in 1939-1940, Joseph Smith came up with a couple of proposals for the Mk III. One of the main ones, which was eventually rolled into the Mk VII/VIII airframe was the enlarged front tanks, increasing standard fuel capacity from 85 to 95 imperial gallons. The Mk VII/VIII airframe also had two 12.5 gallon fuel tanks, in the leading edge of the wings, near the wing root.

If the airships in the Air Ministry, Portal in particular, hadn't been so opposed to the idea of a long range, single seat, single engine fighter in the late 1930s and early 1940s, then a Spitfire with double the range was practical, even in 1940/1941.

I believe that the rear-fuel tank is practical in the post-1940 period for the Spitfire, with a bit or re-arranging of some of the rear fuselage accessories:

A regular Mk V had 85 imperial gallons, and a standard range of 480-500 miles at best cruising conditions. With warm up, climb, fast cruise, combat and reserve allowances, the practical combat radius is about 170-80 miles. Rough rule of thumb is that RAF combat radii were between 35% and 37.5% of cruising range, perhaps a little more as range gets longer.

If we go with two concepts available and flying in Spitfires in 1940 – the enlarged nose tank and the rear fuselage tank – then internal fuel goes from 85 imp gal to 124 imp gal, an increase of about 45%.

Still air cruising range goes up to about 700-730 miles, and combat radius goes up to nearly 250 miles.

However, the big boost comes once you start adding external tankage. Drop tanks were fitted to Spitfire Mk Vbs about half-way through 1941. They came in many flavours, but the standard sizes in 1941 and 1942 were 30 imp gal and then 45 imp gal.

With a 45 imp gal slipper tank, total tankage goes to 169 imperial gallons, or just under double the fuel of a Mk I or Mk II.

So my theoretical 1941 long-range Spitfire Mk V would behave like this.

Allowances:

Warm-up/taxi/take-off (90 gph): 10 gal, no distance, 159 gallons left

20 minutes climb to 20,000 ft @160 mph (32 gph): 13 gal, 50 miles, 146 gallons left

Combat:
5 minutes at full throttle (90 gph): 7.5 gal, 30 miles, 138.5 gal left
15 minutes at fast cruise @ 315 mph: (67 gph): 17 gal, 80 miles, 121.5 gal left

Reserve:
30 minutes reserve @ 220 mph (32 gph): 16 gal, no distance [as its reserve], 105.5 gal left

Range cruise:
3 hours 20 minutes at range cruise @ 220 mph (32 gph): 105.5 gal, 730 miles, 0 gal left.

Total distance:
Climb – 50 miles
Combat – 100 miles
Cruise: - 730 miles
Total: ~880 miles
Combat radius: ~310 to 330 miles.

For every 5 minutes at full power, you can cut about 60-65 miles off the total range. For every five minutes at fast cruise, you can cut about 30-40 miles off the total range.

880 miles range is not too far off Mk VII/VIII performance (it might actually be understating the range a little). With 120 gal internal, the Mk VIII had still air cruise range of 660-740 miles and with a 45 gal slipper tank it had range of 885-940 miles, depending on whether it dumped or retained the slipper tank. The Merlin 66 also consumed a LOT more fuel at full boost of +18 than the Merlin 45 did at +9/+12. In 1944 Mk VIIs did bomber escort trips of 690 miles (round trip) to La Pallice and Mk IXs and Mk VIIs over 600 miles to Meerbeck and Emden.

You can probably quibble with some of the fuel consumption and speed figures, but I've used the RAAF Spitfire Mk Vc figures for 1943 as my baseline. The RAF might have flown at higher boost settings and thus got less range out of their Spitfires.
 
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Don't forget that your long range Spitfire could meet enemy fighters and I don't like the idea to have to fight against Fw 190 or Bf 109 in such a plane over Germany.
cimmex
 
...The RAF had a viable design for a long-range escort fighter: the Spitfire. ...

