P51 with Allison turbo

Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules

A turbo-Allison Mustang would probably be inferior to the two stage Merlin at lower altitudes, (and both are slower than a single stage Allison Mustang) with the performance becoming more equal to each other (and exceeding the single stage) in the 15,000-25,000ft range with the turbo plane coming out on top at around 25,000ft and up. The Turbo-Allison might offer better fuel economy even at high speed cruise (8%-??%) to help compensate for the lack of/smaller rear tank.

It rather depends on the Allison in question, the Merlin in question and the installation details of the turbo-Allison.

I believe Tomo's time line is a bit optimistic. If the First P-38Hs are being delivered (rolled out of factory) in March of 1943 that compares to the Merlin Mustangs being rolled out (slowly) starting in May. Granted by July of 1943 there are around 360 Mustang air frames waiting for engines but while the first 10 P-38Js are built in Aug of 1943 they are built in the Lockheed experimental shop and not a regular production line. For a period of several months (last H delivered in Dec 1943) Lockheed is building both P-38Hs and Js in parallel due to shortages of the new intercoolers. In fact the "H" model was interim model designed after the "J" to use the new Allison engines while the intercooler problem was worked out. The first 226 "H"s built also used the older B-13 turbos instead of the B-33 turbo used on the later P-38s.

P-38Hs used bigger radiators and radiator scoops than the "G"s.

To make any real difference at all ( shift long range escort missions by months and not a few weeks) the "turbo Allison Mustang" (or TAM will probably be limited to the type engine installation used in the P-38G assuming that some sort of suitable intercooler can be designed/built. I would note that the P-63 was supposed to use an intercooler, at least in one version, but the subcontractor responsible failed to come up with a suitable unit even months late. Apparently the 'theory' is easy but the actual design and fabrication is a bit more difficult.
 
Noo, not TAM!! This is a TAM:

http://www.internetoglasi.com/wp-content/uploads/classipress/tamic-hladnjaca-80-944808959.jpg

The 'core-type' inter-coolers were used en masse for the B-17s/24s, being able to work fine for power of 1200 HP at 25000 by the time USA entered the war. So there was both theory, practice and production expertise in this type of inter-cooler, stemming probably from even earlier P-43.
BTW, who was the manufacturer of the inter-coolers used on the P-47?
 
One of the things that seems to have been overlooked in this discussion concerns the practical problems of installing a turbo in a a single engine fighter using a V12 engine. This is a fundamental problem in the sense that a primary motivation for configuring a single engined fighter around a V12 engine is to minimize frontal area. The exhaust ducting, the actual turbocharger/intercooler assembly and the ducting for the compressed air all take up scarce space, add weight and abandon the significant benefit of exhaust thrust. I don't think anybody came up with a satisfactory solution. The XP-37 attempted to make space within the fuselage by repositioning the cockpit to the extreme rear of the fuselage - this was a poor solution from the perspective of pilot visibility and was quickly abandoned. The FW190C used external exhaust ducting and mounted the turbocharger under the rear fuselage - this must have resulted in considerable drag. There were also various Soviet designs, none of which were particularly successful. The XP-39 with its rear mounted engine represented a more radical solution, but suffered from a compromised installation due in part to space constraints. Interestingly, the later (and larger) P-63 used the two stage mechanically supercharged versions of the V-1710 - the turbocharged versions of the engine do not appear to have been seriously considered. The situation was somewhat different for radial engined fighters as the greater fuselage cross-section and shorter engine provided more internal space. Even here, the P-47 mounted the turbocharger assembly in the rear fuselage with the ducting running under the pilot.
 
The distance may or may not have been intentional. Allison found after the war when fooling around with a turbo compound (like the wright turbo compound exhaust gases were touted through a turbine that was geared to the crankshaft for extra power) that the exhaust gas temperature could easily exceed the allowable inlet temperature of the turbine. Allison resorted to injecting ADI fluid (water alcohol) directly into the exhaust manifolds to cool the exhaust for full power runs.
perhaps the long exhaust runs used on the P-47, P-38, B-17 and B-24 bombers ( the last three with several feet of exhaust pipe open to cooling air) helped lower the exhaust gas temperature before it reached the turbine.

The inter-coolers in the bombers took up a fair amount of room as did the ducting. A B-17 had 3 inlets in the wing leading edge for each engine, one was the oil cooler, one was for combustion air and the other was for the inter-cooler air. I would also note that some B-17 instructions give different critical altitudes for the inboard and outboard engines due to the differences in the exhaust and intake ducting.

