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Shortround6
Major General
Not a lot more fuel, Fw 190 carried 114 Imp gallons? P-40 E carried 123 imp gallons? P-40F carried 130 imp gallons If drag at cruising speed/s is 10% worse than the FW 190 than range/endurance is no better.
First four Fw-190A-1s are delivered in June of 1941 or within a week or two of the XP-40F with Merlin first flying. Obviously work on the Merlin P-40 had started months before that. Work on the R-2600 P-40 would have to begin in late 1940 in order for it show up in the middle of 1942. Can't wait for the FW 190 to show up, that is too late.
First four Fw-190A-1s are delivered in June of 1941 or within a week or two of the XP-40F with Merlin first flying. Obviously work on the Merlin P-40 had started months before that. Work on the R-2600 P-40 would have to begin in late 1940 in order for it show up in the middle of 1942. Can't wait for the FW 190 to show up, that is too late.
Shortround6
Major General
A few notes concerning weight and balance between the P-40E and the P-40F and engine availability. Both planes started and took off on the forward wing tank and switched to the belly (external tank) if carried as soon as possible. The difference is that with the E the next tank to be used is the fuselage tank (the one behind the pilot) followed by the main tank (rear wing tank) with the forward wing tank being the "reserve" tank.
The sequence changed on the F, after taking off on the forward wing tank and using the belly tank, if carried, the next tank was the fuselage tank behind the pilot but only until 35 US gallons were left. at that point the forward wing tank was selected again followed by the rear wing tank leaving the approximately 35 gallons in the fuselage tank as the reserve.
Basically they were using about 210lbs worth of fuel in the fuselage tank behind the pilot as a counter weight for the heavier Merlin engine installation.
Please remember that the three internal tanks (and some of the piping) were a legacy from the P-36 even if actual size varied a bit.
The Forward wing tank never changed from being the tank to start on as it received the return vapors and any excess fuel returned from the carb so using it first for a short period of time created space for the returned fuel to go to. On long flights this returned fuel could be used by going back to the forward wing tank near the end of the flight.
The Flight manuals do say both planes had the same sized fuel tanks unlike Americas Hundred Thousand. And that was 157-158 US gallons.
Please note that the Oil tank bounced around. It started behind the engine and forward of the firewall on the P-36 and was shifted to behind the pilot and on top of the fuselage fuel tank on the pointy Nose P-40s and then back to the engine compartment on the P-40E/F and later.
Also please note that Allison had built and was testing engines using 9.60 supercharger gears in the late fall of 1941. (engine for P-40 started testing Dec 5th 1941) A batch of 25 engines had been built for the P-39 and another batch of 25 was built (or was building) for the P-40. These were the first engines with the nitrided crankshaft and some other improvements. The engines failed the 150 test and most were rebuilt using 8.80 gears, These tests and planned power ratings were done using 100 octane or 100/125 fuel and take-off power was limited to 1100-1125hp unlike the later engines using 9.60 gears that were developed and rated using 100/130 fuel and allowed 1200hp for take-off. There was almost a year delay in actually delivering engines with the 9.60 gears. I would also note that using WEP settings on Allisons using the older non-nitrided crankshafts (engines built during 1941 and earlier) might not have been a very good idea. The engines may have stood up to the higher power settings the first few times it was used but the crankshaft had a much lower fatigue life than the later crankshaft. At some point higher engine failure rates ( or more frequent engine replacement/overhaul) would have had to been dealt with.
Supplies of 100/130 fuel may not have been universal (in all theaters) in late 1941 or early 1942 either.
The sequence changed on the F, after taking off on the forward wing tank and using the belly tank, if carried, the next tank was the fuselage tank behind the pilot but only until 35 US gallons were left. at that point the forward wing tank was selected again followed by the rear wing tank leaving the approximately 35 gallons in the fuselage tank as the reserve.
Basically they were using about 210lbs worth of fuel in the fuselage tank behind the pilot as a counter weight for the heavier Merlin engine installation.
Please remember that the three internal tanks (and some of the piping) were a legacy from the P-36 even if actual size varied a bit.
