Quote:
Originally Posted by Skoshi Tiger
I doubt it would be just as likely. If you read the memorandum point one and two,
"A recent increase in the number of engine failures, due to the failure of bearings, is an inication that some pilots are over-stepping the engine limitations laid down in the Pilot's handbook.
2. The use of the automatic boot cut out control enables the pilot to get an emergency boost of +12lbs per sq in. from the engine for 5 minutes when circumstances demand it. Some Pilots "pull the plug" with little excuse on every occasion."
The wording of this memo suggest that the practice of exceeding the limits was quite widespread. Now if it was as you suggest a 50-50 chance of engine failure when the limits were exceeded then the culprits responsible for abusing their engines would be quickly identified and I expect grounded. The practice of exceeding the limits would only become common place if the pilots thought they could get away with it. Maybe thats why they put the wire seal on the boost control to make it obvious to the maintenance staff that it had been used. Then the pilot would have had to justify their use of boost after the mission.
As long as they didn't overheat their engines and the correct fuel was used the boost control still limits the boost available to stop destructive pre-ignition and detonation as a cause of engine damage. (ie if you run the 12lb boost on 87 octane fuel you could get servere and possibly imediate damage from detonation, but not with 100 octane fuel.) So what was left was damage caused by accellerated wear on the engine that was "liable to manifest themselves on some subsequent occasion"
http://www.spitfireperformance.com/dowding.pdf |
Also note section 6
Quote:
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It is in the best interest of pilots...to acquaint the maintenance personnel with the facts so that oil filters may be inspected at the first convenient opportunity to investigate whether damage to the bearings has resulted.
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So using +12 lbs boost did not inevitably damage the engine, but it was better for all concerned that the pilot let the ground crew know that he had gone through the gate - should the pilot neglect to mention that +12 lbs boost was used as Skoshi has mentioned, they could check to see if the throttle wire had been broken.
All frontline RAF aircraft were given a daily inspection whenever possible and this would be when any such issues were found and, if need be, notified in the aircraft's engine log.
BTW Some might remember this thread?
http://forum.1cpublishing.eu/showthread.php?t=20117 £74.50 for a copy of the Mk I Pilot's Notes from Kew? v $15.9 from
http://www.flight-manuals.com/ap1565a-vol1.html Apart from these there don't seem to be many original Spitfire I Pilot's Notes available.
Also note the Defiant used 100 octane and +12 lbs boost - the attachment is dated 24 5 (or 6?) 40 lower LH side