Hello Jabberwocky, Your post reminded me of USAAF flight tests of a Spitfire IX modified for long range:

Spitfire_IX_Long-Range-29may44.jpg

(click on body of image for full size)

Spitfire_IX_MK210-600.jpg
 
Thanks for the insight, Aozora.
Do we know length of the Vulture and war-time Sabres (all with accessories)? The Tornado having no 'weight stability issues'?

added: Sabre II V were 82.2in long, according to the pdf available at WIlliams' site.
added 2: image (here) shows Vulture installation in Tornado. Good call, Aozora, the auxiliary systems seem to take much more space than those of Sabre.
added 3: wuzak's info, from another forum:

The info about the Tornado's flight characteristics vs the Typhoon comes from Crowood's "Hawker Tempest, Typhoon and Sea Fury" by Kev Darling - unfortunately I'm needing a new scanner...
 
No sweat, Aozora, your post # 79 here is spot-on :)

The US-modified Spitfire Mk.IX was outfitted with 43 imp gals tank behind pilot, 2 x 16.5 IG in wing leading edges, and was carrying 2 x 62.5 IG drop tanks.
The Spitfire IX was able to receive the increase of 11 IG for main fuel tanks, ie. from 85 to 96, too. Like it was done for the Mk.VIII from start. The 160-170 IG means ~200 US gallons, that compares well with P-51s without fuselage tanks.
 
Unfortunately, the rear fuselage tanks of the Spitfires were being conceived more as a thing that would increase ferry range (removed from the plane after ferry flight), than something that would be, on purpose, used in combat?
 
Part of the problem is not how much fuel you can stuff in the plane but what kind of handling or "G" loading can it take at various fuel loads. And how the different weight locations affect the center of gravity and handling. Flying a ferry flight with a large fuel load and NEVER pulling more than 2 "G"s is one thing. Many of these planes had flight restrictions with full INTERNAL fuel. Mustangs were good for 8 "G"s at 8,000lbs. at 10,000lbs they were SUPPOSED to be restricted to 6.4 "G"s. Throw in the fact that with some tank location/s full tanks overloaded the local structure and had the plane operating at a less than ideal center of gravity situation (Mustangs were SUPPOSED to burn down the rear fuselage tank to 25 gallons BEFORE switching to drop tanks in peace time).
 
The Spitfire PR Mk IV would took off with 218 IG of fuel, most of the fuel being carried in the leading edge tanks (2 x 66 IG).
 
An "overfuelled" Spitfire was hardly combat capable. The PR ID was nicknamed "the flying bowser". It also carried extra oil,something often overlooked when people increase the theoretical endurance of WWII aircraft.

Wing Commander Tuttle.

"You could not fly it straight and level for the first half hour after take-off. Until you had emptied the rear tank,the aircraft hunted all the time. The centre of gravity was so far back you couldn't control it.It was the sort of thing that would never have got in during peace time,but war is another matter."

Cheers

Steve
 
Reading the report kindly provided by Mike, the Spitfire with 40 imp gals left in the rear fuel tank seem like a combat-worthy airplane?
 
Getting back to the original question: I've now got a copy of British Aircraft Specifications 1920-1949 by Meekcoms and, after a quick look there were no pre-war or wartime specs issued for long-range escort fighters: some examples of specifications issued were:

F.17/39 which was issued around the Beaufighter: The endurance is to be sufficient for 15 minutes at maximum power for level flight, plus 3 hours at most economical cruising speed for duration, plus 1 hour at maximum power for level flight at 15,000 ft.

F.16/40 Vickers-Armstrong fixed cannon gun fighter (Vickers 414): Permanent fuel for 15 minutes at maximum power plus 2 hours at most economical cruising speed at 15,000 ft. plus 15 minutes at maximum power at 20,000 ft. Eight 20 mm cannon guns mounted to fire forward...

F.21/40 Mosquito fighter conversion: Fuel shall be provided for 15 minutes maximum power at sea level for take-off and climb, 3 hours at most economic cruising speed at 15,000 ft. for patrol, and 15 minutes at maximum power at 21,000 ft. for attack.
 
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An "overfuelled" Spitfire was hardly combat capable. The PR ID was nicknamed "the flying bowser". It also carried extra oil,something often overlooked when people increase the theoretical endurance of WWII aircraft.

Wing Commander Tuttle.

"You could not fly it straight and level for the first half hour after take-off. Until you had emptied the rear tank,the aircraft hunted all the time. The centre of gravity was so far back you couldn't control it.It was the sort of thing that would never have got in during peace time,but war is another matter."

