XP-39: pros cons

[P-39 Expert]

And that was a proposed intercooler? I'm curious if a belly radiator of some sort or two ventral radiators like the Spitfire would be workable

So it was further back? On a fighter it'd be under the pilot more or less?

What about the fact that the control linkages would be easier to lay out because of the fact that you don't have any interruptions in the fuselage because of the doors? They just ran them under the doors back to the engine.

There was supposedly a proposal for some kind of higher altitude V-1710 that got cancelled, I'd almost swear I remember hearing that with the P-39. Was this a single stage supercharger with a different gear ratio or a twin-speed set-up? Or was it twin-speed? Maybe the V-1710-59, first attempt at increasing the supercharger gear ratio to 9.6? Unsuccessful because of excessive wear to the supercharger gears. Redesign for wider gears resulted in the successful -83 from August '42.


BTW: While I'm beating a dead horse, I remembered something you stated about the P-63 -- it's wing was moved back by a foot. The changes needed to mount the twin-stage supercharger added some weight and that's why some tankage was moved around and, while a turbocharger would be bulkier and heavier -- if the wings stayed forward by their normal amount, that would mean the space between the wing and the elevator would be much larger, and the wing seems to bear a significant amount of the aircraft's weight, and while I could definitely be wrong, would you be able to have enough leverage to make everything work?

If there was no balance issue with the wing forward then there would be more leverage since the tail was farther away from the wing. But I believe the wing was moved back for balance with the extended tail. Hope this helps.

See above.

 

[Zipper730]

P-39 Expert

1. Would the control cables be lighter if they didn't have to be run under the doors? I figure the more changes in direction would make the cables longer and that would add some weight. Frankly -- I'm not even sure why they added the doors to the design.

2. The V-1710-59 and -83: Were they single-speed or twin-speed? What full-throttle height were they expected to reach? Also, was there anyway for them to have known, reasonably speaking, that the gears would wear-down more easily and would need to be beefed up to work?

3. I thought you said the P-63 was lengthened because the wing was moved back about a foot, and then to give the tail adequate leverage, the longer fuselage gave the tail adequate leverage?

I would have figured

1. P-63
   • If the wing was moved rear-words, the C/L would also go back accordingly and
   • This would produce a stronger nose-down tendency, and need more elevator to provide level flight and maneuvering
   • Making the plane longer and with the elevator further back and you'd get adequate control
2. P-39
   • The P-39 had the wing forward by a foot and thus these problems didn't exist
   • A turbocharger mounted behind the engine would be somewhat heavier and possibly further back than the P-63's set-up which would make the plane tail-heavy
   • Admittedly a longer tail would just make the plane twitcher...

Would it have been acceptable to use two smaller turbochargers in lieu of one? It might sound silly but from what I remember the F6F prototypes used such a set-up. I'm not sure if they would have viewed that as acceptable either as a fix or a start.

 

[P-39 Expert]

P-39 Expert

1. Would the control cables be lighter if they didn't have to be run under the doors? I figure the more changes in direction would make the cables longer and that would add some weight. Frankly -- I'm not even sure why they added the doors to the design. Me either, but they stayed with the plane even through the upgrade to the P-63.

2. The V-1710-59 and -83: Were they single-speed or twin-speed? What full-throttle height were they expected to reach? Also, was there anyway for them to have known, reasonably speaking, that the gears would wear-down more easily and would need to be beefed up to work? Both single speed, Allison never develped a two speed. FTH was about 15000', up from 12000' with the earlier 8.8 geared engines. Allison was hoping for the step up gears to be interchangeable from 8.1 (for two stage engines) to 8.8 (earlier altitude rated engines) to 9.6 (later altitude rated engines) but the load on the gears was too high at 9.6. This was a big disappointment as the earlier -59 engines were tested in late '41 but the redesign pushed them back to mid-late '42, almost a year later.

3. I thought you said the P-63 was lengthened because the wing was moved back about a foot, and then to give the tail adequate leverage, the longer fuselage gave the tail adequate leverage? Yes.

I would have figured

1. P-63
   • If the wing was moved rear-words, the C/L would also go back accordingly and
   • This would produce a stronger nose-down tendency, and need more elevator to provide level flight and maneuvering
   • Making the plane longer and with the elevator further back and you'd get adequate control The wing was moved because the C/G changed, not vice versa.
2. P-39
   • The P-39 had the wing forward by a foot and thus these problems didn't exist C/L and C/G need to be in the same place or plane is out of balance.
   • A turbocharger mounted behind the engine would be somewhat heavier and possibly further back than the P-63's set-up which would make the plane tail-heavy Yes.
   • Admittedly a longer tail would just make the plane twitcher... Should make it smoother instead of twitchier.