The Forward wing tank never changed from being the tank to start on as it received the return vapors and any excess fuel returned from the carb so using it first for a short period of time created space for the returned fuel to go to. On long flights this returned fuel could be used by going back to the forward wing tank near the end of the flight.
The Flight manuals do say both planes had the same sized fuel tanks unlike Americas Hundred Thousand. And that was 157-158 US gallons.
Please note that the Oil tank bounced around. It started behind the engine and forward of the firewall on the P-36 and was shifted to behind the pilot and on top of the fuselage fuel tank on the pointy Nose P-40s and then back to the engine compartment on the P-40E/F and later.
Also please note that Allison had built and was testing engines using 9.60 supercharger gears in the late fall of 1941. (engine for P-40 started testing Dec 5th 1941) A batch of 25 engines had been built for the P-39 and another batch of 25 was built (or was building) for the P-40. These were the first engines with the nitrided crankshaft and some other improvements. The engines failed the 150 test and most were rebuilt using 8.80 gears, These tests and planned power ratings were done using 100 octane or 100/125 fuel and take-off power was limited to 1100-1125hp unlike the later engines using 9.60 gears that were developed and rated using 100/130 fuel and allowed 1200hp for take-off. There was almost a year delay in actually delivering engines with the 9.60 gears. I would also note that using WEP settings on Allisons using the older non-nitrided crankshafts (engines built during 1941 and earlier) might not have been a very good idea. The engines may have stood up to the higher power settings the first few times it was used but the crankshaft had a much lower fatigue life than the later crankshaft. At some point higher engine failure rates ( or more frequent engine replacement/overhaul) would have had to been dealt with.
Supplies of 100/130 fuel may not have been universal (in all theaters) in late 1941 or early 1942 either.
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Shortround6
Major General
A few further notes.
The original Curtiss Hawk 75 used an experimental Curtiss two row 14 cylinder radial of 1670 cu in that weighed 1170-1230lbs (depending on exact model) and weighed 3760 lbs empty, 4843 lbs gross.
Later experimental engines installed were a P & W R-1535 of about 1100lbs and then a Wright Cyclone 9 R-1820G-5 of 1205lbs.
The P-36A got a P & W R-1830-13 that weighed about 1370lbs however empty and loaded weights had gone to 4567 lb and 5470 lbs respectively so something else was going on.
And the P-36A didn't weigh quite enough. From Joe Baugher's web site
" However, the new Curtiss fighters began to encounter an extensive series of teething troubles almost as soon as they reached the field. Severe skin buckling in the vicinity of the landing gear wells had appeared, dictating increased skin thicknesses and reinforcing webs. Engine exhaust difficulties and some weaknesses in the fuselage structure were also encountered. Despite both production line and field fixes, the P-36As were grounded again and again. At one time, the 20th Pursuit Group was down to six serviceable P-36As, and even these planes had to be flown under severe limitations on their speed, aerobatics, and combat maneuvers."
Curtiss did fix it and eventually the Basic airframe was turned into a sturdy fighter that went over 8000lbs and used powerplants (including radiators) that went 1700-1800lbs but how much further could it be pushed?
The original Curtiss Hawk 75 used an experimental Curtiss two row 14 cylinder radial of 1670 cu in that weighed 1170-1230lbs (depending on exact model) and weighed 3760 lbs empty, 4843 lbs gross.
Later experimental engines installed were a P & W R-1535 of about 1100lbs and then a Wright Cyclone 9 R-1820G-5 of 1205lbs.
The P-36A got a P & W R-1830-13 that weighed about 1370lbs however empty and loaded weights had gone to 4567 lb and 5470 lbs respectively so something else was going on.
And the P-36A didn't weigh quite enough. From Joe Baugher's web site
" However, the new Curtiss fighters began to encounter an extensive series of teething troubles almost as soon as they reached the field. Severe skin buckling in the vicinity of the landing gear wells had appeared, dictating increased skin thicknesses and reinforcing webs. Engine exhaust difficulties and some weaknesses in the fuselage structure were also encountered. Despite both production line and field fixes, the P-36As were grounded again and again. At one time, the 20th Pursuit Group was down to six serviceable P-36As, and even these planes had to be flown under severe limitations on their speed, aerobatics, and combat maneuvers."
