No US-built Merlin: plausible developments?

[tomo pauk]

The R-2800 is a bit too big and heavy to serve as a substitute Merlin.

Thanks for bringing us back to the topic
Wouldn't it depend upon the airframe that is about to receive the replacement? I can see the Spitfire as being too light for the R-2800, but not the P-51. We can take a look at the soviet examples - they re-engined the Lagg-3 and Yak-3 with the Ash-82, creating the La-5 and Yak-3U.

The US kept 1/3 (at most) of Packard production, some sources say as little as 20%. If Packard doesn't make Merlins that means no Merlin powered P-40s ( not much of a loss) and No Merlin Mustangs ( a much bigger loss)

Within a scope of this thread: how feasible is the P-51 with 2-stage V-1710/R-2800, for, say, Big Week to be operating in meaningful numbers (the Packard being second source for the V-1710 or R-2800)?

but it also means 36,000-44,000 fewer Merlins for British and Canadian production aircraft. and that is the big loss in this scenario. For existing US engines the R-1820 and R-1830 are too small. The R-3350 is too big and too late. The R-2800 is too big for many applications, It rather leaves the the R-2600 (Hercules replacement in some aircraft and since the Hercules and Merlin both worked on a number of aircraft it might be a small change) and the Allison V-1710, as "plug in" replacements for existing aircraft, at least in a physical size sense.

A Halifax or Lancaster with four R-2800s might be a wondrous airplane but either one with four R-2600s might require a whole lot less redesign. Hurri-bombers with V-1710s might work.

How feasible would be the turbo V-1710s for the British bombers; installation a-la the XB-38? The single-stage V-1710s for the Mossie FBs (plus the Coastal command planes). Beaufighter with V-1710 or single stage R-2800? The Hurricannes loosing the two-speed Merlins, while receiving V-1710s (Merlins go to the heavies)?

In 1940-41 the British NEED another source of engines to power the airframes they are already planning to make in 1942-43. They don't need a source of engines that won't be making large quantities of engines until 1943/44 and need new airframes to make use of the larger engines. They already have 4 engines larger than the Merlin in the pipeline themselves.

Of course they need the yet another source, and Packard was providing them with meaningful number of engines from 1942 on. Not producing the Merlin, it can produce V-1710 in same quantities (or bigger?). With one of their tasks now made easier, Allison can introduce the 2-stage variant easier/earlier?
This should not be read as the 'Allison was every inch as good as Merlin' mantra, but something that should inspire the further discussion about the choices for the W. Allies that do not have US-built Merlins in the ww2.

 

[krieghund]

If there wasn't any US production of the Merlin then the US would have probably arrived at this solution a lot earlier without the politics;

The P-51J with the V1710-119

 

[wuzak]

Thanks for bringing us back to the topic
Wouldn't it depend upon the airframe that is about to receive the replacement? I can see the Spitfire as being too light for the R-2800, but not the P-51. We can take a look at the soviet examples - they re-engined the Lagg-3 and Yak-3 with the Ash-82, creating the La-5 and Yak-3U.

Not sure that the performance would be there for an R-2800 Mustang.

How feasible would be the turbo V-1710s for the British bombers; installation a-la the XB-38?

Not very.

The turbo in the XB-38 was mounted in the standard nacelle in the wing, in its original location, not in the V-1710 engine module. The radiators for the V-1710s were in the wing leading edge between the nacelles, and not in the QEC.

The single-stage V-1710s for the Mossie FBs (plus the Coastal command planes). Beaufighter with V-1710 or single stage R-2800?

V-1710s for Mossie FBs would be possible, but would require changes to suit those particular models. The single sage Allison may not be the best for all FB missions, though, and is definitely not good for PR, NF and B versions.

Most Beaufighters had the Hercules, which wasn't built in the US but had sufficient numbers for what they were being used. No need for the R-2800 here. The number of Merlin models is relatively small - about 600 and, I believe, built before US production of Merlins commences, so no need for a replacement.

The Hurricannes loosing the two-speed Merlins, while receiving V-1710s (Merlins go to the heavies)?

Maybe Hurricane production is cut earlier in favour of the Typhoon and the R-2800 Tornado (single stage). The latter is an interim fighter until the Centaurus powered Tempest II is ready, but since that arrived very late in the war it is essentially replacing the Hurricane.

Of course they need the yet another source, and Packard was providing them with meaningful number of engines from 1942 on. Not producing the Merlin, it can produce V-1710 in same quantities (or bigger?). With one of their tasks now made easier, Allison can introduce the 2-stage variant easier/earlier?

Having Packard involved would surely increase the amount of engineers available for development. If Allison assign some areas of development to Packard (like the V-3420) that would free up their own development time for the two stage project.

 

[wuzak]

If there wasn't any US production of the Merlin then the US would have probably arrived at this solution a lot earlier without the politics;

The P-51J with the V1710-119

Why would taht be the case?

