What was the problem with the allison engine?

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Had Allison's engineers been able to put the effort into gear-driven superchargers that Pratt and Whitney and Rolls-Royce did, it might have been a different story. As it was, there can be little doubt that the V-1710 had more potential than was actually exploited.

The V -1710 was an airship engine! Around the time that the Army was washing its hands of the Curtiss Conqueror, Allison began to develop its own engine, at the request of Allison General manager Norm Gilman. The target was 1,000 hp, and Allison intended that the engine should be large enough to deliver this power easily. A successful V-1710-A was test run in 1931 and delivered 650 hp at 2,400 RPM on 80-octane fuel. Development proceeded slowly until the Navy entered the picture. The Navy, while not losing its attachment to air-cooled power plants for airplanes, needed liquid cooling for dirigibles.

Power-to-weight ratio: 0.90 hp/lb

The Merlin/ PV12 was designed from the out set as a new generation fighter/bomber engine.

The Merlin was the most successful aircraft engines of the World War II era, and many variants were built by Rolls-Royce in Derby, Crewe and Glasgow,as well as by Ford of Britain in Trafford Park, near Manchester. The Packard V-1650 was a version of the Merlin built in the United States. Production ceased in 1950 after a total of almost 150,000 engines had been delivered, the later variants being used for airliners and military transport aircraft.
Also used in tanks.

Power-to-weight ratio: 0.96 hp/lb

Very near the magic 100hp/Lb mark.

Allison V RR/Packard Merlin? No contest.

Cheers
John
 
gjs238 said:
Yeah, why was that?
Click to expand...

Allison were asked to contact the Navy, who were working with the Hall Aluminium Aircraft Co on a flying boat, the XP2H-1. The Navy did talk with Allison on this project, but another angle was to emerge during these talks, that of the power units for airships. The Navy wanted an all-american engine available to replace the German Maybach power plants being used at the time. It gave Allison a contract for a single V1710-A engine, to develop 650hp at sea level. Ultimately, the airship engine supply position was not to materialise as the Macon was lost on the 12th February 1935, and with it went the Navy's airship programme.

Cheers
John
 
The Allison was not designed to be an airship engine. It was designed to fill a future market need for a 1000hp engine with high reliability and good fuel economy. The Army was mildly interested but had no money and suggested Allison see the Navy to see if they had any money/interest. Their only interest was as an airship engine so they funded one engine. The market for airship engines was rather small and would be a poor product for an engine maker just starting out. As a stepping stone to future developments and a chance to use somebody else's money for R&D it makes sense.

The power to weight ratios you posted are worthless because they make no reference to which model or which year or even under what conditions they were calculated.
 
Shortround, please see my post above.
However you stoutly defend the Allison it simply was not as good as the Merlin. We could speculate till the cows come home but, facts are facts and Allison missed the mark in WW2.
The Merlin would also have gone up a blind alley if the evaporative cooling system had not be changed.

Doubtlessly you will scoff at these :
http://www.outlawpulling.com/PDF/Allison Aircraft Engine.pdf
Typo, it was 92 not 90.

