Westland Whirlwind revisited

[Schweik]

It is not quite so simple. The R-2800 was great lump of an engine, even the engine in an early B-26 went 2270lbs with a two speed single stage supercharger. and it needs a huge propeller to turn that power into thrust. It just won't fit/balance in some of the smaller airframes. You have to throw out so much you might as well start over.

Yeah, that was basically my point.

The 109 had a number of problems which get glossed over.

Not by me - I am well aware. Small aircraft in general had problems and represented a compromise, and the Bf 109 in particular had quite a few problems. But the persistence of the design in the front ranks of the war until the very end speaks to the value of speed and performance. I am not of the school that this is the only thing that matters - I am a fan of the Ki-43 and the A6M, and the Yak 1 and so forth. Even the Hurricane for the very early war. But clearly it mattered. It was one of the ways to achieve an effective fighter design - small and fast and high performing.

One of the other reasons Whirlwind was cancelled is that it didn't soar at 25,000 ft. Aside from big and small designs (and the theory circa 1938-1940 that bigger ones would eventually dominate the future) was high vs. medium vs. low altitude. Early on I think most war bureaucracies in every Great Power thought high altitude was the thing. Later, as I have often argued in many threads on here, Tactical environments in many Theaters showed the intense need for good low altitude performance, something that the War Ministry and both aircraft and engine designers eventually realized (hence the Merlin 32, 45, 50 66 and the cropped impellers and LF Spitfires etc.) but that came with experience* and the prevailing attitude was working against the Whirlwind in the early war.

I am not sure where your definition of small, medium and large come from. Certainly the Spitfire has a skinner fuselage than the P-51 but the Spit actually has a slightly larger wing. The radiators, oil coolers and intercooler (on the two stage engines) is also hanging out under the wings (ok part of the cooling matrix is in the wing) vs the Mustang housing a large part of the cooling matrix inside the fuselage. The Mustang has the famous larger fuel capacity (forgetting the rear fuselage tank/s) increased weight but not bulk by much (thicker wing roots)

Just looking at them side by side, the Spit is a bit slimmer and more streamlined to me, the Mustang a bit wider and more squared off. They are close though, really both are in the medium category IMO, Spit on the small side of that threshold and Mustang on the slightly larger side of it, though we know the Mustang probably had less drag.

Part of the Problem the Spits had with the FW 190 is that no first line Spitfire fighter ever had a single stage two speed supercharger. Had they fitted the Merlin XX (and used appropriate boost, say 15lbs) then the FW 190s superiority would have been much less marked.
But the Merlin XX was needed for Hurricanes and bombers.

I didn't know that and it certainly seems like an odd decision, I had assumed that the Merlin 46 had two speeds and was somewhat similar to an XX. The Merlin 45 was an XX with a single speed XX essentially right? Seems like better altitude performance - and two speeds so you have both better low and high altitude performance, would have helped a lot with Spit Vs in the MTO.


* there was also the fetish that the Fleet Air Arm had for low altitude engines which may not have been entirely grounded in reality.

 

[Shortround6]

What kind of advantage the Merlin XX offers vs. Merlin 45 once we're above 12000 ft?

Not much but the higher gear on the supercharger is good for a few thousand feet but then the FW 190 wasn't at it's best in the high teens either was it?
The Merlin XX would have allowed around 100 more HP at the lower altitudes at any particular boost limit. Wouldn't have made the MK V into a 190 killer but the 19-s may have found it harder to get kills?

 

[Schweik]

The Spitfire, like the Bf 109, was the product of pre-war thinking that attempted to bolt the most powerful engine available onto the smallest practical airframe.

Right, and I was emphasizing the perspicacity of that exact pre-war thinking. The merit of that design philosophy was basically speed and performance, the inherent limitation was range, armament and sometimes maneuverability.

The part of that which was in demand in the late 30's was firepower. They wanted a four cannon fighter to knock down bombers more reliably right?

The Whirlwind, though larger than a Spitfire certainly, actually looks fairly diminutive next to a Hurricane despite having a wider wingspan and two engines. It's got a much slimmer fuselage and of course, thinner wings. In terms of design it is a reflection of that 'smallest airframed with the most powerful engine available' - in this case two small Peregrines with 1,700+ hp instead of one medium sized Merlin with ~1,200 hp, giving it the needed power to carry those heavy guns.

I don't know the exact drag coefficient but I suspect the Whirlwind had less drag than a Hurri and would be able to maintain a higher combat speed. It also had a power to weight ratio of about 0.17 compared to about 0.15 for a Hurricane II with a Merlin XX.

