Improve That Design: How Aircraft Could Have Been Made Better (1 Viewer)

[P-39 Expert]

Actual fly-off tests between A6Ms and P-39s proved that anything above 15,000 feet and the P-39 is outclassed by the Zero. Trials using a P-39D against a Zero 21 in August 1942, admittedly an earlier model than the 'N although the 'D model was what was on the frontline at the time, shows that anything above 12,500 feet and it is left behind. During this particular fly-off, the trial had to be called off because the P-39 was low on fuel, and that was during a trial fly-off under controlled conditions. During similar fly-offs with F4U, F4F, P-38 and P-51, no other aircraft ran out of fuel. Actually a P-39D-1, at 7850lbs the heaviest of the 1942 P-39s. Could have easily weighed 7150lbs without redundant equipment and left the Zero behind. In continuous climb from SL they were actually equal up to 14500ft when the D-1 had to reduce power to 2600rpm as it had reached the 5 minute limit. By mid 1942 that was increased to 15 minutes. Even the D-1 was faster than the Zero at all altitudes. Zero did hold more fuel than the P-39.

The F6F however during later trials against a Zero 52 in 1944 proved that above 14,000 feet it was superior in every way, below that height up to 9,000 feet the Zero was faster, but between 9 and 14,000 ft the F6F gradually caught up. The F6F-5 model however was superior in speed to the Zero 52 at all altitudes. All P-39 models were faster than any Zero at all altitudes.

No comparison between the F6F and the P-39 as combat aircraft, to be honest. One is clearly superior to t'other, and their relevant combat histories prove that beyond doubt. See the attached comparison chart, and please note that the P-39N was out of production before the F6F got into combat.

 

[P-39 Expert]

The F6F-3 could also use it's full power with less chance of cooking the engine on a hot day.

The tests for the P-39N were done on two days, one a bit hotter than a "standard day" temp was about 39 degrees F at 11,000ft when the "standard" called for 19.8.

However the 2nd test report on the same airplane was done on a day when the outside temp was -12 degrees C (10.4 degrees F) at 12,000ft and the plane was judged not acceptable as the estimated temperature on a "hot day" would have been 152 degrees C (305.6 degrees F).
The engine was running about 10 degrees C cooler than the earlier test.

WEP isn't much use if you can't use in the tropics or dessert conditions "Hey, Germans, could you only please attack just about at dawn (coolest part of the day) so our engines won't overheat trying to climb up for the intercept, please, please?"

Performance tests were converted to standard day conditions. Opposing planes in combat were flying in the same weather conditions, the faster plane in standard tests would still be faster on a hot day. 1943 P-38 and P-47 overheated at combat power settings. Apparently they all made do.

 

[P-39 Expert]

It took until the fall of 1943 to clear the 2 stage engine for WEP ratings. This including things like the new keystone piston rings. What's the hurry, the P-63 airframe wasn't ready until October. They were going to the Russians anyway.

Without the WEP/water injection the V-1710-93 engine was rated at 1180hp at 21,000ft
which is about 200hp less at 2,500ft lower than the Merlin 61 of spring/summer of 1942, one year earlier. Merlin made more power but wouldn't fit into a P-39 or P-63. Put the -93 into a P-39 in April 1943. Give up on the intercooler and move the carb from the auxiliary stage to the normal position on the engine stage. Now you have 1150hp at 25000ft. Don't worry about WEP, just use military power. No need for intercooling or water injection. No need for the P-63 either.

First P-63s built with the engine flew under restrictions until the engine was cleared.

 

[P-39 Expert]

Double post.

 

[P-39 Expert]

Did it have enough fuel to get home then?
I suggest you look at the charts in the links posted.

Any plane has enough fuel to get home as long as the capacity of the drop tank is less than the internal fuel.

 

[pbehn]

Any plane has enough fuel to get home as long as the capacity of the drop tank is less than the internal fuel.

Only if you ignore the fuel used in combat. A Merlin consumed about three times as much fuel on maximum power compared to economic cruise (150 gal/hr against 50 gal/ hr), I have no reason to think an Allison engine would be much different.

 

[Milosh]

fuel consumption
P39SEFC.pdf (zenoswarbirdvideos.com)

war emergency: 170g/h

 

[P-39 Expert]

Only if you ignore the fuel used in combat. A Merlin consumed about three times as much fuel on maximum power compared to economic cruise (150 gal/hr against 50 gal/ hr), I have no reason to think an Allison engine would be much different.

