What about a turbocharged P36?

[GrauGeist]

Compare the transition from the P-35 to the P-43 and see how much the fuselage was changed to accomodate the powerplant.

If you were to attempt the same changes in the P-36, you will end up with a much different and much larger airframe.

 

[pinsog]

I know it was stretched about a foot or so, wing was basically the same. But they stretched the nose of the P36 to become the P40. They stretched the FW190 to become the 190D. They stretched the ME109. Doesn't seem too insurmountable, but it may have indeed needed an entirely new airplane. Still seems like the P36 would have been good place to start

 

[Shortround6]

We all know the P39 and P40 never received a turbocharger making both of them a dog above 15,000 feet or so. The P35 was never a good performer, poor handling/turning ability and poor workmanship (leaking wing tanks). But the P35 got a turbocharger and became the P43 Lancer with good performance at the time of 350 mph plus and 1200 hp at 25,000 feet while still retaining poor handling and poor workmanship.

The P36 on the other hand, had an excellent climb rate and exceptional maneuverability. What about installing either a Wright 1820 or P&W 1830 with a turbocharger in the P36? It would gain some weight but still shouldn't weigh as much as a P40 or F4F Wildcat and still have 1200 hp at 25,000 feet. Should still retain much of its handling, certainly no worse than the P40 which still turned well, should still out climb a P40 or Wildcat rather easily and do at least 350 mph plus (I would think it would be faster than a P43 Lancer) putting it on a level footing with the Spitfire and ME109 and Zero.

Thoughts?

I think we have been over this before. The P-36 that some people seem to be enamored with was under armed and unprotected. It also only made the the published performance figures (if then) at normal gross weight which means the rear fuselage fuel tank was empty. Fuel capacity of the tanks in the wing center section being little different than a Spitfire's fuel capacity. There were a few structural problems too, buckled wing skins around the landing gear and/or wing roots.
The prototype P-40 was the 10th production P-36 pulled off the production line so 90% or more of any changes were forward of the firewall. Up gunning and fitting protection to the P-36 would have seen a similar rise in weight to the P-40. Beefed up structure to handle the increased weight of guns and protection.
A more complicated engine installation also would increase weight. Unless you can convince the US Army to relax the 12G stress standard adding hundreds of pounds to the engine installation was also going to require weight gains other places.

Please note that the engines used in the P-36 (American models) was good for 2700rpm only for take off. other wise it was limited to 2550rpm. later engines were rated at 2700rpm for take-off and military power and 2550rpm max continuous. they also gained 40-90lbs even for single speed single stage versions.

A P-40C gained 400lbs over the prototype P-40 (re-engined P-36) in empty weight (protection), 515lbs in basic weight (extra guns but no ammo) and 700lbs with ammo and fuel (internal). Granted around 90-100lbs could have saved by not filling the fuselage ammo bins with 380 rounds of .50 cal ammo each. 240-250 rounds would have given 30 seconds of firing time.

A few pictures of the P-43 Lancer can be found here: Republic P-43C/D Lancer Question (72nd Aircraft)

The P-35/43 was a pretty portly fuselage compared to the P-36/40 fuselage. Seversky had designed a sort of general purpose fuselage for their early fighters and there wasn't much difference between the single seat and two seat versions. The R-1830 is 60-100lbs heavier than the V-1710 even in single stage form and adding stages and inter-coolers makes up the difference in radiators and coolant pretty quick.
Most things are a trade off and while a turbo P-36 would certainly have been faster at 25,000ft it may very well have been slower at 15,000ft or under (extra drag)and time to altitude is also a bit suspect. Better but not to extent you might think. US climb figures using military power for the first 5 minutes and then MAX continuous after that.

 

[T Bolt]

Why not put the turbo ductwork on the outside of the fuselage like they did when they tried to put a turbo on the FW 190. Looks ugly and adds drag I'm sure, but would be a faster solution then rebuilding the whole fuselage to fit the ductwork inside

 

[GrauGeist]

The KI-87 had an external installation.

 

[Shortround6]

If you go the site in my previous post there are several pictures of the bottom of the P-43, sorry but I can't seem to get the pictures to show up here.
Think upside P-38. Turbo is exposed on the bottom of the rear fuselage 1/2 way between wing trailing edge and horizontal stabiliser leading edge. Exhaust pipe runs in an open trough at the bottom of the fuselage from about 1/2 way along the wheel wells back to the turbo.
The P-47 was one of the very few planes to hide the turbo completely inside the plane. Keeping the turbine blades cool took priority over streamlining most of the time. A turbine failure could destroy the aircraft if it was bad enough. Many turbo installations had scatter sheilds to protect crewmen from thrown blades.