 

[tomo pauk]

Not much but the higher gear on the supercharger is good for a few thousand feet but then the FW 190 wasn't at it's best in the high teens either was it?
The Merlin XX would have allowed around 100 more HP at the lower altitudes at any particular boost limit. Wouldn't have made the MK V into a 190 killer but the 19-s may have found it harder to get kills?

Quirk might be that Spitfire V have had a lot of problems at altitudes we talk a lot for the ETO - 15000 ft and higher. At high teens, the Fw 190 was in it's element, so it was under 5000 ft (thus saving the whole Typhoon + Sabre program).
What Spitfire V (and other Merlin-powered RAF fighters) needed was adoption of less draggy exhausts (+7-8 mph), a proper carb (equals +10 mph + 1500 ft increase in ceiling) instead of whatever they installed on the Merlins before 1943, and a strict attention to fit and finish (another 10 mph, give or take). Internal BP glass - again more than 5 mph gain. End result is a Spitfire V that reliably does above 380 mph (instead of 360+ mph for run-on-the-mill Spitfire Vs), while climbing and cruising a tad better.

 

[Schweik]

As they realized the improved fuel would allow higher power from smaller, existing engines the need for larger or strange engines (in RR's case the Vulture or the Exe or Cressy) diminished considerably.

Correct me if I'm wrong but my understanding is that the RR Merlin had a smaller displacement (wiki says 1650 "³) than it's arch rival, the DB 600 series (wiki says 1800 "³ for the 601, 2,176 "³ for the 605) and yet was at least it's equal in performance. There is more than one way to skin a cat.

 

[Shortround6]

I didn't know that and it certainly seems like an odd decision, I had assumed that the Merlin 46 had two speeds and was somewhat similar to an XX.

The Merlin 46 was single speed and used an even bigger supercharger than the Merlin 45 which gave it several thousand feet more altitude but hurt it at low altitudes.

The Merlin 45 was an XX with a single speed XX essentially right?

Yes but the single speed sort of split the difference between the gears in the XX so it might have been better around 8-12,000ft but worse at low level and up near 20,000 ft.

* there was also the fetish that the Fleet Air Arm had for low altitude engines which may not have been entirely grounded in reality.

Well, you are the one that says high altitude is somewhat over rated

As you say, it depends on tactical considerations, since it turns out that nobody could hit moving ships from high altitude with level bombers having high altitude fighters (or anti ship bombers) in the FAA wasn't going to change things much. Low altitude engines are good for fighting torpedo bombers and low level bombers.
Plus the RN had to get it's aircraft off of those small (and sometimes slow) flight decks and the low altitude engines offered more power for take-off.

The Merlin III was good for 880hp for take-off at 6lbs boost on 87 octane fuel, the MK VIII Merlin in the Fulmar I was good for 1080hp for take off on 87 octane fuel. (1275hp on 100 octane?)
Fulmars might have really benefited from a two speed supercharger. Actually be able to get off the flight deck and yet fight at higher altitude too. A lot depends on fuel available or what they thought would be available.

 

[Schweik]

I've read a lot of operational history of FAA fighters and bombers struggling due to the low alt rated engines. Including late war ones with very powerful engines. Two speed (or whatever the multi-speed hydromatic method was that Daimler Benz used) is definitely better most of the time IMO if you have the option. Especially for something like Combat Air Patrol.

 

[Schweik]

Quirk might be that Spitfire V have had a lot of problems at altitudes we talk a lot for the ETO - 15000 ft and higher. At high teens, the Fw 190 was in it's element, so it was under 5000 ft (thus saving the whole Typhoon + Sabre program).
What Spitfire V (and other Merlin-powered RAF fighters) needed was adoption of less draggy exhausts (+7-8 mph), a proper carb (equals +10 mph + 1500 ft increase in ceiling) instead of whatever they installed on the Merlins before 1943, and a strict attention to fit and finish (another 10 mph, give or take). Internal BP glass - again more than 5 mph gain. End result is a Spitfire V that reliably does above 380 mph (instead of 360+ mph for run-on-the-mill Spitfire Vs), while climbing and cruising a tad better.

One of the things that surprised me about the MTO operational history is that the Spit V squadrons seemed to routinely get jumped from above by Bf 109s and MC.202s just like the Hurricanes and P-40s did and had to use similar tactics. Not always, or as often because sometimes the Spits arrived at the battlefield at higher altitude (or some of them did, whichever ones which were designated for top cover) and were lucky enough to find Axis fighters below them, but "anecdotally" so to speak based on Shores it seemed pretty routine that they were bounced from above even when flying sweeps and CAP. Both German and British / Commonwealth pilots commented on this.

