Spit IIa is now so much more inferior to the 109

[lane]

Originally Posted by Crumpp

Obviously the RAF was comfortable enough to test it at 12,500 feet on 9-6-39 Merlin III serial number 7491 mounted on Spitfire N3171 up +10.55lbs using 87 Octane fuel.

You've got that all scrambled. N3171 hadn't even flown yet on 9-6-39. The power figures on the engine Inspection and Test Certificate come from "test bed conditions", either at RR, RAE or the dynamometer at AAEE, i.e. the engine wasn't even mounted in an airframe and the engine surely wasn't running at 12,500 feet without an airframe.

[Al Schlageter]

N3171 Ia 413 EA MIII

FF 10-11-39
27MU 13-11-39
AMDP 16-11-39
AAEE 19-3-40 comparison perf trials (Rotol constant-speed prop) with K9793 (2-blade fixed pitch)
CFS 24-2-40 ? for compilation of pilot's notes
ECFS Hullavington 13-6-42
SOC 18-8-45

[41Sqn_Banks]

By the way. The altitude of 12,250 feet that was chosen for the power curve is the altitude used for rated/international rating. This is probably the FTH for climb rating, the RPM is lower than on "All out", thus the FTH is lower under this condition.

Here are some examples for Merlin II/III:
http://www.spitfireperformance.com/L...ertificate.jpg
http://www.spitfireperformance.com/k...ertificate.jpg
http://www.spitfireperformance.com/n...ertificate.jpg
http://www.spitfireperformance.com/k...ertificate.jpg

There is another for Merlin III, but this is probably a prototype or conversion for Merlin XII.


Despite the use of 100 octane fuel the power curve is only done up to +10.6. However +12 or even more boost is possible without detonation. This pretty much spoils the idea that the values from the power curve have anything to do with the physically possible maximum.

How would they measure the engine power during flying anyway? It's likely that these were either calculated values from bench tests at sea level and even if boost above the regular engine limits were used it was under a controlled condition and certainly for very short periods.

[camber]

Originally Posted by lane

You've got that all scrambled. N3171 hadn't even flown yet on 9-6-39. The power figures on the engine Inspection and Test Certificate come from "test bed conditions", either at RR, RAE or the dynamometer at AAEE, i.e. the engine wasn't even mounted in an airframe and the engine surely wasn't running at 12,500 feet without an airframe.

Didn't you see the pic of the RAE Anson with the Merlin mounting on the top

I got a bit confused by the height reference...but of course these are test bed figures.

I would be interested in the test bed setup. For the Merlin hooked to a dynamometer setup, there would be a variable load (allowing rpm setting for any throttle etc. setting) with bhp measurement. To simulate altitude, the supercharger intake could be connected to a chamber of correct maintained underpressure. Then height and rpm could be set and boost/bhp measured.

But to know the real setup would require the actual protocol and equipment used here, which is not in these reports. I would be interested in whether a test run Merlin III could handle +10.5psi boost on the bench (even briefly)with 87 octane without predetonation reducing power, but couldn't these be calculated values in the reports anyway? (actual tests at SL, but corrected for particular FTH etc)