XP-39 II - The Groundhog Day Thread

[XBe02Drvr]

Loose nuts lead to loose screws.

And those lead to unintended heirs.

 

[jmcalli2]

So THAT's why they call them "loose?"

No.

That's way they call them fast.

 

[jmcalli2]

And those lead to unintended heirs.

Heir today, gone tomorrow.

 

[P-39 Expert]

In the report.

When you read it, you'll see the ONLY P-38 was the P-38D model and the ONLY P-39 was the P-39C model. The paragraph B. 3. e. (P-39 vs Spitfire) also reverts to "P-39C" later in the paragraph, further illustrating the typo.

Paragraph B. 1. b. only makes sense if you change "P-39D" to "P-38D" given the context of the report.

Those may not have been typos. The report is dated October 1941. Both the P-39C and the D would have been available, along with the P-38D. The P-38E only began production in September '41 so may not have been available, the F model began production in March '42 so it was definitely not available.

 

[jmcalli2]

Those may not have been typos. The report is dated October 1941. Both the P-39C and the D would have been available, along with the P-38D. The P-38E only began production in September '41 so may not have been available, the F model began production in March '42 so it was definitely not available.

Read the report.

 

[P-39 Expert]

Hi P-39 Expert. You are comapring apples to orange.

The XP-39 had a V-1710-35 with a turbocharger unit. It was rated at 1,150 hp and 3,000 rpm @ 44" MAP at altitude. After the turbo was deleted, the V-1710-35 made 1,050 hp and 3,000 rpm @ 44" MAP at about 9,500 feet. It never hit 390 mph, ever, in level flight. Agree. Except the 1050HP V-1710 was a -33, a derated -35 made for the YP-39 because the -35 hadn't passed the 150 hour test. The -35 that went into the P-39D/D-1/F/P-400 was rated at 1150HP at 12000ft.

The P-39N had a V-1710-85 (E19) engine. It developed 1,410 hp at 3,000 rpm @ 57" MAP. Add 360+ hp to a 360 - 370 mph airplane and you will get a speed increase. The P-39N test on wwiiaircraftperformance shows 398.5 mph at 9,700 feet; 1,420 hp; 3,000 rpm, 59.8" MAP, which is war emergency power plus another 1.5" MAP; at 7,274 lbs. It had 9.6 : 1 supercharger gears, so the service celing was a bit lower than the 8.8 or 8.1 gear units. The -85 was really just a -83 engine driving through 2.23 : 1 reduction unit rather than the 2.00 : 1 unit the -83 used. Agree, except the ceiling for the 9.6 gears was higher than the 8.8 or 8.1 geared units, not lower. The 9.6 gears made about the same power, just about 3000ft higher.

The P-39N was a very different animal than the XP-39 chart shown a few pages above, and it has decent performance. But, by then, the reputation of the P-39 had been established and pretty much nobody in the USAAF wanted it. Most went to the Soviet Union (4,746 P-39s in total) since they mostly got the P-39N and Q models. After being left exposed to winter and harsh conditions in Soviet Service, I seriously doubt many would get the same performance at the same power levels, but the Soviets were not much concerned with the engines since they didn't pay for them, so they likely COULD get the test performance and more at 75 - 80" MAP. I think the chart you are referencing was for the P-39C, not the XP-39. C model had the un-turbocharged -35 engine and weighed around 5800lbs

By that time, the U.S.A. wasn't really sending out new P-39 units to war. We were supplying replacement aircraft and trying to re-equip as was possible. Let's recall that the Pacific was not the theater of priority until Germany was defeated.

Bottom line: The performance of a shiny new P-39N does not mean the XP-39 suddenly got better. Again, I believe we're talking about the P-39C, not the turbocharged XP-39.

Please see above.

 

[Airframes]

Tighter nutsacks required ..................

 

[jmcalli2]

Please see above.

I came across this earlier today:

LiTOT: P-39 index

 

[GregP]

So, where exactly did that pic come from? I've seen the pic before, but never that caption.

 

[P-39 Expert]

So, where exactly did that pic come from? I've seen the pic before, but never that caption.

Definitely the turbo XP-39, scoop for the intercooler and no armament.

