Effect of boost control cutout prior to +12 psi boost modifications

[Seadog]

Originally Posted by Crumpp

Well there you go.

I am sure that did not magically happen either. I believe one of the other snippets talks about measures to prevent the cylinder head cracks that appeared during the test in the form of replacing existing parts with new ones that were not prone to cracking.

That probably paved the way for an increase to 5 minutes.

Either way, the notion of +12lbs being using continuously is pure fantasy.

Believing that pilots routinely violate published limits is gamer thinking and not grounded in reality.

Ahh, no the trials were not successful. They pointed the way to modifications which allowed +12 to be used for 5 minutes just like the previous Emergency rating of +9lbs. In comparison most endurance trial engines have tolerance issues or things like worn supercharger blades. They don't have cracked cylinder heads like in the case of the Merlin trials.



Yes...Normal being the life of the engine in comparison to using +9lbs of boost for 5 minutes. It is not the gamer notion that 12lbs could be used continuously. It is just as the FC directs, when used, it must be dead-lined and cleared by a mechanic for return to service.

First off, I don't think it necessary to have the same discussion on two threads.

I pointed out to you that the gycol gasket leak reported at 49.5 hours of the 50 hr test was unrelated to 12lb/3000rpm operation as the memo states.

11. The use, in an emergency, of this high boost pressure is a definite overload condition on Merlin engine and therefore all occasions on which it is essential to make use of the + 12 lb must be reported by the pilot and recorded in the engine log book so that the engineer officer may be able to assess the reduction in life between overhauls and the need for special inspections.
http://www.wwiiaircraftperformance.org/ap1590b.jpg

Again this does not state a requirement for automatic inspection or grounding of aircraft until the engine is inspected.

Dowding's memo states otherwise, and he states "...that some pilots were pulling the plug with little excuse on every occasion..."
http://www.spitfireperformance.com/dowding.pdf

An engine was flight tested for 49.5 hours of which 8.5 hours were at 12lb boost/3000rpm and the engine life was found to be little effected. I think that you might be having trouble translating some of the documents,
http://www.wwiiaircraftperformance.o...bs-14nov39.jpg
as there is nothing in the above to indicate excessive wear resulting from 12lb/3000rpm operation. The mods required for 12lb operation:
http://www.wwiiaircraftperformance.org/ap1590b.jpg
does mention the need for modified cylinder top joints, but then by definition these changes were all made prior to having the boost cutout modded for 12lb operation and the 14 nov 39 memo states that cylinder head problems were unrelated to 12lb operation, but I guess it was felt that more reliable cylinder head gaskets were a desirable feature in combat aircraft and the Merlin in Perspective discusses the problem with coolant leakage in early Merlins and the design changes implemented to correct it. Rapidly changing cylinder head temps were likely to cause leakage problems but by definition prolonged running at 12lb will result in a stable cylinder head temp.