Rolls Royce 'militarized R' engine - one engine to rule them all?

[ThomasP]

Hey guys,

A few years ago a local wargaming group (of which I am a member) ran an alternate reality WWII naval campaign where WWII did not happen (at least not when it did historically) and instead the situation evolved into a cold war. The combatants in this case were smaller countries being sponsored by the greater powers, in a similar manner to what happened in the historical Cold War period.

The rules of the campaign did not allow submarines or any kind of naval mine other than moored contact types.

The sponsored nations (combatants) had discovered unobtainium as a natural resource, hence money was no limit as such. The build-up to the conflict started in 1935, and any modifications that were practicable could be made (ie the technology exists and the modifications can be accomplished within the time constraints). We included ground forces and land based and naval aviation.

The hot war began on 31 December 1941, so the players had 6 years to implement their concepts.

Many strange and wonderful things occurred and much fun was had.

For my part, among other things, I modified 3 carrier aircraft:

SeaHurricane LF Mk IIIE with folding 'C' type wings/Spit VB armament, and a navalized Merlin 24M (9.75" diameter impeller)

Albacore TB Mk IIIE fitted with a BP Mk II 4-gun turret and the Merlin 24M with a 4-blade prop. (This is not as radical as it might sound, the Albacore specification originally called for accommodating either an air-cooled radial or a modified Kestrel water-cooled type. And a turret was considered but deemed not worth the weight trade-off. When I did the Loading & C.G. calculations, the BP turret balanced out the Merlin installation almost exactly.)

Fulmar FBR Mk IIIE with Spit Mk VB armament and a Developed 'R' engine with Rotol 6-blade contra-rotating prop. (The increased weight forward, based on the installation weights of the Spit Mk XIV, was balanced by the addition of armour plate behind the observer and a small rearrangement of equipment.) The maximum speed was the same as for the SeaHurricane Mk IIIE at about 330 mph, though at a lower altitude. Incidentally, the enlarged radiator required reduced the top speed by about 15 mph.

I figured that it should be practical to develop the 1931 'R' engine into a reliable performer over the 6 years of the pre-war build up. I used the final ratings that were achieved during the 1931 period as the basis. The Developed 'R' was capable of 2300 BHP for 60 minutes using the special fuel mix, with out exceeding charge, oil, or cylinder temperature limits. It could maintain 2500 BHP for 15 minutes. The trade-offs I had to make in order to be able to field the Developed 'R' were the special fuel needed, a relative short 80 hour TBO/replacement, and the space and weight on the carriers for stowage of the special fuel needed. I got around the short TBO by using a quick-change arrangement and a lot of extra engines stowed on the carrier. The special fuel needed (30,000 USgal for 100+ sorties) stowed per UK standards below the WL on the carrier (a modified Illustrious class), reduced the FO load by 350 tons, but was not really a problem in terms of operations.

 

[tomo pauk]

Instead of starting with the R, with its mammoth supercharger, why not improve the Buzzard?

The Buzzard had 800hp from 1,140lb dry weight. With improved technologies, such as the steel backed bearing, and improved fuels it is not inconceivable to see the Buzzard at 1,000lb for not much more weight.

And some strengthening and the power could go up to early Merlin levels, at about the same weight.

Developing the Buzzard would have side stepped the whole ramp head concept.

In my experience of re-purposing race engines for more endurance applications (which I have done on 2 occasions professionally), by the time you add mass to make the bits last long enough, remove half the tiny little tweaks in materials and hand-fettling which are too expensive for mass production, remove the ultra-special fuels and re-tool it to be suitible for making in the dozens or hundreds, you end up with something not much better than you would have done if you just designed from scratch something to do the job properly from square 1.

All sorts of "tiny" issues which didnt matter on the race engine suddenly become show stoppers (eg. torsionals which didnt matter in the race engine at high crank speeds, suddenly ruin engines which are running at slightly lower revs, etc etc).

The reasons why I've suggested that the 'R' is a starting point is that it is/was a known quantity - engine can withstand far greater power levels than the in-service engines. Granted, RR could design an all-new big V12, or start bulking-out the Buzzard.

I think the Merlin was about the ideal balance of size, strength and weight for use in small single-seaters which we had in the 30s, and the Mustang proved that this had in fact not changed a great deal by 1944. This of course ONLY holds true if you have access to the very best fuels, oils and materials. If we had needed to fight the war on 87 octane, we would have been in a really bad place with the Merlin, so there are I think a lot of cavets to either option.

Spitfire was not a small fighter when designed, Hurricane was huge when compared with Bf 109, I-16, D.500 or MS.460.

I think with the Griffon you`re right at the limit of sensible bore size for combustion, and that probably - it will always be possible to "push" a smaller Merlin a bit harder with boost before det sets in, this I think (partially) nullifies the advantage in swept volume the Griffon has over the Merlin providing that 100/130/150 is available as fuel. Later developments with the Jumo213 and of course Sabre showing that ultimately crank speeds needed to go up too. Eventually a bigger Griffon engine would be less amenable to this line of development due to the inevitably larger mass of the pistons etc. So I think overall, what happened probably shows us what the best option was, because the Griffon never became militarily significant, because it simply wasn`t the best overall option.

Griffon was never made in big quantities, and, from British point of view, it came a bit too late, even later than Sabre. So it will indeed never be military significant, even less than the Sabre.

If the war had gone on further we all know that Griffon Mustangs and Mosquitos were planned, but with the jet coming in, I`m not sure we would have bothered with them for the sake of an 18month overlap with the early jets until they took over. I think the Spitfire XIV was a brutal fighter, but the tiny numbers produced tend to suggest it was also not really a necessity and if we HADNT had both engines, I`m unconvinced a Griffon Mustang would have been the escort fighter we needed, which was a war-winner, so I think what actually happened was pretty much what I`d do if I had a time machine and did it again.

You can note that I'm focusing thus far mostly to the late 1930s application, and 1st two-3 years of the war.
The historicall 1-stage supercharged Griffon was not much of hi-alt engine, mostly due to having a small impeller (10.1 in - less than what 1-stage S/Ced Merlins had). With a development of a big V12 from early 1930s and with a bigger impeller, talk 10.5 to 11 in, plus 100 oct fuel, we'd be looking at power figures in ballpark with DB 603A or Jumo 213A, but in 1940/41 - very useful for Mustang, while making Hurricane still competitive, and Spitfire having either parity or superiority vs. anything Germans introduce, including the Fw 190A in 1941 and on.
All of this before the 2-stage S/Ced big V12 is introduced some time of 1942.

 

[jetcal1]

The Boeing P-26 fighter landed at about 80mph in the early version but they were refitted with flaps to get the landing speed into the low 70mph range.
the 149.5 sq ft wing may have helped top speed but take-off and landing on short fields may have been exciting.

landing speeds and take-off/landing distances are one of those pesky details than often don't make it into discussion on why certain countries did certain things or adopted certain airplanes.

My first takeoff in a more conventional 1930's design was in a Fairchild 24 and I was amazed by the short take-off. subsequent flights in a some other vintage aircraft were eye openers as the concept of a airport was vastly different in 1938 than it was in 1946. (The Luscombe was a relative rocket ship in 1938 on 65 HP. But, you weren't going to fly it off a short field as comfortably as the 145 HP Fairchild. And my belief is the wing had more to do with it than HP. Acceleration in the Fairchild was quite leisurely. And, yes I know the Luscombe stalled slower.)