XP-39 II - The Groundhog Day Thread

[P-39 Expert]

Not all VVS squadrons removed the wing guns

No, I'm sure they didn't. I'm also sure that those that kept the wing guns didn't climb as well as those that discarded them.

 

[fubar57]

Your words, "They removed the wing guns and IFF radio equipment, not the voice radios. They removed the .30s and beat the Luftwaffe, but the AAF never did remove the .30s." You would be more correct to say some removed the wing guns. Your words make it sound like it was across the entire airforce

 

[P-39 Expert]

The gearbox armor was 71 pounds out of 172 pounds of armor exculding the windscreen glass. If you add in the wing guns and wing gun ammuntion, that is only 503 pounds, not 1,500 pounds. Is there something you are missing here?

The empty weight of the P-39Q was 5,684 pounds. Then you add windscreen glass, armor, guns and ammunition, oil, fuel, pilot, and parachute. The total useful load was 1,886 pounds, guy, and the pilot was 200 pounds of the 1,886. Remove the pilot and you have 1,686 pounds of armor, guns, ammo, oil, and fuel. We need the oil. We need the fuel. If we don;t have guns and ammo, we might as well not take off. If we ditch ALL the armo, we only save 172 pounds.

Either you are not reading the weight and balance, not reading the posts, or are just being a troll.

Which is it? Help us out here. If you want to remove anything, identify it specifically. Please don't suggest leaving out the oil or fuel or pilot.

If I remove ALL the armor, I can take off just fine. But if I shoot all the ammunition, then I am out of CG aft, not good. Are you understanding this?

You are talking about the P-39Q, but the AAF South Pacific doc was talking about the P-39K. It said that they removed 600+lbs. The print is blurry, I think it said 650lbs but the middle number is illegible. So what did they remove?

Back in the footnotes it describes the P-39K as having 4 .30s in the wings with 1000rounds per gun. Remove those and you save about 400lbs if you include the mounts, chargers, heaters and ammunition boxes. Keep the voice radio and remove the IFF radio which AHT said weighed 110-130lbs. That radio was in the tail so now you need to remove the nose armor, about 71lbs. Now we're pretty close to 600lbs and still within CG. Now this is just a suggestion, I have no way of knowing exactly what was removed.

With 1000rounds per gun for the .30s the normal P-39K weighed about 7850lbs. Reduce that by the 650lbs and the K model now weighs about 7200lbs. with the 37mm cannon, two .50cal MGs, self sealing fuel tanks, armor plate/glass protection for the pilot and oil tank and a voice radio. The AAF South Pacific doc said that the K would now fight at 27000', probably meaning it would still climb at 1000fpm. Certainly adequate for intercepting Japanese bombers and fighting the A6M2.

Should have been done much earlier.

 

[P-39 Expert]

Your words, "They removed the wing guns and IFF radio equipment, not the voice radios. They removed the .30s and beat the Luftwaffe, but the AAF never did remove the .30s." You would be more correct to say some removed the wing guns. Your words make it sound like it was across the entire airforce

One of our friends on this board found a statistic that something like 85% of the Russian P-39s had their wing guns removed. And I'm sure that some of the AAF P-39s had their wing guns removed, but not many.

Do you nitpick every generalization? Or just the ones I make?

 

[fubar57]

Just make correct statements and all is good regardless of who you are

 

[pbehn]

Just make correct statements and all is good regardless of who you are

Many statements are correct, a specific reduction in weight may give a specific increase in climb of 100ft/minute. But that means in ten minutes you have an advantage equal to 3/4 of a lap of a running track, it is all nitpicking. From what I read pilots couldnt tell if they were even higher or lower by a 1000ft at long visual range.

 

[BiffF15]

Many statements are correct, a specific reduction in weight may give a specific increase in climb of 100ft/minute. But that means in ten minutes you have an advantage equal to 3/4 of a lap of a running track, it is all nitpicking. From what I read pilots couldnt tell if they were even higher or lower by a 1000ft at long visual range.

