Spitfire V Versus P-40E

[GregP]

Hi Wayne,

I said what I intended to say, and I said it clearly. The Curtiss XP-37 was both supercharged and turbosupercharged. How much more clear can it be?

The supercharger was integral with the auxiliary section and the turbosupercharger was external and fed the supercharger. They moved the cockpit to the rear to clear all the plumbing.

Allison V-1710 were built in many configurations. They were built as:

1) Normally aspirated:

Note the clear absence of the auxiliary-stage supercharger in this airship engine.

2) Supercharged:

Standard F-Series V-1710 above, with splined propeller shaft and integral supercharger in the auxiliary stage fed by the carburetor. The power section is the crankshaft and cylinders, the nose section is the prop shaft and associated gears. The auxiliary section contains the supercharger, the carburetor, the starter (not shown above ... there is a circular plate bolted one instead), the generator (same as starter above ... circular plate bolted on). So, this engine may well be able to run, but you can't start it! The round torus-shaped thing at the bottom rear is the water pump. The stainless line coming from the carburetor to the supercharger housing feeds fuel directly into the supercharger impeller.

3) Supercharged and turbosupercharged as in the P-38:

Note the turbocharger located in each nacelle boom right at the trailing edge of the wing. I haven't seen a pic of the P-38 setup outside of the P-38 with just the engine and the turbocharger assembly.

4) Turbo-compound:

Note the turbocharger in the auxiliary stage. The high-pressure air feeds the carburetor without an intercooler.

5) 2-stage supercharged:

Auxiliary supercharger stage has the carburetor and it feeds the supercharger impeller directly, without an intercooler.

6) Remote rear drive, as in the XB-42:

The contra-prop would be at the rear of the fuselage, with one V-1710 driving each prop.

7) A proposed V-3420 medium bomber with two V-3420s driving VERY larger propellers:

There are more configurations, but this covers some of the proposed applications.

 

[Dash119]

You mean supercharger not turbo right?

I think some of the confusion here may be in the nomenclature...

During this time period exhaust driven Superchargers were referred to as "Turbo-Superchargers". In modern parlance we just refer to them as "Turbochargers". On the Allison(s) in most P-38's there was an exhaust driven "Turbo-Supercharger" which fed the integral engine driven "Supercharger". So it was in essence a two-stage system with an intercooler between the two types of compressors.

 

[Schweik]

The only turbocharged use of the Allison V-1710 in any but experimental installations was the P-38. In point of fact, the Curtiss XP-37 was both supercharged and turbosupercharged, but they only made 14 of them. The original XP-39 was turbosupercharged but, again, there was only the one airframe.

The Consolidated P-30 (PB-2) had a Curtiss V-1570 and was turbosupercharged, and I have heard people claim it had an Allison, but it didn't. They DID have a Vultee testbed aircraft for the Allison V-1710. Here is a Consolidated A-11, with Curtiss engine:

The Allison V-1710 testbed was the Consolidated XA-11A, but I have never found a pic of it. Just the standard P-30 and XA-11 (not XA-11A) with the Curtiss V-1570 engine ... some with turbosupercharger, and one with enlarged fin ... but that didn't have the V-1710.

Really interesting but you missed my point - what I was trying to clarify was that you used the term 'turbocharger' seemingly in the context of the P-40 and / or P-39, when I think you meant just 'supercharger'...

 

[Schweik]

I think some of the confusion here may be in the nomenclature...

During this time period exhaust driven Superchargers were referred to as "Turbo-Superchargers". In modern parlance we just refer to them as "Turbochargers". On the Allison(s) in most P-38's there was an exhaust driven "Turbo-Supercharger" which fed the integral engine driven "Supercharger". So it was in essence a two-stage system with an intercooler between the two types of compressors.

I'm aware of the difference and the period terminology, though it does bear repeating.

 

[GregP]

Hi Schweik,

If you go read my posts, I stated clearly that the only turbosupercharged application, other than experimentals and the very low-volume P-37, was the P-38.

The term "turbosupercharger," as used in WWII, is what we call a turbocharger today.

If you go up and look at the turbo-compound engine (#4) above, you can clearly see the turbo part at the rear, with the circle of turbine-like blades that the hot exhaust runs through to make it spin. It is connected via a solid driveshaft, to a compressor (the "charger" part) that feeds the integral engine supercharger impeller. So, there are two stages of boost, the compressor at the extreme rear operated by the exhaust gas and the integral supercharger operated by the crankshaft.

 

[wuzak]

Hi Wayne,

I said what I intended to say, and I said it clearly. The Curtiss XP-37 was both supercharged and turbosupercharged. How much more clear can it be?

Hi Greg,

It just stood out to me that you made a point of specifying turbocharging and supercharging for the P-37, but not for the P-38 or XP-39.

Just a case of me overthinking what you were saying.

 

[wuzak]

If you go up and look at the turbo-compound engine (#4) above, you can clearly see the turbo part at the rear, with the circle of turbine-like blades that the hot exhaust runs through to make it spin. It is connected via a solid driveshaft, to a compressor (the "charger" part) that feeds the integral engine supercharger impeller. So, there are two stages of boost, the compressor at the extreme rear operated by the exhaust gas and the integral supercharger operated by the crankshaft.

The turbocompound was based on the 2 stage supercharged engine. The auxiliary supercharger is driven by the engine via a fluid coupling.

The turbine is connected to the auxiliary supercharger and drives the entire engine.

Unlike a turbocharger, there is no bypass of the turbine. The exhaust goes through the turbine all of the time.

The turbine for the turbo-compound V-1710 was an adaption from the larger C-series turbocharger, as used on the P-47.

