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

[fastmongrel]

My father was based in Germany Autumn/Winter 1945 on a squadron with Mustang IIIs and IVs and he said that the rear fuselage tank filler and fuel c0ck on the Mustangs was wired closed with a lead seal on. Any aircraft found without the wire and seal and someone was for the high jump. So it seems like the RAF was very anti the rear fuselage tanks, admittedly this is post war but still seems to show the feelings about them.

 

[Milosh]

The Mossie had its MTO weight reduced when the war ended.

Wouldn't the use of the rear tank on the Spits depend on the mission stona?

 

[stona]

Wouldn't the use of the rear tank on the Spits depend on the mission stona?

Yes,but those notes imply that the RAF was very nervous about the deliterious effect of the rear tank on the CoG and handling. I just wonder if there is any evidence for their routine use during the war? Did those restrictions,i.e.authorisation from a senior officer for their use (at the very least) still apply?
Cheers
Steve

 

[Milosh]

What is the date of the PN you have stona?

The PN for the IX, XI, XVI I have say Sept 1946. If there is no war being fought then one could understand the restrictions on the use of the rear tank. One would need to look at war time PN to see if the same restriction was in place.

 

[nuuumannn]

after a quick look there were no pre-war or wartime specs issued for long-range escort fighters

I think I've mentioned that earlier.

Regarding British long range fighters, the Hornet was probably the closest that officially the British came to an escort fighter; there was never any specification released that stipulated the need for one, but the Hornet had F.12/43 (OR.126) written around it as it was a private venture. Designed initially as a long range fighter to oppose Japanese fighters, according to De Havilland A/c since 1909 by A.J.Jackson, the Sea Hornet (built to N.5/44) was to be used as an escort; "A production order was then placed for the Royal Navy's first twin engined long range escort strike fighter, designated Sea Hornet F. Mk.20."

 

[OldSkeptic]

There was no technical issue with a long range (LR) Spitfire post mid/late 42 (Merlin 60 series of course).
They were built and tested (Quill's book gives an example of an actual flight he did). The USAAF did their own version and flew them across the Atlantic.

I define LR top be Berlin and back. The Mustang by that definition was a VLR (very long range) fighter.

Rather it was RAF's higher command .. what could you call it ... 'blimpishness?" that stopped any usage.
Portal, as already mentioned, was assuring Churchill even in 43 that a LR fighter was impossible, just before the P51 B came out....

The key was that with a rear tank the Spit was unstable at first (as was the Mustang), so you burn that off first, then burn off the drop tank.
You rendezvous with the bombers as part of a layered defence , so you just cruise there.
Then combat and return.

The key is the fuel left for combat and being able to return.

Now I did some calculations ages ago that showed if you took a Spit VIII, with a rear 66 (imperial) gallon tank and a 45 or 90 gal drop tank then you could escort to Berlin and back, with a 15min allowance for combat. And still had about 140 miles left for reserve (22% of the trip to Berlin)

You might want to add a bob weight to the elevator control for the LR MK VIII to make it a bit easier for the pilot for the beginning stages, but in the combat zone you had no problems.
And 15 mins combat is a long time, I used that number to allow for re-climbing, fast evasion, etc at higher speeds before returning to cruise speeds for the return.
The numbers I used were from the actual data sheets for the plane. Most economical cruise of 220mph, plus the fuel usage from the data sheets for the different configurations and combat.

So RAF bureaucracy was the issue (or 'clueless management' in today's terms). Even after they fitted rear tanks to late model Mk IXs, XVIs, XIVs and XVIIIs they were hardly ever allowed to use them.
Note this RAF attitude carried on for long after the war. Range has never been an important spec for fighters to them.

 

[drgondog]

There was no technical issue with a long range (LR) Spitfire post mid/late 42 (Merlin 60 series of course).
They were built and tested (Quill's book gives an example of an actual flight he did). The USAAF did their own version and flew them across the Atlantic.

I define LR top be Berlin and back. The Mustang by that definition was a VLR (very long range) fighter.

