1935-42: Alternative fighters for the RAF allies

[tomo pauk]

Premise of the thread: what kind of alternative fighters would you like to envision for design production in the UK, for the RAF, it's allies and export markets?
By 'alternative', I mean the fighters that at 1st would not be dependable on the newest engines, whether in development or that are about to start production run (Merlin/Peregrine/Griffon, Hercules/Taurus, Sabre). Should be easier to export (less restrictions due to 'legacy' engines lower price), while being able to bulk up the numbers of Hurricanes and Spitfires that will be produced as historically. Aim is also that fighter is easier to license produce in a country less developed than UK. If/when the newer engines are available in numbers, the 'second generation' might be up-engined, but don't bet the farm on the exact date - would be good not to too tightly tailor the airframe with current engine.
One or two engines.
We don't know when or if the 20 mm cannons will be available, so plan accordingly. RAF will need: a fighter with very heavy firepower; a 'turret fighter'; a 'colonial fighter', plus the 'normal' fighters. IOW - several designs.
Job starts in 1935, plenty of time to design start producing.

 

[Shortround6]

Except every 2nd rate fighter produced is a 1st rate fighter not produced.

The factories that produced the majority of allied fighters in 1942-43-44 don't exist, they are bare plots of ground as are hundreds of thousands of sq ft of engine factory "space".

Design teams are small and are not even able to handle the historical work-loads very well, having them split design efforts even more to build (draw/calculate) 2nd rate designs just delays the "good" planes.

Suggest you read the Wiki entry on the Hurricane. Hawker Hurricane - Wikipedia, the free encyclopedia

work started in 1930 or so on a better aircraft than the existing biplanes, it took several years and several redesigns to get to the basic Hurricane, Retracting landing gear being added in 1934 for instance.
First flight by prototype in Nov 1935. First service squadron starts to get them in Dec 1937, two squadrons equipped by Munich crises. 18 squadrons operationa by Sept 1939 and 3 more converting. Hawker had ordered materials for around 600 fighters before he got the official production order.

ANY fighter that does NOT use a Merlin in 1939/40 (unless it gets two Peregrines) is doomed to have lower performance than a MK I Hurricane.
Hurricane, especially with fabric covered wings, is going to be about simple as it gets for "less developed" countries. Both Belgium and Yugoslavia had licenses for the Hurricane and talks were under way with Poland (and maybe others?).

Britain's problem falls back to the Bristol Mercury being pretty much the only alternative productionengine in this time period. A 1938 Jane's shows the Mercury at 840hp at 14,000ft. The Best Kestrel had 745hp at 14,500ft. Weights are not far apart but Kestrel had several hundred extra pounds of radiators and coolant.
Perhaps the British could import American engines sooner

Turret fighter with low powered engine gets a Blackburn Roc clone. And so on.

"Bulking" up British numbers using planes that were inferior (or not much better than) existing 2nd line aircraft (Gladiators, Lysanders, Defiants or Blenheims) is just going to allow the Germans, Japanese and Italians to run up higher scores without changing the outcome of the battles any.

 

[tomo pauk]

Thanks for the overview.

But, since I am like I am: maybe a fighter with 12 Brownings and 2 Mercuries? Similar 'turret fighter' (forgetting for the moment that it was a blind alley) that also has forward firing guns? Also:

ANY fighter that does NOT use a Merlin in 1939/40 (unless it gets two Peregrines) is doomed to have lower performance than a MK I Hurricane.

Would a Whirlwind-sized fighter with 2 Kestrels will be too bad?

 

[Shortround6]

You also have to contend with the British (and some other countries) take off and landing requirements.
Whirlwind had to get exemptions for higher than normally allowed tire pressures and was much criticized initially for high take-off and landing speeds.

And development time.

Last one delivered December 1937.

When do you get 4 gun turrets?
When do you get Brownings?

What can you leave off The Blenheim in order to fit 8-12 forward firing guns and/or a 4 gun turret.

Or for a bit smaller plane the Fokker G 1

max speed 295mph with Mercury engines.

If you want to use lower powered engines than the 1st line planes and carry close to the same war-load and take-off in the same distance you need a bigger wing which will probably weigh more and have more drag. Before you start going on about high lift devices please remember that slats seldom, if ever, help with the take-off run and first use of Fowler flaps was on the Lockheed 14 (Electra) airliner which first flew in the summer of 1937. The high lift devices also add a bit of drag even when retracted so use was always a trade-off.