 

[GregP]

Nice find, Shortround. Those are some interesting pics and I see in one of the magazines that there is a group considering the possibility of restoring a P-43 from the parts scrounged from several airframes. It would be good to see one flying again, even if it is the only one.

I know of at least 3 working turbos that are flying, too. Perhaps another can be assembled from good parts.

 

[FLYBOYJ]

Great pics SR!!! Did anyone notice the welds on the ducting behind the camera? Hand welded, by today's standards really crude but functional...

 

[FLYBOYJ]

Great P-43 pics here...

Forums / USAAF / USN Library / Republic P-43 Lancer - Axis and Allies Paintworks

 

[kool kitty89]

The KI-87 had an external installation.

View attachment 308874

If you go the site in my previous post there are several pictures of the bottom of the P-43, sorry but I can't seem to get the pictures to show up here.
Think upside P-38. Turbo is exposed on the bottom of the rear fuselage 1/2 way between wing trailing edge and horizontal stabiliser leading edge. Exhaust pipe runs in an open trough at the bottom of the fuselage from about 1/2 way along the wheel wells back to the turbo.
The P-47 was one of the very few planes to hide the turbo completely inside the plane. Keeping the turbine blades cool took priority over streamlining most of the time. A turbine failure could destroy the aircraft if it was bad enough. Many turbo installations had scatter sheilds to protect crewmen from thrown blades.

I believe all turbochargers used operationally during the war (except maybe the P-47's cowl-shrouded arrangement -which incedentally would have been nice on the P-38M for hiding turbine glow) used exposed bare turbocharger installations with the turbine and exhaust manifold exposed to the slipstream. (this goes for the B-17 and B-24 too, there's exposed turbos there in the engine necelles, on the trailing edges of the undersides; not obvious in most pictures but it became super obvious after playing IL-2 some years back) The XP-39 used this mounting arrangement as well. (and a horrendously poor oil cooler, intercooler, carb intake, and even problematic wing-embedded radiator intake/outlet arrangement -I've been meaning to start a more focused topic for the P-39 though, including some of the ammunition configuration issues that came up in this thread, so I won't draw it out here and now)

The P-47's shrouded exhaust may have been a superior arrangement though as far as drag went. (in theory it could have reduced turbulence while producing a small amount of RAM+jet thrust from the turbine exhaust and air ducted over the hot turbine exhaust manifold -still probably net drag, but potentially at least negating a lot more drag than leaving it totally bare)

Why not put the turbo ductwork on the outside of the fuselage like they did when they tried to put a turbo on the FW 190. Looks ugly and adds drag I'm sure, but would be a faster solution then rebuilding the whole fuselage to fit the ductwork inside

The turbo installation on the Fw 190 is an extremely poor example and definitely good evidence to leverage against the 'turbocharged P-40 was a bad idea' argument. (including the relatively good performance with the bare DB 603A and nature of inline engine vs radial -a turbocharged BMW 801 might have fared far better and indeed BMW had an exceptionally well configured turbocharged 801 'power egg' module that could have been fitted to the 190 with some adjustment for CoG -which was also done for Jumo 213 and DB 603 mountings for similar reasons of nose length and weight increase, but that 801 wasn't available to FW for testing, it appears to have been ready for production and even optimized for minimal strategic materials, but likely had material and production resources diverted to getting the BMW 003 into production instead -and FW doesn't appear to have made any attempts to mate the Hirth-manufactured turbocharger used with the 603 to a standard 801 model)




That said, I think the P-40 had some possible potential for turbocharging, but the P-36 was much better suited for such overall (or more likely P-40 regressed to R-1830 -like the P-40 fitted with a 2-stage 1830 for P&W trials that managed 385 MPH at altitude -albeit this was one of the original P-40 runs without armor or self sealing material added and also omitting the armament, but that's still much more impressive performance than either the XP-40 or XP-42 -though the XP-42's ultimate cowl/fan/spinner arrangement might have improved that 2-stage R-1830 installation as well).

