Problems with British wartime high power piston engines

I have two questions about British wartime high power piston engines :-
With hindsight, given all its' problems, and that Bristol had to assist in it's development, would it have been better to cancel the Napier Sabre as soon as practicable, and merge Napier's resources with Bristol, and use them on Centaurus development/production?
Also, could the Rolls-Royce Vulture have been made to work, without a complete redesign?

cheers,
Robin.

It had become apparent that a longe-range heavily loaded bomber like the Manchester had problems when it lost one engine... the Vulture problems were well on the way to being sorted but RR thought their efforts should go into the Merlin and putting 4 Merlins onto the Manchester could be achieved without too much hastle... using Blenheim power pods..Avro could modify wing jigs quite easily so the Lancaster was born. So the question is should we have used it in this application... would the Hawker Tornado been a better bet than a Sabre-Typhoon.Consider if the Merlin supercharger technology had been used to do a proper high-altitude version (by the way the prototype 2-stage Merlin supercharger used the impeller from the Vulture added to existing Merlin impeller). One of the problems with Centaurus was cost of manufacture ..about twice the Merlin; Sabre I seem to remember is 4 times the Merlin. The problem at Bristol was leadership... no Fedden... so Napier's resources would not necessarily have helped as they were leaderless too!

The established reciprocists let Ministers down over Hypers. Amply funded from 1935, schemed into numerous applications by 1938, planned for such new production investment as Standard-managed Walton Agency (for Sabre), what was delivered was modest and sad. Ministers disliked putting Pratt on Warwick, but where was Centaurus? etc. That is why Whittle thought to have receptive ears for his lobbying to Nationalise the entire aero-engine industry, and to distance his gyre from failed pistoneers. Nuffield peddled Pratt licence in Wolseley. Ministers persevered...and Griffon, Centaurus did ultimately come good. Deerhound, Sabre, Vulture, Crecy, Exe did not. “Peregrine,Vulture,Sabre,Hercules VI, Centaurus,Griffon are outstanding examples of (hopes) disappointed or deferred” Postan,Official History, War Production, P167.

Note that the advanced British engines tended to have high BMEP and specific power. This meant the compnents were under a great deal of stress and, when coupled to high boost pressure, led to a lot of component failures (as have such combinations throughout the history of reciprocating piston engines). The sleeve-valve engines were an even more demanding case, the drive systems for which requiring a lot of carefully machined components with even greater precision than poppet-valve designs.

alertken said:

Ministers persevered...and Griffon, Centaurus did ultimately come good. Deerhound, Sabre, Vulture, Crecy, Exe did not. “Peregrine,Vulture,Sabre,Hercules VI, Centaurus,Griffon are outstanding examples of (hopes) disappointed or deferred” Postan,Official History, War Production, P167.

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Whilst I would agree that the Sabre was "deferred" I think it is difficult to say it did not come good- the type ultimately powered over 3,300 Typhoons, over 1,000 Tempests and had the war gone on it would have powered many more as well as all the Fury's that would have been acquired by the RAF.

Whilst the Sabre is not a legendary engine like the Merlin or the R2800 it certainly played a significant part and formed a major part of british tactical airpower in the late war period.

alertken said:

Ministers persevered...and Griffon, Centaurus did ultimately come good. Deerhound, Sabre, Vulture, Crecy, Exe did not. “Peregrine,Vulture,Sabre,Hercules VI, Centaurus,Griffon are outstanding examples of (hopes) disappointed or deferred” Postan,Official History, War Production, P167.