Before the P-51 was fitted with a 2 stage Merlin was there any push for a high altitude version from the USAAF?

 

[Shortround6]

Thanks for bringing us back to the topic

No problem

Lets see if I can take these one at a time.

Wouldn't it depend upon the airframe that is about to receive the replacement? I can see the Spitfire as being too light for the R-2800, but not the P-51. We can take a look at the soviet examples - they re-engined the Lagg-3 and Yak-3 with the Ash-82, creating the La-5 and Yak-3U.

The Ash-82 was more of a R-2600 sized engine. R-2600 "B" --1980lbs, Ash-82--1984lbs, Hercules XI--1850lbs, R-2800 A series with single stage two speed supercharger 2270lbs, R-2800 with two stage supercharger 2480lbs without inter-coolers and ducts. And that is just for the engines. The R-2800 needs a bigger propeller if you want to get the full benefit. At most times the R-2800 was giving about 15% more power than an R-2600 but also weighed about 15% more, a bit better in the power to frontal area ratio though. Like I said before some planes might not have too much trouble. Wellington with two R-2800s? Lots of room to shift things around to balance the weight. Beaufighter with two R-2800s? you have added over 1/2 ton as far forward as you can go with the weight. Halifax? maybe but while certainly more powerful you have added over a ton to the empty weight and if you use the power you WILL suck down more fuel. You have the power to lift it but you may need to beef up parts of the plane to stand up to the extra weight and power, like heavier landing gear. Possible but no longer a "plug in" replacement.

Within a scope of this thread: how feasible is the P-51 with 2-stage V-1710/R-2800, for, say, Big Week to be operating in meaningful numbers (the Packard being second source for the V-1710 or R-2800)?

as far as the R-2800 goes. the Merlin instillation a P-51B/C went about 3246lbs not including fuel system or oil. The R-2800 system in the F6F-3 went 3917. Almost 700lbs more and ALL forward of the front wing spar unlike the P-51 which had several hundred pounds (400-500?) behind the rear spar? P-51 used a 11'2in 4 blade prop. F6F used a 13'2 in 3 blade prop. Unless you use a smaller prop the same thrust line is going to mean a lot of plowed up runways
using a smaller prop may be a problem, I am not sure how much of the propeller disk in front of the engine really contributes to the thrust. The R-2800 is 52in in diameter or 4 ft 4 in. Merlin is 30 in wide (2ft 6in) and 40 something high but it tapers and is smaller in height at the front than the rear.
North American may be able to design an R-2800 powered fighter, it may even use the same wing as the P-51, I just don't think much else would be the same. And you can pretty much kiss off long range bomber escort missions. You have a higher drag airplane with a thirstier engine. Not a recipe for long range. Army figured combat radius for bomber escort at 310mph true airspeed at 25,000ft for the cruise portion of the mission profile.

the 2-stage V-1710 is a possibility but it is far in the future in the summer of 1940.

How feasible would be the turbo V-1710s for the British bombers; installation a-la the XB-38? The single-stage V-1710s for the Mossie FBs (plus the Coastal command planes). Beaufighter with V-1710 or single stage R-2800? The Hurricannes loosing the two-speed Merlins, while receiving V-1710s (Merlins go to the heavies)?

1. "turbo V-1710s for the British bombers". I have mentioned this before, feasible but at the cost of higher maintenance costs. Power eggs with turbos could be a problem, turbos liked a little distance between the engine and the turbo, longer exhaust duct meant cooler exhaust hitting turbo blades and thus longer life for the turbo.
2. " The single-stage V-1710s for the Mossie FBs (plus the Coastal command planes)". Again feasible but why? without WEP settings Allisons (in historical models) top out at 1325hp for take off. And the engine in the A-36 could only hold 1325hp to 3200ft without going into a WEP setting. Fitting low altitude Allisons to these planes means really low altitudes. No choice of even trying to fly/fight at 10-20,000ft. Fitting higher altitude Allisons means too little power for take-off.
3. Beaufighter? The Allisons won't give the power for either night fighter missions compared to Merlin XX or Hercules engines and won't give the needed power for strike missions. Weight and balance problems with R-2800s have been mentioned before.
4. Hurricanes? possibly the best choice but again you are really limiting the plane to well under 10,000ft.

Of course they need the yet another source, and Packard was providing them with meaningful number of engines from 1942 on. Not producing the Merlin, it can produce V-1710 in same quantities (or bigger?). With one of their tasks now made easier, Allison can introduce the 2-stage variant easier/earlier?

Is Allisons task made easier? or do Allison have to help oversee production in a separate facility for the first few months/year?
This also skips over the British problem, how much engineering time do they spend on all these alternate engine installations rather than getting the engine they want that will drop into the airframes with little or no engineering time spent?
Substituting R-2600s for Hercules engines might be simpler. It at least solves a big part of the power problem for the 4 engine bombers and thus frees up Merlins for other uses.

