P51 with Allison turbo

[nuuumannn]

I think they'd have needed a few Griffon Spitfires or other planes with improved perfroamance over the Merlin and had definitely decided they wanted to use the Griffon before they'd order it into domestic production, much less license it in the USA. I could be wrong, but I don't think so.

You could be right, Greg, but the USAAF did show interest in the idea. The fact that the XP-78 was progressed with instead was most likely down to expediency and as you've said getting the Griffon into production in the USA would have been a big commitment. That doesn't mean that if the requirement was there that it definitely wouldn't have happened; the interest was there and the Americans were waiting for examples from Roll-Royce for testing. Since the Mustang was never converted (with the exception of post-war racers, that is!) to be powered by the Griffon by RR, who would have led the development like the Merlin Mustang, then I guess it wasn't going to happen. A Mock-up was built however, using Mustang I wings and empennage, but it was not completed.

Initially when the Merlin Mustang was suggested in 1942 the British planned for Rolls to build the Merlins and Gloster in England to build the airframes, since the requirement was for British squadrons. Because the P-51 was such a success it is often overlooked that the work on the Mustang in Britain and America was specifically to fulfil a British need and the USAAF's interest in the early stages of its development (1940 - 42 time period) were out of contractual requirement, rather than for a serious intent; I'm sure there were USAAF individuals who were keen on the Mustang, but it was largely regarded in America as a 'British' aircraft.

 

[GregP]

Hey SHortround,

I think it was POSSIBLE from a production standpoint, but not politically possible unless specifically for the British. I thought I made that clear. If not, it should be clear now, huh?

So, yes, it COULD have been done, but was a very remote possibility that would have required strong British incentive to make it work.

In the event, it NEVER happened except for one Reno racer (with contra-props) that is SLOW compared with the Merlin planes, so the premise above is at least viable.

 

[nuuumannn]

So basically the Early Mustang was going to use the Allison or nothing.

That's right.

 

[nuuumannn]

So, yes, it COULD have been done, but was a very remote possibility that would have required strong British incentive to make it work.

I agree, Greg.

 

[wuzak]

The Merlin was a known quantity by the time it was licensed and you seem to think they would license the Griffon before they knew how thw US would do building Merlins and before they knew how the Griffon would perform in an aircaft.

There were a few aircraft that were waiting for various Griffons. As with the Merlin, it would be a request by the British to have a US manufacturer build the Griffon. Remember that the majority of Packard Merlins still ended up in British aircraft - Spitfires, Mosquitoes Lancasters.

Hives (of Rolls-Royce) was very happy with the Griffon 61 and described it as "the best fighter engine in the world".

They might have done so, but I don't believe it. I think they'd have needed a few Griffon Spitfires or other planes with improved perforamance over the Merlin and had definitely decided they wanted to use the Griffon before they'd order it into domestic production, much less license it in the USA. I could be wrong, but I don't think so. The war was turning around at that time and they were fighting on more or less even terms.

A proposal for a Griffon Spitfire was made in 1939, if not before. The Griffon was modified so it could more easily fit in the Spitfire. The Griffon was very much wanted, by the RAF and by the service that originally requested it - the FAA.

Hives was critical of Supermarine for not progressing the aerodynamics of the Spitfire and for not moving faster on the Griffon Spitfire. They knew that the Griffon Spitfire would have higher performance.

The thing that stopped a trial of the Griffon Mustang was that NAA thought that too much engineering time would be required for the conversion, whereas the conversion to the Merlin 61 was much less involved.

Hi Wuzak! Hope you are having good holidays!

Yes, so far. But I wish summer would turn up for more than one day at a time!

How are your holidays going?

 

[drgondog]

The Flying Test Bed derived from a Miles Proposal included a design for a mid fuselage mounted Griffon utilizing existing wing and aft section including tail from Mustang I. It proceeded from November 1943 to completion of mockup November 1944. It had no priority but was also intended to be able to switch out various engine configurations including axial flow jet engines.

Great concept but nothing to match Meteor or P-80 as they were real by the time the Griffon concepts proceeded.

 

[Balljoint]

When discussing the Mustang, it's a bit contra intuitive to keep in mind that prior to June, 1943 the plane was a bit of an ugly duckling in production only because of the improbable A-36 use in CAS. At that time the US War Department –Robert Lovett- started preaching the need for long range fighter escorts for bombers. Arnold, who had previously considered such a plane unnecessary and technically impossible, got religion and called for a long-range escort fighter. Initially, the P-47 was used to provide medium range escort of course. But the P-51B serendipitously proved to be the ideal long-range escort fighter. This mission required a balance of performance compromises that resulted in a plane that in theory is intrinsically at a performance disadvantage to short-range interceptors. The Mustang was little disadvantaged

Perhaps the question is whether the Griffon -or turbo Allison- would have, on balance, been a better choice for this mission. For shorter range needs, the Griffon Spitfire was a pretty good plane. At least prior to the TA-152 –and maybe not then with Merlin improvements- the Merlin seems the right choice.