 

[jmcalli2]

So, where exactly did that pic come from? I've seen the pic before, but never that caption.

The link above the pic.

Here it is again:

LiTOT: P-39 index

Look for the link, "XP-39 seen on the ground from 11 o'clock" near the bottom of the page.

General contents for that site:

LiTOT: Content

I had forgotten about the site. Glad I re-found it. A lot of information on many types there.

 

[ddwhitney]

The basis for removing the turbo from the XP-39 were the results of the Full-Scale testing done by NACA in 1939. The attached figure is from page 38 of that report and is also shown in context in Vee's For Victory, page 85.
The goal was to exceed 400 mph, which could be done by removing the turbo installation, cleaning up the airframe, and fitting the altitude rated V-1710-31(E2A) with 8.8:1 supercharger gears and a larger carburetor, rated for 1,090 bhp at 13,200 feet.

 

[jmcalli2]

The basis for removing the turbo from the XP-39 were the results of the Full-Scale testing done by NACA in 1939. The attached figure is from page 38 of that report and is also shown in context in Vee's For Victory, page 85.
The goal was to exceed 400 mph, which could be done by removing the turbo installation, cleaning up the airframe, and fitting the altitude rated V-1710-31(E2A) with 8.8:1 supercharger gears and a larger carburetor, rated for 1,090 bhp at 13,200 feet.View attachment 608920

Gee, it looks like NACA was full of it.

 

[P-39 Expert]

The basis for removing the turbo from the XP-39 were the results of the Full-Scale testing done by NACA in 1939. The attached figure is from page 38 of that report and is also shown in context in Vee's For Victory, page 85.
The goal was to exceed 400 mph, which could be done by removing the turbo installation, cleaning up the airframe, and fitting the altitude rated V-1710-31(E2A) with 8.8:1 supercharger gears and a larger carburetor, rated for 1,090 bhp at 13,200 feet.View attachment 608920

AAF had to remove the turbo if they were going to get a plane in production by 1941. Which they did and produced a good airplane, except that they let the weight get too high.

 

[tyrodtom]

Gee, it looks like NACA was full of it.

The full size wind tunnel at Langley Field was limited to 125 mph, so those are estimates.
Plus was EVERY modification suggested by those wind tunnels test ever applied to a real P-39 ?

 

[GregP]

No.

 

[SaparotRob]

Please expand above.

 

[pbehn]

AAF had to remove the turbo if they were going to get a plane in production by 1941. Which they did and produced a good airplane, except that they let the weight get too high.

You cant really complain about the weight increase when it was caused by stuff needed by a war plane. They all increased in weight.

 

[P-39 Expert]

You cant really complain about the weight increase when it was caused by stuff needed by a war plane. They all increased in weight.

They could have been a lot more judicious about what they put into the plane in the early models D/F/K/L/P-400. The later models with the uprated engine were fine as they were. The basic airframe was light enough. They didn't need the .30cal wing guns, after all they had a 37mm cannon and two .50cal MGs. And the 100lb nose armor plate was redundant, no other planes had their nose reduction gear armored. Those items total around 300-500lbs, depending on the amount of .30cal ammunition carried. A fully equipped P-39D without those items weighed about 7150lbs versus up to 7850lbs normal gross weight. Russians deleted the wing guns and the IFF radio and did really well with it.

 

[pbehn]

They could have been a lot more judicious about what they put into the plane. The basic airframe was light enough. They didn't need the .30cal wing guns, after all they had a 37mm cannon and two .50cal MGs. And the 100lb nose armor plate was redundant, no other planes had their nose reduction gear armored. Those items total around 300-500lbs, depending on the amount of .30cal ammunition carried. A fully equipped P-39D without those items weighed about 7150lbs versus up to 7850lbs normal gross weight. Russians deleted the wing guns and the IFF radio and did really well with it.

But that was the "thing" and we have been through it before. Whatever the theoretical advantages of a mid engine design the practical disadvantages were against it. The Spitfire and Hurricane just had to put the stuff in. There are few sleeker designs than the early Bf109s but by the end of the war they were like a soccer player who took up steroids and bodybuilding with lumps bumps and blisters all over the place.