A lot of the performance of turbo Allison Mustang depends on the inter-cooler installation. how effective it is and how much drag it creates, the more effective (in general) the more drag.
 

We can recall the XP-60A, that, while not as slender as Spitfire or Bf-109, was still well away from bulky radial engined fighters (at least vs. the ones with plenty of engine power). The exhaust ducting was there routed within fuselage confines. The exhaust ducts of the 'usual' V-12-engined fighters were protruding in the slipstream anyway. The Merlin Mustang was featuring intercooler, along with it's piping, while added a 85 gal fuselage tank, so there was plenty of space aft the pilot of the P-51. Some people consider the weight of a turbo installation is a booga-boo for the V-1710, yet the complete power-plant weight of a turbo 'assisted' V-1710 was about equal of the two-stage Merlin.

and abandon the significant benefit of exhaust thrust.
Click to expand...

There was almost nothing to abandon, vs. Allison Mustang - the engine was making 600-650 HP at 25000 ft, so we have well under 100 HP worth of exhaust thrust? Call it ~700 HP total, a far cry against the turbo V-1710.


Curtiss with XP-37 made a fault - the exhausts were too close to the turbine, that would lead to turbine issues due to overheating. Main issue might be that whole turbo system was a far less understood thing in 1937, contrary to 1940-42.

The FW190C used external exhaust ducting and mounted the turbocharger under the rear fuselage - this must have resulted in considerable drag.
Click to expand...

The Fw-190 was having fuel tanks where P-51 had it's coolers, so everything went 'outboard'. Agreed that drag penalty was probably a major one.

There were also various Soviet designs, none of which were particularly successful.
Click to expand...

Soviets were also trying to design the turbo system in XP-37 layout, and that will not work until the air-cooled turbine blades are designed and produced. 1st to issue that were Germans IIRC, with BMW-801 in Ju-388?

The XP-39 with its rear mounted engine represented a more radical solution, but suffered from a compromised installation due in part to space constraints.
Click to expand...

Again, being among the 1st was more of a shortcoming than advantage. The inter-cooler(s) of the XP-39 was laying next to the fuselage, without boundary layer separator or diverter - that plays havoc with boundary layer entering the intercooler, lowering the performance, while adding to drag. 2nd, the intercollers were featuring no shutters - no control of cooling was possible. The USAF was demanding 50% of cooling performance, they were getting only 25%? That and other things were also contributing to the XP-39's drag, so much that NACA estimated that 50 mph can be earned just with aerodynamics cleanup.

Interestingly, the later (and larger) P-63 used the two stage mechanically supercharged versions of the V-1710 - the turbocharged versions of the engine do not appear to have been seriously considered.
Click to expand...

I'm afraid you're wrong here - the only way for the P-63 to receive a turbo engine was to have the turbine with air-cooled blades, and such a turbo was developed by Wright and was considered. It was to have the inter-cooler fitted, of 'Packard type (from Merlin )', ie. air-to-water type.


The 1st sentence is slightly misleading - the P-47 was about a meter longer than P-51, with fuselage maybe as twice as wide as P-51, so no wonder the internal space was far greater. It was also capable to accommodate 370 gals of fuel. The length of engine section (firewall to prop shaft) was maybe as twice as long as the R-2800 itself; the Packard Merlin pretty much 'ended' next to the firewall.
Another thing is also wrong as misleading - not all of the ducting was running under the pilot in P-47.
 
The thing with exhaust thrust is that you got your 100hp (or whatever) for about 30lbs of weight and a very small increase in drag.

Some of the "bugaboos" about weight come not only from the total amount but where it is. Try sticking an 85 gallon tank in the back of a P-51A or A-36, heck stick a 60 gallon tank back there and watch happens ( I will do it from the ground thank you). There may very well be room for it but the CG will be WAAAY out of wack. Not only is the two stage engine heavier than the Allison but the Prop used on a P-51B was about 100lbs heavier than the prop on a Allison P-51 ( it was almost 70lbs heavier than the prop used on a P-38J) while the fuel tank is not back by the tail wheel but located immediately behind the pilot and above the radiator duct. rear end of the tank is about even (or just a touch behind) the rear of the radiator.

Now maybe the Turbo Allison Mustang needs a 480-490lb prop to handle the power or maybe you can just bolt 100-150lbs of armor steel somewhere behind the prop to counter balance the weight going in behind the pilot.

P-47 was one of the few turbo aircraft with a buried turbo installation. ALL the cooling air for the inter-cooler and the turbo was brought in and gotten rid of by ducts. P-38s, B-17s, B-24s depended on hanging the turbo out in the slipstream for some of the turbo cooling.