In planning your mission you have already deducted reserves for takeoff, combat and landing from total fuel. Use your drop tank for warmup and taxi, switch to internal for the actual takeoff, then back to the drop tank asap (normally less than a minute) so that your internal fuel should be almost full. After dropping the external tank (or turning for home if there is no combat) you should have full internal fuel including reserves for combat and landing. If there is no combat and landing goes smoothly there will still be the reserves for combat and landing in your internal tank.

 

[Milosh]

 

[P-39 Expert]

View attachment 609816

Interesting, I had seen this chart before and the -63/83/85/93 engines had military power for 15 minutes but the original -35 was still rated for only 5 minutes even though it had a war emergency rating from late 1942.

 

[pbehn]

In planning your mission you have already deducted reserves for takeoff, combat and landing from total fuel. Use your drop tank for warmup and taxi, switch to internal for the actual takeoff, then back to the drop tank asap (normally less than a minute) so that your internal fuel should be almost full. After dropping the external tank (or turning for home if there is no combat) you should have full internal fuel including reserves for combat and landing. If there is no combat and landing goes smoothly there will still be the reserves for combat and landing in your internal tank.

That is a different issue, if you fly to a point using only a 110 gal drop tank, then use your internal tank for 15 mins @ 170 gal/hr how much internal fuel do you have left? Will it get you back as far as your external tank took you?

 

[GregP]

I make a motion we improve the forum by avioding the P-39 until such time as real-world use and results come into play.

If you look at aerial victories by type and theater, the legacy of the P-39 becomes apparent. First, let's remove the essentially non-participating fighters like the P-26, P-35, P-36, P-43, P-70, F2A, Beaufighter (lend-lease), TBF/TBM, P-61, and the SBD. That leaves the P-38, P-39, P-40, P-47, and P-51 (including F-6 and A-36), F4F/FM-2, F6F, and F4U, and Spitfire (only the MTO) which is most of our fighters.

If we just look at the Pacific, the Spitfire wasn't used by the U.S.A. and it drops out. The Lowest total victories is 288 by the P-39/P-400. Next would be 297 by the P-51 since it got to the Pacific essentially at the end of the war. The FM-2 is next at 422, followed by the P-40 with 661. It continues going up from there.

If we get out of the Pacific only and look at the entire war, the lowest victory tally is 321 by the P-39 / P-400, followed by the Spitfire in the MTO/ETO with 379, and it goes up from there.

The Mosquito, P-26, P-35, P-36, P-43, P-70, F2A, and Beaufighter only scored 58 victories combined, so they don't really count as major fighters in service with the U.S.A. . The TBF/TBM outscored them all combined with 98 victories, but isn't a fighter.

So, we have had 100+ pages and all this "it could have been a great airplane" about the fighter with the lowest score of any major fighter in service with the U.S.A. . The P-51, in all theaters, scored 5,954 victories, followed by the F6F with 5,168. Why we are so concerned with the fighter with the least victories in WWII in U.S. service? It was NOT a good airplane for anything other than short-range, low-altitude missions. We didn't fly many of those except to keep the P-39 drivers current in their airplanes.

 

[pbehn]

I make a motion we improve the forum by avioding the P-39 until such time as real-world use and results come into play.

If you look at aerial victories by type and theater, the legacy of the P-39 becomes apparent. First, let's remove the essentially non-participating fighters like the P-26, P-35, P-36, P-43, P-70, F2A, Beaufighter (lend-lease), TBF/TBM, P-61, and the SBD. That leaves the P-38, P-39, P-40, P-47, and P-51 (including F-6 and A-36), F4F/FM-2, F6F, and F4U, and Spitfire (only the MTO) which is most of our fighters.

If we just look at the Pacific, the Spitfire wasn't used by the U.S.A. and it drops out. The Lowest total victories is 288 by the P-39/P-400. Next would be 297 by the P-51 since it got to the Pacific essentially at the end of the war. The FM-2 is next at 422, followed by the P-40 with 661. It continues going up from there.

If we get out of the Pacific only and look at the entire war, the lowest victory tally is 321 by the P-39 / P-400, followed by the Spitfire in the MTO/ETO with 379, and it goes up from there.

The Mosquito, P-26, P-35, P-36, P-43, P-70, F2A, and Beaufighter only scored 58 victories combined, so they don't really count as major fighters in service with the U.S.A. . The TBF/TBM outscored them all combined with 98 victories, but isn't a fighter.

