Allison and Merlin in a P-51

[MiTasol]

There is an online copy/transcript of the report here:

E-GEH-16

Interesting report that

 

[emu27]

I think you have the wrong end of the stick on several items - the most glaring being that the Mustang was designed for the RAF - NOT the USAAC

Where in the world do you get the notion that I said the aircraft was designed for the US forces?

It really wasn't. Certainly no more than the P-40 or P-39 were designed as "Army Co-operation" aircraft.

And if it was the case, it would have been unlikely that the Mustang would have changed from the 8.8:1 supercharger gear to the 9.6:1, which was aimed at better altitude performance.

It really was should you wish to read the aircrafts history. The Army Co-operation role included keeping enemy aircraft off their backs, FW 190 for instance, read about the Dieppe raid. The introduction of the 190 caused the British much concern and were anxious to get the -51 so as to counter it, to the extent that they considered building the -51 in the UK, part of that worry was when the Spitfire IX might reach operational status.

The supercharger ratio change would have been a performance enhancement, but doesn't change the fact that the aircraft's raison d'être was Army Co-0peration as the British called it. Airborne attacks on the troops were not made from high altitude, Stuka etc were the trouble.

 

[wuzak]

It really was should you wish to read the aircrafts history. The Army Co-operation role included keeping enemy aircraft off their backs, FW 190 for instance, read about the Dieppe raid. The introduction of the 190 caused the British much concern and were anxious to get the -51 so as to counter it, to the extent that they considered building the -51 in the UK, part of that worry was when the Spitfire IX might reach operational status.

The supercharger ratio change would have been a performance enhancement, but doesn't change the fact that the aircraft's raison d'être was Army Co-0peration as the British called it. Airborne attacks on the troops were not made from high altitude, Stuka etc were the trouble.

The Mustang/P-51 was designed as a fighter, to be better than the P-40.

The limiting factor in its use as a general fighter was its engine, which had a low critical altitude. Army cooperation is what it could do, not what it was designed for.

The higher gear ratio increased its altitude a few thousand feet, but not enough.

The fact is that very shortly after the first Mustang I arrived and was tested in England there were moves to put either the Merlin XX or Merlin 61 into the Mustang airframe.

Rolls-Royce even pushed, at one stage, for it becoming the RAF's primary fighter, instead of the Spitfire, fitted with Merlins, of course. It was proposed to ship airframes across from NAA and have Merlins fitted at conversion centres in the UK.

The Mustang entered service in the RAF only a few months before the IX. And the IX was at Dieppe as well. The IX was an interim development of the V fitted with the Merlin 61. The VII/VIII, which were to be the definitive 2 stage Spitfires, had some aerodynamic improvements, but change over to their production would take too long in light of the Fw 190 threat (don't forget the Bf 109F-4 either), so the IX was built.

The Spitfire III possible would have matched the Bf 109F-4 and Fw 190A, but that was also passed over due to the amount of mods to the airframe, the time it was taking to get a prototype built and the fact that the Hurricane needed Merlin XXs more than the Spitfire. The Mk V was built instead, based on the Mk I airframe with the Merlin 45 fitted.

In a similar story, the Typhoon was designed to replace the Spitfire and Hurricane. But its engine was also not very good at altitude, so it too was relegated to low/medium altitude work.

 

[wuzak]

The V-1710 engines in the Mustang Mk.I aircraft "as delivered" did not have an automatic boost control. On the V-1710 engines on the Mustang Mk.IA, they were initially fitted with a Delco-Remy or later a Claudel Hobson automatic boost control, however these proved troublesome and prevented the engines from developing the required level of "over-boost" required, when combined with the modifications (cropping) conducted on the supercharger vanes to improve performance below 10,000ft. (Sources: Various AIR and AVIA files held in UK Archives relating to Mustang Aircraft, Air Ministry Mustang Mk.I and Mk.IA Pilots Notes, Erection and Maintenance Manuals AP Series, original diaries, personal papers, original service documents and interviews with surviving RAF aircrew and groundcrew who flew and maintained Mustang Mk.I, Mk.IA, Mk.II aircraft in RAF service 1942 to 1945.)