Rather it was RAF's higher command .. what could you call it ... 'blimpishness?" that stopped any usage.
Portal, as already mentioned, was assuring Churchill even in 43 that a LR fighter was impossible, just before the P51 B came out....

The key was that with a rear tank the Spit was unstable at first (as was the Mustang), so you burn that off first, then burn off the drop tank.
You rendezvous with the bombers as part of a layered defence , so you just cruise there.
Then combat and return.

The key is the fuel left for combat and being able to return.

You have several good points. Elaborating here is the key point that the theoretical maximum range is that point where you have ample Internal fuel every time to return home after 15-20 minutes of combat at Military Power, which for a Merlins ~ 4x Cruise consumption, and for ETO at least 20-30 minutes to fool around in bad weather to get on the ground safely For US sized formations this could be 24-30 minutes in Perfect weather.

Now I did some calculations ages ago that showed if you took a Spit VIII, with a rear 66 (imperial) gallon tank and a 45 or 90 gal drop tank then you could escort to Berlin and back, with a 15min allowance for combat. And still had about 140 miles left for reserve (22% of the trip to Berlin)

You might want to add a bob weight to the elevator control for the LR MK VIII to make it a bit easier for the pilot for the beginning stages, but in the combat zone you had no problems.
And 15 mins combat is a long time, I used that number to allow for re-climbing, fast evasion, etc at higher speeds before returning to cruise speeds for the return.
The numbers I used were from the actual data sheets for the plane. Most economical cruise of 220mph, plus the fuel usage from the data sheets for the different configurations and combat.

While 220 mph has been used as a rule of thumb, for the US escort problem that is too slow to a>) actually R/V with a bomber force that departed English skies two hours before your force takes off. and b.) not only Ess in high cover but also protect yourself by being able to throttle up and accelerate to meet a fast moving German force in time to intercept.

The B-17 at 26,000 feet is doing 150mph IAS[ and ~205+ mph TAS. The B-24 is doing 175mph IAS at 22,000 and close to 215TAS... so if you are cruising to R/V at 220, you never arrive until the bombers are returning from the target.

So RAF bureaucracy was the issue (or 'clueless management' in today's terms). Even after they fitted rear tanks to late model Mk IXs, XVIs, XIVs and XVIIIs they were hardly ever allowed to use them.
Note this RAF attitude carried on for long after the war. Range has never been an important spec for fighters to them.

The RAF also did not fully utilize the Mustang III block numbers (mid serial no. P-51B-7 which had the 65 gallon tank installed at the factory) with many missions completely fueled up.

For your calc purposes 300-310 mph TAS for the cruise to make a deep R/V might be more useful to predict the actual Spit capability to provide LR escort to Berlin.

 

[OldSkeptic]

Not disagreeing with you at all as you have made good points. Careful planning would be the key to success. The most economical cruise speeds (of which the Mustang was about 20moh faster) would have been an issue of course, but good planning would help (perhaps a Mosquito to guide?). On the shorter ranged missions naturally faster cruise speeds could have been used.

And, you are (again) correct to bring up weather issues. But bad weather meant that the USAAF bombers were equally limited and tasked to closer targets.

So the issue is, could a LR Spit been a useful escort fighter until the Mustang numbers built up, I think the answer is yes.
After there was sufficient Mustangs the LR Spit would still have been a useful contribution as a 'fill in' fighter, that is covering the intermediate ranges, until the Mustangs met and took over escorting.

More importantly, it would have meant that, when the great slaughtering happened, USAAF bombers would have had escorts over much of Germany in mid to late 43.

 

[drgondog]

Not disagreeing with you at all as you have made good points. Careful planning would be the key to success. The most economical cruise speeds (of which the Mustang was about 20moh faster) would have been an issue of course, but good planning would help (perhaps a Mosquito to guide?). On the shorter ranged missions naturally faster cruise speeds could have been used.

