Allison and Merlin in a P-51

[denny]

Regards the Allison in the P-51

Could the Merlin 2-Stage have been mated to the Allison without much fanfare.?

If that WAS possible, would the P-51 have the same gas mileage with the Allison as the Merlin.

Could Allison have kept up with the demand for Allison motors, in a P-51 from 1944 onward.?
Thank You

 

[MiTasol]

Only by designing a new accessory housing.

That does not do much apart from house. mount and/or drive the carburetor, starter, generator, vac pump, fuel pump, camshafts, magnetos, gun synchronizers, fuel pump, oil pump, coolant pump, hydraulic pump, cuno filter, etc, etc.

In short, everything except the prop and the prop governor.

 

[denny]

Only by designing a new accessory housing.

That does not do much apart from house and/or drive the starter, generator, vac pump, fuel pump, camshafts, magnetos, gun synchronizers, fuel pump, oil pump, coolant pump, hydraulic pump, cuno filter, etc, etc.

In short, everything except the prop and the prop governor.

Oh.....so.....just those 12 or 15 things then.?

 

[Dash119]

Carb on the Merlin was updraft, carb on the Allison was downdraft...

 

[tomo pauk]

Regards the Allison in the P-51

1 - Could the Merlin 2-Stage have been mated to the Allison without much fanfare.?

2 - If that WAS possible, would the P-51 have the same gas mileage with the Allison as the Merlin.

3 - Could Allison have kept up with the demand for Allison motors, in a P-51 from 1944 onward.?

1 - It was mated for test purposes, and it seems to have worked. At least per 'Vee's for victory' book.
2 - Yes, if not better, since V-1710 have had the greater compression ratio.
3 - They certaily could, especially since P-40 was being phased out, ditto the P-39, and USAAF didn't want the P-63.

 

[Reluctant Poster]

Regards the Allison in the P-51

Could the Merlin 2-Stage have been mated to the Allison without much fanfare.?

If that WAS possible, would the P-51 have the same gas mileage with the Allison as the Merlin.

Could Allison have kept up with the demand for Allison motors, in a P-51 from 1944 onward.?
Thank You

Alison production peaked in 1943. It was the only major US engine to actually decline in 1944 going from 21,604 to 20,191 with numbers dropping month by month. In the last 1/2 of the year it was basically producing at 1/2 capacity. In contrast Packard was increasing production rapidly and further more Continental was scheduled to start producing Merlins and Oldsmobile was being brought in to produce components for Merlins. Packard produced 15,084 engines in 1943 and 22,969 in 1944.

 

[pbehn]

It could be done, the question would be whether it could have been got into production in numbers to make a difference, and if it wasnt better than the Merlin why do it? The P-82 twin Mustang first flew as the war was coming to an end.

"Economy" depends on many things, I have read that the RAF found the the Mustang MkI to be more economical in low altitude low speed conditions because the Allisson engine ran more smoothly at low revs.

 

[denny]

It could be done, the question would be whether it could have been got into production in numbers to make a difference, and if it wasnt better than the Merlin why do it? The P-82 twin Mustang first flew as the war was coming to an end.

"Economy" depends on many things, I have read that the RAF found the the Mustang MkI to be more economical in low altitude low speed conditions because the Allisson engine ran more smoothly at low revs.

Yeah, i was think "Economy" along the lines of bomber escort to Berlin........stuff like that.
The reason videos always give for the P-51, with Merlin, saving the day for The 8th Air Force.

 

[Reluctant Poster]

It could be done, the question would be whether it could have been got into production in numbers to make a difference, and if it wasnt better than the Merlin why do it? The P-82 twin Mustang first flew as the war was coming to an end.

"Economy" depends on many things, I have read that the RAF found the the Mustang MkI to be more economical in low altitude low speed conditions because the Allisson engine ran more smoothly at low revs.

The P-82 was intended to be Merlin powered but after VJ day Packard lost the licence. The Allison contract was cancelled shortly after VE day. Allison actually had to set up a new production line.
The Allison engine did not perform as well as the Merlin and had significant problems. According to Ray Wagner in Mustang Designer, Edgar Schmued hated the Allison.

People for some reason beat on the Merlin as being some sort of gas hog, quoting SFC as if that were the whole story whereas in practice the Merlin accomplishments speak for themselves. Merlin powered Mosquitoes and Mustangs flew some of the longest missions of the war in their category of aircraft. In fact the world record for non stop flight set in 1947 was by a Merlin powered P-82B.
The Merlin had the most efficient cooling system of any water cooled engine. They worked very hard before WWII to reduce the drag of their cooling system and it paid off. Read Chapter VIII of Development of Aircraft Engines by Robert Schlaifer

 

[pbehn]

The P-82 was intended to be Merlin powered but after VJ day Packard lost the licence. The Allison contract was cancelled shortly after VE day. Allison actually had to set up a new production line.
The Allison engine did not perform as well as the Merlin and had significant problems. According to Ray Wagner in Mustang Designer, Edgar Schmued hated the Allison.

