V-1710 supercharger development potential

Discussion in 'Aviation' started by gjs238, Feb 17, 2015.

  1. gjs238

    gjs238 Well-Known Member

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    The V-1710 supposedly was designed with a General Motors philosophy to build-in production and installation versatility with a "modular" design to facilitate mass production and provide multiple installation options.

    However, did the fundamental design limit development of the integral supercharger - did the design limit or prevent a multi-speed supercharger and/or an integral 2-stage supercharger?

    Ironically, the RR Merlin, perhaps not designed with the mass production philosophy and modularity of the V-1710, turned out to have much greater supercharger development potential, with multi-speed and multi-stage versions being developed.

    Was the V-1710 basic supercharger design flawed in this regard?


    From Wikipedia:
    The engine design benefited from the General Motors philosophy to build-in production and installation versatility. The engine was constructed around a basic power section from which different installation requirements could be met by fitting the appropriate accessories section at the rear and an appropriate power output drive at the front.

    The front of the engine could have one of a number of different output drives. The drive might be a "long-nose" or close coupled propeller reduction gear, an extension drive to a remote gearbox, or a gearbox that could drive two wing-mounted propellers from a fuselage-mounted engine.

    The engine could be set up for right-hand or left-hand rotation, and could be used with a "tractor" or "pusher" propeller. Another feature of the V-1710 design was its ability to turn the output shaft clockwise or counter-clockwise by assembling the engine with the crankshaft turned end-for-end, by installing an idler gear in the drive train to the supercharger, camshafts, and accessories, installing a starter turning the proper direction, and re-arranging the ignition wiring on the right side to accommodate a changed firing order. No change to the oil and Glycol circuits was needed.

    This approach allowed easy changes of the supercharger(s) and supercharger drive-gear ratio. That gave different critical altitude (the maximum altitude at which the engine could produce full power) ratings ranging from 8,000 to 26,000 feet (2,400 to 7,900 m).
     
  2. Shortround6

    Shortround6 Well-Known Member

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    We have been over this a number of times in old threads.

    In the late 1930s everybody's superchargers were pretty crappy compared to what was to come in just a few years. In the Mid 1930s GE, designer and builders of the turbos were ALSO supplying supercharger designs and parts to both Wright and P&W. Allison, at times, actually subcontracted parts (like impellers) to/for GE which sold them to Wright and P&W. With 87 octane (or lower) fuel the engines couldn't use much boost and the faults of the superchargers were masked because of this. This was also the reason for the interest in the turbo. The turbo was not supposed to increase manifold pressure but to "fool" the engine into "believing" it was a sea level. Exhaust back pressure and intake to the carburetor/engine supercharger were supposed to be at or near sea level values and the intercooler was supposed to limit air intake temperatures to 100 degrees F, thus allowing sea level (or close to it) power at high altitudes.

    The better fuels (and better engine materials) allowed more boost to be used and showed that the existing supercharger designs weren't that good. They took more power to compress the air and heated it more than theory said they should. This was more noticeable at the higher pressure levels. Wright and P&W started their own supercharger design depts.
    The Allison supercharger as used on the long nose engines wasn't that far behind the supercharger used on the early Merlins. The engine was actually a bit under rated due to other problems besides the supercharger. The engine was 'rated' at 1090hp at 13,200ft compared to the Melrin's 1030hp at 16,250ft. The Allison should have been good for about 970-980hp at 16,250ft. The supercharger was capable of holding 42in (about 6lbs boost) to about 12,000ft (no RAM).
    Rolls Royce got Hooker and the supercharger 'game' was never the same.

    Much later (end of war/post war) Allison's got larger diameter superchargers and some experimental engines got two speed gearboxes/clutches. There may have been nothing to prevent such equipment from being fitted earlier except the lack of engineering capacity. Initial concepts for such engines started in 1942 and some of the parts (12 counter weight crankshaft and stronger crankcase and cylinder blocks) were incorporated into engines that did see service during the war.
     
