Did the RAF have designs for a long range escort fighter?

[OldSkeptic]

Good to see this is developing beyond our original discussion. Firstly Nincompoop; I think you are taking my "happy with the fighter" quote out of context; the reason I said it was to counter Drgondog's assertion that the Allison engine performance was a dog. Considering the Mustang was faster and had a greater range than any British or American fighter then in service at that time,

Yes the P51A really came into its own post Normandy as a superb low level photo Rec /tac air plane though it, of course, did tremendous good work in that field before then. It's low level performance was superb.
The 2nd TAF used them right up until they had none left.

 

[tomo pauk]

That would be the Mustang I (P-51), not the Mustang II (P-51A); the P-51A mostly served in India and MTO. Major difference being the engine with better altitude capability, 4 HMGs in wings only, and wing racks.

 

[drgondog]

Good to see this is developing beyond our original discussion. Firstly Nincompoop; I think you are taking my "happy with the fighter" quote out of context; the reason I said it was to counter Drgondog's assertion that the Allison engine performance was a dog. Considering the Mustang was faster and had a greater range than any British or American fighter then in service at that time, NAA were happy with it as a fighter and of course they would look at continuing development; goes without saying. Of course the Americans were investigating higher altitude performance in their fighters, XP-60 and P-38 development and also we all know that Allison were working on improving the altitude performance of the V-1710 to reinforce this, but it was the RAF evaluation team that examined the first production examples in the States (the first AG345 flew for the first time on 1 May 1941) that realised its altitude performance was below what was required over Europe, but this still did not seem to deter from the USAAF putting the order in in July '41. And no, I can't tell you have experience with project development and improvement in industry, not that it's relevant or anything.

Nuuumaann - I did indeed state that the Allison V-1710 was a dog but the comment was in context of future great role as escort fighter. The P-51A was very fast on the deck to 10,000 feet but as stated in various comments in this thread was not deemed 'quite enough' in ETO by RAF. Taken into further context, these RAF evaluations culminated in their suggestion of a mating between P-51 airframe and Merlin 61.

As to NAA being 'Happy", yes to a degree but the P-38 and P-47 got the orders. The first USAAF P-47 Production cntract was September, 1940 and August for first USAAF P38...and it was not 'lost' on the NAA execs that a.) P-40's and P-39's were getting USAAF production orders, and b.) NAA was not, despite superior performance. The Mustang funding was sourced solely from Lend Lease and that program was to terminate in September 1942.

The first XP-51 was delivered to USAAF in August 1941 but the first RAF Mustang I production model (AG345) rolled off the line in April 1941 and first flown by Lewis Walt on April 23, 1941. AG346 flown in trials from early July and was accepted by RAF in August, 1941...and first to be shipped to UK.

The reason I wander through the history is that a.) USAAF didn't fly the XP-51 and did not include it in the evaluations of the P-38, PP-39, P-40, P-43, P-47, XP-60, P-66 etc. The most interesting part was the issuance of Board of Officers, October 27, 1941in which 8 production plus 18 experimental fighters were evaluated - but not the P-51. The Board issued an opionion that the prime mission was "to destroy enemy bombers. It must be able to overcome or evade such hostile pursuit as it may encounter". This report was a Major alert to NAA and according to Horkley, was the initiative for NAA to actively campaign with USAAF. It should also be notedthat the Board deemed that the P-40 and P-39 by overweight (proportional to total) and underpowered/restricted to low/medium altitude of the Allison. The decision to experiment with the Packard Merlin 1650-1 in te the P-40F and the 1650-3 in the XP-60 arose from this Paper's recommendations.

So, NAA was in an R&D funding starvation situation until ASAAF let the A-36 contract in April 1942, followed by P-51A contract in June 1942. By that time NAA already knew that most of the P-51A production would shift to P-51B, if successful.

Drgondog, sounds like you've had some fascinating discussions with people about these things, would have been real interesting to sit in and listen.

I grew up as an Air Force brat living at places like Eglin AFB and Edwards AFB, and fighter pilots and test pilots were an integral part of my life until my father passed away in 1979. I also co-op'ed at Lockheed before I graduated with my Aero degree. I have had an enduring fascination with Airpower and aircraft - which was the driving force to study both aviation and airframe technologies including aerodynamics and structures.