First time that I have heard of the V-1710's impeller being cropped.

The Merlin 45M had its impeller cropped to 9.5 inches - the same size as the regular V-1710 impeller.

 

[ThomasP]

As far as I know all the operational war-time V-1710 marks used the Ø9.5" impeller for the engine mounted supercharger, no cropping. At some point late in the war an improved Ø9.5" impeller was developed where the vanes were modified to give significantly better efficiency (in terms of HP absorbed by the supercharger) - but as far as I know this mod did not become operational during the war. The only new impeller diameter for the engine mounted supercharger that became operational (that I am aware of) was the Ø10.25" impeller in the post-war 'G' series, used only in the P-82.

 

[Reluctant Poster]

Love to hear of the significant problems.

The Allison was the preferred engine by those doing low level Rhubarb type missions because it provided greater range through better fuel economy and was more robust, being better able to endure abuse, so good in fact that they removed the boost control in order to increase manifold pressure. When the Merlin production line started the USAAC operating in Africa put forward a proposal (have a copy) to keep the Allison powered version in production because of its superior qualities in the low level role. The Merlins forte was its high altitude capability. The better economy of the Allison was due to its ability to run at very low RPM that the Merlin was unable to match.

On what page does he make that statement?

People tend to forget that the Mustang was originally designed as an Army Co-operation aircraft ie low level operations, for which the Allison was the perfect choice.

The Allison had significant problems in its tubocharged version. The list of excuses for its problems is endless but the fact is it was found wanting at crunch time.
Page 159 of the paper back version of Mustang Designer quotes Schmued at length. He bames Allison and the DoD for ruining a great plane.
On the next page Wagner writes "When working right, which was seldom…" Wagner also quotes the Case History of the F-82E F and G as stating "33 hours of maintenance were required for each hour flown.

 

[denny]

The Allison had significant problems in its tubocharged version. The list of excuses for its problems is endless but the fact is it was found wanting at crunch time.
........................

Was that in any plane other than the P-38.?

 

[Reluctant Poster]

Was that in any plane other than the P-38.?

Fortunately not.
The Allison did well at low level but that was a limited niche. I would also point out that he Merlin 32 was optimized for low altitude and it out performed the contemporary Allison used in the A-36.

 

[denny]

Fortunately not.
The Allison did well at low level but that was a limited niche. I would also point out that he Merlin 32 was optimized for low altitude and it out performed the contemporary Allison used in the A-36.

Did the P-38 have problems or issues with its turbo system throughout the war. Or did they just have troubles making it work at the wars beginning.?
Thank Yiou

 

[Reluctant Poster]

Did the P-38 have problems or issues with its turbo system throughout the war. Or did they just have troubles making it work at the wars beginning.?
Thank Yiou

The P-38 was thrown off the job of high altitude escort in the ETO because of all the problems suffered during the winter of 1943 to 1944. The 8th AF replaced the P-38s in 3 fighter groups with P-51s in July 1944 with the remaining group lasting until September before it received P-51s.
It is claimed that the P-38 L solved everything yet when it came to providing very long range escorts for the B-29s bombing Japan the USAAF selected the P-51. At much the same time as 100 P-51s went to Okinawa, a 100 brand new P-38L were sent to guard the Aleutians.

 

[emu27]

It really wasn't. Certainly no more than the P-40 or P-39 were designed as "Army Co-operation" aircraft

Army cooperation is what it could do, not what it was designed for.

It really was. The British wanted NAA to build P-40's for the Army Cooperation role but NAA said we could build a better aircraft than the P-40. The RAF had an Army Cooperation Command, along with Bomber Command, Fighter Command, and Coastal Command, the AC Command was disbanded on 31st March 1943. The RAF used the Allison aircraft primarily for tactical reconnaissance, low level fighter and ground attack (Army Cooperation - close support fighter to our US friends). From "FROM ARMY CO-OPERATION TO FIGHTER RECONNAISSANCE – DEVELOPMENTS 1939-1945" by Peter Elliott.