Would a Whirlwind-sized fighter with 2 Kestrels will be too bad?

with lower powered engines you have to lighten it up to get get it of the ground in the required distance/s. You may need bigger tires. Landing speed in 1936/37?
Whirlwind use magnesium alloy rear fuselage skinning for better strength to weight ratio than aluminium skinning available at the time. The rest of it's construction was neither cheap or easy according to it's critics. Using lower powered engines in a simplified air-frame (for your export customers?) is going to result in a bigger airframe or a heavier one (or both).

 

[wuzak]

How about this?

Martin-Baker MB 2 - Wikipedia, the free encyclopedia

 

[wuzak]

How about this?

Martin-Baker MB 2 - Wikipedia, the free encyclopedia

 

[pbehn]

For the life of me I cannot understand why work was not done earlier on putting cannons into the Hurricane instead of the Spitfire, the wing had space for it and if Bader's Big Wing had cannons even 1 per wing taking on unescorted bombers things would have been different.

The Hurricane wasnt a great aircraft in 1939/40 but it did have the great strength of being easy to produce and repair, the UK may have been short of pilots, Merlins and Spitfires they would never be short of Hurricanes

 

[tomo pauk]

Re. MB-2:
Retractable U/C instead of fixed, ejector exhausts instead of 'holes' (plus a dividing plate, so the exhaust gasses don't get in the intake; or a longer intake) and that's about it? The wing is not to big nor too thick, but it is neither 'Spitfire-thin' - not too draggy?

...
When do you get 4 gun turrets?
When do you get Brownings?

'Brownings' meant .303 MGs; turret as historically.

What can you leave off The Blenheim in order to fit 8-12 forward firing guns and/or a 4 gun turret.

All of the bombs, half of fuel tanks, 3rd crew member
Jokes aside, not a base for a fighter.

Or for a bit smaller plane the Fokker G 1
max speed 295mph with Mercury engines.

Gloster was proposing the twin engined turret fighter with 625 hp Bristol Aquila engines, with f/f guns, that went to became the F.9/37 eventually (but no turret here, 3 slanted cannons instead).

If you want to use lower powered engines than the 1st line planes and carry close to the same war-load and take-off in the same distance you need a bigger wing which will probably weigh more and have more drag. Before you start going on about high lift devices please remember that slats seldom, if ever, help with the take-off run and first use of Fowler flaps was on the Lockheed 14 (Electra) airliner which first flew in the summer of 1937. The high lift devices also add a bit of drag even when retracted so use was always a trade-off.

Mercury or Dagger complete powerplant will weight some 500 lbs less than a complete Merlin III powerplant, the difference in take off power was some 150 HP vs. hi-alt Mercury; Dagger VIII was making more power for TO. However, 500 lbs is a major weight when we discuss fighters weighting 6000 lbs for take off. Lower powered engine in a lighter smaller aircraft will also need less fuel, that will need less protection. Say 20 imp gals less than in Hurricane = another 150 lbs (without protection when installed).
The Mercury engines were quite early to have 2-pitch 3-bladed props?
The Fokker D.XXI managed with 174 sq ft wing, I'm not sure that Holland and Finland have had all paved runaways. The MS 406 also managed with 184 sq ft wing.

with lower powered engines you have to lighten it up to get get it of the ground in the required distance/s. You may need bigger tires. Landing speed in 1936/37?
Whirlwind use magnesium alloy rear fuselage skinning for better strength to weight ratio than aluminium skinning available at the time. The rest of it's construction was neither cheap or easy according to it's critics. Using lower powered engines in a simplified air-frame (for your export customers?) is going to result in a bigger airframe or a heavier one (or both).

I'd go with something sized in-between the Whirlwind and Fw 187, it will perform not so good as Whirly, but should beat the Fw (more power, a tad smaller).


What about a wooden fighter? Arframe production should not collide with metal aircraft, due to different skill sets of the workforce and tooling needed?

 

[Shortround6]

The British were critically short of engineers and draftsmen. Many companies were forced to abandon proposed projects in order to concentrate on only a few projects in order to get them done in a timely fashion. Trying to design multiple 2nd rate aircraft in 1935-40 would have simply made things worse for the British.
Then you have the already mentioned engine problem, what was available and in what numbers. Kestrels were not "free" and Peregrines were not made out of ultraexpensium.
More Kestrels could only be had the "cost" of fewer Merlins.
Bristol was already working pretty much flat out building the Mercury and Pegasus with a dribble of sleeve valve engines. Where do additional Bristol engines come from?
The Dagger was a terrible engine.
Less said about the Armstrong Siddeley engines the better.