This should not be read as the 'Allison was every inch as good as Merlin' mantra, but something that should inspire the further discussion about the choices for the W. Allies that do not have US-built Merlins in the ww2.

At times the Allison was every bit as good as the Merlin, unfortunately, the summer of 1940 was not one of those times. In the summer of 1940 the Allison supercharger was as good as the supercharger on the Merlin III and Merlin X, unfortunately the Allison "C" series reduction gear was suspect and the block needed a bit of beefing up. AND Hooker had started his work and the Merlin XX was ready with the improved single stage supercharger. Allison had the improved "E" and "F" series engines in test but not ready for production just yet. you have choice of the Merlin with a somewhat proven track record (several thousand single speed engines built and second generation supercharger having passed tests coupled with two speed drive proven on Merlin X) compared to the promising but unproven Allison. Allison had to rework hundreds of their already delivered "C" series engines at their own expense in 1941 to bring them up to rated power. Building a factory to make "E" and "F" series engines could have been trouble free, it could also have been a disaster.

 

[krieghund]

Why would taht be the case?

Before the P-51 was fitted with a 2 stage Merlin was there any push for a high altitude version from the USAAF?

The push that was there to put the Merlin into the P-51 would be the push to take the USAAF blinkers off and develop the appropriate supercharger the V-1710 which should have been done in the beginning of its development.

 

[Edgar Brooks]

If Packard doesn't build Merlins what engine choice do the British have in the summer of 1940 to power their planes? .

They use Rolls-Royce engines, which is what they did, anyway. The contract, with Packard, was not signed until September 3rd., 1940, and the first engine was produced in September 1941.

For Wuzak's question:
"Another alternative - what if Rolls-Royce foresaw a need for more Griffons, and requested Packard set up a new line for them, to run alongside the Merlin? I imagine the decision would be mid 1941, after the Griffon had some testing behind it or had flown in the Spitfire (Mk IV - which flew in late 1941).

It was already thought of, and Packard were given a set of Griffon drawings at the same time as they received those of the Merlin.

 

[wuzak]

It was already thought of, and Packard were given a set of Griffon drawings at the same time as they received those of the Merlin.

But not proceeded with obviously.

Any reason given?

 

[Edgar Brooks]

None that I can find; the "gestation period," for the Griffon was possibly so long that the need for large numbers no longer existed once it was available.

 

[Shortround6]

They use Rolls-Royce engines, which is what they did, anyway. The contract, with Packard, was not signed until September 3rd., 1940, and the first engine was produced in September 1941.

I am sorry I didn't phrase that better. In the summer of 1940 the British were looking for ANOTHER source of engines that would not come on line until late 1941 or early 1942. Not engines to be delivered in 1940. The Deal was signed with Packard after the deal with Ford America fell through. The question in this thread is what other engine choices were there for this "alternative plant". Or failing this plant what other US engines could have filled in.

My position is there isn't much choice of engine.
It has to be an engine that can power first line combat planes 1 1/2 years to 4 (?) years in the future which rules out marginal engines like the Bristol poppet valve engines or more P&W R-1830s. It has to start delivering engines as soon as possible which rules out engines that are still in testing (or in flux, changing specifications of an engine while still tooling up is a sure way to delay deliveries) which, in 1940, rules out things like the Griffon, Sabre or Centaurus. It also has to be an engine the Americans can use or will use. American policy is that they will not allow American factories to tool up for and make weapons, engines and aircraft that the US services cannot/will not use. Should things in England go south (turn pear shaped- insert expression) the Americans don't want to be stuck with factories tooled up to make weapon types the Americans don't want like happened in WW I. It also has to be an engine that will fit into existing (design wise) or planned (near term) British aircraft. This again rules out the Griffon, Sabre, Centaurus. It does no good in 1942 to have a factory spitting out 300 Sabres a month if the Typhoon and the XXX medium bomber both turn out to be crap. It also does no good to be making hundreds of airframes a month if the selected engine is crap.
So the English have two choices, the Merlin and the Hercules. Merlin is proven and shows a lot of development potential. Hercules shows potential but is unproven and difficult to make. From an American view point they already have a selection of radial engines but only one V-12 and that is just barely coming on line. According to some it has much more potential (NIH at work?)than the Merlin but any other American liquid cooled engines are years away from production. A second liquid cooled V-12 may prove useful to the Americans in the next few years. AS outlined in a previous post only the Wright R-2600 is in a position of offering the right amount of power, in a package of the right size/weight and being built in a numbers at all to be a viable alternative to the Merlin for British aircraft and that is as a Hercules substitute.

Even by process of elimination the Merlin comes out as the only logical choice.

