Early Mustangs-performance/experience?

[wuzak]

Well, I think the main "what If" airplane for the V-3420 application was the Douglas XB-42. It offered a level of performance unequaled until jet bombers came along. I'll be posting some XB-42 design info later this week.

The XB-42 used 2 V-1710s mounted on either side of the fuselage, not a single V-3420.

Most dual engines were failures. The RR Vulture did make a great contribution by accident when its supercharger was used as the 1st stage of the RR Merlin 60 series. The V-3420 seems to have done quite well in all its applications, but with possible exception of the XB-42 the designs themselves were either bad ideas or not really needed.

The two stage supercharged Merlin was more or less stumbled onto by mistake.

The Vulture's supercharger impeller may have been used in tests for the 2 stage supercharger, but the Merlin 60 did not use it.

And it was no accident that Rolls-Royce were experimenting with 2 stage engines. It was a plan to create a high altitude engine for a high altitude bomber.

By 1942 every knew that you needed much bigger engines than 1649 cu in and that was where the focus was. The Merlin was clearly too small; in fact it was the smallest displacement front line engine of the war. Even the A6M3 had 1700 cu in. The too slow F4F and P-36 had 1830 cu in. Even the in-line engined French fighters of 1940 had over 1800 cu in. Taking the first stage off the Vulture and adding it to the Merlin was just to make it a back up to the turbocharged radial to be used on the high altitude Wellington. The truly brilliant part was Sir Hooker's liquid cooled aftercooler. Only after they built that back up engine to support what turned out to be a bad idea did they realize they had produced a war-winner.

Since 1929 and the Schneider Trophy 'R' engine, Rolls-Royce knew the answer was rpm and boost. Rolls-Royce used that formula more than any other manufacturer of the war.

 

[MIflyer]

They used two V-1710's but fed them into a V-3420 gearbox. A V-3420 could have been used.

Yes, as I mentioned they were developing a high altitude version of the Wellington and wanted a back-up to the radial with turbo, American style, which was the preferred option. They were not trying to super-supercharge a Merlin to make a better fighter engine. They built the modified Wellington and it went into service to a very limited degree, but, like the Ju-88R that inspired it, was pretty much a waste of time. The future focus was on larger engines, Naiper Sabre and Griffon and so forth.

The first stage of the Merlin supercharger was based on the Vulture, according to the man who designed it. Of course Packard redesigned it.

 

[wuzak]

They used two V-1710's but fed them into a V-3420 gearbox. A V-3420 could have been used.

Maybe, maybe not.

The engines were located quite a way forward and on either side of the fuselage. Shafts from the engines were angled to the gearbox at the rear.

So any engine equipped with a drive shaft could have driven them.

I doubt a production version would have adopted the V-3420, as the twin V-1710s were a more developed package.

Yes, as I mentioned they were developing a high altitude version of the Wellington and wanted a back-up to the radial with turbo, American style, which was the preferred option. They were not trying to super-supercharge a Merlin to make a better fighter engine.

It was Hives who suggested that the two stage engine be used in the Spitfire. So, no, it wasn't originally intended for fighters, but was quickly adopted for the role.

The first stage of the Merlin supercharger was based on the Vulture, according to the man who designed it. Of course Packard redesigned it.

I would have to read his book again, but I believe the original test rig used the Vulture supercharger impeller.

The Merlin 61 used a 11.5" first stage impeller, the Vulture had a 12" impeller.

In any case, Rolls-Royce were working on the Griffon, which had a ~13" impeller. That could have been adapted to the role as well, but only for testing.

The majority of the 2 stage Merlins had a 12" first stage impeller. The RM.17SM had a 12.7" first stage and a larger second stage (10.7"?) compared to the normal (10.1"?).

Packard did not redesign the supercharger - they used a different drive system, an epicyclic gearbox which, IIRC, was engineered by Wright.

 

[IdahoRenegade]

Without changing the supercharger, a second speed would add power at lower altitudes and not increase the critical altitude.

Though, for the V-1710 it could have allowed the 9.6:1 gears for HI gear and 8.8 (?) for LO gear, so as gaining some altitude performance without losing low altitude performance.