Wood construction is all over the place when it comes to weight. DH construction was about as good as it got. Some other companies could not build wooden structures anywhere near as light as metal structures. Yes wood construction requires different skill sets than metal but it also requires adequate supplies of the right kinds of wood, it requires proper glues. Japanese tried to build a wooden Ki 84, it came out 600lbs heavier than the metal one. The Bell XP-77 came out over-weight (Bell seemed to have a problem estimating weights no matter what the material). Air Ministry authorized the Armstrong Whitworth A.W.41 Albemarle to be part made of wood, it failed in part due to be being over weight for installed power. Bf 109s with wooden tail components got extra "armor" under the oil cooler to get the CG back in place.

British also have the propeller problem, Yes the Mercury got 2-pitch 3-bladed props fairly soon, Gloster Gladiators did not. Some Gladiators got metal fixed pitch 3 blade props.

If first line aircraft like Hurricanes and Spitfires were not getting getting good props until 1940 the chances of the 2nd line aircraft getting them were about zero.

Mercury or Dagger complete powerplant will weight some 500 lbs less than a complete Merlin III powerplant

This might very well be right for the Mercury, it is not right in regards to the Dagger. The Dagger III went 1285lbs. The Dagger VIII went 1390lbs but that may include the Napier provided airscoops on the top and bottom of the engine.
BTW the Dagger changed from a down draft carb on the III to an updraft carb on VIII. I don't know what those scoops on the MB2 are but the intake duct has got to be a bit twisted if they are the carb intakes.

The Fokker D.XXI managed with 174 sq ft wing, I'm not sure that Holland and Finland have had all paved runaways. The MS 406 also managed with 184 sq ft wing.

The Fokker D.XXI carried 1/2 the armament of a Hurricane, The MS 406 weight of armament is also lower than a Hurricanes. And more importantly, neither could do the job. The British need aircraft that can take on the Germans flying Bf 109s. Planes that can take on the Russian airforce, especially in 1940 and 41 are NOT first line aircraft in the west at that time. They might have worked against the Italians. Sending them to the far east to fight the Japanese just means the Japanese pilots get provided more target practice.

You have said other places that the pilot was the most expensive piece of the whole equation. This is true even if it took the Air Ministry a while to realize it. However adding armor, self sealing tanks and BP windscreens to low powered planes hurts their performance even more than the high-powered planes. What are you going to do, use thinner armor on the pilot back plates of the lower powered planes? Smaller BP windscreens?
If you can't scale pilot protection (use only small pilots?) The protection becomes a bigger percentage of aircraft weight.

 

[wuzak]

BTW the Dagger changed from a down draft carb on the III to an updraft carb on VIII. I don't know what those scoops on the MB2 are but the intake duct has got to be a bit twisted if they are the carb intakes.

Surely they are cooling plenums?

 

[Shortround6]

The is a scoop on each side of the cowl just behind the exhaust ports and just below the upper row.

trouble is that on the early engines the carb intake is higher than the exhaust outlets

and on the later engines the carb is well below (and behind?) the position of the scoops.

 

[tomo pauk]

The British were critically short of engineers and draftsmen. Many companies were forced to abandon proposed projects in order to concentrate on only a few projects in order to get them done in a timely fashion. Trying to design multiple 2nd rate aircraft in 1935-40 would have simply made things worse for the British.

The engineers and draftsmen turned, in 1935-40, quite a few aircraft from napkin sketches into flying hardware. Just monoplane fighters: Vickers Venom, Bristol type 146, MB-2, two Glosters, plus 4 fighters that RAF accepted in service, plus Fulmar = ten designs. With bombers, transports, civil aicraft, hydro/flying boats, and other naval aircraft counted in, that is serious number of aircraft.
What will be a problem is turning the flying prototypes into mass produced aircraft, as you've noted. One of reasons I've mentioned a wooden fighter.

I'll like to return to the foreign countries trying to license produce the Hurricane: all was fine until there are Merlins to be purchased. Problems arose when that was not the case, Yugoslavs went to have DB 601A installed in their Hurris. A more widely spread engine in an airframe better suited for it avoids these problems.

Then you have the already mentioned engine problem, what was available and in what numbers. Kestrels were not "free" and Peregrines were not made out of ultraexpensium.
More Kestrels could only be had the "cost" of fewer Merlins.
Bristol was already working pretty much flat out building the Mercury and Pegasus with a dribble of sleeve valve engines. Where do additional Bristol engines come from?
The Dagger was a terrible engine.
Less said about the Armstrong Siddeley engines the better.

