V-1710-39 power curve
- Thread starter Trilisser
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Shortround6
Major General
I am not sure the engine was officially cleared for it 60". In any case it shouldn't be too far off from a later engine with 8.80 supercharger gears. 1580-1590hp at 2500ft depending on actual manifold and backfire screens? This is without ram so either a few more inches could be squeezed out or a few thousand more feet of altitude.
- Thread starter
- #4
Shortround6
Major General
You had two model engines in the P-40 with 8.80:1 ratios, the -39 and the -73. The -73 had some strengthened parts which the-39 did not. The -39 could make the same power as the -73 but the question is for how long?
There may be some question as to how much power these engines were making at the reported boost pressures.
The standard power charts are for sea level and 15 degrees C or 59/60 degrees F. air at that temperature has a density of 1.2250 kg per cubic meter. at 30 degrees C (86 degrees F) the air density is 1.1644 kg per cubic meter or 95% and at 35 degrees C (95 degrees F) it is 1.1455 kg per cubic meter or 93.5%. This is assuming the sea level pressures at these temperatures is the standard 1 atm or 101.325 kPa.
Planes operating in the Darwin/New Guinea area or in North Africa may have been down 5-10% in actually power due to temperature to begin with. Over boosting a -39 engine from 56in to 60 in at 35degrees C might just Bring the actual power back to "book" (56in) levels. You do have the hotter intake charge pushing you closer to detonation limits though.
None of the charts in "Vees for Victory" show 60in for the -39 engine. However they were rated on different fuels. the -39 was rated on 100 octane while the -73 was rated on 100/125 and they were actually run on 100/130 in most combat zones, the -39 being out of production for quite some time when the Dec 1942 memo was issued.
Without over revving the engine the supercharger was simply not capable of supplying much more than 65-68in (?)pressure static ( no ram) at sea level so power output is also very dependent on aircraft speed. how much power do you have at 290-300mph in level flight or how much power do you have at 150mph while climbing? The supercharger cannot supply more than 60in pressure at 2500ft static and 56in at 4300ft static.
In any case, unless there is a difference in intake manifolds or backfire screens the -39 and -73 are going to give the same power at the the same rpm and manifold pressures. Same supercharger, same carburetor, same supercharger gear ratio.
There may be some question as to how much power these engines were making at the reported boost pressures.
The standard power charts are for sea level and 15 degrees C or 59/60 degrees F. air at that temperature has a density of 1.2250 kg per cubic meter. at 30 degrees C (86 degrees F) the air density is 1.1644 kg per cubic meter or 95% and at 35 degrees C (95 degrees F) it is 1.1455 kg per cubic meter or 93.5%. This is assuming the sea level pressures at these temperatures is the standard 1 atm or 101.325 kPa.
Planes operating in the Darwin/New Guinea area or in North Africa may have been down 5-10% in actually power due to temperature to begin with. Over boosting a -39 engine from 56in to 60 in at 35degrees C might just Bring the actual power back to "book" (56in) levels. You do have the hotter intake charge pushing you closer to detonation limits though.
None of the charts in "Vees for Victory" show 60in for the -39 engine. However they were rated on different fuels. the -39 was rated on 100 octane while the -73 was rated on 100/125 and they were actually run on 100/130 in most combat zones, the -39 being out of production for quite some time when the Dec 1942 memo was issued.
Without over revving the engine the supercharger was simply not capable of supplying much more than 65-68in (?)pressure static ( no ram) at sea level so power output is also very dependent on aircraft speed. how much power do you have at 290-300mph in level flight or how much power do you have at 150mph while climbing? The supercharger cannot supply more than 60in pressure at 2500ft static and 56in at 4300ft static.
In any case, unless there is a difference in intake manifolds or backfire screens the -39 and -73 are going to give the same power at the the same rpm and manifold pressures. Same supercharger, same carburetor, same supercharger gear ratio.
- Thread starter
- #6
Shortround6
Major General
A Mustang, being faster than a P-40, can generate more RAM. If the supercharger can supply 65-68in static at sea level perhaps 340mph+ can supply another 4-7in of pressure?
from a test the British did a Mustang with a -39 spec engine (later engine refitted with 8.80:1 gears) held 56in to 7900ft or a gain of 3600ft in altitude of "static" or looked at another way around 3.2 in pressure? Perhaps less after before being multiplied in the blower?
While these are very impressive numbers at sea level and help explain the combat performance at low level that seems out of line with the "normal" book figures (Military power rating) it is also obvious that the power goes away very quickly with height and is even worse when trying to climb.
http://www.wwiiaircraftperformance.org/mustang/ap222speed.gif
If you follow the curve down and extend it the engine might have been able to pull 60 in at a bit over 6000ft, but a P-40 would be at a lower altitude because of the lower speed.
or this test with a -73 engine?
Mustang II Performance Trial
Held 60in to 4400ft instead of the chart 2500ft for static but look at the climb
Held 60 in to 800ft and was at 55in at 4000ft. In level flight it could make 50in at 10,000ft but in a climb only 45 in. Roughly a 10% loss in power in the climb vs full speed level flight.
Again, they were not over revving in the tests.
I don't doubt that those boost pressures were used or seen at times but unless the plane is right at sea level the ability of the plane to use them is limited or non-existent without over revving the engine and even a few thousand feet of altitude can make a big difference in power, especially trying to climb. The test Mustang lost 20% of its climb rate by the time it hit 6,000ft.
The same engine, installed in a P-40 or P-39 (same spec) will give different full throttle heights because of the different air intakes and the different amounts of ram.
from a test the British did a Mustang with a -39 spec engine (later engine refitted with 8.80:1 gears) held 56in to 7900ft or a gain of 3600ft in altitude of "static" or looked at another way around 3.2 in pressure? Perhaps less after before being multiplied in the blower?
While these are very impressive numbers at sea level and help explain the combat performance at low level that seems out of line with the "normal" book figures (Military power rating) it is also obvious that the power goes away very quickly with height and is even worse when trying to climb.
http://www.wwiiaircraftperformance.org/mustang/ap222speed.gif
If you follow the curve down and extend it the engine might have been able to pull 60 in at a bit over 6000ft, but a P-40 would be at a lower altitude because of the lower speed.
or this test with a -73 engine?
Mustang II Performance Trial
Held 60in to 4400ft instead of the chart 2500ft for static but look at the climb
Held 60 in to 800ft and was at 55in at 4000ft. In level flight it could make 50in at 10,000ft but in a climb only 45 in. Roughly a 10% loss in power in the climb vs full speed level flight.
Again, they were not over revving in the tests.
I don't doubt that those boost pressures were used or seen at times but unless the plane is right at sea level the ability of the plane to use them is limited or non-existent without over revving the engine and even a few thousand feet of altitude can make a big difference in power, especially trying to climb. The test Mustang lost 20% of its climb rate by the time it hit 6,000ft.
The same engine, installed in a P-40 or P-39 (same spec) will give different full throttle heights because of the different air intakes and the different amounts of ram.
- Thread starter
- #8
SR6: all true, though my point was that settings well above handbook ratings were used. As for over revving, one gets an impression from Whitney that the V-1710 was more tolerant to it than most others, especially the DB 605, whose manual states quite sternly that any engine with which 2800 rpm +2 % has been even momentarily exceeded must be removed and sent to factory...
Venturi
Airman
Excellent thread.
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