Interestingly enough, the Mustang Best Cruise setting with 110 gallon fuel tanks was 32" MP, 2250rpm, 281mph(TAS) at 25000 feet for 57gallons per hour. Once tanks were dropped then 29" 2050rpm, 303mph at 25,000 feet (a 9760 pounds GW plus 2x110x6 for the 110gal tanks =~11080 GW at Engine Start time. With no loitering around waiting for a 48 ship formation to assemble, the Mustang would be at ~ 10900 pounds at 25000 feet (assuming 25+gal burn of internal fuselage tank). Significantly higher cruise settings could be achieved (331mph) with a sacrifice of 1/2 mile pergallon from 4.91mpg to 4.49 for a Stettin/Munich radius mission.

BTW - IIRC the Mossie cruised faster than the Mustang..

At moment of dropping tanks the P-51D would be ~ 9600 pounds with 184 gallons in the wings and 60 gallons in fuselage tank (not expecting combat in this scenario) - at which point he gains 22 mph TAS instantaneously and increases power and miles per gallon as he burns more fuel and loses more weight.
This link gets you to the complete report - click on Full Report link at bottom of this section.
P 51D Performance Test


And, you are (again) correct to bring up weather issues. But bad weather meant that the USAAF bombers were equally limited and tasked to closer targets.

There may be some truth to that for the mission planners as they looked at the forecasts - but weather over Germany dictated the Mission plans more than English weather (for the bombers). They were a.) much better instrument pilots, and b.) the Navaids and CGI capability for bomber bases/aircraft were much more sophisticated. Fighter - not so much. I.e. My father was FAR better equipped for English/European weather coming from 2200 hrs in Training command in both fighters and B-26s. When he came to Steeple Morden he was immediately pressed into service as Instrument instructor for the 355th FG as part of his day job. Typical replacements showed up with ~ 250-350 hours total flight time.)

So the effect of the planning was a.) allow more time to assemble, b.) delay mission to see how much it cleared up, c.) adjust let down and approach times accordingly. If the weather was clear over targets - the fighters went, with rare exception in 1944-1945.

So the issue is, could a LR Spit been a useful escort fighter until the Mustang numbers built up, I think the answer is yes.
After there was sufficient Mustangs the LR Spit would still have been a useful contribution as a 'fill in' fighter, that is covering the intermediate ranges, until the Mustangs met and took over escorting.

The LR Spit, IMO, would have been better than either the P-47 or P-38 - given equivalent range, for a Spit IX comparable performance.

More importantly, it would have meant that, when the great slaughtering happened, USAAF bombers would have had escorts over much of Germany in mid to late 43.

Very much agree.

 

[OldSkeptic]

I think we are agreeing totally.

The LR Spit would have been wonderful in 43 and its role steadily taken over by Mustangs as they came available when it would have allowed even greater range bombing missions.

The LR Spit would have been a great support fighter to them even after they had sufficient numbers. As per the layered escort system.
Numbers help a lot, would have made the mission planers job a lot easier ("use P-47s to here, LR Spits to there, Mustangs thereafter" sort of thing)

The 20mph figure I quoted was at the most economical cruising speed as per the pilots note on the Mustang III (from the same site).
Just used for maximum range calcs as an example, not as it was used in every mission.

The Mustang in that mission configuration was capable of truly amazing ranges, that's why I call it a VLR aircraft.
Incredible basically. Boy was it a good plane, not perfect of course (none were or are even now), but very, very good.
I've actually flown in one (P51D in NZ) ... wonderful is not big enough a word.

 

[drgondog]

Old Skeptic - is it possible you are thinking 'greatest loiter (time in air) time' rather than longest range? The bottom of the Drag Bucket was in the 280-320 mph range depending on altitude and GW..for 25,000 it is 281/303 respectively with the data I supplied above - this is where the highest L/D (~14+) ratio exists for the airframe after tanks are dropped

Your number is closer for SL depending on GW and clean.

Your 220mph figure would consume less gph at 25000 but would not be best for Max Range for the Mustang/Packard Merlin 1650-3 or -7 as the L/D ratio is lower and Induced Drag is greater than Profile Drag at 220mph..

http://www.wwiiaircraftperformance.org/mustang/P-51D_15342_AppendixB.pdf

This is the cruise setting summary for the P-51D-15 per the tests (average) with +/- 6% deviation according to the report

Did you post the Mustang III link above?

