Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained) (1 Viewer)

P-39 Expert · Jul 8, 2021

Shortround6 said:
The 7100lbs is quite a trick.
Take a P-30D-1 and take out the wing guns (95lbs) and 115lbs of armor (leaving you with the armor & BP glass of a P-39C) and you get just over 6400lbs of tactical empty aircraft.

Now we can add fuel and ammo.

120 gallons of fuel is 720lbs OOPS, we are over 7100lbs.
118 gallons of fuel? OOPS we have no ammo.
160lbs worth of ammo (no .30 cal), we are down to 91 gallons of fuel

Oh yeah, forgot about about the 88lbs worth of ballast weights.
No problem, just don't put in any ammo for one of the .50 cal guns and leave out another 4 1/2 gallons of fuel.
well we can take out one 50cal since we don't have ammo for it.
and put back in about 12 gallons of fuel.

May I present you with the
Superfighter P-400
one 20mm with 60 rounds and one .50 cal with 200 rounds.
about a gallon less fuel than a Spitfire.

Yeah, I can see the British jumping all over that one.

Edit: If you take out one .50 cal and 200rounds of .50 cal ammo how much ballast do you have to put back in?

Not much of a trick really. Figures from AHT. Would do columns, but I can't seem to make columns work.

P-400 empty 5550, 2x50cals 139, ammo 200rds/gun 129, 20mm 127, ammo 32, armor plate/glass (as P-39N w/o nose armor) 122, oxygen and gunsight 11, pilot/chute 160, fuel (120gal) 720, oil 71, total 7061. Deduct 50 from armament provisions (205 in empty weight since you don't have the 30cal wing guns) and total weight is 7011. This plane would have worked well in NG since radar wouldn't be there until fall '42 and by then newer models would be available. For service in GB add the 110lb IFF set for a total of 7121. Personally I would like a total of 120rds of 20mm ammo Like the Spitfire) so add another 32lbs.

Go here to see what a 7075lb P-39 will do. http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2988.pdf Climb would have been 3720fpm up to 12400' (critical alt. for -35 engine as in the P-39D/D-1/F/K/L).

Noe before I get jumped for the circular argument please note that I am just responding to Shortround's post.

pbehn · Jul 8, 2021

P-39 Expert said:
Not much of a trick really. Figures from AHT. Would do columns, but I can't seem to make columns work.

P-400 empty 5550, 2x50cals 139, ammo 200rds/gun 129, 20mm 127, ammo 32, armor plate/glass (as P-39N w/o nose armor) 122, oxygen and gunsight 11, pilot/chute 160, fuel (120gal) 720, oil 71, total 7061. Deduct 50 from armament provisions (205 in empty weight since you don't have the 30cal wing guns) and total weight is 7011. This plane would have worked well in NG since radar wouldn't be there until fall '42 and by then newer models would be available. For service in GB add the 110lb IFF set for a total of 7121. Personally I would like a total of 120rds of 20mm ammo Like the Spitfire) so add another 32lbs.

Go here to see what a 7075lb P-39 will do. http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2988.pdf Climb would have been 3720fpm up to 12400' (critical alt. for -35 engine as in the P-39D/D-1/F/K/L).

Noe before I get jumped for the circular argument please note that I am just responding to Shortround's post.

Do you believe that test? From sea level to rated altitude the rate of climb was the same, a completely linear plot? And at 25,000ft the RoC was almost 1,000ft min?

The time to climb to 25,000ft is exactly the same as a Spitfire I with Merlin MkIII and Rotol prop, but 1.4 mins less than a Spitfire II with Merlin XII Spitfire Mk IIA Performance Testing

Thumpalumpacus · Jul 8, 2021

Shortround6 said:
My opinion, somebody over speced the ammunition load. At full cycle rate they had 50 (five zero) seconds of firing time for the .30 cal guns. 300 rounds gives 15 seconds. The 20mm gun had 6 seconds. The 37mm with 30 rounds had 12 seconds. The .50 cals had around 20 seconds depending on actual rate of fire. Perhaps 300 rounds may not be enough, but anything over 500 rounds was probably too much.

