Escort Spifire

[drgondog]

Shortround noted on subject of single engine vs twin engine fighters "It turns out that most of them weren't very good escort fighters but shows that most air staffs didn't believe it was possible to build single engine long range escorts."

The primary AAF Combat leaders, notably Spaatz and Eaker, did not believe that a long range single engine, high altitude capable fighter was possible in the formative years leading to WWII as well as 'observer status' in 1940-1941. The change from "impossible to maybe" was fueled by the progress reports from Tommy Hitchcock during the RR/RAF experimental conversion MustangX. The conversion from "Maybe to Probable" was fueled by the early performance achieved with the XP-51B 41-37352 between December 1942 to flight tests under AAF control at Eglin in May 1942. The conversion of "Probable to Practical" was stimulated by NAA rapid response to General Barney Giles directive to NAA to increase internal fuel in June 1943, followed by first flight w/85 gallon fuselage fuel tank on July 14, 1943.. Then it was all about NAA being able to craft a field modification 85 gallon fuselage tank kits (plus oxygen supply relocation and increased capacity) while the production insertion was placed at the first P-51B-10 and mid C-5 blocks.

"A P-38 on internal fuel (410 gallons) had an operational radius of 275 miles as outlined above. The P-51B with out rear tank was godd for 150 miles and a P-47 with 305 gals internal was good for 125 mile radius and with 370 internal was good for 225 miles."

SR - the timing of the 2x55 gallon leading edge kits was about 2 months following the installation of the first US Depot mods for the P-51B-5. The first ETO bound 85 gallon kits for the P-51B-1 and -5 already in theatre was December 1943.

The first 55 gallon LE tank kits for the P-38J were released in December, 1943 for delivery to ETO (first) and were retro-fitted to J-5 and -10 already delivered to 55th and 20th FG's. Until the first Berlin missions in March 1944, the P-38 FGs did not have enough conversion kits installed to effectively send in Group level quantity to Berlin. The P-51B groups were going to Schweinfurt during Big Week beginning Feb 20. Until that late February 1944 timeframe the P-38J on 300 gallons of fuel had a Combat radius of 150 miles, the P-51B on 184 gallons was 150 miles, and P-47D on 305 gallons was 125 miles - all at 25,000 feet. The P-47D-25 with 370 gallons had an extended Combat Radius of 225 miles but not in Group level combat ops until July, 1944.

The addition of 110 gallons (from 300 to 410) for the P-38J took the CR to 275mi; the addition of 85 gallons for P-51B/C (from 184 to 269) took the CR to 375 miles - still 150 miles past the best range of the P-47D-25 and 100 miles past the P-38J-15 through L.

"Early P-38s without self sealing tanks would hold 400 gallons, the self sealing tanks dropped capacity to 300 gallons and the lat emodels with under engine intercoolers and leading edge tanks went to 410 gallons.

The P-38 was not designed as an escort fighter but as an interceptor with twice the endurance of a single engine interceptor and shows the problems the designers of the time had in providing single engine performance with high endurance/long range."

Historically, both Spaatz and Eaker were both 'becoming convinced' that the P-51B was probably going to emerge as the preferred escort fighter by the end of October 1943 as it became clear that the P-38H was experiencing too many operational issues and even with external tanks, the P-47D-25 was not getting to ETO for another nine months.

 

[Shortround6]

Thank you Drgondog, I was using the P-38 more as an indicator of what was possible in 1937-40 rather than suggesting it as a solution later in the war.
The requirement that lead to the P-38 called for an interceptor (not escort fighter) that had the same armament, same top speed and and same climb to altitude as the requirement that lead to the P-39. ONLY difference was the requirement that lead to the P-38 called for twice the endurance at speed.
"Kelly" Johnson figured that the performance could be met using a single engine of 1500hp (1000hp was needed for the primitive P-39) but since no 1500hp engine was available (1937) he went with two 1000hp engines.

Both requirements/specifications were modified before hardware flew.

