An Allison V-1710 with a two-speed supercharger in 1942 (10 Viewers)

[MiTasol]

I think you are right but we have very little data on that machine so do not know how they covered CofG. It is definitely my favorite P-40 looks wise

 

[tomo pauk]

Installing the two stage engine in the P-40 and P-51 would have required a total redesign of the aircraft.

Probably not greater then when they moved from P-51A to P-51B.

The engine is much longer which would require moving the firewall aft and there is virtually no room to do that before you have to move the cockpit aft.

Let's not make a mountain out of the mole hill. There was a host of aircraft that received the longer and/or heavier engines and became much better - Spitfires, Italian fighters, Bf 109, Fw 190, indeed the P-40 and P-51. Problem was actual availability of these engines, not that the engineers were unable to find the way to fit them.

Alternatively you would have to extend the rear fuselage and move a lot of weight in to it to maintain CoG and most of that weight would be ballast. The long nose and additional weight would both have a negative affect on maneuverability and performance.

See the aircraft mentioned above - the much better engines more than cancelled the negative effects of the aircraft becoming bigger and heavier. Unlike the addition of firepower and protection.

 

[BarnOwlLover]

If you have a copy of drgondog's P-51B book available, find the plans where the P-51 was set up for using the V-1710-45 and the RR Griffon. Both would've required similar amounts of redesign according to the text in the book and the images' caption.

It has to be remembered at least until the V-1710-119 and -140 series that Allison basically ran sequential superchargers (single stage superchargers set up in series) as opposed to the more integrated approach that Rolls-Royce did with the Merlin and Griffon.

Also, the XP-51J was several inches longer than the XP-51F/G due to the length of the Allison due chiefly to the supercharger arrangement. Though by that stage the way Allison was doing their two stage superchargers did mean that the XP-51J was basically identical to the F/G from the firewall on back.

However, the change to the -45 would've meant a much bigger design change than the switch from single stage V-1710s to the two stage Merlin. That's a huge part of the reason there were no more Allison Mustangs built after 1943, as most of the A-36 and P-51A tooling was used to make the P-51B/C/D/K, et al until the lightweight based P-51H entered production.

 

[tomo pauk]

If you have a copy of drgondog's P-51B book available, find the plans where the P-51 was set up for using the V-1710-45 and the RR Griffon. Both would've required similar amounts of redesign according to the text in the book and the images' caption.

I have the book, what page is that?

Also, the XP-51J was several inches longer than the XP-51F/G due to the length of the Allison due chiefly to the supercharger arrangement. Though by that stage the way Allison was doing their two stage superchargers did mean that the XP-51J was basically identical to the F/G from the firewall on back.

Seems like NAA was far further with integration of the 2-stage V-1710 on the P-51 than with the integration of the Griffon.

However, the change to the -45 would've meant a much bigger design change than the switch from single stage V-1710s to the two stage Merlin. That's a huge part of the reason there were no more Allison Mustangs built after 1943, as most of the A-36 and P-51A tooling was used to make the P-51B/C/D/K, et al until the lightweight based P-51H entered production.

Unlike the -45 and the other 2-stage V-1710s, the 2-stage Merlins were powering the Mustangs already in 1942, and were available as real, series-produced engines from the mid-1943 at Packard. Availability of engines is the key, and here the 2-stage Merlin is the winner. Just having the 2-stage V-1710s available from the late 1943 on will not cut it unless there is perhaps the third source of Mustang airframes come late 1943.

 

[BarnOwlLover]

Seems like NAA was far further with integration of the 2-stage V-1710 on the P-51 than with the integration of the Griffon.

I don't remember what page it's on, and I have to get ready to leave my house soon for several hours, so I can't look it up right away, but the plans are I believe either late in the chapter about Building the Mustang despite US opposition, or early in the Birth of the Merlin Mustang chapter (the latter has a concept sketch for a Merlin powered P-51 that I wish I had in high resolution).

But the XP-51F/G/J were very different animals design-wise vs the Mustang I though the P-51D/K, in that they were designed primarily to British load standards, and by the time they flew, Allison were on the -119 engine, not the -45 that the earlier two stage Allison study was based on.

It seems that NAA would've had to have for the -45 moved the front firewall back about 2 inches at least. This was a design change that NAA ultimately felt wasn't worth pursuing due to significant tooling changes and the RAF and ultimately USAAF needed/wanted Mustangs now. Hence my point about the Allison Mustang tooling being re-used to make Merlin P-51s.

