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.

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.

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

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!

Well there you go...

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

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.

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.

Spit is only worse if you are one of the noobs flying around on the deck, turning circles kicking up dust.

My wingman and I confronted some Spitfires up high over England two nights ago and they were extremely formidable.

Can we please put this tired topic to rest?

Dear Crumpp,

I think this is incorrect about the Spitfire boost control cutout. It actually had quite different roles pre and post modification.

The original boost cutout was a true "cutout" in case of failure of the boost controller (which controls at +61/4psi). It gives full throttle valve control back to the pilot, enabling him to get +20psi boost (full unthrottled supercharger output) at ground level if he desired. Of course with either 87 or 100 octane this would not be a good idea.

There is no documented use of the original boost cutout as a combat boost system I am aware of, but it would be possible. The pilot would need to be very careful not to exceed a boost level that caused predetonation or engine damage, and the boost would continuously change with rpm, height and throttle position.

That document giving 10.55 psi boost is very interesting. As Banks suggested, it appears to be the boost attained with full throttle and (unmodified) boost cutout pulled at height. The height is about right. Interesting in that such a high boost was usable at all in a Merlin III on 87 octane.

However it is very unlikely that pilots were ever authorised to use the unmodified boost cutout as emergency power because the risk of instant degradation of engine performance was high (especially at low altitudes)

When the boost cutout was modified it was actually no longer a "cutout". It became a boost setpoint changer from +6 1/4 to +12 psi. It then became authorised as a practical combat boost (in conjunction with 100 octane fuel) that Dowding could fret over.

camber

Guidelines for use of boost control cut-out in unmodified condition, January 1939: http://forum.1cpublishing.eu/attachm...0&d=1334682385