 

[Shortround6]

Part of the reason in giving the time line is to show how far down the road combat use is made from initial decisions. NAA did about the shortest ( or one of the shortest) design/build jobs with Mustang and followed it with a an almost equally short major redesign.
Basically they were betting that things would actually work out right when they placed the production orders. A turbo Allison P-51 could have been a success or it could have been a big flop. It would have gone into combat with an engine one or two "generations" different than the engine available when work started. Work started on the Mustang several months before the "deal" to make Merlins in the US was signed. Merlin available in the Spring of 1940 wasn't even the Merlin XX so backtrack on the Allison the same amount, granted you had the engine makers promising engine XXX would make YYYY for power in 18-24 months but we have the knowledge now to KNOW what engines would become available at what power and when making second guessing some of the decisions rather easy.

 

[drgondog]

When discussing the Mustang, it's a bit contra intuitive to keep in mind that prior to June, 1943 the plane was a bit of an ugly duckling in production only because of the improbable A-36 use in CAS.

Actually the A-36 contract was a special award by Arnold who recognized the potential of the Rolls/Mustang X activity, which was in April to October 1942 with NAA just one month later with XP-51B taking its first flight. In the ETO Eaker began to see that unescorted daylight operations were going to be rough. Losses in late 42 and early 43 when the 8th started bombing targets were taking loss rates above 5%. Arnold only had money for dive bombers and set up NAA with A-36 to keep the P-51 in production through the expected flight of both the Mustang X and the P-51B - then followed up with a transition of the P-51A production order to the P-51B

At that time the US War Department –Robert Lovett- started preaching the need for long range fighter escorts for bombers. Arnold, who had previously considered such a plane unnecessary and technically impossible, got religion and called for a long-range escort fighter.

What would your source for this be? "Air Force Spoken Here" by Eaker and "Forged in Fire" by Cooper offer insight from all the 'bomber Generals" during the 1942/mid 1943 escalation of concerns and dialogue to/from Arnold. Had the 'call for a long range fighter' been initiated by Lovett at the time of the A-36, with subsequent action by RAF?Rolls and NAA - the first P-51B would have arrived in mid 1944 at earliest.

Initially, the P-47 was used to provide medium range escort of course.

The Spitfire initially provided short range escort after the Africa campaign yanked all the P-38s from 78FG, as well as 1st and 14th FG which were stripped from 8th AF and sent south. The 31st FG (all Spit) followed and the RAF plue 4th FG (Spits)were left holding the bag... from November 1942 through April 1943 when the 4th, 78th and 56th became operational in P-47s. It wasn't until mid summer 1943 that the Jugs made Germany and such trips were all localized in Western Germany - not easy to describe as mid range. Bremen-Frankfurt-Bordeaux was a maximum penetration for the 8th AF P-47s into mid February.

But the P-51B serendipitously proved to be the ideal long-range escort fighter. This mission required a balance of performance compromises that resulted in a plane that in theory is intrinsically at a performance disadvantage to short-range interceptors. The Mustang was little disadvantaged

Perhaps the question is whether the Griffon -or turbo Allison- would have, on balance, been a better choice for this mission. For shorter range needs, the Griffon Spitfire was a pretty good plane. At least prior to the TA-152 –and maybe not then with Merlin improvements- the Merlin seems the right choice.

The Griffon at that time was in far too small quantity and designed for lower altitude performance than the 1650-3 Packard Merlin, which was an excellent application for initial Mustang engagements as the 29,000 ft FTH performance was so much better that the FW190A6/7 and Bf 109G-6 from 18,000 feet to ceiling.

Over time the ops analysis showed that most ETO escort combat broke down to 25%-75% high to low altitude engagements and the 1650-7 was the better engine for 8th AF Mustangs.

 

[Balljoint]

Agreed on the A-36 –my point being that the plane with perhaps the best aero design of the war was produced as a dive bomber to keep it alive. Of course this was due to the P-51A being a low altitude machine so dive bombing or reconnaissance were the two options.