The whole thing shows the balance between ammo carriage, gunnery, and hitting-power. Is fifteen seconds of thirty-cal sufficient for more than one target? Six seconds of 20-mm seems to make a big demand on gunnery training, too.

P-39 Expert · Jul 8, 2021

pbehn said:
Do you believe that test? From sea level to rated altitude the rate of climb was the same, a completely linear plot? And at 25,000ft the RoC was almost 1,000ft min?

The time to climb to 25,000ft is exactly the same as a Spitfire I with Merlin MkIII and Rotol prop, but 1.4 mins less than a Spitfire II with Merlin XII Spitfire Mk IIA Performance Testing

Yes, actually better than that.

pbehn · Jul 8, 2021

P-39 Expert said:
Yes, actually better than that.

But actually not, that was the issue, the P-39 as delivered was nowhere near its obviously fake test reports. If it was as good as you claim it wouldnt have had such a negative reception, and wouldnt have had you arguing for years about taking weight off. Look at the link I posted, climb is not linear, they put an average in the test report for the P-39, the same average as the Spitfire, complete horse crap, like the 400MPH top speed.

P-39 Expert · Jul 8, 2021

pbehn said:
But actually not, that was the issue, the P-39 as delivered was nowhere near its obviously fake test reports. If it was as good as you claim it wouldnt have had such a negative reception, and wouldnt have had you arguing for years about taking weight off. Look at the link I posted, climb is not linear, they put an average in the test report for the P-39, the same average as the Spitfire, complete horse crap, like the 400MPH top speed.

Fake test report? That's a Wright Field official test. Just like most of the other tests on wwiiaircraftperformance.org. That's what Wright Field did, they ran official performance tests for the AAF. Seriously?

buffnut453 · Jul 8, 2021

P-39 Expert said:
Fake test report? That's a Wright Field official test. Just like most of the other tests on wwiiaircraftperformance.org. That's what Wright Field did, they ran official performance tests for the AAF. Seriously?

You've ignored a whole host of real-world data that didn't match your world view. It's pretty rich of you to criticize anyone else for behaving in exactly the same way.

GrauGeist · Jul 8, 2021

There's a reason why the Army guys in the PTO nicknamed the P-400 a "P-40 with a Zero on it's tail"...

FLYBOYJ · Jul 8, 2021

P-39 Expert said:
Noe before I get jumped for the circular argument please note that I am just responding to Shortround's post.

And note that because of some of your outrageous claims, you're an open target providing it stays somewhat civil and I commend our replying membership for showing some restraint.

FLYBOYJ · Jul 8, 2021

P-39 Expert said:
Fake test report? That's a Wright Field official test. Just like most of the other tests on wwiiaircraftperformance.org. That's what Wright Field did, they ran official performance tests for the AAF. Seriously?

But it was flown by "Joe Pilot"

wuzak · Jul 8, 2021

P-39 Expert said:
Fake test report? That's a Wright Field official test. Just like most of the other tests on wwiiaircraftperformance.org. That's what Wright Field did, they ran official performance tests for the AAF. Seriously?

Was it an actual production line example, or one specially prepared for the test?

And maybe not in the configuration that was ordered.

A few of the test reports on wwiiaircraftperformance.org start with " Report on flight tests of Bell P-39X airplane at the manufacturer's plant.". Does this mean that it was tested by the company and the report relayed to the USAAF via Wright Field? Or did Wright Field test the plane, but since it was at the manufacturer's plant it may have been souped up?

Shortround6 · Jul 8, 2021

P-39 Expert said:
Not much of a trick really. Figures from AHT. Would do columns, but I can't seem to make columns work.