You're in an enviable position to be able to get access to these guys and the resources you can. I live in the middle of nowhere in a small country on the other side of the world from you! If I was in your position I'd be divorced for neglecting my family, by now! As for conversations between RAF and American personnel about better altitude, you can guarantee they happened; yep, chit-chat makes the world go round, but when you get to something as important and as urgent - remember, at that time (late '41 early 42) the British were struggling to cope with the Fw 190 - and as pertinent as a fighter with exceptional performance it was bound to get tongues wagging and pens writing. These RAF guys with 26 Sqn that received the Mustang in January '42 had encountered the Fw 190, so discussions regarding offering better performance than their foe led to quite a bit of discussion and evidence shows they were real pleased with the performance of the Mustang - altitude performance aside. As it was, the Mustang I could match the Fw 190 on even terms. Regarding Atwood and Schmued, it seems that Legarra and Bouchelle of NAA did much of the leg work from the British side of things; these two guys seemed to have spent some time in the UK, with visits to Hucknall to view progress on the Mustangs being converted there.

True but Schmeud and Horkey were visitors in 1940 and early 1942 as well as Atwood.

Aozora, interesting information and although I hadn't seen that book and it would be interesting to see the rest of that chapter, I was aware that two Mustangs from the original USAAF order were to be kept aside for evaluation, because this was a condition of the approval that a US company was to build aircraft for the British who were at war, since the USA was not at that stage.

Two P-51A aircraft were pulled for the XP-51B conversion. 41-37352 and 41-37421. The Packard Merlin 1650-3 (allegedly from XP-60D cancellation) failed bench tests and delayed the first flight from late October plan to November 1942 -actual.

The Merlin XX/28/Packard Merlin 1650-1 was never installed

The decision to evaluate them fitted with Merlins didn't come until later, not when the contract to build was signed. At Wright field there was discussion of fitting these aircraft with the V-1650-1 (Merlin 28 ) supplied by Packard for trials, (this is the crux of the matter) and conventional wisdom states this was in conjunction with the suggestion by Rolls Royce of fitting such an engine, as an interim to allay fears by the Air Staff that there wouldn't be enough Merlin 61s for the Spitfire and the Mustang, in May 1942. British reps from A&AAE Boscombe Down had been to the States (when - sometime earlier than mid May 42?) to discuss the fitting of a Merlin 28 to the Mustang, but their response was not encouraging, correspondence states that "...it did not get any further". By June the Americans had promised that by July they would have a Merlin 28 Mustang in the air, which affirms initial consideration and investigation, but the conversion didn't happen. By August 1942, Kindleberger had contacted the USAAF about the unfeasibility of the Merlin 28 and preference for the 61 instead.

The entire conversations regarding the installation of the 1650-1 after May 1942 was contingency based on the 'newness' of the 1650-3 and the issues that NAA were concerned about regarding the multiple challenges encountered with the 1650-1. An added complication is that the Merlin 61 had catastrophic failures at 12 pounds boost at Wright Pat in July, 1942 (due to connecting rod and carburetor issues) if the 4 September 1942 letter from General Lyons to Hives is referenced. This failure kept NAA from planned first flight and re-directed the engine test bed to 1650-3

If anyone can supply it, I'd like to see further reference to Wright Field's investigation of the V-1650-1 for the two XP-51s they had; it'll make interesting reading. Would the USAF Museum be a good source for this?

I haven't had any luck at USAFHRC on specific correspondence and have re-focused on the Boeing archives.

Personally I don't think the XP-51s ever had a Merlin installed.

 

[drgondog]

Yes the P51A really came into its own post Normandy as a superb low level photo Rec /tac air plane though it, of course, did tremendous good work in that field before then. It's low level performance was superb.
The 2nd TAF used them right up until they had none left.

I suppose definition of 'came into its own' needs to be further defined. The P-51A and A-36 had a great record in MTO in 1943and also soldiered well in CBI well before D-Day. IIRC, in the ETO only the 67th TRG had P-51A's for Recce and they were being phased out in D-Day timeframe..