Curtiss did fix it and eventually the Basic airframe was turned into a sturdy fighter that went over 8000lbs and used powerplants (including radiators) that went 1700-1800lbs but how much further could it be pushed?
kool kitty89
Senior Master Sergeant
With all the discussion that's gone on regarding fitting some model of R-2600 to some modification of the Curtiss model 75, 81, or 87 airframe, I think it's at least fair to argue that investing in developing such an aircraft would have been more worthwhile than the XP-46 project, and a more viable parallel development with the XP-40D and likely initiated significantly earlier than the Merlin P-40 project.
Even down-rating take-off power to better comply with toque and related stability limitations seems like it would've been acceptable if overall performance proved promising once in the air. Though with take-off and low-altitude power being overkill in general, a lighter simplified single-speed R-2600 running only in the high gear ratio may have been worth pursuing. (yes, more complicated logistics initially, and not worth doing unless such an aircraft actually showed promise, but in full-scale production, such an engine should be slightly cheaper to manufacture than the contemporary 2-stage variants on top of being shorter and lighter and at least potentially available sooner than either the 9.6 ratio V-1710 or V-1650-1) All that really depends on how early things get started, though. (it's also somewhat akin to the arguments in favor of the lighter, earlier single-speed BMW 139 over the heavier 801)
I'm also not sure, but with the lower power range in mind, the lighter early models using aluminum crankcases might have had more long-term (or larger scale) production adapted into fighter engines rather than phased out. (and yes I also remember that development of the R-2600 slowed down/became troubled once the US entered the war and its chief designer was barred from the project due to German citizenship, though this is less directly relevant for pre-1940 developments)
Aside from that, the issue of prop clearance and prop RPM is something that was in question (in several other threads as well), and going by the 16:9 reduction gearing of the common 'bomber' R-2600s, you really wouldn't want faster prop speeds than that on a fighter either given the tip-speeds of an 11' prop (akin to that of the P-40D) would already be higher at max continuous 2400 RPM with 16:9 reduction than at 2600 RPM with 2:1 reduction on a V-1710, while take-off RPM ratings would push the V-1710 prop speeds a bit higher (1/2 of 3000 RPM vs 9/16 of 2600 RPM, or 1500 vs 1462.5 RPM at the prop) but still quite close.
Additionally, the props used on the Model 75 appear to have been smaller than the 11' of the P-40D given this document:
http://www.wwiiaircraftperformance.org/P-36/Curtiss_Hawk_75-A_Detail_Specifications.pdf
For the R-1820 Cyclone 9 powered variant:
10 ft 6 in propeller and 1616 rpm rotation rate (16:11 ratio, 2350 rpm R-1820)
10 ft 1 1/2 in prop and 1519 rpm rotation (16:9 reduction, 2700 rpm R-1830)
I did some simple geometry calculations regarding tip speed in flight conditions (taking net velocity of the angular motion from the rotation + perpendicular flight velocity, simple 90 degree pathagorean theorem type stuff), and while those props and rotation rates really wouldn't be cutting it close (except in dives at fairly high altitudes, mostly >400 mph and >20,000 ft) you wouldn't be getting supersonic tip speeds, though cold climates would narrow this margin.
Going up to the 11 ft prop and the higher rotation rates of either the V-1710 or (most) R-2600s could be more problematic though and cutting it somewhat closer, so going with bomber-sized props (or P-47/Corsair sized ones) really wouldn't be an option even aside from problems with torque or (especially) ground clearance.