Would it have been acceptable to use two smaller turbochargers in lieu of one? It might sound silly but from what I remember the F6F prototypes used such a set-up. I'm not sure if they would have viewed that as acceptable either as a fix or a start.

P-39 was too small for a turbo, much less two. See above for more answers. Just my opinions. Thanks.

 

[wuzak]

Allison did develop 2 speed supercharged versions of the V-1710, but none of these went into production.

These include:
V-1710-E29 - number built not known, ratios 7.48/9.60 (not certain)
V-1710-F11R - 1 built, ratios 6.44/8.80
V-1710-F16 - 0 built, ratios 6.44/8.80
V-1710-G2R/L - number built not known, ratios 7.76/8.80
V-1710-G2RA - number built not known, ratios 7.76/8.80
V-1710-G3R - 8 built, ratios 7.48/8.80
V-1710-G4L - 0 built, ratios 7.76/8.80
V-1710-G4R - 0 built, ratios 7.76/8.80

Per Dan Whitney, Vees for Victory, Appendix 3.

Note that the 2 speed supercharged engines had (or would have had) a larger impeller of 10.25in, compared with 9.5in for the standard impeller. I believe that 10.25in also happens to be the impeller size used in most single stage Merlins.


The Grumman F6F never had 2 turbochargers.

The XF6F-2 used an experimental Birman type mixed flow turbocharger - which probably means it had axial and centrifugal compressors. Initially it was to have been fitted with the R-2600 (not sure if that ever flew), but was later fitted with the R-2800 connected to the turbocharger.

Looked at a few sources, including Grumman F6F Hellcat - Wikipedia, Graham White, Allied Aircraft Piston Engines of World War II, and Graham White, R-2800 Pratt & Whitney's Dependable Masterpiece and am not really any closer to knowing if the XF6F-2 ever flew with the R-2600.

 

[Zipper730]

Me either, but they stayed with the plane even through the upgrade to the P-63.

So I'm not the only one to think the car door idea was weird?

Both single speed, Allison never develped a two speed. FTH was about 15000', up from 12000' with the earlier 8.8 geared engines. Allison was hoping for the step up gears to be interchangeable from 8.1 (for two stage engines) to 8.8 (earlier altitude rated engines) to 9.6 (later altitude rated engines) but the load on the gears was too high at 9.6. This was a big disappointment as the earlier -59 engines were tested in late '41 but the redesign pushed them back to mid-late '42, almost a year later.

The P-39 had a little ram compression effects if I recall right?

Yes.

Okay, we're on the same page regarding length

P-39 was too small for a turbo, much less two.

It might sound silly but two turbos running in parallel can be quite small compared to one normal turbo. It would allow the effect of one big turbo in a smaller place. That's why I mentioned it.

Allison did develop 2 speed supercharged versions of the V-1710, but none of these went into production.

Do you have any idea why?

Note that the 2 speed supercharged engines had (or would have had) a larger impeller of 10.25in, compared with 9.5in for the standard impeller. I believe that 10.25in also happens to be the impeller size used in most single stage Merlins.

Nice touch...

The XF6F-2 used an experimental Birman type mixed flow turbocharger - which probably means it had axial and centrifugal compressors. Initially it was to have been fitted with the R-2600 (not sure if that ever flew), but was later fitted with the R-2800 connected to the turbocharger.

The first supercharger I knew of to use axial-flow was Eastman Jakob's work. Do you know anymore about the Birman-type?

 

[wuzak]

So I'm not the only one to think the car door idea was weird?

The Tornado and early Typhoons had a car door.

The Spitfire had a half door on one side.

It might sound silly but two turbos running in parallel can be quite small compared to one normal turbo. It would allow the effect of one big turbo in a smaller place. That's why I mentioned it.

The problem is what is available.

General Electric were producing B and C type superchargers, which were both too big to be used as a pair on the V-1710.

Two small turbos probably took up more space than one large turbo, though.

Where two turbos were used instead of one was for performance reasons. On C-series turbocharger may not have provided enough air for the R-3350 in the B-29, so they used two B-series turbos.

Do you have any idea why?

No orders.

One of the two speed engines was to be for the post-war DC-4M as an alternative replacement for the Merlins. But that didn't go ahead.

The first supercharger I knew of to use axial-flow was Eastman Jakob's work. Do you know anymore about the Birman-type?