The V-1710 trades a lot more when it's turbocharged, both added bulk/drag and loss of exhaust thrust. (the lack of a well-optimized de-turboed P-38 with RAM intakes and ejector exhaust is likely the only reason it doesn't show off some of these interesting characteristics -the Lightning Mk.I was a hack that made for the worst of both worlds and is not a useful example of the airframe's potential without turbochargers)


The R-1830 gains far less from exhaust thrust OTOH, and the P-36/P-40 airframe is already well matched to the R-1830's dimensions in height, but slims out quite a lot in width making room for bulging the fusealage sides somewhat for added ducting without increasing frontal area (and, more importantly, only modest increase in wetted area). Intercooler drag would be the bigger concern, namely from providing large enough scoops and ducting to allow sufficient airflow for the full turbo capacity (or end up stuck with the P-38's situation of insufficient intercooling and inability for the turbocharger to operate at full rated RPM due to excessive charge heating). Now, remember superchargers need intercooling too and similarly designed impellers/diffusors should produce simialr charge heating as well (and require similar cooling), but heat leakage from the exhaust turbine tends to lead to some degree of added charge heating as well, I believe. (I may be mistaken here) The bigger issue was that these were POWERFUL turbochargers intended to drive the R-1830 or R-1820 at full rated power up to vastly higher altitudes than the 2-stage superchargers in question were rated for, and while just using a smaller turbo seems an attractive option, I think they simply didn't exist in mass production or operational use (parts commonality with the B-17 or B-24 would be ideal, and those had critical altitudes well above the ~20,000 ft of early-war 2-stage superchargers) so that just leaves under-utilizing said turbo and eating the larger weight/bulk of that while sticking with more modest intercooling that could nestle into the cowl, grouped with the oil coolers (as with the F4F, F4U, F6F, etc) though designing the fusealage side ducting to act as a surface intercooler (like the P-38's wing intercoolers) as a pre-cooler for the main intercoolers in the nose/cowl might have helped a fair bit too. (a large, rear-mounted intercooler like the P-47 used probably wasn't the most practical idea here)

Additionally, using as similar design configurations as possible between the V-1710 powered P-40 and turbo or 2-stage supercharged R-1830 variants would also be best on the manufacturing end if multiple types ended up being manufactured or just to allow easier shifts from the P-40 (which was already in production in 1939) to a souped-up R-1830 derivative.

Turbocharging also has the potential advantage of being adapted to the 1450 HP R-2000 later in the war, since it never adopted a 2-stage supercharger and a 2-speed single stage unit would be less appealing to displace the 2-stage R-1830. (unless of course, demand for Curtiss's fighter drove P&W to implement a 2-stage R-2000) WEP or even unsanctioned overboost of the R-1830 itself would probably be limited by cooling fin design given the R-1830 never saw the substantial redesigns that the R-2800 did to allow its increased power levels. (water injection would be of little to no relevance here either, and switching to a late-war R-1820 with WEP and possibly water injection would have been a worse trade-off for drag than the R-2000)


As far as turbo installation goes: the P-47's overall ducting arrangement seems best, but likely with the air intake severely cut back (no massive intercooler to cater to and associated drag) and relatively minimalistic added belly contours to enclose exhaust ducting on either side of the lower fuselage/wing (yes, beneath the fuel tanks, just like the P-47, with associated insulation and firewalls added/modified if needed)

 

[kool kitty89]

The fuel capacity, armament, armor, and overall weight would be the remaining factors here, and are the real-world factors that already DID plague the P-40, particularly with the more substantial changes to the airframe the P-40D and later models saw. (lots of weight gain there, changing of the cockpit position, canopy, fuel tanks, new wing with .50" gun mounts -and initially hispano mount provisions in the D model- tons of weight gain due to structural redesigns, larger radiator and oil coolers, and added armor, modest gain in fuel capacity over the P-40C and loss over the P-40B -with its metal tanks and linatex style self sealing coating- or Hawk 75A-2, plus later extended rear fuselage to accomodate the Merlin's added weight iirc)

The critical factors here could ALSO have benefited the P-40 itself, careful attention to detail in keeping weight down, selecting armament optimized for fighter vs fighter combat (and lightly built bombers) over bomber interception, etc. (though the point was already made for the superiority of the .50 BMG during the BoB -or when employed against any linatex -or laminated leather- style external self sealing material on metal tanks, not well suited to 13 mm projectiles, let alone 20 mm -explosive and incendiary properties aside)