 

[Edgar Brooks]

One item, only occasionally touched on, but of paramount importance, is aircraft balance, aka CofG. It was decided, mid-1940, that fighters needed cannon, to cope with German bombers, and as ground-attack airframes. For the latter task, the Hurricane IIC was seen as the ideal, and, as early as August 1940, its appearance was urgently required. However, the (mere) extra 4" nose length meant that the (also preferred) larger oil tank could not be fitted, since that would have made the nose even longer, and pulled the CoG too far forward.
Hawker were prepared to consider fitting the Griffon into the Hurricane, but this entailed raking the mainspars forward, to keep the CoG within limits, and the Air Ministry were not prepared to countenance this, telling Cam (who had drawings prepared) to forget it, and concentrate on the Tornado/Typhoon; 29-4-41, the decision was taken that no further development of the Hurricane should take place. To give you an idea how touchy the Hurricane was, on the Mk.I, if it was fitted with the Watts two-blade wooden propeller, armour plate could not be fitted behind the pilot.
The Spitfire IX coped with the Merlin 61 by having lumps of lead fitted near the tail wheel, and shifting the oxygen bottles to the rear; on the Griffon-powered XIV, even more lead was fitted into the fin. Bigger, heavier engines are all very well, but you need bigger, heftier airframes to cope; look at the size/weight of the Typhoon, compared to the Hurricane.

 

[rinkol]

The two stage Merlin also had some major advantages that should be emphasized:

- relative early availability;
- inclusion of an intercooler from the beginning;
- compact layout (at least in comparison with the V-1710s having either the auxiliary stage supercharger or turbosuperchargers).

Even the single stage Merlin, from the XX version, had a two speed supercharger. In comparison with the versions of the V-1710 that were available during the war, this made it a much better choice for bombers such as the Halifax and Lancaster (note that the aforementioned planes would not benefit much from turbosuperchargers).

 

[tomo pauk]

Not sure that the performance would be there for an R-2800 Mustang.

Why not? In case the 2-stage R-2800 can be fitted, the resulting plane is far less draggy heavy than the F4U. Sorta heavier more powerful Hayate?

Not very.

The turbo in the XB-38 was mounted in the standard nacelle in the wing, in its original location, not in the V-1710 engine module. The radiators for the V-1710s were in the wing leading edge between the nacelles, and not in the QEC.

Thanks.

V-1710s for Mossie FBs would be possible, but would require changes to suit those particular models. The single sage Allison may not be the best for all FB missions, though, and is definitely not good for PR, NF and B versions.

Agreed, that's why I'm suggesting FB only, as it would freed up the Merlins for the other uses/verdions on the Mossies.

Most Beaufighters had the Hercules, which wasn't built in the US but had sufficient numbers for what they were being used. No need for the R-2800 here. The number of Merlin models is relatively small - about 600 and, I believe, built before US production of Merlins commences, so no need for a replacement.

The need for the engines other than Hercules could arose in case the Hercules engines need to be used for the heavies, so 'something' built in the USA could do the task decently.

Maybe Hurricane production is cut earlier in favour of the Typhoon and the R-2800 Tornado (single stage). The latter is an interim fighter until the Centaurus powered Tempest II is ready, but since that arrived very late in the war it is essentially replacing the Hurricane.

Well, I'd really love to see a 2-stage R-2800 in a Hawker in 1943

Having Packard involved would surely increase the amount of engineers available for development. If Allison assign some areas of development to Packard (like the V-3420) that would free up their own development time for the two stage project.

Seem we have differing opinions for this (making job easier for Allison). In case of Packard, that company did have had core manpower, experience in engine manufacturing, and the funding was historically allocated for them anyway (for Merlin production).

 

[tomo pauk]

The Ash-82 was more of a R-2600 sized engine. R-2600 "B" --1980lbs, Ash-82--1984lbs, Hercules XI--1850lbs, R-2800 A series with single stage two speed supercharger 2270lbs, R-2800 with two stage supercharger 2480lbs without inter-coolers and ducts. And that is just for the engines.
The R-2800 needs a bigger propeller if you want to get the full benefit. At most times the R-2800 was giving about 15% more power than an R-2600 but also weighed about 15% more, a bit better in the power to frontal area ratio though.

The lighter Ash-82 replaced the lighter M-105; the heavier R-2800 would replace the heavier V-1710. The intercoolers can go to to the place previously occupied by the cooler radiators.
We can also take a look at the Spitfire, that 'swallowed' far heavier engine (Griffon) without too much trouble.
Thanks again for the numbers.

Like I said before some planes might not have too much trouble. Wellington with two R-2800s? Lots of room to shift things around to balance the weight. Beaufighter with two R-2800s? you have added over 1/2 ton as far forward as you can go with the weight. Halifax? maybe but while certainly more powerful you have added over a ton to the empty weight and if you use the power you WILL suck down more fuel. You have the power to lift it but you may need to beef up parts of the plane to stand up to the extra weight and power, like heavier landing gear. Possible but no longer a "plug in" replacement.

