V-1710 supercharger development potential

The Lion was a W-12, not a V-12.

Good points Shortround.

Joe Yancey has shelves of Allison valve springs and some have "collapsed" over time. Most are as good as the day they were made. We tested each spring before installing it in an overhauled engine. Today, valve springs are one of the things you CAN have made new, if necessary.

Somehow, nobody seems to want to make Allison or Merlin sodium-filled Stellite valves or valve seats with Stellite for warbirds, despite the Kennametal Stellite Company, inventor of Stellite, still being in business. The Allison doesn't need the valve seats, but the Merlins have a valve seat that screws in and breaks off at the "proper torque" value ... at least according to Rolls-Royce. I have seen them loosen in use but, to be fair, only in one Merlin that I know of. The seat cannot losen in the Allison as it an integral part of the head.

Heck, if you want to cut new seats in an Allison, you have to search out the old, long-nose valve grinders. They don't make them anymore, though you CAN still get stones.

Both engines' installed populations, including the "runners" that start but are not in a plane, car, or boat, could use an influx of new valves. Several could use new camshaft and not a few new crankshafts. I think there are enough Allison cylinder liners around for years yet, but the Merlin crowd could use some of them ,too. As long as we're asking for parts, main bearings and cam bearings would be appreciated, too.

Let's face it, the life spans of the existing warbirds would take a huge jump if someone restarted production of the Merlin and the Allison, even if on a limited basis.

GregP said:

A Merlin -61 makes WAY more sense to me for a V-1650-7 since the P-51D, it's primary mount, usually operated at 20,000 to 35,000 feet, at least in Europe.

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The -7 was used in the P-51B/C as well as the D/K, and deployed because it had slightly better power in the middle altitudes through a lower FTH, while the -3 was significantly better above 26000 feet.

Greg,
With the introduction of the P-51C-5-NT onto the Dallas production line and the P-51B-15-NA in the Inglewood production line, the Packard V-1560-7 engine was adopted as standard.

P-51B
42-106739/106978 North American P-51B-15-NA
43-24752/24901 North American P-51B-15-NA
390 a/c

P-51C
Of the 1750 built all but 350 42-102979/103328 North American P-51C-1-NT used the -7 engine.

1950 used the -3 engine
1790 used the -7 engine

They may have switched to a more "medium" altitude engine because the anticipated shift to higher altitudes did not occur or occurred after the the engine switch was made.
Fw-190s with radial engines never got very good at much over 20,000ft. The Germans took a while to get the big supercharger DB605s in service. While some 109s did have GM-1 it was certainly not all 109s used for bomber interception.

The -7 offered about 100-110 more HP for take-off than the -3 at the same boost and may have helped with the bigger fuel load?

SR - I would expect that the extra TO Power (1490 vs 1380) of the -7 over both the -3 and the -9 would have been nice to have

I still think the V-1710 had good potential for development as a 2-stage engine, but it was never funded by the USA.

Anyone else have an opinion about it?

Greg - Not sure if you've seen or worked on any RR, DB or Junkers engines to make an informed comparison, but I would love for someone to be able to say, "The way the V-1710 was mechanically configured, there is no way a Merlin 2-stage supercharger configuration could have been installed on a V-1710 without major redesign."

I'm wondering if the modular approach Allison took with the V-1710 design precluded a RR 2-stage supercharger layout.

An extreme example would be the DB engines with their sideways mounted superchargers, radically different from a RR or Allison setup.

GregP said:

I still think the V-1710 had good potential for development as a 2-stage engine, but it was never funded by the USA.

Anyone else have an opinion about it?

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I agree that there was a good potential for the V-1710 with 2-stage supercharger.
It was funded by the USA, otherwise it is very much possible that there would not be any to power the P-63; support funding for that was a bit late, esp. when we look at USN material support for 2-stage engines of P&W (even Wright produced a handful of 2-stage R-2600s!).

The aux stage was not exactly what I had in mind.

I was talking about a 2-stage, integral supercharger, similar to the Merlin. Had one been developed, I'm sure it could have been debugged and put into service. Of course, that's an assumption on my part and probably qualifies as a "what if," but they worked out the rest of the bugs, so I am extrapolating.