  3. tomo pauk

    tomo pauk Creator of Interesting Threads

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    There was V-1710-131 (military nomenclature; Allison nomenclature V-1710-G3), prototype series of 8 engines with an 'integral' 2-speed supercharger, S/C ratios of 7.48:1 and 9.60:1. Take off power 1600 HP @ 3200 rpm, military rating in high gear 1220 HP @ 3000 rpm @ 15500 ft. The previous G2-R/L (right/left turning) was also projected as a two speed engine, intended for civil aircraft, none produced. The G series are late-war/post-war development, though.
    The V-1710 with integral 2-stage S/C was also attempted, apparently in early 1944. After a convoluted work, the two-stage S/C and intercooler from V-1650-3 were mated with V-1710, the resulting power was in the ballpark with V-1650-3. Per Vee's for victory, pg. 333.

    .

    IMO, the whole modularity thing from the V-1710 was rather a waste. No bombers ever flew in combat with it, that is discounting fighters their derivatives being bombed up. Once there was a need for the Merlin to be built in more modern factories, it was duly modified for that and result was the great quantity of modern engines available when it mattered the most. I don't agree that Merlin have had 'much greater supercharger development potential', more about that just under.

    The integral supercharger of the V-1710 have had one main disadvantage vs. Merlin - it was too small. Merlin was at 10.25 in of impeller diameter, the DB-601E was at 260mm (just a bit over 10in), the V-1710 was at 9.50 in. The Merlin 46 and 47 received yet a bigger S/C, 10.85 in, the full throttle height was at 22000 ft (4000ft greater than at Merlin 45). That was unmatched for a single stage supercharged engine until DB installed a 290mm S/C from DB-603A on the DB-605A thus creating the DB 605AS. The DB-603A was also to receive yet bigger S/C, resulting in the DB-603E with greater power at altitude (sometimes the DB-603AA and DB-603AS are mentioned as having big superchargers).
    For how much the size of S/C mattered, we can compare the pictures of the RR Buzzard and RR 'R' (racing) engines - much greater S/C was installed in the R engine.

    Another shortcoming - the elbow, feeding mixture from carb to S/C, have had the throat area of just 24.4 sq in. The carburetor throat area shrunk down from 41.3 sq in to 24.4 sq in. Smaller throat area = more losses = less power.
    For comparison, the carburetor of the Packard Merlin V-1650-1 was at 38.3 sq in, the two stage V-1650-7 used one with 46.4 sq in of throat area. As early as February 1938, the USAF have had a report noting that 'Merlin II has a very much enlarged induction system to handle the large quantity of low density air...' and recommending that V-1710 would need to have similar induction system.

    A question will emerge - why such a small S/C and restricted inlet elbow? Much has to do with USAF's fixation with turbos. The Airacuda, XP-37, XP-38, XP-39 - those were the 1st fighters intended to have V-1710, and turbo was to be there to do much of compression, so the engine will 'believe' that is still on sea level while being at 20-25000 ft. Such engines have had even smaller carb, with 24.4 sq in of throat area, and was followed by the similarly dimensioned inlet elbow. Once the turbo was gone, the engine had to do with smalish S/C.

    I'd say that auxiliary supercharger, as historically, was only viable alternative, the timing being much more of an issue than any other.

    [/QUOTE]

    The higher altitudes were domain of 2-stage versions.
     
  4. stan reid

    stan reid Member

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    #4 stan reid, Feb 17, 2015
    Last edited: Feb 17, 2015
    I remember these engines with their "stock" superchargers used during the 1960s in the Arfons Bros. (and others) dragsters and Land Speed Record cars. They were also used in the Gold Cup boats (I believe with turbochargers in at least one example) but the Rolls-Royce engines proved more successful there. To my knowledge, RR engines weren't used in any dragsters probably because of limited availability here in the U.S. when drag racing was just getting started. Rolls-Royce engines were used in some LSR cars prewar. To this day, Allison engine machines often show in tractor pulls.
     