Perhaps the P-60 was fully enclosed too.
 
No doubt that exhaust thrust was a god thing, with superb bang-for-buck value. OTOH, if the prop thrust is low at altitude (due to low prop HP), the total thrust is still not going to make a plane to perform at there. Unfortunately, the single stage V-1710 belonged to that 'category'.
As for CoG issues, we can recall that early Mustang/Apache have had also two HMGs under the the engine (150 lbs worth with extras? plus ammo, closer to CoG); the god (= heavier) prop will be needed for a more powerful engine. All that combined will keep 'frontal weight' closer to 2-stage Merlin installation. The turbocharger of B type was circa 300 lbs, vs. 600 lbs worth of fuel in fuselage tank. The turbo need to be located as feasible as close to pilot/CoG. Inter-cooler radiator will be lighter, using air instead of liquid as working medium.
Interestingly enough, the P-51A have had fuselage MGs deleted, and no CoG issues arosed - it was nose-heavy with those MGs?
The XP-60A seem to have had even more buried turbo than P-47, at least by looking at theses pics?
 
Picture of the fuselage guns on a Mustang, they are further forward than most other planes.

http://www.timadamsphotography.com/9570 A-36 Apache gun detail.jpg

P-60



Not only has a standard P-40 radiator oil cooler set up (apparently) but an air inlet in each wing root. Granted the Mustang can use original radiator but the air inlet in each wing root have got to feed intake air and inter cooler air.



or intercoolers are in the wing root extensions. It appears that vent/s are in the fuselage side/s to let out cooling air for turbo or exhaust?
Please note that there are air inlets at the front of each exhaust manifold fairing at the front of the engine ( cooling air down outside of exhaust pipes leading to turbo?

this is the same airframe with a non-turbo Merlin:



The radiator looks pretty horrible but we can see that the trubo plane picked up a bit bulk all over.
 
I believe the air inlets were inteks for the exhaust manifold shroud cooling air.

They actually had a fire on the ground one day when they didn't get airborne quickly enough. Perhaps these inlets were added after that happened, but they certainly look like exhaust shround cooling air to me.
 
when talking about 'no benefit in high performance' Compared with historical Allison Mustangs, the turbo would offer significant boost in hi-alt performance.
Click to expand...

This was based on your earlier statement in post 13 that it would offer 'next to nothing' compared to a two-speed two-stage Merlin. Having read about the P-60, and I admit there are gaps in my knowledge, what issues were suffered with the V-1710/turbo variants, XP-60A and B with GE and Wright turbo-superchargers respectively that meant they weren't continued with? The XP-60A first flew in November 1942 and fearing that its performance was not going to be sufficient Curtiss modified the XP-60B with an R-2800 and redesignated it the XP-60E. Surely that's a reason not to undertake such a modification?

The only, yet important feature of 'my' contraption is that it can offer a workable high altitude and long range capabilities already in early 1943, in good numbers, while for the Merlin Mustang the Allies must wait until late 1943.
Click to expand...

This is somewhat optomistic alright. Far too optomistic. In order to fit a turbo unit in a Mustang you'd have to redesign the entire aircraft, with the possible exception of the tailplane. You might as well start from scratch with a whole new aircraft. There's no way you'd have one ready in that time frame; incorporating the modifications necessary would not be as simple as placing the turbo units into airframes already completed as they are finished.

As for the Super Mustang and availability of Griffon 61 engines; here's a quote from a letter from Hives dated 28 June 1942 that Freeman responded to with the quote I posted earlier;

"We are now running a Griffon 61 on test and are very pleased with it. It is the best fighter engine in the world, but there will be no aeroplane for it. In spite of us delivering the first Griffon engine to Supermarines last November, their first machine, which can only be considered a 'mock-up' because it has been flying with only the standard Spitfire wings, has only completed 22 hours in the air..."

Rolls had production Griffon 61s ready for late 1942. Like Freeman stated; if airframer and engine manufacturer pulled their finger out a Griffon 61 engined 'Super Mustang' could break records for getting a front line fighter into service; one could have flown for the first time in early to mid 43. I doubt sincerely that Allison, NAA and any of the turbo-charger manufacturers could have a 'TAM' ready in the same time frame and even if by some miracle they did, a Griffon engined Mustang would outperform it at any rate.
 
nuuumannn said:
This was based on your earlier statement in post 13 that it would offer 'next to nothing' compared to a two-speed two-stage Merlin.
Click to expand...

