Spitfire V Versus P-40E

[Shortround6]

What was the cost to manufacture the Allison V-12 vs the Merlin V-12?
I heard the Merlin used almost twice as many parts, compared to the Allison?

There are parts and there are parts.
Both are V-12s with 4 valves per cylinder.
The Merlin used quite a number of screws/nuts/washers to hold valve covers and other things on and perhaps more fasteners to hold some of the internal parts in place.
It does take more time to deal with all the extra fasteners but using the total number of "parts" to try to compare cost is rather bogus.

How many machine operations to make each crankshaft could be similar or way different depending on the machinery available.

 

[Reluctant Poster]

There are parts and there are parts.
Both are V-12s with 4 valves per cylinder.
The Merlin used quite a number of screws/nuts/washers to hold valve covers and other things on and perhaps more fasteners to hold some of the internal parts in place.
It does take more time to deal with all the extra fasteners but using the total number of "parts" to try to compare cost is rather bogus.

How many machine operations to make each crankshaft could be similar or way different depending on the machinery available.

Here's what the Fedden Mission had to say about production of the V-1710

 

[Reluctant Poster]

Here is the Fedden Mission on the subject of Packard production

 

[Todd Secrest]

There are parts and there are parts.
Both are V-12s with 4 valves per cylinder.
The Merlin used quite a number of screws/nuts/washers to hold valve covers and other things on and perhaps more fasteners to hold some of the internal parts in place.
It does take more time to deal with all the extra fasteners but using the total number of "parts" to try to compare cost is rather bogus.

How many machine operations to make each crankshaft could be similar or way different depending on the machinery available.

deleted.

 

[GregP]

Hi Todd,

For the cost difference:

One way you might look at it is by man-hours expended per engine overhaul. They have records for this for every month of the war from Jul 43 through Aug 45 in the Army Air Forces Statistical Digest of WWII, Table 115.

The two engine types you asked about were the Merlin (or V-1650) and the Allison (or V-1710).

For the V-1650:
Man-hours started out in Jul 43 at 462 hours.
For the entire war by month: High: 592 man-hours; Average: 320 man-hours; Low: 190 man-hours.

For the V-1710:
Man-hours started out in Jul 43 at 376 hours.
For the entire war by month: High: 376 man-hours; Average: 191 man-hours; Low: 117 man-hours.

Let's be fair and acknowledge that the average comes down as the workers get familiar with the engine. So, let's use the average: On average, it took 320 man-hours to overhaul a Merlin and 191 man-hours to overhaul an Allison. So, they can overhaul an Allison in 59.7% of the time it took for a Merlin.

I worked at a shop that overhauls Allisons for almost 4 years. In that time, we did some work on a couple of Merlins. Everything in a Merlin took longer, not just because we weren't as familiar with the Merlin, but also because the design is harder to work on in general (takes longer). As an example, in service you have to tighten the cylinder hold down nuts every 25 hours of operation. On an Allison, the cylinder banks are torqued down to 1,100 foot-pounds and never have to be touched until overhaul. Valve seats are another difference. You screw in the Merlin valve seats until they snap off the stud. Allison valve seats are permanent and are harder and more easily ground. Merlin valve seats are not so easily ground and are more likely to be replaced and than ground. I'd say that manufacture of a Merlin would take about 20 - 30% longer for machining and 40% longer for assembly.

So, let's try an example using 25% longer for manufacture. Say we can make an Allison V-1710 with 40 hours of casting, 300 hours of machining, and 50 hours of assembly. The casting should be very slightly longer for the Merlin, so it might come in at 50 hours casting, 375 hours of machining, and 70 hours assembly. The Allison takes 390 hours total and the Merlin takes 495 hours total.

Now, I pulled those Allison numbers above out of my hat (and by extrapolation, the Merlin numbers as well), but the percentages won't be too far off. So, my estimate is the Merlin takes, in total, about 27% more time and cost to manufacture, give or take a bit, and it takes about 40% more time to overhaul a Merlin when compared with an Allison overhaul.

Here's the thing, in my experience, the Merlin is as reliable as an Allison in field operation (after the initial Allison faults were ironed out ... took about 9 months or so), but the Allison runs longer before an overhaul is needed in non-turbo operation (P-39 / P-40 / A-36). I say non-turbo operation because today (my experience), almost all Allisons are operated without the turbochargers. If you think it might be hard to find parts for an Allison V-1710, try finding parts for an 85-year old turbocharger! If you needed high-altitude performance, the Merlin was your better choice for WWII. If you were flying in the PTO or Med, either one would do fine. The Allison cost was less to manufacture and overhaul, but it wasn't really a factor for military operations since the units didn't pay for aircraft ... they operated them. The Merlin used slightly more fuel than the Allison but that, too, was of little consequence because they had enough fuel for operations.

In service, there was little to choose between them once the initial problems with the Allison were ironed out, unless higher altitudes were required. If they were, the Merlin was the choice if there WAS a choice. Mostly, there wasn't a choice. If your unit flew P-38s, you generally didn't have the option to trade them in for P-51B/C/D/Ks. The USAAF made that choice for you, and U.S. units didn't GET Merlins until we started accepting P-51B/Cs, so we are talking after the summer of 1943 to come off the assembly line and late 43 or into 44 before our guys were flying Merlins overseas, at least in P-51s. So, we only had about a year and a half of time when we were operating both engines in numbers. The Brits were operating them together far longer than we were.