P-400 empty 5550, 2x50cals 139, ammo 200rds/gun 129, 20mm 127, ammo 32, armor plate/glass (as P-39N w/o nose armor) 122, oxygen and gunsight 11, pilot/chute 160, fuel (120gal) 720, oil 71, total 7061. Deduct 50 from armament provisions (205 in empty weight since you don't have the 30cal wing guns) and total weight is 7011. This plane would have worked well in NG since radar wouldn't be there until fall '42 and by then newer models would be available. For service in GB add the 110lb IFF set for a total of 7121. Personally I would like a total of 120rds of 20mm ammo Like the Spitfire) so add another 32lbs.

Go here to see what a 7075lb P-39 will do. http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2988.pdf Climb would have been 3720fpm up to 12400' (critical alt. for -35 engine as in the P-39D/D-1/F/K/L).

Noe before I get jumped for the circular argument please note that I am just responding to Shortround's post.

You know, even in New Guinea the US pilots might have like to have a radio. Just maybe they would like to talk to the other plane or to their base? Wing waggling as a form of communication is rather over rated.
This was the radio the US used in some of it's P-39s.

File:SCR-522 Data.png - RadioNerds

radionerds.com

About 90lbs

The weight charts in the P-39D-1/D-2 manual specify the radios by model number.

This has been gone over in some of the previous posts.
The IFF weighed around 45lbs How much is the actual unit and how much is in "electrical" and how much is in "furnishings" I don't know.

I Have no idea why but in AHT the P-400 has 205lbs of "armament provisions" but a P-39D-2 with the same 20mm cannon, the same two .50 cal machine guns and the same four .30 cal wing guns has 147lbs of "armament provisions". How you came up with 50lbs of it for the wing guns I don't know.
There are a few other spots where you seem to pick and choose your weights.

BTW your 7011lb P-39 won't get far because you forgot to put 2 gallons of oil (15lbs) into the reduction gear box behind the prop. No, it is not included in the empty weight but it is included in the tactical empty weight in the pilots manual.

As far a seeing what a 7075lb P-39 would do..........ROFLMAO.

It is a 6689lb P-39 and it won't even make level speed without failing to meet both coolant and oil temperature requirements.
level speed is usually much easier to cool than climbing because you have a lot more air going through the cooling system per minute.
No surprise it fails to meet cooling requirements when climbing. This is for both oil and coolant.
Perhaps the "D"s got better cooling? or a more positive method of controlling the exit flap/s?

This is one reason the argument goes circular. You ignore contradictory information (like the radios) and come up with your own, most favorable numbers. The only way to come up with 11lbs for gun sight and oxygen in your example is to use the gun sight from the P-400 and the oxygen weight number from the P-39D-2. The numbers for the D-2 are only 13lbs so it makes no practical difference. But why juggle the numbers to begin with?

Glider · Jul 8, 2021

I often like to stand back and take a simplistic view of things and I keep having the same thought.

If any aircraft designer, of any aircraft, military or civil, of any nation, ever, could save even 150lb in weight and improve performance. They would be doing cartwheels around the hanger, paying for all the drinks in the bar that night and no doubt get a promotion.

Yet here we have tens of thousands of engineers in the field and hundreds more in Bell who couldn't see these simple, easy, obvious changes, that would save vastly more 150lb. There's a reason for that.

Also Russia used it in the main as a low / medium level fighters where its performance was good, but not exceptional, at least when compared to a Typhoon which no one would say is the best fighter of the war.

The next observation is that everyone gets sucked into debating X mph or Y climb rate and everyone tends to forget the rather nasty handling problems that the P39 had.

Finally, Russia was offered what they were offered and these tended to be what was left over after the requirements of the USAAF and RAF had been met. I wouldn't mind betting that if they had been offered the P47 in the same numbers, instead of the P39 they would have dropped the P39 like a hot potato.

GrauGeist · Jul 8, 2021

Glider said:
I often like to stand back and take a simplistic view of things and I keep having the same thought.

If any aircraft designer, of any aircraft, military or civil, of any nation, ever, could save even 150lb in weight and improve performance. They would be doing cartwheels around the hanger, paying for all the drinks in the bar that night and no doubt get a promotion.