It is also possible they could have simply made up and adapter plate and molted in teh Merlin S/C unit. Again, that never happened, either.

Good thing the merlin was there and developed as the war went along. The Griffon never DID replace the merlin in service, good though it was.

gjs238 said:

Greg - Not sure if you've seen or worked on any RR, DB or Junkers engines to make an informed comparison, but I would love for someone to be able to say, "The way the V-1710 was mechanically configured, there is no way a Merlin 2-stage supercharger configuration could have been installed on a V-1710 without major redesign."

I'm wondering if the modular approach Allison took with the V-1710 design precluded a RR 2-stage supercharger layout.

An extreme example would be the DB engines with their sideways mounted superchargers, radically different from a RR or Allison setup.

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I've actually been meaning to pose the possibility of Allison mounting an auxiliary supercharger in a DB/Jumo style side position, particularly given the (potentially) shorter length and better ram intake position in a P-39/63 configruation. (might have made the modifications to the XP-39E less dramatic too)

The aspect of the RR 2-stage approach that the V-1710 couldn't follow was a single shaft 2-stage design. Any added supercharger stages would be more or less used like a turbocharger, independently driven from the single-speed integral supercharger. This is fairly similar to the approach Pratt and Whitney took for their 2-stage designs, Allison just didn't have the funding or resources (internal or external) of P&W to carry out that development early on, and even most later developments were more primitive than what the superchargers on the R-2800 had developed into. (lack of intercooling was a big issue ... adapting a liquid intercooler arangement akin to the P-38J/L's -or Merlin's- would have made a world of difference)


That aside, the other limiting factor was supercharger design. Allison's own designs may have been reasonable enough, but paled in comparison to Rolls Royce's. Size/space constraints for the integral mounting point may have been a limiting factor too, but the roughly equivalent 9.5" diameter impeller used on the 'cropped' Merlin 50 series still performed significantly better than the Allison's at similar speed (the higher displacement of the engine made up for some of the difference -higher power at lower boost). With Merlin quality supercharger design, the single-stage Allison might have reasonably matched the Merlin 45 or 47 or even exceeded them a bit.

Stanley Hooker quality compressor design applied to GE's turbos might have had some significant improvements too. (including lower intercooling requirements for given boost pressure)

There is NOTHING whatsoever that precludes the Allison block from using a 2-stage case exactly like the Merlin. I have seen them side by side, without superchargers and there isn't a lot of difference. The only penalty I can see is a small bit of added length, and the Merlin unit has that, too. Of course, it would also need an intercooler similar to the Merlin, whether in the same place or not is an issue for debate. On the V-1710-119, it WAS in the same place.

The auxiliary drive on most later Allison WAS a hydraulic coupling. It just wasn't mounted sideways.

I submit the Allison V-1710-119 was a match for the Merlin in all categories, but was overtaken by the jet engine. Had development continued, for some reason, it would have given good service. But, jets were the new darlings of the military and essentially killed the big piston engines. Too bad, but at least a few still exist today.

The fact that the V-1710 "caught up" to the Merlin in it's -119 guise in no way detracts from the brilliance of the Merlin. It just means Allison also developed a good engine that had equivalent performance. Unfortunately, it never made the war and only flew in a few experimental aircraft. It was a case of "too late" for thw war effort, but "too late" beats the crap out of "never."

Most of the planes I love had Merlins or radials, but I DO love the P-38. Nothing else like it in the sky when the sky is full of WWII aircraft. That could change if someone restores a Fokker G-1, a P-61, or perhaps a Savoia-Marchetti SM.92, or a few others. I keep wainting for the Twin Mustang restoration to result in a flying aircraft.

That would be nice to see at an airshow, huh?

I think there was no technical reason why Allison could not have built a two stage supercharger like the Rolls-Royce designs.

Why they didn't is probably more to do with the philosophy of Allison, particularly with regards to modularity and the ease of manufacture.