At the risk of being a bit strategy centric, Lovett, assistant secretary of war for air during June, 1943 -after a tour of bomber bases in England, pitched Arnold to afford a long-range escort fighter his immediate attention. If the discussion at page 144, Masters of the Air by Donald L. Miller is correct, Lovett's recommendation precipitated Arnold's memo requiring a long-range fighter escort, though not mentioning the P-51. Miller generally does his homework on documented events though he sometimes gets caught passing on discredited scuttlebutt. In any event the discussion is at page 144.

The whole fighter escort development is a bit confusing in that it morphs from an Eighth Air Force bomber protection operation to a D-day air superiority mandate from Eisenhower. Under Doolittle the bombers were less objects of protection –though they were in fact much better protected- than bait for to draw in LW fighters for the escorts to deal with. On June 6 the allies enjoyed air superiority over Western Europe.

 

[wuzak]

The Griffon at that time was in far too small quantity and designed for lower altitude performance than the 1650-3 Packard Merlin, which was an excellent application for initial Mustang engagements as the 29,000 ft FTH performance was so much better that the FW190A6/7 and Bf 109G-6 from 18,000 feet to ceiling.

Over time the ops analysis showed that most ETO escort combat broke down to 25%-75% high to low altitude engagements and the 1650-7 was the better engine for 8th AF Mustangs.

I agree that the Griffon was being built in low quantities at the time (mid to late 1942), but I disagree about the altitude performance. The Griffon specified for the Mustang was the 61, the two stage version which was directly equivalent to the Merlin 61, then the only 2 stage Merlin in production.

 

[wuzak]

A Griffon Mustang (as opposed to the FTB) would have been shorter legged than the Merlin Mustang, but when it was proposed (1942) the long range Mustang was not required, nor had it been realised.

The aim of sticking the Merlin in the Mustang was not to create a long range escort fighter, but to create a fighter with better altitude performance. And so it would have been with the Griffon.

When the USAAF realised the need and started pushing for a long range escort fighter they started a new program - the Fisher XP-75. Lucky that the P-51B was able to do the task, because the P-75 wasn't going to be around in any numbers before mid to late 1944, at the earliest.

 

[GregP]

Hi Wayne,

So far, so good, thanks! I gave myself a new 120° die grinder for Christmas.

Looks like my work on the F-86 is winding down for awhile. I still have work to do, but we don't have the parts yet, so I'll be free to have some fun.

I've been filling in with stripping the control surfaces of our Mitsubishi Zero for recovering. I still need to brighten them to eliminate some minor surface corrosion. And I'm cleaning up the elevators for Ed Maloney's P-51 'Spam Can" in preparation for bringing them up to new looks. They have a few dents from 70 years of hangar rash and need to look "new." We are doing that now, while the tail is off the plane. So Spam Can will be down awhile longer, but will look much better when she flies again soon.

Still looking at engineering. Maybe it will break this year and I'll actually have to work again.

 

[V-1710]

It all makes me think of what a mess the XP-37 was........

 

[nuuumannn]

The aim of sticking the Merlin in the Mustang was not to create a long range escort fighter, but to create a fighter with better altitude performance. And so it would have been with the Griffon.

Exactly, for the British, not for the Americans; this is what all of that effort was for; equipping the RAF with a suitable fighter to tackle the Fw 190 and Bf 109F and it is often forgotten that the Allison engined Mustang I could actually do that and beat them at low to medium altitudes. The Griffon 61 would have given the Mustang oodles of altitude performance; look at what the two-speed two-stage Griffon did for the Spitfire VIII in production as the Spitfire XIV.

 

[nuuumannn]

I give myself a new 120° die grinder for Christmas.

...and your wife gives you a pack of Y-fronts and some chocolates! Keep up the great work at the museum, Greg.

 

[GregP]

Hi nuumannn,

No wife, so I give myself something. Nobody else much does.

Works great and ensures a continuing supply of various die grinders. In fabrication, they are very useful and maybe indispensible. This one was Chigago Pneumatic. Normally a great unit ... but THIS one doesn't have a teasing trigger, so it's pretty much an off-or-on unit. Fortunately, it a relatively slow and so doesn't matter much. In the future, I'll stick with Ingersol-Rand die grinders for value-to-cost and great teasing triggers.

 

[drgondog]

Agreed on the A-36 –my point being that the plane with perhaps the best aero design of the war was produced as a dive bomber to keep it alive. Of course this was due to the P-51A being a low altitude machine so dive bombing or reconnaissance were the two options.