Fair points.

as far as the R-2800 goes. the Merlin instillation a P-51B/C went about 3246lbs not including fuel system or oil. The R-2800 system in the F6F-3 went 3917. Almost 700lbs more and ALL forward of the front wing spar unlike the P-51 which had several hundred pounds (400-500?) behind the rear spar? P-51 used a 11'2in 4 blade prop. F6F used a 13'2 in 3 blade prop. Unless you use a smaller prop the same thrust line is going to mean a lot of plowed up runways
using a smaller prop may be a problem, I am not sure how much of the propeller disk in front of the engine really contributes to the thrust. The R-2800 is 52in in diameter or 4 ft 4 in. Merlin is 30 in wide (2ft 6in) and 40 something high but it tapers and is smaller in height at the front than the rear.

I've already covered the installation of the intercoolers, so they should balance the rest of the powerplant decently.
As far as the prop goes, P-47 was using the 12,2 ft prop, 4 bladed, early on. NAA can be smart and use the system from the P-47 (extend able gear strut).

North American may be able to design an R-2800 powered fighter, it may even use the same wing as the P-51, I just don't think much else would be the same. And you can pretty much kiss off long range bomber escort missions. You have a higher drag airplane with a thirstier engine. Not a recipe for long range. Army figured combat radius for bomber escort at 310mph true airspeed at 25,000ft for the cruise portion of the mission profile.

The R-2800 powered P-51 would be far less draggy than F4U, far less weight, with more internal fuel (assuming the disposition of the fixed fuel tanks as it was in 1944), it's able to carry 2 drop tanks from day one (unlike the P-47). Granted that it would be using more fuel than the real Merlin P-51, but also far less than the P-47/F4U.

the 2-stage V-1710 is a possibility but it is far in the future in the summer of 1940.

Of course, but so is the 2-stage Merlin for the P-51.

1. "turbo V-1710s for the British bombers". I have mentioned this before, feasible but at the cost of higher maintenance costs. Power eggs with turbos could be a problem, turbos liked a little distance between the engine and the turbo, longer exhaust duct meant cooler exhaust hitting turbo blades and thus longer life for the turbo.
2. " The single-stage V-1710s for the Mossie FBs (plus the Coastal command planes)". Again feasible but why? without WEP settings Allisons (in historical models) top out at 1325hp for take off. And the engine in the A-36 could only hold 1325hp to 3200ft without going into a WEP setting. Fitting low altitude Allisons to these planes means really low altitudes. No choice of even trying to fly/fight at 10-20,000ft. Fitting higher altitude Allisons means too little power for take-off.
3. Beaufighter? The Allisons won't give the power for either night fighter missions compared to Merlin XX or Hercules engines and won't give the needed power for strike missions. Weight and balance problems with R-2800s have been mentioned before.
4. Hurricanes? possibly the best choice but again you are really limiting the plane to well under 10,000ft.

1. Well, turbos were many things. Being simple was not amongst them.
2. 1-stage V-1710 for Mossie, why? Because the USA is not building Merlins, so the RAF/MAP need to do some reshufling of those. I was thinking more about the 8.80 SC ratio engines, not the really low level ones.
3. NF job is obvioulsy not for the 1-stage V-1710s. The strike fighter can use the lower weight and lower drag of the inline to make good for the loss of the ~10% of the power, and can also use the WEP (1590 HP at 4500 ft, no ram) for the, well, war emergency
4. Not really so, with the 8.80 SC ratio engines. That should do up to 15000 ft.

Is Allisons task made easier? or do Allison have to help oversee production in a separate facility for the first few months/year?

ng
Packard was not a newcomer into engine business, and the whole US inline story (actually, the V-1710 story) starts receiving more funding, better priority and more government attention (positive, hopefully )

This also skips over the British problem, how much engineering time do they spend on all these alternate engine installations rather than getting the engine they want that will drop into the airframes with little or no engineering time spent?

Obviously the British would not re-engine all of their engines, but the designs that would still been serving them good in decent numbers. Using the US engine would free up their engine production for the other designs where such a change would prove troublesome, either from the production or performance standpoint.

Substituting R-2600s for Hercules engines might be simpler. It at least solves a big part of the power problem for the 4 engine bombers and thus frees up Merlins for other uses.

You mean with Packard-built R-2600s? IIRC Beufighter was tried with R-2600 historically.

At times the Allison was every bit as good as the Merlin, unfortunately, the summer of 1940 was not one of those times. In the summer of 1940 the Allison supercharger was as good as the supercharger on the Merlin III and Merlin X, unfortunately the Allison "C" series reduction gear was suspect and the block needed a bit of beefing up. AND Hooker had started his work and the Merlin XX was ready with the improved single stage supercharger. Allison had the improved "E" and "F" series engines in test but not ready for production just yet. you have choice of the Merlin with a somewhat proven track record (several thousand single speed engines built and second generation supercharger having passed tests coupled with two speed drive proven on Merlin X) compared to the promising but unproven Allison. Allison had to rework hundreds of their already delivered "C" series engines at their own expense in 1941 to bring them up to rated power. Building a factory to make "E" and "F" series engines could have been trouble free, it could also have been a disaster.

