Modelling engine wear and WEP limitations

[Seadog]

Originally Posted by Crumpp

What you don't seem to understand is that engine is overloaded just as FC says. That means it can fail.

If it does not fail the first time, it's life is dramatically shortened in comparison to just running the engine at its rated maximum continuous power of +7lbs.

That is why FC dictates the engine is dead-lined, the use of +12lbs entered into the maintenance logs, and the engine must be inspected by a mechanic before it can be returned to service.

If your engine fails in an airplane, their is no re-fly button. It is the pilot life on the line and he only has ONE.

In accidents resulting from engine failure in flight, if the pilot deviated from published operating standards for the engine, it is a factor in the engine failure in EIGHTY FIVE PERCENT of the engine failures recorded by the FAA.

Let that sink in for a moment.

http://www.wwiiaircraftperformance.o...bs-14nov39.jpg
The trials here:

state:

This test was terminated at 49.5 hours (8.5 hours at 12lb boost) by a cylinder head glycol leak in one cylinder, the joint being of an early unshrouded type which has given similar trouble under normal flying conditions.

So the failure was of a gasket which was known to be prone to failure for reasons unrelated to 12lb/3000rpm operation, but as is reported; "...the life of the Merlin engines under the emergency 12lbs boost conditions should be very little reduced from the normal..."

[B] Dowding states:

6. It is in the interests of pilots themselves, when operations with the enemy may have resulted in engine limitations being exceeded, 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 result.

so this is not anything like a requirement for an enforced engine check after using 12lb/3000rpm for more than 5 mins.

The Merlin in Perspective, p.39, states that, at 3000 rpm, a bearing could run with the oil cut off for 15 seconds before the temp started to rise. Bearing failures in the early Merlins (p.36)were most likely to be caused by excessive rpm (3600rpm+) during prolonged dives at reduced power leading to oil starvation and due to improper design features which were corrected in later versions. 12lb/3000rpm operation was not a factor.

Engine failures in flight are almost always due to fuel starvation due to improper engine management.

It would be nice if you could provide some sources.