Cheers

Steve

If instability for the first half an hour to hour of flight is the only draw-back, I'd suspect the RAF would have gladly accepted it. Only two of the PR MK ID/Mk IVs had the rear fuselage tank anyway. The rest were built without the 29 gal rear tank.

Armed, Merlin powered Spitfires proved capable of operating with more than 210 imperial gallons, on combat missions. Drop tanks were a bit of a game changer.

In late-build Mk IXs it was found that when the extra rear fuel tanks (44 gal) were fitted, the aircraft became longitudinally unstable above 145 mph - the Spitfire never having the best longitudinal stability anyway. As speed increased, the aircraft became progressively less stable and required constant 'hands on' flying to remain straight and level.

By the time 1/2 the rear tank had been burned off (22 imp gal - about 70 kg) the Spitfire began to return to normal behaviour. It was recommended that a Spitfire not engage in combat before before the rear fuel tank was emptied though.

The implication for this is that the rear tank must be the first used in the aircraft. With my proposed/theoretical long-range Mk V with the 29 gal rear fuel tank, this is actually solved fairly simply by a little juggling of tanks during flight.

Warm-up, taxi and take off consume around 10 gal. I'd suggest the rear fuselage tank is used for this.
Climb to 20,000 ft would consume another 13-17 gal. I'd actually suggest that the 30/45 gal drop is used for climb.
Then the pilot switches back to the rear fuselage tank to use up the remainder of the fuel in the tank. The remaining 19 gal is enough for about 35 minutes slow cruising (220-225 mph), or for about 15 minutes at fast cruise (315-330 mph). If form up occurs over the Channel, that means the pilot is still only going to be about 100-120 miles into France, at best.

With the rear tanks used for warm up/take-off and the drop tanks used for climb out/form up, the Spitfire still has full front tanks (95 gal) and either 13 gal or 28 gal left in the drop tanks, around 70% of total fuel load left. Even if the pilots are required to 'pickle' their tanks off early, 95 gal is still enough for 15 minutes at fast cruise, five at full combat power and then another 2 and a bit hours at a cruise speed of 220-225 mph (32 gph), or about 1 and a half hours at a slightly more aggressive speed/fuel setting (45 gph and 285-290 mph).

Its still a 4 hour aircraft, not a seven hour aircraft like the later P-51s, but with the rear tank and drop tank its no slouch. In 1942/early 1943, the Spitfires of the RAF were limited to a combat radius of 200-210 miles and usually operated no further than 175 miles. The P-47 had a radius of about 240 miles, but usually operated no further than 210 miles. By mid-1943 the P-47's practical radius is out to 250-275 miles (with 75 gal external tank), and it takes until late in 1943 before its over 350 miles (with 108 gal tank).

Load up the Spitfire with the big forward tanks and the rear fuselage tanks and all of a sudden you've got a bird with a pratcial 275-300 mile combat radius in late 1941/early 1942. That's far enough to maybe support the 8th AF out to the German border, possibly the Rhur, depending on flight profile/route taken.
 
An "overfuelled" Spitfire was hardly combat capable. The PR ID was nicknamed "the flying bowser". It also carried extra oil,something often overlooked when people increase the theoretical endurance of WWII aircraft.

Wing Commander Tuttle.

"You could not fly it straight and level for the first half hour after take-off. Until you had emptied the rear tank,the aircraft hunted all the time. The centre of gravity was so far back you couldn't control it.It was the sort of thing that would never have got in during peace time,but war is another matter."

Cheers

Steve

Now on LR escort mission the Spit would have used the fuel in the rear tank before the contact with enemy fighters in ETO (targets in Eastern Holland, NW Germany). Of course one would not use routes that crossed the Strait of Dover with full rear tank, that would have been too risky, but filled with amount of fuel needed to cross Channel it would still have been useful for range extension.

Juha
 
P-51 had the same flight restrictions when the fuselage tank was full of fuel. It managed to do OK in the escort job.
 
Hello Steve
is that from post-war PN as mine, 1946. In peacetime safety consideration have more weight than in wartime.

Juha
 
In peacetime safety consideration have more weight than in wartime.
Juha

Maybe,within reason. Is their any evidence that the advice was contarvened during the war? Did those Marks of Spitfire operate routinely with filled rear tanks?
Cheers
Steve
 

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