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Ministers, and civil servants, were actually quite good at backing winners and understanding commitments. Rolls-Royce had realised the gargantuan job of improving the Merlin whilst also developing the Peregrine, Vulture and Exe. Hives asked to be released from such a large development undertaking in order to concentrate on the Merlin development and the huge production orders, the development of the Griffon, initially for naval application, and to run down the other programmes. This was agreed to and so Hooker, Rubbra and Lovesey set about keeping the Merlin at the forefront of development whilst ramping up production at Crewe; and putting resources behind Ford for the Trafford shadow factory as well as their own shadow factory around Glasgow not to mention Packard in the USA. All these required a commitment of key personnel to smooth the inevitable issues, technical and organisational that arose along the way. As the war continued RR did start work on the PI26 Crecy engine which was the last word in stretching all the technologies to the limit! Also towards the war's end the Pennine, a larger version of the Exe was built and run. The Exe itself served as the power for the Battle 'taxi' and gave many hours of satisfactory trouble free service. The Centaurus suffered from a lack of leadership commitment at Bristol and also the Shadow factory for it proved problematic especially as Fedden had been pushed out.
Napier's issues with the Sabre were incredibly serious, with the Typhoon being a glider for a period. EE takeover put some commitment into the top team and with the aid of Bristol who made some sleeves from existing material stock and allowed Napier to demonstrate that a huge improvement in reliability was possible along with help from Derby to address bearing cooling issues, meant that the Sabre was no longer in terminal decline. Again getting the shadow factory up to speed was a time-consuming activity. RR were asked to do a Sabre replacement in a similar manner to the Griffon being a Merlin successor. This was the Eagle II.
Fell, the chief engineer on the Deerhound told me that with resource commitment the engine could have been a runner but other priorities delayed it and then the Turbine age arrived to upset every piston engine developer's dreams.
The Griffon was being developed in readiness to replace the Merlin.
So what would an Exe, Deerhound, Centaurus, Griffon be installed in if they had come along earlier?
The gold standard of development may be this curve?

As I implied above, the Sabre suffered in providing high power at altitude and in 1943 there started a project to put this right . The 36 liter Sabre was schemed with a two-stage supercharger and interstage charge cooling (may actually be after stage cooling as per 2-stage Merlin and Griffon.. no real point doing it in between from a thermodynamic point of view, I believe) delivering 25 lb/sq in boost. This was finally built in 1947! It was to deliver 3350 bhp vs the 1941 Sabre V figure of 2600 bhp. This is a multiplier of 1.2885 ... if we take the Merlin figure of 2600 bhp for 1941 and apply the Sabre multiplier we get 1906 bhp which was available in 1943. So we might assume that with the right team driving the project at Napier this may have been available about the same time. So what price a Typhoon with altitude performance in going into service late '43?
The drawing below is the E122 which was number allocated to this Sabre. It was, I think, never actually run at Napier but the engine itself was passed to Derby by the Air Ministry who also cancelled further Sabre work but did allow resources to switch to Ministry funded gas turbine work... probably a good move. In the meantime the back-up programme for the Sabre replacement at Derby, initiated when Sabre was looking like a failure was actually under way with the Eagle 22 46 litre H24 engine delivering 3200bhp with 18lb'sq in boost; first run in 1944 the RR engine went in early versions of the Wyvern.
The E122 Sabre layout is shown in accompanying drawing

Tartle,

Thanks for the excellent post, do you know what sort of altitude performance Napier were aiming for in the E.122? by 1946 the Griffon 130 with the three speed two stage supercharger could maintain over 2,000 hp at 20,000ft.

A Fury with the E.122 would have been an incredible fighter!

Still working on that one.. there must be a performance graph hidden in a file somewhere. The drawing was published in Vassey's book 'By Precision into Power'. He states that most paperwork was destroyed when Napier Aero Engines Ltd was wound up in the 60s. I have found 'stuff' in amazing places so there is still hope? One thing he did publish is a list of the project E numbers that A J Rowledge started when he was appointed chief draughtsman in 1903.
Another Sabre related one is E123, a paper project converting the Sabre into a 2-stroke engine of 4000hp! I have only recently got sight of the book so am busy combining it with the contents of my tea chest(s).
Fred Morley who steered the Spey projects once told me that he had helped with the original Sabre problems and said the major issue with such a high performance engine was that it was really an oil-cooled engine as it was the parts water couldn't reach that determined the integrity and the lifetime of components such as sleeve and piston, con rod etc.
Photos below show the development challenge of the more conservatively rated Eagle 22!

Thanks for the great posts.

Regarding the Sabre, I think that the criticisms of Napier's management and the commentary on how things changed after EE were brought on to the scene are borne out by the way in which the power output from the engine, the early Typhoons were flying with 2,200hp but by 1945 the Sabre VII was running at 3,055 hp in Fury prototypes and as we see from the E.122 there was a development path to 3,350hp. It is also interesting to note that due to the large base power of the Sabre VII the type would still give 2,000hp at 20,000ft. The E.123 sounds very interesting, I also recall a proposal for a 32 cylinder Sabre.