 

[OldSkeptic]

Sorry drgondog I should have typed +30mph for the Mustang III, not 20mph.

From the Pilots notes:
Most economical cruise speed at 20,000ft: 253mph.
at MWM: an astonishing 405mph (with the -7 engine, 395mph , for the -3), though that reduced range by 40%.
http://www.wwiiaircraftperformance.org/mustang/mustang-III-ads-3.jpg
http://www.wwiiaircraftperformance.org/mustang/mustang-III-ads-7.jpg
http://www.wwiiaircraftperformance.org/mustang/mustang-IV-ads.jpg

Spit IX was 220mph and 328mph (which reduced range by 45%), as I said you could push it to being a LR fighter, but the Mustang was in a class by itself.

The purpose of my calculations was to work out whether or not you get a Spit as an escort to Berlin.
The answer is yes, though very careful planning and good fuel discipline would have been necessary (yes I did adjust for the extra fuel consumption caused by the 45 or 90 gallon tank).
And you would have had to spend most of the time at most economical cruising speed, so that was about the limit you could get.
Closer German targets would have been easier with more options in terms of cruise speed, loiter/combat time.

For the Mustang (whether B or D) you could either go much further on a most economical setting, or run at much higher cruise speeds for the shorter ranges (giving greater tactical flexibility).
Additionally you had far greater loiter/combat time.
The exact choice (as per your links and other data) would depend on the mission, tactical requirements and number of aircraft available.

 

[nuuumannn]

There was no technical issue with a long range (LR) Spitfire post mid/late 42 (Merlin 60 series of course).

Interesting, but there might have been more mileage out of building Mustang Is fitted with 60 Series Merlins from the outset instead of Allisons, rather than converting Spits for the long range role. Obviously, the airframes would have to be shipped to Britain for the fitting of Merlins. The first 60 Series Merlin engined Spitfire first flew three weeks after the Fw 190 entered service, so time wise it could be done, hypothetically speaking. Rolls-Royce fitted Merlin 65s to five Allison engined Mustang Is and these were called the Mustang X, first flying in October 1942 and demonstrating excellent performance. One aircraft reached 433 mph at 20,000 ft during testing.

 

[OldSkeptic]

Interesting, but there might have been more mileage out of building Mustang Is fitted with 60 Series Merlins from the outset instead of Allisons, rather than converting Spits for the long range role. Obviously, the airframes would have to be shipped to Britain for the fitting of Merlins. The first 60 Series Merlin engined Spitfire first flew three weeks after the Fw 190 entered service, so time wise it could be done, hypothetically speaking. Rolls-Royce fitted Merlin 65s to five Allison engined Mustang Is and these were called the Mustang X, first flying in October 1942 and demonstrating excellent performance. One aircraft reached 433 mph during testing.

Even fitting Mustangs with Merlin XX series would have made a difference though it would have struggled at bit at the high escort altitudes (but been very useful for other purposes though).

Trouble was the the 60 series Merlins were not available when the P-51A first came out.
And it took a bit of time for people to twig to the idea. At that time neither the British or the American saw the P-51 as a fighter, let alone a VLR escort fighter.
So it really was inspired by the small amount of British and North American people who saw its terrific potential and pushed for it (including Rolls Royce, hat tip to them, without their belief in it, it would never have happened).

Note the P51A was a great low level aircraft and the British used it for tac rec right up until they had none left in late '44, a greatly underestimated plane.

The USAAF desperately needed escorts, at least as far as the Ruhr and a bit beyond. A LR Spit, many of which could have been conversions, would have been of inestimable value in the mid-late 43 period.
Took a long time build up Mustang numbers too, even in early 44 they didn't have many. And Packard was struggling to get its 60 series production up to speed (they did a great job, especially since you consider that they were basically just a luxury car manufacturer before the war, got to take your hats off to them).
I think it was (from memory) suggested at one point to use RR Merlins as a stop gap, but the USAAF knocked that on the head, mainly because of maintenance concerns (if anyone can clarify that it would be useful).