When trying to adapt an existing fighter to the long range escort role something has to give. Or several somethings. Airfield length, rate of climb, turning ability, both size of circle and the ability to maintain height in a tight turn. Loss of speed with extra internal fuel is probable the least of the problems.

 

[pbehn]

If the P51 was designed from the start as an escort fighter is there anything that would be changed?

 

[Tkdog]

I think you can look at what they did with the later models and see the answer. Also the twin mustang for very long range escort. That's as about as far as propellers were going to take them.

 

[pbehn]

I think you can look at what they did with the later models and see the answer. Also the twin mustang for very long range escort. That's as about as far as propellers were going to take them.

The P 51H was of course a new plane but based on the earlier models, I was wondering if there were any parts of its design that could have been improved.

 

[Shortround6]

If the P51 was designed from the start as an escort fighter is there anything that would be changed?

It was designed in early 1940.
In early 1940 what did you have for engines in the immediate future?
AS in Historically they had built 138 Mustangs by Jan 1st 1942. You need a viable, in production engine in the summer of 1941.

 

[wuzak]

If the P51 was designed from the start as an escort fighter is there anything that would be changed?

The problem is that the engine that made the P-51 viable as a long range escort didn't exist* when the NA-73X was being developed.

The other issue was that the NA-73X was developed under British contract and, as has been mentioned previously, the British didn't much need long range escorts because they quickly moved to night bombing.

*The 60-series Merlin was being developed around that time as a high altitude bomber engine. But I doubt anybody knew anything about it in the US. The 60 series Merlin was dropped into a Spitfire III airframe, which first flew in September 1941. An equivalent V-1710 was years away as well.

 

[pbehn]

I was just wondering if the P51D had any fundamental flaws in service which could have been avoided with 20/20 hindsight

 

[wuzak]

I was just wondering if the P51D had any fundamental flaws in service which could have been avoided with 20/20 hindsight

If they had known they were going to use a more powerful engine with 4 blade prop they may have added extra control/stabilizer surface area to enhance stability.

As they did with the H.

 

[drgondog]

If the P51 was designed from the start as an escort fighter is there anything that would be changed?

By 8th AF definition, an escort fighter had to have long range and adequate fighter vs fighter maneuverability and speed at bomber altitudes.

Well, not speaking for Schmued but - The only inline engine available was the V-1710 single stage/single speed supercharger, which was inadequate from the very beginning without turbos - Whatever came out of NAA in 1940 would not be the P-51.

 

[stona]

By 8th AF definition, an escort fighter had to have long range and adequate fighter vs fighter maneuverability and speed at bomber altitudes.

Exactly, and herein lies the British problem. The bombers were expected to operate by day (in 1938 most missions were expected to be by day, despite the blurring of the line between night and day bombers) and be self defending.
The RAF's latest fighters were, as Saundby, then Director of Operational Requirements explained in May 1939

"...intended for Home Defence i.e. the destruction of enemy bomber aircraft in circumstances in which they are unlikely to meet with enemy fighter aircraft."

To this end endurance had been intentionally sacrificed to give advantages elsewhere, principally speed and firepower.

The British had a long range fighter in 1940. It was NOT the result of an Air Staff Requirement, but had been offered by Bristol as a cannon fighter that could be quickly developed by a redesign of the Beaufort torpedo bomber. The resulting Beaufighter did find a niche as a long range fighter, particularly in a maritime protection and anti-shipping role, but an escort fighter it most certainly was not.

As the 8th AF's requirements show, a suitable fighter to escort the bombers, in circumstances where it would certainly meet with enemy fighters, required more than just the necessary range.

Cheers

Steve

 

[drgondog]

The P 51H was of course a new plane but based on the earlier models, I was wondering if there were any parts of its design that could have been improved.

The XP-51F early test flights in February/March, 1944 with the 1650-3 highlighted the continued lack of yaw stability experienced with the P-51B/C following introduction of Merlin 61/four blade prop system. Ditto the XP-51G and J later. It should be noted that the NA-105 contracts began at the same time the XP-51B emerged and ran parallel to the introduction of the P-51B/C and D. The dimensions were very similar to the P-51B/C/D.