Yep, A/S engines were not that suitable for a fighter.
The problem with Dagger VIII is that it was a lousy replacement for the Pegasus. In a bomber, it needed to go in emergency RPM and boost to beat Pegasus, while being 250 lbs heavier. We don't know how good the cooling was in 250 MPH bomber, vs. a 300 mph fighter. How much the max take off setting was used in a fully laden bomber, vs. a fully laden fighter? All these things can push the engine into overheating, let alone combined.
The tooling for Kerstrels was around for quite a few years, and some of it will not suit Merlin production, but will future Peregrine production. I agree that Peregrine was not made of ultraexpensium

Wood construction is all over the place when it comes to weight. DH construction was about as good as it got. Some other companies could not build wooden structures anywhere near as light as metal structures. Yes wood construction requires different skill sets than metal but it also requires adequate supplies of the right kinds of wood, it requires proper glues. Japanese tried to build a wooden Ki 84, it came out 600lbs heavier than the metal one. The Bell XP-77 came out over-weight (Bell seemed to have a problem estimating weights no matter what the material). Air Ministry authorized the Armstrong Whitworth A.W.41 Albemarle to be part made of wood, it failed in part due to be being over weight for installed power. Bf 109s with wooden tail components got extra "armor" under the oil cooler to get the CG back in place.

Thanks for this overview.

British also have the propeller problem, Yes the Mercury got 2-pitch 3-bladed props fairly soon, Gloster Gladiators did not. Some Gladiators got metal fixed pitch 3 blade props.
If first line aircraft like Hurricanes and Spitfires were not getting getting good props until 1940 the chances of the 2nd line aircraft getting them were about zero.

A more emphasis on production of the 2-pich and variable pitch props might come in handy? Buy at Hamilton Standard? License production of those, either in UK or Canada? British were not shy to purchase licenses, from Farman's S/C drives to Bren/Oerlikon/HS/Bofors.

This might very well be right for the Mercury, it is not right in regards to the Dagger. The Dagger III went 1285lbs. The Dagger VIII went 1390lbs but that may include the Napier provided airscoops on the top and bottom of the engine.
BTW the Dagger changed from a down draft carb on the III to an updraft carb on VIII. I don't know what those scoops on the MB2 are but the intake duct has got to be a bit twisted if they are the carb intakes.

The scoops are for cooling.
The cooling system for the V-12 of nominal 1000-1100 HP will come at 320-330 lbs for a 'close-coupled' version like he one found at Fulmar. A more 'spread away' system will go at 350+ lbs (Spitfire, Hurricane, Mustang I). Dagger was at 925 HP of nominal power, shaves as bit on prop and oil system. So it's close to 400 lbs; granted, not 500, but close enough.

The Fokker D.XXI carried 1/2 the armament of a Hurricane, The MS 406 weight of armament is also lower than a Hurricanes. And more importantly, neither could do the job. The British need aircraft that can take on the Germans flying Bf 109s. Planes that can take on the Russian airforce, especially in 1940 and 41 are NOT first line aircraft in the west at that time. They might have worked against the Italians. Sending them to the far east to fight the Japanese just means the Japanese pilots get provided more target practice.

Under 'they managed' I've meant 'they managed to take off' - despite small wing and take off power. The MC 200 also managed, so did the Bf 109 versions with MF FF and Jumos.
Granted, the Fokker carried half of the armament, but extra 200-250 lbs worth of guns ammo does not sound like a reason for the wing area of 174 sq ft to grow 50%.
By 1941, the 'other' fighter can get the better engine, per 1st post here. So the Japanese (or other) cannot rack scores so easily.

You have said other places that the pilot was the most expensive piece of the whole equation. This is true even if it took the Air Ministry a while to realize it. However adding armor, self sealing tanks and BP windscreens to low powered planes hurts their performance even more than the high-powered planes. What are you going to do, use thinner armor on the pilot back plates of the lower powered planes? Smaller BP windscreens?
If you can't scale pilot protection (use only small pilots?) The protection becomes a bigger percentage of aircraft weight.

One of remedies is to use more powerful engines as they became more available.

