An Allison V-1710 with a two-speed supercharger in 1942 (11 Viewers)

[MiTasol]

Effect of humidity is on pdf p7&8.

Thank you.

 

[Jugman]

In any case Sir Stanley Hooker's solution for the two stage Merlin had to be exceptionally brilliant because Nobody Else seems to have thought of it.

And as for octane ratings, note that 73 octane was the "normal" aircraft engine fuel in the late 1930's. P&W built the R-2000 version of the R-1830 to ensure equal performance even when using lower octane gasoline.

Liquid after/intercooling wasn't a new idea. The coolant weight (40lbs) alone is about the weight of a complete air-to-air intercooler installation. Add in the weight of piping, coolant tank, pump, and the heat exchangers the installed weight will be about three times that of an air-to-air type.
In short weight was a major trade-off. Considering RR's "powe plant" concept they arguably would have been better served by switching to a down draft carb and mounting an intercooler under the engine.

If by "normal" you mean most common that was 87oct by far. Well at least in the US I don't know about other nations . The next most common was 80oct.

 

[MIflyer]

In short weight was a major trade-off.

I hardly think so. The big trade off, especially for a fighter, was DRAG. Think about what it took to get air through that air-to-air intercooler. The liquid intercooler/aftercooler just had to be smaller than the air-to-air one. The other big and largely underappreciated factor was temperature control. Very easy to do with liquid cooling. Challenging with air-to-air. Undercooling was the problem with the P-38's up through the H model, which used leading edge intercoolers, which were great for drag but a challenge for manufacture and inadequate for cooling. The H used the same engines as the J but had less power available. Then with the beard type intercoolers on the J and L overcooling was the major problem, especially in the ETO.

 

[don4331]

There were a couple items I wanted to comment on:

While the French government graciously waived patent royalties to the UK while was fighting the Germans; there is ulterior motive - the French government in exile want the UK government to waive room & board for them.​

And patents were one of the few source left for French government in exile to generate income (and what politician doesn't need income).​

On the other hand, the Americans need to play by the rules on patents, as they want everyone else to respect their patents.​

​

Note: This also would apply for Daimler Benz patents of the fluid drive of the supercharger. Allison would have had to pay the Germans (until war was declared).​

​

For the "C" series Allison, they were having issues with the reduction gearing - because of the internal/external gear setup, the crankshaft gear was overhung. And the overhung gear deflected under power. The result was while the V-1710 could meet 1,045hp, it could meet the USAAF requirement for more (1,090hp) without failure before reaching the 150 hours requirement. (From Vees for Victory)

So, 2 speed drive doesn't buy anything on a "C" series as the reduction drive is the power limiting item.​

Allison's solution is the "F" series with a more conventional for V-12, 2 external gear drive which allows for bearings on both sides of the gear = less deflection.

The problem for an early 2 speed drive - the "C" series takes the supercharger drive off the reduction gear.

This has advantage in that the long shaft allows engineer to "tune out" vibrations. (RR Griffon uses similar supercharger drive from the front of the engine).​

​

When Allison changes to a "F" series, they change the supercharger to the rear of the engine (fancy shaft in shaft to do the same tuning out of vibrations).

So, if you have started your 2 speed drive on a "C" series, and tuned out the vibrations for both low and high speed, when Allison changes to "F" series, you're starting over.

Also, note, in order to run higher boost pressures, the RAF was "deleting" the boost controller. But if you delete the boost controller from a 2 speed engine, you lose the automatic shifting. You can rig up a manual shift mechanism, but that takes more technical ability than just disconnecting a linkage.

Now, I have a couple questions which I didn't find answers for:

For the RAF which were running higher boost pressures: Where they still running the straight ethylene glycol in their -39s? (as recommended by Allison) Or had they "diluted" the coolant with H2O?? (As Allison does with the more powerful -73 engines).​

​

As we now know, the 50/50 ethylene glycol/water cools better than straight ethylene glycol.​

​

So, better crankshafts later in production, 100/130 fuel vs 100/100 and better liquid cooling = ability to handle more power albeit lower altitude.

I couldn't find any models of V-1710 with better altitude performance with the original 9.50" impeller than those with 8.80:1 gears​

I can find lots with 9.60:1 gears, but they make the same power at the same altitude (more/less) as the 8.80:1 ones.​

(Lots with Turbos which are better, lots with the later 10.25" impellor which are better)​

But I might have missed one...​

 

[Steamed_Banana]

The 9.60:1 supercharger on the 1710, starting with the V-1710-81, had a critical altitude about 4,000 ft higher. The -39 and -73 had a critical altitude of about 12,000 ft. The -81 was at 16,000 or a bit more.