The Curtiss Tomahawk, however, was available and in 1941 the re-equipment of fourteen squadrons began. Serviceability proved to be poor, due to engine problems, and at the start of 1942 the decision was made to reequip with the Mustang.

The Allison-engined Mustang I proved to be a very capable reconaissance fighter – fast and a stable platform for photography – and it eventually equipped all the home-based AC (Army Cooperation) squadrons. Unlike the Tomahawk, however, the Mustang was not able to take vertical photographs.

From "Mustang" by Robert Grinsell,

The initial RAF unit to receive the Mustang I was 26 Squadron based at Gatwick, which took delivery of one of the new aircraft from Speke in January 1942. By March, the Mustang began to appear in the inventories of several other Army Co-operation units whose main task was to support the British army in training exercises up and down the length of Britain in preparation for future combat operations on the European mainland. Due to the fact that the Mustang was essentially in training, and no current need existed for it as a fighter interceptor, delivery of it to the various units was slow and several experimental modifications were evaluated. The one which was to have not only a major impact on the air supremacy of the Allied Forces in later years, but one which may have also played a major role in determining the overall outcome of World War II, was the installation of the Rolls-Royce Merlin powerplant into four Mustang ls. The success of these aircraft convinced the U.S. Government to place an order for two Packard-built Merlin powered prototypes, designated XP-78 (North American designation NA-101). These aircraft were to provide the basis for the later model P-51B model of the Mustang which offered long-range high-altitude bomber escort and interceptor capabilities.

The first combat operations in which the Mustang was used as an offensive weapon occurred on 10 May, 1942, when a single aircraft of 26 Squadron took off from Gatwick on a reconnaissance sortie to the French coast. The pilot photographed parked Luftwaffe aircraft at Berck airfield and then swung his Mustang around for a strafing pass at the various vehicles and supplies lined up along the outskirts of the field. On his way home, the pilot sighted a supply train and again banked his aircraft to attack. In less than two hours the Mustang was back at Gatwick, but it had set the stage for almost continuous Mustang "reconnaissance and destroy" (called "Popular" by the RAF) sorties into German-held French territory. The first known casualty of a Mustang occurred two months later when, in ]uly, 1941, 26 Squadron reported the loss of aircraft AG 415 during a strafing mission near Le Touquet, France.

With the combat worthiness of the Mustang I being proven daily, the RAF decided to expand its role and during the late summer and early fall of 1941 assigned the aircraft to Coastal Command duties which included the escort of slower more cumbersome anti-shipping bomber aircraft, and in low-altitude fighter interception sorties against wave-top flying Fw 190s which were carrying out deep interdiction raids against British coastal harbors and ports. In addition, the Mustang units were assigned to "Seek-and-Destroy" sorties over the coast of France to strafe specific targets such as trains, transport convoys and military installations.

Engines.......................................................................................Horsepower
.................................................Supercharger Ratio.....T/O......At Rated Alt........Rated Altitude
Mustang I......1710-39..........................8.8...................1150.............1150.......................11,800
Mustang II.....1710-81.........................9.6....................1200.............1125.......................14,600
A-36.................1710 -87........................7.48.................1325.............1325..........................2,500

All supercharger impellers are 9.5 inches diameter

 

[pbehn]

It really was. The British wanted NAA to build P-40's for the Army Cooperation role but NAA said we could build a better aircraft than the P-40. The RAF had an Army Cooperation Command, along with Bomber Command, Fighter Command, and Coastal Command, the AC Command was disbanded on 31st March 1943. The RAF used the Allison aircraft primarily for tactical reconnaissance, low level fighter and ground attack (Army Cooperation - close support fighter to our US friends). From "FROM ARMY CO-OPERATION TO FIGHTER RECONNAISSANCE – DEVELOPMENTS 1939-1945" by Peter Elliott.

The Curtiss Tomahawk, however, was available and in 1941 the re-equipment of fourteen squadrons began. Serviceability proved to be poor, due to engine problems, and at the start of 1942 the decision was made to reequip with the Mustang.

The Allison-engined Mustang I proved to be a very capable reconaissance fighter – fast and a stable platform for photography – and it eventually equipped all the home-based AC (Army Cooperation) squadrons. Unlike the Tomahawk, however, the Mustang was not able to take vertical photographs.