The E.122 was chosen, in January 1945, as the engine for the production version of the Blackburn Firecrest; however this was abandoned in October 1945 when it was found that the use of the Sabre would require the engine to located behind the pilot in order to offset the engines greater weight: this in turn added greater weight to the whole aircraft so orders for three E.122 Firecrests were cancelled. This left the E.122 without a platform and perhaps explains why it took until 1947 to actually build it.

As for the importance of the engine, over 5,000 Sabre powered Tempests, Typhoons and Furys were ordered and at D-Day the RAF had 27 squadrons of Typhoons, 18 of which were ground-attack units within 2nd Tactical Air Force which formed a major part of that forces tactical offensive capability.

27 April,1938. RAF Expansion Scheme 'L' approved; "Compulsion" to cease civil work and move much UK engineering into munitions. New Air Ministry Agency Factories funded, 1938/39 (such as Glasgow-for-Merlin, 5/39). <1,000h.p Merlin, Mercury, Pegasus, Dagger now; >1,000h.p Merlin, Hercules, Sabre asap please. AM Freeman has by now told Fairey to stop peddling Wright, General A/c ditto Hispano, Nuffield ditto Pratt and instead to help make things happen NOW!

Thin R&D teams are trying to match Wright/Pratt at 2,000h.p, while making 1,000h.p types pass 150 endurance tests and be production-repeatable by labour that had not served a craft apprenticeship. This is the sense in which I made the Sabre comment about not "coming good": this design was difficult to make by diluted labour, difficult for 19-year-olds to keep serviceable in the field.

In anticipation of Hyper power, Air Ministry issued Specs and funded prototypes intended to displace 1935-designs in time for the expected show of 1941. So:
ASM Boarhound was for Heavy Bomber AW.48 to Spec. B.1/39, to which V-A bid V.405 with Griffon, Gloster bid with a mix of Hercules VI and Centaurus;
Centaurus was for much, in 1938, but firstly for Warwick and Hawker "B" (Bristol-built Tempest II): A.M had no intention of building Wellington and Hurricane through 1944; Sabre was for Hawker P.1005 high speed bomber, for Firebrand (yes, initiated in 1940!), and for Hawker "N" (Gloster-built Typhoon);
Griffon was for Firefly, and the Blackburn bid, B-28 to Spec. B.3/40, light recce-bomber;
Exe was for Barracuda;
Vulture for Hawker "R" (Avro-Yeadon-built Tornado).
Of the Hawkers, "N" was seen as soonest, best, such that (by then MAP) attempted to have the airframe built by Bell, the engine by GM* and in Canada.

The development of Merlin, like that of Spitfire, saved our bacon. While I here criticise dearth of operable UK Hypers (Sabre arriving just in time for D-Day), which protracted feeble designs past their best (Whitley was built to July,43: “obsolete” in an A.M. Report of August,’38!), I have no doubt that entirely comparable pain preceded US Hypers. Didn't engines dish more B-29s than did enemy defences?

(corrected #24 below, 15/8: Chrysler)

The Hyper story as a whole is fascinating.

Everyone in the late 1930s was convinced that it was the killer technology for the next generation of high-speed aircraft - but none of the engines ever worked as well as, or delivered much more power per cm3 or lb than conventional engines pushed to higher BMEPs with multi-stage blowing/intercooling, higher octane ratings, water/methanol or nitrous.

In the process, a remarkable number of aircraft procurement plans were more or less run into the ditch (Bomber B being the biggest example, closely followed by all the USAF's unconventional fighters, with Typhoon/Tempest having been made much more complicated than necessary).

Tartle's Merlin chart says it all. (It's in Setright, by the way.) Even allowing for brochuremanship, the fact is that the P-51H Allison V-1650-9 was officially rated at 2280 hp is important given that the US goal for Hyper was 1 hp/cu in.

Mind you, I'd still love to see a Sabre-powered Unlimited at Reno...

There's a very good discussion of US Hyper experience in Graham White's SAE book on WWII engines. Adding to what LO wrote, another objective of Hyper was to enable embedding engines within wings or very low profile nacelles. The cooling problems of such installations made them impractical even ignoring the (very)fundamental problems with the base engines themselves.