  5. Shortround6

    Shortround6 Well-Known Member

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    The problem with trying to use post war sea level racing use as a comparison tool is that it ignores the altitude problem.

    The long nose "C" series engines, according to factory charts, could pull 62in of manifold pressure (15lbs boost) and make 1700hp at sea level at 3000rpm. The later engines got even better superchargers (although nothing compared to a two stage) and could do a bit better.
    the race boats and certainly the dragsters may not have held the engines to 3000rpm either. Increasing engine speed by even 100 rpm increased supercharger impeller speed by 710-960 rpm depending on supercharger gears fitted.
    Much different trade offs were made between power, rpm, over-haul life (or times between engine blow-ups, which is different) in the gound or sea level racers and with aircraft.
     
  6. gjs238

    gjs238 Well-Known Member

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    Thanks guys, great replies!
    I wasn't thinking so much about the history and attributes, but the mechanical engineering aspect of making the V-1710 supercharger multi-speed or 2-stage.

    It seems that either this was much more difficult or impossible to do on the V-1710 than with the RR Merlin, or Allison did not have sufficient resources to do the job.
     
  7. tomo pauk

    tomo pauk Creator of Interesting Threads

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    The 2-stage V-1710 were also multi-speed - the auxiliary stage was powered via hydraulic coupling (the engine stage S/C was still 1-speed, ie. fixed gear ratio). Only the 1st few experimental 2-stage engines were outfitted with 2-speed gearbox, again only for auxiliary stage.

    Compared with Rolls-Royce, Allison was probably provided with less resources pre-war; most of resources went to engines Army was 'co-designing' with Lycoming and Continental, that went nowhere. The experience of RR in designing and building V-12 engines was greatest in the world, both for military aircraft and racers - while we can say that Allison also have had experience in racing engines, those were for car racing, and don't stand a comparison with RR.
    It is my understanding that UK Air Ministry and/or RAF have great confidence in RR to come out with a great engine, and were willing to pay the company for advances. The US Army have had much more strict relations with (at least) Allison, even negotiating that Allison will forget the almost a million US$ if they want a permission to export their engines abroad.
    A good part of work strain in Allison went to different V-1710 configurations (turbo, non-turbo, pusher, with extension shaft, double V-1710 with it's iterations; bomber aircraft being intended airframe for many of the versions, that also got nowhere) that further stretched thin Allison design staff. The internal spur reduction gear was a weak spot of the engine, that needing a replacement with external spur red. gear.
     
  8. Shortround6

    Shortround6 Well-Known Member

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    There may have been a physical aspect. The original rear accessories gear case was too narrow to fit the thicker gear needed to handle the desired 9.60 gear ratio. if the desired air flow was 10,000lbs per minute the 8.80 gear needed about 210hp while the 9.60 gear needed 250hp to drive it. If there wasn't room for a thicker gear was there room for a two speed drive mechanism?
    And what needed to be changed? Some Merlin factories built single speed engines for quite some time while at least one of the factories building two speed engines changed to two stage (with two speeds) fairly quickly.
    IF the engine side of the gear casing is cast into the crankcase block and just a cover is put on do you need to to change the crankcase molds at the casting facility? Do you just need a thicker "cover" and by the way the "cover" may very well be the engine side of the supercharger casing.

    Not great but.

    allison_cutawaya.jpg

    The gear train at the rear ran not only the supercharger but the vacuum pumps, hydraulic pumps, coolant pumps, oil pumps, etc. most came in separate shafts/gears. But major changes to the rear of the engine might have meant a lot of fooling around. Adding an auxiliary supercharger spaced away from the main engine may have meant more of the original accessories section could be kept.

    More good pictures/drawings. Allison V-1710 Construction and Installation Details
     
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  9. stan reid

    stan reid Member

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    Sorry to go off topic for a minute but does anyone know why these engines weren't dohc? Was it cost or that the increase in power didn't significantly make up for the extra weight or, being bulkier, the loss in aerodynamics?
     