From "Mustang" by Robert Grinsell,

Engines.......................................................................................Horsepower
.................................................Supercharger Ratio.....T/O......At Rated Alt........Rated Altitude
Mustang I......1710-39..........................8.8...................1150.............1150.......................11,800
Mustang II.....1710-81.........................9.6....................1200.............1125.......................14,600
A-36.................1710 -87........................7.48.................1325.............1325..........................2,500

All supercharger impellers are 9.5 inches diameter

This is wrong in my opinion, before any Mustang Mk Is were delivered the UK was technically bankrupt and Lease lend kicked in, the British were only going to get what the USA didnt want. By the time any Mustang Is were issued to squadrons at Gatwick the USA was at war with Japan and Germany. That changed the whole game. The P-40 was tried in tactical recon and couldnt do it. It could work in N Africa, that 21 miles of water and the defences beyond it changed the whole game.

 

[ColFord]

First time that I have heard of the V-1710's impeller being cropped.

The Merlin 45M had its impeller cropped to 9.5 inches - the same size as the regular V-1710 impeller.

The cropping of the impellor was a RAF developed modification and was applied to all the Allison V-1710 engines proposed to be installed in operational RAF Mustang Mk.I, Mk.IA and Mk.II aircraft. It was on the list of modifications that the RAF had that had to be performed on a Mustang to be considered fit for operational flying. The effect of the cropping of the impellor was to improve engine performance below approximately 8,000ft and particularly enhance it in the zero to 4,000ft range. The RAF had sought technical advice on the modification from Rolls-Royce and a number of other aviation engine specialists in the UK.

Some of those authors quoted in those book extracts need to get their facts straight. The ACC Mustangs were given in mid-1942, as a way of getting more operational experience and to get more experience in flights of longer duration requiring more precise navigation, sorties supporting the Royal Navy and Coastal Command - "Jim Crow" and "Lagoon". These were reconnaissance sorties within defined areas along the Dutch, Belgian and French coasts. The advantage these sorties had over the other types being used by Coasal Command at the time for shipping reconnaissance, was that the Mustangs were quicker, could defend themselves better, and having sighted a convoy they were back at base making the report earlier, which allowed planning for any potential attack on the convoy to commence in a more timely manner. There are no recorded sorties of ACC Mustangs escorting Coastal Command bombers on attacks on convoys. One type of sortie flown on a number of occasions was providing fighter cover, outside the usual range of Spitfires and Hurricanes, to RN MTBs and MGBs returning following night time operations close to the enemy coast, especially operations off the islands at the northern most end of the Netherlands and northern Germany and in the south around the Channel Islands - the Mustangs could loiter considerably longer over the returning RN vessels than the other RAF fighter types of the time. Some sorties were also tasked to look for German E-Boats in the early evening as the headed out from their bases and early morning as they headed back to their bases, with any E-Boats found to be attacked by strafing. RAF ACC Squadrons did fly sorties doing long range bomber escort to the Bostons and Venturas of 2 Group RAF in late 1942 and into early 1943.

As for the statement by Elliot about the Mustang not being able to carry a vertical camera - WRONG! (Elliot's article in the RAF Historical Society Journal is a simplistic view of the subject at best, in particular most of his quoted references are largely policy files - only four of his long list of references are actual references that cover operational activity.) As soon as the first Mustang Mk.I arrived in the UK, options and ways to fit it with a vertical camera were examined. A number of different options were proposed and considered and explored with NAA - both their technical representatives in the UK and via cable with NAA in the USA. NAAs initial responses were "can't be done", however engineering staff within ACC persisted and came up with a number of different options which were manufactured, installed and trialled. Eventually two vertical installations entered limited operational service and given the true test of being used on operations. One of the installations was further refined and in early 1943 a finalised design was accepted for wide scale adoption and implementation across the ACC Mustang Squadrons. (As an aside, following the RAF initial approaches, the design and engineering staff at NAA did start to look at the matter of both oblique and vertical camera installations for the Mustang and did come up with their own designs which were eventually the basis for the USAAF Allison Mustangs to be used in the Tac/R role. Comparatively the RAF designs were simpler, not as elegant, but were easy to manufacture and maintain, the NAA one was to a degree over engineered, included functionality not required in normal use and was eventually the basis for the final design adopted by the USAAF for all their Tac/R Mustangs.)

