Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained) (2 Viewers)

[P-39 Expert]

Can we get back to the ranges quoted in the pilot's manual?

The fuel from sea level figure from the Takeoff, Climb and Landing chart should not be used to compute range, or the instructions in the Flight Operation Instruction Chart (range chart) would say so.

The ranges in the range chart have already been adjusted down to reflect both the fuel used in climbing from 5000ft and the miles of range gained during the climb.

 

[Glider]

Please expand above.

Actually I (and in my opinion no one else) needs to expand on anything.

Lets sum it up

The P39N1 operating at temperatures that were higher than normal acceptable operating levels turned in a good performance but it should be noted that this was at the cost of a very low range and without any payload. This operating at above normal temperatures is no small thing. You can get away with it for a certain period of time but sooner or later it will bite you.

The Typhoon another aircraft of a similar era matched the performance of the P39N1 in the early years and comfortably exceed the performance of the P39N1 from early1944 on. It should also be noted that the Typhoon carrying 2,000lb of bombs had a greater range than the P39N1 when clean and about 1,000 miles with drop tanks.

There is no doubt that the P39N1 has a better performance than the Typhoon at 25,000 ft but the range of the P39N1 would be close to miserable at that altitude and the chances of a successful interception low, make that very low if your spotted when climbing up.
In the real world if you were fighting Typhoons then at 25,000 ft you would be taking on the Spit IX and good luck with that. Even the Spitfire had a better range than any version of the P39 from late 1944 on, and no one would claim that the range of the Spitfire was it's strength.

You can of course add additional fuel tanks but then you effectively end up with the P39Q which has a much lower performance. You can of course tweak the performance by removing the two 0.5 in the wings of the P39Q but that would make little difference to the speed. Worth noting that the Me109 with 2 x 20mm underwing guns only lost 8mph when carrying them and the 0.5 was a lot smaller so the difference is likely to be no more than 4 mph.

You have a lot of fantasies about how to change the performance of the P39. New engines, removing armour, adding fuel tanks, deleting equipment with hardly any evidence (because there is next to none that exists) to back up your assertions that such changes were Easy, Obvious, Simple, Straight forward. Yet has been pointed out to you on any number of occasions, tens of thousands of flight engineers, hundreds of engineers/designers at Bell and thousands of pilots many of whom fought and died in the P39. Educated, trained and experienced people who knew every bolt, cable and rivet in the aircraft didn't make those changes. Why, because they knew it couldn't be done. Yet you, with no training or experience know better than all these people

I was an Artificer in the Fleet Air Arm specialising in airframes and engines. This was a training regime that took five years and I know that your statements and assumptions are puerile. I use that word deliberately because if you look up the definition, it fits. There are many others on this forum with infinitely more training and experience than myself in aviation, these are people I listen too and learn from, people who have also told you with supporting evidence that its impossible. Yet you again, know better than all of us.

No, we do not need to expand , you need to expand to give evidence to support your massive assumptions, and/or explain why you have such omnipotent knowledge on this subject.

 

[Shortround6]

Can we get back to the ranges quoted in the pilot's manual?

The fuel from sea level figure from the Takeoff, Climb and Landing chart should not be used to compute range, or the instructions in the Flight Operation Instruction Chart (range chart) would say so.

The ranges in the range chart have already been adjusted down to reflect both the fuel used in climbing from 5000ft and the miles of range gained during the climb.

It depends on how you want to compute the range.

The USAAF, rightly or wrongly, in their comparisons charts did not credit any horizontal movement in the climb to 25,000 ft cruising altitude. This was to allow for forming up and rendezvousing with the bombers. If you want to come up a figure for range/radius to compare to the planes listed in the chart then you have to use the conditions the chart says.

You have yet to explain how a plane that reaches 5000ft gets to 20,000-25,000 without using addition fuel over and above the fuel needed to cruise at 5,000.

Please show in the manual or on the charts where it says " ranges in the range chart have already been adjusted down to reflect both the fuel used in climbing from 5000ft and the miles of range gained during the climb" It sure doesn't say that on the P-39Q charts.


If you wish to use your method of range commutation then please compute the ranges for the planes you are comparing to the same way.

BTW, everybody should read the fine print at the bottom of the Climb charts for all aircraft.