 

[Shortround6]

I hardly think so. The big trade off, especially for a fighter, was DRAG. Think about what it took to get air through that air-to-air intercooler. The liquid intercooler/aftercooler just had to be smaller than the air-to-air one. The other big and largely underappreciated factor was temperature control. Very easy to do with liquid cooling. Challenging with air-to-air. Undercooling was the problem with the P-38's up through the H model, which used leading edge intercoolers, which were great for drag but a challenge for manufacture and inadequate for cooling. The H used the same engines as the J but had less power available. Then with the beard type intercoolers on the J and L overcooling was the major problem, especially in the ETO.

View attachment 872950

Thank you, that is about the best photo of a B-24 intercooler that I have seen.
It really shows the size of the intercooler itself and the ducting leading from the turbo to the intercooler and the ducting leading from the intercooler to carburetor.
One has to imagine the duct leading from the intake on the side of the nacelle, past the engine and through support ring and back to the intercooler.
It is not so much the weight but the number of cubic feet the installation requires.

 

[Shortround6]

The 9.60:1 supercharger on the 1710, starting with the V-1710-81, had a critical altitude about 4,000 ft higher. The -39 and -73 had a critical altitude of about 12,000 ft. The -81 was at 16,000 or a bit more.

Allison figures for the 8.80 gears are for 11,700 or 12,000ft without backfire screens. With 9.60 gears they were claiming 15,500ft but 25hp less.
This is zero RAM. The P-39 engines were rated the same.
Performance with RAM is better in some P-40s. One test of a P-40N-5 shows 16,400ft at 350mph.
But only 14,000ft while climbing.
P-39s seem to have had problems. Some P-39s seem to have getting 1060-1080hp at 15,000ft while climbing. 45hp or so low while flying at 500ft less?
Maybe there was trouble with some of the intakes?

 

[ThomasP]

re

And as for octane ratings, note that 73 octane was the "normal" aircraft engine fuel in the late 1930's.

The British adopted 87 octane as standard in 1932 and rated all subsequent engine development using this fuel, while the US adopted 87 octane as standard about a year later. France was using 87 octane as standard from about 1935(I think), as were Japan and Italy. Germany was using 87 octane s standard by the Spanish Civil War for sure, maybe sooner.


re weight of US WWII air-air intercooler systems for turbos

The weight of the B-2 turbocharger unit (ie not including intercooler and such for cooling or ducting for transport of air) used on the P-38E/F, P-43 series, B-17C/D/E/F/early-G, B-24C/D/E, etc, was 135 lbs each. The B-11 turbocharger unit weighed 144 lbs each. The B-13 weighed weighed 135 lbs each and B-33 weighed 138 lbs each as used in the P-38G and H respectively. The only numbers I have run across for the total weight of the turbocharger system (including air-air intercooler and ducting) was listed as 310 lbs each as fitted in the P-38E/F..

P-38E/F turbocharger system with ducting and wing LE air-air intercooler for a weight of 310 lbs

The weight of the C-1/-21 and C-31 turbocharger unit used on the P-47C/D series weighted 230 lbs and 235 lbs respectively. The weight of the CH-5 series used on the P-47M/N and P-61 series weighed 260 lbs each. The weight for the complete turbo installation (with air-air intercooler system and ducting) for the P-47C/D was over 600 lbs.

P-47 turbocharger system with ducting and air-air intercooler for a weight of 600 lbs+

I have not been able to find the weight of the intercooler/aftercooler systems used with the 2-stage superchargers on the F4F, F6F, or F4U.

 

[drgondog]

It's a bit of a mystery to me why the P-51A didn't do better than it did. I've learned about roll rate being an issue which was fixed in the B/C/D, but why didn't they go back and fix it in the A as well? I also don't think the Americans flying them in Burma and a bit in the Med were pushing the engines as hard as the British were, in spite of this guy's memo. It seemed like a type which had more potential than it reached, and it could have been flying in improved form and in some numbers far earlier. An 'improved' P-51A NA-73 type could have been very helpful in the South Pacific in 1942 and probably into 1943. The P-40s were contributing a lot, the P-51A was faster, climbed better and had better range. So potentially could have been a better escort fighter and a better interceptor.

It's almost worth another thread of it's own...

The P-51A was a 'placeholder' for the P-51B-1 and B-5 while awaiting the Flight Test results of both the Rolls-Royce/RAF and the XP-51B. The P-51A didn't introduce the new aileron developed in parallel with the XP-51 #1 flight tests at Langley in summer 1942 simply because the production material orders and designs and tooling for the P-51A were already well advanced.