(For an expanded brief history of camera installations in RAF ACC Mustangs see "P-51B Mustang: North American's Bastard Stepchild that Saved the Eighth Air Force" by Bill Marshall and Lowell Ford, Osprey Publishing, UK, 2020 - pages pp163-169.)


[h3][/h3]

 

[don4331]

Every engine has strengths and weaknesses:

As noted, a Merlin supercharger was mounted remotely to an Allison and basically performed the same. However the supercharger failed shortly into the test, the exact cause was never confirmed but the speculation was that by being remote it wasn't kept up to same temperatures that it would have it was directly mounted to the crankcase.

Early aircraft engines used brass floats to control the fuel level in the carburetor – rising to stop fuel flow, sinking to allow fuel in. If the floars weren't properly soldered shut or developed leaks in service, they would sink and fuel would flow overflow the carb. With an updraft carb, the excess fuel simply falls to the ground. With a downdraft carb, it usually flows somewhere bad – into the intake flooding the engine, over the red hot exhaust causing fires, etc.

The American auto industry, with engines like the flat head v-8, were making better downdraft carbs. And let's not forget Allison is a subsidiary of GMC, an automotive company.

Aside: Peregrine and Vulture, RR latest 2 engines pre-War and the post war Merlin 130s were downdraft. Downdraft is a better configuration, but sometimes you have to stick with what is working.

Allison will have marginally better economy as it has ~10% higher compression ratio (CR). The Merlin with 10% lower CR, can build ~10% higher boost. The higher boost comes at a cost as it takes more power to drive the supercharger. But the end result is the Merlin more than makes up for the 60 in^3 it is short on displacement with more power.

The engineers at Allison developed very sophisticated intake manifolds that "rammed" air into the cylinders at optimum rpm. The engine was also developed for turbocharging. The combination of the 2 meant the camshaft timing was fairly mild allowing the engine to run smoothly at less than 50% power, again allowing it to be more economical.

The engineers at RR, concentrated on a better supercharger and used a "sewer pipe" to deliver air to the cylinders. As the Merlin wasn't designed for supercharging, they used pretty radical cam timing (Merlin idling sounds angry and when at operating speed mean). The use of radical cam timing meant the Merlin was prone to backfiring. As RR didn't have a fancy ram air manifold, they had not issue installing "flame traps" in intake ports to stop the issue. (Flame trap is a number of thin plates which stop the backfire from entering the engine).

For the Allison engines in the P-82 had 2 stage superchargers and more radical cam timing. The result was backfires, which without the flame traps, went through the entire intake, intercooler and supercharger. (Think AA Fueler blower explosion). Allison engineers didn't want to give up their fancy intake manifolds for flame traps, so Allison got a bad rap.

As you might recall from high school chemistry, it takes a huge amount of energy to boil water*. RR engineers used this fact by allowing very limited, very local boiling in their engines around the exhaust valves. Once mixed with coolant in the engine, the water vapour is return to water again but the mixture is very hot. As the mixture is very hot, you need a smaller radiator because there is greater temperature difference with outside air. So, Merlin gets away with less than ½ the cooling water of the Allison.

It's also why you can't turbocharge a Merlin – the exhaust is running so close to thermal limits that the extra heat from restricting exhaust exit melts the head.

Early P-38s issue was Lockheed didn't anticipate flying for extended periods of time at high altitude. The decision to use the outer wing leading edge as an intercooler appeared to be stroke of genius. But unfortunately, in conditions that 8th​ AF found themselves in, planes were flying at cruise speed for hours in -30° cold. And the load on the turbocharger wasn't enough to have them creating enough warm air to justify the intercooling but there was no way to limit it. The carb/engine on the Allison wasn't designed for operating in that environment for extended periods.