So, as usual, it was a numbers game and the LR Spit would have been a great stopgap and support for that crucial 9 month period.
It would have also given the RAF a lot more tactical options too, they would finally have been able to hammer the Luftwaffe in France for example and even enable Bomber Command to do daylight raids for certain types of missions.

The tragic thing was that it was available in the necessary time period, just was ignored. People kept saying you can't make a LR fighter and various people kept putting their hands up going "we've done it with the Spit and we've got an even better one (Mustang) coming along a little bit later' ... and no one lat the top listened. Bizarre.

 

[wuzak]

I think it was (from memory) suggested at one point to use RR Merlins as a stop gap, but the USAAF knocked that on the head, mainly because of maintenance concerns (if anyone can clarify that it would be useful).

I think Packard Merlins destined for the USAAF had SAE splined output shafts, while those for the RAF and built in Britain had British splined shafts.

 

[OldSkeptic]

Yes Wuzak that makes sense, but there might have been work arounds. With the usual wonderful 20-20 hindsight we all apply an attempt (which could have failed of course) might have been a good idea.

 

[nuuumannn]

Trouble was the the 60 series Merlins were not available when the P-51A first came out.

They were around when the Mustang I was under production, however (The P-51A was not a Mustang I - that type was supplied to the RAF only). The first Mustang I reached the UK in October 1941, at which point the Merlin 61 was already in production for the Spitfire - the first of which, the Mk.III N3297 had already been converted to fit a 61 and flew for the first time on 27 September 1941. Obviously, any supply of Merlin 61s to Mustang airframes sitting about would mean that Spitfire Vs on the production line would not receive them, therefore there wouldn't be any Spit IXs in July 1942. Timewise, since the Spit IX entered service in July 1942, its feasible that refitting Mustang I airframes with the Merlin 61s could be done by mid/late 1942. It also fits with Rolls having their first flying Mustang X (powered by a Merlin 65) in October of that year.

I think it was (from memory) suggested at one point to use RR Merlins as a stop gap, but the USAAF knocked that on the head, mainly because of maintenance concerns

My proposal is not so far fetched as precisely what I suggested was actually prepared for (although in a later time frame) - 500 engine assemblies for Merlin 61s for fitting to Allison engined Mustang Is were prepared by Rolls at Hucknall, partially because it was feared that the fitting of '61s to Spit Vs on the production line might not last - in the event it went on as the Mk.IX well into 1944. It was proposed that if there was a shortage of Merlin 61s, the Packard built 1,390 hp Merlin 28 was to be fitted to Mustang Is in the USA. Another idea was to assemble Mustang Is in the UK and its likely that this was to be undertaken by Air Services Training at Hamble, with Rolls supplying the engines, of course. Meetings involving NAA personnel and British Air Ministry personnel took place to ratify all this, but in the end, there was doubt about the feasibility of it all. One peculiarity was that at that time Lancasters were receiving Packard Merlins, so the sending of American built airframes to the UK for British engines was considered 'hardly reasonable' according to minutes of a meeting between Lord Hives of RR and Wilfred Freeman in 1943. There were also modification issues between engine and airframe that needed to be resolved between the fitting of Merlin 61s to Allison airframes that were eventually fixed by Packard in redesigning the nose of the Mustang to accommodate the V-1650-7 engine. The first US Mustang to fly with a two-speed two-stage Merlin was the XP-51B, basically a P-51A fitted with a Merlin 61 that had been sent to the USA - to Wright Field for testing, on 30 November 1942. All this also doesn't take into account the urgency of getting the Mk.IX into service to tackle the Fw 190.

With the usual wonderful 20-20 hindsight we all apply an attempt (which could have failed of course) might have been a good idea.

Don't ya love it here!

 

[OldSkeptic]

Good points Nuuumannn and thanks for the information, very useful and great research. I've filed that away and will shamefully steal it for future comments...

Personally I'd have loved to have seen a Merlin XX series engined Mustang.
It would have been a hot mid altitude aircraft, more than an equal to the FW-190A series in the majority of flight regimes.

