The Armstrong Siddeley Cougar an alternative engine for the RAF

I wrote this as a starter for a Gloster F5/34 naval fighter story but havent been able to construct a decent timeline.

In 1932 Armstrong Siddeley released its latest engine the 32.7 litre (1995ci) 14 cylinder Tiger a 700hp 2 speed supercharged engine perfect for high performance aircraft. It was a development of the 14 cylinder Armstrong Siddeley Big Cat series of engines that went back as far as the WWI RAF8 engine.

Unfortunately the big Cat engines had always had a problem with vibration which the AS engineers had tried to stop by increasing the strength of the crankcase and the bearings. These workarounds had so far ameliorated the problem but not made it go away and whilst the problems had been bearable in a 450hp engine the new faster revving 750hp plus Tiger had reached the limits of the 2 bearing crank design. The engine had the potential to give more power but increasing revs past 2000rpm just resulted in a big bang and a crank failure.

In 1935 Tommy Sopwith owner of Hawker Aircraft bought Armstrong Siddeley and Gloster Aircraft and he decided that stretching the old design was no longer possible or sensible and a clean sheet design was needed for a new engine. The Air Ministry was contacted to see if a new engine with a potential of 1000hp would be suitable for future aircraft designs, the Air Ministry gave non committal answer saying it would be evaluated for new bomber designs. This was enough for the Hawker Siddeley board to give the go ahead.

A new design incorporating all the latest technology and the all important 3 bearing crankshaft was laid out and by early 1936 the new engine called the Cougar was on the test bed.

The Tiger had managed to limp to 800hp at 2,100rpm by this time but the new Cougar romped to 2,700 rpm with no vibration problems. It was decided immediately to cancel all future development of the Tiger and concentrate on the new Cougar.

Work started on a flying version of the engine and a Hawker Hart biplane bomber was obtained to be the test aircraft. The hart with a 600hp Kestrel was good for 185 mph but with the new Cougar MkI in a neat full chord cowling rated at 975hp it managed to peak at 222mph.The Air Ministry was impressed by the new engine and financed the building of a new shadow factory to build it but still thought of it as a Bomber engine specifying it as the engine for the AW Whitley Night Bomber.

Glosters, Bristol and Vickers had all built prototypes for a new fighter to specification F5/34 but Bristol and Vickers were stuck with the comparatively weak Bristol Mercury. Glosters on the other hand fitted their aircraft with a AS Cougar MkX producing 1075hp on 87 Octane. The longer heavier engine caused some stability problems but a quick fix of a tail fillet solved the problems. In competition with the Hawker Hurricane MkI fitted with a RR Merlin MkII producing 1030hp showed the Gloster to be 5mph slower but with a climb to 20,000ft a whole minute quicker.

The RAF was impressed with the new Gloster fighter but preferred not to adopt an air cooled engine for home use. However the Admiralty heard of the new fighter and engine combination and requested a trial of the fighter loaded with ballast to replicate a navalised version. The Gloster F5/34 now called the Buzzard proved to be a fine handling aircraft but needed bigger flaps to slow down the landing speed for carriers.

In October 1939 the Royal Navy ordered 150 Buzzard MkIs equipped with an AS Cougar MkXII producing 1180hp and Fowler flaps but no folding wings. A 2nd order for 150 folding wing Buzzard MkIIs with a AS Cougar MkXV producing the same power but capable of using +12psi boost to give 1340hp for 5 minutes below 12,000ft was placed at the same time to be started as soon as the order for MkIs was finished.


Cougar 14-cylinder supercharged two-row air-cooled radial engine

  • Bore: 5.5 in (139.7 mm)

  • Stroke: 6.0 in (152.4 mm)

  • Displacement: 1,995 in³ (32.7 l)

  • Length: 64.6 in (1,641 mm)

  • Diameter: 50.8 in (1,290 mm)
Cougar MkIII 1090hp fitted with Claudel Hobson carburettor, DeHavilland 2 pitch propellor and single speed supercharger. Fitted to Whitley MkIV.

Cougar MkVI 1200hp fitted with Claudel Hobson Carb, DeHavilland Constant speed propellor and 2 speed supercharger. Fitted to Whitley MkV

Cougar MkXXI 1400hp fitted with Claudel Hobson carb Rotol propellor and 2 speed supercharger. Fitted to Wellington MkX Halifax MkII and Short Sunderland MkIII.

Cougar MkX 1180hp fitted with Claudel Hobson carb, DeHavilland constant speed prop and 2 speed supercharger. Fitted to Buzzard MkI

Cougar MkXV 1180hp fitted with Bendix Stromberg pressure carb and 2 speed carb. Fitted to the Buzzard MkII

Cougar MkXXX 1600hp Fitted with Bendix carb, Rotol prop and single speed low level supercharger. Fitted to Fairey Barracuda MkII and Hawker Hurricane MkIV.