Each of the Lycoming and Continental hyper projects slowly died as wartime funding was directed to production radials and the Allison and Packard/RR Merlin inline programs. When Luke Hobbs convinced the Army to let P&W abandon the H-24 sleeve-valve engine in favor of the R-4360, it was the end of the Hyper story.

Oh and re: your comment about Sabres at Reno, this year's winner of the AIAA student design competition was an unlimited racer. Might be a fun Friday item for the Ares blog.

alertken said:

Thin R&D teams are trying to match Wright/Pratt at 2,000h.p, while making 1,000h.p types pass 150 endurance tests and be production-repeatable by labour that had not served a craft apprenticeship. This is the sense in which I made the Sabre comment about not "coming good": this design was difficult to make by diluted labour, difficult for 19-year-olds to keep serviceable in the field.

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On this I agree, the Sabre's maintenance issues are well documented, but lumping it into the same category as the Exe, Deerhound and Crecy seems excessive.

The development of Merlin, like that of Spitfire, saved our bacon. While I here criticise dearth of operable UK Hypers (Sabre arriving just in time for D-Day), which protracted feeble designs past their best (Whitley was built to July,43: “obsolete” in an A.M. Report of August,’38!), I have no doubt that entirely comparable pain preceded US Hypers. Didn't engines dish more B-29s than did enemy defences?

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The importance of the Merlin is difficult to understate, not just Spitfires and Hurricanes but ultimately Lancasters and Mosquitoes, it was Britain's primary means of air defence and primary means of air offence. It is also worth mentioning that NAA made the Merlin do truly wonderful things in the Mustang (as LO alludes to) and one wonders what structural reasons prevented the UK from doing the same. Of course the Mustang is not the only example, between Blenheims and Whitleys 2TAF No2 group operated Bostons and Mitchells whilst the Buckingham failed and was replaced by a (cancelled) order for Invaders. Then there is the Spitfire 21 and Spiteful fiasco whilst NAA turned out tuned Mustangs, Republic pumped out Thunderbolts, Vought produced the Corsair and Grumman the Hellcat of turkey shoot fame; many of each operated by the UK. Certainly the low cost of lend-lease plays a part but to be blunt about it, US industry out-designed the UK.

I wonder why Napier didn't add a turbocharger (or twin turbos) to the Sabre to boost the high altitude performance. The installation would have been bulkier than two stage supercharging but it would not have consumed that much engine power. The British industry already had a lot of experience in turbine design but it seems turbochargers were not really considered on British aircrafts - not even on bombers or nightfighters (in contrast to American aircrafts like P-38, P-47, P-61c, B-17, B-24, B-29). Rolls Royce tried a compound turbine on the Crecy but this engine didn't mature. Even in Germany, despite the shortage of nickel and other high temperature materials, companies experimented a lot with turbocharging, like the BMW 801j (serial production), DB 621 (twin turbo), DB 623 (twin turbo), DB 624 (turbo compound), DB 625 (twin turbo), Jumo 205 and 207 (turbo diesels, serial production), Jumo 222 (some), etc.

Apologies for not replying sooner, but I've been struck down with a malfunctioning PC...
Thank you all for your informative replies, once again, you've the gaping holes in my knowledge...
Regarding the Sabre being stopped in favour of the Centaurus, I had it in mind that this would permit the Centaurus to appear in production quantities sooner, thus it could replace the Sabre in the Hawker fighters ('Tornado II' and Tempest II instead of Typhoon and Tempest V), and hopefully offer increased reliability. My belief for this is that Centaurus builds on Hercules experience, as well as Bristol radial engine experience in general, whereas the Sabre was effectively a clean sheet of paper design.
Further, the Centaurus would be applicable to re-engine other Hercules-engined aircraft, Halifaxes, Beaufighters, etc, with the appropriate modifications.
On the Vulture, my main reason for asking was that I've never seen a decent account of this engines problems. Most accounts merely state 'insurmountable technical difficulties', or some such. 'The Great Gunston', in 'Rolls-Royce Aero Engines', talks of a design fault in the big end arrangement, mentioning 'mating surfaces fighting each other', and an article by an uncredited authgor on Typhoon development in an old 'Air Enthusiast' speak of a spate of conrod bolt failures, but other than this, I've seen nothing.
Secondly, since, as I understand it, the Vulture was effectively a 'Double Kestrel', if it's problems were overcome, would a version based on the Merlin have appeared? And if so, would it have displaced the Griffon? Would there even have been a Griffon-based engine of this type?...
I agree, it's impossible to overstate the importance of the extent of the development of the Merlin during the war. The Merlin was *the* war-winning engine, especially in the ETO.