That same argument also kept the P-51H--based on an evolution of the XP-51F/G--from going into production in 1944. NAA said that they could have the P-51H in service by the fall of 1944, but the USAAF objected and told them to hold on. This was out of fears that re-tooling the Inglewood factory to make the P-51H/L (and the P-82, though that was already on order) would significantly impact deliveries of the P-51D, which was sufficient or more than sufficient vs all but the German jets in terms of performance (and of course the Germans were having issues with the Me-262 in terms of production/delivery and keeping them flying).

 

[special ed]

I remember a certain expert on P-39s saying the engine would have been only 2 1/2 inches longer. Various comments were, the rear firewall would have to be moved rearward, necessitating a redesign. My solution, although I did not mention it, would have been the same solution when fitting a 1956 Plymouth V-8 into my 1948 Plymouth replacing the six.
I used a sledge hammer on the firewall to dimple it to allow the right cylinder head to fit. Ran fine until it met a 1957 Ford 2-door hard top.

 

[Steamed_Banana]

The key thing here though is really to get it done in time to make a difference, i.e. before the P-51Bs and Cs become available, and during, preferably early, in 1943. I think 1943 was the big pivot year. We know that they put the two speed supercharger in the P-40 without too much trouble, and got these into action in 1942, and they worked really well (though they eventually did need to lengthen the tail by about two feet for high speed stability and takeoff swing). Is there any reason to assume this would be any harder or more challenging in a P-51A or a P-39?

What would a P-38 be like with something like Merlin XX engines instead of the turbo?

 

[MIflyer]

They were?

Yep, postwar P-51 Training Manual.

 

[MIflyer]

The engine is much longer which would require moving the firewall aft and there is virtually no room to do that before you have to move the cockpit aft.

For the 2 stage V-1710 as used in the P-63 and P-82 that is indeed true. The added 1st stage was connected to the V-1710 by a external shaft coupled to the starter drive. They obviously were really trying to keep that original accessories section unchanged, despite the fact that it could be unbolted from the "short block."

 

[tomo pauk]

Yep, postwar P-51 Training Manual.

Any that is posted on this site?

 

[MIflyer]

Any that is posted on this site?

Don't know. There are a lot of P-51 pilot's manuals and the one I am quoting I have only in paper, as far as I know.

 

[tomo pauk]

We know that they put the two speed supercharger in the P-40 without too much trouble, and got these into action in 1942, and they worked really well (though they eventually did need to lengthen the tail by about two feet for high speed stability and takeoff swing).

A funny way of saying that 'Merlin XX have had a 2-speed S/C'
I'm not sure why would we make a bugaboo of the 2-speed S/C installations, either.

Is there any reason to assume this would be any harder or more challenging in a P-51A or a P-39?

The P-51 installation should've been easy-peasy. Probably the P-39 installation should've also been feasible, if the CoG can be kept happy.

What would a P-38 be like with something like Merlin XX engines instead of the turbo?

Probably as good as the P-38G?

Don't know. There are a lot of P-51 pilot's manuals and the one I am quoting I have only in paper, as far as I know.

Care to post a picture?

 

[Steamed_Banana]

A funny way of saying that 'Merlin XX have had a 2-speed S/C'
I'm not sure why would we make a bugaboo of the 2-speed S/C installations, either.

it does still add some length to the engine, but apparently not that much.

The P-51 installation should've been easy-peasy. Probably the P-39 installation should've also been feasible, if the CoG can be kept happy.

Seems likely

Probably as good as the P-38G?

I wonder. Max HP would be similar or a bit better (1325 hp -1350 for P-38G? vs 1490 hp for Merlin XX, though Allison with turbo is probably better at 20,000 ft or higher), but with probably a good bit lighter weight? And more reliable of course.

Weight of the turbos on the P-38 was 700-940 lbs, according to ze google.

Merlin XX is roughly 1,600 lbs vs 1,350 lbs for the Allison V 1710.

So 3,640 lbs for two Allisons + Turbo vs 3,200 lbs for two Merlin XX (or some theoretical equivalent). So it seems like 440 lb weight improvement. Not wild improvement but not trivial.

Care to post a picture?