Also note this issue of supersonic prop speeds would also create some problems with V-1710 overreving, though mostly at high altitude and using 3,400 RPM engine speeds in level flight. (for high alt emergency climb, it might be plausible, but in level flight at 17,000 ft with Mach 1 at around 1050 fps, you'd be hitting supersonic tip speeds at 259 mph) 3200 RPM gives much more practical leeway for boosting top speed, but still runs it fairly close for practical purposes. (just some food for thought in line with Allison potentially performing sufficient testing to allow more regular use of overrev on the E/F series engines, particular with more moderate loads at higher altitudes, somewhat like certain DB 601 models were allowed: though the V-1710 seems to have had a much wider margin for safety in general than the DB engines, or Merlin for that matter; the C-series V-1710 being abused by the AVG and possibly some Colonial units may have also set an additionally conservative president for Allison with their later series engines on top of their limited funding and resource allotment)
Also note that document lists wing guns loading from the top of the wings, with internal ammunition boxes. (it also mentions link and shell retention boxes that may be installed below the ejection chutes of the fuselage guns, so some internet article references to external amunition boxes are likely incorrect, but could be misidentification of detachable link retention boxes for training purposes, retaining spend cartridge cases and belt links: which would better fit the 'cartridge case retainer box' description used on Baugher's website) There's mo mention of external ammo boxes ever being used on the P-36 (or other Hawk models) that I've managed to find on official documents, and this document seems to point to both the single-gun and 2-gun installations in wings used ammunition boxes fitted within the wings and loaded through panels on the upper section of the wing, nothing underneath.
However, in as far as things actually mounted underwing: note alternate armament installation provisions:
1 .50 cal gun below each wing (200 rpg), 1 20 mm oerlikon cannon below each wing (75 rpg), 1 23 mm Madsen cannon below each wing (100 rpg).
The .50 cal option seems most appealing, and might have been a viable trade-off for some speed loss on the P-40B/C/Tomohawk for the added firepower (matching the F2A) prior to the modified 4-gun wings of the Model 87. (and deletion of nose guns entirely) Additionally, the drag added to a radial engine powered fighter would be proportionally smaller than the P-40 itself, and perhaps a more valuable trade-off for relatively limited performance change. (especially for the bulkier R-1820 or a hypothetical R-2600) Incidentally, a 4x .50 cal armed 2-speed Cyclone powered variant might have fared the best in British use as BoB era interceptor, of the Hawk variants available at that time. (fast enough to chase bombers at most altitude in that conflict, much better at damaging fuel tanks and armor, even with ball ammo, thanks to massive hydrostatic shock, and superior roll-rate to anything else in the sky at the time, allowing a totally different sort of out-maneuvering than the simple level turning ability the Hurricane showed; plus all-around lighter controls at high speeds, even if this was curtailed by the higher drag of the engine installation slowing dive acceleration ... perhaps less so when weighed down with armor and tanks wrapped with sealing material; plus good all-around visibility)
Also oddly, there appears to be a substantial weight gain on the R-1830 powered model and I can't work out particular reasons for this.
Even down-rating take-off power to better comply with toque and related stability limitations seems like it would've been acceptable if overall performance proved promising once in the air. Though with take-off and low-altitude power being overkill in general, a lighter simplified single-speed R-2600 running only in the high gear ratio may have been worth pursuing. (yes, more complicated logistics initially, and not worth doing unless such an aircraft actually showed promise, but in full-scale production, such an engine should be slightly cheaper to manufacture than the contemporary 2-stage variants on top of being shorter and lighter and at least potentially available sooner than either the 9.6 ratio V-1710 or V-1650-1) All that really depends on how early things get started, though. (it's also somewhat akin to the arguments in favor of the lighter, earlier single-speed BMW 139 over the heavier 801)
I'm also not sure, but with the lower power range in mind, the lighter early models using aluminum crankcases might have had more long-term (or larger scale) production adapted into fighter engines rather than phased out. (and yes I also remember that development of the R-2600 slowed down/became troubled once the US entered the war and its chief designer was barred from the project due to German citizenship, though this is less directly relevant for pre-1940 developments)
Aside from that, the issue of prop clearance and prop RPM is something that was in question (in several other threads as well), and going by the 16:9 reduction gearing of the common 'bomber' R-2600s, you really wouldn't want faster prop speeds than that on a fighter either given the tip-speeds of an 11' prop (akin to that of the P-40D) would already be higher at max continuous 2400 RPM with 16:9 reduction than at 2600 RPM with 2:1 reduction on a V-1710, while take-off RPM ratings would push the V-1710 prop speeds a bit higher (1/2 of 3000 RPM vs 9/16 of 2600 RPM, or 1500 vs 1462.5 RPM at the prop) but still quite close.