Given the experiences of the yaw stability noted in the very early RAF/RR testing, first the DFF was introduced as a retro fit kit, then installed in production beginning with P-51D-5-NA 44-13903 and P-51C-10-NT 44-107253, then the tall tail was tested on P-51D-5 at both NACA and NAA, then both were introduced in the NA-105 XP51G in middle of flight tests.

The experiences of Mustang X in 1942 through February 1944 with P-51B/C/D and XP-51F led to major P-51H design changes including extending the fuselage length , reducing the fuse tank volume and size, moving the engine CG slightly forward and increasing the empennage area by ~20%,to make substantial improvements in yaw stability.

Interestingly, the AAF did not buy the XP-51G as the projected range of the XP-51G without fuselage fuel tank was only 70 mile combat radius more than a conventional P-51B-1 before kit inst'l. That said it made with combat load, 45,000 feet ceiling (limited by no cabin pressurization), 495mph level flight speed and climbed 7,500 feet per minute. It would have matched any interceptor in the world in 1944

 

[stona]

When I see claims for the speed of the P-51 on long range missions I am reminded of an anecdote told by Leon 'Woodie' Spears, who surely needs no introduction here.

"I had an air combat encounter in Kitten when my flight of about five aircraft escorted a... I believe it was a British Mosquito reconnaissance plane over a target area. He led us while we kept him in sight. We escorted him to the Munich area to this German ball bearing factory. As soon as he started his photo run, we backed off a little so he could do his work. He had to fly straight and level. The Mosquito was a very fast plane. When we came back from the target area he just out ran us. We could not keep up with him because of his speed. We heard him say on the radio "Ta, ta, chaps!""

Cheers

Steve

 

[Jugman]

The Sabre engine should have been shot, stabbed and strangled while still in the crib. And the remains disposed of well out to sea. The Griffon was effectively a 2000hp engine. Considering that a single stage Griffon was 700lbs lighter than a Sabre and a two stage griffon was still 500lbs lighter.

I agree with the sentiment but your weight range is a little bit over the top. An early single-stage Griffon weighed in at ~1900lbs and a the two-stage models ~2090lbs*. The Sabre II weighed in at 2360lbs and the Sabre VII at 2540lbs. The lighter weight figures often seen for the Griffon (1790/1980 Single/Two-stage) appear to be without the ignition system and carburetor. I have seen a pretty consistent 110lbs variation in weight between the same or very similar models. For example Lumsden lists the weight of the Griffon 57 as 2050lbs. but the manual says it weighs 2160lbs. The weight of the ignition system and carburetor should cover that difference.

Specific weight between them was pretty close. Really the big problem with the Sabre was that it cost so much more per hp than other engines in its power range.

 

[pbehn]

The Sabre had many other problems other than cost per horse power. In the field in winter in France they had to be kept warm or they wouldn't start meaning that were started and run periodically through the night. Apart from the man hour imposition on ground staff France is not that cold in winter, if they were on the eastern front I doubt the engines could be allowed to stop for more than minutes.

 

[chuter]

..
Rolls Royce Mustang conversion

...

A purely parenthetical post:

Hey! This photo shows one of the several enlarged tail fins of the RR Merlin Mustang prototype. This one is has the fin leading edge extended forward like the early P-40K fin but without the P-40K's additional dorsal fillet extension. All this because of the destabilizing effect of the extra prop blade and, in this installation, the barn door like cowl sides.

Carry on.

 

[wuzak]

If, after the BoB, you decided you want to have a LR fighter Spitfire, would you concentrate that effort on the Griffon Spitfires?

The Griffon Spitfire was under development since 1939. The IV first flew in late 1941 (about the same time as the III + Merlin 61).

 

[Juha2]

I noted that the article doesn't mention Mk VII, only 140 built but they flew the longest Spit escort mission in the ETO I'm aware of.

Hello
PR Spits were able to cover Berlin, at least, from GB.

Longest Spitfire escort mission in ETO I'm aware was that made by 131 Sqn on 11 Aug 44 to La Pallice, 690mls and took 3 hours 50 min. They were flying Spit VIIs.