To do a 2 stage design like Rolls-Royce would require a complete new supercharger design. In the case of Allison's two stage design, the engine stage supercharger remained the same, while the Auxiliary stage supercharger was, essentially, a bolt on module. The core of the two stage engines with the carbuerretor attached to the engine stage supercharger, instead of the auxiliary stage, were identical, or near enough to, the equivalent turbocharged version.

GregP said:

There is NOTHING whatsoever that precludes the Allison block from using a 2-stage case exactly like the Merlin. I have seen them side by side, without superchargers and there isn't a lot of difference. The only penalty I can see is a small bit of added length, and the Merlin unit has that, too. Of course, it would also need an intercooler similar to the Merlin, whether in the same place or not is an issue for debate. On the V-1710-119, it WAS in the same place.

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There seemed to be some difficulty in making the integral supercharger variable speed (there's some references to 2-speed single stage models, but I haven't seen more specifics on how that was configured -or even it it was some oddity like having the integral stage removed entirely and running only an 'auxiliary' stage).

Using 2 stages geared at a fixed speed similar to the existing engines (without intercooling or water injection) doesn't seem like it'd solve much aside from perhaps providing boost/altitude performance beyond the structural limits of the single integral stage. (still suffering from practical limits of power consumption and charge heating along with fixed FTH -aside from using engine RPM to vary supercharger RPM) You'd also need strong enough gearing to allow for the load -the main limit that delayed the 9.6:1 supercharger speed)

I suppose if they did manage to configure something like that AND manage better efficiency than what happened with existing single stage impellers, it might have been worthwhile. (ie if, for whatever reason, the specific engineering limits on Allison's compressor designs favored such a configuration -in terms of power absorbed and heat generated during compression- compared to what RR -or German engines, and some American radials- managed with single-stages, then it would have been worthwhile)
Obviously, including some form of intercooling between those stages (or adding water injection) would change the game.

The auxiliary drive on most later Allison WAS a hydraulic coupling. It just wasn't mounted sideways.

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Yes, which is why that configruation came to mind, particularly given Bell was the only one to actually use 2-stage Allisons during the war it seems like tailoring them to those machines would make sense. (I was imagining the supercharger intake positioned somewhere along the lines of the intercooler scoop of the XP-39 -though smaller ... maybe still a bulged faring if the side-mounted impeller housing extended too far beyond the engine perimeter)

I submit the Allison V-1710-119 was a match for the Merlin in all categories, but was overtaken by the jet engine. Had development continued, for some reason, it would have given good service. But, jets were the new darlings of the military and essentially killed the big piston engines. Too bad, but at least a few still exist today.

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It still would have been very significant for the P-82s that had so much service trouble with the more primitive 2-stage Allisons they adopted for mass production.

2 speed V-1710 is another worthwhile point.
I believe that was a major advantage of the V-1650 powered P-40F and P-40L.

You know, I have spoken with a few former pilots and crew chiefs and have been told the Allison was awful by a few; have been told the pilots weren't operating them properly by a few, and have been told the maintenance was pretty much ignored by still others ... since jets were the darlings they were trying to "kill off" the last remaining pistons.

I am at the point where I do not belive any of them. It appears there were issues, but it is VERY hard to get down to what caused them, the Allison, lack of training in operating procedures, bad maintenance, or whatever.

When I worked for Joe Yancey, he built a G-6 and it is still running fine. Of course, it is being run by someone who is a private owner and is operating it as Joe told him to, and he doesn't ask for WER EVER. much less "frequently."

Tough to know what they were experiencing 50 - 65 years ago.

I'll allow there were issues, but am really not sure what the actual issues were.

In the Merlin world, I have seen one owner have metal in the oil at 25 hours. When it was fixed, he now has 850 hours on it and is running strong. So ... the Allison is not the only engine with some rather anomalous issues that crop up every once in awhile. The Merlin in the museum's 'Spam Can" P-51D has 900 hours on it and purrs sweetly every time it starts. Last time it needed service, they just changed the rings! Go figure.

GregP said:

You know, I have spoken with a few former pilots and crew chiefs and have been told the Allison was awful by a few; have been told the pilots weren't operating them properly by a few, and have been told the maintenance was pretty much ignored by still others ... since jets were the darlings they were trying to "kill off" the last remaining pistons.

