Besides the props, what are the diferences between the P-39 and P-63?

[Zipper730]

P-63 was irrelevant in my opinion. Bell and the AAF could have installed the two stage Allison in a P-39 easily enough and had them from May '43 (when the engine was in production) instead of waiting until basically the end of '43 for the P-63 to get into production.

And if the had a liquid intercooler they'd be good to go right there.

And I did not say that they lacked the space for the intercooler. In fact, Allison designed and tested a liquid cooled intercooler (not aftercooler) for ther two stage engines, so there was no need to affect Merlin production, not there was any reason it would have.

I'm confused, some people are telling me that it had ADI in lieu of intercooling, others a liquid intercooler...

When did they start research on liquid intercoolers?

 

[wuzak]

I am not sure on the timeline with Allison 2 stage engines.

The first two stage engines had the carburettor mounted on the auxiliary supercharger. This gave space for an intercooler between stages, if required.

I couldn't find a picture of a 2 stage engine with a liquid:air intercooler, but the intercooler looked an awful lot like the aftercooler on a 2 stage Merlin.

I did find this pdf with pictures and drawings of the E-series V-1710.

At some stage, Allison decided to change the 2 stage engine so that the carburettor was on the engine stage supercharger, like their regular single stage engines. The Auxiliary supercharger would bolt onto that and feed the carburettor with compressed air - sort of like a turbocharger would.

This arrangement precluded the use of a liquid:air intercooler, as there was no space.

 

[Jugman]

And if the had a liquid intercooler they'd be good to go right there.

I'm confused, some people are telling me that it had ADI in lieu of intercooling, others a liquid intercooler...

When did they start research on liquid intercoolers?

No production two-stage V-1710 had any type aftercooler or intercooler but it was always intended to have one. The original aftercooler design was abandoned in December, 1943 do to a combination of technical problems with the unit and the Material Division not authorizing the fabrication orders. They had a mock up of the V-1710-119/F32 in January, 1944 with its box type aftercooler. This configuration was not tested until July on workhorse engine EX-50. The first F32 was not ready until April, 1945.

 

[Zipper730]

At some stage, Allison decided to change the 2 stage engine so that the carburettor was on the engine stage supercharger, like their regular single stage engines. The Auxiliary supercharger would bolt onto that and feed the carburettor with compressed air - sort of like a turbocharger would.

This arrangement precluded the use of a liquid:air intercooler, as there was no space.

Why did they do that?

No production two-stage V-1710 had any type aftercooler or intercooler but it was always intended to have one.

Okay

 

[wuzak]

Why did they do that?

So the core engine would be the standard single stage V-1710 and the auxiliary stage would be a bolt on component.

 

[Jugman]

The carburetor on the auxiliary caused a 2" hg drop in pressure at the inlet. In addition the Allison controlled the auxiliary stage speed by measuring the absolute pressure at the carburetor, this apparently caused the auxiliary stage to run slower than it should for a given altitude. Moving the carb between stages gained ~3,000ft in critical altitude.

 

[P-39 Expert]

The carburetor on the auxiliary caused a 2" hg drop in pressure at the inlet. In addition the Allison controlled the auxiliary stage speed by measuring the absolute pressure at the carburetor, this apparently caused the auxiliary stage to run slower than it should for a given altitude. Moving the carb between stages gained ~3,000ft in critical altitude.

Agree, why they didn't start with the carb in the normal place on the back of the engine like the P-38 (and other turbocharged engines) is a mystery to me. The 3000' increase in critical altitude was significant. And with the carb on the engine the intake duct for the auxiliary stage didn't need to feed a downdraft carbueretor but could have been at any angle (updraft, downdraft, sidedraft or any other angle), greatly easing design problems. Probably caused by the AAF like a lot of other problems that Allison had (backfire screens, fuel injection, etc.). Hindsight is 20/20.