Dang, nothing to dispute here

 

[Shortround6]

The lighter Ash-82 replaced the lighter M-105; the heavier R-2800 would replace the heavier V-1710. The intercoolers can go to to the place previously occupied by the cooler radiators.
We can also take a look at the Spitfire, that 'swallowed' far heavier engine (Griffon) without too much trouble.

I've already covered the installation of the intercoolers, so they should balance the rest of the powerplant decently.
As far as the prop goes, P-47 was using the 12,2 ft prop, 4 bladed, early on. NAA can be smart and use the system from the P-47 (extend able gear strut).

The M-105 was actually fairly close to the V-1710 in weight. According to some sources 1268lbs. With the radials there is some shift (small) in the engines center of gravity rearward in relation to the aircraft's center of gravity. The La-5 is about 14cm shorter than a Lagg-3, not a lot but every bit helps. The La-5 was nose heavy enough that armament was limited and we don't have good details on other equipment sights or ballast. P-51 intercooler and radiator were filled with a water/glycol mixture which weighs a lot more than air Sticking the intercoolers under/behind the pilot gives you a P-47 without the turbo. You don't need the exhaust ducts but you need ducts to carry the intake air from the first stage of the supercharger to the belly mounted intercooler/s and then ducts to bring the intake air back to the engine carburetor/second stage. Intake air inlet needs to be near the 1st stage supercharger section. Cooling air for the intercooler can be brought in from under the engine (F6F or P-47) or from under belly scope but the intercoolers for the R-2800 do not weigh anything like the radiators on the Merlin unless you design and build a air/liquid intercooler for the R-2800 instead of the air/air system that they did use.

You could use 12'2" props and extending landing gear, But every change from the Allison powered Mustang is more engineering time and more testing.

Griffon required much larger radiators behind the CG than the Merlin did which helped balance things, plus ballast.

The R-2800 powered P-51 would be far less draggy than F4U, far less weight, with more internal fuel (assuming the disposition of the fixed fuel tanks as it was in 1944), it's able to carry 2 drop tanks from day one (unlike the P-47). Granted that it would be using more fuel than the real Merlin P-51, but also far less than the P-47/F4U.

I am not sure where the far less drag is coming from. Yes you have a smaller, lighter wing but moving the intercoolers from behind the engine to the rear/belly of the fuselage may not be a low drag option. We know that a radial P-36 had 22% more drag than P-40 so even if the bigger diameter (and greater appetite for air) R-2800 installation only has 12-15% more drag than the Merlin that will mean a 12-15% higher fuel burn even if you can keep the R-2800 from having to operate at a rich mixture setting.
A P-51D clean can do 335mph at 25,000ft burning 59 gallons an hour. A Corsair at 21,500 ft and doing 282mph is burning 61.2gallons and hour and at 338mph at 21,500ft is burning 127 gallons an hour. It has to shift into rich mixture to hit this speed.
A P-47 at 25,000ft clean burns 95 GPH to do 300mph and 145GPH to do 337mph.

Of course, but so is the 2-stage Merlin for the P-51.

True, neither one should be a consideration for what engine to pick in 1940.

2. 1-stage V-1710 for Mossie, why? Because the USA is not building Merlins, so the RAF/MAP need to do some reshufling of those. I was thinking more about the 8.80 SC ratio engines, not the really low level ones.
3. NF job is obvioulsy not for the 1-stage V-1710s. The strike fighter can use the lower weight and lower drag of the inline to make good for the loss of the ~10% of the power, and can also use the WEP (1590 HP at 4500 ft, no ram) for the, well, war emergency
4. Not really so, with the 8.80 SC ratio engines. That should do up to 15000 ft.

The Allisons are are bit late to the game. There are two basic models using 8.80 gears that need to concern us. The F3R (-39) model which was good for 1150hp take-off and 1150hp at 11,700ft, While not in production in 1940 we may assume it was in the planning stages. WER is not approved in US service until Dec 1942 although the British were using high than book pressure much earlier. These engines do not show up in production until the summer of 1941 and are eventually cleared for 1490hp at 4300ft.
The Merlin XX which was coming into British service in the summer of 1940 and was the Engine that Packard signed to produce was good for 1280-1300hp for take-off and 1240hp at 11,500ft low blower and 1120hp 18,500ft high blower at 12lbs boost. If the British use the higher boost limits for the XX they can get 1480hp at 6,000ft low blower and 1480hp at 12,500ft high blower. The later F4R Allison engine used the P-40 K was strengthened and while rated at 1325hp for take-off and 1150 at 12,000ft it was rated for 1580hp WER at 2500ft. While the beginnings of this version go back a ways it did not enter production until late 1941 and the first P-40K with one does not roll out the factory door until May of 1942.
Even with 8.80 gears too much power is being given up at all but the lowest altitudes (under 5000ft) to make this a good choice. Coupled with the 10% or so loss of power for take-off (unless over boosting is used) and it really looks less than attractive.