For some reason the US did not use standard temperature and pressure for these charts. They used 0 degrees C (32 degrees F) instead of 15 degrees C/59 degrees F.
Some charts, like the P-39Q chart leave the correction blank, other charts say 10% increase in climb time for EVERY 10 degrees C above 0.

 

[FLYBOYJ]

Can we get back to the ranges quoted in the pilot's manual?

The fuel from sea level figure from the Takeoff, Climb and Landing chart should not be used to compute range, or the instructions in the Flight Operation Instruction Chart (range chart) would say so.

The ranges in the range chart have already been adjusted down to reflect both the fuel used in climbing from 5000ft and the miles of range gained during the climb.

(Beating the horse)

So you're trying to tell us that if I'm going to plan a mission, I plan to fly to 5000' then plan my range? What if I want to take off and climb to 10,000 feet. what if I climb to 5000 feet and then decide to go 20,000? Do I do this flying in circles? Do I disregard the climb gradient? Can you show us where it specifically says on the chart "the ranges in the range chart have already been adjusted down to reflect both the fuel used in climbing from 5000ft and the miles of range gained during the climb"?

 

[FLYBOYJ]

It depends on how you want to compute the range.

The USAAF, rightly or wrongly, in their comparisons charts did not credit any horizontal movement in the climb to 25,000 ft cruising altitude. This was to allow for forming up and rendezvousing with the bombers. If you want to come up a figure for range/radius to compare to the planes listed in the chart then you have to use the conditions the chart says.

You have yet to explain how a plane that reaches 5000ft gets to 20,000-25,000 without using addition fuel over and above the fuel needed to cruise at 5,000.

Please show in the manual or on the charts where it says " ranges in the range chart have already been adjusted down to reflect both the fuel used in climbing from 5000ft and the miles of range gained during the climb" It sure doesn't say that on the P-39Q charts.


If you wish to use your method of range commutation then please compute the ranges for the planes you are comparing to the same way.

BTW, everybody should read the fine print at the bottom of the Climb charts for all aircraft.

For some reason the US did not use standard temperature and pressure for these charts. They used 0 degrees C (32 degrees F) instead of 15 degrees C/59 degrees F.
Some charts, like the P-39Q chart leave the correction blank, other charts say 10% increase in climb time for EVERY 10 degrees C above 0.

You beat me to the punch!

 

[Shortround6]

"Wings had the SPACE to mount fuel tanks where the wing guns were mounted. "

You would have space in two dimensions. Now the question is it was smart.

Fuel tanks fitted between the forward spar and the Main spar, the distance narrows between the spars the further out you go.
The wing gets thinner there further out you go. The wing at the W-2 position indicated on the drawing is less than 8 inches thick at max, it is a bit thicker where the machine guns are.

Self sealing fuel tank material is pretty much constant thickness and weight per sq ft. A long, skinny, thin tank is going to use a lot more self sealing material than a short fat tank of the same capacity. a tank with an assumed thickness of 6.5 inches (allowing for Self sealing material as a guess, corrections welcome) you need almost 2 sq feet of tank to hold ONE gallon.
Granted that is worst case, but it shows that fuel tanks in the last few feet of a wing are poor proposition. Lots of tank weight for not that big an increase in fuel. A tank at mid point in the wing may hold 50 % more fuel per sq ft of wing area than tank in the outer wing for the same weight of self sealing material due to being thicker.
when outer wing tanks are full role response is poor.


"N was not a low altitude plane."

Engine peaked at 15,000ft or so. Yes there were lower altitude planes but many fighters had engines that peaked in the 20,000ft foot range.
Spitfire II engine peaked 17,500ft in the summer of 1940.

edit: I made a mistake in estimating the area of wing needed per gallon of fuel, it is actually about 1/4 of a square foot.
However the thicker part of the wing will still hold more fuel for the same amount of (or nearly) of self sealing material. More weight in the wing tips means poor roll response.

 

[FLYBOYJ]

For some reason the US did not use standard temperature and pressure for these charts.

And that is why (from the charts I was working with) I was stating you can't use true air speed. The chart gave no conversion or no instructions to do so.

"Wings had the SPACE to mount fuel tanks where the wing guns were mounted. "

You would have space in two dimensions. Now the question is it was smart.