Apparently there was a 2 speed V-1710 prototype model at some stage, but it did not make it into production.

Regarding supercharger impeller sizes, the V-3420 used a single 10" impeller. Which would seem to be way undersized.

For comparison, the Vulture (2600ci) had a 12" impeller, the Griffon (2240ci) had ~13" impeller.

Was there a particular reason a larger impeller and housing was never incorporated on the Allison? Given that the SC was a separate assembly bolted on the rear of block (correct?) it seems like it wouldn't have been that difficult to cut in. OTOH, funds and engineering resources were in short supply from Allison with their current production, which I guess explains so little effort to develop a 2 stage/2 speed SC.

BTW, thanks to all that took the time to reply to the thread. Very interesting and informative, still going through the links. In awe of the amount of knowledge here.

 

[wuzak]

Was there a particular reason a larger impeller and housing was never incorporated on the Allison? Given that the SC was a separate assembly bolted on the rear of block (correct?) it seems like it wouldn't have been that difficult to cut in. OTOH, funds and engineering resources were in short supply from Allison with their current production, which I guess explains so little effort to develop a 2 stage/2 speed SC.

BTW, thanks to all that took the time to reply to the thread. Very interesting and informative, still going through the links. In awe of the amount of knowledge here.

Money, perhaps. Or time.

Or they were still wedded to the idea of the turbo, as the supercharger did not need to do as much.

Tomo mentioned some experimental V-1710s that had larger impellers, and the 2 stage engines had a larger 1st stage/auxiliary supercharger impeller (12 1/8"), but used the standard 9.5" main supercharger impeller. This was because the V-1710 2nd stage was set up to mimic a turbo (ie variable speed), as much as possible.

Most single stage Merlins had 10.25" impellers (vs 9.5" for the V-1710), while most 2 stage engines had 12.0"/10.1"

The RM.17SM had 12.7"/10.7" impellers.

The single stage Griffons, at least the early ones, had superchargers of 9.75" or 10.1" diameter, while the 2 stage ones had 13.4" and 11.3".

 

[tomo pauk]

Was there a particular reason a larger impeller and housing was never incorporated on the Allison? Given that the SC was a separate assembly bolted on the rear of block (correct?) it seems like it wouldn't have been that difficult to cut in. OTOH, funds and engineering resources were in short supply from Allison with their current production, which I guess explains so little effort to develop a 2 stage/2 speed SC.

Combination of lack of time (V-1710 was already lagging back vs. for example DB 601, let alone Merlin), small design team at Allison, dilution of effort towards several sub-versions of the engine (turbo/non-turbo, external + internal spur reduction gear, pusher + tractor engine, with or without extension shaft, plus flirting with X24 and W24 spin-offs), along with USAAC favorizing (= money) hi-per engines that they showed through the throat of Continental and Lycoming - all of this meant that the V-1710 got a better engine-driven S/C too late.
Focus towards turboing every military engine by USAAC/AAF was also a factor for over-looking 2-stage supecharging by the AAC/AAF, while USN materialy supported the work at P&W (possibly at Wright, too) with 2-stage S/C. Thus there was a 2-stage R-1830 in series production by mid-1941, and 2-stage R-2800 by winter of 1941/42.

 

[drgondog]

Tomo - brain fart on P-39. I meant P-63 as that is what we were talking about. The P-39 was not long enough to stuff the various Allison's designed for two speed/stage supercharged engines.

 

[Shortround6]

Combination of lack of time (V-1710 was already lagging back vs. for example DB 601, let alone Merlin), small design team at Allison, dilution of effort towards several sub-versions of the engine (turbo/non-turbo, external + internal spur reduction gear, pusher + tractor engine, with or without extension shaft, plus flirting with X24 and W24 spin-offs), along with USAAC favorizing (= money) hi-per engines that they showed through the throat of Continental and Lycoming - all of this meant that the V-1710 got a better engine-driven S/C too late.
Focus towards turboing every military engine by USAAC/AAF was also a factor for over-looking 2-stage supecharging by the AAC/AAF, while USN materialy supported the work at P&W (possibly at Wright, too) with 2-stage S/C. Thus there was a 2-stage R-1830 in series production by mid-1941, and 2-stage R-2800 by winter of 1941/42.