It's very difficult to tell the altitude of another airplane that's more than a few miles away. The difficulty lies in the true horizon line isn't visible to the eye. The one you see is at the edge of your visual acuity, not the true line. With that in mind, guys tend to use the one we see and use that as level with us. It's below and by how much varies with the range away from us the target aircraft is. In the Eagle the HUD displays the true horizon line, and it's about 2" above the visible line.

Airliners have Traffic Collision Avoidance System (TCAS) and in my airliner displays difference in altitude of other aircraft as plus or minus in thousands of feet (and hundreds if close enough IIRC).

Cheers,
Biff

 

[pbehn]

It's very difficult to tell the altitude of another airplane that's more than a few miles away. The difficulty lies in the true horizon line isn't visible to the eye. The one you see is at the edge of your visual acuity, not the true line. With that in mind, guys tend to use the one we see and use that as level with us. It's below and by how much varies with the range away from us the target aircraft is. In the Eagle the HUD displays the true horizon line, and it's about 2" above the visible line.

Airliners have Traffic Collision Avoidance System (TCAS) and in my airliner displays difference in altitude of other aircraft as plus or minus in thousands of feet (and hundreds if close enough IIRC).

Cheers,
Biff

They are human senses, touching a straw bale with your shoulder going through a chicane at 90MPH at Carnaby feels a lot faster than blasting down the back straight at Silverstone at 130 MPH which at times felt oddly like standing still. When I have been high up in a civilian aircraft looking at others I could see, when the ground is 40,000 ft below you have no idea whether they are higher or lower and as far as I know they were probably not at the same height (due to safety protocols) but most of them seemed to be.

 

[GregP]

It has BEEN expanded on, P-39 Expert. Nothing more is needed.

 

[Ivan1GFP]

Weight was actually only reduced by 600+lbs which allowed the P-39K to fight at 27000'. Best Japanese bombers G4M came in at 18000'-22000'.

Service ceiling of 27,000 feet does NOT mean the P-39K can fight there. It just means that it can FINALLY reach 27,000 feet.

- Ivan.

 

[XBe02Drvr]

the K would now fight at 27000', probably meaning it would still climb at 1000fpm. Certainly adequate for intercepting Japanese bombers and fighting the A6M2.

Whoever wrote that document must have been a number crunching ground pounder, certainly not a combat pilot. While a P39 that had been able to straggle it's way up to 27000' could probably manage an insipid diving firing pass on bombers several thousand feet below, there's no way a P39 with its single stage, single speed Allison, its inefficient airfoil, and its higher wing loading is going to fight effectively against an A6M2, with its higher lift, lower drag, and lighter loaded wing, despite the fact its engine performance will be degraded as much as the Cobra's.
Standard format flight test reports will give you all sorts of interesting numbers, but they can't measure combat performance. Aggressively maneuvering an airplane near its service ceiling is a lot like driving a car fast around a race course on glare ice. The margin of control is pretty slender. It was a lot of fun, back in the day.

PS: How many pages does it take for a thread to qualify for the EPIC category? Think this one will make it someday?

 

[wuzak]

Back in the footnotes it describes the P-39K as having 4 .30s in the wings with 1000rounds per gun. Remove those and you save about 400lbs if you include the mounts, chargers, heaters and ammunition boxes. Keep the voice radio and remove the IFF radio which AHT said weighed 110-130lbs. That radio was in the tail so now you need to remove the nose armor, about 71lbs. Now we're pretty close to 600lbs and still within CG. Now this is just a suggestion, I have no way of knowing exactly what was removed.

AHT says 110-130lb for "Other (Radio)". It does not say that was for IFF only, but for radio equipment, which may be more than one type and multiple units, the difference in weight is possibly due to differences in the types being carried.