People for some reason beat on the Merlin as being some sort of gas hog, quoting SFC as if that were the whole story whereas in practice the Merlin accomplishments speak for themselves. Merlin powered Mosquitoes and Mustangs flew some of the longest missions of the war in their category of aircraft. In fact the world record for non stop flight set in 1947 was by a Merlin powered P-82B.
The Merlin had the most efficient cooling system of any water cooled engine. They worked very hard before WWII to reduce the drag of their cooling system and it paid off. Read Chapter VIII of Development of Aircraft Engines by Robert Schlaifer

I know, but I was replying to the OP. If the Allisson had a RR supercharger tagged on it would also be in part a licensed product. One of the reasons I posted "Economy" depends on many things", is because er economy depends on many things. The P-51 was 30MPH faster than a Spitfire in top speed but was faster than a Spitfire at all engine settings, so went further on the same fuel/hour, the P-51B?c D was more economical because of its airframe and same (as you say) in a Mosquito. Additionally, the Allisson may have run smoother at low revs, low altitude, but that may be because it was optimised for low altitude use anyway, my knowledge of superchargers doesnt stretch that far. but generally there is no free lunch with engines, the single stage Merlin was better at higher altitudes so maybe low speed "lumpiness" was the price paid, it frequently is with tuned engines.

 

[kmccutcheon]

They worked very hard before WWII to reduce the drag of their cooling system and it paid off. Read Chapter VIII of Development of Aircraft Engines by Robert Schlaifer

Another wonderful reference is Hucknall - The Rolls-Royce Flight Test Establishment by David Birch, published by the Rolls-Royce Heritage Trust in 2017.

 

[MiTasol]

Carb on the Merlin was updraft, carb on the Allison was downdraft...

And that also bolts directly to the Accessory housing assembly

 

[wuzak]

1 - It was mated for test purposes, and it seems to have worked. At least per 'Vee's for victory' book.
2 - Yes, if not better, since V-1710 have had the greater compression ratio.

1. As I understand it, the Merlin supercharger was not directly connected to the V-1710, but driven separately. Performance was very much the same, being dictated by the supercharger performance.

2. Later V-1710s also got a drop in CR, to the same as the Merlin. The higher CR allows for better economy, but reduces the boost that cam be run.

 

[emu27]

The Allison engine did not perform as well as the Merlin and had significant problems.

Love to hear of the significant problems.

The Allison was the preferred engine by those doing low level Rhubarb type missions because it provided greater range through better fuel economy and was more robust, being better able to endure abuse, so good in fact that they removed the boost control in order to increase manifold pressure. When the Merlin production line started the USAAC operating in Africa put forward a proposal (have a copy) to keep the Allison powered version in production because of its superior qualities in the low level role. The Merlins forte was its high altitude capability. The better economy of the Allison was due to its ability to run at very low RPM that the Merlin was unable to match.

According to Ray Wagner in Mustang Designer, Edgar Schmued hated the Allison

On what page does he make that statement?

People tend to forget that the Mustang was originally designed as an Army Co-operation aircraft ie low level operations, for which the Allison was the perfect choice.

 

[wuzak]

The Allison was the preferred engine by those doing low level Rhubarb type missions because it provided greater range through better fuel economy and was more robust, being better able to endure abuse, so good in fact that they removed the boost control in order to increase manifold pressure. When the Merlin production line started the USAAC operating in Africa put forward a proposal (have a copy) to keep the Allison powered version in production because of its superior qualities in the low level role. The Merlins forte was its high altitude capability. The better economy of the Allison was due to its ability to run at very low RPM that the Merlin was unable to match.

The Allison Mustangs had lower drag, due to being less powerful and requiring less cooling. This played a role in the performance of the Mustang I/II vs the III/IV at low level, including fuel economy.

I'm not sure that running very low rpm was a wise thing in a combat zone.

People tend to forget that the Mustang was originally designed as an Army Co-operation aircraft ie low level operations, for which the Allison was the perfect choice.

It really wasn't. Certainly no more than the P-40 or P-39 were designed as "Army Co-operation" aircraft.

And if it was the case, it would have been unlikely that the Mustang would have changed from the 8.8:1 supercharger gear to the 9.6:1, which was aimed at better altitude performance.

 

[MiTasol]

Love to hear of the significant problems.