cheers,
Robin.

robunos said:

Regarding the Sabre being stopped in favour of the Centaurus, I had it in mind that this would permit the Centaurus to appear in production quantities sooner, thus it could replace the Sabre in the Hawker fighters ('Tornado II' and Tempest II instead of Typhoon and Tempest V), and hopefully offer increased reliability. My belief for this is that Centaurus builds on Hercules experience, as well as Bristol radial engine experience in general, whereas the Sabre was effectively a clean sheet of paper design.

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Actually the Sabre was the third in a line of Napier H engines starting with the Rapier before moving to the Dagger and then the Sabre. The primary problem was a lack of leadership and direction at Napier's. Something that was largely solved when English Electric entered the scene. Whilst the Sabre had its own unique set of maintenance hurdles one gets the impression that Napier on its own could not break of the small volume, hand-craft, high performance mentality- something that was compounded by their own relatively thin staff that prevented them from supporting the production effort at Walton (Shadow factory to make up for the small capacity of the Napier factory at Acton). The Walton factory itself suffered from a lack of skilled labour, both machinists and management, and this certainly contributed to some of the reports of defective engines being delivered.

The Sabre needed to be developed by a large and well lead company with an established manufacturing base, it was instead developed by a small and poorly lead company that lacked a major manufacturing capability and the resources to rapidly develop one to support a still developing engine. However, one must not forget that in the second half of the war Sabre powered aircraft formed a very large part of RAF tactical airpower.

Great info! Many thanks Tartle!

A couple of things;

alertken - I believe it was the Centaurus that GM were going to build in Canada not the Sabre.

American hypers were all failures -Continental IV1430, Lycoming H2470, Pratt and Witney H3730, Wright R2160 Tornado - some were killed because their makers were too busy with other projects, some because they just didn't work as well as hoped. With the exception of Allison and the V1710, US manufacturers were unsuccessful outside their comfort zone of 14 and 18 cylinder radials.

Robunos - the RR Heritage books have good info on the Vulture, IIRC 'RR Piston Aero Engines' from them has all the details (sorry my books currently all boxed so can't check) the biggest problem was lubrication (which was the cause of the engine failures and fires) RR say they solved them as the axe fell. The notion of a Vulture with Merlin pots is intriguing - there was a 24 cylinder 'H' engine schemed based on Merlin cylinder blocks that had a projected P-W ratio better than Eagle 22, but I've always thought that Eagle 22 was so heavy because RR were determined to push both piston speed and boost pressures through the roof with that engine so it had to be beefy. Perhaps Tartle can confirm or correct that?

the Sabre was the third in a line of Napier H engines starting with the Rapier before moving to the Dagger and then the Sabre

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I'm aware of the Rapier and Dagger, However these were air-cooled with poppet valves, I believe. Also these had the cylinder axis vertical, rather than horizontal. In contrast, the Centaurus was effectively an enlarged, 18-cylinder version of the Hercules, itself basically a two-row Perseus, and all of these engines were based on the experience leading back to the Jupiter of 1918.
I'm not denying that the Sabre eventually came good, but speculating that the Centaurus could have got there earlier, and with less trouble (and perhaps more cheaply too).
@Nick Sumner. Where can RRHT books be obtained from? I've never seen them for sale...
THanks also for your thoughts on the Vulture. What I'd read had led to believe that the nature of the problem was overstressing of the big ends, which led to me musing if the problem could have been solved by, ironically, going the Napier route of two crankshafts, even though this would incur a size and weight increase...
This then generates another dimension; should more have been made of the Fairey P.24? From the little I know of it, it seems very attractive indeed. Should this have replaced the Sabre in production?

cheers,
Robin.