Not sure why debating about that - I still stand by my statement about what the Turbo P-51 would've offered vs. both single-stage V-1710 and vs. 2-stage V-1650. The main advantages would be the major increase in hi-alt performance vs. historic P-51/P-51A and earlier availability vs. P-51B, again, as stated before.


The main reason not to pursue further with P-60 project was to allow Curtiss to concentrate more on production and development of the P-40. The cancellation of P-60 contract (almost 2000 fighters ordered, per AHT?) was supplanted with a contract for more P-40s, and Curtiss was to build P-47s under licence. The changes were in effect from February 1942.
With P-47 in pipeline (2 factories, plus what was expecting from Curtiss), there was hardly a way that P-60A would've been capable to offer anything better (bar combat radius on same fuel), yet the USAF decided to cover it's bets and test the XP-60 in different engine configurations (shortly after production was cancelled?).


Here we disagree.


I've already agreed that a Turbo P-51 would never be able to better the Griffon Mustang (2-stage variant). Talk about 440 mph vs. 470-480, for 1944 era service engines? The 1st Spitfire squadron was activated some time in January 1944, so it would be maybe April/May for the Griffon P-51 to enter the fray in ETO? If RR have indeed had the two-stage Griffon ready for production in late 1942, then it's too bad there were no Spitfires (and other?) flying with it in combat from Spring of 1943. Instead, it was the Spitfire V bearing the brunt until February of 1944.
 
Some interesting information here.


But what I was suggesting, was designing the P51 with the Allison turbo from the very beginning. Not adding it to the historic P51 aircraft.
 
I very seriously doubt a Griffon-engined Mustang at all under any circumstances.

In the political reality of the time the US would not order a Mustang developed for the USA with a British engine. That the Mustang got the Merlin was done becuase it was basically ordered for British use and we kept a few for US evaluation. When it was realized how good it was, we adpoted the Merlin-engine Mustang. Deliberately ordering a plane for US use with a British engine would not have been politically possible.

Development for British use might have been possible, but the order and contract would have to have come from the UK. I am not very well versed on the political situation in the UK from the point of view of internal politics, but I wonder if the British would have ordered an American aircraft with a Griffon when they had yet to experience the Merlins made in the USA. I am under the impression they did not expect the US-built Merlins to be very good, and wonder if they could have ordered a new British engine not yet in front-line British fighters to be put into a foreign aircraft for domestic use.

So I'm not saying it might not have been a good one ... it probably would have been. I am saying it would not have been very politically possible unless the order came from the UK.

We have had these discussion before and still we seem to keep trying to intermesh British hardware into US service. Wasn't ever going to happen unless the equipment was built for British use and worked well enough to interest the US military. Could easily happen post-war and did. Witness the USAF's adoption of the B-57 Canberra (with US engines and US-designed cickpit), but wasn't really possible in WWII.
 

The Merlin Mustang was driven by the British. As would a Griffon Mustang.

When Rolls-Royce started the Mustang X program there were three engines proposed for installation into the Mustang - the Merlin XX, the Merlin 61 and the Griffon.

The only impediment to a Griffon Mustang in US service would have been the low production rates of Grffons - that was because of no US licence production and the high priority given the Merlin in the UK.
 

Americans used a number of British engines in the 1940s. Or perhaps Ameritish engines or Britican engines. The P&W J42 and J-48 engines being licensed Rolls-Royce engines or started as licensed Rolls Royce engines (P did take them beyond what R-R did) and the B-57 was powered by Armstrong Siddeley Sapphire as modified by Wright. The Sapphire can trace back to the Metrovick though I doubt there was a single interchangeable part aside from some nuts and bolts.
 
Tomo, thanks for the info on the P-60; don't know a whole lot about it.


It was too bad. I suspect your idea of how long these things might take is a little optomistic, however, like your assumption modifing existing Mustangs might take. The first Griffon 61 engined Spitfire VIII (JF317) first flew on 4 March 1943. There's no reason a Griffon engined Mustang modified by Rolls-Royce couldn't have been flying in a similar time period. The Spitfire Mk.IX entered squadron service in June 1942, so, no, the Spitfire V did not bear the brunt until February 1944. The first Spitfire fitted with a 60 Series Merlin, Mk.III N3297 first flew on 27 September 1941.

The Merlin Mustang was driven by the British. As would a Griffon Mustang.
Click to expand...

As indeed it was, Greg (thank you wuzak). The plan to equip the Mustang with a Merlin was initially driven by the British for Britain, but for obvious reasons it was in America's interests to be involved. NAA and Packard were enthusiastic about the proposal from the outset and the USAAF were kept in the loop also from the start. There would be little difference if a Griffon was fitted instead and like with the Merlin engined Mustang Xs, Rolls-Royce would most likely have done the first conversion. The quotes I provided from the letters were between Hives of Rolls-Royce and Wilfred Freeman Vice Chief of Air Staff, RAF.

