XP-39 II - The Groundhog Day Thread

[Milosh]

Could helium tank be installed in the P-39 to make it lighter?

 

[DerAdlerIstGelandet]

So are we just making up our own formulas now? With simpler methods?

Why the hell does Boeing and Lockheed pay so much for these engineers? I'm going to recommend to my boss that we replace all the engineers with guys from web forums. Not only will we save a lot of money, we'll improve the F-22's performance. At least on paper...

 

[GregP]

Wait, I HAD my Harry Potter chocolate frogs brainfood! I SHOULD be a genius ... but, of all the things I have lost, I miss my mind the most!

 

[Stig1207]

Hey windhund 116, the Soviet Union used them throughout the war ... VERY effectively, and they stayed in service until at least 1949. The last aerial victory of WWII was by A Soviet P-39 against an Fw 189 on 9 May 45. The last Luftwaffe victory was by an Me 262 against a Soviet P-39 on 8 Aug 45.

The P-39, in Soviet service achieve the highest number of victories of any U.S. type, in any conflict. Strange, considering the U.S.A. didn't like them or come up with successful tactics for employing them. That was left to the Soviet Union. The P-39 was always a formidable ground attack airplane, but the Soviet Union mostly used them in an air-to-air role, in support of ground forces ... though they DID fly all types of missions in Soviet service.

I am not sure exactly when it as retired from U.S. service, but it was after WWII as some were still operational in 1946.

Greg, please see post #700 Messerschmitts do not want to burn and fall and #726 Summary.

The phenomena called overclaiming can really skew the actual results dramatically.

 

[windhund116]

Hey windhund 116, the Soviet Union used them throughout the war ... VERY effectively, and they stayed in service until at least 1949. The last aerial victory of WWII was by A Soviet P-39 against an Fw 189 on 9 May 45. The last Luftwaffe victory was by an Me 262 against a Soviet P-39 on 8 Aug 45.

The P-39, in Soviet service achieve the highest number of victories of any U.S. type, in any conflict. Strange, considering the U.S.A. didn't like them or come up with successful tactics for employing them. That was left to the Soviet Union. The P-39 was always a formidable ground attack airplane, but the Soviet Union mostly used them in an air-to-air role, in support of ground forces ... though they DID fly all types of missions in Soviet service.

I am not sure exactly when it as retired from U.S. service, but it was after WWII as some were still operational in 1946.

Must have been a fairly formidable ground assault airplane, if the Soviets thought so. Since they did have the famous IL-2 Sturmovik, from fairly early in the Great Patriotic War.

 

[P-39 Expert]

Must have been a fairly formidable ground assault airplane, if the Soviets thought so. Since they did have the famous IL-2 Sturmovik, from fairly early in the Great Patriotic War.

Their main role was battlefield air superiority. Escorting bombers and intercepting German bombers.

 

[Peter Gunn]

Could helium tank be installed in the P-39 to make it lighter?

See page 16 post #306 of this thread...

 

[Peter Gunn]

There you guys go again; speaking in tongues and handling serpents at worship!

HEY! Careful now, you're treading into dangerous territory, Troll George and I own the copyrights to snark in this here forum. I'm the one that's easily confused when you big brain types start spouting all your book learnin' nonsense. (check how many times I've had to take drgondog to task...)

It's hard to countenance this faux pas on your part but I can be magnanimous in this instance, George on the other hand, well, he's the one you have to watch out for.

 

[P-39 Expert]

Ouch, my ears! LOL!

Hi MiTasol -

Based on the loading chart for the P-39Q and the numbers calculated by Ivan earlier, I came up with a few items...

At 7075 pounds, wheels up, the CG arm is 134.22. Within the envelope but very aft.

First, the wheels up and wheels down moment numbers on the chart are wrong, off by a smidge.

But if we use the CG range of 130.1072 - 136.5584 you'll find that if you use half fuel and expend all ammo, you're right at the aft CG (I came up with 136.58) Funny that when I did the same calculation with 1/4 tanks I came up with similar CG numbers.

If anyone wants to see my math, I can scan my calculations.

Would like to see your calculations, thanks.

 

[Milosh]

See page 16 post #306 of this thread...

But that would make the a/c very unstable > tail heavy. I was thinking in the outer wings.

 

[FLYBOYJ]

Would like to see your calculations, thanks.

I tossed my numbers when this discussion seemed over.

Look at Greg's calculator, he's got it down pretty good and you're able to play with some of things we discussed.

The error on the page I mentioned, I'll post later

 

[GregP]

Hey Stig1207!

Overclaiming? Surely you jest.

Never happened, especially on the Russian Front where Stalin never executed anyone for lack of performance!