Some Spits also definitely seemed to perform better at high altitude than others. In part this seems to have just been variation of what came out of factory, in part and increasingly over time it was due to field modifications. Some Spits had one pair of cannon or two of machineguns removed, some had armored windscreen removed, some got the sanding and waxing and putty treatment on wings and fuselage like many of the Merlin P-40s did. Of course the biggest problem seemed to be the Vokes filter.

 

[tomo pauk]

...
Yes but the single speed sort of split the difference between the gears in the XX so it might have been better around 8-12,000ft but worse at low level and up near 20,000 ft.
...

Low gear on the Merlin 20s: 8.15:1 ratio; high gear: 9.49:1
The only ratio of the Merlin 45 being 9.089:1
At the end of the day, both were making ~1200 HP at 18000 ft, and ~1500 HP at 11000 ft (that is with plenty of boost once cleared for, +16 psi), no ram. The Merlin 45 being about 150 lbs lighter, granted without the benefits of the low speed gear.

 

[stona]

The part of that which was in demand in the late 30's was firepower. They wanted a four cannon fighter to knock down bombers more reliably right?

.

The two things that drove British fighter design in the 1930s were the quest for speed and firepower. You are absolutely correct that endurance was sacrificed in the pursuit of these two. The fuel capacity of the Spitfire and bomb carrying ability were reduced or deleted when the decision was taken to increase the armament to eight machine guns.

Eight machine guns was very heavy armament in the mid/late 1930s. It was double the armament of the Bf 109 E-1, which was still being delivered to Luftwaffe units in France in September 1940 ( Of the 323 Bf 109s delivered to the units at the English Channel as late as September 1940, exactly 100 were E-1s). Most aircraft had two or four machine guns and some carried a single cannon. A single cannon in a fixed gun fighter was considered undesirable by the British, as the chances of actually scoring any hits were considered slight.

The British were looking for cannon armament, but in the mid 1930s it took two engines to lift more than one cannon. This soon changed with the Bf 109 and Spitfire, but a war will move things along remarkably quickly. The Tornado was supposed to be the first British S/E fighter to lift four cannon, but that turned into a bit of a debacle and eventually the Typhoon arrived much later than anticipated.

 

[tomo pauk]

The British were looking for cannon armament, but in the mid 1930s it took two engines to lift more than one cannon. This soon changed with the Bf 109 and Spitfire, but a war will move things along remarkably quickly.

Spitfire was not among the 1st of the 1-engines fighters to carry more than one cannon. Before the Spit, there were versions of the I-16, Bf 109, P.24 and He 112 carried two cannons in the air.

 

[Kevin J]

What kind of advantage the Merlin XX offers vs. Merlin 45 once we're above 12000 ft?

None.

 

[stona]

Spitfire was not among the 1st of the 1-engines fighters to carry more than one cannon. Before the Spit, there were versions of the I-16, Bf 109, P.24 and He 112 carried two cannons in the air.

Yes, but I was referring to the BoB. The Spitfire and Bf 109 both got two cannon in this period, though the Spitfire's was somewhat 'experimental'.

The He 112 never entered service (did one fly in Spain?), but would you swap an eight gun Spitfire for a I-16 or P.24 ?

 

[tomo pauk]

Yes, but I was referring to the BoB. The Spitfire and Bf 109 both got two cannon in this period, though the Spitfire's was somewhat 'experimental'.

Doh. The Bf 109s in the BoB carried two cannons as a rule, unlike the Spitfires.

The He 112 never entered service (did one fly in Spain?), but would you swap an eight gun Spitfire for a I-16 or P.24 ?

He 112 entered service in Spain and Romania. I've never questioned the Spitfire's qualities (there was a lot of them), but anyway we slice it it was not on forefront of having cannons installed (again, not a mistake of Supermarine's design team).

 

[wuzak]

The Tornado was supposed to be the first British S/E fighter to lift four cannon, but that turned into a bit of a debacle and eventually the Typhoon arrived much later than anticipated.

The Tornado and Typhoon were both, initially, specified with 12 x 0.303".

At some stage development of the 4 cannon version began, but the initial production Typhoons still had the 12 mg.

 

[wuzak]

* there was also the fetish that the Fleet Air Arm had for low altitude engines which may not have been entirely grounded in reality.

That may have had something to do with getting the aircraft off the goddamn deck.

 

[Shortround6]

Correct me if I'm wrong but my understanding is that the RR Merlin had a smaller displacement (wiki says 1650 "³) than it's arch rival, the DB 600 series (wiki says 1800 "³ for the 601, 2,176 "³ for the 605) and yet was at least it's equal in performance. There is more than one way to skin a cat.