A very good post except for the bolded part. The early development of the Continental was a strange combination of design by Army but manufacture and test by Continental, with the Army paying for development and testing in very small stages, lots of single cylinder and two cylinder test rigs. Continental put either none of their own money (or very little) into the project. The Lycoming project either started later or crept along at very slow speed (a few test cylinders?) until a few Continental engineers, fed up with slow pace of development at Continental left and joined Lycoming. Lycoming did put about 1/2 a million dollars of their own money into the project with the Army coming up with another 1/2 million (but not all at once).

If the Continental and Lycoming projects were run like the Allison projects ( I have no information one way or the other) then the Army was continually late in payment for work done, which would make any company hesitant to expend too much time/effort in advance of payment. Army owed Allison around 900,000 dollars at some point in 1939 and Allison had to "forgive" the Army debt (agree to not get paid) in return for permission to sell engines to the French and British. Hardly a situation in which a small company (or even large ones) would spend large amounts of money on experimental projects.

 

[Peter Gunn]

*SNIP*

BTW, thanks to all that took the time to reply to the thread. Very interesting and informative, still going through the links. In awe of the amount of knowledge here.

I'll second that with enthusiasm. Not much these gents don't know on the subject.

Also, this is the type of thread that warms the cockles of my heart, Mustangs and 1710 Allison's? Sign me up.

More to the point, is seems to me that if the 1710 had a 2 speed 2 stage supercharger, it would have fit in the original frame of the Mustang yes? And if so I'll assume that the snazzy little "smiling" intake under the prop would be still on top of the cowl ala P-51A. If so that'd be a small cosmetic price to pay I'll admit, but my other question, wasn't the Allison a couple hundred pounds lighter then the Merlin and had fewer moving parts? Or is my memory failing.

Also fuel consumption, which is more efficient? Just curious that if the V-1710 could deliver Merlin like performance using the two stage/two speed supercharger (or close to it), would it have had better fuel economy?

I realize there are a lot of "ifs" in that, but I always thought the V-1710 got short changed for many of the reasons SR6, Tomo et al have provided.

Thanks.

PS By the way Idaho, I give you Bacon for starting this thread.

 

[IdahoRenegade]

I'll second that with enthusiasm. Not much these gents don't know on the subject.

Also, this is the type of thread that warms the cockles of my heart, Mustangs and 1710 Allison's? Sign me up.

More to the point, is seems to me that if the 1710 had a 2 speed 2 stage supercharger, it would have fit in the original frame of the Mustang yes? And if so I'll assume that the snazzy little "smiling" intake under the prop would be still on top of the cowl ala P-51A. If so that'd be a small cosmetic price to pay I'll admit, but my other question, wasn't the Allison a couple hundred pounds lighter then the Merlin and had fewer moving parts? Or is my memory failing.

Also fuel consumption, which is more efficient? Just curious that if the V-1710 could deliver Merlin like performance using the two stage/two speed supercharger (or close to it), would it have had better fuel economy?

I realize there are a lot of "ifs" in that, but I always thought the V-1710 got short changed for many of the reasons SR6, Tomo et al have provided.

Thanks.

PS By the way Idaho, I give you Bacon for starting this thread.

From what others have posted here, the core Allison engine (block, heads, crank, etc) as opposed to "powerplant" with SCs, intercoolers, etc, was in some ways superior to the Merlin. (OK, maybe not superior but better in some areas). Significantly fewer parts, and much longer life between major rebuilds. I believe it also proved stronger in post-war racing applications, able to tolerate more boost. I believe others have posted that Allison con-rods were modified to use in Merlins in racing trim. Could be wrong-will be interesting to hear from the pros.

Bacon good!

 

[tomo pauk]

...
More to the point, is seems to me that if the 1710 had a 2 speed 2 stage supercharger, it would have fit in the original frame of the Mustang yes? And if so I'll assume that the snazzy little "smiling" intake under the prop would be still on top of the cowl ala P-51A. If so that'd be a small cosmetic price to pay I'll admit, but my other question, wasn't the Allison a couple hundred pounds lighter then the Merlin and had fewer moving parts? Or is my memory failing.

