Westland P.9 Whirlwind (2 Viewers)

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If you go to a radial you would need more power to maintain the performance.

A Tiger has substantially more frontal area than the Peregrine.
 
frontal area of a Peregrine is 5.0 sq ft. Bristol Mercury is 14.5 sq ft and the Tiger is 14.1 sq. ft. The Tiger is a dead end with out a major redesign. The Mercury has a little stretch left in it but it's streamlining is for crap, Exhaust ports are
on the front of the cylinders and low drag radial cowlings are several years away.

The Dagger seems to bit a lacking also, it was only a 1027 cu in engine and while 1000hp was a notable achievement there may have been cooling and reliability problems with the MK VIII. getting another 50% power may be a pipe dream. The Big problem with aircooled engines was keeping them cool. Overhead cams take up valuable cooling fin space on the heads and more and better finning was needed everywhere on the radials that did show big increases in power with 100/130 fuel and higher. It also weighed as much or slightly more than an early Merlin but of course had no radiators. But radiators can be mounted on or just to the rear of the CG to help balance things. Increase side area of bigger nacelles forward may require bigger tail surfaces or extended fuselage to counteract. Possible but more work and more delay.

Changing 96 spark plugs was also going to be a real joy.
 
The essence of Halford's philosophy for the Dagger was that there were better returns from running the engine twice as fast as having it twice as big. He also saw it as a complete unit; a power egg as the Merlin package became called. Development would have followed a different route to conventional types. Yes higher boost but also higher revs. Yes it would need more cooling (That is why the Spitfire MkIX has 2 radiators and MkV 1.) But more air is no heavier even if it incurs more drag. I acknowledge the oil cooling demand would also rise.

My preference for the Dagger is that it could have been done at the time. It really was possible. A 100 octane Dagger is well capable of 1,000bhp but even an 850 bhp one matches the Peregrine. It would be better if it could be developed even further but we could still have a 2,000bhp fighter in 1941, even 1940 if decisions were taken early enough.

If a Peregrine Whirlwind can (just) reach Antwerp then a Dagger one with drop tanks can reach into Germany (albeit not far). In 1939, when planning assumed RAF bases striking from France, this would be a daylight fighter escort that can reach past the Ruhr. Forget the leading motorised Panzer Divisions.

The bulk of the German army was horse drawn for logistics and artillery. Low level Battles and Blenheims, with Whirlwind provided local air superiority, can isolate the blitzkreig divisions from their support. Let alone cannon/bomb Whirwinds performing their own GA missions.

France did not fall with Dunkirk. The French army fought for weeks thereafter and British forces were still being pumped in through the North West together with French troops extracted from Dunkirk. Without rear support the German advanced would have stalled and a stable front develop and with that French morale and will to fight would have strengthened. Yes the BEF was a tiny portion of the Allied armies (even if the RAF was a far greater player in the air war) but the Germans could not have left their whole northern flank exposed if the Pas de Calais region were free to mount a counter attack.

However, reigning back the imagination, my point is that it was perfectly possible for the Whirlwind to have remained in production and been worth the resources. If Dagger production was limited then shadow produce Mercury Whirlwinds and Westland produce Dagger Whirlwinds.

Dagger Whirlifighters and Mercury Whirlibombers? Who needs Battles and Spitfires? Ah, 20/20 hindsight vision!
 
OK. We have tried the Merlin, Taurus, Dagger and Tiger. How about the Mercury? Peregrine power on 87 octane, reliable and in production. Wanted for Blenheims but this is becoming less important just as the Peregrine is being shut down. Lighter weight than the Peregrine and quite suitable for tropical service. Maybe the weight saved could go into increased armour for a GA role.

Essentially we are seeking a sound, available production engine in the 850 to 1,100 bhp class. Ideally air cooled to free up inner wing space for fuel.

Peregrine is going out of production.
Merlin is in too high a demand (we now know Petter was able to fit it.)
Taurus is otherwise wanted for Albacores and Beauforts.
Tiger is too unreliable.
Mercury can be available but at the end of it's development.
I have to go with the Dagger. Available, useable and with development potential.......

This sounds like a Westland design committee meeting or exactly what they faced 70 years ago.

Based upon all theses questions and problems at the time and with the aircraft already in operation, was the Whirwind even needed?
 
RAF in ww2 never needed 4 cannon (day) fighter - and that was what the Specification called. Hence, Whirlwind was not needed.

What RAF might've used is 'British P-38', or, a 'pre- DH Hornet' - a fighter able to project power at great distance, while having a performance on par with single-engined fighters. So it's just too bad Peter didn't conceive Whirlwind to be slightly bigger, with Merlins aboard from day one.
 
The essence of Halford's philosophy for the Dagger was that there were better returns from running the engine twice as fast as having it twice as big. He also saw it as a complete unit; a power egg as the Merlin package became called. Development would have followed a different route to conventional types. Yes higher boost but also higher revs. Yes it would need more cooling (That is why the Spitfire MkIX has 2 radiators and MkV 1.) But more air is no heavier even if it incurs more drag. I acknowledge the oil cooling demand would also rise.

Both Friction and stress in the reciprocating parts go up with the square of the speed. One of the reasons that the 1027cu in Dagger weighed close to the 1650 cu in Merlin. It wasn't going to rev much faster, it was already at 4200rpm and a piston speed of 2625fpm. While the piston speed looks low compared to the Merlin the "corrected piston speed" which tries to take into account the size of the pistons give the Merlin a Piston speed of 2846 fpm (instead of 3000fpm) and the Dagger 2681fpm instead of the 2625fpm. Equalling the Psiton speed of the Merlin means about 4450rpm which is only about a 6% increase in airflow (or power) while increasing friction and stress by over 12%.
With cooling marginal (at best) at 1000hp any major increase in power is going to call for a major redesign of the cooling arrangements which include both the finning on the cylinder barrels and the heads. I would note that ANY air cooled radial that showed significant increase in power used redesigned cylinder heads or cylinder barrels or both. The Hercules went through about 5 or more different Cylinder heads, each with improved finning, the Wright Cyclone went through a succession of heads and barrels. Often these new heads and barrels were heavier than the old ones. Radials had more room for the fins to "grow" than an inline engine.
The Dagger had a full throttle altitude of 8750ft. Change the supercharger gear to one that gave a full throttle height of 15,000ft like the Peregrine and the full power will go down. Or put a low altitude gear into the Peregrine and watch the power go up at low altitude. The Dagger probably gives within a few % of the power of the Peregrine at 15,000ft.

However, reigning back the imagination, my point is that it was perfectly possible for the Whirlwind to have remained in production and been worth the resources. If Dagger production was limited then shadow produce Mercury Whirlwinds and Westland produce Dagger Whirlwinds.

Dagger Whirlifighters and Mercury Whirlibombers? Who needs Battles and Spitfires? Ah, 20/20 hindsight vision!

Mercury Whirlwinds would be even slower. You want a tank buster with 40mm cannon with Mercury's? Just take the Blenheim, clip the wings a bit, ditch the turret and hang a pair of 40mms under the fuselage.
 

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