Yet here we have tens of thousands of engineers in the field and hundreds more in Bell who couldn't see these simple, easy, obvious changes, that would save vastly more 150lb. There's a reason for that.

Also Russia used it in the main as a low / medium level fighters where its performance was good, but not exceptional, at least when compared to a Typhoon which no one would say is the best fighter of the war.

The next observation is that everyone gets sucked into debating X mph or Y climb rate and everyone tends to forget the rather nasty handling problems that the P39 had.

Finally, Russia was offered what they were offered and these tended to be what was left over after the requirements of the USAAF and RAF had been met. I wouldn't mind betting that if they had been offered the P47 in the same numbers, instead of the P39 they would have dropped the P39 like a hot potato.

While I agree with all stated here, I do have to mention that the Soviets were given 200 P-47s and they were unimpressed.
The P-47's strength lay with it's performance at medium to high altitudes where little combat took place.
They need maneuverable aircraft at low to moderate altitudes and the P-47 was not able to meet those needs.
So the ones they had were mostly used for long range recon or defense of specific areas.

Glider · Jul 9, 2021

I stand corrected

Snautzer01 · Jul 9, 2021

GrauGeist said:
They need maneuverable aircraft at low to moderate altitudes and the P-47 was not able to meet those needs.

For low/middle they should have used it as a fighter bomber. Think the usaaf P-47 fighter bombers guys did all right by all accounts

pbehn · Jul 9, 2021

P-39 Expert said:
Fake test report? That's a Wright Field official test. Just like most of the other tests on wwiiaircraftperformance.org. That's what Wright Field did, they ran official performance tests for the AAF. Seriously?

Yes, the rate of climb is the same at 3 consecutive readings, so they have taken one time to climb value and put the average before that. It was probably done by a "joe pilot". Wright field is above sea level but the quote a rate of climb at sea level.

Juha3 · Jul 9, 2021

P-39 Expert said:
Not much of a trick really. Figures from AHT. Would do columns, but I can't seem to make columns work.

P-400 empty 5550, 2x50cals 139, ammo 200rds/gun 129, 20mm 127, ammo 32, armor plate/glass (as P-39N w/o nose armor) 122, oxygen and gunsight 11, pilot/chute 160, fuel (120gal) 720, oil 71, total 7061. Deduct 50 from armament provisions (205 in empty weight since you don't have the 30cal wing guns) and total weight is 7011. This plane would have worked well in NG since radar wouldn't be there until fall '42 and by then newer models would be available. For service in GB add the 110lb IFF set for a total of 7121. Personally I would like a total of 120rds of 20mm ammo Like the Spitfire) so add another 32lbs.

Go here to see what a 7075lb P-39 will do. http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2988.pdf Climb would have been 3720fpm up to 12400' (critical alt. for -35 engine as in the P-39D/D-1/F/K/L).

Noe before I get jumped for the circular argument please note that I am just responding to Shortround's post.

Heh, Bell clearly thought, that the USAAF only used small, slim pilots, who did not want to wear parachute, that was late corrected in -39Q table, pilot 200 lbs incl 20 lbs for the chute, P-400, gunsight 2.3 lbs, oxygen equip. 30.0, for P-39D 4.4 and 8.2 lbs. There is also for P-400 109.9 lb for radio.

P-39 Expert · Jul 9, 2021

wuzak said:
Was it an actual production line example, or one specially prepared for the test?

And maybe not in the configuration that was ordered.

A few of the test reports on wwiiaircraftperformance.org start with " Report on flight tests of Bell P-39X airplane at the manufacturer's plant.". Does this mean that it was tested by the company and the report relayed to the USAAF via Wright Field? Or did Wright Field test the plane, but since it was at the manufacturer's plant it may have been souped up?

Production line example.

There were only 20 -C models produced.

Wright Field test personnel, tested at the manufacturer's plant to facilitate service/repair.

Milosh · Jul 9, 2021

http://www.wwiiaircraftperformance.org/P-39/P-39C_Chart-Bell_Aircraft-1400.jpg

Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained) (1 Viewer)

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