 

[Zipper730]

So the core engine would be the standard single stage V-1710 and the auxiliary stage would be a bolt on component.

This fit the profile for the V-1710's earlier on. Unless you were willing to add a pair of scoops to either side like the XP-39, you'd be shit out of luck.

 

[P-39 Expert]

This fit the profile for the V-1710's earlier on. Unless you were willing to add a pair of scoops to either side like the XP-39, you'd be shit out of luck.

What would the scoops be for?

 

[Jugman]

Agree, why they didn't start with the carb in the normal place on the back of the engine like the P-38 (and other turbocharged engines) is a mystery to me. The 3000' increase in critical altitude was significant. And with the carb on the engine the intake duct for the auxiliary stage didn't need to feed a downdraft carbueretor but could have been at any angle (updraft, downdraft, sidedraft or any other angle), greatly easing design problems. Probably caused by the AAF like a lot of other problems that Allison had (backfire screens, fuel injection, etc.). Hindsight is 20/20.

They probably put the carb body on the auxiliary stage to avoid the three extra bends needed.

 

[P-39 Expert]

They probably put the carb body on the auxiliary stage to avoid the three extra bends needed.

The three bends being in the duct from the auxiliary stage to the carb on the back of the engine?

 

[Zipper730]

So the core engine would be the standard single stage V-1710 and the auxiliary stage would be a bolt on component.

Though I know I replied to this earlier, when they originally designed the liquid intercooler, they were designing the first and second stage with a liquid intercooler between them right? Why not a bolt-on intercooler and supercharger (this might sound stupid, but that's how you learn).

What would the scoops be for?

An air-to-air intercooler.

 

[Shortround6]

Just because you use a liquid intercooler doesn't mean you don't need some sort of intake for it. It may not be a large as an air to air intercooler but you need cool air flowing over the hot liquid at some point. Also please note increased size of radiator in order to handle the increased power. Especially at altitude.

 

[P-39 Expert]

So the core engine would be the standard single stage V-1710 and the auxiliary stage would be a bolt on component.

Exactly. All contemporary Allisons were the same, improvements were normally applied to all the engine models. Only differences were the internal supercharger gear ratios which were interchangeable and the location of the reduction gear (conventionally on the "F" or remotely on the "E"). But the power sections of all the the Allisons were the same and the auxiliary stage supercharger was a bolt-on addition which worked on both the E and F models. So this was really not a new engine, just the auxiliary stage was new. No intercooler, WEP used water injection on the P-63 which was the only user of a production mechanical two stage Allison.

 

[Jugman]

Though I know I replied to this earlier, when they originally designed the liquid intercooler, they were designing the first and second stage with a liquid intercooler between them right? Why not a bolt-on intercooler and supercharger (this might sound stupid, but that's how you learn).

An air-to-air intercooler.

My understanding is the Allison was to use an aftercooler located down stream of both superchargers integrated into the intake manifold.

 

[tomo pauk]

...
No intercooler, WEP used water injection on the P-63 which was the only user of a production mechanical two stage Allison.

P-82 also used 2-stage V-1710s.

 

[Zipper730]

I know it's weird how sometimes you miss something totally, and then a day or more later it all connects

Okay, from what I gather

1. Early V-1710: Had an integral supercharger with provision for a bolt-on supercharger and intercooler. When so configured: Airflow went from the carburetor intake to the auxiliary-stage supercharger, then to the air-to-air intercooler, and from that point to the inlet manifold. From this point it would go through the main-stage supercharger, and then to the cylinders.
2. Proposed V-1710 Two-Stage Configuration: Airflow went from the carburetor intake to the first-stage, then second-stage superchargers, and from that point to the liquid-cooled after-cooler, which was integrated into the inlet manifold. From there it went to the cylinders.

And if I understand the exchanges correctly (and I could be wrong)...

