Modelling engine wear and WEP limitations

[Seadog]

Originally Posted by Blackdog_kt

The mustang's 67" of MP is equivalent to the Spits +12lbs, the 109's 1.45 Ata and so on and so forth, take your pick, in the sense that they are not meant to be ran for eternity because things will start to break. Maybe not on this sortie or the next, but definitely something will give after a few missions, especially if i push it that way on every single sortie and the mechanics follow your reasoning of not inspecting it afterwords


As another example, for later mark Spitifires like the Mk.IX it was advised to take off with a mere +9lbs no matter if it could do +12, +16 or +25 and that's a pretty critical phase of flight in terms of power reserves in case something goes wrong.



[/b]

The Spit 9 was approved for 12, or 18lb boost, on TO depending on the variant:
https://lh6.googleusercontent.com/-U...ngine_data.jpg
The Merlin 61 and 63 were approved for 12lb on T0 and 5MIN at 15.25lb for Combat.

The Merlin 66 was approved for 18lb for TO and 5min at 18lb for combat.

The V-1650-3 and -7 used on the P51-B, C and D was approved for 15.25lb (61") on TO and was basically equivalent to the Merlin 63 but had a special WEP rating of 18lb for 5min, not present on the Merlin 63, so the V-1650 -3,-7 were running beyond the equivalent of 12lb on a Merlin III.

If you try and use 18lb boost on TO, for example, you will end up with major engine torque issues that will make the whole process extremely dangerous, while 9lb will get the Spit off the ground in a very short space and was a lot safer.

Regarding 12lb/3000rpm, I made a solid proposal which is based upon operational data:

I have read through every source on the Merlin engine that I have, and all the combat reports at:
http://www.wwiiaircraftperformance.org/
From what I can gather, Merlin engine failures, were primarily random events and the main culprit was manufacturing defects/design faults that eventually break the engine. The 50 hour 12lb/3000rpm test is an example of this, where the engine was cycled 100 times at 5min/20min at 12/4.5lb boost and eventually developed a coolant leak from a defect that plagued service engines that were not being run past 6.25lb.

The Merlin in Perspective states that fighters had a higher propensity for coolant leaks than bombers because fighters were cycling engine power from very low to very high much more frequently, but this was still not a common occurrence.

The next greatest problem was bearing failure from oil starvation, and again 12lb boost had little to do with this except for prolonged steep climbs, as per Dowding's memo, but probably the greatest cause was inverted flying and prolonged dives that caused excessive (~3600) RPM.

1939 Merlin TBO:
Fighters: 240 hrs
Bombers: 300 hrs

repair depots:
1942 onward: 35% of engines were there due to time expiry.

1942 onward: average engine under repair had 60% of nominal life, or 144 hrs for a fighter engine and 180 hrs for a bomber engine.

I would propose the following:

Any engine has a 65% probability of random major engine failure, during 240 hrs of operation, or about 160 sorties. Another way to express that would be a 6.5% probability of one aircraft out of 16 having major engine failure on a typical mission. I don't know how to model the use of 12lb/3000 rpm for more than 5mins, but a simple way would be be multiply the failure probability by, say 1.15, to simulate the increased RPM and stress on the engine.

[TomcatViP]

One thing that I wld like to see is a parameter including the way player move the throttle fwd and back to simulate the damaging effect of walling the throttle (just like it was on initial release ?)

[Crumpp]

One thing that I wld like to see is a parameter including the way player move the throttle fwd and back to simulate the damaging effect of walling the throttle (just like it was on initial release ?)

That is good idea to reward game players who operate their virtual machine correctly.

Real pilots follow published procedures because they understand the engineering margins are narrow and the procedure is in place to get the best performance from your engine. The procedures are there for a reason, to keep your engine developing the maximum power it can deliver.

In the real world, the penalty for abusing your engine is reduced power and an increased risk of catastrophic failure. It should be the same in your game.

You start out with a given potential for maximum power and as you abuse the engine, that power potential is reduced. By the time you finish slamming the throttle, improper propeller use, mixture control use, supercharging gearing misuse, not adhering to temperature rates, and running the motor over-boosted, you could end up with a 900 hp engine at the end of the sortie. No funny noises, just a gradual loss of power. That means your performance will noticeably degrade as you abuse the engine. That loss would effect the airplanes combat performance.

It is not realistic to consider hours flown or previous abuse. It is a game and cannot simulate such things. You get one airplane and at the beginning of the sortie it is new. Depending on how you treat the engine you could land with the same power potential or you could land a worn out aircraft that is no longer combat effective.

This would have to be clearly published in the game manual along with "proper operating procedures" or the whining would be legendary.

Such a system would reward the players who understand their aircraft and can integrate proper operations with proper tactics. You would have a much better simulation of WWII air combat.

[TomcatViP]

+1

Great! Now who wld make a FM model resulting from a kick in the a$$ from an angry Chief mechanics ?!