The Allison was the preferred engine by those doing low level Rhubarb type missions because it provided greater range through better fuel economy and was more robust, being better able to endure abuse, so good in fact that they removed the boost control in order to increase manifold pressure. When the Merlin production line started the USAAC operating in Africa put forward a proposal (have a copy) to keep the Allison powered version in production because of its superior qualities in the low level role. The Merlins forte was its high altitude capability. The better economy of the Allison was due to its ability to run at very low RPM that the Merlin was unable to match.

On what page does he make that statement?

People tend to forget that the Mustang was originally designed as an Army Co-operation aircraft ie low level operations, for which the Allison was the perfect choice.

Hi Emu
I think you have the wrong end of the stick on several items - the most glaring being that the Mustang was designed for the RAF - NOT the USAAC (and even Wackypedia gets that right). The USAAC wanted none to the point that the first two USAAC aircraft were donated by NAA to force an evaluation.
I cannot comment on the fuel burn but the reliability and service life of the Allison was definitely better than the Merlin.
I have never heard of any operator removing the boost control and in fact the early Allisons did not have boost control at all - it was a late addition whereas the Merlin had it somewhat earlier. Some pilots "removed" the wire that limited throttle travel on the Allison to get more power - maybe that is what you are thinking of.

 

[ColFord]

Extract from USAAF Report on RAF Use of the Mustang Mk.I and Mk.IA aircraft dated 26 August 1943.

QUOTE:
Performance of the Mustang I and IA

32. The record of the Mustang I is excellent. The pilots all like to fly it and its success has been due to its reliability, simplicity and the fact that it is faster than any contemporary aircraft at low and medium altitudes.

33. This aircraft is powered with the Allison 1710-39 engine having a rated power of 1150 H.P. at 3000 R.P.M. and 44" Hg. at 12,000 ft. The engine was originally equipped with an automatic boost control limiting the manifold pressure at the lower altitudes to 44". The British remove this so as to get the vastly increased performance at lower altitudes thru the judicious use of over-boost. As has been mentioned before, they have had exceptionally good service out of these engines and due to its smoothness at low RPM's, they are able to operate it so as to obtain a remarkably low fuel consumption giving them an operational range greater than any single engine fighter they possess (the fact that the Merlin engine will not run well below 1600 prevents them from obtaining an equivalent low fuel consumption and therefore limits its usefulness for similar operations).

34. Actual combat has proven that the aircraft can run away from anything the Germans have. It's only inferior points are that it can't climb as well as the ME-109 and FW-190 and that at the slower speeds of close combat it loses effectiveness of aileron control and therefore has a poor rate of roll – but its turning radius with a slight amount of flap is shorter than either of the German aircraft.

35. In view of the British experience, it is felt that we have a plane excellently fitted and suited for long range, low altitude daylight intrusion and for a medium altitude escort fighter to accompany our medium bombers. It must be realized that an aircraft will fulfil the conditions for a medium bombardment escort fighter might not be completely suitable for a long range intruder due to the inability on the part of the engine to run at the exceptionally low R.P.M. necessary for such long range operation. This is also assuming an operation which will allow a major portion of such missions to be made over waters where interception would be unlikely, such as from North Africa or the Mediterranean Islands to the mainland.

36. In view of the British operation and the fact that we have an approved war emergency rating on the 1710-39 engine of 56", it is suggested that immediate steps be taken to remove the automatic boost controls from our P-51 airplanes in this theatre and that the instrument dials be marked with the proper lights. The British have operated at full throttle at sea level (72" Hg) for as much as 20 min. at a time without hurting the engines. According to them, the Allison is averaging 1500 hours between bearing failures as compared to 500 to 600 hours for the Merlin. The Allison, they have found, will drag them home even with the bearing ruined.
END QUOTE


The V-1710 engines in the Mustang Mk.I aircraft "as delivered" did not have an automatic boost control. On the V-1710 engines on the Mustang Mk.IA, they were initially fitted with a Delco-Remy or later a Claudel Hobson automatic boost control, however these proved troublesome and prevented the engines from developing the required level of "over-boost" required, when combined with the modifications (cropping) conducted on the supercharger vanes to improve performance below 10,000ft. (Sources: Various AIR and AVIA files held in UK Archives relating to Mustang Aircraft, Air Ministry Mustang Mk.I and Mk.IA Pilots Notes, Erection and Maintenance Manuals AP Series, original diaries, personal papers, original service documents and interviews with surviving RAF aircrew and groundcrew who flew and maintained Mustang Mk.I, Mk.IA, Mk.II aircraft in RAF service 1942 to 1945.)