Adding to the problem, the leading edge intercooler didn't have enough cooling for full power, and the available fuel, while it met the 100 octane requirement lean, didn't meet requirement under boost at rich setting. Add in some sluggish controls as engines are out in wings, oil used in controls congealed in cold and you get engine failures.

Westland had similar issues with the hydraulic throttle on the Whirlwind – great idea, you don't need to worry about cables changing length as plane flexes, etc. Unfortunately, the oil got thick at altitude and pilots couldn't pull throttle back after going full power, resulting in blown up Peregrines. As a result, the engines get a rap for bad altitude performance. But it wasn't the RR engine, it was the implementation.

For the Allison, the late P-38J and L is the sweet spot, not too much power to cause the backfire issue, enough and controllable intercoolers, so as keep engine working like top. Unfortunately, twins use 2X the fuel as single, so why use up your limited logistics when the P-51 is right there. Same thing happens in Korea – P51 is used as ground attack plane even though P-47s and F4Us are available and better planes for that role as the R-2800 burns 2X the fuel as the Merlin.

Typhoon wing and engine both weren't good at attitude. But it was a beast down low.

I do wonder why Allison/GE never pushed for a turbocharged Allison Mustang. If you remove the fuselage tank, there would be room for the turbo. Routing of intake and exhaust wouldn't be any different from Thunderbolt in concept.

*While I am saying water, I know it is a water/glycol mix.

 

[wuzak]

As noted, a Merlin supercharger was mounted remotely to an Allison and basically performed the same. However the supercharger failed shortly into the test, the exact cause was never confirmed but the speculation was that by being remote it wasn't kept up to same temperatures that it would have it was directly mounted to the crankcase.

In the Merlin the oil was, IIRC, shared with the engine, so it was warmer than when the supercharger was separate. That possibly would reduce the housing temps and affect the bearing clearances, leading to the failure.

Early aircraft engines used brass floats to control the fuel level in the carburetor – rising to stop fuel flow, sinking to allow fuel in. If the floars weren't properly soldered shut or developed leaks in service, they would sink and fuel would flow overflow the carb. With an updraft carb, the excess fuel simply falls to the ground. With a downdraft carb, it usually flows somewhere bad – into the intake flooding the engine, over the red hot exhaust causing fires, etc.

The American auto industry, with engines like the flat head v-8, were making better downdraft carbs. And let's not forget Allison is a subsidiary of GMC, an automotive company.

Aside: Peregrine and Vulture, RR latest 2 engines pre-War and the post war Merlin 130s were downdraft. Downdraft is a better configuration, but sometimes you have to stick with what is working.

Most US aero engines of WW2 used injection carburettors, which do not care which direction they are pointing. Rolls-Royce also developed injection carburettors for the Merlin and Griffon later in the war. Reading Callum's book it seems that direct and port fuel injection were tested in both the US and UK, with neither adopting them. And it took years to get injection carbs into service in British engines.

The engineers at Allison developed very sophisticated intake manifolds that "rammed" air into the cylinders at optimum rpm.

That was a solution to a problem they were having at the time. IIRC they were getting uneven mixture distribution.

The engine was also developed for turbocharging. The combination of the 2 meant the camshaft timing was fairly mild allowing the engine to run smoothly at less than 50% power, again allowing it to be more economical.

I dispute the claim that the V-1710 was developed for use with turbochargers.

It was first designed as an airship engine, which did not have a supercharger at all - but was reversible in flight. That last bit made changing from RH to LG rotation somewhat easier.

I don't believe Allison ever tested the V-1710 with a turbocharger on a test stand until after the Bell XFM and Curtiss XP-37 had flown. If it had been developed with turbocharging in mind I would have thought it would have been fitted with the turbo for running on the test stand.

As you might recall from high school chemistry, it takes a huge amount of energy to boil water*. RR engineers used this fact by allowing very limited, very local boiling in their engines around the exhaust valves. Once mixed with coolant in the engine, the water vapour is return to water again but the mixture is very hot. As the mixture is very hot, you need a smaller radiator because there is greater temperature difference with outside air. So, Merlin gets away with less than ½ the cooling water of the Allison.