 

[P-39 Expert]

Service ceiling of 27,000 feet does NOT mean the P-39K can fight there. It just means that it can FINALLY reach 27,000 feet.

- Ivan.

As has been explained before, a standard P-39D/F/K/L at normal weight before any weight reduction had a service ceiling of over 30000' as defined by still climbing at 100fpm. The term "service ceiling" was obviously being used incorrectly in the AAF South Pacific report. Why would the General be pleased that a P-39K that had been lightened by 650lbs have a "service ceiling" below that of a standard P-39K? The meaning of "service ceiling" in the report obviously referred to an altitude at which the plane could fight.

 

[P-39 Expert]

AHT says 110-130lb for "Other (Radio)". It does not say that was for IFF only, but for radio equipment, which may be more than one type and multiple units, the difference in weight is possibly due to differences in the types being carried.

AHT actually says "Misc Equip-Radio" 129lbs in the "Basic Weight" section along with the guns and armor plate. In the "Empty Weight" section "Communication" is listed at 80lbs. Leads me to believe "communication" was the voice radio.

 

[Milosh]

As has been explained before, a standard P-39D/F/K/L at normal weight before any weight reduction had a service ceiling of over 30000' as defined by still climbing at 100fpm. The term "service ceiling" was obviously being used incorrectly in the AAF South Pacific report. Why would the General be pleased that a P-39K that had been lightened by 650lbs have a "service ceiling" below that of a standard P-39K? The meaning of "service ceiling" in the report obviously referred to an altitude at which the plane could fight.

... because the atmospherics are different in different parts of the world. That is why you see "adjusted to standard atmosphere" of data sheets.

 

[P-39 Expert]

Many statements are correct, a specific reduction in weight may give a specific increase in climb of 100ft/minute. But that means in ten minutes you have an advantage equal to 3/4 of a lap of a running track, it is all nitpicking. From what I read pilots couldnt tell if they were even higher or lower by a 1000ft at long visual range.

And a larger reduction in weight would give a larger increase in climb, right?

 

[P-39 Expert]

This is simply not true. By 1943 the single stage Griffon Spitfire was in service, the Alisson engine P-51 was superior to the P-39. There is the Typhoon the P-47 how does it compare to the Hellcat and Corsair? A clipped and cropped late model Spitfire MkV was a good performer at low level on higher octane and boost, it would do a lot better if you take the cannons and armour out of it but that was specified military equipment, this discussion has been part of the P-39 history since the moment it arrived on UK shores, it is why they only did one mission from UK and all were then sent to Russia.

According to the tests, the P-39N (available from Nov 1942) outclimbed the Griffon Spitfire and was about the same speed. The N would substantially outclimb the P-51A (same engine) and was very close in top speed. The N outclimbed the 1943 Thunderbolt, Corsair and Hellcat substantially at 20000', just like I said. The P-39N was equipped with full armament including the wonderful four .30s for the tests, no weight reduction needed.

 

[pbehn]

And a larger reduction in weight would give a larger increase in climb, right?

Yes, strap a pilot to the engine and it will take off vertically, give him a colt revolver to confront the enemy. It is clear you think climb is everything, you even consider the P-39 to be superior to all other planes in service in 1943 because of it, it is no longer a serious discussion. No one in 1943 saw the P-39 as an answer to anything except possibly the need for trainers. I see you have re booted the discussion back to the start with "the British put unnecessary weight on it". Every possible thing that can be discussed has been on this and other threads. Yes taking weight off improves performance, taking guns and armour off a military machine does not improve performance because it becomes less of a military machine, quoting survivor bias is no answer to the issue.

 

[Peter Gunn]

If nothing else, this thread has been good for garnering positive ratings such as BACON - WINNER - AGREE and of course plain old LIKEs.

 

[pbehn]

If nothing else, this thread has been good for garnering positive ratings such as BACON - WINNER - AGREE and of course plain old LIKEs.

This topic has been discussed longer than the P-39 was in service.