On armament: It should also be noted that it was the British, not the Americans that insisted on mounting more guns on the Kittyhawk/Warhawk, Wildcat/Martlet, and Mustang. Many Navy pilots preferred the 4-gun arrangement of the F4F (though the issues with kinks and jams in the F4F-3's installation weren't ideal, the lower weight and particularly higher ammunition capacity were preferred) this may also have been less from British Pilot preference, and more Air Ministry doctrine/thinking. (the Mustang I's 2x .303 and 4x .50 BMG would probably have served fine stripped to just 4x 50s, 2 synchronized, 2 in the wings -A-36 crews often removed the synchronized guns but that was with 4 .50 cal guns already in the wings) The P-51A, B, and C all sported 4 gun armaments and it wasn't until the D that the array of 6 became standard. (by which time it was more genuinely needed if still not always superior to the 4-gun arrangement, though the D was also heavier and poorer performing than the B/C for more reasons than the armament)

Improvements in the browning to up rate of fire (similar to the FN Browning) would have helped with synchronization losses too, even if such boosted speeds were witheld from standard unsynchronized use for conservative wear/reliability reasons. (even with the slower RoF, the nose mounted arrangement had advantages, especially if you could do away with wing guns entirely -mixed wing and nose guns is a bit less nice and takes training for both sorts of convergence and gunnery to make good use of, unlike the P-38 -the only all-nose armmed USAAF fighter) On the plus side, 550-600 RPM would reduce the barrel-burning nature of the M2 if fired too long. (for pilots a bit more naturally heavy on the trigger)


Starting with the Tomahawk as the base, adapting the wings to carry 1 .50 cal gun each (for a F2A-2 style armament) would have been a good compromise, but with the radial engine it might be possible to add 2 more .50s to the fuselage sides and go all-nose without much increase to drag, or any at all if hidden in the expanded fuselage sides along with turbo-supercharger outlet ducting. (obviously positioning the guns to avoid barrel heating of that air flowing into the nose intercoolers) With the Allison's change in nose geometry with the F-series, the guns would probably have to be omitted from the over-cowl position and possibly introduced under fuselage embedded above the radiator as well as 2 in the fuselage sides. (or possibly all four in the fuselage sides as cheek mounts, or ... in the case of a turbocharged V-1710, embedded in the fuselage 'cheeks' themselves caused by the necessary ducting)

Avoiding wing mounted guns also frees up a lot of space for potential fuel tankage without having to engineer fuel cell compartments around weapons compartments (and possibly be forced to add more mass outboard of the wing and compromise roll rate). Fuel tanks added to the region the wing guns would otherwise be (particularly all the useful space towards the center and leading edge of the thicker, inboard portion of the wing just outboard of the wheel housing) and could make the fighter into a good long-range intruder or high altitude escort fighter. (in the case of turbocharging or decent 2-stage supercharing ... or some proper refinement of a single stage allison supercharger to match/beat the Merlin rather than sticking with the known faults in favor of volume production -not to mention securing more funds to properly test WEP earlier and possibly even clear overrev for WEP) Leaving space for wing-mounted radiators would also be a huge help in reducing the P-40's drag, especially with the larger radiators needed to use power settings much beyond the old C series (V-1710-33)

Also remember how limited the armament of the BF-109F was and still somewhat modest 2x MG 131 and 1x MG 151/20 configuration. (4x synchronized .50s in the nose would be a fair match for that, especially given the Curtiss built fighters would be more rugged due to typical aggressive USAAF structural requirements)



On top of all that, remember the intrinsic adantages the P-36 and P-40 held over the Spitfire and Bf 109 (and to lesser extent 190 .... and massive effect Hurricane, Zero, and Oscar): exceptional roll rate, light controls at all speeds (but especially so at high speeds) and ability to out-maneuver other aircraft in similar ways to the P-47. This is important as it also meant that even in overweight configurations, the added dive 'thrust' of that weight could be exploited to full extent rather than having controls freeze up during a power dive. This is also a good reason to avoid putting lots of added weight in the outboard wing sections. (aside from perhaps tip-tanks ... in hindsight given their tendency to have winglet-like properties that reduce drag and increase aileron effectiveness -and thus roll rate when not filled with fuel)