The Merlin used pressure cooling, which raised the boiling temperature of the water/glycol mix above 100C. Generally it is undesirable for the cooling medium to become steam, but I don't know if your claim is true or false. The V-1710 also had pressure cooling, though it was developed a little later.

I am also unsure as to the claim that the Merlin needed less than half the coolant.

It's also why you can't turbocharge a Merlin – the exhaust is running so close to thermal limits that the extra heat from restricting exhaust exit melts the head.

I would guess that had Rolls-Royce decided to to turbocharge the Merlin that the supercharger drive ratio would have been reduced from a critical altitude of somewhere between 10,000ft and 20,000ft, and this would have led to less heat being generated in the supercharger and less heat in the combustion chamber, and lower load on the exhaust valve.

Also, the turbos were designed to run with back pressures not much more than an open exhaust at sea level.

Early P-38s issue was Lockheed didn't anticipate flying for extended periods of time at high altitude. The decision to use the outer wing leading edge as an intercooler appeared to be stroke of genius. But unfortunately, in conditions that 8th​ AF found themselves in, planes were flying at cruise speed for hours in -30° cold. And the load on the turbocharger wasn't enough to have them creating enough warm air to justify the intercooling but there was no way to limit it. The carb/engine on the Allison wasn't designed for operating in that environment for extended periods.

The engine around which the P-38 was designed, including its leading edge intercoolers, were 1,150hp maximum. The improvement in the V-1710's power made the intercoolers obsolete.

I do wonder why Allison/GE never pushed for a turbocharged Allison Mustang. If you remove the fuselage tank, there would be room for the turbo. Routing of intake and exhaust wouldn't be any different from Thunderbolt in concept.

And reduce the range by doing so?

 

[ColFord]

I do wonder why Allison/GE never pushed for a turbocharged Allison Mustang. If you remove the fuselage tank, there would be room for the turbo. Routing of intake and exhaust wouldn't be any different from Thunderbolt in concept.

NAA did a design & engineering study on the Allison Mustang to look at putting a turbo supercharged engine onto it, and the changes required to accommodate the engine, all the associated plumbing, increased cooling requirements meant that it was not a modification, it was going to require a whole new fuselage structure to accommodate it. Combined with the increased fuel consumption, they then had to look where to put the additional fuel, which then got into a circular argument about what else in the design had to be moved to make room for more fuel, then where what had been moved to make room for more fuel tanakge, where that would go.......... Already, in terms of size and engineering requirements, the option of using a R-R Merlin, either manufactured in the UK or the USA made a better option as the changes required in the initial considerations looked to be simpler to implement as modifications to the existing airframe rather than a total re-work and redesign - with all that was associated with that in terms of new tooling if it went into production..

 

[Deleted member 68059]

Regards the Allison in the P-51

Could the Merlin 2-Stage have been mated to the Allison without much fanfare.?

If that WAS possible, would the P-51 have the same gas mileage with the Allison as the Merlin.

Could Allison have kept up with the demand for Allison motors, in a P-51 from 1944 onward.?
Thank You

You can do anything if you have enough time to modifiy the parts and get production going, but broadly, NO (or at least not very usefully) because the 1710 had a significantly
lower knock limit than the Merlin, so you could use it to get better high altitude performance, but it would always be slightly inferior in peak power to the Merlin-so-equipped.

Eventually Allison moved to higher pressure cooling and changed the coolant specifications, which would have narrowed that gap down, but that wasnt done
until the engine was fitted to the F82.

If you want to beat the Merlin with the 1710, you would need to do more than just copy the supercharger. As I`ve said in my book, the overall layout of the 1710 was in many respects better than the Merlin (the crankcase split down the crank line is better, and so is the combustion chamber, and the cylinder head ports are MUCH better than the Merlin), but we`re entering "what-if" terratory than needs Allison not to have had the huge slump in development effort in the 30`s.