I am at the point where I do not belive any of them. It appears there were issues, but it is VERY hard to get down to what caused them, the Allison, lack of training in operating procedures, bad maintenance, or whatever.

<SNIP>

Tough to know what they were experiencing 50 - 65 years ago.

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I think this relates to what drgondog was trying to explain earlier.

gjs238 said:

2 speed V-1710 is another worthwhile point.
I believe that was a major advantage of the V-1650 powered P-40F and P-40L.

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Nope. The major advantage of the V-1650-1 was that it featured a bigger supercharger, with a less restricted inlet elbow (the 'item' connecting carburetor and impeller). That was worth 3000-4000 ft of rated height, or a difference of ~200 HP vs. a V-1710 with 9.60:1 S/C gearing at 20000 ft.
More supercharger speeds means the engine is more flexible. It won't give altitude capability just because it is a 2-speed engine - compare Merlin 45 (1-speed S/C) vs. Merlin XX (2-speed S/C).

added: 2-speed V-1710 would make it interesting for bomber applications, though

GregP said:

The aux stage was not exactly what I had in mind.

I was talking about a 2-stage, integral supercharger, similar to the Merlin. Had one been developed, I'm sure it could have been debugged and put into service. Of course, that's an assumption on my part and probably qualifies as a "what if," but they worked out the rest of the bugs, so I am extrapolating.

It is also possible they could have simply made up and adapter plate and molted in teh Merlin S/C unit. Again, that never happened, either.

Good thing the merlin was there and developed as the war went along. The Griffon never DID replace the merlin in service, good though it was.

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There was a V-1710 with Merlin 2-stage supercharger inter-cooler. It took a while, and wrecked some S/C in the process, but the end result was a power vs. altitude same as 2-stage Merlin.

I don't get it why the V-1710 with aux S/C is such a boogaboo.

gjs238 said:

2 speed V-1710 is another worthwhile point.
I believe that was a major advantage of the V-1650 powered P-40F and P-40L.

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Partially yes, but partially just the altitude rating combined with a more efficient supercharger design (and a sheer larger supercharger). Had Packard been producing single speed Merlin 45s rather than XXs, the disparity in altitude performance would have been similar but the merlin would have lost a bit more power down low (and a bit of weight).

The 9.6:1 supercharger V-1710s got a lot closer to Merlin 45 performance levels, but still a few thousand feet lower FTH. It's hard to say how much might have improved with larger impellers and/or diffusor casings allowed ... and the same things limiting those also limited the 2-speed gearing configuration I believe. The integral supercharger on the V-1710 didn't leave space to allow variable speed gearing or larger supercharger and initially even limited maximum single speed gear ratios. (the 8.8:1 speed was in part limited by the gearing they could manage to fit and how much strain it could take)

Actual performance and efficiency (in terms of pressure for given power consumption and charge heating at a given RPM) of the integral supercharger didn't seem to change much or at all from the V-1710s of 1940 and those of 1944. (changes in screens, filters, and ram inlet, duct and manifold design had more affect on things)

Changes on the single-stage merlins were far more dramatic (same for the single stage german engines) That includes performance for the smaller 9.5" impeller blower used on the low altitude merlin 50 series. (compared to the 8.8 blower Allison it still had a significantly higher FTH and similar power -depending particular WER ratings compared ... Allison always made more power at less boost, but also always at lower critical altitudes)


And again, I am curious as to whether examples listed (by USAAF documentation) to be single stage but variable speed (and often larger than 9.5" for the impeller) might have been engines with the integral stage deleted entirely and a single external hydraulically coupled supercharger stage was used exclusively.

GregP said:

I am at the point where I do not belive any of them. It appears there were issues, but it is VERY hard to get down to what caused them, the Allison, lack of training in operating procedures, bad maintenance, or whatever.

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Seems more likely an 'all of the above' situation, perhaps hard to nail down what issues were most critical or even if any one set of problems was consistently critical.

Also hard to tell what issues might have been specific to the P-82 itself given A. there were no merlin powered variants in service to directly compare records to, and B. there were no single engined Mustangs fielding similar V-1710 powerplants to compare either.