People at NAA managed to shove in the 2-stage supercharged V-1710 under the hood of the XP-51J, plus under the hood of the P-82. The XP-51J was to feature intercooler, unlike other 2-stage V-1710s.
Please note that 2-stage S/Ced V-1710s didn't use 2-speed drive. Instead they used variable speed drive for 1st stage (like the well known DB engines used for their S/C), while the 2nd stage was always driven via just one set of gears, ie. 1-speed drive.
2-stage V-1710 was almost as heavy as the 2-stage Merlin, ~1650 lbs dry (plus another 100 lbs if they were to feature intercooler) vs. 1690 lbs for eg. Packard Merlin V-1650-3 (that was intercooled as-is); those V-1710s were longer by ~15 in. Extra length can be seen when the XP-40Q is compared with usual P-40s.
1-stage 1-speed S/Ced Merlin and V-1710 were within a few lbs, with Merlin making better power earlier; the 2-speed Merlins were a bit heavier (it was worth it).
Number of moving parts was probably in the ballaprk, though it is claimed the V-1710 have had less different parts.

Also fuel consumption, which is more efficient? Just curious that if the V-1710 could deliver Merlin like performance using the two stage/two speed supercharger (or close to it), would it have had better fuel economy?

Fuel consumption was also in the ballpark, though the V-1710 was able to better handle low rpm foer 'extra-low' power and better consumption. That setting worked well when there was no danger that some Axis aircraft might jump up around.
The best potential for favorable consumption was with turbo V-1710, however that choice was not always applicable in realities of ww2.

 

[tomo pauk]

From what others have posted here, the core Allison engine (block, heads, crank, etc) as opposed to "powerplant" with SCs, intercoolers, etc, was in some ways superior to the Merlin. (OK, maybe not superior but better in some areas). Significantly fewer parts, and much longer life between major rebuilds. I believe it also proved stronger in post-war racing applications, able to tolerate more boost. Could be wrong-will be interesting to hear from the pros.

Until the pros chime in.
Merlin was designed with one of lowest compression ratios of the era (carry-over from days of RR Kestrel, if not earlier) - 6:1, vs. for example V-1710 6.65:1. For a supercharged engine: lower CR = engine is supposed to withstand bigger boost; more boost = more power. In reality it was so - Merlin was using more boost and made more power on same fuel and supercharger size. Especially with changes in construction of the engine block.
Time between overhauls was indeed ~50% longer for the V-1710.

 

[pbehn]

From what others have posted here, the core Allison engine (block, heads, crank, etc) as opposed to "powerplant" with SCs, intercoolers, etc, was in some ways superior to the Merlin. (OK, maybe not superior but better in some areas). Significantly fewer parts, and much longer life between major rebuilds. I believe it also proved stronger in post-war racing applications, able to tolerate more boost. I believe others have posted that Allison con-rods were modified to use in Merlins in racing trim. Could be wrong-will be interesting to hear from the pros.

Bacon good!

Much of the construction of the Merlin v the Allison was to do with production engineering. The Merlin should have been a side note in history used only on the Spitfire Hurricane Defiant and Battle, which were to be replaced by the Typhoon/Tornado. This would probably have been just a few thousand units over many years. To produce more, much more quickly and with enough investment you can have bigger castings but they need more dedicated machine tools jigs etc.

 

[wuzak]

Much of the construction of the Merlin v the Allison was to do with production engineering. The Merlin should have been a side note in history used only on the Spitfire Hurricane Defiant and Battle, which were to be replaced by the Typhoon/Tornado. This would probably have been just a few thousand units over many years. To produce more, much more quickly and with enough investment you can have bigger castings but they need more dedicated machine tools jigs etc.

Don't forget the Lancaster and Mosquito.

The reality is that the Merlin was in demand for a number of aircraft and, had the Spitfire been superseded by the Typhoon, there would have been other uses.

And without the Merlin, the P-51B, D, etc would not have been possible and the USAAF would not have had a performance benchmark for the V-1710, which may have improved less rapidly than historically.