 

[Shortround6]

The engineers and draftsmen turned, in 1935-40, quite a few aircraft from napkin sketches into flying hardware. Just monoplane fighters: Vickers Venom, Bristol type 146, MB-2, two Glosters, plus 4 fighters that RAF accepted in service, plus Fulmar = ten designs. With bombers, transports, civil aicraft, hydro/flying boats, and other naval aircraft counted in, that is serious number of aircraft.
What will be a problem is turning the flying prototypes into mass produced aircraft, as you've noted. One of reasons I've mentioned a wooden fighter.

Actually a few of the planes listed illustrate the problem. the Bristol type 146 was designed to the specification F.5/34 but first flight by prototype wasn't until 11 February 1938 at which time not only was the Hurricane in production but first aircraft had started to be delivered to service squadron/s. The Bristol was behind by at least a year and closer to two years. As for one of the Glosters: from Wiki" By the time the F.5/34 began its flight tests, the 8-gun Hawker Hurricane was in service and the Supermarine Spitfire in production so that further development of the Gloster fighter was abandoned." Granted it goes on to say " However, compared to its contemporaries, test pilots found the F.5/34 prototypes had a shorter takeoff, better initial climb, were more responsive and manoeuvrable due to ailerons that did not become excessively heavy at high speed. Handling was considered very good and the all-round cockpit visibility was far better than the other designs." However you run into the engine problem. Both are powered by the Mercury engine and without major work there was no more power to be had. The only possibility is using a Perseus engine and even that is only going to get a few more HP until sometime in 1941 even if you can get it to match Hercules power per liter. Of course you have to solve the sleeve valve production problem too. Switching engines to Taurus or American radial means a delay of a number of months in planes that are already running late.

I'll like to return to the foreign countries trying to license produce the Hurricane: all was fine until there are Merlins to be purchased. Problems arose when that was not the case, Yugoslavs went to have DB 601A installed in their Hurris. A more widely spread engine in an airframe better suited for it avoids these problems.

We are back to which more widely spread engine? the more widely spread engines are down on power (in some cases waaay down) and/or have limited development potential.
Most countries and foreign companies are only interested in licencing aircraft and engines that fall in a narrow band. It has to be more modern than they can design themselves but it has to have enough of a "track record" to be a somewhat proven design. Very few, if any, Countries/companies licensed experimental aircraft or engines. They wanted value for their money, not to be funding other peoples research.
Some countries were limited as to who would deal with them and others had different ideas of how long they had to rearm.

The problem with Dagger VIII is that it was a lousy replacement for the Pegasus. In a bomber, it needed to go in emergency RPM and boost to beat Pegasus, while being 250 lbs heavier. We don't know how good the cooling was in 250 MPH bomber, vs. a 300 mph fighter. How much the max take off setting was used in a fully laden bomber, vs. a fully laden fighter? All these things can push the engine into overheating, let alone combined.

It doesn't look like that good a fighter engine either, FTH was 8000-8500ft without ram. Power at 14-16,000ft wasn't much better (if as good) as the Mercury.

The tooling for Kerstrels was around for quite a few years, and some of it will not suit Merlin production, but will future Peregrine production.

"Tooling" covers two things. the jigs and fixtures used to hold the parts in the machines, the gauges used to measure them and the lathes, milling machines, drill presses,etc the jigs and fixtures are mounted on. The Jigs, fixtures and gauges specific to the Kestrel could be give/sold to someone else but RR is going to need every single lathe, milling machine, drill press and broach they have.

A more emphasis on production of the 2-pich and variable pitch props might come in handy? Buy at Hamilton Standard? License production of those, either in UK or Canada? British were not shy to purchase licenses, from Farman's S/C drives to Bren/Oerlikon/HS/Bofors.

Britain had fooled around with controllable pitch propellers back in the 20s. Henry Selby Hele-Shaw being one of the inventors, however, like many things the idea was ahead of the ability to manufacture and the biplanes of the time had such a limited speed range that there was considerable argument about wither the benefits outweighed the cost (money, weight, maintenance). Unfortunately the "wisdom" of the time tended to stick and prejudiced the Air Ministry against the variable pitch/constant speed prop for years to come. de Havilland had bought the Hamilton Standard license in 1933 but they were trying to sell to an air ministry that didn't want to buy. Rotol was formed by both Bristol and RR not only as a competitor but as a 2nd source as both Fedden and RR management knew the better props would be needed soon even if the air ministry had both thumbs firmly inserted in their collective backside.