  10. gjs238

    gjs238 Well-Known Member

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    Greg P around? :)
     
  11. Shortround6

    Shortround6 Well-Known Member

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    You use dohc when you think that a sohc won't control the valves well enough. IE, the valves can/will 'float' at the rpm desired. If the springs can close the valves against the inertia of the valve weight, cam follower/rocker arm in a quick enough fashion the dohc are not needed. Late model Allisons did use much stronger springs than early ones but that had more to do with the much higher intake manifold pressure pressure blowing the intake valves open early (or delaying closing) than trying to turn more rpm.
     
  12. gjs238

    gjs238 Well-Known Member

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    RE: DOHC
    How fast were these engines turning compared to today's DOHC automobile/motorcycle engines?
     
  13. stan reid

    stan reid Member

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    Thanks! Yes, I can see that at the lower rpm anything you might gain from dohc (less reciprocating weight would probably be about it) likely wasn't of any real significance.
     
  14. Shortround6

    Shortround6 Well-Known Member

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    The Allison and Merlin topped out at 3,000rpm, while making power, they were allowed a certain amount of overreving while diving but the throttle had to be part closed (like over half) But they used some really big valves compared to car engines.

    Springs had to handle weight times the sq of the speed, Lift wasn't that bad .533in (?). I can't find the diameter at the moment.
     
  15. GregP

    GregP Well-Known Member

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    #15 GregP, Feb 17, 2015
    Last edited: Feb 18, 2015
    First it didn't need dual overhead camshafts since it had 4 valves per cylinder and they were all actuated by a single camshaft that did not have wear problems. The valve rockers are roller units and it works quite well.

    About the supercharger, it is a modular design and larger single-stage impellers were tried. But the design was specified by the US Army originally and it was specified as a single supercharger stage for the low to mid-altitude boost and a turbosupercharger (the name at the time for a turbocharger as it is called today) as the high-altitude boost system. Then they withheld the turbos from all the fighters but the P-38. It had some issues at the start, but they were worked out within about 6 months here in the U.S.A. ... it took about another three months to work them out in Europe because we didn't know how much different European fuel was from US fuel. When we found out, they could then replicate the problem on the test stand and they figured it out.

    So the turbo was deleted from the P-39 and was never offered to Don Berlin for the P-40.

    With the modular design it was certainly possible to develop a 2-stage or even more stages of supercharging, and Allison offered this option to their primary customer, the US Army Air Corps on at least 2 or 3 occasions and was told no thanks each time. Allison ws a relatively small company and when your major customer does not want to fund a development, it doesn't get funded by anybody ... and it didn't.

    Eventually Allison DID develop and auxiliary stage that was flown in the P-63, but it wasn't quite the same as an integral 2-stage similar to the Merlin unit developed by Sir Stanley Hooker. The USAAC / USAAF got exactly what they ordered. The V-1710 has enourmous potential for development, but the arrival of jet engines coupled with the rather obvious end of WWII coming down the pike spelled the end for big piston development, and Allison put their design staff to working on jet engines and merely finished out the wartime production contracts for the V-1710 as they saw the handwriting on the wall, just like everyone else did, too.

    Today the Allison is a very relaible and long-lasting warbird engine, but it has a limited number of airframes it is suitable for. It flies in the P-38, P-39, P-40, P-63, several kit-built Spitfires that look WONDERFUL and offer 95% of the performance of a real Spitifre for MUCH less cost, some Yak-3's and Yak-9's, and there is one left-turning Allison V-1710, the ONLY left-turining unit that is not in a P-38, flying in Paul Allen's Ilyushin Il-2. There are many in boats and the Allison wins almost all of the European tractor pulls in its class that happend to include Merlins.

    There are few airstrips in Europe, relatively, but they have LOTS of fields, so tractor pulls are popular.