Cougar MkXXI 1600hp fitted with Bendix carb, DeHavilland prop and 2 speed 2 stage carb, Fitted to Buzzard MkIII and Beaufighter MkV.
 
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Very nice though I think you meant to say 'romped to 2,700rpm' rather than 2,700hp. This makes a good alternative the Alvis engines as used in the 'Peerless Air Ministry'. So much so that I might borrow it for a rewrite at some time!!
 
Very nice though I think you meant to say 'romped to 2,700rpm' rather than 2,700hp. This makes a good alternative the Alvis engines as used in the 'Peerless Air Ministry'. So much so that I might borrow it for a rewrite at some time!!

Good spot I have edited out the typo.

Borrow away I had a timeline of a naval fighter roughly drawn out but couldnt quite tie it all together in a way made sense. There was a real life AS Cougar but it was a post war 9cylinder 19 litre engine that never made it to production. I pinched the Cougar name, the engine dimensions of the real life AS Tiger and the performance of the Mitsubishi Kinsei.
 
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Going to a 3-bearings design is a must, indeed.
Minor issue might be that pushing for +12 psi for a radial engine is a tall order, especially before advent of 130 grade fuel or ADI, and that 2-stage superchargers should not be considered as granted for anyone in the UK bar Rolls Royce. Granted, a 2-stage Cougar would've looked good on 4-engined bombers.
Any luck going for 18 cyl engine from the base cylinders, sorta Homare+?
 

Driftless

Donor
How useful is the comparatively smaller diameter of the Cougar vs some of the larger diameter Bristol engines? At least for that pre-war time frame.
 
Going to a 3-bearings design is a must, indeed.
Minor issue might be that pushing for +12 psi for a radial engine is a tall order, especially before advent of 130 grade fuel or ADI, and that 2-stage superchargers should not be considered as granted for anyone in the UK bar Rolls Royce. Granted, a 2-stage Cougar would've looked good on 4-engined bombers.
Any luck going for 18 cyl engine from the base cylinders, sorta Homare+?

The same cylinder dimensions and power per cylinder but in an 18 cylinder engine gives 42.05 litres and 1500 hp in the early versions increasing to 2050hp in my later versions. What sort of +psi would be sensible for an air cooled radial on 100 octane. To preserve the power the engine could be expanded to 5.75 bore 6.0 stroke engine dimensions this would boost capacity to 35.75 litres 2181 cubic inch.
 
How useful is the comparatively smaller diameter of the Cougar vs some of the larger diameter Bristol engines? At least for that pre-war time frame.

My idea was for a more compact lighter engine than the Bristol Hercules. The Cougar takes its external dimensions from the AS Tiger and the diameter of that was 50.8 in (1,290 mm). This is only slightly bigger than the P&W R1830 and Mitsubishi Kinsei making it easy to fit into similar size aircraft like the Gloster F5 and Bristol 146 plus the Hurricane when it was used in the Desert and Burma as a fighter bomber..
 
good combination, any idea on weight?

The Pratt&Whitney R1830 was around 1300 pounds
The Mitsubishi Kinsei was around 1250 pounds
The AS Tiger was 1200 pounds

The Cougar is going to be around 1350 pounds for an early version allowing for heavier construction than a Kinsei probably growing to 1700 pounds for later higher powered versions
 
Specifications (R-1830-S1C-G)
General characteristics
  • Type: Fourteen-cylinder two-row supercharged air-cooled radial engine
  • Bore: 5.5 in (139.7 mm)
  • Stroke: 5.5 in (139.7 mm)
  • Displacement: 1,829.4 in³ (29.978 l)
  • Length: 59.06 in (1,500 mm)
  • Diameter: 48.03 in (1,220 mm)
  • Dry weight: 1,250 lb (567 kg)
Components
  • Valvetrain: Two overhead valves per cylinder
  • Supercharger: Single-speed General Electric centrifugal type supercharger, 1:7.15 speed increase
  • Fuel system: Two-barrel Stromberg carburetor
  • Fuel type: 95-100 octane rating gasoline
  • Cooling system: Air-cooled
  • Reduction gear: Epicyclic gearing, 2:3
Performance
  • Power output:
  • 1,200 hp (895 kW) at 2,700 rpm for takeoff
  • 700 hp (522 kW) at 2,325 rpm cruise power at 13,120 ft (4,000 m)
  • Specific power: 0.66 hp/in³ (29.83 kW/l)
  • Compression ratio: 6.7:1
  • Specific fuel consumption: 0.49 lb/(hp•h) (295 g/(kW•h))
  • Power-to-weight ratio: 0.96 hp/lb (1.58 kW/kg)
 
The same cylinder dimensions and power per cylinder but in an 18 cylinder engine gives 42.05 litres and 1500 hp in the early versions increasing to 2050hp in my later versions. What sort of +psi would be sensible for an air cooled radial on 100 octane.