A.A. Griffiths wrote a paper in 1927 about an axial flow compressor for a gas turbine. Over the next decade he, and his associates, designed and experimented with axial flow compressors, including a counter-rotating axial flow compressor.

Germany certainly did have people working on axial flow compressors in the late '30s.

As for the Birman type turbo, I don't have any specific information, other than it was tried on an XF6F-2, one of the XF4Us (can't recall dash number) and was to be fitted to one of the XP-60s powered by the V-1710 (not sure if it was XP-60A or XP-60B), that it didn't work well and was unreliable, and it was described as a "mixed flow" design.

 

[P-39 Expert]

Anybody know anything about the Birman supercharger?

 

[wuzak]

In White's book about the R-2800 he calls the unit used in the XF4U-3 a Turbo Engineering turbocharger and XF6F-2 as a Birman (Turbo Engineering) turbocharger.

This is what the installation looked like on the XF4U-3

From Category:XF4U-3 Corsair - Wikimedia Commons

and on the XF6F-2

from Wikimedia Commons

 

[Shortround6]

Would it have been acceptable to use two smaller turbochargers in lieu of one? It might sound silly but from what I remember the F6F prototypes used such a set-up. I'm not sure if they would have viewed that as acceptable either as a fix or a start.

The problem wasn't so much the turbo itself and if comparing turbos try to compare turbos of the same generation and pressure ratios. Car (or diesel truck) turbos are all over the place.

The problem is so much the turbo itself but the ducts needed to get the exhaust to the turbo, the ducts needed to get the air to and from the turbo and the need for an intercooler (which can take up more volume than the turbo) and without the turbo much of the altitude advantage of using a turbo goes away.

 

[Zipper730]

No orders.

When were the superchargers you listed developed?

 

[wuzak]

When were the superchargers you listed developed?

Late in the war.

 

[Zipper730]

Late in the war.

Like 1944 or 1945?

 

[fubar57]

Like 1944 or 1945?

I can't even......

 

[tyrodtom]

P-39 Expert

1. Would the control cables be lighter if they didn't have to be run under the doors? I figure the more changes in direction would make the cables longer and that would add some weight. Frankly -- I'm not even sure why they added the doors to the design..

Why would you think the doors would require longer control cables ? The control stick yoke has connections in the floor right in front of the seat, like any other aircraft of that era, door or canopy hasn't got any effect on the length of the control cables.
And would you really think the weight of the control cables is any significant weight ?

 

[Zipper730]

Why would you think the doors would require longer control cables?

Looking back on it, I don't actually know why I said what I did. I'm curious if any linkages ran along the sides? It seems that the aft sliding canopy would be more conventional and easier.

 

[GrauGeist]

Looking back on it, I don't actually know why I said what I did. I'm curious if any linkages ran along the sides? It seems that the aft sliding canopy would be more conventional and easier.

The P-39/P-63 had car doors because the cockpit framing provided structural support to the airframe.

 

[P-39 Expert]

The P-39/P-63 had car doors because the cockpit framing provided structural support to the airframe.

I think the car doors were part of the turnover structure which was part of the framing. In my opinion it didn't need the turnover structure, just added weight that most other fighters didn't have. Without the turnover structure a bubble canopy could have been used eliminating the car doors and improving visibility. The framing wasn't really necessary for structure, the whole forward fuselage was based on the two longitudinal beams that ran from the nose to aft of the engine providing a very robust "canoe" that also kept the drive shaft straight. Altogether a good structural solution even without the turnover structure or framed canopy. Just my 2 cents worth.

 

[Zipper730]

I can't even......

I meant like 1944 late, or 1945 late. Depending on interpretation, either could be considered late.

 

[Zipper730]

My questions...

1. V-1710-35
   • What's the engine critical altitude (no ram)?
   • What's the aircraft critical altitude (ram) on the P-39D?
2. V-1710-59
   • What was the proposed engine critical altitude (no ram)?

 

[P-39 Expert]

My questions...

1. V-1710-35
   • What's the engine critical altitude (no ram)?
   • What's the aircraft critical altitude (ram) on the P-39D?
2. V-1710-59
   • What was the proposed engine critical altitude (no ram)?

1. -35 was 11700'-12000' no ram without backfire screens. Critical altitude for the P-39D was 13800' with ram and no backfire screens per wwiiaircraftperformance.org.
2. -59 was 1100hp at 13800' (coincidence) with screens. Later 9.6 production models without screens was 1125hp at 15500'.