could the Allison engine have done what the Rolls Royce Merlin did?

Navalwarrior said:

Resp:
The USN used an inline aircraft engine in their PT Boats.

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Yes and no.

The Packard M-2500 was a marine engine developed from a 1920s aircraft engine. The aircraft engines pretty much maxed out at about 800hp at 2000rpm supercharged and while a few were supercharged they were very rare. Engine went about 1200lbs. depends on reduction gear. and supercharger, could hit 1600lbs depending on version.

The more common boat engine, the 4M-2500 was rated at 900hp at 2000rpm continuous. 1200hp at 2400rpm for one hour out of 25 and for emergency use only 1350hp at 2500rpm restricted to 15 minutes in one 10 hour period. The engine and reversing gear (includes clutch) with perhaps exhaust manifolds (?) went 2950lbs. I have no idea how much the reversing gear weighed. Starter and generator may also have been included?
Engine construction was a bit strange for 1940 but very common in the 1920s. Each cylinder was a individual tube closed on one end with the valve seats in the closed "head" of the cylinder. A stainless steel water jacket was welded around each cylinder, a "valve housing" ran the length of all six cylinders and held the valve mechanism The over head cam, rocker shafts, rocker arms valves springs, etc. It was one piece made out of aluminium and was interchangeable left to right. Just turn it around so the inlet side was inside the V.
So far I have not found a manifold pressure.
USN manuals can be found on line.

I have no idea what was changed between the aircraft versions and the Marine versions.

GregP said:

The supercharger could have changed anytime, and eventually did. They went from a 9.5" impeller to a 12.25" or a 12.18" impeller late in the series. To be specific, the first Allison (numerically by dash number) that had the larger impeller was the V-1710-97, which was the first of the G-series engines. The engine had a 9.60 : 1 gear ratio, the auxiliary section had a 7.485 : 1 gear ratio, and the propeller gear ratio was geared down 2.36 : 1.

The 12.18" impellers were in the -125 and -127 engines.

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The 12.25" and 12.18" impellers were for the auxiliary stage of the 2 stage supercharger.

The main/engine stage remained 9.5" for the duration of the war.

There were a couple of experimental 2 speed single stage engines that used a 10.25" supercharger impeller, but these did not make production.

10.25" is the same diameter as the supercharger impeller on the bulk of Merlin single stage engines.

Most Merlin 2 stage engines had superchargers of 12.0"/10.1" diameter, with early versions using 11.5"/10.1".

The RM.17SM, which passed the type test but was never produced or given a dash number, had larger supercharger impellers of 12.7"/10.7".

Thank you for the info SnowyGrouch.

ThomasP said:

Hey guys,

On the subject of the use of tungsten in the WWII turbos. Do we know if there was any tungsten actually used in the US turbos? I ask because as far as I see it there would be no need for it, and there were no applicable(?) alloys (as far as I know) in existence at the time.

The reason that I say this is an alloy such as Stellite would be far easier to use in the high temperature environment of the turbo. At the time (late-1930s) it could be cast into complex shapes, hot drawn and forged, and electroplated in relatively thick layers. Stellite is a cobalt based alloy - there is no Tungsten used.

Otherwise, for tungsten, the only useful alloys (I think) available at the time would be the tool steels in the T series (T2 and T4 for example) but fabricating the shapes needed for the turbos would be very difficult, probably not really feasible at the time, and if you could make them they they would be enormously expensive. As far as i can imagine, the only possible practical use in a turbo might be for bushings or bearings. But, again there are other materials that would be more usable (EG Stellite and M series tool steels). Also, if Tungsten based tool steel was used, the amount of tungsten used in the alloys would not have been enough to interfere with the production of HVAP. The amount of tungsten used in tungsten-carbide cutting tools, however, might have been enough to do so.

I believe that GE (and others?) concentrated on early titanium alloys, the temperature resistance (not as high as tungsten alloys or Stellite) was high enough, at least in theory. Titanium bearing ore was difficult to process at the time, and manufacturing it was also difficult, plus extreme temperature cycles (such as in turbos) would have caused cracking in most of the alloys available at the time.

Having said all the above, I thought that the main problem was simply inexperience with the complex problem of very high temperatures combined with wear of the bushing/bearing surfaces at extremely high rpm.

I admit that I am not intimately familiar with the materials used for the various parts of the WWII GE turbos. Does any one have info on what parts used tungsten alloys? I would appreciate the info.