The aileron for the P-51B-1 hinged on two points as the P-51A, but had a beefed up aft spar to absorb the loads of the 5 degree increase in throw angle. All subsequent P-51B/D models had a three point suspension. I have never seen the structural analysis for the aft spar for either the P-51A or P-51B-1 but suspect there was a torsion issue introduced into the aft spar to obviate a kit release to simply introduce the new aileron into the P-51A. By the time the P-51A was introduced in CBI in October 1943 the last production item had been delivered months prior and both the P-51B-1, P-51B-5 and P-51C were in full production.

The very first Mustang article with +/- 15 degree ailerons was P-51B-1 #1 completed save engine on March 30, 1943.

As to being useful in SWPA - yes simply because the P-51A wing was very similar to the A-36 save the dive brake related features, including both bomb and wing fuel tank mount and fuel feed. Its range would have been very similar to the P-38. As a practical matter, no version of the Mustang could have been introduced anywhere into US service as early as summer 1942 unless General Echols had ordered purchases in early 1941 before the first Mustang I production version first flight. The A-36, then the P-51A had been shoved down Materiel Command (Echols) throat by Plans Division AAF-HQ. The Dallas facility was not operational, and Inglewood was fully applied to B-25, AT-6 and Mustang I production.

To your earlier question about the Allison two speed/two stage engine introduced much earlier into the Mustang line, it was impossible to replace the Merlin type integral two speed/two stage supercharger engine design because the Allison auxiliary supercharger design was too long, altered forward CG too much and required a major redesign of the airframe to move the wing forward. Only the XP-51J and later the P-82E airframe accommodated the Allison V-1710-119 and -143 engines. in 1945 the engine performed inconsistently for the XP-51J at NAA and they gave it to Allison for further development. The -143 never performed well above Military Power and effectively emasculated the F-82 performance compared to Merlin powered P-82B.

 

[Engineman]

Let's be fair to Allison here:

Then in '38, they get an order for 59 V-1710s! (RR is making more Kestrels per month, and they're building Merlins, Griffons and Vultures in addition).

Being fair it GE, the compressor of the Kestrel has peak efficiency of 37% at this point. Then, as note earlier, RR tasks Ellor with improving that and he does - to 70%!​

Again being fair to both Allison and GE, a 1710 in^3 with 6.5:1 compression only need 4" (2 psi) of boost (33" manifold pressure) @ 2,600 rpm to achieve the 1k hp which the USAAF specification requires. The difference between a 40% and 70% efficient supercharger is minimal.

​

Hi,

Just to note that "in '38", RR were mainly building late Kestrels, new Peregrine, new Vulture and the Merlin II. Griffon production began in '42 with the Griffon II.
Regarding supercharger efficiency. Usually, quoted efficiency will be the best achieved and relates to the total percentage of energy used by the supercharger compared to the amount of energy actually converted into the pressure rise. The difference is the energy lost, mostly to unwanted extra heating the compressed air through inefficiency.
In '38 the RR Kestrel supercharger was the 60% efficient version, having been improved in '35 from the earlier 37% version.
Hooker wrote that the Merlin III supercharger was 65% efficient when he examined it in '38. He improved this value by changes he designed to 75% and those improvements appeared
in the production two-speed Merlin XX in '40 and the single-speed Merlin 45 in '41.
The technology of the improvements was carried forwards into later developments. Obviously, different companies had different levels of expertise at particular times.
As I explained above, supercharger inefficiency usually results in excessive charge heating, so the difference between a 40% and 70% efficiency is important.

Cheers

Eng

 

[Steamed_Banana]

The P-51A was a 'placeholder' for the P-51B-1 and B-5 while awaiting the Flight Test results of both the Rolls-Royce/RAF and the XP-51B. The P-51A didn't introduce the new aileron developed in parallel with the XP-51 #1 flight tests at Langley in summer 1942 simply because the production material orders and designs and tooling for the P-51A were already well advanced.

The aileron for the P-51B-1 hinged on two points as the P-51A, but had a beefed up aft spar to absorb the loads of the 5 degree increase in throw angle. All subsequent P-51B/D models had a three point suspension. I have never seen the structural analysis for the aft spar for either the P-51A or P-51B-1 but suspect there was a torsion issue introduced into the aft spar to obviate a kit release to simply introduce the new aileron into the P-51A. By the time the P-51A was introduced in CBI in October 1943 the last production item had been delivered months prior and both the P-51B-1, P-51B-5 and P-51C were in full production.