The P-36/P-40 airframe was generally very clean and well designed for its era, cleaner than the P-43, F4F, F2A, and cleaner than the 109 and spitfire (look at the speeds it managed in spite of being overweight and underpowered). The F2A was never fitted with an R-1830, so the potential drag improvements there are harder to guess (performance with roughly similar R-1820s seems in the ballpark, but the F2A has a bulkier fuselage -if still much slimmer than P-43 and F4F- so it's harder to make even a general guess to that sort of pairing, plus the F2A had a smaller wing, but high-lift high-drag airfoil and thicker 18% root -then again, so did the F4U) I will say the P-36 benefitted more from the R-1830's slim size than the F4F did (which gained very little indeed given its large overall diameter and bulk -and wing area, when comparing R-1820s and 1830s of similar power/altitude performance) and the P-36 airframe almost certainly wouldn't have been as well matched to the FM-2's powerplant than the Wildcat was. (and for that matter, the non-water-injected earlier models of similar power at alitude could have been used on the F4F with little loss over the 2-stage R-1830 while the P-36 would gain far more from the drag reduction, especially with the eventual refinements offered by the XP-42 program -albeit more likely in time to be adopted with the R-2000)




And all that said, a final comment on a potentially more useful alternate use of Curtiss manufacturing and design ability: instead of second-sourcing the P-47, they could have taken on the task of developing a turbo-less P-38 derivative for medium/low-altitude duties (extremely useful in the MTO and PTO both as a fighter and fighter-bomber -though prior to those theaters becoming obvious in general, such a performance realm WAS the preferred specification for USAAF fighters pre-war, with a greater emphasis on cooperation and ground-attack ability). The P-38 was more expensive than the P-47 (and much more so than the P-40) true, but a stripped down derivative would be somewhat cheaper and more so easier to maintain and operate while also totally sidestepping the turbocharger problems the early P-38s were having on top of the compressibility issues far far worse in the high altitude flight envelope over Europe (due to cold and thin air allowing faster acceleration in a dive and lower ambient speed of sound). If that program was organized early enough, it might have even been possible to have a Curtiss P-38 accepted for operational duty before the P-38F arrived ... really it's not all that hard given just now long it took the P-38 to even get that far. (with Curtiss ignoring all but the problems relevant to operation at/below 15,000 ft or somewhat higher in warm climates -lack of heating and mach-tuck issues both avoided, they could have started shifting manufacturing and tooling up for the P-38 based on earlier models with only a few final detail changes left open to fix, particularly the wing fillet additions that eliminated the buffeting problem, while applying their experience with the P-40's intake/exhaust design to make a pretty efficient turbo-less nacelle for the P-38)

Given the problems the P-47G suffered this might have been no more foolproof, but it seems at least possible that they'd have fared better (and had somewhat more in common with P-40 experience and prior work) with the P-38. Second-sourcing the P-39 might have been more trouble too given its heavier use of new/novel technology than the P-38. (all the electrical equipment with miles of wiring -literal miles I believe- and some specialized modular mass production techniques for the airframe itself that worked very well for Bell but might not have been so nice for Curtiss)

In a best-case scenario, Curtiss engineers working on solving some of the P-38's problems independently of Lockheed might have been able to speed up progress on both fronts, sharing findings with Lockheed while keeping up with progress on that end as well. (plus, I believe the P-38 and P-40 already had some parts commonality in the curtiss electric propellers used on some models ... in fact the retention of that rather small 3-blade Curtiss-electric propeller late in the P-38's run has been criticized for being too small to properly take advantage of the added engine power, while the same has been argued against Curtiss for retention of that aging unit on the P-40 -the P-39, P-51, and P-47 all went though multiple propeller changes to rather significant degree while the P-38K's larger area 3-blade prop was refused for production due to delays on the assembly line it would cause ... not sure if any 4-blade props might have avoided that by retaining similar spinner diameter -the P-51 and P-39 both avoided nose geometry redesigns by keeping any prop/hub/spinner changes to ones compatible with the existing geometry) The P-40D and YP-38 obviously had to change nose/nacelle/spinner geometry due to the engine dimension and thrust-line changes ... and I assume lowering the engine mount to maintain the P-40B/C thrust line would have been more problematic. (or ... maybe it wouldn't have been if they'd moved the radiator(s) to the wings, allowing the upper nose geometry to remain more constant along with the thrust line ... and had more room at the top of the engine for cowl-mounted .50s)

Hmm, actually, yes, maintaining a more Tomahawk-like fuselage/nose structure and fitting a row of 4 guns to the nose top and/or sides (or possibly even 6 later on when the added firepower was needed) and relocating the radiators to the wing or wing center section (and making up the center section fuel space with wing-mounted cells) would have been one of the better options for the Allison powered P-40 as well, with or without turbocharger.