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The statement that Stellite does not contain Tungsten is not true, some varieties do, for example Stellite 6 contains 4-6% Tungsten. From what I have been able to ascertain early turbos used Stellite 6 for their blades , however the bulk of production used Stellite 21 which does not contain Tungsten and has the advantage of being able to be cast, which greatly simplified blade production. See the following link

Our Company History

Continuing my harping.
One of the improvements suggested by NACA in the attached paper replaces the pipe joining the two supercharger stages with a lower pressure drop design.View attachment 576951

As you can see the bends in the NACA design are much more gradual. According to the NACA tests, this simple change increased power by 10 HP. If two badly designed elbows can cost that much horsepower think of how much power was wasted in the Allison's convoluted intake manifold. I amazed that Allison still didn't understand flow at this late a stage.

That is a horrible tight bend on the standard duct I have seen ride on mowers with better intakes

Hi Wayne,

When the supercharger impellers come in 2 sizes, it was obviously a 2-stage engine.

As you know from visiting here, Joe has a couple of 10.25" superchargers in his inventory. They fit the standard V-1710 crankcase.

In the picture above, you can see the more gradual turn doesn't fit in the same vertical space. So, as long as you HAVE that room, you can make the change. If you don't have that room, you can't. If it were me and I didn't have the room, I'd make a bulge there to help the engine ... but you can't make a bulge in a wing spar easily. So, I guess it depends on where the connector is located as to whether or not the change is reasonable.

Reluctant Poster said:

Continuing my harping.
One of the improvements suggested by NACA in the attached paper replaces the pipe joining the two supercharger stages with a lower pressure drop design.
As you can see the bends in the NACA design are much more gradual. According to the NACA tests, this simple change increased power by 10 HP. If two badly designed elbows can cost that much horsepower think of how much power was wasted in the Allison's convoluted intake manifold. I amazed that Allison still didn't understand flow at this late a stage.

Click to expand...

fastmongrel said:

That is a horrible tight bend on the standard duct I have seen ride on mowers with better intakes

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Too bad that NACA found it fit to test and suggest improvements for the V-1710 in 1946.

Snowygrouch said:

This is correct, the efficiency of the 1st stage is the most critical, and poor 1st stage performance is multiplied by each subsquent stage. They do not add, they multiply; its just that often the efficiecies are so low that from inspecting the total pressure ratio of a 2-stage compressor, its easy to think its added (e.g Merlin-61 total PR is about 6:1, but from the individual
stages you might expect nearer 8 or 9 if multiplied - hence an easy mistake to make.).

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Not just in superchargers either. Early low bypass engines like the (cough, cough!) TF30 and early F100's.

Thanks for the info Reluctant Poster.

Reluctant Poster said:

Continuing my harping.
One of the improvements suggested by NACA in the attached paper replaces the pipe joining the two supercharger stages with a lower pressure drop design.View attachment 576952View attachment 576951View attachment 576954

As you can see the bends in the NACA design are much more gradual. According to the NACA tests, this simple change increased power by 10 HP. If two badly designed elbows can cost that much horsepower think of how much power was wasted in the Allison's convoluted intake manifold. I amazed that Allison still didn't understand flow at this late a stage.

Click to expand...

Very interesting, I did not know that NACA was doing engine related research as well. Especially to the point of designing replacement parts.
I had assumed their work was limited to air-frame aerodynamics.
In this case, NACA is really pulling some of the load for Allison and/or Bell.

The document refers to the original elbow as "the standard Bell elbow."
Does that imply that Bell designed that elbow, not Allison?

tomo pauk said:

Too bad that NACA found it fit to test and suggest improvements for the V-1710 in 1946.

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They hadn't been asked before then. Do note, however, that it's mentioned in the introduction that the USAAF and Allison had known of the problem before this.

Navalwarrior said:

Resp:
The post WWII production F-82 used the Allison engine, as the Packard Merlin production license was about to expire. The F-82 had outstanding performance.

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Don't:
Upon further research: "It was found that Allison-powered F-82 models (C models) demonstrated a lower top speed and poorer high-altitude performance than earlier Merlin-power versions." The C model used Allison V-1710-100 engines. Only 20 production F-82B models were made using the British designed Merlin engine.

Navalwarrior said:

Don't:
Upon further research: "It was found that Allison-powered F-82 models (C models) demonstrated a lower top speed and poorer high-altitude performance than earlier Merlin-power versions." The C model used Allison V-1710-100 engines. Only 20 production F-82B models were made using the British designed Merlin engine.

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From what I remember reading, the Allison-engined F-82s were about 20 mph, or about 5% slower, than the Merlin-engined aircraft.

V-1710 as installed on P-82 have had less power at altitude than the Merlins on P-82s.