 

[GregP]

The engine shown above as 4) is identified in several references, including Vees for Victory as the V-1710-127 turbocompound engine. You can see that the exhaust is fed directly to the turbine, and the compressor feeds the carburetor. There is ALSO a coupling path to the crankshaft, but the exhaust comes out the turbine at the rear only.

The output of the rear compressor feeds the carburetor and the fresh air intake is between the turbine and the compressor, but there is ALSO a mechanical AND fluid coupling to the crankshaft, according to Vees for Victory.

It was a successful prototype, but the war was winding down and it never made production or flew, AFAIK. With exhaust gas temperatures of 1,750 - 1,825°F, the "state of the art" was being pushed, metallurgically, anyway. But we never got the chance to see how it would play out.

 

[Schweik]

I don't want to beat it to death, I think you just made a typo when you were talking about P-40s etc. running "without their turbochargers". Maybe I read it wrong.

 

[GregP]

More of a misunderstanding, likely due to my wording.

To me, running non-turbo can mean either the turbo is not operating or is not present. In the case of the P-39 and P-40, the turbocharger was not present, except for the turbocharger in the XP-39. In the case of P-38s running today (except for ONE unit that still runs them), the turbos are locked in stationary position, and so function only as an exhaust outlet. For the rest of them, the small intake below the trailing edge of the wing (see the Planes of Fame P-38J-20 below)

used to be the fresh air intake for the turbocharger. Since we aren't running the turbos, and most of the rest of them aren't either, they have been modified. The intake under the spinner is divided into 3 segments. The outer two section are oil cooler intakes and the center intake used to be fresh air for the intercooler.

Today, the center section is the carburetor fresh air intake and the original turbo fresh air intake is blocked off. If you aren't running a turbocharger, you don't need an intercooler. This thing is already expensive enough to operate!

The "we" above is the Planes of Fame Museum, not me. Hopefully that is clear.

 

[Schweik]

Yes thank you! But they do still use the regular superchargers on the other Allisons, right?

 

[Dash119]

Since the Supercharger on the Allison, and for that matter the Merlin, is integral to the engine itself there is no way to bypass or disconnect it. Although I suppose that a highly modified tractor puller engine might eliminate the installation...

 

[Schweik]

That's what I figured, just wanted to confirm.

 

[MIflyer]

My friend Ward Duncan, who was maintenance chief of the 9th PRS, said he was a bit concerned about bypassing the usual turbo intake, since there was no provision for carb heat to take care of any icing. He was specifically talking about Glacier Girl.

 

[GregP]

I probably could find out specifically about Glacier Girl given a bit of time but I am not worried. The owner does all his restorations the right way. I'm sure he has some provision for carb heat, especially seeing as how the prototype P-38 was lost to carb icing.

Nobody who actually flies his warbirds would leave that off, and the owner of THIS warbird flies it.

 

[GregP]

Corect above, any Allison V-1710 is supercharged, assuming it is not an early dirigible engine, that is. I really don't know if any of the early dirigible engines have survived. I have personally seen maybe 150 Allisons, and have not seen one as yet. Perhaps one or possibly even more survives somewhere. The horsepower rating would likely be a bit less than 1,000 hp, if so but, if it IS a V-1710, at least the parts fit!

 

[MIflyer]

While working on my 1978 Celica years ago found that the temperature switch that applied vaccum to an actuator that drew in hot air over the exhaust manifold was defective. In fact it had never been hooked up during dealer prep. I then consulted the manual and found that the system was designed to control the inlet air temp to the carb at 110F. As designed the Carb heat was always on! I would have been always driving in a desert. I wired in an electrical switch to actuate the carb heat when I thought it was necessary, just like I do in an airplane.

 

[BiffF15]

I probably could find out specifically about Glacier Girl given a bit of time but I am not worried. The owner does all his restorations the right way. I'm sure he has some provision for carb heat, especially seeing as how the prototype P-38 was lost to carb icing.

Nobody who actually flies his warbirds would leave that off, and the owner of THIS warbird flies it.

Greg,

Which P38 still flies with its turbos operating?

Cheers,
Biff

 

[GregP]

Hi Biff,

Seems like it is "Tangerine" out of Tilamook, but I could be mis-remembering that. Steve Hinton (as well as a few other folks around the P-38 world) would know, but I don't see him much these COVID days. Did see him last Saturday, but didn't ask this question at the time. I went to see Rob Patterson fly our F1U-1a Corsair in a demo and check out the GT 350 Mustang club that was visiting the museum that day (I drove my Mustang GT in).

Always nice to hear an R-2800 running, and great to see the Museum and Fighter Rebuilders guys again.

Next time I see him, I'll ask.

 

[P-39 Expert]

Was there some kind of cooling issues during climb? Oil temps high? It would have helped if 3000 R.P.M. could have been used as well as the same boost as with level flight, for example 44" Hg. while climbing. I was hoping I could work up a 44" Hg./3000 rpm curve extrapolated from the Australian test but the 2600 R.P.M. used sort of complicates that notion.

Allison and the AAF increased combat power (3000rpm) limit from 5 minutes to 15 minutes in mid '42, about the same time that they finally got rid of the backfire screens. I don't know if the two were related but I suspect so. The new 15 minute limit greatly increased climb and ceiling in the tests since the rpm had to be reduced to 2600 after 5 minutes before mid '42. After mid'42 combat power (3000rpm) was used all the way up to service ceiling.

P&W had their combat power (2700rpm) limit increased from 5 minutes to 15 minutes at the same time. But their normal power of 2550rpm was so close to combat power (2700rpm) that it didn't make that much difference.