 

[tomo pauk]

I wonder. Max HP would be similar or a bit better (1325 hp -1350 for P-38G? vs 1490 hp for Merlin XX, though Allison with turbo is probably better at 20,000 ft or higher), but with probably a good bit lighter weight? And more reliable of course.

The power of a non-turbo engine that has reasonably good exhausts stacks and ram air intake is much better than the 'book' values. The power chart of the Merlin XX series can be found here, includes the post-war versions. At 20000 ft, the engine will do 1030-1040 BHP. Exhaust thrust, at that altitude, can add 10-12% more power to the power delivered to the prop, a thing that the turboed engine does not have since the energy of the exhaust gasses is used to turn the turbo.
Then we have the ram effect a fast aircraft (were at about 400 mph territory here) can add 4000+- ft to the rated altitude. For the Merlin XX, that means that, at 20000 ft, the engine will be making the same power the static engine does at about 16000 ft, or about 1200 BHP. Add 10% from the exhaust thrust, and were at 1300+ HP worth of power at 20000 ft.

FWIW, there is a table at pg. 22 in 'The performance of an supercharged aero engine' by the RR heritage trust. The aircraft in question is Hurricane II, and their numbers for 20000 ft altitude and 335/340 mph speed are, respectively
- brake HP: 1073/1126
- ejector horse power (ie. power from the ejector exhausts): 113/126.8

At 25000 ft, the power was 960 brake + 107.2 ejector.
A faster aircraft will gain a bit more, both wrt. the exhaust thrust and the ram effect.

A few caveats - if the exhausts are botched, like attaching them together into one or two pipes, the exhaust thrust/power will go down; big exhausts can be draggy (compare, perhaps, P-39 vs. Hurricanes and Spitfire V and earlier); not all the ram air intakes are good/great.

tl;dr - there is a lot of good things going on for the Merlin XX on a P-38 or a P-51, the problem is to have them in the required quantity unless the P-40 does not get them, or unless the British are willing to forget the Hurricane II/IV come late 1942.

 

[Steamed_Banana]

The power of a non-turbo engine that has reasonably good exhausts stacks and ram air intake is much better than the 'book' values. The power chart of the Merlin XX series can be found here, includes the post-war versions. At 20000 ft, the engine will do 1030-1040 BHP. Exhaust thrust, at that altitude, can add 10-12% more power to the power delivered to the prop, a thing that the turboed engine does not have since the energy of the exhaust gasses is used to turn the turbo.
Then we have the ram effect a fast aircraft (were at about 400 mph territory here) can add 4000+- ft to the rated altitude. For the Merlin XX, that means that, at 20000 ft, the engine will be making the same power the static engine does at about 16000 ft, or about 1200 BHP. Add 10% from the exhaust thrust, and were at 1300+ HP worth of power at 20000 ft.

FWIW, there is a table at pg. 22 in 'The performance of an supercharged aero engine' by the RR heritage trust. The aircraft in question is Hurricane II, and their numbers for 20000 ft altitude and 335/340 mph speed are, respectively
- brake HP: 1073/1126
- ejector horse power (ie. power from the ejector exhausts): 113/126.8

At 25000 ft, the power was 960 brake + 107.2 ejector.
A faster aircraft will gain a bit more, both wrt. the exhaust thrust and the ram effect.

A few caveats - if the exhausts are botched, like attaching them together into one or two pipes, the exhaust thrust/power will go down; big exhausts can be draggy (compare, perhaps, P-39 vs. Hurricanes and Spitfire V and earlier); not all the ram air intakes are good/great.

tl;dr - there is a lot of good things going on for the Merlin XX on a P-38 or a P-51, the problem is to have them in the required quantity unless the P-40 does not get them, or unless the British are willing to forget the Hurricane II/IV come late 1942.

I'm really still thinking here about an Allison equivalent or near-equivalent to the Merlin XX, just using Merlin XX for shorthand since we know the specs and it had a combat history with an American fighter.

Although having said that, there were certainly a lot of wasted Merlin XX engines, which either should never have been built (or not beyond a few prototypes) like say, the Defiant and / or should have never been built after say 1942, like the Hurricane IIs deployed the CBI, and quite a few edge cases like Beaufighters or various bombers which were probably better with the inline engines. A lot of the Packard-Merlin V-1650-1s given to the British per the licensing agreement were used in aircraft that never left Canada, or were (for some reason) re-engined after being shipped to the UK.