(the very good ports would have been good for fuel economy, as you could have made the same power with a fraction less boost, as the ports will "let in" more charge. So
you can save a bit of supercharger driving horsepower, maybe a couple of percent economy improvement, the Merlin`s very good superchargers meant they could "get away" with awful ports, and so avoid retooling the cylinder head castings)

 

[Jugman]

I dispute the claim that the V-1710 was developed for use with turbochargers.

It was first designed as an airship engine, which did not have a supercharger at all - but was reversible in flight. That last bit made changing from RH to LG rotation somewhat easier.

I don't believe Allison ever tested the V-1710 with a turbocharger on a test stand until after the Bell XFM and Curtiss XP-37 had flown. If it had been developed with turbocharging in mind I would have thought it would have been fitted with the turbo for running on the test stand.

The V-1710 project began May 7, 1929 and from the very outset it was intended to be a 1000ph engine compatible with turbosupercharing and fuel injection. The first contract for A V-1710 was signed by the Navy on Jun 26, 1930 for one 750hp with a 8.25" supercharger running at 8:1 and a 3:2 reduction gear. The first Army engine contract is dated January 5, 1933. This model was specified as 750hp engine with the understanding that a 1000hp is the desired power. This contract was also first one state that the engine needs to be compatible with turbosupercharing and fuel injection. The contract for the V-1710-4 airship engine wasn't signed until January 24, 1933.

 

[Shortround6]

I would dearly love to see some actual "proof" that the P-40 or the Mustang I were designed for army co-operation.

Not quotes from old books but USSAC memo's or a paragraph (or more) from the specification/requirement.
This furphy is enduring one.

two things.
1. The XP-40 and the initial few P-40s had about the worst armament for strafing/ground attack of any combat aircraft in the US inventory of the time. US had pretty much standardized on four .30 cal for "attack" planes for strafing in the early 30s and anything after that, up to and including the A-20, had those four guns.
1a, The XP-40 and early P-40s (up to the "C") had either no bombs or six 20lb bombs(?) as payload. Which is a lighter bombload than even the P-26 Peashooter and much less than the Seversky P-35. Curtiss offered up to an 850lb bomb load on export Hawks (500lbs under the fuselage and 150lbs under each wing) so the capability/engineering was already there. It just needed somebody to check off the box/es on the order form. Hundreds of P-40s and hundreds of Tomahawks built with no bomb racks for a ground attack/army co-operation aircraft????

2. When XP-40 and early P-40s were ordered they got the engine with the highest FTH available/promised by any US engine maker. Things did change in the next few years but the Allisons with the 8.80 supercharger gears were good for 1040hp at 14,300ft which was, with the exception of the Merlin III, just about the highest FTH you are going to find. A number of other engines are close though. But this was the best altitude engine the Army could get in the spring of 1939 (turbos and 2 stage mechanical superchargers were not ready for squadron service in 1939/early 1940).


The engine used in the Mustang I and the P-40D/E was also good for 1040hp at 14,300ft, it was just allowed to use a bit more boost lower down for the 1150hp rating at 11,700ft.
Both the Mustang I and P-40D/E were ordered before the BoB really started so nobody really knew what altitudes they would be fighting at in 1941.

 

[emu27]

I would dearly love to see some actual "proof" that the P-40 or the Mustang I were designed for army co-operation

It was the purpose to which the aircraft were put. The RAF had a Fighter Command and an Army Cooperation Command, although Army Command ceased to exist on 31 March 1943 the Allison Mustang was still performing Army Cooperation work up until VE day by the only Allison squadron remaining, 26 Squadron. From memory all, bar perhaps one or two squadrons, the Allison Mustangs went to Army Cooperation Command. All Merlin aircraft went to Fighter Command. Once again, remember the Mustang was designed, developed at the behest of the RAF to fulfill a RAF requirement - Army Cooperation, the only US involvement was giving permission to NAA to devote the resorces and to supply the aircraft. Beyond that the US had absolutely no interest in the aircraft, it was not for some time that the US understood what a jewel was hiding in the woods.

Mustang I - Squadrons - 2, 4, 16, 26, 63, 168, 169, 170, 171, 225, 31, 239, 241, 268, 285, 309, 400, 414, 430, 516, 613
Mustang II - 2, 225, 268,