So, we have had 100+ pages and all this "it could have been a great airplane" about the fighter with the lowest score of any major fighter in service with the U.S.A. . The P-51, in all theaters, scored 5,954 victories, followed by the F6F with 5,168. Why we are so concerned with the fighter with the least victories in WWII in U.S. service? It was NOT a good airplane for anything other than short-range, low-altitude missions. We didn't fly many of those except to keep the P-39 drivers current in their airplanes.

Great post, I agree with all except the part in bold. for the USA the greatest use of the P-39 in my opinion was as an advanced trainer IN THE USA. There were 1934 accidents 369 were fatal and 865 airframes wrecked, that isnt a reflection on it as a trainer but more its level of use. Many pilots did advanced training in USA and then completed combat training "on type" in UK or elsewhere, they will not be on those statistics which are purely for USA. The accident numbers are completely out of proportion to its production numbers and combat use when compared against other US fighters. A trainer isn't a spectacular role, but someone has to do it and I can see a lot of advantages to tricycle U/C in a training centre. United States World War II Aircraft Loss Statistics during Flight Training

 

[GregP]

Verey good point, pbehn. The P-39 was often the first fighter that new pilots flew after advanced training. Naturally, it would be one of their favorites if not THE favorite since it had much higher performance than an AT-6, which was likely the highest-performance aircraft they had fown to date in training.

I should not have left out the training use of the aircraft.

Cheers.

 

[Shortround6]

"If you want to use 95% of the gross weight for the performance, fine use it.
BUT make sure the plane you are comparing to is also at 95% and not 100-102% That's how the AAF (and British) tested their planes. Full of fuel, but the quoted weight in the test was the average weight of the plane for that particular flight.
The P-39N will still beat the F6F-3, just not by as much."

I have tried to point out the difference before but you are not getting it.

The chart that you keep posting for the F6F-3 with your dots for the P-39N was for the F6F-3 at 12,500lbs.
trouble is that the gross weight for an F6F-3 with full internal fuel and ammo was from around 12,200 to 12,450lbs depending on the exact airplane (weights did vary a few percent) and exact outfit/fittings. Plane the chart is for had three bomb racks/drop tank stations/racks. The slightly lighter "standard" planes only had the center line station.
What is the performance of the F6F-3 at 11,600lbs? ie, 95%
Not as good as the P-39N but not as bad as your chart shows.

"and then we have the HUGE problem of the P-39 having no combat power rating at 20,000ft. It doesn't even have a full military power rating. Sure you can run it at 3000rpm but the supercharger will NOT supply even the 44.5in of MAP for military power. The engine can only make about 880-885 hp at 3000rpm. This is the big reason it has such good range at 20,000ft.
The engine isn't making any power. Even worse at 25,000ft. On that paltry horsepower the P-39 still did 385mph and climbed at 2650fpm at 20000ft. At 25000ft it did 370mph and climbed at 1950fpm. For 1943 the speed is good but the climb is excellent. Look at the P-39/F6F chart."

How about we look at the following.

Plane.................P-40N-1...............P-39M-3...............P-39N-1....................P-39Q-5.................P-51A.....................P-63A-9
weight................7413lbs................7430lbs................7274lbs......................7821lbs.................8000/7730lbs...........8950lbs.
Speed................371mph................373mph.............389.5mph....................371mph..................408mph..................400mph
altitude............17,300ft..................15,900ft..............16,100ft.......................15,000ft....................17,500ft.................16,000ft
power................1125hp...................1125hp...............1125hp.......................1140hp......................1125hp..................1285hp

climb
15,000ft.............2680fpm................2640fpm..............3340fpm...................2840fpm..................2610fpm................3390fpm
power..................1090hp...................1040hp.................1060hp....................1050hp......................1090hp..................1360hp.
20,000ft.............1970fpm.................2000fpm..............2630fpm...................2200fpm..................1980fpm...............2660fpm
power...................905hp.....................880hp...................885hp........................882hp.........................910hp...................1175hp
25,000ft.............1400fpm.................1400fpm..............1940fpm....................1570fpm..................1350fpm................2020fpm.
power................750hp.........................725hp....................745hp.........................740hp......................760hp.....................985hp.

All except the P-63 were using Allison engines with 9.60 supercharger gears. Fuel and ammo loads seemed to vary a bit.
Yes the P-39Q and the P-63 had the external .50 cal pods.
The P-39 has less drag than the P-40. The P-40 and P-51 seem to have better ram effect on their inlets?
The P-51A took off at 8000lbs but the speed ratings were at lower weight for each altitude.

