Modelling engine wear and WEP limitations

[ICDP]

Originally Posted by Seadog

In Nov 1940, the Merlin XX was given "official" approval to use 12lb/3000rpm but strip inspections were not required after its use:

The Merlin 60 series engines were cleared for 15 and 18lb boost for combat and again strip inspections were not required after use:

An oil filter check was recommended, which probably took about 10mins.

The above data is from the Spit 9 Pilot's notes and from a Merlin 60 series maintenance manual.

Meaning that at some stage prior to the Merlin XX was introduced strip inspections were required after overboost was used. Good info, it seems +12lbs boost on the Merlin II, III and XII was limited to a short amount of time... oh I don't know, 5 minutes maybe

[Seadog]

Originally Posted by ICDP

Meaning that at some stage prior to the Merlin XX was introduced strip inspections were required after overboost was used. Good info, it seems +12lbs boost on the Merlin II, III and XII was limited to a short amount of time... oh I don't know, 5 minutes maybe

No strip inspections were not required on the Merlin III when using 12lb boost for less than 5min and probably not when used for more, depending on the state of the oil filter upon inspection. Dowding's memo is clear on this.

[Crumpp]

strip inspections were not required after its use:

It means the engine was not required to be stripped apart and internal tolerances checked. That is done at overhaul.

The engine must be inspected according the document you just posted.

It clearly states the engineer must asses the reduction in life of the motor from using emergency boost.

That means done by performing an oil analysis, oil change, compression check, and overall inspection of the condition of the motor.

They might check the crank play as well. All of that only takes a few hours to perform and will tell a mechanic the health of the engine and it requires a reduction in life.

For example, if the compression check ends up with a cylinder not making the correct compression values or the composition/type of the metal in the oil will tell a mechanic if the engine life is nearing its end.

[Seadog]

Originally Posted by Crumpp

It means the engine was not required to be stripped apart and internal tolerances checked. That is done at overhaul.

The engine must be inspected according the document you just posted.

It clearly states the engineer must asses the reduction in life of the motor from using emergency boost.

That means done by performing an oil analysis, oil change, compression check, and overall inspection of the condition of the motor.

No, the Merlin engine service manual is pretty clear, that a simple oil filter check was all that was required. Dowding's memo states the same. The engineer officer is always assessing the life of a engine and the regular engine checks are quite sufficient for that.

[TomcatViP]

Well if my car manufacturer would hve include in normal servicing the check of my "Oil filter" as soon as I passed 4000 rpm well... I wld hve run directly to buy a full set of spare engines
What do you think they were looking for ?

[Crumpp]

oil filter check

Seadog,

You have many misguided conceptions about airplanes. Have you ever owned an airplane?

Of course not. You would know this is standard when changing the oil. Every time you change the oil, you cut the filter apart, examine the filter element inside and analyze the oil.

A new engine makes metal and once broken in, an engine makes metal when something is wrong. This metal comes from many different sources in the engine and a mechanic can tell what is going on with your engine from it.

Steel shavings for example generally represents cam wear, valve issues, or ring wear. Aluminum is generally bearing wear. Small flakes of aluminum, depending on the amount is normal or can be excessive. It all depends on the engine type being analyzed.

Chunks of metal are of course very bad.

A sample of the oil is then taken and sent to a lab for microscopic analysis.

Yes, It was a requirement to inspect the engine after each use of emergency power. It was an overload condition for the motor and the reduction in service life had to be assessed by a mechanic and the use of it logged before the aircraft was returned to service.

Combine that with compression checks and an overall inspection will tell a mechanic much about the health of an engine. That is pretty much what is done every year during annual or every 100 hours for commercial/military aircraft to gauge the airworthiness of the aircraft.

Those are the facts based on the documents you posted. Nowhere does the fantasy notion that the Merlin could run in an overloaded condition for as long as necessary exist. It was limited and it was tough on the engine when it was used. The use of Emergency Power had to be logged, the engine inspected, and upon passing that inspection returned to service.

It is that simple, bud.

[Seadog]

Originally Posted by Crumpp

Those are the facts based on the documents you posted. Nowhere does the fantasy notion that the Merlin could run in an overloaded condition for as long as necessary exist. It was limited and it was tough on the engine when it was used. The use of Emergency Power had to be logged, the engine inspected, and upon passing that inspection returned to service.

At least you've given up on this fantasy notion of a strip inspection after every use.

In the BofB the average fighter never survived past 100 hours. This is not civil aviation and trying to look at the battle, where the average pilot had a high certainty of death (probably 25 - 40% in RAFFC) as the same as a flying a light aircraft under VFR conditions is ludicrous. No pilot gave a damn about the engine on an aircraft - that aircraft existed solely to destroy the enemy and bring the pilot back safely. RAFFC had lots of spare aircraft and spare engines and pilots had no qualms about expending them at a furious pace: RAFFC lost about 2.5 SE aircraft per pilot fatality.

Pilots could and did run engines at 12lb/3000rpm for a long as they needed to, and in the final analysis, no one really cared, as long as it gave them the edge in combat, which was why the RAF changed over to 100 octane fuel.

A Merlin III will run at 12lb/3000rpm until the fuel runs out. Given a sufficiently large sample size, this will result in a modest increase in in-flight engine failures, but fuel consumption considerations will always be uppermost in the pilot's mind given the low endurance of these aircraft, and this will be the primary limiting factor.