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The ramming manifold was a myth. The lengths were too short. The name seems to have come from the shape resembling a rams horns.Every engine has strengths and weaknesses:
As noted, a Merlin supercharger was mounted remotely to an Allison and basically performed the same. However the supercharger failed shortly into the test, the exact cause was never confirmed but the speculation was that by being remote it wasn't kept up to same temperatures that it would have it was directly mounted to the crankcase.
Early aircraft engines used brass floats to control the fuel level in the carburetor – rising to stop fuel flow, sinking to allow fuel in. If the floars weren't properly soldered shut or developed leaks in service, they would sink and fuel would flow overflow the carb. With an updraft carb, the excess fuel simply falls to the ground. With a downdraft carb, it usually flows somewhere bad – into the intake flooding the engine, over the red hot exhaust causing fires, etc.
The American auto industry, with engines like the flat head v-8, were making better downdraft carbs. And let's not forget Allison is a subsidiary of GMC, an automotive company.
Aside: Peregrine and Vulture, RR latest 2 engines pre-War and the post war Merlin 130s were downdraft. Downdraft is a better configuration, but sometimes you have to stick with what is working.
Allison will have marginally better economy as it has ~10% higher compression ratio (CR). The Merlin with 10% lower CR, can build ~10% higher boost. The higher boost comes at a cost as it takes more power to drive the supercharger. But the end result is the Merlin more than makes up for the 60 in^3 it is short on displacement with more power.
The engineers at Allison developed very sophisticated intake manifolds that "rammed" air into the cylinders at optimum rpm. The engine was also developed for turbocharging. The combination of the 2 meant the camshaft timing was fairly mild allowing the engine to run smoothly at less than 50% power, again allowing it to be more economical.
The engineers at RR, concentrated on a better supercharger and used a "sewer pipe" to deliver air to the cylinders. As the Merlin wasn't designed for supercharging, they used pretty radical cam timing (Merlin idling sounds angry and when at operating speed mean). The use of radical cam timing meant the Merlin was prone to backfiring. As RR didn't have a fancy ram air manifold, they had not issue installing "flame traps" in intake ports to stop the issue. (Flame trap is a number of thin plates which stop the backfire from entering the engine).
For the Allison engines in the P-82 had 2 stage superchargers and more radical cam timing. The result was backfires, which without the flame traps, went through the entire intake, intercooler and supercharger. (Think AA Fueler blower explosion). Allison engineers didn't want to give up their fancy intake manifolds for flame traps, so Allison got a bad rap.
As you might recall from high school chemistry, it takes a huge amount of energy to boil water*. RR engineers used this fact by allowing very limited, very local boiling in their engines around the exhaust valves. Once mixed with coolant in the engine, the water vapour is return to water again but the mixture is very hot. As the mixture is very hot, you need a smaller radiator because there is greater temperature difference with outside air. So, Merlin gets away with less than ½ the cooling water of the Allison.
It's also why you can't turbocharge a Merlin – the exhaust is running so close to thermal limits that the extra heat from restricting exhaust exit melts the head.
Early P-38s issue was Lockheed didn't anticipate flying for extended periods of time at high altitude. The decision to use the outer wing leading edge as an intercooler appeared to be stroke of genius. But unfortunately, in conditions that 8th AF found themselves in, planes were flying at cruise speed for hours in -30° cold. And the load on the turbocharger wasn't enough to have them creating enough warm air to justify the intercooling but there was no way to limit it. The carb/engine on the Allison wasn't designed for operating in that environment for extended periods.
Adding to the problem, the leading edge intercooler didn't have enough cooling for full power, and the available fuel, while it met the 100 octane requirement lean, didn't meet requirement under boost at rich setting. Add in some sluggish controls as engines are out in wings, oil used in controls congealed in cold and you get engine failures.
Westland had similar issues with the hydraulic throttle on the Whirlwind – great idea, you don't need to worry about cables changing length as plane flexes, etc. Unfortunately, the oil got thick at altitude and pilots couldn't pull throttle back after going full power, resulting in blown up Peregrines. As a result, the engines get a rap for bad altitude performance. But it wasn't the RR engine, it was the implementation.
For the Allison, the late P-38J and L is the sweet spot, not too much power to cause the backfire issue, enough and controllable intercoolers, so as keep engine working like top. Unfortunately, twins use 2X the fuel as single, so why use up your limited logistics when the P-51 is right there. Same thing happens in Korea – P51 is used as ground attack plane even though P-47s and F4Us are available and better planes for that role as the R-2800 burns 2X the fuel as the Merlin.