Of note, in the second half of 1943, the RAF/Air Ministry had to put in a special request to get a production run or allocation of additional Allison V-1710 engines from the USA in order to meet their expected engine wastage rate for their Mustang Mk.I and Mk.IA aircraft that were expected to be in service by the time of the invasion of Europe and to sustain them over a period of heavy operational use leading up to and after the Invasion. This was so that sufficient engine spares were available to do engine changes on Mustangs without having to wait for engines to be overhauled or repaired. The request also included key major and minor overhaul parts 'sets' and consumables eg pistons, piston rings, gasket sets. Considerable pressure was brought to bear and the order was fulfilled in early 1944, the shipment of the required engines and parts being given shipping priority from the USA to UK and split across a number of ships so that loss of any one ship would not cause the complete or significant loss of the required spares.

 

[MiTasol]

Thanks for that Col

Do you have a link to the original report so I can read the whole thing?

 

[ColFord]

There is an online copy/transcript of the report here:

E-GEH-16

I got my original hard copy of the report from the USAF Historical people about 20-25 years ago, along with copies of a range of other relevant reports.

To put the original USAAF report in context, the RAF officer they interviewed was Wing Commander P Dudgeon DFC, who had flown the Mustang Mk.I and Mk.IA operationally in 1942 and 1943, including most recently command of one of the RAF ACC Mustang Squadrons. At the time he was interviewed by the USAAF he had recently taken up a staff posting with HQ Army Co-operation Command in the middle of the transition via Fighter Command to 2 Tactical Air Force. He had significant operational experience with ACC, including on Westland Lysanders over France and Belgium in 1940, then with various ACC Squadrons flying Curtiss Tomahawks and North American Mustang Mk.I and IA through until mid-1943. In his ACC staff role he had access to the full range of information on the then current status of the RAF Mustang Mk.I and Mk.IA operations, aircraft modification and engineering status, etc, etc and was able to call on the various experts within the HQ to provide information to respond to the USAAF questions.

 

[ColFord]

The Allison Mustangs had lower drag, due to being less powerful and requiring less cooling. This played a role in the performance of the Mustang I/II vs the III/IV at low level, including fuel economy.

I'm not sure that running very low rpm was a wise thing in a combat zone.




It really wasn't. Certainly no more than the P-40 or P-39 were designed as "Army Co-operation" aircraft.

And if it was the case, it would have been unlikely that the Mustang would have changed from the 8.8:1 supercharger gear to the 9.6:1, which was aimed at better altitude performance.

The RAF pilots flying the Mustangs developed a technique for their operations that required longer range. They had a set of engine/boost/rpm settings that allowed a lower rpm and boost setting that gave a low fuel consumption but relatively "fast" speed cruise (around 240 to 250 mph). They would use that for the over water crossing to a point close to the enemy coast. They then went to a higher rpm and boost setting that gave a moderate fuel consumption (around 270mph) , accellerated up to a higher speed, then went to a higher rpm and boost for the crossing of the enemy coast (around 300-320mph) and penetration into the occupied area beyond the main coastal defence belts. They then went back to a rpm and boost setting that gave them a good higher speed cruise around 270mph, from which they could accelerate rapidly if intercepted or needed extra speed to engage a target of opportunity, but one that still gave good fuel consumption. The setting they used had been determined by extensive test and practice flying over the UK and gave a good balance between speed/performance and fuel economy, plus avoiding engine setting that led to things like spark plug fouling or excessive oil cooling. They also had engine managment practices they used during periods of extended 'cruising' to vary engine setting to reduce engine issues. Exit from enemy occupied territory and return to base in the UK was a reverse set of engine setting to those used on the approach.

A number of the pilots had the opportunity to fly both the Allison engine and Merlin engine Mustangs. In their opinions it was "horses for courses", both the Allison and Merlin having their strengths and weaknesses depending on what you were using them for. A number of the pilots I knew had flown comparative back to back tests between the Allison engine Mustangs and Merlin engine Mustangs to produce technical reports comparing the two and suitability of Merlin engine Mustangs for the Tac/R role. Some of them flew operational tours on both types, so had a real life basis for their comparisons. Down low, Allison was best below 10,000ft, ran smoothly, gave good fuel economy, relatively easy engine for the pilot to manage. Merlin below 10,000ft did not run so well, even the special LF Merlin variants did not run as smoothly or as at low rpm as the Allison, comparatively burned more fuel to attain same airspeed at lower altitudes. But get the Merlin 12,000ft and above and it came into its own and performed much better at the higher altitudes, but that required more fuel to produce more horsepower. They also considered the Merlin required more careful management by the pilot and more regular adjusting to keep engine settings where they were required.