Obviously the British would not re-engine all of their engines, but the designs that would still been serving them good in decent numbers. Using the US engine would free up their engine production for the other designs where such a change would prove troublesome, either from the production or performance standpoint.

Substituting R-2600s for Hercules engines might be simpler. It at least solves a big part of the power problem for the 4 engine bombers and thus frees up Merlins for other uses.

You mean with Packard-built R-2600s? IIRC Beufighter was tried with R-2600 historically.

I believe there were a few other airframes that got R-2600s on an experimental basis. There was a plan to build Short Stirlings in Canada powered by R-2600s, with two airframes converted. edit> or 4 airframes with 2 flown?<

The R-2600 maybe a viable replacement for the Hercules.

Edit> Later versions of the Merlin XX include the Merlin 21 used in early Mosquitoes, pretty much the same ratings as the XX, The Merlin 23 with 1390hp available for take-off and 1435hp at 11,000ft using 16lbs boost, used in the Mosquito Mosquito I, II, IV, VI, XII and XIII and the Merlin 25 with 1610hp for take off and 1510hp at 9,250ft using 18bs boost used in the Mosquito VI and XIX. Packard versions sometimes varied by 20-30hp but Packard engines include the Merlin 31 and 33 ( a Merlin 23) used in Canadian and Australian Mosquitos. The Merlin 38 used in Lancaster Is and IIs (1400hp take off) and the Merlin 224 225 also used in Lancasters Mosquitoes respectively with 1635hp for take-off and 1680hp at 2500ft in low blower at 18lbs. None of these are two stage engines.
In 1940 these higher powered versions were in the future and needed 100/130 fuel and engine modifications to reach 18lbs of boost. 12-14lbs boost was achievable with with British 1940 100 octane fuel.
Perhaps the V-1710 could have been developed to reach these power levels. A two speed supercharger drive would have helped take-off power a lot. It would have been worth an easy 100 hp for the take-off ratings.

 

[KiwiBiggles]

I am not sure where the far less drag is coming from.

Smaller laminar flow wing, without the ghastly (from an aerodynamic POV) inverted gull-wing of the F4U. I know the 90° wing/fuselage junction of the F4U is very efficient, but the P-51 is quite slab-sided anyway, so its interference drag at the root would be quite low. The drag coming off that kink in the F4U wing would swamp any gains at the root. I think the fuel consumption figures you quote bear this out.

 

[tomo pauk]

Plenty of good points, SR6, thanks

The M-105 was actually fairly close to the V-1710 in weight. According to some sources 1268lbs. With the radials there is some shift (small) in the engines center of gravity rearward in relation to the aircraft's center of gravity. The La-5 is about 14cm shorter than a Lagg-3, not a lot but every bit helps. The La-5 was nose heavy enough that armament was limited and we don't have good details on other equipment sights or ballast.

The armament of the La-5 was of bigger weight than of Lagg-3: 2 cannons vs. 1 cannon 2 LMGs. With installation of the heavier engine, the 2 HMGs are also out from the plain P-51.

P-51 intercooler and radiator were filled with a water/glycol mixture which weighs a lot more than air Sticking the intercoolers under/behind the pilot gives you a P-47 without the turbo. You don't need the exhaust ducts but you need ducts to carry the intake air from the first stage of the supercharger to the belly mounted intercooler/s and then ducts to bring the intake air back to the engine carburetor/second stage.

Merlin P-51 needed to cool the both the engine and intercooler via the aft belly radiator, so the fuselage changes were undertaken in order to provide for that. This time around, the air ducts would be installed to feed the inter cooler radiators.
Agree about air being of lower weight than the water/glycol mix

Intake air inlet needs to be near the 1st stage supercharger section. Cooling air for the intercooler can be brought in from under the engine (F6F or P-47) or from under belly scope but the intercoolers for the R-2800 do not weigh anything like the radiators on the Merlin unless you design and build a air/liquid intercooler for the R-2800 instead of the air/air system that they did use.

No quarrels about that.

You could use 12'2" props and extending landing gear, But every change from the Allison powered Mustang is more engineering time and more testing.

Agreed again. We could note the Merlin Mustang was delayed also, airframes waiting for the engines. In this time line, the R-2800s being produced by yet another capable manufacturer such a hiccup is less likely to happen (not likely at all?).

Griffon required much larger radiators behind the CG than the Merlin did which helped balance things, plus ballast.

No free lunch, even for the redoubtable Spitfire
The radiators at the Griffon spitfires were mounted far more in front than it was case for the P-51. Circa twice as close to the CoG, Spit XII/XIV vs. P-51B-K.