Reluctant Poster said:

The statement that Stellite does not contain Tungsten is not true, some varieties do, for example Stellite 6 contains 4-6% Tungsten. From what I have been able to ascertain early turbos used Stellite 6 for their blades , however the bulk of production used Stellite 21 which does not contain Tungsten and has the advantage of being able to be cast, which greatly simplified blade production. See the following link

Our Company History

Click to expand...

As a matter of general interest, the attached is a history of strategic metals in WWII.

tomo pauk said:

Too bad that NACA found it fit to test and suggest improvements for the V-1710 in 1946.

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Too bad Allison couldn't design it properly in the first [place. Any company that relies on an outside entity to correct their mistakes will fail more often than not.
In any event the actual testing was done during the war.

Reluctant Poster said:

Too bad Allison couldn't design it properly in the first [place. Any company that relies on an outside entity to correct their mistakes will fail more often than not.
In any event the actual testing was done during the war. View attachment 577350

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Thank you for the excerpt.
BTW, about the 1st sentence - RR was buying the bearings at Allison before ww2 because their bearings didn't work. They also used Farman-designed 2-speed drive for their superchargers.

tomo pauk said:

Thank you for the excerpt.
BTW - RR was buying the bearings at Allison before ww2 because their bearings didn't work. They also used Farman-designed 2-speed drive for their superchargers.

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RR was never afraid to buy in components they felt outsiders could do better. They built their own carburetors (including the prototype Merlins) but realized the SU carb had an excellent method of controlling mixture vs altitude so they adopted that instead of their own.

Their bearings didn't work? Is there evidence showing that was the case? Rolls Royce saw a better way to do things and they did what successful organizations often do and took out a licence allowing them to produce a better product.
Here is an interesting discussion on RR Kestel and Merlin bearings in another forum
RR Kestrel Gilman Bearings

Thanks for the link, Reluctant Poster. Nice info. In that link, one poster asks how Allison "renews" bearings. As it happens, I have some experience with Allison main bearings.

The standard crankshaft main journals are 3.7475 inches diameter with 0.0045 inches clearance between bearing and crankshaft. The only main bearing sizes are standard and 0.002 inches under, which means the bearing is 0.002 inches thicker than standard to allow for wear. The main bearing number stamped into the bearing faces the pilot in the #1 cylinder. The bearings are tapered and the standard bearings should have a 0.1865 inch taper.

The bearings themselves have 0.040 inches of Silver plated onto the steel and 0.002 inches of lead plated over the Silver. Copper is flashed on the outside of the shell half. The Allison V-1710 runs pressurized oil through the hollow crankshaft and the mains all have oil holes in them, so the mains get oiled while the engine is running. This is also why a "dry" engine should be pre-oiled before turning it over. If the engine has not been run in a while, it should be pre-oiled before turning the crankshaft over to save the main bearings.

When the mains are changed, the old bearings can be collected and sent out to have them re-plated to new specifications. When they are installed, the bearings need to be fitted to the crankshaft. Most competent modern overhaulers use plastigage for clearance, and ALL new bearings need to be scraped the old way to get proper clearance. I know one overhauler who has an original Allison factory overhaul main bearing gauge that gets assembled into the mains to check for clearance. You lay it into the mains, assemble the case, and torque the mains to spec. When you do this, you should be able to turn the gauge by hand. If not, the bearings are too tight.

If you actually run one with mains that are too tight, the engine may seize within 20 - 30 minutes of flight or run time, and the cases, crankshaft, and rods will show signs of high heat by turning a bit blue-black. Joe Yancey found that in an Allison that had been installed into the P-38 "Brooklyn Bum" when he checked the engine after the aircraft came back to the U.S.A. from the U.K. If it had been run for longer than about 30 minutes, the engine would have seized.

It is important which way the crankshaft goes into the engine. When viewed from the accessory end, position the first crank throw at 12 o'clock. If the next throw points left, then it is left hand turning, viewed from the supercharger end. If the next throw points right then it is right-hand turning, viewed from the supercharger end. Serial numbers were originally stamped on supercharger end.

Left-hand and right-hand engines need different ignition harnesses. When you turn the crankshaft around (and install the idler gears and other-handed starter) for a left-hand engine, the inside cylinder wires have to be reversed in the harness. Another idler gear is also installed so the camshaft turns in the proper direction for the other-turning crankshaft.

All Allisons should be right-hand turning except for the left-hand engine on a P-38 and the odd built-up left-hand engine if someone wants to put an Allison into an IL-2 or MiG-3. Paul Allen's IL-2 up in Seattle (Flying Heritage Museum) has a left-hand turn Allison by Joe Yancey in it, as does the MiG-3 flying occasionally in Moscow.