Specifications for the Merlin 61.
Data from Jane's[96]
General characteristics
Type: 12-cylinder, supercharged, liquid-cooled, 60° "Vee", piston aircraft engine.
Bore: 5.4 in (137.16 mm)
Stroke: 6.0 in (152.4 mm)
Displacement: 1,647 cu in (27 L)
Length: 88.7 in (225.3 cm)
Width: 30.8 in (78.1 cm)
Height: 40 in (101.6 cm)
Dry weight: 1,640 lb (744 kg)[nb 13]
Components
Valvetrain: Overhead camshaft, two intake and two exhaust valves per cylinder, sodium-cooled exhaust valve stems.
Supercharger: Two-speed, two-stage. Boost pressure automatically linked to the throttle, coolant-air aftercooler between the second stage and the engine.
Fuel system: Twin-choke updraught Rolls-Royce/S.U. carburettor with automatic mixture control. Twin independent fuel pumps.
Fuel type: 100/130 Octane petrol.
Oil system: Dry sump with one pressure pump and two scavenge pumps.
Cooling system: 70% water and 30% ethylene glycol coolant mixture, pressurised. Supercharger intercooler system entirely separate from main cooling system.[80]
Reduction gear: 0.42:1
Performance
Power output:
1,290 hp (962 kW) at 3,000 rpm at take-off.
1,565 hp (1,167 kW) at 3,000 rpm at 12,250 ft (3,740 m, MS gear)[nb 14]
1,580 hp (1,178 kW) at 3,000 rpm at 23,500 ft (7,200 m, FS gear)
Specific power: 0.96 hp/cu in (43.6 kW/L)
Compression ratio: 6:1
Fuel consumption: Minimum 39 Imp gal/h (177 L/h), maximum 88 Imp gal/h (400 L/h)[nb 15]
Power-to-weight ratio: 0.96 hp/lb (1.58 kW/kg) at maximum power.

Cheers
John
 

I don't believe I am defending the Allison. I am correcting a lot of misapprehensions you seem to have about it though. And some rather blatant examples of not evidence like the record flight. A great achievement by both the Pilots and and the Merlin engines but they didn't "choose" the Merlins over the Allison at the time because the Allison powered version of the plane was undergoing preliminary flight trials.

You might also want to read your own sources a bit better.

" The Allison Division of General Motors began developing the ethylene glycol-cooled
engine in 1929 to meet a US Army need for a modern, 1000 hp (750 kW), engine to fit
into a new generation of streamlined bombers and fighters. To ease production the new
design could be equipped with different propeller gearing systems and superchargers,
allowing a single production line to build engines for everything from fighters to
bombers.
The U.S. Navy purchased the first V-1710s, the B model (the only V-1710 that did not
have a gear driven supercharger) in 1931 and installed them on the airship aircraft
carriers the Akron and Macon."
Navy doesn't purchase an Allison engine until 2 years after the project starts and the yet the Allison was designed as an "airship" engine?

By the way, that web site has the wrong diameter impeller for that model Allison and if you divide 1325hp by 1445lbs you get 0.9169, not 0.90. of course the 1325hp figure is the wrong figure for a -85 engine also.

A lot of my "facts" come from the Book "Vees for Victory" by Danial Whitney. He may have gotten a few things wrong or had a few typos but I want something more than just a website before I throw out his data.
 
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I seem to recall that the Allison was superior to the Merlin in North Africa due to less maintenance issues from the environmental conditions. I am going to check Bodie, but I think they did a study on using Merlins in the P-38 that surprisingly indicated a significant weight gain and no increase or possibly a decrease in overall performance. Have either of you read anything about these issues.
 
It is true, Allison engined P-40's fared better than their Merlin engined counterparts in North Africa. It seemed that the Allison was more tolerant of ingesting sand then the Merlin was. The fact that the Allison used downdraft carburetors (with the intake above the propeller) probably kept more sand out of the engine than the Merlin's updraft carburetors did. Some Merlin powered P-40's in North Africa were re-engined with Allisons.

'Vees For Victory' covers the Merlin powered P-38 proposal. It appeared that there would have been no improvement in performance, and of course there was a heavy demand for Merlins in other aircraft.
 
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gjs238 said:
What I meant was, why the need for liquid cooled engines on dirigibles?
Or, what's the matter with air cooled engines on dirigibles?
Click to expand...

At the time (late 20s/early 30s) air-cooled engines had a higher fuel consumption per horsepower hour than the liquid cooled engines did. With flight times measured in days instead of hours this fuel consumption difference more than canceled out the higher weight per horsepower of the liquid cooled engines. Since arrangements were made to service the engines in flight (mechanic access) most liquid cooled leaks could be reached and repaired. Dirigibles also liked to be able to recapture the moisture in the exhaust to use as ballast. Some dirigible engines were actually constructed that could be reversed in rotation, if not while actually running, in just a few seconds in order to give reverse thrust (including the early Allison v-1710 airship engine) . Reversible pitch propellers not being available yet.
Allison had worked on a airship engine from 1927 on till 1929 or a bit later when the project was transfered to the GM Detroit Diesel division. It was a 6 cylinder inline two stroke diesel engine with a roots supercharger. Planned HP was 900. Allison did other airship work including remote shafts and gear boxes that allowed the propellers to be rotated 90 degrees for forward thrust or vertical lift.
 