All performance should be at altitudes where the WEP settings stop having any effect.
The P-63 is about 23% heavier than the P-39N, however the P-63 has 28-32% more power in the climb scenarios and 14% more power in the highspeed flight (it is a bigger airplane)

The P-39N seems to have a performance way, way out of line with the other planes that cannot be explained away with just a few hundred pounds of weight.
All planes and engines are going to vary a few percent.

You also need to figure out what a plane needs in order to maneuver at 20,000ft, while it is pretty much the same as lower altitudes things are getting further out. The stall speed is higher for one thing. You need to go faster in just level flight. Now bank 60 degrees (2 Gs) or more and if you are at anywhere near max speed you have to slow down or loose altitude. Maybe both. The lower wing loading airplanes have an advantage.
Nobody thought the P-51A was a high altitude plane even though it could hit 395mph at 25,000ft (at 7617lbs) because it could not sustain speed in a turn or regain speed or altitude quick enough after performing manuever/s.

 

[pbehn]

Verey good point, pbehn. The P-39 was often the first fighter that new pilots flew after advanced training. Naturally, it would be one of their favorites if not THE favirote since it had much higher performance than an AT-6, which was likely the highest-performance aircraft they had fown to date in training.

I should not have left out the training use of the aircraft.

Cheers.

The same could possibly be said about the P-51B and C. If it takes 200 hours to train a pilot on type and a Merlin needs a rebuild after 250 hours plus an airframe needs an overhaul after 500 hours, how many were worn out if not actually wrecked before they took off for a combat mission?

 

[Shortround6]

In planning your mission you have already deducted reserves for takeoff, combat and landing from total fuel. Use your drop tank for warmup and taxi, switch to internal for the actual takeoff, then back to the drop tank asap (normally less than a minute) so that your internal fuel should be almost full. After dropping the external tank (or turning for home if there is no combat) you should have full internal fuel including reserves for combat and landing. If there is no combat and landing goes smoothly there will still be the reserves for combat and landing in your internal tank.

Nobody would follow that procedure, on a routine basis, there is too much chance of error/problems. Every time you switch tanks (and the left and right tanks were selected separately, not together), there was a chance of sucking an air bubble.
While they often did not wait until they were at 5000ft to switch over common practice was to get the landing gear retracted and get enough altitude to either restart the engine if it stopped or to turn and dead stick the plane on the runway (or alternate runway). Most planes did route the excess fuel from the carb to one of the internal tanks so that it was slowly refilled in flight, This was to whatever tank on the airplane was also the reserve tank.
This procedure is actually more efficient because if the internal tank the return line is routed to is full the excess fuel is dumped overboard. Note that this is the only way to get fuel from the drop tank into the internal tank.
also note that if the selector switch (five positions----off, left, right, reserve, and belly tank) is set to the right tank the left tank will slowly refill in flight,
A long range flight could be conducted with just 5 tank switches,
1. start on reserve (left tank) switching from off.
2. after 20 minutes change to belly tank and run dry
3. change to right tank and run dry.
4. change to left tank and run dry.
5. change to reserve and land or bail out.
6th change is moving the tank selector back to off when shutting down the engine.

This is from the manual for the P-39K & L.

 

[Admiral Beez]

Hi P-39 Expert,

Damn, where's my P-39 filter?

How about early development and adoption of three blade, variable pitch props for the Spitfire and Hurricane? This may get us to an earlier Sea Hurricane, for starters.

 

[P-39 Expert]

"If you want to use 95% of the gross weight for the performance, fine use it.
BUT make sure the plane you are comparing to is also at 95% and not 100-102% That's how the AAF (and British) tested their planes. Full of fuel, but the quoted weight in the test was the average weight of the plane for that particular flight.
The P-39N will still beat the F6F-3, just not by as much."

I have tried to point out the difference before but you are not getting it.

The chart that you keep posting for the F6F-3 with your dots for the P-39N was for the F6F-3 at 12,500lbs.
trouble is that the gross weight for an F6F-3 with full internal fuel and ammo was from around 12,200 to 12,450lbs depending on the exact airplane (weights did vary a few percent) and exact outfit/fittings. Plane the chart is for had three bomb racks/drop tank stations/racks. The slightly lighter "standard" planes only had the center line station.
What is the performance of the F6F-3 at 11,600lbs? ie, 95%
Not as good as the P-39N but not as bad as your chart shows.