Robunos - HS 16 Rolls-Royce Piston Aero Engines - a designer remembers is available direct from RR here

http://www.rolls-royce.com/about/heritage/publications/

Or you can search for it on

www.bookfinder.com

but it seems to be more expensive there.

I think the big end problems were exacerbated by the lubrication problem

tartle said:

The Griffon was being developed in readiness to replace the Merlin.

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This is from Colin Sinots's 'The RAF and Aircraft Design: Air Staff Operational Requirements1923 - 1939

This is refering to what became the Battle







Now my understanding that this 'Griffon' wouldn't be the 'Griffon' that we actually got but how would this Griffon have compared to the Merlin and actual Griffon if developed?

robunos said:

Regarding the Sabre being stopped in favour of the Centaurus, I had it in mind that this would permit the Centaurus to appear in production quantities sooner, thus it could replace the Sabre in the Hawker fighters ('Tornado II' and Tempest II instead of Typhoon and Tempest V), and hopefully offer increased reliability. My belief for this is that Centaurus builds on Hercules experience, as well as Bristol radial engine experience in general, whereas the Sabre was effectively a clean sheet of paper design.

Click to expand...

I've seen a referenece to Freeman not liking Bristol radials and ordering the Centaurus to be removed from the Tornado so delaying the whole Centaurus fighter possibility, given his other decisions that seems a bit out of character, has anyone else seen any referenece to that?

Nick Sumner said:

Great info! Many thanks Tartle!

A couple of things;

alertken - I believe it was the Centaurus that GM were going to build in Canada not the Sabre.

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Apparently Feddon was in Canada to discuss this but was recalled.

It has been pointed out elsewhere how happy Bristol would be about handing over sleeve valve know how to General Motors.

NS/PMN1: it was both. I, too, have MAP, 5/40 exploring GM Centaurus. Then P.Butler,Air Arsenal N.America,MCP,2004,p.34 has: UK Lend/Lease Requisition No.151, 9/4/41, for 750 Bell Typhoons: MAP "had hoped to have (Sabre) built by Chrysler (so my bad to say GM), and also considered using...R-2800 (so Hawker "B", "N", "R" and "P"!)...But political and other obstacles to producing a Br.design in US were too great".Just as cash and operability constraints limited UK buys (pre-Lend/Lease) of US engines.

We're in danger of circular discussion here. Some authors have lain lapse of 1939/40 Requirements and designs (some with Hypers) at Beaver's door, for priority on 5 NOW! types, summer 1940. Well, quite so...for now, but not forever, once we survived into winter. Picture yourself as Freeman, RAE and his staff, 1938/39 trying to disseminate new technology for 1941 while NOW! delivering some utility. Resources could go into Dagger or Sabre, Hercules or Centaurus, Merlin or Griffon et al. His options, I suggest were: 1): duplication (B+N+R) v. bet the farm on one... (which?); and 2): build death traps now as education templates, v. hold the new factories idle waiting for proper types...(which?) .

OP asked: could Hyper pain have been avoided? I suggest...only by taking up one of those options, in 4/38 Expansion Scheme "L"...which would have left RAF with a few parent-built Blenheims, Battles and bi-planes in May,1940. Not good.

To wade further into the defence of the Sabre I think think there are other issues at work in its reputation. Not only did it suffer from being developed by a small and poorly managed team and from being manufactured by ill-suited labor, but it also seems to have been tainted by the initially poor performance of its first platform. It is also worth noting that in 1945/6 the Sabre VII was generating 500hp more than the production Centaurus variants at the time. It was not until the DPI variants appeared much later that the Centaurus caught up.

Another alternative for consideration may be that it could have been possible to terminate the various Martin Baker projects (I know everyone loves the MB.5 but what was the point?) and push that team together with Folland to pursue the Fo.117/118 as the Centaurus fighter leaving Hawker to focus on the Sabre powered Typhoon/Tempest/Fury and Vickers-Supermarine to focus on the Griffon powered Spitfire/Seafire/Spiteful/Seafang.

Leaving Napier, who effectively had no other credible production engines in 1940, to develop the Sabre whilst RR focussed on the in production and in use Merlin and Bristol to focus on the also in production and in use Hercules easily seems the most logical approach. Perhaps a better question is why the Hercules itself was not pushed further faster, the Hercules 763/773 family (1948) was making 2,185 hp on 115/145 octane fuel for instance with some qouting the 760 series with 2,300hp at takeoff which compares very favourably with the late variant Merlins.