And some useful cross-sections of the P-40, Hawk-75, and P-47 for reference.

http://www.histaviation.com/Hawk_75_A-2_Drawing_1424x926.jpg (fuel tank capacity listed too -appears identical to the P-40B's arrangement with a total of 135 imp gal or 162 US gal)

http://images.fineartamerica.com/images-medium-large/p-40-tomahawk-iib-science-source.jpg (equivalent to the P-40C, note the modified fuel tank arrangements -these should be proper self-sealing cells, not modified metal tanks like the P-40B and Tomahawk IIA, with fuel capacity of 134 US Gallons or approximately 112 imp gal)

https://s-media-cache-ak0.pinimg.com/736x/f9/37/d0/f937d068f17625f9fb18c3f0986b87e2.jpg
P-40E 122.8 imp gallon capacity or 147.4 US gal (I believe it's officially 148 US gal, and slightly off due to rounding errors partially on the part of those imperial figures)


http://www.wardrawings.be/WW2/Image...-USA/Files/1-Fighters/P-47/Boards/Board-2.jpg
http://www.airwar.ru/image/idop/fww2/p36/p36-2.gif (for P-47 P-36 profile cross-section cutaway comparison)


Also remember the P-39 carried 120 US gal of self-sealing fuel cells in the inboard portion of the wing in spite of also housing 4x .30 cal guns (and capacity for 1000 RPG), so with proper attention to detail (and redesign of the wing ribs to accomodate cells) it should have been fairly easy to expand the P-40's fuel capacity substnatially, possibly while also embedding the radiator (and possibly oil coolers too) in the belly/wing-center section in place of those fuel tanks. (akin to the P-39's radiator and oil cooler core placement) The P-40 also gives a hell of a lot more space for adding a turbocharger than the P-39 does. (especially if compromising to use existing turbochargers aimed at capacities and altitudes perhaps a fair bit beyond the real needs of a fighter for the time -or at least not worth the trade-offs for weight and bulk of the unit AND intercooler installation ... the P-39 might have accomodated a SMALL rear/saddle mounted turbo had they been available)



Finally, aircraft designers (or engine manufacturers) could have taken the lead away from GE by working on liquid cooled intercooler designs rather than those huge air to air ones. (that would definitely make a turbo on the P-40 workable, and probably the P-39 too ... perhaps P-51 as well with the rear tank omitted and some CoG adjustment -remember turbos also mean better fuel consumption and range, particularly at cruise where exhaust thrust is useless anyway)

The P-38 and (especially P-47) would have benefitted somewhat less, but it would have been a far more elegant solution than the chin intercoolers on the P-38, and would have freed up fuselage space for some added fuel capacity in the P-47. (within CoG constraints, of course) Perhaps more significantly, it would have allowed the P-47 to lose much of its 'gut' along with the removal of that large intercooler. (OTOH, using a LIQUID intercooler on a radial engine might be problematic ... unless designed around using oil to cool it rather than water/glycol ... that might have been workable but the viscosity of oil might not promote good flow at the temperatures desired for air intercooling, in any case -oil or water- the radiator would likely be grouped up front with the oil coolers, thus leaving only a small turbocharger impeller air intake scoop needed at the rear -liquid intercoolers also make small targets, unlike the big block in the P-47's rear that could get holes punched in it and lead to a loss of manifold pressure)

The P-51 would NOT have been the aircraft that it was without the liquid intercooler exchange. A conventional air to air cooler (a la F4U/F6F -likely of similar size too, given the mass flow involved) would have added substantially more drag to the P-51 ... or anything using the 2-stage merlin for that matter. (the other option, of course, was no intercooler at all, a la the minimalistic V-1710 Aux stage -and a small number of 2-stage R-1830s for that matter; in which case either VERY high octane fuel was needed for WEP -like 100/150, or water injection had to be employed -which risks corrosion of the engine if used too soon before landing and shut-down -you need to burn off all traces of water and methanol in the system or risk corrosion, particularly to aluminum components in contact with the methanol -steel alloys and cast iron tolerate methanol/water fine, about as well as plain water, but aluminum is not so nice)

 

[Shortround6]

Please, please, please !!! Forget about fuselage mounted .50 cal guns. The Big .50 took to synchronization about like cats take to water. British found that it often cycled under 500rpm when synchronized, maybe you could get it to 600rpm when the wing guns were doing 800-850rpm. With the weight of the .50 cal you want all the punch you can get for the installed weight, not crippled by synchronizing gear. There is a reason that only few planes used fuselage mounted .50s later in the war and they were legacy installations from the early part or even pre war design. (except for the P-75 and the less said about that the better)

 

[GrauGeist]

Aside from the syncro issues, cowl mounted MGs take up a great deal of space that could be otherwise dedicated to engine components...