I am not sure where the far less drag is coming from. Yes you have a smaller, lighter wing but moving the intercoolers from behind the engine to the rear/belly of the fuselage may not be a low drag option.

The wing is still of the laminar flow type, of smaller profile and area. The Merredith effect is still there. So the drag reduction is no problem, P-51 vs. F4U.

We know that a radial P-36 had 22% more drag than P-40 so even if the bigger diameter (and greater appetite for air) R-2800 installation only has 12-15% more drag than the Merlin that will mean a 12-15% higher fuel burn even if you can keep the R-2800 from having to operate at a rich mixture setting.
A P-51D clean can do 335mph at 25,000ft burning 59 gallons an hour. A Corsair at 21,500 ft and doing 282mph is burning 61.2gallons and hour and at 338mph at 21,500ft is burning 127 gallons an hour. It has to shift into rich mixture to hit this speed.
A P-47 at 25,000ft clean burns 95 GPH to do 300mph and 145GPH to do 337mph.

Thanks for the figures.
The R-2800 P-51 will have to use the 2x110 gals drop tanks (instead of more common 75 gals), and the range after those are dropped would be less (vs. Merlin P-51, same int. fuel).

For the rest of the post - later, really got to go to bed

 

[Shortround6]

The wing is still of the laminar flow type, of smaller profile and area. The Merredith effect is still there. So the drag reduction is no problem, P-51 vs. F4U.

The laminar flow is debatable, you will get people arguing both sides. The wing is smaller in profile and area ( and not fabric covered . Meredith effect may take some work. You need a good heat source for the Meredith effect to really work. A V-1650-3 Merlin had a total cooling requirement of 777hp being dissipated by the radiator/oil cooler and inter cooler I believe. 120hp of that is from the intercooler. Granted the intercooler of the R-2800 may be trying to get rid of more heat than the Merlin's intercooler radiator but even at 200hp worth of heat (a WAG) it may not be worth the bulk of the duct. In theory it can be done but theory and practice seemed pretty far apart. Getting exhaust thrust to work on radial engines takes a bit of work also. It is a trade off between thrust and drag. the highest thrust for a radial engine will use an individual stack for each cylinder but that also means the highest drag although it also may be the lightest exhaust system. The F4U-1 and F6F-3 did not use exhaust thrust although later models did.

Another problem with the Fat-51 is the extra weight, even if,if,if,if you can get the CG right (reposition the wing?) you have added over 700lbs (minimum) to the empty weight of the plane which went from 7325-7580lbs (with fuselage tank?) "B""C" basic weight (empty +trapped oil + guns + pyrotechnics) this is going to mean higher take-off and landing speeds and without beefing up the structure, some bent airplanes in combat. The P-51 was good for 8 "G"S at 8000lbs. any increase lowered the allowable "G" limit. at 9,000lbs it is good for 7.11 "G"s the Fat-51 is over 10,000lbs with 4 guns and normal wing tanks. 6.4 "G"s. and at 10,500lbs ( rear tank full even if you can get the CG to work for combat) and you are down to 6.09 "G"s. there is a 50% safety factor but it has gone from 12 "G's to just over 9 at this point. The bigger engine and prop may require a larger tail and on it goes and goes. The Fat-51 will weigh with 110 gallon tanks what a Merlin-51 would weigh with the next size tanks.

Don't be too tired to work, stay safe.

 

[tomo pauk]

Thanks

All this debate, or my trying to 'engineer' the P-51 around something other than Merlin points at the fact that Merlin Mustang was a such an outstanding airplane - with R-2800 'shoehorned' on it, it looses the endurance (at least that); with 2 stage V-1710 (as those mounted at P-63A, so early-mid 1944 time frame) the performance at 20000-35000 ft is not that great as with Merlin.

Some other questions: in case the RAF is really lacking the engines for their heavy bombers, how about introducing Liberator in the night bomber units (British-built heavies assume more the task of ASV, to balance this out)? Maybe the (X)B-28 gets produced, despite being only a twin? The 2-stage Packard Merlins are available for the RAF only in 1944, so the 2-stage V-1710s are used in that year?

 

[wuzak]

Some other questions: in case the RAF is really lacking the engines for their heavy bombers, how about introducing Liberator in the night bomber units (British-built heavies assume more the task of ASV, to balance this out)? Maybe the (X)B-28 gets produced, despite being only a twin? The 2-stage Packard Merlins are available for the RAF only in 1944, so the 2-stage V-1710s are used in that year?

What time frame are you talking?

The Liberator had more range than the British heavies, especially when bomb bay fuel tanks could be used as large bomb loads were not required.

On the other hand it lacked the bomb bay flexibility that the Halifax and Lancaster offered, and could not carry the larger bombs (ie the 4000lb HC "cookie") that BC favoured from 1943.

When would the XB-28 have appeared?