Additionally, the props used on the Model 75 appear to have been smaller than the 11' of the P-40D given this document:
http://www.wwiiaircraftperformance.org/P-36/Curtiss_Hawk_75-A_Detail_Specifications.pdf
For the R-1820 Cyclone 9 powered variant:
10 ft 6 in propeller and 1616 rpm rotation rate (16:11 ratio, 2350 rpm R-1820)
10 ft 1 1/2 in prop and 1519 rpm rotation (16:9 reduction, 2700 rpm R-1830)
I did some simple geometry calculations regarding tip speed in flight conditions (taking net velocity of the angular motion from the rotation + perpendicular flight velocity, simple 90 degree pathagorean theorem type stuff), and while those props and rotation rates really wouldn't be cutting it close (except in dives at fairly high altitudes, mostly >400 mph and >20,000 ft) you wouldn't be getting supersonic tip speeds, though cold climates would narrow this margin.
Going up to the 11 ft prop and the higher rotation rates of either the V-1710 or (most) R-2600s could be more problematic though and cutting it somewhat closer, so going with bomber-sized props (or P-47/Corsair sized ones) really wouldn't be an option even aside from problems with torque or (especially) ground clearance.
Also note this issue of supersonic prop speeds would also create some problems with V-1710 overreving, though mostly at high altitude and using 3,400 RPM engine speeds in level flight. (for high alt emergency climb, it might be plausible, but in level flight at 17,000 ft with Mach 1 at around 1050 fps, you'd be hitting supersonic tip speeds at 259 mph) 3200 RPM gives much more practical leeway for boosting top speed, but still runs it fairly close for practical purposes. (just some food for thought in line with Allison potentially performing sufficient testing to allow more regular use of overrev on the E/F series engines, particular with more moderate loads at higher altitudes, somewhat like certain DB 601 models were allowed: though the V-1710 seems to have had a much wider margin for safety in general than the DB engines, or Merlin for that matter; the C-series V-1710 being abused by the AVG and possibly some Colonial units may have also set an additionally conservative president for Allison with their later series engines on top of their limited funding and resource allotment)
Also note that document lists wing guns loading from the top of the wings, with internal ammunition boxes. (it also mentions link and shell retention boxes that may be installed below the ejection chutes of the fuselage guns, so some internet article references to external amunition boxes are likely incorrect, but could be misidentification of detachable link retention boxes for training purposes, retaining spend cartridge cases and belt links: which would better fit the 'cartridge case retainer box' description used on Baugher's website) There's mo mention of external ammo boxes ever being used on the P-36 (or other Hawk models) that I've managed to find on official documents, and this document seems to point to both the single-gun and 2-gun installations in wings used ammunition boxes fitted within the wings and loaded through panels on the upper section of the wing, nothing underneath.
However, in as far as things actually mounted underwing: note alternate armament installation provisions:
1 .50 cal gun below each wing (200 rpg), 1 20 mm oerlikon cannon below each wing (75 rpg), 1 23 mm Madsen cannon below each wing (100 rpg).
The .50 cal option seems most appealing, and might have been a viable trade-off for some speed loss on the P-40B/C/Tomohawk for the added firepower (matching the F2A) prior to the modified 4-gun wings of the Model 87. (and deletion of nose guns entirely) Additionally, the drag added to a radial engine powered fighter would be proportionally smaller than the P-40 itself, and perhaps a more valuable trade-off for relatively limited performance change. (especially for the bulkier R-1820 or a hypothetical R-2600) Incidentally, a 4x .50 cal armed 2-speed Cyclone powered variant might have fared the best in British use as BoB era interceptor, of the Hawk variants available at that time. (fast enough to chase bombers at most altitude in that conflict, much better at damaging fuel tanks and armor, even with ball ammo, thanks to massive hydrostatic shock, and superior roll-rate to anything else in the sky at the time, allowing a totally different sort of out-maneuvering than the simple level turning ability the Hurricane showed; plus all-around lighter controls at high speeds, even if this was curtailed by the higher drag of the engine installation slowing dive acceleration ... perhaps less so when weighed down with armor and tanks wrapped with sealing material; plus good all-around visibility)
Also oddly, there appears to be a substantial weight gain on the R-1830 powered model and I can't work out particular reasons for this.