Also consider that if it was done you're looking at a stress analysis of the area and more than likely more reinforcing, unless you limit maneuvers, don't self seal the tanks and fly that fuel off first. (Thinking out loud, giving every opportunity for the old dog to succeed)

 

[GregP]

The area behind the cockpit is not hard to access, but you have to pull the engine access panels to get to the engine. You might have to pull a panel above and / or below the aux-stage supercharger to get to it, but it should not require frequent service. The visibility rearward was not great. If you look straight back, you might see the carb-S/C airscoop, but the view rearward was generally not great.

For radio access, I THINK you can open up one or both of the rear canopy sides pretty easily, but will have to check that next Tuesday. I SHOULD have checked that when I took the pics. I was working on the P-63 yesterday, but I was under the belly, not on top. I was fitting a new belly panel that covers the drop tank connection. Not exactly a vital restoration task, but the devil is in the details. The airplane is coming along very nicely. I am not a regular member of the restoration crew, and was helping make new cowling internal connections (Dzus panels) for a Grumman Mallard until that P-63 panel needed to be fitted.

Cheers everyone. Have a great weekend!

 

[SaparotRob]

When I read Gregp's (not Greg) posts, I am reminded of the Packard Automobile advertisements.
"Ask the man who owns one."

 

[GregP]

I very definitely do NOT own a P-63. But Yanks Air Museum does. I am not a regular crew member, but get to it almost every day I am in there. They have some very interesting aircraft and items. For instance, they have a main landing gear from a Bf 110 displayed. I've never seen anything else from a real, live Bf 110, so it is interesting.

I'll ask about posting some pics and, if they say it is OK, I'll do it. If they say not to, I won't.

 

[SaparotRob]

"I very definitely do NOT own a P-63."
Close enough.

 

[FLYBOYJ]

The area behind the cockpit is not hard to access

Hey Greg, to clarify, area behind the cockpit behind the pilot's head. That's where radios or IFF would go

 

[pbehn]

There is no doubt that the P39N1 has a better performance than the Typhoon at 25,000 ft but the range of the P39N1 would be close to miserable at that altitude and the chances of a successful interception low, make that very low if your spotted when climbing up.
In the real world if you were fighting Typhoons then at 25,000 ft you would be taking on the Spit IX and good luck with that. Even the Spitfire had a better range than any version of the P39 from late 1944 on, and no one would claim that the range of the Spitfire was it's strength.
.

I doubt it if you apply the same principles of taking out things that weigh a lot. Take the armour cannon and IFF out of a Typhoon and how does it go? Comparing to a 1943 P-39N why not compare to a Tempest Mk V, first production aircraft flew June 21 1943.

 

[FLYBOYJ]

My bold/italics.

I think this sums up the P-39/63 pretty well. When I read Yeager's autobiography back in the '80's, I got the impression it was a pretty good plane to fly, but not to fight in. Although he did say that he would have happily gone to war in it if he had to. Now a guy like that would probably do alright in it but I doubt he would want to take it above 20,000 feet and fight. Who would?

Also in what environment? England? Port Moresby? Guadalcanal? Africa?

 

[GregP]

Hi FBJ,

The museum P-39 has a radio there (old radio, not modern). I have never seen a P-63 with an original radio mounted there, but have also not exactly been looking for that feature, either.

A short search in Google came up with this:

Now, that LOOKS like a radio to me, but it could be a dishwasher for all I know about it. I'm betting radio, though. That is only one pic, and I didn't really see many others with an old black box in that location. If you had any rearward visibility, that would seem to take care of removing it, wouldn't it? On the plus side, you can see the rear canopy is held in with Dzus fasteners, offering access to the radio.

Incidentally, the panel I was trying to fit yesterday on the P-63 covers up the connection hole in the belly for the tank shown above. I didn't get it finished, but fitting a panel and getting the Dzus fastener holes lined up exactly is not a really fast undertaking. It is easier if you have an existing panel to copy, but we are fitting one from scratch, without any drawing. So, some good old head scratching is required.

The pic shows up in my edit window, but not when I post, so I'll try a link;

https://www.skytamer.com/1.2/2009/20090113-318.jpg

 

[Shortround6]

don't self seal the tanks and fly that fuel off first. (Thinking out loud, giving every opportunity for the old dog to succeed)

Possible, but you still have flammable fumes in the tank space unless you fit a purge system. Nitrogen, CO2 or cooled engine exhaust.