 

[tomo pauk]

Merlin also powered the 1st Halifaxes, and it turned the Whitley into an useful bomber. Plus, Tornado/Typhoon was ill suited to replace the Battle, that was a long range bomber, nor they could do any of night fighting well. Merlin-powered Fulmar was no great performer, but it got it's job done.
With Merlin, Rolly Royce hit the sweet spot - neither to small/light, nor too big/heavy, with a capable supercharger that got substantially better several times as development progressed, with improvement in power (partialy due to it's internal stregth, partialy due to fuel, plus improvements and refinements), not too thirsty. Basically, what 40mm Bofors was to light AAA, Merlin was to the aircraft engines, with a catch that aircraft engines were far more important in the big picture of ww2 than any kind of light AAA.

 

[pbehn]

Don't forget the Lancaster and Mosquito.

I wasn't Wuzak but at the time that the Merlin was being developed the Mosquito didn't exist. The Manchester became the Lancaster when the Vulture programme was suspended but this took some very quick work in Avro, the Lancaster very nearly did not go into production, similarly the Halifax was not originally ordered with Merlins, that was changed earlier on though. Behind the timeline posted above is the failure of the Vulture and chronic problems with the Sabre. The UK went from planning to phase out the Merlin to making the MErlin the main engine on most front line bombers and fighters.

 

[pbehn]

Merlin also powered the 1st Halifaxes, and it turned the Whitley into an useful bomber. Plus, Tornado/Typhoon was ill suited to replace the Battle, that was a long range bomber, nor they could do any of night fighting well. Merlin-powered Fulmar was no great performer, but it got it's job done..

I was discussing the situation when the Merlin was first designed. If anyone in Rolls Royce had been told that 150,000 would be made they would probably have fainted, but then they would have designed an engine made slightly differently.

 

[tomo pauk]

I wasn't Wuzak but at the time that the Merlin was being developed the Mosquito didn't exist. The Manchester became the Lancaster when the Vulture programme was suspended but this took some very quick work in Avro, the Lancaster very nearly did not go into production, similarly the Halifax was not originally ordered with Merlins, that was changed earlier on though. Behind the timeline posted above is the failure of the Vulture and chronic problems with the Sabre. The UK went from planning to phase out the Merlin to making the MErlin the main engine on most front line bombers and fighters.

Problems with Vulture and Sabre didn't have anything to do with Merlin being produced in three (four?) factories in the UK, plus a deal with Ford, then Packard to produce it under license - and that was happening already by mid-1940.

 

[pbehn]

Problems with Vulture and Sabre didn0t have anything to do with Merlin being produced in three (four?) factories in the UK, plus a deal with Ford, then Packard to produce it under license - and that was happening already by mid-1940.

The Typhoon prototype had already been delayed by then, the Halifax had already had its engines re specified in 1937.

from wiki
During July 1937, Handley Page was instructed that the HP56 should be redesigned to utilise a four engine arrangement as opposed to the original twin engine configuration; by this point, the Vulture had already been suffering from reliability and performance problems.[3] The rival Avro 679 proceeded into service as the Avro Manchester, which was powered by a pair of Vulture engines, but was only built in a limited quantity due to the type suffering substantially from engine-related difficulties.[citation needed] The redesign increased the wingspan from 88 ft (27 m) to 99 ft (30 m) and added 13,000 pounds (5,900 kg) of weight.[3] In September 1937, the use of four Rolls-Royce Merlin engines were specified by the Ministry; according to aviation author Phillip J. R. Moyes, the redesign to adopt the four Merlin engine configuration had been "much against the company's wishes".[3]

 

[tomo pauk]

I hear what you are saying.
However, IMO, there is quite a long distance between statement 'The UK went from planning to phase out the Merlin to making the MErlin the main engine on most front line bombers and fighters' and 'The Typhoon prototype had already been delayed by then, the Halifax had already had its engines re specified in 1937.' I'd like to know who said that UK was planning to phase out Merlin, and in what year.
The Air Ministry of the UK knew before the war that they will eventually phase out the Merlin, but with commitment to mass production much before BoB, that phasing out was not a matter of months, but years.