 

[nuuumannn]

Very interesting post Drgondog, lots of great information, some of it new to me and you've answered a couple of questions I had to ask. Sounds like you've had the dream life hanging about the likes of Palmdale and Edwards and meeting these old guys.

True but Schmeud and Horkey were visitors in 1940 and early 1942 as well as Atwood.

Yes, sorry, that wasn't meant so much as a contradiction to your comment, but to add to it that the other two guys travelled back and forth during the Mustang X development as well. According to an interview I read with him, Atwood was at RAE at Farnborough in 1939 investigating the Meredith papers.

the first RAF Mustang I production model (AG345) rolled off the line in April 1941 and first flown by Lewis Walt on April 23, 1941.

This is news to me since a book I have states that AG345 first flew on 1 May 1941 - ahh, no, just found it in another book I have, yep - 23 April 1941 (or April 23, since we are talking Yankinese).

Here's s letter dated 14/10/42 sent by Jimmy Elor of RR at Packard in Detroit regarding the conversion of the XP-51b that might be of interest;

You have apparently beaten us to it on the flight of the 61 Mustang. Hope the performance is up to expectations. At the request of the US aircraft constructors, the carburettor inlet flange face distance from the crankshaft centreline has been reduced to a minimum in order to facilitate the arrangement of the air intake scoop without its projecting too far into the airstream. The first flight engine is now installed in the aircraft and a flight is expected in about three weeks time but dated by radiator delivery. North American are still keen on installing a number of machines with the V-1650-1 but no decision has reached on this project yet [contrary to the August 28th letter where USAAF personnel mention that Kindleberger stated the Merlin 28 is out].

The first production V-1650-3 is scheduled for December 15th. Packard will start delivery early next yearworking up to 225 engines per month in May. This depends on the supply of machine tools promised by Washington on a high priority. It is thought this figure will be stepped up considerably as the job progresses. No major difficulties have been encountered, but the piling up of endurance runs has been held up due to lack of V-1650 engines. Number One engine is about half way through its final approval runningunder altitude conditions at Wright Field. These tests have been held up by plant failure and the damage to the supercharger when the sludge collected in the rotor shaft recess. The satisfactory completion of these tests is necessary before any machines will be permitted to fly. A second engine will be endurance running at packard and the official Air Corps type test will follow the 50 hours flight development running at Wright Field."

When NAA were investigating the Merlin 20-series/V-1650-1 for the P-51/Mustang I, was it intended for the USAAC/F or the RAF?

From the prompting by Rolls Royce it would have initially been for the RAF since RR suggested the Merlin XX as an interm - as stated earlier, although the USAAC/F interest in the type escalated after British interest in pressing for a Merlin powered Mustang, which led to the P-51B, so in the long run for both, really.

 

[tomo pauk]

Our member (Glider) kindly provided the copy of a document about the increased fuel tankage, along with corresponding ranges for Spitfire IX and Tempests, some time ago. The ranges are achieved under M.E.C. - most economical cruise, so usual caution is needed (= don't fly over enemy territory on M.E.C.). I'll repost it here.
The Tempest received a fuel tank in starboard leading edge, in order to have fuel increased from 162 to 192 IG - am I right about that? The document is dated as of Sept. 7th 1944. The Tempest should behave better with all internal fuel tankage than Spitfire (talking about long range modifications)?

 

[Aozora]

The Tempest also had the advantage of using two custom designed 45 or 90 Imp gal low drag drop tanks. In operational service with 2TAF it was found that the Tempest lost only about 5-10 mph when carrying the 45 gal versions and it became standard practice not to jettison them when empty.

(Shores and Thomas 2nd TAF Vol 4, page 595)

Can't find any figures showing how the Spitfire's slipper tanks affected performance.

 

[wuzak]

Can't find any figures showing how the Spitfire's slipper tanks affected performance.

It seems the 9 gal tank knocked 20mph from the speed of a XIV:

COMBAT PERFORMANCE WITH 90 GALLON LONG-RANGE TANKS

50. As the Spitfire XIV has a very short range it has been assumed that when a long-range tank is to be carried, it is most likely to be the 90 gallon tank rather than the 30 gallon or 45 gallon. Pending further instructions, no drops or trials have been carried out with the 30 gallon or 45 gallon tanks. The aircraft's performance with either can be estimated from the results given below of trials with the 90 gallon long-range tank.