 

[DerAdlerIstGelandet]

Actually I (and in my opinion no one else) needs to expand on anything.

Lets sum it up

The P39N1 operating at temperatures that were higher than normal acceptable operating levels turned in a good performance but it should be noted that this was at the cost of a very low range and without any payload. This operating at above normal temperatures is no small thing. You can get away with it for a certain period of time but sooner or later it will bite you.

The Typhoon another aircraft of a similar era matched the performance of the P39N1 in the early years and comfortably exceed the performance of the P39N1 from early1944 on. It should also be noted that the Typhoon carrying 2,000lb of bombs had a greater range than the P39N1 when clean and about 1,000 miles with drop tanks.

There is no doubt that the P39N1 has a better performance than the Typhoon at 25,000 ft but the range of the P39N1 would be close to miserable at that altitude and the chances of a successful interception low, make that very low if your spotted when climbing up.
In the real world if you were fighting Typhoons then at 25,000 ft you would be taking on the Spit IX and good luck with that. Even the Spitfire had a better range than any version of the P39 from late 1944 on, and no one would claim that the range of the Spitfire was it's strength.

You can of course add additional fuel tanks but then you effectively end up with the P39Q which has a much lower performance. You can of course tweak the performance by removing the two 0.5 in the wings of the P39Q but that would make little difference to the speed. Worth noting that the Me109 with 2 x 20mm underwing guns only lost 8mph when carrying them and the 0.5 was a lot smaller so the difference is likely to be no more than 4 mph.

You have a lot of fantasies about how to change the performance of the P39. New engines, removing armour, adding fuel tanks, deleting equipment with hardly any evidence (because there is next to none that exists) to back up your assertions that such changes were Easy, Obvious, Simple, Straight forward. Yet has been pointed out to you on any number of occasions, tens of thousands of flight engineers, hundreds of engineers/designers at Bell and thousands of pilots many of whom fought and died in the P39. Educated, trained and experienced people who knew every bolt, cable and rivet in the aircraft didn't make those changes. Why, because they knew it couldn't be done. Yet you, with no training or experience know better than all these people

I was an Artificer in the Fleet Air Arm specialising in airframes and engines. This was a training regime that took five years and I know that your statements and assumptions are puerile. I use that word deliberately because if you look up the definition, it fits. There are many others on this forum with infinitely more training and experience than myself in aviation, these are people I listen too and learn from, people who have also told you with supporting evidence that its impossible. Yet you again, know better than all of us.

No, we do not need to expand , you need to expand to give evidence to support your massive assumptions, and/or explain why you have such omnipotent knowledge on this subject.

 

[Shortround6]

I may have done the math wrong but I seem to get about 211hp needed to lift a 7000lb weight 5,000ft in 5 minutes. If this is anywhere near right (correction more than welcome) this would be in addition to whatever power the plane needs to maintain a certain speed at a given altitude. Or about 10.55 gallons of fuel (211 hp X 0.6 lbs per hp hour divided by 12 (for the 5 minutes) in addition to the fuel burned to cruise at level flight.

Is this wrong?

 

[GregP]

From pure physics, 1 hp = 33,000 ft-lbs/ 1 min, so lifting 7,000 lbs a distance of 5,000 feet in 5 minutes should take 212.12 hp. But that would be using something like a pulley block and tackle. For airplanes, the formula above is much more that lifting a weight. But, you know that.

I went to wwiaircraftperformance.org and found a P-39 test dated 17 Jul 41. It is a P-39C (SN: 40-2988).

The test data showed 1,150 hp available from 0 - 5000 feet, and a constant rate of climb between those altitudes of 3,720 fpm. The aircraft came in at 6,689 pounds. Using a standard rate of climb formula: RC = 33,000 * ((PA - PR)/(W)), where PA = power available (hp), PR = power required for level flight (hP), W = weight (lbs), I get 3,720 fpm when the power required for level flight is equal to 395.97 hp. That leaves 754 excess horsepower to get 3,720 fpm. This takes into account for coefficient of lift, the relative efficiency of the propeller airfoil, makiing lift from forward airspeed, etc.