Maybe not that simple. Ira Eaker first flew the P-51 just after pearl Harbor and believed it to be the best fighter. He had flown both the P-38 and P-47 earlier. He also observed that it was underpowered but convinced engine technology would solve that problem. Fast forward to mid -1943 when Eaker and Arnold were battling each other over results in ETO. Eaker articulated his belief that German day fighters could always prevail over B-17/B-24 in good weather, given sufficient numbers and urged prioritizing German a/c industry.

Lovett acted as an intermediary and met with Arnold in June and on July 7, 1942 Arnold called a truce, expressing his confidence in Eaker but the conversation according to Lovett was more about Arnold's steadfast belief that unescorted daylight bombardment with B-17/B-24 would be sufficient while Eaker was calling for P-47 w/long range tanks, P-38s and P-51's with external tanks. Lovett specifically believed that the P-38 was The solution but had high hopes for the P-51.

It should be noted that Everybody (Arnold, Eaker, etc) Knew that long range fighters were needed - but in 1940-42, they didn't exist because the parallel technology of airframe, internal fuel and engine weren't ready.

Arnold takes responsibility for the delay in realizing the full potential of the 51 but he didn't have the funds to 'jump start' the introduction of the P-51 into the AAF inventory in October 1941 when the Fighter design reviews took place - hence the work started on the A-36 in April 1942 with actual contract award in August 1942. By that time NAA was deep into the P-51B and The RAF was nearly ready to fly the Mustang X with Merlin.

Note - when the discussed meeting between Lovett and Arnold was held in June 1943, the First P-51B was rolling off the production line

At the risk of being a bit strategy centric, Lovett, assistant secretary of war for air during June, 1943 -after a tour of bomber bases in England, pitched Arnold to afford a long-range escort fighter his immediate attention. If the discussion at page 144, Masters of the Air by Donald L. Miller is correct, Lovett's recommendation precipitated Arnold's memo requiring a long-range fighter escort, though not mentioning the P-51. Miller generally does his homework on documented events though he sometimes gets caught passing on discredited scuttlebutt. In any event the discussion is at page 144.

The whole fighter escort development is a bit confusing in that it morphs from an Eighth Air Force bomber protection operation to a D-day air superiority mandate from Eisenhower. Under Doolittle the bombers were less objects of protection –though they were in fact much better protected- than bait for to draw in LW fighters for the escorts to deal with. On June 6 the allies enjoyed air superiority over Western Europe.

A better book for you is "Air Force Spoken Here" by Ira Eaker and assisted by James Parton - Eaker's Aide. The best place to begin on this subject is Chapter 16, page 261 and leads up to a detailed discussion from Lovett regarding the letter exchanges and political/military complexities of the May-July 1943 period leading up to the August Ploesti/Regensburg/Schweinfurt battles.

 

[tomo pauk]

Wonder how far fetched is this idea:
(historically: ) USAF doe not have the funds for more fighters, but id does have for (dive?) bombers. The Mustang I is recognized as a performer.
So, non-historically, USAF decides (instead to going for A-36), to change the contract with Curtiss, where some 500 P-40s will receive dive brakes, thus becoming dive bombers. Those dive bombers will be purchased by bomber's funds. The newly-freed fighter's funds will be spent on NAA's fighter (hopefully with V-1710-81 engine).

 

[Koopernic]

No place for the turbo. Allison finally built a decent (sub par to Merlin) supercharger for the 1710-143 in 1945 but it had significant detonation issues at max boost. Still, had that engine been available in 1942, the P-51A would have been the best fighter in the world.

I would have to qualify and say yes and no but ultimately claim that it could have been done.

The Merlin engine P-51B took nearly 2 years to get into production. Surely in that time the turbo Allison could have been fitted. Now in terms of the space issue.
1 Q: Where would the intercooler be fitted?
A: The same place the Merlin had its water cooled intercooler: behind the engine.
2 Q: Where would the turbo supercharger be fitted?
A: The same place the Merlin had its mechanical supercharger: behind the engine and underneath the supercharger.

Of course the assembly would have been somewhat larger, but its hard to imagine that it would be so much that it could not be dealt with by a slight nose extension of the P-51.
The twin Mustang was for instance some 18 inches longer. The P-51B had nearly every panel redesigned compared with the P-51A so given the redesign this was not much to go a little further.

The problem may have been that the NACA's advice to the Army Air Corps which was that the turbo supercharger should be kept separate from the engine connected by ducting. Integral turbochargers, which were integrated into the engine and shipped in a single package would have to be used with such a P-51 turbo Allison.

The advantage would likely be
1 The same top speed, likely higher speed at high altitude, say above 25,000-30,000ft
2 Much better cruise fuel consumption and therefor escort range.
3 Higher service ceiling and climb rate at high altitude.