Drops
51. The aircraft was fitted with assistor springs as for the Spitfire IX. Two drops were made with empty tanks at 50 ft and 25,000 ft, A.S.I. 250 mph, with no trouble. Cine photographs were taken and show the tank dropping quite clear of the aircraft. Further trials would be necessary to check these results thoroughly.

Speeds
52. About 20 m.p.h. is knocked off the maximum speed and correspondingly off the speed at intermediate throttle settings. The aircraft is still faster than the FW.190 (BMW.801D) and the Me.109G above 20,000 ft.

Climb
53. Climb is most affected. With a half-full tank its maximum climb becomes identical with the Spitfire IX without the tank. Even with a full tank it can therefore climb as fast as the FW.190 or Me.109G. Its zoom climb is hardly affected.

Dive
54. So long as the tank is more than 1/3 full, the dive acceleration is similar.

Turning Circle
55. The Spitfire XIV now has a definitely wider turning circle than before, but is still within those of the FW.190 (BMW.801D) and Me.109G.

Rate of Roll
56. Similar.

Conclusions
57. Even with the 90 gallon tank, the Spitfire XIV can equal or outclass the FW.190 (BMW.801D) and the Me.109G in every respect. Its main advantages remain the tight turn and maximum climb.

From Spitfire Mk XIV Testing

 

[Aozora]

It seems the 9 gal tank knocked 20mph from the speed of a XIV:



From Spitfire Mk XIV Testing

Yes, just read that in The Spitfire Story ; looks like Camm's low drag tanks and faired mountings worked quite well - wonder how much benefit they would have conferred on the P-51?

 

[wuzak]

Yes, just read that in The Spitfire Story ; looks like Camm's low drag tanks and faired mountings worked quite well - wonder how much benefit they would have conferred on the P-51?

How much did the P-51's tanks cost in speed?

 

[drgondog]

How much did the P-51's tanks cost in speed?

I linked the flight tests earlier in the Spit vs Hellcat thread. Of course it depends on altitude and cruise speed, but the cruise speeds for various external stores are here http://www.wwiiaircraftperformance.org/mustang/P-51D_15342_AppendixB.pdf

If you pick same miles per gallon between racks only (lowest gpm at 4.94gpm) and 2x110 externals (highest gpm =4.92mpg) at 25000 feet - the clean cruise speed 381mph/77gph fro 'clean' is 100mph over the two 110gal best cruise speed 281mph/57gph

Mission planning revolved around a.) distance to target, b.) distance to R/V, c.) distance from R/V to target and back to B/E point, d.) distance from Break escort to base... and weather.

For a really long mission the 25000 281mph/57gpm cruise and escort (while still using the tanks) data would be normally used but if the Fighter Group got off late then best cruise is out the window until they catch up... if the fighters had to wait they would switch to lowest fuel consumption and loiter at lower speed, higher altitude until R/V

 

[tomo pauk]

If I may return to the Tempest V and it's range vs. speed vs. fuel tankage capabilities.
The Tempest, on 'Most economical cruise' was making 285 mph, and on 'Max weak mixture power', it was 390 mph (http://www.wwiiaircraftperformance.org/tempest/tempest-v-ads-sabre-IIb.jpg), all at 20000 ft. On MEC, using 158 imp gals, after subtracting 39 gals of allowance, the range was 680 miles (or 740, with 162 gals, per table posted at post #146 - but no allowances here?). 15 min of combat power subtract 315 miles from that, so the 'return range' is now 365 miles (with no reserves).
Now, the British have modified the Tempest V (unfortunately, too late to matter), adding new fuel tank, the fuel being 192 gals now, range on internal fuel being stated as 890 miles on MEC (same table, post #146). We must allow for fuel used for TO and climb, that should cost us at least 60 miles of range (now: 830 miles). 15 min of combat cost 315 miles - range is 515 miles now; again, no reserves.

added: found it on another forum, by Edgar Brooks:

Cruise, for the Tempest Typhoon was set at 3150 rpm, and for maximum range, the best speed was 210mph IAS, and it was recommended that boost higher than +3psi should not be used, and rpm could go as low as 2000, though it might be found that the minimum needed (to keep the engine smooth) might be 2150.