 

[nuuumannn]

thanks for the information, very useful and great research. I've filed that away and will shamefully steal it for future comments

You're welcome, glad to be of assistance! (takes a bow...)

I've done a bit of thinking about the period of 1941 to 1942 with the arrival of the Fw 190 on the scene and its implications; it had a dramatic effect on British planning and resulted in the escalation of several important fighter programmes, including the Griffon engined Spit and, of course the Merlin engined Mustang. The two-speed-two-stage Merlin was already on the cards in mid 1941 as the Merlin 60 was originally intended for a high altitude version of the Vickers Wellington with a pressurised cabin, the Mk.VI and it was Hives of RR who asked the pertinent question, "What would be the result if we fitted a Merlin 60 to a Spitfire?" This was before the Fw 190 went into service, so everything was already in place for that engine to take prominence. The Merlin 60 was essentially a Merlin 45 - as fitted to the Spit V, but with the bigger blower, so it was relatively easy to get into quick production once the need arose.

 

[drgondog]

Interesting, but there might have been more mileage out of building Mustang Is fitted with 60 Series Merlins from the outset instead of Allisons, rather than converting Spits for the long range role. Obviously, the airframes would have to be shipped to Britain for the fitting of Merlins. The first 60 Series Merlin engined Spitfire first flew three weeks after the Fw 190 entered service, so time wise it could be done, hypothetically speaking. Rolls-Royce fitted Merlin 65s to five Allison engined Mustang Is and these were called the Mustang X, first flying in October 1942 and demonstrating excellent performance. One aircraft reached 433 mph at 20,000 ft during testing.

The impediment for the Mustang I and II Allison replacement was that a.) the bottleneck in Merlin engine production at Packard which had prioritized production assignments for the Lancaster and were just getting their production runs in early 1941, and b.) as you mentioned the necessity to actually modify and test the Mustang X. It was further complicated with Merlin XX allocations to P-40F in late 1941 and 42... Packard couldn't schedule an engine to NAA.

You can make a baby with one mother in 9 months but you can't make one in one month with 9 mothers.. there is a gestation period between concept and manufaturing release.. (as you know)

I had conversations with Ed Horkey in the 60's regarding the Mustang Team's consideration of a higher performance Mustang with Rolls Royce engines. It wasn't feasible to design the original airframe to accomodate the Merlin without making changes to the original lines which were well on their way to final design - and there was no sourcing for the Merlin in 1940-41. Further, it was suspected that significant work would have to be accomplished with ducting/radiator changes for the more powerful Merlin (true)

Conceptually, the NAA team was thinking about the preliminary design changes which would be required as RAF informed NAA of their thinking in early 1941 as Mustang I was going into production for delivery to the UK, but no design resources were permitted to detract from the conversion from Prototype to Production phase for RAF deliveries.

The timelines between start of Serious practical thinking at NAA and RAF was somewhere between December 1941 and February 1942. At that time all the Merlin XX built by Packard were prioritized for the P-40F so the Brits took the lead with The Mustang X.

At the date for Pearl Harbor the USAAF at Wright Pat had flown the XP-51 exactly 1 hour despite having it there in August 1941. The XP-51 had been ready for the Army in April 1941 but it took the Army nearly a year to start testing because they were too busy fooling around with the P-66, the P39, the P-43, and P-38/47 prototypes.

Net - ALL the push for high altitude capability was NAA/RAF, Packard was jammed for Lancaster and P-40F, Allison totally screwed up their commitments for V-1710-39's which delayed NAA and RAF production lines by nearly 4 months.

As a side note, Allison also failed to deliver a.) a V-1710-39 and b.) one with correct wiring harness, requiring NAA to redesign the engine mounts at the time the airframe was ready to first fly. This and subsequent screw ups by Allison (including P-82)created animosity from NAA to Allison that lasted Looooong after WWII ended.

I heard from several sources that when a choice could be made between Allison and Pratt or Wright or GE, that NAA would choose the latter.

The USAAF bears most of the burden for the slow introduction of the P-51B/Packard Merlin marriage..