Hercules was doing +8 psi in 1942 (previously +7). Mercury was excellent, +9 psi on early 100 oct. BMW 801D did around +5.5 early on, while with much better fuel (no worse than Allied 130 grade) it upped to about +8.5 psi.

To preserve the power the engine could be expanded to 5.75 bore 6.0 stroke engine dimensions this would boost capacity to 35.75 litres 2181 cubic inch.

2181 cu in means it is equivalent to the R-2180. 'A' did 1400 on 91-100 oct, the post-war R-2180E went above 1600 HP with water injection/ADI.
The R-2000 was supposed to give 1600 HP with ADI and turbo on the XF5U; 1350 HP sans ADI.
 
Mitsubishi Kinsei -44
  • Type: 14-cylinder air-cooled twin-row radial engine
  • Bore: 140 mm (5.5 in)
  • Stroke: 150 mm (5.9 in)
  • Displacement: 32.3 L (1,970 cu in)
  • Length: 1,646 mm (64.8 in)
  • Diameter: 1,218 mm (48.0 in)
  • Dry weight: 545 kg (1,202 lb)
Components
  • Valvetrain: Overhead valve, one inlet and one exhaust valve per cylinder, pushrod operated.
  • Supercharger: Centrifugal, single speed.
  • Oil system: Triple section pump, one pressure pump, two scavenge pumps.
  • Cooling system: Air-cooled
  • Reduction gear: Planetary gear, 0.7:1 ratio.
Performance
  • Power output: 1,075 hp (802 kW) at 2,500 rpm at 2,000 m (6,560 ft) maximum.
  • Specific power: 24.8 kW/L (0.56 hp/cu in)
  • Compression ratio: 6.6:1
  • Power-to-weight ratio: 1.5 kW/kg (0.9 hp/lb)
 
Right I think the Cougar needs a little rethink. The bore will be increased by 0.25 inch making the Cougar a 35.7 L 2180 ci engine. This shouldnt alter the engine diameter but will allow for greater power at lower boost. The engine weight will have to go up by about 200 pounds though.

The R2000 Twin Wasp is a good comparison it was designed to be built to a lower standard for transport aircraft and 87 Octane
https://en.wikipedia.org/wiki/Pratt_&_Whitney_R-2000_Twin_Wasp

Cougar 14-cylinder supercharged two-row air-cooled radial engine

  • Bore: 5.75 in (139.7 mm)

  • Stroke: 6.0 in (152.4 mm)

  • Displacement: 2180 in³ (35.75 l)

  • Length: 64.6 in (1,641 mm)

  • Diameter: 50.8 in (1,290 mm)

  • Weight 1500 lbs (680 kgs)
 
Right I think the Cougar needs a little rethink. The bore will be increased by 0.25 inch making the Cougar a 35.7 L 2180 ci engine. This shouldnt alter the engine diameter but will allow for greater power at lower boost. The engine weight will have to go up by about 200 pounds though.
...

Good decision. That way we/you have small, up to 1100 HP engines covered by Bristol, 1200-1600 HP covered by Cougar, and 1600 HP and upwards covered by Hercules.
 
Just crunched the numbers on the Bristol Mercury and realised a 14 cylinder version is very close to the Cougar.
If you divide the Mercury figures by 9 and times by 14 you get approx 38 liter 1500 pounds weight and 1400 hp.

I know a 14 cylinder Mercury wouldn't be exactly those figures but it shows the specs of the Cougar aren't far off what Bristol could have done by not disappearing down the sleeve valve rabbit hole for several crucial years.
 
Good decision. That way we/you have small, up to 1100 HP engines covered by Bristol, 1200-1600 HP covered by Cougar, and 1600 HP and upwards covered by Hercules.

Don't forget the 18 cylinder version though I don't think there's any big Cat names left. Armstrong Siddeley Kitty Kat might not cut it
 

Driftless

Donor
Don't forget the 18 cylinder version though I don't think there's any big Cat names left. Armstrong Siddeley Kitty Kat might not cut it

How about Bobcat, Caracal, Ocelot, Margay; but they're all on the smallish size Or Saber-tooth, but they haven't been around for a while.....;)
 
How about Bobcat, Caracal, Ocelot, Margay; but they're all on the smallish size Or Saber-tooth, but they haven't been around for a while.....;)

I think there was an Ocelot engine but I like Bobcat. The Sabre tooth tiger wasn't a cat apparently it was a type of giant Sloth.
 
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