210 mph IAS being the speed required by the USAF, and stated at tables describing P-38/47/51 fighters' combat radii. So Tempest fits the need nicely, and with great mileage to boot.

 

[drgondog]

Tomo - I doubt if any practical escort mission ever used less than 250mph cruise.. doing 210 to escort bombers is like driving 25 in Texas - "You don't ever arrive"

 

[tomo pauk]

It was 210 mph IAS; the TAS, on Most Economical Cruise setting was, at 285 mph (at 20000 ft).

 

[drgondog]

Silly little distinction between I and T.....I just had a dyslectic read..

 

[stubbsy]

I'm skeptical of such statement.

Well, it is pretty accurate. See the Journal of Military History article entitled 'A Blind Spot? The RAF and Long-Range Fighters 1936-1944' in the Vol 78 No 2 April 2014. The abstract says:

This paper examines why the RAF maintained its view that it would be
neither appropriate nor prudent to protect its bombers with long-range
fighter escort until the time, late in the day, when the U.S. Army Air
Forces' trials to increase the Spitfire fighter's range proved otherwise.
The paper argues that some senior RAF officers, who believed that
long-range fighters were unnecessary, lacked the conceptual dexterity
needed after the RAF's bombers' vulnerability to single-engined fighters
became apparent, and that these failings were hidden by a culture of
obedience to perceived wisdom that existed within the RAF.

 

[stubbsy]

The Chief of Staff of the RAF, Marshall Portal, did not believe a single engine fighter with that sort of range could be built, thus no resources were allocated for this purpose.

The reference for Portal's views is John Terraine 'The Right of the Line' which shows how Portal replied to Churchill claiming that "increased rand can only be provided at the expense of performance and manoeuvrability". On 27 May 1941, again in reply to Churchill, Portal wrote 'The long range fighter whether built specifically as such, or whether given increased range by fitting extra tanks, will be at a disadvantage compared with the short range high performance fighter'

A week late on 3 Jun said that long range fighters were suitable for "regular employment only in areas where they will not be opposed by enemy short range fighters".

'A Blind Spot? The RAF and Long-Range Fighters 1936-1944' explains how he came to these conclusions and why the RAF did very little to extend the range of the Spitfire.

 

[Edgar Brooks]

'A Blind Spot? The RAF and Long-Range Fighters 1936-1944' explains how he came to these conclusions and why the RAF did very little to extend the range of the Spitfire.

If he does say that, it's rather worrying, since increasing the Spitfire's range was nothing, whatsoever, to do with the RAF; it would have involved (and did involve) the manufacturers, the Air Ministry, Local Technical Committees, and the companies' Resident Technical Officers.
As a result of this, extra fuel was shoehorned permanently into the VII, VIII, XIV, XVI, XVIII, 21, 22 24. It was also possible to fit temporary tanks into the V IX, which, with the big 170 gallon ferry tank underneath, meant that the IX, at the end of 1942, could fly direct from Gibraltar to Malta without recourse to an aircraft carrier.
The main reason for the need for extra range was Leigh-Mallory's fatuous "Leaning into Europe" policy, which caused the loss, and deaths, of many good pilots; it's probably not generally realised, now, just how much L-M was hated, at the time. One very bitter pilot, in the 1960s, told me how it was felt that he climbed to his promotions on the backs of dead pilots, and there was a general sigh of relief when he died in a crash.

 

[drgondog]

IIRC none of the major powers except Japan specified long range/high performance for a fighter prior to WWII. Considering the low power of the available engines, the fact that it was a radial with higher fuel consumption than equivalent power in-lines, the A6M was a truly spectacular achievement.

Candidly the belief that it 'couldn't be done' in the late 1930's by the Western Powers military establishment really centered on US and Great Britain as the only two Air Forces with dedication to Strategic Daylight Bombing. Each believed that their aircraft could achieve the goals with acceptable losses without escort, although the US also recognized that fighter aviation technologies were accelerating at an alarming rate in 1940.