    If the V-1710 is built correctly, it is a very good engine. If not built correctly, it ... like any other decent engine that is not to spec, has problems. The best way to build one correctly is to FOLLOW THE BOOK to the letter. There are about 4 shops left that overhaul Allisons in the U.S.A.

    In retrospect, it would have been a wise thing to fit a Merlin supercharger stage to an Allison at LEAST for testing, but I don't know if they did. There is no evidence they did ... but there is also no evidence they didn't, so the only people who really know have probably passed away. With no evidence of it, I am left thinking the integral 2-stage unit was never built, if it ever existed and, if it DID exist, it was probably never completed and run.

    In the end, the Merlin was and is a great engine if ever there was one, and the Merlin-powered planes did the high-altitude work, except for the P-38, and the Allison-powered planes did a lot of the low to medium-altitude work.

    Things might have been different ... but they weren't. The same basic turbocharger helps boost the P-47 along at high-altitude, so we KNOW it is a decent unit. The supercharger is ALSO a decent unit, but not up to the standard of Hooker's superchargers on the 2-stage Merlin. Those babies are works of art. In fact, the impeller of an early Whittle jet engine is essentially a large Merlin inpeller design.
     
  16. gjs238

    gjs238 Well-Known Member

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    Is the V-1710 arrangement so different from the Merlin that it precludes a Merlin-like setup? (assuming one had the time and $)
    For example, the DB 601/603/605 supercharger arrangements were physically much different than the RR Merlin or V-1710.

    Never mind 2-stage, the V-1710 never made it to 2-speed.
     
  17. kool kitty89

    kool kitty89 Well-Known Member

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    Is that why it took so long for 9.6:1 supercharger V-1710s to enter production? I've been wondering about that, but considered it was related to other issues like charge heating issues with earlier variations of the supercharger or simply lack of demand/interest.

    As it was, the 9.6:1 ratio engines were only slightly weaker at altitude than the likes of the Merlin 45 or 20 series (or V-1650-1) and even that discrepancy was probably due mostly to the excellent Hooker-based supercharger designs rather than inadequecies on Allison's part. (ie a larger supercharger might not have helped much ... just a universally more /efficient/ one -ie better boost with less charge heating for given power consumption)

    Not sure if going higher than 9.6:1 would have hit other mechanical limits ... again, but charge heating involved would have certainly limited max boost. (depending on fuel type and possibilities of ADI/water injection -I assume a water injection system would have been much simpler and less costly to engineer than a 2-stage supercharger configuration ... then again, WI would have been a godsend to early model P-38s with intercooler issues yet nothing was forthcoming there ... )



    I wonder if sending such proposals to individual aircraft manufactuers might have been another option for securing funding ... or at least swaing the Army for its need. Then again, I'm not sure how that sort of action would mesh with military bureaucracy at the time, or if it could have caused friction between Allison and the Army.

    Were Pratt and Whitney's 2-stage supercharger developments funded in-house or NAVY supported? I seem to recall the auxiliary superchargers used on the R-1830 and R-2800 were somewhat similar in configruation to the sort eventually employed on the V-1710 (hydraulically clutched and running independently from the integral single-speed supercharger stage, including lacking any sort of intercooling -until late model R-2800s- though water injection was offered fairly early on for the 2-stage 2800s).

    The 2-stage R-1830s were in production around the time of the Battle of Brittain even ... though the altitude range those engines manage weren't really spectacular compared to single-stage engines tuned well for high-alt. (I think some 2-speed R-1820s even came close ... and German designs certainly did well with mostly single-stage superchargers; still, I suppose the point here is P&W's design philosophy could have fit very well with Allison's ... P&W just got the engineering funding much much earlier)
    Good thing for the Wildcat too given the F4F was a dog without that engine.