"OK, you two guys get one rifle and 5 rounds. When the first man is killed, the second man takes his rifle and continues fighting! In the Soviet Army, it's hard not to be a hero!"

 

[XBe02Drvr]

HEY! Careful now, you're treading into dangerous territory, Troll George and I own the copyrights to snark in this here forum.

And I contest those copyrights as invalid! Call your attorney; see you in court. Or would you prefer pistols at twenty paces or sabers toe to toe? In that case, call your second; see you on the meeting ground.

It's hard to countenance this faux pas on your part but I can be magnanimous in this instance, George on the other hand, well, he's the one you have to watch out for.

Well, St George awarded me a "Funny" for this post, so I see no threat there...unless there's an implied "Farm" after it, in which case, "Them's fightin' wuhds, Suh!"

 

[Peter Gunn]

And I contest those copyrights as invalid! Call your attorney; see you in court. Or would you prefer pistols at twenty paces or sabers toe to toe? In that case, call your second; see you on the meeting ground.

*SNIP*

 

[XBe02Drvr]

View attachment 598944

My challenge, your call, Sir: pistols or sabers? I have a matched pair of John Wilkes Booth style .41 cal Derringers. Will that suffice? Our seconds will attend to the loading, if that suits.

 

[fubar57]

​

 

[Peter Gunn]

My challenge, your call, Sir: pistols or sabers? I have a matched pair of John Wilkes Booth style .41 cal Derringers. Will that suffice? Our seconds will attend to the loading, if that suits.

Being a Southern Gentleman, I choose pistols suh...

Yours:

Mine:

Unless you prefer long guns, but I warn you suh, I'm a master tactician when it comes to those...

 

[FLYBOYJ]

Would like to see your calculations, thanks.

Follow up to my previous post:

XP-39 II

Basic weight and balance - weight x arm = moment

Moments on chart;

Wheels up - 1016062

Wheels down - 1011053

My math;

7570 x 134.22 = 1016045.4 wheels up

7570 x 133.56 = 1011049.2 wheels down

 

[jmcalli2]

P-39 weight was always confusing. Actually the early P-39D and the much later P-39Q-1 empty weights were about the same. AHT lists the D at 5523lbs and the Q-1 at 5680lbs but the Q-1 had the additional IFF radio that weighed about 120lbs. Empty weights of all the production P-39 models (D/F/K/L/M/N/Q) were about the same.

Loaded weights varied because of the differences in .30cal ammunition and armor plate, both of which were included in the "load" total and not the empty weight. .30cal ammunition boxes held 1000 rounds per gun but normal load was 300 rounds per gun, a difference of about 200lbs. That's why you sometimes see 7650lbs and 7850lbs quoted al loaded weight. The armor plate varied from about 265lbs on the P-400 to about 195lbs on the later N and Q models.

The British went a little crazy with armor on the P-400 by armoring the oxygen bottles etc. Compare that 265lbs to the contemporary P-40E with 111lbs of armor plate and glass. Deleting the 100lb nose armor that didn't protect anything and a few small pieces outside of the rear armored glass would get the armor plate/glass to a more reasonable 130lbs while still providing excellent protection.

It is interesting to compare models' weights as tested. Most test reports tell you that they have ammo on board, etc. On some reports you need to click on the "See entire report HERE" to get the weights.
The 'as tested' weights grew from 6592 in the YP-39 to 7871 in the P-39Q. That's a significant change at just under 20%, while bhp went up from 1090 to 1420, ~30%.


Model...........weight as tested in pounds.........bhp................max speed.................time to 15,000'

YP-39..............................6592.......................1090..................368 mph....................4.6 min

P-39C.............................6689........................1150..................379 mph...................~4.3 min

P-39D.............................7525........................1150.................Not given....................Not given

P-39D.............................~7800......................1170.................368 mph....................5.7 min

P-39D.............................7450........................1172.................370 mph....................Not given

P-39M.............................7430........................1420.................385.5 mph.................4.38 min

P-39N.............................7274........................1420.................398.5 mph.................4.15 min

P-39N.............................7301........................1390................. Not given..................3.82 min

P-39Q.............................7871........................1405.................385 mph....................4.5 min

P-400 British tests..........7845........................Not given...........355 mph...................~5.3 min


Source: P-39 Performance Tests

 

[Stig1207]

Hey Stig1207!

Overclaiming? Surely you jest.

Never happened, especially on the Russian Front where Stalin never executed anyone for lack of performance!

"OK, you two guys get one rifle and 5 rounds. When the first man is killed, the second man takes his rifle and continues fighting! In the Soviet Army, it's hard not to be a hero!"

It is the elephant in the room.

Btw, what is your source for this?

The P-39, in Soviet service achieve the highest number of victories of any U.S. type, in any conflict.