Spit IIa is now so much more inferior to the 109

[NZtyphoon]

Originally Posted by 41Sqn_Banks

It's interesting to note that publications from 1938 and 1939 give maximum take-off engine speed of 2850 rpm for both Merlin II and III. Publications from 1940 give 2850 for Merlin II and 3000 rpm for Merlin III. The increase is not associated with the use of 100 octane fuel.

This most likely has a great deal more to do with the adoption of two speed and CS propellers; in 1938 the majority of the Hurricanes and Spitfires were still using the fixed (coarse) pitch two bladed wooden props, so the maximum allowable rpm was fixed at 2,850.

The Merlin III had the universal prop shaft allowing de Havilland or Rotol propellers to be fitted, and the availability of two-pitch and especially CS props would have allowed for higher rev limits with less strain on the engine than a fixed-pitch unit. It also makes sense that in wartime some restrictions are lifted to allow for maximum power. One of the reasons 100 Octane fuel was originally adopted was to allow greater take-off power.

[41Sqn_Banks]

The Hurricane I Pilot's Notes mention that during take-off 2850 RPM will not be achieved with fixed-pitch propeller.
IIRC the Merlin II was only able to take the DH propeller (2-pitch and later converted to CSP) and the Merlin III could take both. Some early Merlin II were not able to take a CSP at all as they didn't have a connection to drive the CSP unit. I can't remember where I've read this ...

[Crumpp]

CS props would have allowed for higher rev limits with less strain on the engine than a fixed-pitch unit.

No they won't allow for higher rpm. It is also not less strain on the engine. CSP's are much harder to aerodynamically balance while a fixed pitch is very easy and will run with less vibration. RPM is a function of the engine speed and reduction gearing. You can change those items to increase rpm to adjust for different propellers. If you mount a fixed pitch propeller that is grossly underpitched for the application, you will also see an rpm increase and very soon have a big bill to pay.

You control the manifold pressure and rpm in a CSP unit. Fixed pitch, you can only control the rpm and manifold pressure is irrelevant.

That is why the RAF amended their definitions in 1937!

With a two position fixed pitch, the Spitfire pilot is controlling rpm and not manifold pressure. The airplane is equipped with a manifold pressure gauge but it serves as a diagonistic tool only. He flys the airplane by rpm setting.

If you read the Spitfire Mk I Operating Notes, the maximum rpm is the same for all propellers.

It seems very likely that RAF pilots were authorized to "pull the tit" on their aircraft using 87 Octane fuel with a lower manifold pressure boost gain. It appears to be independant of 100 Octane fuel use.

[Crumpp]

The Hurricane I Pilot's Notes mention that during take-off 2850 RPM will not be achieved with fixed-pitch propeller.

Exactly why you cannot draw blanket conclusions from engine instructions! All installations are different, even with the exact same engine/propeller combination.

The Spitfire Operating Notes distinguish between the Merlin II and Merlin III by rpm. The Merlin II is restricted to 2850 rpm and the Merlin III to 3000rpm. In a dive, both engines can momentarily achieve 3600 rpm. The run up can be deciving too as the engine is not under an airload.

[Crumpp]

I just reread the Spitfire and it does make a distinction between the Rotol and DeHavilland propellers on run up. The Operating Notes on a Merlin engine make no such distinction.

The difference in rpm is probably due to lack of airload on run up unless Rotols were not mounted to Merlin III's.

[Crumpp]

Anybody notice you do the run up on a Spitfire at full throttle!!!

Wow, that must have been beast and no wonder the Operating Notes require TWO men holding down the tail!

[Crumpp]

The following publications give 2850 RPM for Merlin II and 3000 RPM for Merlin III:
Notes for Pilot's on Merlin II, III and IV - 1940
Merlin II and III & V Aero Engine, 2nd Edition A.L. 4 - 1940
Spitfire Pilot's Notes - 1940

Well there you go...

In 1940 the Merlin III was given an rpm increase to 3000 rpm.

[41Sqn_Banks]

Originally Posted by Crumpp

Exactly why you cannot draw blanket conclusions from engine instructions! All installations are different, even with the exact same engine/propeller combination.

Sorry forgot to mention that the Hurricane I Pilot's Notes are from 1939. I think it also give only limits for Merlin II an not III.

The following publications give 2850 RPM for Merlin II and III:
Notes for Pilot's on Merlin II and III - 1939
Merlin II and III Aero Engine, 2nd Edition - 1939

The following publications give 2850 RPM for Merlin II and 3000 RPM for Merlin III:
Notes for Pilot's on Merlin II, III and IV - 1940
Merlin II and III & V Aero Engine, 2nd Edition A.L. 4 - 1940
Spitfire Pilot's Notes - 1940

[TomcatViP]

it has more to do with the airstream ard the prop, hence the aircraft speed in that case (fixed pitch).

Max rpm is more a function of admissible eng wear. It always a trick for eng manufacturer to increase rpm to raise the number of HP available.

I think tht latter in the war, the Merlin's limits were raised to 3k rpm [confirmed - see above].

There is nothing hidden here: just like you ride your bicycle, you can't reach your max rpm at high gear starting from rest.

The Hurri had a thicker wing, so it didn't need so much speed at T.O as the Spit. Hence the T.O pitch setting wldn't need to be as lean as tht one for the spit. If the Merlin was tuned for both aircraft, it wld seems normal tht the max admissible rpm for the Merlin wld hve been fixed as a ref for the Spit and then wld hve differed slightly with the Hurri.

This are only supposition. Take it only as it shld be.

[gimpy117]

I don't agree when we say the Spit is worse. It sure as heck isn't. I caught a Spit down low and toyed with an ME-109 for a good while untill he yo-yo'ed me. I decided to loop around and to to find where he was. unfortunately he got off a very small burst that seemed to get my roll controls somewhere. I just broke off, let a buddy deal with him as he was pretty shot up and I was guns dry...and used my rudder to induce roll to get home.

So really, He who has E wins. And if you catch an ME-109 Down low (which happens often) it's his funeral. The only huge advantage I can tell the ME-109 has is those 20mm cannon that can shred you pretty fast.

The Spit if anything still retains energy really, really well in turns and such. The only reason it's not cleaning house is because ME-109 pilots aren't playing their game (or at least the patient ones) and son't get into a turn fight where the spit will just about enter at the same speed it came out of the turn.