That is what I remember now that you mentioned it. Could it also be that GM design and manufacturing philosophy encouraged looser parts tolerances than Rolls Royce? I also recall that the Hawker Hurricanes had problems in Africa for the same reason.
 
Lighthunmust said:
That is what I remember now that you mentioned it. Could it also be that GM design and manufacturing philosophy encouraged looser parts tolerances than Rolls Royce? I also recall that the Hawker Hurricanes had problems in Africa for the same reason.
Click to expand...

I really doubt that Allison's had looser parts tolerances than Rolls-Royce, at least enough looser to eat dirt and sand without wrecking the engine. All of these aircraft engines were, compared to even car engines of the 60s, 70s and 80s, lightly built and highly stressed, engines that will tolerate 12-15lb of boost for minutes on end do not have sloppy, ill fitting rings. The blowby into the crankcase would be tremendous. A leaking intake valve could spell disaster. Backfires into the intake manifold could and did wreck intake manifolds, superchargers, carburetors and in some cases blew parts of the intake duct off the aircraft. Sloppy main bearings on a 5 foot long crankshaft in a 1000-1400hp engine would make for a might short lived engine also.
 

Loose is a relative term. I certainly get your point about what too loose can do. Whether looser tolerances did or did not contribute to reliability in desert conditions; you have more faith in GM than I do. Rolls Royce had a history of making tight engines for air racers, not so much GM. Remember the GM design and manufacturing philosophy is what birthed the P-75.
 
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I think GM was capable of manufacturing most any precision device to whatever tolerance the specifications called for, be it an aircraft engine, a diesel engine, a complete aircraft, or a gun. And I think GM was without peer when it came to manufacturing percision devices in quantity. Vast, almost unimaginable quantities. If the Allison was 'looser' than a Merlin, it was certainly designed that way, not the result of haphazard manufacturing.

I have been told that at low altitudes the Allison powered P-51 and P-51A would outperform the later Merlin powered models. I would imagine the lighter weight of the early P-51 would come into play if in fact this is true. I don't have any data to back that claim up, perhaps one of you has more details?
 

GM is a large corporation, just because on Division of GM made a mistake or or one division made stamped sheet metal parts of rather loose tolerances doesn't mean that ALL their divisions couldn't make quality products. This is also 1940 GM as a corporation is 22 years old with many fits and starts, I am not sure there was time for a GM "design and manufacturing philosophy" to take root. Cadillac at the time was one of the quality car companies in the world, It took another 15-25 years for them to coast on that reputation.
Without a break down of the actual clearances used and tolerances allowed it is rather pointless to comment on which was looser. In some cases they didn't measure things the same way.
I have found out that R-R allowed (at least at overhaul) a maximum weight variation of 1 OZ between the pistons in one engines. Allison allowed 0.030lb or just under 1/2 ounce.
Piston to cylinder fit isn't specified the same way.
Allison has min and max dimensions at top and bottom of the cylinder (.015-.019 and .030-.034) while The Merlin has specifications for measuring at 90 degrees to gudgeon pin at the top of the piston (0.030-0.034 new-0.045 worn) and in line with gudgeon pin at the bottom of the piston (0.020-0.024 -0.035 worn).

Most figures are from the "Aircraft handbook" by Fred Colvin McGraw-Hill 1942, 5th edition. If somebody else wants to go through a 1/2 dozen pages of tables of allowable tolerances to PROVE the Allison was looser be my guest.
 

It was not just the weight, the P-51B had a 7in vertical splice in the fuselage and so had more frontal area and more skin drag. Scoop on the bottom was a bit bigger too.
 