What was true in their beliefs (US)is that long range/high performance was only achievable with two engines, requiring big fighter to enable large storage of fuel - and given the technology of the day did not request proposals from the US aviation industry to submit bids for a long range/high performance/single engine fighter in the 1940 The USAAF Pursuit Board over looked the Mustang when considering the "Future Development of Pursuit Aircraft". The concluded that an "all purpose fighter could not be built to fight anywhere and anything" - and concluded that the Army's focus should be to destroy enemy bombers and evade such hostile pursuit as it may encounter".

The earlier Request for Data R40-C (February 1940 when the XP-51 was on the drawing board to propose to RAF) did not reach out to NAA - but did specify latest technologies including invitations for laminar flow wings. From that, several aircraft were propsed, built and tested including the XP-49, 54, 55, 56, 58, 60, 61, 62, 71 - plus Bell's XP-39E, 59 and 63.

Only the P-61 would ever fly combat with American pilots.

As discussed and re-hashed many times the technology for the long range escort had not come to fruition to solve the following - Very Low Drag, High performance/lightweight engine, large fuel capacity - in 1940. There was no two stage, two speed merlin, or a flying fighter with high performance/low drag airframe and large internal fuel capacity.

The A6M achieved the goal for medium altitude Naval fighter application by ruthlessly stripping all weight possible, sacrificing aircraft and pilot safety - which was an anathema to Western Allied thinking.

Only two powers had the combination of a.) existing strategic bomber force, b.) commitment to achieve long range bombing results, and c.) the wealth to spend on protecting them and thus drive the technologies to do so with long range fighters. The Brits were doing Ok with Night bombing, night fighters in the form of Mossie's - which were essentially capable against all the LW night fighters except the Me 262 which was way too late.

Near the end of the war the question of diverting critical resources of a nearly bankrupt nation in the case of Britain - the question is "why" when the US have multiple daylight fighter types for daylight bombardment, and long range night interceptors required a two man crew to achieve interception and destruction of night LW fighters. In 1944 and 1945, what was in the conceptual stage that would be so much better than the P-61 and the Mosquito that it was worth diverting funds to reciprocating fighters when Jet propulsion was clearly the next level in performance.

There was no 'solution' for short range (relatively speaking) jet fighter aircraft for long range escort and the existing escorts were doing just fine except for Me 262.. but there was no answer to the Me 262 per se, in either case.

The P-51 was a happy convergence of a.) great design unfettered by AAF bureaucracy, b.) an airframe which could readily adapt to a larger and better engine, c.) dire need to accelerate conversion of the Allison P-51 and production of the P-51B, and the prior planning and implementation of large scale production output of Packard Merlin engines in the US for other airframes (Lancaster and P-40F)

 

[Shortround6]

I would also note that the A6M actually had a low specific fuel consumption in cruise AND many/most Japanese long range missions took place over water or sparsely populated areas of China and SE Asia.

This means few, if any, AA guns along the route. It also means few, if any, interceptor fields along the route. A much more economical cruise speed (and fuel consumption) can be used than would be practical in Europe.

Imagine the Japanese trying to bomb Guadacanal IF the Americans had had air strips on Santa Isabel and/or New Georgia Island/s around 150 miles closer to Rabual? Japanese would have been forced into higher cruise speeds both incoming and out going for several more hours. Putzing along at 160-190mph (indicated) at low/medium levels is a sure way to get 'bounced' as the British found out pretty early in the "lean forward" campaign.

The USAAF figured a P-51 with 180 US gallons (150 Imp gal) inside and 150 US gallon outside was good for about a 425-450 mile radius. P-51 had less drag than the Spitfire. It is just under 400 miles from Colchester to Hamburg.

Now try to fly not a MK IX Spit but a MK V with a Merlin 45 (about 100 hp less than a Merlin 61 for take off at 12lbs boost) and have the MK V still holding 120 Imp gallons in internal tanks after it drops it's drop tank/s. Trying to build a long range fighter before Hooker (improved single stage superchargers) and on 87 octane fuel (even if they can get constant speed props) and every couple of hundred pounds is really going to affect performance of the fighter.