Friday Update, February 10, 2012

[Robo.]

Originally Posted by Kwiatek

Well nothing is such simple like you think.

Generally rising fuel octan casue higher engine ratings - it is clearly show in many different manuals for different planes ( Spitfire MKII, Tempest etc).

Brackets - 87 octan fuel, no brackets - 100 octan fuel engine ratings.

It was possible (but not common) to fill Spitfire Mk.II's Merlin XII with 87 octane fuel, hence the brackets.

Originally Posted by Kwiatek

I dont want to lead academic debate but there is any info that document about Merlin III new engine ratings is taken from XII development (eg Merlin III that became XII after various modifications) - it is only someone speculation.

That is not a speculation but a known and well documented fact. I suggest you get more information (other that those available to anyone online) before you offer your services to 1c. No offence ment, just a frank observation. You are, of course, totally right about assuming that higher octanes allowed higher boosts, but you happen to be wrong here as for Merlin development history and few important details that give a bigger picture. I found it quite amusing as you, an expert in BoB fighter performance, came over to a2a with that post. You surely don't lack confidence.

Originally Posted by Kwiatek

Some short uptades in Spitfire MK1 Merlin III manuals said only that with 100 Octan fuel +12 lbs boost was allowed for emergency power - there is no mention about full engine ratings with 100 Octan.

Of course, 100 octane fuel was necessary to achieve the +12lbs. boost in BCC-O setting on both Merlin III and Merlin XII, but the actual nominal rating has not changed to +9lbs on Merlin III. That was purely later mark Merlin (XII) with different coolant and various modifications (or improvements over Merlin III) that allowed higher boost, not the higher octane fuel itself.

Early Merlins as such were able producing much higher MFPs, but the nominal ratings were considered safe by the manufacturer and MoD and they were certainly +6.25lbs for Merlin III no matter what fuel you poured in it. The document you present confused you because there was certain time when the Merlin III has been further developed (as it was always the case with RR) and only later became Merlin XII.