Typhoon wing and engine both weren't good at attitude. But it was a beast down low.
I do wonder why Allison/GE never pushed for a turbocharged Allison Mustang. If you remove the fuselage tank, there would be room for the turbo. Routing of intake and exhaust wouldn't be any different from Thunderbolt in concept.
*While I am saying water, I know it is a water/glycol mix.
Simples, the RAF ACC Squadrons when they were re-equipped with the Curtiss Tomahawk, each retained two or three Lysanders to perform the tasks that the single seat Tomahwak could not. It was also a reason why not all RAF Squadrons were re-equipped with the Tomahawk. Some like No.16 Squadron and No.309 (Polish) Squadron stayed with the Lysander until the Mustangs arrived and went directly from Lysander to Mustang without operating the Tomahawk. The ACC Tomahawk Squadrons did still practice and use in exercises with the Army such old school arcane skills as message dropping using a weighted bag with streamers attached which certainly had its origins in WW1. Also why a number of the ACC Squadrons and the Wings to which they were attached in this timeframe were given communications aircraft, types like the Percival Proctor, d.h. Dominie and even some impressed small civilian 'tourer' type aircraft to ferry high rankers around.How they managed the all important duties of message pick up with a hook and string or ferrying high ranking officers to staff meetings has not been revealed.
Thankfully the RAF didnt add dropping off and picking up spies and operatives into the Mustang design brief. The role of army cooperation and tactical recon changed with the fall of France. It changed again after D-Day when the Spitfire Mk XIV was found to be a good aeroplane. An army involved in a fight on a land front has an interest in what is going on behind the front, but is most interested day to day in what is were a few miles away, half of Spitfire Mk XIVs carried a camera.Simples, the RAF ACC Squadrons when they were re-equipped with the Curtiss Tomahawk, each retained two or three Lysanders to perform the tasks that the single seat Tomahwak could not. It was also a reason why not all RAF Squadrons were re-equipped with the Tomahawk. Some like No.16 Squadron and No.309 (Polish) Squadron stayed with the Lysander until the Mustangs arrived and went directly from Lysander to Mustang without operating the Tomahawk. The ACC Tomahawk Squadrons did still practice and use in exercises with the Army such old school arcane skills as message dropping using a weighted bag with streamers attached which certainly had its origins in WW1. Also why a number of the ACC Squadrons and the Wings to which they were attached in this timeframe were given communications aircraft, types like the Percival Proctor, d.h. Dominie and even some impressed small civilian 'tourer' type aircraft to ferry high rankers around.
If people want to dive into Royal Air Force Operations and Strategy, from the RFC in WW1 through the interwar years and currently up until 1943, I can commend the series of currently five books written by Greg Baughen. He has taken the path of going back to the original files held in the UK Archives, RAFHB, RAFM and multiple other sources including personal papers and memoirs of many of the key players. From this research he has produced an insightful analysis of the policies, strategies, politics (at the Government, Service and inter-Service levels) and especially the personalities (with their individual backgrounds and biases) that shaped the direction of the RAF over those years.
Why would they?Thankfully the RAF didnt add dropping off and picking up spies and operatives into the Mustang design brief
It changed in British service. It had already changed (or perhaps never changed?) in some other services that always expected at least part of their Air Forces to take part in the land battle. Some of them may not have been very good at it but they hadn't ruled it out.The role of army cooperation and tactical recon changed with the fall of France.
Which is why the RAF study in 1944 - after D-Day - concluded that the best replacement for the Allison Mustang for the Tac/R role with the RAF, was another Allison Mustang. In particular they wanted what was essentially a Mustang Mk.II, with the 4 x 20mm cannon armament of the Mk.IA, fitted with a Malcolm Hood, and fitted with twin oblique and one vertical camera mount. Given that they could not get what they wanted as NAA had closed the Allison engine Mustang production line when Merlin engine Mustang production commenced they had to look at alternatives.It changed again after D-Day when the Spitfire Mk XIV was found to be a good aeroplane. An army involved in a fight on a land front has an interest in what is going on behind the front, but is most interested day to day in what is were a few miles away, half of Spitfire Mk XIVs carried a camera.