"and then we have the HUGE problem of the P-39 having no combat power rating at 20,000ft. It doesn't even have a full military power rating. Sure you can run it at 3000rpm but the supercharger will NOT supply even the 44.5in of MAP for military power. The engine can only make about 880-885 hp at 3000rpm. This is the big reason it has such good range at 20,000ft.
The engine isn't making any power. Even worse at 25,000ft. On that paltry horsepower the P-39 still did 385mph and climbed at 2650fpm at 20000ft. At 25000ft it did 370mph and climbed at 1950fpm. For 1943 the speed is good but the climb is excellent. Look at the P-39/F6F chart."

How about we look at the following.

Plane.................P-40N-1...............P-39M-3...............P-39N-1....................P-39Q-5.................P-51A.....................P-63A-9
weight................7413lbs................7430lbs................7274lbs......................7821lbs.................8000/7730lbs...........8950lbs.
Speed................371mph................373mph.............389.5mph....................371mph..................408mph..................400mph P-39 was the second most aerodynamic behind the P-51. Seems
altitude............17,300ft..................15,900ft..............16,100ft.......................15,000ft....................17,500ft.................16,000ft logical it would be the second fastest. BTW why include the P-63?
power................1125hp...................1125hp...............1125hp.......................1140hp......................1125hp..................1285hp It had a two stage engine.

climb
15,000ft.............2680fpm................2640fpm..............3340fpm...................2840fpm..................2610fpm................3390fpm
power..................1090hp...................1040hp.................1060hp....................1050hp......................1090hp..................1360hp.
20,000ft.............1970fpm.................2000fpm..............2630fpm...................2200fpm..................1980fpm...............2660fpm P-39 was the lightest of this group, logical that it had the best climb.
power...................905hp.....................880hp...................885hp........................882hp.........................910hp...................1175hp
25,000ft.............1400fpm.................1400fpm..............1940fpm....................1570fpm..................1350fpm................2020fpm.
power................750hp.........................725hp....................745hp.........................740hp......................760hp.....................985hp.

All except the P-63 were using Allison engines with 9.60 supercharger gears. Fuel and ammo loads seemed to vary a bit.
Yes the P-39Q and the P-63 had the external .50 cal pods.
The P-39 has less drag than the P-40. The P-40 and P-51 seem to have better ram effect on their inlets?
The P-51A took off at 8000lbs but the speed ratings were at lower weight for each altitude.

All performance should be at altitudes where the WEP settings stop having any effect.
The P-63 is about 23% heavier than the P-39N, however the P-63 has 28-32% more power in the climb scenarios and 14% more power in the highspeed flight (it is a bigger airplane)

The P-39N seems to have a performance way, way out of line with the other planes that cannot be explained away with just a few hundred pounds of weight.
All planes and engines are going to vary a few percent. So, we have another bad test? Those Wright Field test pilots could test every plane in the AAF inventory, but somehow all their P-39 tests were wrong?

You also need to figure out what a plane needs in order to maneuver at 20,000ft, while it is pretty much the same as lower altitudes things are getting further out. The stall speed is higher for one thing. You need to go faster in just level flight. Now bank 60 degrees (2 Gs) or more and if you are at anywhere near max speed you have to slow down or loose altitude. Maybe both. The lower wing loading airplanes have an advantage.
Nobody thought the P-51A was a high altitude plane even though it could hit 395mph at 25,000ft (at 7617lbs) because it could not sustain speed in a turn or regain speed or altitude quick enough after performing manuever/s.

Expand above.

 

[P-39 Expert]

Nobody would follow that procedure, on a routine basis, there is too much chance of error/problems. Every time you switch tanks (and the left and right tanks were selected separately, not together), there was a chance of sucking an air bubble.
While they often did not wait until they were at 5000ft to switch over common practice was to get the landing gear retracted and get enough altitude to either restart the engine if it stopped or to turn and dead stick the plane on the runway (or alternate runway). Most planes did route the excess fuel from the carb to one of the internal tanks so that it was slowly refilled in flight, This was to whatever tank on the airplane was also the reserve tank.
This procedure is actually more efficient because if the internal tank the return line is routed to is full the excess fuel is dumped overboard. Note that this is the only way to get fuel from the drop tank into the internal tank.
also note that if the selector switch (five positions----off, left, right, reserve, and belly tank) is set to the right tank the left tank will slowly refill in flight,
A long range flight could be conducted with just 5 tank switches,
1. start on reserve (left tank) switching from off.
2. after 20 minutes change to belly tank and run dry
3. change to right tank and run dry.
4. change to left tank and run dry.
5. change to reserve and land or bail out.
6th change is moving the tank selector back to off when shutting down the engine.

This is from the manual for the P-39K & L.

All AAF fighters had multiple internal tanks and carried external tanks. Procedure was the same on all of them.