    Aside from that, the V-1710 itself had some nice advantages over the Merlin in terms of production cost/volume, maintanence, and ability to run lean at significantly lower RPM (and specific fuel consumption). Especially for that latter reason. (the latter advantage alone might have been enough to make even the intercooler-less 2-stage Allison's more attractive on the likes of the P-51 than the Merlin 60 series ... had they been in volume production by early 1943, and available for testing some 6 months prior to that)
     
  18. GregP

    GregP Well-Known Member

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    Well gjs238,

    Your assertion above is not quite correct. The Allison DID make it to 2-speed.

    The XV-1710-131 was similar to the V-1710-97 except it was fitted with a 2-speed (7.485 : 1 and 9.60 : 1), single stage supercharger and had a different comprression ratio (6.5 : 1).

    This engine flew in the XC-114 and the YC-116. It didn't make it intoa US fighter, but it flew.

    It also isn't much known, so probably almost everyone else thought so, too.

    It also made it to 2-stage with the auxiliary stage. It wasn't an integral 2-stage, but was 2-stage.
     
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  19. tomo pauk

    tomo pauk Creator of Interesting Threads

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    If I may (just love to talk about engines, in hope that sometimes it makes sense)

    The difference was not that small - 4000 ft (for power of 1125 HP); by 1944 it was 3000 ft, but by then Merlin 45 was yesterday's news. Size of supercharger was an important thing, if greater power at altitude is wanted, as seen when Merlin 46 or 47 were compared with Merlin 45 or 50, plus a host of DB engines that got bigger S/C.

    Considering what the ww2 USA funded and get working, adding the auxiliary S/C to the V-1710 looks like crumbs. What was needed was a timely go-ahead signal by USAF, followed by some funding.

    Germans went ahead with DB 605AM (ie. 'plain' 605A with water-alcohol injection). Above 6 km, it was making maybe 50 PS more than 605A? Contrary to that, the worse 2-stage V-1710 beats the best 1-stage V-1710 'F' by 7000 ft, when both engines were making 1125 HP.
    The greater rated altitude, the more sense it makes using the ADI, IMO. The P-47 and F4U/F6F benefitted immensely by ADI, so did the DB 605ASM. Agreed that ADI would be a great thing for the P-38s, not just early types. It would make much more sense on a 2-stage V-1710, than on 1-stage, benefits were felt up to 28000 ft with late war trial engines.

    The USN funded the P&W 2-stage development in a significant amount, both the R-1830 and R-2800 versions. The USAF did not considered the 2-stage R-2800 until the P-61 was discussed. Maybe having a Navy-backed engine was was not looked favorably by Army?
    The 2-stage R-2800 did not featured hydraulic coupling like the V-1710, it was 'simple' mechanically clutch with off/1st-speed/2nd-speed possibility. The intercooler was incorporated from the get-go in the 2-stage R-1830 and R-2800, the XF4-U flew with it in May 1940. Water injection was offered later than that, 1942-43.


    The 2-stage V-1710 in a P-51 would be much a better investment than to go with P-63. Not quite as performer at high altitudes as Merlin Mustang until maybe second half of 1944, but still a very useful aircraft for PTO and MTO.
    Granted, timing was the key issue.
     
  20. Shortround6

    Shortround6 Well-Known Member

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    It's the primary reason but a lot depends on the actual time line. The Allison engine company/division during the 30s was a very small company and Allison actually had three sub divisions/sections. How much they overlapped I don't know but Allison was a major maker of hard shell bearings and supplied many other companies. This was the major money maker. They also made gear drives and other precision engineering equipment. In the late 20s ALL Packard aircraft engines that used reduction gears used Allison supplied gear sets. They also supplied the gear sets and shafting for many of the US Navy's Airships in 30s.
    As for the V-12 Allison engine part of the business, by the end of 1937 Allison had delivered 16 engines since 1932. 7 of them in 1937. 1938 would see deliveries rise to 14 for the year and 1939 would see 48 (?) delivered. 1940 saw 1178? (accounts/tables differ). 1941 saw over 6400 engines delivered. Allison had offered/suggested a two stage supercharger to the Army in 1938. How solid that offer was I have no idea ( actual drawings/calculations or just a vague suggestions to test interest?) Obviously Allison was pretty busy just getting actual mass production going in 1939/40. in 1937 they had 322 employees (and made just under 1/2 million bearings) and by the end of 1940 they had 4303. Obviously just getting into mass production took a lot of effort.