 

[Shortround6]

GE made two basic superchargers during WW II. The B series (developed from the F, go figure??) which was sized to handle engines from below 1000hp to around 1500-1600hp. Later versions were better for the higher power levels. The C series was supposed to handle from the mid/hi teens to something over 2000hp worth of airflow. again late war models were improved a bit. Please note that the B-29 used two "B: series turbos in parallel.
GE compressor designs really weren't the best, a fact that the turbine drive tended to hide. Since the exhaust had more than enough power to drive an inefficient compressor it didn't matter as much until you get to the intercooler design. The inefficient supercharger heats up the intake charge more for the same amount of compression as a more efficient supercharger.
However we really have no figures for how efficient the P&W supercharger/s were or at least not in common sources.
Intercooler design was also a constantly evolving "art".
U.S. Army doctrine was for the turbo installation to provide sea level air-pressure to the carb inlet (or carb deck) at 100 degrees F.
The engine supercharger providing the actual manifold boost. Usually between 44-49in (around 7-9lbs) which may have pretty close to the limit using US 100 octane fuel pre-war.
Not only does a 1400hp engine require 16-17% more induction airflow than a 1200hp engine, if you are using the same engine and just boosting the pressure using the turbo then the air going in the carb is hotter. The intercooler needs 16-17% more air to cool the intake charge assuming the intake charge didn't get hotter. With the extra temp you need even more airflow. P-38s changed the engine supercharger gear several times instead of trying to use the turbo to boost pressure so a good part of their problems was just added airflow rather than higher temperatures of the intake charge.
Inter-coolers, or more accurately, the companies that made them weren't all that common as Bell tried to out source them for the P-63 (not uncommon, many parts/sub assemblies were out sourced) but the company (or companies?) selected failed to even come up with prototype units in a timely fashion forcing bell to rely on water injection. I would bet that B-24s and B-17s used intercoolers form outside suppliers rather than build them in house.
Turbos got better and were allowed higher rpm in later models which helped airflow and pressure.
Please note that B-17s are sometimes listed as having different critical altitudes for the outboard engines and inboard engines due to differences in the intercooler ducting. And B-17s had a lot of room to arrange things compared to a single engine fighter.
Inter cooler design did get better but it was hardly pick the desired one out of a catalog
Another look at the P & W test Hack;

Note what seems to be exhaust stains on the side behind the cowling and the absence of normal exhaust stubs like on the P-36 or F4F. Maybe not the exhaust thrust of a V-12 but better than a number of radials? Also please note the even worse view over the nose compared to a P-36 or P-40.

 

[Shortround6]

Another photo, B-24 under construction showing inter cooler core in the inner nacelle.

Now perhaps a bomber that runs at max continuous for long periods of time while climbing/forming up at relatively slow speeds needs a bigger inter-cooler than fighter that is moving faster (mass airflow per minute?), I don't know but intercoolers for turbo charged air cooled engines are not small items to tucked into convenient corners or nooks/crannies in an existing airframe. You also need smooth appropriate sized ducts to minimize internal drag and maximize the effectiveness of the intercooler core/matrix.

 

[wuzak]

GE made two basic superchargers during WW II. The B series (developed from the F, go figure??) which was sized to handle engines from below 1000hp to around 1500-1600hp.

I believe the F stood for Form. The XP-39 used, IIRC, a Form 10 turbo, while the YP-37 used the Form 13, which was later redesignated B-1.

 

[wuzak]

Another photo, B-24 under construction showing inter cooler core in the inner nacelle.

Now perhaps a bomber that runs at max continuous for long periods of time while climbing/forming up at relatively slow speeds needs a bigger inter-cooler than fighter that is moving faster (mass airflow per minute?), I don't know but intercoolers for turbo charged air cooled engines are not small items to tucked into convenient corners or nooks/crannies in an existing airframe. You also need smooth appropriate sized ducts to minimize internal drag and maximize the effectiveness of the intercooler core/matrix.

That shows one advantage of a liquid to air intercoolers.

The radiator, the part exposed to the airflow, can be remotely positioned for best aerodynamic effect.