Shortround6
Major General
In reverse order, a 185lb increase in powerplant weight is responsible for most of the weight difference between the Cyclone model and the Twin Wasp.
Drag is not the big the problem with using .50 cal guns in the wings (or under). weight is. 400 rounds of .50 cal ammo weighs about 120lbs or as much as 2000 rounds of .30 cal ammo. weight of the guns is about 150lbs for a pair of .50 cal. it is about 95lbs for FOUR . 30 cal guns. IF you are using the Higher cycle rate .50s then you have about 15-16 seconds of firing time. Navy pilots didn't like 240rpg on 6 gun Wildcats.
In the BoB you would have had the 600rpm guns, four 50.s would have been putting out about 36 bullets a second (at best), a four gun WIldcat in the Pacific was putting out about 52 bullets per second. Wildcat not having to put up with synchronized guns in addition to having the faster firing guns.
The guns are not a problem in themselves, they do add to the weight problem .
AS in "A pilot's protective shield of 1/4" armor plate may be installed to the rear of the pilots seat" in the " optional equipment section. Weight of armor is not included in base figures. Neither are protected fuel tanks.
I would also note that the radio is also an extra as is an electric starter.
Bringing a Hawk 75 up to the standards of even a P-40B is going to add around 260-270lbs just for protection, radio and electric starter. Now throw in the added guns/ammo. Your 12G load rating just went in the toilet, requiring a bit of extra weight to get back.
Turning ability may suffer only a little bit but climb is starting to take it in the neck. And climb is related to sustained turn.
As for:
" .....Though with take-off and low-altitude power being overkill in general, a lighter simplified single-speed R-2600 running only in the high gear ratio may have been worth pursuing. (yes, more complicated logistics initially, and not worth doing unless such an aircraft actually showed promise, but in full-scale production, such an engine should be slightly cheaper to manufacture than the contemporary 2-stage variants on top of being shorter and lighter and at least potentially available sooner than either the 9.6 ratio V-1710 or V-1650-1) All that really depends on how early things get started, though. (it's also somewhat akin to the arguments in favor of the lighter, earlier single-speed BMW 139 over the heavier 801)
I'm also not sure, but with the lower power range in mind, the lighter early models using aluminum crankcases might have had more long-term (or larger scale) production adapted into fighter engines rather than phased out. (and yes I also remember that development of the R-2600 slowed down/became troubled once the US entered the war and its chief designer was barred from the project due to German citizenship, though this is less directly relevant for pre-1940 developments)"
Not at all sure where this came from, ie the bolded part. There was NEVER an 2 stage production version of the R-2600. There were a total of 12 experimental/development engines with 2 stage superchargers. 9 of one model , one of another and 2 of a 3rd type. Plus a few experimental turbos. The two speed drive to the single stage supercharger was worth about 15-20lbs and had a negligible impact (if any) on engine length.
I would also note that the steel crankcase was actually lighter than the aluminum crankcase in addition to being stronger. the difference of 30-60lbs between the aluminium crankcase engines and steel crankcase engines was due to other changes.
An Allison went around 1350-1310lbs (the long nose ones were heavier) and the cooling system was about 300lbs (varies a bit depending on model). The R-2600 went about 1935lbs for the lightest version. You are really going to have to do a LOT of work to take out several hundred pounds. Plus the weight of the bigger prop and oil systems.
Without a low drag cowling comparable to the FW 190s sticking an R-2600 on a P-40 airframe wasn't really going to get you anything. The early P-40 had 22% less drag than a P-36 (R-1830 engine). The early R-2600 (1600hp take-off) had 1400hp at 11700ft in high gear or about 21-22% more than the Allison in the P-40D/E. (1150hp at 12,000ft)
Drag is not the big the problem with using .50 cal guns in the wings (or under). weight is. 400 rounds of .50 cal ammo weighs about 120lbs or as much as 2000 rounds of .30 cal ammo. weight of the guns is about 150lbs for a pair of .50 cal. it is about 95lbs for FOUR . 30 cal guns. IF you are using the Higher cycle rate .50s then you have about 15-16 seconds of firing time. Navy pilots didn't like 240rpg on 6 gun Wildcats.