Second, why would you believe the Merlin was a double overhead cam? Download a pdf manual from this forum and check it out to be sure.

 

[Todd Secrest]

Hi Todd,
Second, why would you believe the Merlin was a double overhead cam? Download a pdf manual from this forum and check it out to be sure.

I just assumed the Merlin was dual overhead cam, but never thought to check that fact out.
(As the merlin was said to have more parts)

 

[GregP]

There is a manual section. On the place where you select "Aviation," look down a bit and see "Technical," and go to "Engines." You can find pdf manuals for service and overhaul for most of the important engines.

Cheers! no disrespect intended with the comment above.

Oh, and the estimate above would be for similar single-stage engines. The different might be a bit more for the Merlin 60 series and the rest of the 2-stage units.

 

[Schweik]

You mean supercharger not turbo right?

 

[Conslaw]

The British system used boost pressure above standard sea level pressure.

It is usually indicated by the plus (+) or minus (-) sign in front of the boost number. +16psi boost is 30.7psi absolute pressure.

So the MAp of +16psi is ~62.5inHg.

Ok, so you add sea level pressure to the conversion factor, which is just under 30 psi. That makes sense. Thank you.

 

[GregP]

Hi Schweik,

No turbocharger. Just to be clear, aircraft Allison V-1710s all had an integral supercharger. I think there might be some PT boat Allisons that did NOT have a supercharger. I have seen one, complete with drive gear, but did not pay any attention at the time to the supercharger because it was on a storage shelf and I couldn't see the accessory end of it since there were other Allisons on either side of it. It may or may not have had the supercharger. The power section looked identical to a V-1710, at least from the front quarter view.

The P-38 has both an integral supercharger and a remote turbocharger. The control system for the turbocharger gave some initial issues in the ETO in the P-38 in WWII. Today, not many Allisons actually run the turbocharger except for tractor-pull engines, many of which have rather exotic setups ... not many WWII turbos ANYWHERE are running. I think there is ONE P-38 and ONE P-47 that have operating turbochargers, but that was a few years back when I KNEW they were operating. Might still be operating, but also might not ... sort of depends if they had any major issues with the turbos, and the cache of spare turbo parts if so.

Here's an "exotic" setup:

The engines LOOK stock, but I have seen pics of Allisons in tractors that look like the supercharger was replaced with Hilborn injection:

Like the one above. That intake setup is nothing any WWII vehicle ever saw.

At any time, it isn't difficult to lock the turbocharger from the system. All you have to do is lock the wastegate so it bypasses the turbocharger, and then lock the exhaust turbine so it doesn't rotate. Presto, non-turbo operation.

I'd pretty much assume that the operating B-17s and B-24s (or PB2Ys) also are running in non-turbo mode since parts for their turbos aren't any easier to find, and there is NO reason for any of them to be at 25,000+ feet today. Even the B-29 "Doc" was restored without operating power recovery turbines. I could be wrong and maybe someone IS running turbos, but I'd have to see that to believe it.

 

[Schweik]

Right, but you keep saying turbocharger, which for the Allison, was only on the P-38. The P-40, P-39, P-51A had the integral supercharger, are you saying they bypass that?

 

[GregP]

No, the supercharger is running when the crankshaft is turning. The carburetor feeds the supercharger impeller, which exits directly into the intake manifold. Can't shut off the S/C without shutting off the engine.

The S/C impeller is the small turbine-looking thing on the right, under the carburetor.

 

[Schweik]

I say non-turbo operation because today (my experience), almost all Allisons are operated without the turbochargers. If you think it might be hard to find parts for an Allison V-1710, try finding parts for an 85-year old turbocharger! If you needed high-altitude performance, the Merlin was your better choice for WWII. If you were flying in the PTO or Med, either one would do fine. The Allison cost was less to manufacture and overhaul, but it wasn't really a factor for military operations since the units didn't pay for aircraft ... they operated them. The Merlin used slightly more fuel than the Allison but that, too, was of little consequence because they had enough fuel for operations.

I assume you are referring to P-38s here then?

 

[Dimlee]

Something like 8 or 9 months out of the year depending which part of the gigantic front line you are talking about, there was often a fairly low cloud ceiling which prevented high flying planes from seeing the battlefield or lower flying aircraft.

8 or 9 months of such weather - probably, but only in the northern part of the Eastern Front, from the Leningrad/Pskov region and up.

 

[Schweik]

So clear skies over Moscow year round?

 

[Dimlee]

So clear skies over Moscow year round?

So - not.

 

[Schweik]

Right. So .. gloomy roughly 7 months out of the year? 6?

Average Weather in Moscow, Russia, Year Round - Weather Spark

 

[Dimlee]

Something like that, but there are periods of sunny weather even in the winter when high pressure settles. I lived in Moscow for 10 years not counting many trips before and after. Sky diving season was early April to end October/early November, as I remember.

 

[GregP]

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.

 

[wuzak]

In point of fact, the Curtiss XP-37 was both supercharged and turbosupercharged, but they only made 14 of them.

Did you mean to say that there was an additional supercharger on the XP-37 and YP-37 other than the engine stage supercharger on the V-1710?

The XP-37 (1 made) and YP-37 (13 made) were turbocharged and supercharged the same way the P-38 was.