General Patton once said
“We have got by due to persistence and on the ability to make plans fit circumstances."
Ely Devons was an economist. Between 1940 and 1945 he became the first Chief Statistician for the Central Statistics Office, then Director of Statistics, and finally the Director General of Planning, Programmes and Statistics with the MAP. He wrote a book "Planning in Practice: Essays in Aircraft Planning in Wartime". In the appendix he sets out the issues facing planners in mid 1944 as they tried to plan component production requirements up to the end of 1945. I thought worth scanning part of the appendix relevant to the topic.

...and the rest of Devons.

PMN1 etc,
The original Griffon was a derated 1931 Schneider 'R' engine ...here are a couple of pics. It has the same bore and stroke as the 'R' which was carried through to the wartime Griffon which was in fact an entirely new engine, being technologically a new version of the latest Merlin technology plus some ideas that could not easily be put into an engine already in massive production at Fords etc.

Robunos... the Fairey P24 was a nice concept but being developed at Fairey meant it was short of muscle in the manpower department.
I have a spec for the moderately superchrged version which reads
rated power: 1,500 bhp @ 2,600 rpm
max Take off power: 1,540 bhp @ 2,300 rpm
rated altitude: 9,500 feet
normal rpm: 2,600 rpm not normally exceeded for continuous cruising at any altitude.
max permissible rpm: 3,000 not to be used for more 5 minutes consecutive running.
diving rpm: 3,150 rpm at not more than 1/3rd throttle opening.
max permissible boost: +3 lbs/sq in.(for not more than 5 mins)
rated boost: +2lbs/sq in.
fuel: DTD 230 [ I think is 87 octane]
bore: 5.25"
stroke: 6.0"
capacity: 3118 cu. in (51 litre)

The flight engine rating data is:
rated altitude: 10,000ft
rated boost: +1/2 lb/sq in
max permissible boost: +3 lb/sq in
normal rpm: 2,400
take off rpm: 2,
bhp @ 2,400 rpm @ 10,000 ft - 1,275
bhp @ 2,750 rpm @ 10,000 ft - 1,425
bhp @ 2,130 rpm @ +3 lb/sq in boost - 1,300

The engineer who gave me the spec originally worked on this but was subsequently employed at RR.. was this another reason for interest in an 'H'? The engine is now at Yeovilton. See pics here

RR had a look at the concept and maybe this led to the Merlin 'H' project which crudely put had an angle of 180 degrees between cylinders and then two were put close together each driving one of two contra rotating propeller shafts... being independent, like the P24 one half could be idled to reduce power and consumption. It would have developed 3500 to 4000 hp at 17,000 feet altitude. Advantage over P24 would have been the use of standard Merlin parts for critical moving components. Until I can get to an A3 scanner here is a two part scan from the RRHT cutaways book.

Nick... the reason the Eagle 22 was relatively heavier is because they were conservative at the beginning but also to get the relative speeds down to improve reliability..
There is a parameter known as Mean Piston Speed that turns out to have a good correlation with engine reliability. Measured in ft/sec values of 2600 for cruise and 2900 for take off seem to be the boundaries between a reasonable engine life and one that begins to reduce reliability. A blanket figure of 3000 is often taken as the limit between engines that stay in one piece and those that have issues and are likely to break unexpectedly. Modern F1 Grand Prix racing engines can operate at 3800 and we know how long they last and what happens when things go wrong!
MPS is calculated as Speed [(rpm) x stroke (in.)]/6.

Napier Sabre V has T/O rpm of 3800 and at maximum rating 4000rpm; cruise is 3250 rpm; stroke is 4.75 in. dry weight 2360 lb
P/W 1.29
MPS= 3008 @ T/O
3166 @ max
2573 @ cruise

Eagle 22
max rating 3200 bhp, 3500 rpm
stroke 5.125 so MPS = 2989 dry weight 3900 lb gives P/W = 0.82

Merlin 61:
1290 bhp at 3,000 rpm stroke 6.0 so MPS = 3000 dry weight 1640 lb gives P/W = 0.96
note MPS is same number as rpm! so T/O MPS =2900 and cruise MPS = 2600.