In the BoB you would have had the 600rpm guns, four 50.s would have been putting out about 36 bullets a second (at best), a four gun WIldcat in the Pacific was putting out about 52 bullets per second. Wildcat not having to put up with synchronized guns in addition to having the faster firing guns.
The guns are not a problem in themselves, they do add to the weight problem .
AS in "A pilot's protective shield of 1/4" armor plate may be installed to the rear of the pilots seat" in the " optional equipment section. Weight of armor is not included in base figures. Neither are protected fuel tanks.
I would also note that the radio is also an extra as is an electric starter.
Bringing a Hawk 75 up to the standards of even a P-40B is going to add around 260-270lbs just for protection, radio and electric starter. Now throw in the added guns/ammo. Your 12G load rating just went in the toilet, requiring a bit of extra weight to get back.
Turning ability may suffer only a little bit but climb is starting to take it in the neck. And climb is related to sustained turn.
As for:
" .....Though with take-off and low-altitude power being overkill in general, a lighter simplified single-speed R-2600 running only in the high gear ratio may have been worth pursuing. (yes, more complicated logistics initially, and not worth doing unless such an aircraft actually showed promise, but in full-scale production, such an engine should be slightly cheaper to manufacture than the contemporary 2-stage variants on top of being shorter and lighter and at least potentially available sooner than either the 9.6 ratio V-1710 or V-1650-1) All that really depends on how early things get started, though. (it's also somewhat akin to the arguments in favor of the lighter, earlier single-speed BMW 139 over the heavier 801)
I'm also not sure, but with the lower power range in mind, the lighter early models using aluminum crankcases might have had more long-term (or larger scale) production adapted into fighter engines rather than phased out. (and yes I also remember that development of the R-2600 slowed down/became troubled once the US entered the war and its chief designer was barred from the project due to German citizenship, though this is less directly relevant for pre-1940 developments)"
Not at all sure where this came from, ie the bolded part. There was NEVER an 2 stage production version of the R-2600. There were a total of 12 experimental/development engines with 2 stage superchargers. 9 of one model , one of another and 2 of a 3rd type. Plus a few experimental turbos. The two speed drive to the single stage supercharger was worth about 15-20lbs and had a negligible impact (if any) on engine length.
I would also note that the steel crankcase was actually lighter than the aluminum crankcase in addition to being stronger. the difference of 30-60lbs between the aluminium crankcase engines and steel crankcase engines was due to other changes.
An Allison went around 1350-1310lbs (the long nose ones were heavier) and the cooling system was about 300lbs (varies a bit depending on model). The R-2600 went about 1935lbs for the lightest version. You are really going to have to do a LOT of work to take out several hundred pounds. Plus the weight of the bigger prop and oil systems.
Without a low drag cowling comparable to the FW 190s sticking an R-2600 on a P-40 airframe wasn't really going to get you anything. The early P-40 had 22% less drag than a P-36 (R-1830 engine). The early R-2600 (1600hp take-off) had 1400hp at 11700ft in high gear or about 21-22% more than the Allison in the P-40D/E. (1150hp at 12,000ft)
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GregP
Major
Shortround,
Out of curiosity only, with regard to post 163, can you quote any actually higher failure rate data for any particular crankshaft? I have not seen these data. If not, where does this statement come from?
We have run both 6 and 12-counterweight crankshafts at VERY high rpm levels with regard to WWII levels, all with no failures, even in tractors running 4,600 rpm for a tractor pull, sometimes for years before rebuilds. Not one single crank failure of either 6 or 12-counterweight variety. A few other things HAVE failed, but not cranks, even one that was bent by .050 inches, was straightened with a hydraulic press... and is still running in a boat.