    As it was, the 9.6:1 ratio engines were only slightly weaker at altitude than the likes of the Merlin 45 or 20 series (or V-1650-1) and even that discrepancy was probably due mostly to the excellent Hooker-based supercharger designs rather than inadequecies on Allison's part. (ie a larger supercharger might not have helped much ... just a universally more /efficient/ one -ie better boost with less charge heating for given power consumption)

    you can only spin an impeller so fast, yes pushing them harder does increase the charge heating but at some point (depending on diameter and rpm) the tips on the impeller go supersonic and set up shock waves inside the supercharger and efficiency really goes to pot in a hurry. Water injection does nothing for this. At the start of the war nobody was getting more than about 2.8 compression ratio out of a single stage compressor. By the end of the war they were getting about 4.0 The Merlin 61 got about 5.3-5.4. Single stage was never going to match a two stage if the two stage was any good.


    Market forces varied. There wasn't much demand for civil high altitude aircraft, even the Boeing 307 airliner with pressurized fuselage (and using B-17 wings, under carriage and tail parts) use either single speed or two speed superchargers no turbos.
    Engines for military aircraft were purchased by the government and shipped to the aircraft factories for installation. Yes, some aircraft manufacturers could propose new aircraft (or new models) based off proposed engine modifications (and did, part of the reason for the "high" altitude Allison to begin with, high altitude being the ones with 8.77 or 8.80 gears compared to the 6.48 or 7.10 gears in the early turbo engines).

    I believe the P W engines were privately funded although the Navy may have expressed interest. Patents date from 1938 and two aircraft with two stage P&W R-1830s took part in the 1939 Army fighter trials that lead to the selection of the P-40. P W had only been designing their own superchargers for couple of years and these early two stage set ups apparently weren't very good. There may have been cooling issues with the engines too.
    ALL P&W two stage superchargers used inter-coolers. This was part of the problem, the two stage powered planes were slower (due to weight and drag) than the same airframe with a single stage engine until they got above 15,000ft or so. But for some reason the early R-1830 two stage engines didn't make a lot of power up high so the performance advantage up high wasn't all that great.

    The engine used in the two trial planes was good for 1200hp at take-off at 2700rpm, there was no military rating (common on pre war US engines) and "normal" rating ( actually max continuous) was 1050 at 4,000ft ( second stage not in use) 1050hp at 11,000ft and 1050hp at 17,500ft all at 2550rpm. Just a little later P&W was able to offer a single stage, single speed engine (a one off) for the P-36B that gave 1100hp for take off at 2700 rpm and also gave 950hp at 14,3000ft at 2700rpm.

    Germans did well because the big engines required less boost 1.3 Ata is only about 4.5lbs boost and 1.42 ATA is only about 6.2lbs boost (or about 42.6in) the 109 was also rather smaller (less drag) and over 1000lbs lighter than F4F.

    The two stage in F4F was good for 1000hp at 19,000ft at 2550rpm ( P&W never seems to have given it a military rating at 27000rpm) I don't know if this was a limitation due to cylinder cooling or due to heating of intake charge in spite of intercoolers or a propeller problem (governor didn't work right) or what. I would note however that the auxiliary supercharger was probably taking several hundred HP to drive so the cooling load on the cylinder fins in the thinner air at 19,000ft may have been part of the problem.

    There is a pilots manual on the F4F on this site, go to the American manuals index; http://www.ww2aircraft.net/forum/other-mechanical-systems-tech-/manual-index-american-36322.html

    And while they don't really explain the limits are rather clearly spelled out.
     
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