The very first Mustang article with +/- 15 degree ailerons was P-51B-1 #1 completed save engine on March 30, 1943.

As to being useful in SWPA - yes simply because the P-51A wing was very similar to the A-36 save the dive brake related features, including both bomb and wing fuel tank mount and fuel feed. Its range would have been very similar to the P-38. As a practical matter, no version of the Mustang could have been introduced anywhere into US service as early as summer 1942 unless General Echols had ordered purchases in early 1941 before the first Mustang I production version first flight. The A-36, then the P-51A had been shoved down Materiel Command (Echols) throat by Plans Division AAF-HQ. The Dallas facility was not operational, and Inglewood was fully applied to B-25, AT-6 and Mustang I production.

Very interesting and full of useful data points, thank you.

To your earlier question about the Allison two speed/two stage engine introduced much earlier into the Mustang line, it was impossible to replace the Merlin type integral two speed/two stage supercharger engine design because the Allison auxiliary supercharger design was too long, altered forward CG too much and required a major redesign of the airframe to move the wing forward. Only the XP-51J and later the P-82E airframe accommodated the Allison V-1710-119 and -143 engines. in 1945 the engine performed inconsistently for the XP-51J at NAA and they gave it to Allison for further development. The -143 never performed well above Military Power and effectively emasculated the F-82 performance compared to Merlin powered P-82B.

I was not (that I can remember?) proposing the Allison approach to a two stage or aux. supercharger engine on the Mustang, my query that you were responding to up above was really just for one with improved ailerons. That alone would have made it more viable. If I understood your post it sounds like it was more than just aileron rigging there was an actual wing design change with the P-51B. The next significant factor would then of course be moving up production of NA-73 / P-51A type aircraft by a year or more, which you also effectively addressed.

But part of the reason I was advocating for a two speed supercharger as a kind of interim solution in a 'what-if' scenario is precisely because the two stage supercharger seems like it would A) take longer to develop and adapt to an Allison, B) take up more space, and C) possibly require a more extensive redesign.

We know that they did in fact successfully adapt the P-40 to the two-speed Merlin XX, which did in fact produce a very helpful 'stop-gap' fighter, so presumably the same could have been done with an Allison. There was some speculation in the thread about adapting the two-speed system from the Pratt and Whitney engines, or possibly also their two-stage system (which, if I understand correctly, physically took up much less space than the system Allison did eventually come up with), though the full technical ramifications of the latter are not fully clear to me.

There is also the interesting scenario of adopting components from a French supercharger system (Farman brothers IIRC?) which would require paying a licensing fee. Then this comes down to what could be negotiated with the Free French so that Allison wouldn't be burdened by expensive licensing costs.

 

[don4331]

Hi,

Just to note that "in '38, RR were mainly building late Kestrels, new Peregrine, new Vulture and the Merlin II. Griffon production began in '42 with the Griffon II.
Regarding supercharger efficiency. Usually, quoted efficiency will be the best achieved and relates to the total percentage of energy used by the supercharger compared to the amount of energy actually converted into the pressure rise. The difference is the energy lost, mostly to unwanted extra heating the compressed air through inefficiency.
In '38 the RR Kestrel supercharger was the 60% efficient, having been improved from the early 37% version since '35.
Hooker wrote that the Merlin III supercharger was 65% efficient when he examined it in '38. He improved this value by changes he designed to 75% and those improvements appeared
in the production Merlin XX in '40 and the Merlin 45 in '41.
As I explained above, supercharger inefficiency usually results in excessive charge heating, so the difference between a 40% and 70% efficiency is important.

Cheers

Eng

My point was when the Kestrel V / Allison V-1710 in XP-38 / XP-39 were only making 1.5 / 2 psi boost respectively, the difference between 40% and 70% wasn't significant (<4%) as per my chart There were lots of other issues with the engines that RR and Allison needed to focus on that provided more results.

When RR /Allison get into the 10psi range, the difference become significant: Not just the 10% increase in Density ratio, but the fact that the nearly 50°R temperature increase makes mixture more susceptible to pre-ignition, and the power losses driving the compressor.

And things get really significant when you get into the 20psi (70" Hg) range.

 

[MIflyer]

Thank you, that is about the best photo of a B-24 intercooler that I have seen.

I can't find my picture of the intercooler up inside the wing of a B-17. Air came in through the leading edge of the wing and seems to have exited through slots on the rear upper surface of the wing.