 

[Shortround6]

It can be but the only engines to use liquid to air coolers were the RR ones and they are more properly called after coolers. They cool the intake charge after all the compressing is done. The American engines did all of their cooling between the 1st and 2nd stag.
I will grant that there was some sort of coolant passage in the supercharger housing on the Merlins and Griffon but the vast majority of the cooling was done in the matrix in the box at the rear of the engine.
The Americans need to duct the air from the first compressor (either mechanical or turbo) to the cooler and then duct it back to the carb inlet with the carb mounted on the 2nd compressor housing on the turbo engines.
RR just ran the intake air from the inlet to the carb, from the carb to the inlet of the 1st compressor, then to the inlet of the 2nd compressor and then to the after cooler and then to the intake manifold.
The turbo system is a lot more stretched out to begin with and a small inter-cooler matrix isn't going to change a large part of the ducting.

 

[Peter Gunn]

All fascinating stuff guys, learned a ton. I also found it entertaining that I can see this same set of discussions going on in the aviation industry offices of the time. Someone says "Hey, how about we try a turbocharger on the P-36" and they actually end up with the historic P-47, almost like here. Great stuff guys, enjoyed every post.

 

[gjs238]

And all that said, a final comment on a potentially more useful alternate use of Curtiss manufacturing and design ability: instead of second-sourcing the P-47, they could have taken on the task of developing a turbo-less P-38 derivative for medium/low-altitude duties (extremely useful in the MTO and PTO both as a fighter and fighter-bomber -though prior to those theaters becoming obvious in general, such a performance realm WAS the preferred specification for USAAF fighters pre-war, with a greater emphasis on cooperation and ground-attack ability). The P-38 was more expensive than the P-47 (and much more so than the P-40) true, but a stripped down derivative would be somewhat cheaper and more so easier to maintain and operate while also totally sidestepping the turbocharger problems the early P-38s were having on top of the compressibility issues far far worse in the high altitude flight envelope over Europe (due to cold and thin air allowing faster acceleration in a dive and lower ambient speed of sound). If that program was organized early enough, it might have even been possible to have a Curtiss P-38 accepted for operational duty before the P-38F arrived ... really it's not all that hard given just now long it took the P-38 to even get that far. (with Curtiss ignoring all but the problems relevant to operation at/below 15,000 ft or somewhat higher in warm climates -lack of heating and mach-tuck issues both avoided, they could have started shifting manufacturing and tooling up for the P-38 based on earlier models with only a few final detail changes left open to fix, particularly the wing fillet additions that eliminated the buffeting problem, while applying their experience with the P-40's intake/exhaust design to make a pretty efficient turbo-less nacelle for the P-38)

Given the problems the P-47G suffered this might have been no more foolproof, but it seems at least possible that they'd have fared better (and had somewhat more in common with P-40 experience and prior work) with the P-38. Second-sourcing the P-39 might have been more trouble too given its heavier use of new/novel technology than the P-38. (all the electrical equipment with miles of wiring -literal miles I believe- and some specialized modular mass production techniques for the airframe itself that worked very well for Bell but might not have been so nice for Curtiss)

In a best-case scenario, Curtiss engineers working on solving some of the P-38's problems independently of Lockheed might have been able to speed up progress on both fronts, sharing findings with Lockheed while keeping up with progress on that end as well. (plus, I believe the P-38 and P-40 already had some parts commonality in the curtiss electric propellers used on some models ... in fact the retention of that rather small 3-blade Curtiss-electric propeller late in the P-38's run has been criticized for being too small to properly take advantage of the added engine power, while the same has been argued against Curtiss for retention of that aging unit on the P-40 -the P-39, P-51, and P-47 all went though multiple propeller changes to rather significant degree while the P-38K's larger area 3-blade prop was refused for production due to delays on the assembly line it would cause ... not sure if any 4-blade props might have avoided that by retaining similar spinner diameter -the P-51 and P-39 both avoided nose geometry redesigns by keeping any prop/hub/spinner changes to ones compatible with the existing geometry) The P-40D and YP-38 obviously had to change nose/nacelle/spinner geometry due to the engine dimension and thrust-line changes ... and I assume lowering the engine mount to maintain the P-40B/C thrust line would have been more problematic. (or ... maybe it wouldn't have been if they'd moved the radiator(s) to the wings, allowing the upper nose geometry to remain more constant along with the thrust line ... and had more room at the top of the engine for cowl-mounted .50s)

Have Curtiss manufacture the P-51 or even A-36 under license.