 

[tomo pauk]

I'm really still thinking here about an Allison equivalent or near-equivalent to the Merlin XX, just using Merlin XX for shorthand since we know the specs and it had a combat history with an American fighter.

The V-1710 certainly have had a far greater potential than it was taken advantage from in ww2. A good supercharger on it would've made a world of difference.
Perhaps removing the engine-stage S/C and just mating the big aux supercharger, together with the hydraulic drive, would've been good both from the perspective of ease of installation and the altitude capability standpoints? We will not be getting the altitude power of the 2-stage V-1710, but we might get the engine that is in the ballpark of the DB 605A, or an engine that is better than the Merlin XX family above 15000 ft?

Although having said that, there were certainly a lot of wasted Merlin XX engines, which either should never have been built (or not beyond a few prototypes) like say, the Defiant and / or should have never been built after say 1942, like the Hurricane IIs deployed the CBI, and quite a few edge cases like Beaufighters or various bombers which were probably better with the inline engines. A lot of the Packard-Merlin V-1650-1s given to the British per the licensing agreement were used in aircraft that never left Canada, or were (for some reason) re-engined after being shipped to the UK.

Any alternative history of the RAF that is worth reading has the Defiant die in the crib. Frees up 1000+ Merlins etc, and allows that BP can make Spitfires. A surplus of Spitfires by early 1940 removes the need for Hurricane to get the best engine of the world of 1940 - the Merlin XX.
The Merlin-powered Beaufighter was IIRC unloved by the crew.

Add the three together, and there is a host of Merlin XXs up for the grabs.

 

[Steamed_Banana]

Merlin XX powered Spitfire V also sounds pretty good...

 

[Shortround6]

On the Allison the early problems with 9.60 gears was that the gears were not strong enough to take power load of the higher gear ratio. Breaking teeth was not good.
The Allison was blessed and cursed by axillary section. A lot of needed 'recesses' were cast-into/machined out of the rear of block and covered by a one-piece plate (?).
This eased manufacturing but it made it harder to change things. In late 1942 they figured out how to make the cover plate deeper (remember that several pumps/accessories would have to be spaced out to suit) to fit in wider/stronger supercharger gears to handle the load.
This was part of the problem with fitting a two speed gear box. They had to change a lot of the back of the engine to do it and in 1941-42 they needed every Allison engine they could get. The inside of the Allison supercharger was part of the rear of the engine block?

On basic supercharger design there only so fast you can turn an impeller. If the speed of the impeller tips exceeds the speed of sound in the supercharger the shockwaves really screw up the air flow. Due to the pressure and temperature of the air in the supercharger the speed of sound in the supercharger is somewhat higher than sea level at standard pressure/temperature but most supercharger desingers don't want to exceed it by much more than 10% (?).
Allison using 9.60 gears has a tip speed of 1193fpm.
A Merlin 46 had a tip speed of 1290fpm using a 10.85 impeller and 9.089 gears.
Merlin 45 had a tip speed of 1248 using a 10.5 impeller and 9.089 gears.

Some of the Factories than made Merlins only made single speed or two speed engines, some made both.

Allison tried to mount a Merlin supercharger on the back of Allison engine but they broke it. The less than totally rigid mounting allowed too much flex and when you are spinning things in the high 20,000rpm range even small vibrations add up?

 

[Howard Gibson]

The Allison (as shown by RAF recon Mustangs) was a great engine at low altitude. For that stuff, a two speed supercharger might not have gained much.

A two speed supercharger should work better at most altitudes. If you only have one speed, you have to pick an altitude at which your engine runs effectively, and cross your fingers and hope you don't need to fly fast at other altitudes. The extreme example of this were the Merlins with single-speed single-stage "cropped" superchargers used on LF Seafires and on some Spitfire_Vs. A Seafire_LFIIIc could keep up with a Spitfire_IX up to around 6,000ft. After that, its performance dropped off. The aircraft were useless above 10,000ft.

On a two-speed supercharger, your low gear means that your supercharger consumes less engine horsepower, making more of it available to drive the propeller.

 

[Shortround6]

On a two-speed supercharger, your low gear means that your supercharger consumes less engine horsepower, making more of it available to drive the propeller.

It also means that the supercharger is not heating the air as much so the air is,,,,
1, denser
2. lower temperature means you can use a bit more boost before detonation sets in.
3. Not temperature related but you can open the throttle more on carbureted engines and not have as much pumping loss.