The American Military view of a Griffon in the Mustang was dependant on the delivery of examples to the USA; the following is from a letter to Hives from Brig Gen. A.J. Lyon Air Technical Section of the ETO US Army dated 4 September 1942;

"Colonel Chidlaw [Army Air Forces Air Material Command] reports no action has been taken relative to the Griffon engine, as there is little doubt that the Mustang would have to be largely redesigned to instal [sic] this engine. They ask, however, to be advised regarding the delivery date of two Griffon 61 engines and spare parts, and to be sent complete information on this engine, including sufficient data to study its possible installation, as soon as possible."

It's likely this never took place. Priority was obviously placed on the XP-78 as the Merlin engined P-51 was initially designated in USAAF nomenclature.

As for building the Mustang with a turbo-supercharged Allison from the outset; in 1940 when the initial requirement for fighters was issued by the British Purchasing Commission it had asked Curtiss for P-40s and was referred to NAA for production of these. Curtiss couldn't help because it was engaged in existing production contracts. NAA placed enormous priority on getting the NAA-73X airframe constructed in the quickest possible time, any delay with a turbo unit would have held up production; Allison would have to guarantee that it was workable and production ready.

Also, the British would not want an engine layout that had not been tried and tested in service to be placed in an entirely new aircraft built by a firm with no experience in fighter design. That would be a big risk to British plans; the idea of going to the United States was to get aircraft, as many as it could, as quickly as it could. The British knew they were taking a gamble with NAA building a new fighter, so it was fortunate that NAA got the airframe right with little risk in terms of powerplant. I doubt sincerely that the British would allow this choice of engine arrangement; I have read, though I can't find a reference that the British stipulated the V-1710 bercause of its commonality with existing P-40s.
 
Last edited:
Hi Shortround,

First Happy Holidays.

I believe all those engines were post WWII. The GE-IA, our first jet engine, was a copy of the Whittle engine. The GE I-16 was the first US improvement to the IA. The IA had 1,200 popunds of thrust and the I-16 had, surprise ... 1,600 pounds of thrust. It was eventually upgraded to 2,000 pounds of thrust by GE, not by Rolls Royce, at least for the units in US use. It becasme the J-31.

The J-42 was a license-produced Nene. Concerned that the Nene (J-42) would not have the potential to cope with future weight growth in improved versions of the Panther, Luke Hobbs, vice president of engineering for P&W's parent company, the United Aircraft Corporation, requested that Rolls-Royce design a more powerful engine based on the Nene, which Pratt Whitney would also produce.

By 1948, Rolls-Royce had designed the Tay turbojet, also a centrifugal-flow design. However, as Rolls-Royce was then developing an improved design with an axial compressor, which would become the Avon, the development and production of the Tay turbojet was left to Pratt Whitney. However, Rolls-Royce retained the rights to the Tay outside of the United States.


Hi Wuzak! Hope you are having good holidays!

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.

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.
 
Last edited:
to put a little perspective on an early Mustang using anything but the Allison, in 1941 NAA built 138 Mustangs, 66 of them in December. Packard built 45 Merlin XX series engines in 1941, 26 of them in December. So basically the Early Mustang was going to use the Allison or nothing. Now once you have the Mustang production line tooled up and running building Allison powered Mustangs, how long is it going to take to design and tool up for the Mustang TWO, using the alternative engine package of your choice?

Please remember that NAA got a contract to build 2 Merlin powered prototypes on July 25th 1942, Aug 26th 1942 sees 400 P-51Bs ordered "off the drawing board" and the first flight of the XP-51B takes place on Nov 30th 1942 and the plane is grounded for a number of days as the radiator and air scoop are redesigned due to over heating. First production plane is rolled out in May of 1943. P-51Bs will not see combat until the fall of 1943.
 
You must log in or register to reply here.

Users who are viewing this thread

Total: 1 (members: 0, guests: 1)

Similar threads

M
P-39 Turbo - Here We Go Again
Replies
13
Views
2K
GregP
S
State-of-the-art Japanese fighters with western engines
Replies
10
Views
453
GregP
S
First P51 lost in war was due to?
Replies
9
Views
1K
ColFord
S
Spitfire with proper meredith effect
2 3
Replies
41
Views
4K
Shortround6
S
Allison WER Test early 1944
Replies
4
Views
844
GregP
Menu
Log in
Register