Oil temperature and other things that might kill your engine.

[reflected]

Originally Posted by Viper2000

120ºC coolant temperature = engine failure.

The cruising temperature should be 95ºC.

3000 rpm is fine for combat.

At +6¼ psi boost you need at least 2080 rpm to avoid detonation. This is important with 2 position props. You can't just change to coarse pitch at full throttle, because you're likely to go below the minimum rpm for your boost and break something. Therefore with a 2 position prop I throttle back to 0 boost before switching to coarse pitch.

Oil temperature should be 90ºC for cruising and 95ºC max.

weird..I have the pilots notes, and it says 120C for 30 min, and even 135 C for 5 minutes. Good to know about the minimum rpm though, thanks! Oil temperatures are always around 95, nothing I can do...can you achieve combat performanced with these limitations? or do you just cruise and do some sightseeing?

[Viper2000]

Originally Posted by reflected

weird..I have the pilots notes, and it says 120C for 30 min, and even 135 C for 5 minutes. Good to know about the minimum rpm though, thanks! Oil temperatures are always around 95, nothing I can do...can you achieve combat performanced with these limitations? or do you just cruise and do some sightseeing?

The figure of 135ºC for 5 minutes would apply for pure glycol cooling.

The 120ºC max is for 70% water, 30% glycol at 15 psi.

The Merlin III should be pure glycol. However, the pilot's notes which ship with the CE have limits appropriate to pressurised water/glyclol; since the page with the engine limits on it is dated January 1942, I suspect that what probably happened was that by then the engines had been modified to pressurised water/glycol cooling.

A complicating factor is that the Merlin III was the last Merlin to use pure glycol cooling; from the Merlin IV onwards all subsequent marks used pressurised water/glycol.

This means that the 120ºC limit is correct for the Spitfire II with Merlin XII, and would also be correct for the Hurricane II with Merlin XX. But AFAIK the Spitfire I and Hurricane I were both still using pure glycol cooling during the battle and should be subject to the limits you have posted.

NB - I am assuming that the 120ºC limit in the Pilot's Notes that ship with the CE is correct for 1942 and that the various mods for water cooling had been embodied by that time (the other option might be that it's a typographical error). I don't have documentary evidence as to when/if the Merlin III was converted to water cooling.

However, as far as the sim is concerned, the engine will break if you exceed 120ºC coolant temperature.

[reflected]

Viper: OK, thanks, I'll give it a try. Also, would using too much boost kill the engine on its own? Without exceeding the temperatures?

[Viper2000]

Originally Posted by reflected

Viper: OK, thanks, I'll give it a try. Also, would using too much boost kill the engine on its own? Without exceeding the temperatures?

IRL yes, but not very quickly unless you really cane the poor thing.

Even using combat boost for too long could cause failure, but it's not really deterministic; working the engine harder increases the probability that something will break.

If you had access to 150 grade fuel in 1940 then a new Merlin III would be capable of +25 psi at sea level for a safe life of about 15 minutes; this was used with the Speed Spitfire, N17. The 150 grade fuel in question was very different from the late war production stuff; it was one of Rod Banks' special concoctions of alcohol and benzol etc. with vast quantities of TEL. Totally uneconomic, and suitable only for breaking records. But probably quite influential in the Merlin's development programme because it showed what the engine was capable of given sufficient supercharge; the development programme therefore basically consisted of improving the supercharger and strengthening the engine to survive high power running for an economically viable useful life.

In the sim you can't really use too much boost because Spitfire I seems to only give +6¼ psi with the cutout activated.

Spitfire II gives +8ish; some say that this is just because full scale deflection of the cockpit instrument is +8, but I don't think so because the no-cockpit view instruments go up to +12 but still show +8ish with the cutout activated.

You can break the engine with too much boost at low rpm, which is why it's important to throttle back before changing to coarse pitch.

You can also get "exhaust header" failures if you run at high boost & high rpm for very extended periods, which is fair enough, albeit perhaps somewhat over-done for a new engine, as failure usually took a few hours of abuse unless there was a bad weld or something.

[Plt Off JRB Meaker]

The British fighter engines are really fickle,it has taken me ages to get to grips with them.

I appreciate your plight,from all accounts after flying Spits and Hurricanes the Bf110 and Bf109 sound much more easier to get to grips with.