Great reply! That probably settles the issue of loose tolerances. Even in 1940 I believe Rolls Royce had a better reputation for precision. Didn't the Allison also have less parts than the Merlin? If true perhaps that was a factor also.
 
The Merlin built by RR tended to be assembled using the "Master craftsman" approach, where components such as pistons were closely matched. A teacher I had in college flew P-51's in WWII and he said his personal airplane had a RR Merlin rather than a Packard one and that it made a big difference.

Or so he said anyway. One day I had flown my Ercoupe into Kissimmee, Florida and a man visiting from Scotland came over to admire it. As we chatted the P-51D Crazy Horse taxied by. "That's not a RRRoolllsss RRRoooycee." he said. I said, "What do you mean it's not a Rolls Royce? it's a P-51D. Its a Packard Rolls Royce Merlin V-1650."

He replied "Well, it's toooo smooooth to be a RRRoolllsss RRRoooycee."

I told him that I heard that the RR Merlins were smoother running than the Packards. He said he heard that the Packards were smoother than the Rolls Royces. Turned out he rebuilt Rolls Royce motorcars as a hobby so he may well have known what he was talking about.

Of course many of the Merlins flying today have what are known as "transport heads" which were built postwar for the Canadian Merlin powered copy of the DC-4. They were designed to be smoother running and longer lasting and are much sought after by warbird operators.

When Allison built the TF-41 version of the RR Spey engine for the A-7D and the USAF started overhauling it that had some big problems. Once I was sent to Myrtle Beach AFB with the orders to get the A-7D's there flying again - all were grounded for an bleed air duct problem. I got them all flying - all that had engines, which was only about half of the 80 that were based there. I later was told that RR tended to stack up part assemblies and match drill them to get closer tolerences, and Allison had copied that, so dismantling engines and then trying to put them all back together without keeping track of which part went with which engine was asking for trouble.

As for Allison parts in the Merlins, that is the rods, which are more solid than the Merlin rods and almost exactly the same dimensions, except I think in the bearing area.

I understand that Merlins had far, far, more individual parts than did the V-1710.
 


I always hope to be educated more than educating when participating in these discussions. Posts like the above are why I enjoy being a member of this forum. Great Post MIflyer!
 
Lighthunmust said:
I always hope to be educated more than educating when participating in these discussions. Posts like the above are why I enjoy being a member of this forum. Great Post MIflyer!
Click to expand...


Me too. Well said.

Allison V-1710 Engine - USA

I'm sure I have read somewhere that Allison used US automotive techniques to build their engines rather than the master craftsman approach of RR.
So, in theory, the Allison should have been available by the 1000 and built to an acceptable standard. Given that wartime aircraft were not built to last...
Tools for the job etc.

Art Afons used Allisons to power in Green Monster land speed record car as well.
Green Monster Number 2 was painted by Arfons' mother to resemble the World War II Curtiss P-40 Flying Tigers fighter airplane, with an open mouth showing large teeth. The top speed of the car was estimated at 270 miles per hour (435 km/h), and it could reach 140 miles per hour (225 km/h) in nine to ten seconds from a standing start. Running on passenger car tires, the car required four wheels on the rear drive axle to withstand the power. At the first World Series of Drag Racing at Lawrenceville, Illinois, it clocked the highest top speed at 132.35 miles per hour, and eventually a world record of 145.16 mph.
The later cars had various paint schemes where green was not necessarily the dominant color. The six-wheeled Green Monster Number 6 became the first dragster to break 150 miles per hour in the quarter mile. Green Monster Number 11, Art Arfons' favorite, hit 191 miles per hour to beat Don Garlits.
Arfons used an Allison V1710 V12 airplane engine in several of the Green Monsters. The Allison V12 powered the P-40 as well as many other aircraft including the P-51A, P-39 Aircobra, P-38 Lighting, P-63 and others.

Shortround, Is this true? I'm blowed if I can find the source to confirm the US car engine line build technique.

Cheers
John
 
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