It did have the displacement you list but I don't know what your point is.
The Peregrine was 1296 cu in (as was the Kestrel)
The Exe was 1,348 cu in
the Merlin was 1650 cu in
the Griffin was 2240 cu in
the Vulture was 2592 cu in

The Sabre was 2238 cu in.

The Exe used sleeve valves and 24 cylinders and ran at 4200rpm.

to get a rough idea of an engines ability to make power you need to figure the air flow, displacement times 1/2 the rpm times the intake pressure will get you close. So if the engines ran at close to the same speed and used the same fuel power was dependent on displacement.
if your fuel limits the pressure inside the cylinders it limits the amount of fuel that can be burned in the cylinder each time it fires and limits the power.
The DB engines never ran at the same speed as the Merlin and never ran at the same intake pressures, by the time the Germans got to 1.42 Ata (very roughly 6lbs of boost) the British were well beyond it.
There is certainly more than one way to skin a cat but the ability of the better fuels to support much higher pressures inside the cylinders ( result of higher manifold pressures) meant that smaller engines could do the work of larger ones that used lower PN fuel.

at any given moment in time the fuel limited the internal cylinder pressure for one countries engines. Not all engines had the same exact limit (air cooled engines generally had lower limits) and engines with really small cylinders had a bit of an advantage.

 

[Schweik]

My point was that when it comes to engine power size isn't everything, smaller (and usually higher revving) engines could perform just as well.

In fact the fastest and longest ranged single-engine fighter in WW2 to see any kind of large scale combat was one of the smaller ones, the P-51B/C.

So bigger wasn't always better.

 

[Shortround6]

ah, you do realize that 100/130 fuel allows about 30% higher pressure in the cylinder acting on the pistons than 100/100 fuel and that 100/130 fuel allows about 90% higher pressure than 87 octane fuel?
the octane scale is not linear and the PN (Performance Number) is used for anything over 100 octane (100 octane is where the two scales crossover, 87 octane is actually 68.29 on the PN scale.

A Merlin using 18lbs of boost (32.7lb total) is flowing about 58% more air than a Merlin using 6lbs (20.7lb total) of boost. It might be somewhat less dense to the higher amount of heat. Not all the extra power makes it to the prop shaft but I hope you get the idea. The better fuel allowed the smaller engine (the Merlin) to make close to the same power as the bigger engines had been planned to make on the older fuel with little change in size and only a small change in weight. A smaller engine like the Peregrine could also expect (with development) to make the same sort of increase in power but it was never going to catch the Merlin since it started at 78.5% of the Merlin's displacement and used the same max RPM. even if you could boost the rpm by about 10% to get the pistons speeds roughly equal that doesn't make up for the total difference in displacement.

The Mustang could not do what it did using an engine running on 87 octane fuel, in fact it could not do what it did running on 100/100 fuel (British BoB fuel was 100/115-120)

The Sabre used lots of small cylinders and lots of RPM to make it's power but even with 100/130 fuel it didn't come close to what the Merlin and Griffon used for intake pressure.
This change in fuel took around 5-6 years, the fuel was available in 1942. It took a while to figure out which engines could use really high boost and which could not.

RR may have seen (my opinion here) the Griffon as a lower cost, lower risk engine engine to get them the same power as the Vulture once they had the better fuel and been willing to dump the Vulture.

 

[wuzak]

A smaller engine like the Peregrine could also expect (with development) to make the same sort of increase in power but it was never going to catch the Merlin since it started at 78.5% of the Merlin's displacement and used the same max RPM. even if you could boost the rpm by about 10% to get the pistons speeds roughly equal that doesn't make up for the total difference in displacement.

Interestingly, the Vulture was initially rated at 3,200rpm compared to the Peregrine's 3,000rpm. Even at 3,200rpm the Peregrine would not match the piston speed of the Merlin.

If the Peregrine had the same piston speed and same BMEP it would have 14.3% less power.

RR may have seen (my opinion here) the Griffon as a lower cost, lower risk engine engine to get them the same power as the Vulture once they had the better fuel and been willing to dump the Vulture.

The Griffon was a request from the FAA, and then some bright spark at the MAP figured it could be used for the Spitfire. It was, therefore, a much more useful engine than the Vulture or Peregrine, each of which was being used in limited types.

If the resources that was spent on the Griffon was instead used on the Vulture I'm sure that the Vulture would be the more powerful of the two. Indeed, the Vulture had been test at 2,500hp before cancellation.

But they could not have both, so the more useful was the one that continued. And it probably didn't hurt that it was less technically challenging.


Someone upthread mentioned the Crecy. Rolls-Royce wanted to cancel that too, but were not allowed to by the MAP.