Under 'they managed' I've meant 'they managed to take off' - despite small wing and take off power. The MC 200 also managed, so did the Bf 109 versions with MF FF and Jumos.
Granted, the Fokker carried half of the armament, but extra 200-250 lbs worth of guns ammo does not sound like a reason for the wing area of 174 sq ft to grow 50%.
By 1941, the 'other' fighter can get the better engine, per 1st post here. So the Japanese (or other) cannot rack scores so easily.

Well, something was going on as the Bristol 146 had a 220sq ft wing for 4600lbs and the Gloster F.5/34 had 230sq ft for 5400lbs. MB 2 had 212 sq ft.

Not all countries had the same take-off and landing requirements and the British ones may have been severely impacted by those two bladed fixed pitch props. Some other counties getting on the constant speed (or at least variable pitch) several years before the British Air Ministry.

One of remedies is to use more powerful engines as they became more available.

For the British the only more powerful engines that became available were the Merlin and Hercules, unless they could buy P&W R-1830s or Wright R-1820s. While the Mercury and Pegasus got a bit better with 100 octane fuel it wasn't a lot better and it didn't change the FTH any.

 

[stona]

How about this?

Martin-Baker MB 2 - Wikipedia, the free encyclopedia

I wouldn't fancy flying one of those against a Bf 109 E.

The A&AEE's February 1939 report on the type gives a long list of problems which needed fixing. A substitute Spitfire it most definitely was not.

Cheers

Steve

 

[tomo pauk]

Some power charts for engines that might power the alternatives. Sorry for big pictures, scaling them down blurs them:

860 HP at 16000 ft; light engine; shortcoming: a bit too bulky 9 cyl:

780 HP at 16000 ft; less bulky than Pegasus and a bit lighter; an useful increase of power (including take off power) when 100 oct is available (ie. as good as not available prior 1939):

860 HP at 16000 ft; (looks like it was as bulky as Pegasus??):

770 HP at 16000 ft; benefits vs. radials: power at lower altitudes, less drag, easier installation of ejector exhausts; shortcoming vs radials: weight, disputable reliability on highest power setting:

 

[Shortround6]

Thank you, you pretty much have it. The Mercury and Perseus were 24,9 liter engines and there is only so much you can do with that displacement. The contemporary (sort of, it was bit later in timing) Wright R-1830G205A (2 speed supercharger) engine got 1000hp at 14,200hp Military power using 100 octane fuel from 29.9 liters. So the Mercury was actually a very close match for power per liter at that altitude. The Wright engine also weighed 1320 lbs.
Without major work the Mercury and Perseus were pretty much maxed out.
Pegasus was also pretty much maxed out. It's long stroke meant higher rpm was pretty much out of the question.
That leaves you with the Dagger and there is only so much that small cylinders and high rpm can do for you. It was about 20% smaller in displacement than a Kestrel or Peregrine so it needs to spin 20% faster to flow the same amount of air at the same boost pressure. Then you run into the internal friction problem. Not much growth there without a lot of work. And as per the chart 770hp at 16,000ft just isn't enough unless you leave a lot of stuff out of the airplane.
BTW about 80% of the internal friction in a engine comes from the pistons (and rings) scrubbing the cylinder walls. The Dagger at 4200rpm is scubbing 23% more area than a Merlin at 3000rpm.
It was an interesting experiment and had fuel stayed at 87 octane it might have shown the way forward (or not) but it couldn't be modified easily to take advantage of higher octane fuels (get more cooling like later R-1820s and R-2600s and R-2800s and they needed considerable/total redesign)

 

[tomo pauk]

Few questions: what are real diameters of Bristol radial engines? Wikipedia lists the Perseus at 55.3 in (source: Lumsden), more than Mercury and on par with Pegasus.
Was Merlin III allowed for more than 6.25 boost for take off in 1940/BoB-only/1941?

 

[Shortround6]

1938 Jane's and a few editions of Wilkinson's give 52 in dia for the Perseus.

I can look a bit more if you want. Flight magazine has some articles on the engines showing th eincrease in finning and changes in cylinder heads (multiple changes) just up to 1939.

ANd please remember that nobody was going to take out a license for a sleeve valve engine until Bristol figured out how to do it on a production basis. They may talk about it but nobody was signing on the dotted line.

 

[tomo pauk]

The 52 in is a more believable figure.
The engines for foreign customers will much more likely involve Mercury or Pegasus.

 

[yulzari]

Well the choices might open up if Bristol avoids the love affair with sleeve valves with (crudely speaking) a double row Mercury and a double row Pegasus. Thus a 1,700bhp and a 2,200bhp radial. Double rowing 4 valve headed motor can't be worse than developing sleeve valves.