Rolls-Royce 'R'
Stroke= 6.6, max rating 2350 bhp @ 3200 rpm Dry weight 1640 lb P/W = 1.54
MPS = 3520

Conclusion ... Merlin is on the boundary of acceptable for T/O and cruise; Sabre is moving towards racing category and Eagle draws back. If Sabre could be made reliable enough to take-off with confidence it would cruise ok... but could you rely on combat rating? This is one reason that tbo was lower than other engines.
Hope that helps.

Tartle - Have you ever run across anything that explains how come the Battle/P-24 combo ended up at Wright Field?

Peter Masefield writes in his autobiography, Flight Path, that the Battle was designed around the P-24 - hence its miserable performance with the Merlin.

Bulman (long-time senior AM/MAP engine R&D man), An Account of Partnership, RRHT,2001,P.349 has Halford moving (briefly, unhappily, and IIRC, early,1944) to RR with Sabre, which "Very soon...emerged with very little modification as (RR) Eagle".

Alertkin,
Bulman's memoir was published after his death and a decision was made not to do more than minor edits in order to preserve his authentic voice... that doesn't mean that his recollections were correct. In the 1960s Fred Morley told me he was involved in assessing how the lubrication of the Sabre could be improved, at the same time as Bristol was helping with the ovality problem of the sleeve valves. This would account for the need for a Sabre at Derby. Remember that the Eagle 22 has a swept volume 25% greater than the Sbre at 46 li vs 36.65. I noted above in another post that the last Sabre development was sent to Derby for their interest but it was far too late in the day to have an influence on the mechanical layout which was fixed and running by that time. That might be what was remembered. Note also the Eagle incorporated RR's experience on Crecy, Pennine and Exe sleeve valve experience and incorporated into the engine, which differed from the Sabre in many ways.
It was not uncommon for engines from different companies to arrive at another's door. When I was a stress engineer on Advanced Projects I stressed every big fan engine going; and in the turbine office I worked on other engines... I found the first performance calcs that I did ...on an Allison lift jet years prior to the XJ-99 collaboration.... something I had completely forgotten!

Thank you. Musicians, I believe, "sample" others' work.

Alertken ...and earlier they 'riffed'. Good way of thinking about it, not thought of it like that before.
As to P24 in America:
My notes of a conversation, 8/10/1965, with Frank Greaves who tested the P24 said

LowObservable:
"Fairey hired A. G. Forsyth to design the 'perfect engine. Forsyth had worked at the DEngRD dealing with all the designs of engines submitted by the manufacturers. He had therefore a great store of useful knowledge to apply to the Fairey engine. He designed the Prince, a V-12 of 26 litre capacity to compete with the Kestrel. Although no orders were placed it did have the effect of speeding up RR Kestrel development. Forsyth went ahead in October 1935 with the totally new P.24, aimed at carrier-based aircraft. Twin-engine reliability was to be gained (for the first time in any engine) by having two halves each comprising a vertically opposed 12-cyclinder unit with a side supercharger, with pressure-glycol cooling. Each crankshaft was geared to its own coaxial propeller of Fairey constant speed type. Each half engine was tested throughout 1938 (the test bed could not handle the 2,200 total horsepower), and on 30th June 1939 the P.24 was flown in a Battle (K9370). With a potential for 3,000hp, the P.24 was considered for the Hawker Tornado and then the P-47 Thunderbolt, the Battle flying some 250hrs at Wright Field in 1942, but wartime pressures forced the termination of what was a very promising engine. The Americans argued in the evaluation report that it was an undeveloped prototype and would require a great deal of effort to get it ready for production".

This is reason for the request to borrow Fairey Battle with P24......

Thank you Mr T. Please accept 2 free Internetz in recognition of your awesomeness.

We could read our own discussion group posts too!

Bearing in mind the help Napier needed to get the Sabre workable in a decent time we could assume that RR and B carried on helping and the rate of power increase followed the Merlin curve... see below. Also if RR and B had been invoved from the start then the blue curve would lurch six months to the left (time 1st squadron of Tiffies had to 'train' whilst Sabre was fixed) .. giving a high power VII early 1944... That means Fury will be earlier and have better topside performance... makes you ponder doesn't it?