Formula from Aerodynamics for Naval Aviators, as I recall. This is, of course, a slightly better than first-order estimate. Still, it lets you make an estimate of rate of climb improvements with additional power. So, if we went from 1,150 hp to 1,325 hp in the same airplane at the same weight, we'd expect 4,583 fpm rate of climb. The thing is, I doubt there is much utility in a P-39C at 6,689 pounds. There isn't much fuel nor much ammunition.

Cheers, SR6!

Oh, and let me know if I missed any math in there, too. I make enough mistakes to know it can happen again!

 

[P-39 Expert]

Actually I (and in my opinion no one else) needs to expand on anything.

Lets sum it up

The P39N1 operating at temperatures that were higher than normal acceptable operating levels turned in a good performance but it should be noted that this was at the cost of a very low range and without any payload. This operating at above normal temperatures is no small thing. You can get away with it for a certain period of time but sooner or later it will bite you. P-38, P-47 and P-51 also had higher than acceptable operating temperatures. See my past post in this thread.

The Typhoon another aircraft of a similar era matched the performance of the P39N1 in the early years and comfortably exceed the performance of the P39N1 from early1944 on. It should also be noted that the Typhoon carrying 2,000lb of bombs had a greater range than the P39N1 when clean and about 1,000 miles with drop tanks. Not sure where you are getting this range figure, Typhoon had a huge engine and not a large fuel capacity. And by 1944 the P-39 should have had a two stage engine. I'm talking about 1943.

There is no doubt that the P39N1 has a better performance than the Typhoon at 25,000 ft but the range of the P39N1 would be close to miserable at that altitude and the chances of a successful interception low, make that very low if your spotted when climbing up. Range of a 120gal P-39N with a 110gal drop tank is about the same as a 1943 P-47 with the same drop tank. Long previous thread about that. Still, not great range but more fuel could be carried internally.
In the real world if you were fighting Typhoons then at 25,000 ft you would be taking on the Spit IX and good luck with that. Even the Spitfire had a better range than any version of the P39 from late 1944 on, and no one would claim that the range of the Spitfire was it's strength. Uh, what 1943 plane could take on a Spit IX? Ultralight plane with a two stage Merlin, I have always stated that a P-39N couldn't keep up with a Spitfire IX at high altitude. Good thing we weren't fighting Spitfire IXs.

You can of course add additional fuel tanks but then you effectively end up with the P39Q which has a much lower performance. You know that adding fuel to the wing would mean removing the wing guns, right? About the same weight. You can of course tweak the performance by removing the two 0.5 in the wings of the P39Q but that would make little difference to the speed. Exactly 14mph per wwiiaircraftperformance.org. I'll take it. Worth noting that the Me109 with 2 x 20mm underwing guns only lost 8mph when carrying them and the 0.5 was a lot smaller so the difference is likely to be no more than 4 mph. 14 mph, look at the tests.

You have a lot of fantasies about how to change the performance of the P39. New engines, removing armour, adding fuel tanks, deleting equipment with hardly any evidence (because there is next to none that exists) to back up your assertions that such changes were Easy, Obvious, Simple, Straight forward. Yet has been pointed out to you on any number of occasions, tens of thousands of flight engineers, hundreds of engineers/designers at Bell and thousands of pilots many of whom fought and died in the P39. Educated, trained and experienced people who knew every bolt, cable and rivet in the aircraft didn't make those changes. Why, because they knew it couldn't be done. Yet you, with no training or experience know better than all these people I believe the Soviets made almost exactly these changes and defeated the Luftwaffe with it.

I was an Artificer in the Fleet Air Arm specialising in airframes and engines. This was a training regime that took five years and I know that your statements and assumptions are puerile. I use that word deliberately because if you look up the definition, it fits. There are many others on this forum with infinitely more training and experience than myself in aviation, these are people I listen too and learn from, people who have also told you with supporting evidence that its impossible. Yet you again, know better than all of us. All I know is what is in wwiiaircraftperformance.org, pilots manuals, Vee's for Victory, Soviet history and some hearsay from men like Chuck Yeager. And I don't know what puerile means. And you misspelled specializing.

No, we do not need to expand , you need to expand to give evidence to support your massive assumptions, and/or explain why you have such omnipotent knowledge on this subject.

Please expand above.