Juha

According to Jefford's RAF Squadrons their base at that time was RAF Culmhead, situated at Churchstanton on the Blackdown Hills in Somerset, England. The straight line distance between Culmhead and La Palliceen is appr. 550 km/340 mls. IIRC the distance was so long that the escorting Spits would not have had much fuel for combat if the LW had intercepted the bombers but it was predicted that the mere sight of the Spits would be enough to keep German fighters for attacking the bombers at that stage of the war and so it happened the few German fighters sighted declined to engage. Spit Mk VIII, non-pressuried Mk VII, could achieve with a 90 ImpGal drop tank 6.6 AMPG at 291 mph TAS.

Other point is the claim in the article that "Compared with the slippers, the torpedoes were little used." When one looks the photos in Shores & Thomas, 2nd Tactical Air Force Vols 1 - 4, when Spits have a drop tank it is almost invariable a 44 gal torpedo type.

I agree with the critics of the article, too iffy for me too, and Mk IXs were coming out in large numbers from Castle Bromwich just because it was a rather simple development from Mk V, to produce Mk VIIIs with its reinforced fuselage and other mods there would have meant less production because of the need changes in production resources. Same disturbances would have happened if they would have wanted the mods in the fuselage and wings of Mk IX mentioned in the article.

 

[Peter Gunn]

The XP-51F early test flights in February/March, 1944 with the 1650-3 highlighted the continued lack of yaw stability experienced with the P-51B/C following introduction of Merlin 61/four blade prop system. Ditto the XP-51G and J later. It should be noted that the NA-105 contracts began at the same time the XP-51B emerged and ran parallel to the introduction of the P-51B/C and D. The dimensions were very similar to the P-51B/C/D.

Given the experiences of the yaw stability noted in the very early RAF/RR testing, first the DFF was introduced as a retro fit kit, then installed in production beginning with P-51D-5-NA 44-13903 and P-51C-10-NT 44-107253, then the tall tail was tested on P-51D-5 at both NACA and NAA, then both were introduced in the NA-105 XP51G in middle of flight tests.

The experiences of Mustang X in 1942 through February 1944 with P-51B/C/D and XP-51F led to major P-51H design changes including extending the fuselage length , reducing the fuse tank volume and size, moving the engine CG slightly forward and increasing the empennage area by ~20%,to make substantial improvements in yaw stability.

Interestingly, the AAF did not buy the XP-51G as the projected range of the XP-51G without fuselage fuel tank was only 70 mile combat radius more than a conventional P-51B-1 before kit inst'l. That said it made with combat load, 45,000 feet ceiling (limited by no cabin pressurization), 495mph level flight speed and climbed 7,500 feet per minute. It would have matched any interceptor in the world in 1944

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.

By 8th AF definition, an escort fighter had to have long range and adequate fighter vs fighter maneuverability and speed at bomber altitudes.

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

 

[drgondog]

When I see claims for the speed of the P-51 on long range missions I am reminded of an anecdote told by Leon 'Woodie' Spears, who surely needs no introduction here.

"I had an air combat encounter in Kitten when my flight of about five aircraft escorted a... I believe it was a British Mosquito reconnaissance plane over a target area. He led us while we kept him in sight. We escorted him to the Munich area to this German ball bearing factory. As soon as he started his photo run, we backed off a little so he could do his work. He had to fly straight and level. The Mosquito was a very fast plane. When we came back from the target area he just out ran us. We could not keep up with him because of his speed. We heard him say on the radio "Ta, ta, chaps!""

Cheers

Steve

As always, It depends. The pilots you refer to had to get back home on the internal fuel remaining.

Max Cruise and max continuous power for the P-51D at 25,000 feet was ~400-410 mph true at 89-97gph for 46"MP/2700 RPM. Book Cruise for best range/racks only was 303mph TAS at 2050RPM/29"MP and 52 gph.

The Mossie Definitely did Not want to hang with the P-51s throttled back coming home from Munich.