• Technical problems popped up with the two-stage configuration with liquid-cooled intercooler/after-cooler including the fact that the configuration
  • Caused a reduction in manifold pressure, whereas the earlier configuration (supercharger, carburetor, supercharger, cylinders) produced 3000 feet extra to the aircraft's critical altitude
  • Auxiliary-stage speed was measured by absolute pressure in the carburetor, which resulted in the stage running slower than it should: Where did they normally control the auxiliary speed from? Why did they change it?
• They reverted to the earlier arrangement which had the bolt-on supercharger/turbocharger (take your pick), with the same configuration (supercharger, carburetor, supercharger, cylinders).

 

[P-39 Expert]

I know it's weird how sometimes you miss something totally, and then a day or more later it all connects

Okay, from what I gather

1. Early V-1710: Had an integral supercharger with provision for a bolt-on supercharger and intercooler. When so configured: Airflow went from the carburetor intake to the auxiliary-stage supercharger, then to the air-to-air intercooler, and from that point to the inlet manifold. From this point it would go through the main-stage supercharger, and then to the cylinders.
2. Proposed V-1710 Two-Stage Configuration: Airflow went from the carburetor intake to the first-stage, then second-stage superchargers, and from that point to the liquid-cooled after-cooler, which was integrated into the inlet manifold. From there it went to the cylinders.

And if I understand the exchanges correctly (and I could be wrong)...

• Technical problems popped up with the two-stage configuration with liquid-cooled intercooler/after-cooler including the fact that the configuration
  • Caused a reduction in manifold pressure, whereas the earlier configuration (supercharger, carburetor, supercharger, cylinders) produced 3000 feet extra to the aircraft's critical altitude
  • Auxiliary-stage speed was measured by absolute pressure in the carburetor, which resulted in the stage running slower than it should: Where did they normally control the auxiliary speed from? Why did they change it?
• They reverted to the earlier arrangement which had the bolt-on supercharger/turbocharger (take your pick), with the same configuration (supercharger, carburetor, supercharger, cylinders).

You are almost there.

All Allisons (all WWII aircraft engines) had an internal supercharger.

Forget about the intercooler/aftercooler for the mechanical (not turbo) second stage. Never worked properly and there was no room in the P-39/63 structure. This was decided fairly early on in development.

Moving the carbueretor from the second stage to the normal location on the back of the engine was one of the last developments and only applied to the last 222 P-63 engines (of almost 5000) produced. Why this concept wasn't used from the beginning escapes me as it improved manifold pressure and critical altitude.

So, with no intercooler the order would be: Air ducted from outside into the carbueretor on the second stage, compressed by the second stage, ducted to the first stage and into the intake manifold and to the cylinders.

The last 222 engines (carb moved from first stage to normal position on back of engine) had air ducted from outside to the second stage, compressed then ducted to the carb mounted in the normal position on the back of the engine then into the adjacent internal first stage and the intake manifolds and cylinders. Only difference was position of carb.

Function of the intercooler was performed by water injection during WEP (war emergency power). Hope this helps.

 

[Shortround6]

The water injection system weighed 50 lbs empty and when full took 186lbs of the water/alcohol mix. (25 US gallons)
This was supposed to be good for 15 minutes at 75in map rating and a bit longer at lower manifold pressure settings.

 

[Zipper730]

You are almost there.

All Allisons (all WWII aircraft engines) had an internal supercharger.

Far as I know all the ones used on fixed-wing, heavier-than-air aircraft employed them, those that were proposed for airships seemed the exception to the rule. I just used the term "auxiliary" stage for the second stage.

Forget about the intercooler/aftercooler for the mechanical (not turbo) second stage. Never worked properly and there was no room in the P-39/63 structure. This was decided fairly early on in development.

It's not about the P-39/P-63, it's about the V-1710 design.

So, with no intercooler the order would be: Air ducted from outside into the carbueretor on the second stage, compressed by the second stage, ducted to the first stage and into the intake manifold and to the cylinders.

Okay, I understand the layout.