Out of curiosity only, with regard to post 163, can you quote any actually higher failure rate data for any particular crankshaft? I have not seen these data. If not, where does this statement come from?
We have run both 6 and 12-counterweight crankshafts at VERY high rpm levels with regard to WWII levels, all with no failures, even in tractors running 4,600 rpm for a tractor pull, sometimes for years before rebuilds. Not one single crank failure of either 6 or 12-counterweight variety. A few other things HAVE failed, but not cranks, even one that was bent by .050 inches, was straightened with a hydraulic press... and is still running in a boat.
Shortround6
Major General
I can't give you any figures because that is a supposition on my part. However it has nothing to do with the 12 counter weight crankshaft and a lot to do with a chart on page 409 of Vees for Victory showing the difference in endurance of the 3 different 6 counter weight crankshafts.
The original "plain" crankshafts were good for around 93 X10*3 lbs per sq in stress for very short term (100,000?)cycles falling to 70 X10*3 by 0.7 million cycles after which the line flattens out and the crankshaft can run 70 X10*3 lbs per sq in stress pretty much forever (10 million cycles)
The Shot peened Crankshaft started at about 112-113 X10*3 lbs per sq in and fell off much more slowly to 90 x10*3 by 3 million cycles and then stayed flat to 10 million cycles.
The Nitrided crankshaft started at 150 x10*3 lbs per sq in and fell to 120 X10*3 by 3 million cycles and then stayed flat to 10 million.
The Nitrided crankshaft was introduced to production in very early 1942.
This means roughly 64,000+ engines were produced with the nitrided crankshaft (minus the 12 counter weight engines) and any spare cranks manufactured from early 1942 on were the nitrided version. There may have been 8300 to 9000 engines built with the two versions of the earlier crankshafts in 1939-41 and a good number of them went overseas in combat aircraft and were lost.
On shear numbers alone the nitrided crankshafts out number the early cranks about 8 to 1 and in numbers available to engine restorers the the number of early crankshafts is probably much, much lower. Not a problem as the nitrided crank will drop right into an early engine.
Post 163 was in part an answer to people who think you can abuse an early model Allison the same way you can abuse the later versions ( official WEP ratings and such) and get the same results/life out of the engine.
The 1942 and later crankshafts will operate essential forever at a stress level almost 30% higher than the stress level that would cause failure in plain steel crank in about a hundred thousand cycles.
The original "plain" crankshafts were good for around 93 X10*3 lbs per sq in stress for very short term (100,000?)cycles falling to 70 X10*3 by 0.7 million cycles after which the line flattens out and the crankshaft can run 70 X10*3 lbs per sq in stress pretty much forever (10 million cycles)
The Shot peened Crankshaft started at about 112-113 X10*3 lbs per sq in and fell off much more slowly to 90 x10*3 by 3 million cycles and then stayed flat to 10 million cycles.
The Nitrided crankshaft started at 150 x10*3 lbs per sq in and fell to 120 X10*3 by 3 million cycles and then stayed flat to 10 million.
The Nitrided crankshaft was introduced to production in very early 1942.
This means roughly 64,000+ engines were produced with the nitrided crankshaft (minus the 12 counter weight engines) and any spare cranks manufactured from early 1942 on were the nitrided version. There may have been 8300 to 9000 engines built with the two versions of the earlier crankshafts in 1939-41 and a good number of them went overseas in combat aircraft and were lost.
On shear numbers alone the nitrided crankshafts out number the early cranks about 8 to 1 and in numbers available to engine restorers the the number of early crankshafts is probably much, much lower. Not a problem as the nitrided crank will drop right into an early engine.
Post 163 was in part an answer to people who think you can abuse an early model Allison the same way you can abuse the later versions ( official WEP ratings and such) and get the same results/life out of the engine.
The 1942 and later crankshafts will operate essential forever at a stress level almost 30% higher than the stress level that would cause failure in plain steel crank in about a hundred thousand cycles.
Okay, so they'd be in the roots, and the turbo would stay down below?
Would it be possible to shift the battery/radio behind the cockpit & shift the cockpit?
Was this a problem with the P-38?
I'll give it a read...