First Mustang Mk.I issued to No.26 Squadron RAF, 9 January 1942. The Squadron CO had been test flying a Mustang Mk.I since mid-December 1941. A lot of the delay between No.26 Squadron getting the first of their Mustang Mk.I in January 1942 and onwards is around the rate that aircraft were being reassembled after arrival in the UK, then getting the priorities for the identified modifications from the service trials at A&AEE and AFDU, with the wrangling that then went on about issuing unmodified Mustangs to Squadrons and who would be responsible for modifying them once issued to the RAF. Politics between Ministry of Aircraft Production, Ministry of Supply and Air Ministry, plus time taken to consult with NAA and Allison about some of the issues identified from the trials and early use by No.26 Squadron and identify the solutions to those issues. Also determine was it something the responsibility of NAA or Allison to fix (via their contractors in the UK) or was it a MAP, MoS or AM responsibility. By the beginning of April 1942 the solutions to the issues were in train, who was responsible for what had been sorted, manufacturing of parts for the required modifications had been given the go ahead, and the orders were given for the aircraft to be issued to Squadrons - initially unmodified aircraft so Squadrons could commence conversion onto the type. It then took a few weeks for the aircraft that had already been assembled to be prepared for collection by the Squadrons. So from mid-April 1942 the wider issue to Squadrons commences. By June 1942 the second tranche of Mustang Mk.I Squadrons had completed their conversion and work up, had swapped unmodified for modified Mustangs and commenced operations.The state of the art in fighters and fighter engines changed between the summer of 1940 and the fall of 1941 When Mustang Is were coming of the production line, let alone April of 1942 when they are issued to a service squadron.
Speaking of the P-82 (I remember seeing one at Shepherd AFB when I went to A&E school there), i was told it had counter-rotating props. Do you know how they did that? I'm curious whether they added gearing, reversed the engine, or modified the engine to run the opposite way.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.
I presume it had idler gear like those in the P-38.Speaking of the P-82 (I remember seeing one at Shepherd AFB when I went to A&E school there), i was told it had counter-rotating props. Do you know how they did that? I'm curious whether they added gearing, reversed the engine, or modified the engine to run the opposite way.
I presume it had idler gear like those in the P-38.
Later Merlins in the Hornet were also "handed" with idler gear.
My knowledge of the Merlin doesnt stretch that far. Was a new crank case and cover absolutely necessary just to change rotation, the Merlins for the Hornet had downdraught carburettors and re arranged coolant pumps. Wiki simply states it had idler gear in the reduction casing.V-1710s reversed the engine and put an idler gear in the supercharger/accessories drive train.
Merlins put an idler gear in the prop reduction gear.
It required a new crankcase and cover in the case of the Merlin.
My knowledge of the Merlin doesnt stretch that far. Was a new crank case and cover absolutely necessary just to change rotation, the Merlins for the Hornet had downdraught carburettors and re arranged coolant pumps. Wiki simply states it had idler gear in the reduction casing.
Nice post. I wonder if 430 squadron R.C.A.F. doesn't deserve some mention here. They were still equipped with Mustang I when they started converting to Spitfire XIV in Nov 44.For the most recent, probably one of the best researched and currently the most accurate books on the early development of the Mustang, including how the British came to order the Mustang from North American Aviation, I can commend "P-51B Mustang: North American's Bastard Stepchild that Saved the Eighth Air Force" by Bill Marshall and Lowell Ford, Osprey Publishing, UK, 2020. Bill is a member of this forum and engaged with a lot of Mustang researchers and operators globally in researching this book, and a number of members of this forum also are noted in the acknowledgements. Bill and Lowell went back to the basics, original period source documentation, including a lot of material from the Boeing Archives, who hold the original North American Aviation documentation quoted in the book, as well as a deep dive into the USAF Archives.