 

[Engineman]

My point was when the Kestrel V / Allison V-1710 in XP-38 / XP-39 were only making 1.5 / 2 psi boost respectively, the difference between 40% and 70% wasn't significant (<4%) as per my chart There were lots of other issues with the engines that RR and Allison needed to focus on that provided more results.

When RR /Allison get into the 10psi range, the difference become significant: Not just the 10% increase in Density ratio, but the fact that the nearly 50°R temperature increase makes mixture more susceptible to pre-ignition, and the power losses driving the compressor.

And things get really significant when you get into the 20psi (70" Hg) range.

Hi,

Yes, you are correct that at low powers and low supercharge, the actual losses are low, but the implications of inefficiency are there and failing to make the process efficient will
have grave implications for your technological capability in future development. Hooker (and others) saw this in 1938 as soon as he moved into supercharger work. Fortunately,
for RR and the Allies, Hooker made great strides forward with this.
Of course, RR were working with 20psi Boost in 1929 and had an inside appreciation of the problems from an early stage.

Cheers

Eng

 

[Steamed_Banana]

Hi,

Yes, you are correct that at low powers and low supercharge, the actual losses are low, but the implications of inefficiency are there and failing to make the process efficient will
have grave implications for your technological capability in future development. Hooker (and others) saw this in 1938 as soon as he moved into supercharger work. Fortunately,
for RR and the Allies, Hooker made great strides forward with this.
Of course, RR were working with 20psi Boost in 1929 and had an inside appreciation of the problems from an early stage.

Cheers

Eng

And do you have a sense of where Pratt and Whitney / GE fit into this?

 

[Steamed_Banana]

As far as the licensing issue for the Free French, wouldn't it make sense to offer a trade for some of the improved fighter aircraft if the new engine was produced?

They ended up getting a few P-40Fs, one squadron GC II/5 "La Fayette" was equipped with them, but more could have been very helpful.

The Free French also got a bunch of P-39s (they got 165 - 200 P-39s which ultimately equipped at least three squadrons that I could find: GC 1/3 "Corse", GC 3/3 "Ardennes", and GC I/5 "Champagne" used them) and other aircraft which were arguably unsuitable for combat against the Germans and Italians, and the P-39s in particular turned out to be death traps for some of their veteran and ace pilots who were killed in accidents. A two-speed supercharger version of the P-39 might have been much more effective, as (possibly) might a two-speed (instead of turbo) engined P-38.

We also know that the Merlin XX P-40s were quite good, but available in short supply. An Allison-engined variant might have been as good or better, and seems like it could have been available in much larger numbers.

For the US, having more and more effective Free French fighter units in the MTO would have been helpful. For the government of France in exile, having more good fighters (and a higher survival rate for their veteran and new pilots) would also be a desirable outcome, I would think.

 

[Engineman]

And do you have a sense of where Pratt and Whitney / GE fit into this?

Hi,
As a casual observer, I would say that GE did very well in the development and mass-production of their turbochargers, for a wide range of American combat aircraft and their
engines. Some comments are made about the complexity of installation and in-combat operation of the earlier units. However, I do not know enough to make further points myself.
Calum Douglas does touch on these units in his books TSHR and TSCT.

Cheers,

Eng

 

[Steamed_Banana]

Hi,
As a casual observer, I would say that GE did very well in the development and mass-production of their turbochargers, for a wide range of American combat aircraft and their
engines. Some comments are made about the complexity of installation and in-combat operation of the earlier units. However, I do not know enough to make further points myself.
Calum Douglas does touch on these units in his books TSHR and TSCT.

Cheers,

Eng

I'm also referring here specifically to the two speed superchargers used by P&W etc., which (I gather) GE also had a hand in

 

[MIflyer]

The P-51A was a 'placeholder' for the P-51B-1 and B-5

Stunning to think that following the completion of the A-36A production run they built all 500 of the P-51A's in just one month. On reason for building them was replacing the P-51-1 aircraft that had been "stolen" from the RAF Mustang Mk IA order.

But I think that for both the RAF and the USAAF they'd have been better off to just have made an extra 500 A-36A's instead. The RAF was wishing they had some A-36A's to support Operation Overlord, the Spit IX being a rather poor fighter bomber. I can't imagine that the A-36A would have inferior to the Mustang MkIA for the "Army Co-Operation" role. Less high altitude performance but they hardly needed that anyway.

 

[MIflyer]

For the "C" series Allison, they were having issues with the reduction gearing - because of the internal/external gear setup, the crankshaft gear was overhung.

The Vees for Victory book says that the USAAF told Allison that type of gearing had never worked before and there was no reason to expect that it would.