The North American Mustang Mk.I was ordered as a fighter. It ended up, in some ways, via a set of circumstances to be the right aircraft available at the time when it eventually arrived in the UK to meet an emerging need for a modern, high performance, single seat, fighter type aircraft to be used in the fighter reconnaissance role by the Squadrons in Army Co-operation Command. They had already proven the fighter reconnaissance concept via use of Curtiss Tomahawks, but the serviceability and performance of the Tomahawks left something to be desired and the Mustang looked to be a way better option. (Or another way to look at it is that there was great pressure coming from the War Office for the RAF to get dive bombers - the Stuka fixation - and orders had been placed for a range of dive bomber types such as the Vultee Vengeance and Brewster Bermuda, which it had been proposed to equip the RAF ACC Squadrons with, and that would not have ended well..................). In some ways there were politics at play, and Fighter Command, passing the Mustang on to Army Co-operation Command and being presented to the War Office as "ACC being given the most advanced US fighter produced to date to arrive in the UK" (which it was at the time) went a long way to stifling any negative comments from the War Office about the RAF not giving ACC suitable aircraft to operate. (There are a heap of files in UK Archives covering the procurement of the Mustang and the deliberations and inter-service politics and inter-command politics of how the Mustangs ended up with ACC). Fighter Command also at that time had a certain fixation with high altitude performance for fighters based around potential German use of high altitude bombers with pressurised cabins for the crew to conduct a bombing campaign against the UK, plus high rate of climb for the point interceptor home defence fighter role. So more than just Fighter Command experience from the BoB at play in their assessment of the Mustang.
By VE-Day, there were FOUR RAF Squadrons operating the North American Mustang as one of their primary types.
No.516 Squadron was using an enlarged flight of Mustang Mk.I aircraft in a non-operational role as was No.285 (AA Support) Squadron.
No.516 provided the air component, particularly artillery and naval gunfire direction support to the Joint Operations Training School at Dundonald in Scotland.
No.285 (AA Support) Squadron provided target aircraft for AA practice using Mustang Mk.I in March to July 1945 at Weston Zoyland.
No.26 Squadron had re-equipped with the Mustang Mk.I in January 1945, having operated the Spitfire Vb since early 1944, and were flying operationally providing naval gunnery direction to units of the RN Home Fleet and Free French Navy against German hold out ports along the French, Belgian and Dutch Coasts. They re-equipped with Spitfires again when they joined BAFO in June 1945.
No.268 Squadron RAF was equipped with Mustang Mk.IA and Mk.II aircraft and was using them operationally up to and beyond VE-Day. On VE-Day they were in the process of re-equipping with the Spitfire FR.XIVe, and had a mix of both types used on operations. No.268 Squadron relinquished the last of its operational Mustang Mk.II aircraft (reluctantly) in late August 1945.
A couple of Mustang Mk.I and Mk.II aircraft continued in use until early 1946, mainly attached to Group Support Units and various Training Establishments, primarily used as personal "hacks" for senior officers with those units.
Of the Allison engine variants of the Mustang, the RAF used operationally the Mustang Mk.I, Mustang Mk.IA, Mustang Mk.II and A-36A
Squadrons to use the Mustang Mk.IA: No.II(AC), No.63, No.168, No.170, No.268
Squadrons to use the Mustang Mk.II: No.II(AC), No.268.
No.225 Squadron RAF initially used Mustang Mk.I aircraft in the UK, leaving their Mustangs there when the unit was posted to the MTO and re-equipped with Hurricanes and Spitfires in late 1942. They 'borrowed' for a short period commencing in April 1943, four P-51 aircraft (equivalent to the Mustang Mk.IA) from the USAAF to give them a longer-range capability until Spitfires with fittings for long range slipper tanks arrived.
No.14 Squadron RAF also borrowed some P-51s (equivalent to the Mustang Mk.IA) aircraft from the USAAF which they used for about 4 weeks in 1943 to do some long range recce work, primarily into areas where the units usual Martin B-26 Marauders had been encountering regular enemy fighter opposition and a number of losses had occurred.
No.1437 Strategic Reconnaissance Flight borrowed six A-36A Mustangs from the USAAF in the MTO which were used in a fighter reconnaissance role in the absence of other suitable aircraft from RAF sources in the MTO at the time. After a period of heavy use, the surviving A-36s were passed on and used by a number of RAF P-40 units to assist them in conversion training getting ready to re-equip with Merlin engine Mustang Mk.III aircraft.
One A-36A flown in trials in the UK by the Aeroplane and Armament Experimental Establishment.
Oh, I think if you read the Operations Record Books of 2 and 430 Squadrons you'll find that the Spitfire XIV equipped units acquitted themselves quite admirably in the Tac/R role. They could also engage enemy aircraft successfully when opportunities presented themselves such as here and here and here and here and hereThe Spitfire FR.XIVe was the next best alternative, but it lacked a number of features that were considered to be 'essential' for the Tac/R role, including limited range on internal fuel. Some of the identified shortcomings would get covered off in the Spitfire FR.XVIII which followed later.