merlin and wep

[john9001]

this is mostly about the merlin, the WEP thing has hashed enough on other posts and hitec has explained it's use in AH. Wile i would like to see a more realistic WEP what hitec has done is ok with me.

i found this web site on the merlin engine and thought some of you might find it interesting

http://www.unlimitedexcitement.com/Pride%20of%20Pay%20n%20Pak/Rolls-Royce%20Merlin%20V-1650%20Engine.htm


it covers it's use in A/C and also post war use in race boats.

of interest; the allision used turbo charging and the merlin used 2 stage super charging, the super charger had it's own cooling system completely separate from the eng cooling system.

the throttle on the merlin had a temp stop at mil power and to go to "WEP" all you did was break the seal and go to full throttle (max manifold press) , the seal was to let the crew chief know the eng had been overstressed so he could log it for maint reasons, ( it would shorten time to overhual)

there was no mention of overheating under wep, so did the eng have unlimited wep?

also , the merlin had water/menthol injection, now some people say the water/menthol injection adds a power boost, but according to Rolls Royce it is used to prevent detonation that can damage a eng.
running too high a manifold press and/or advanced timing could cause detonation.

44MAG

[Pei]

now some people say the water/menthol injection adds a power boost, but according to Rolls Royce it is used to prevent detonation that can damage a eng.

Too high manifold pressure can lead to premature detonation: the point of water/meths injection was to allow the manifold pressure to be raised to levels that would otherwise lead to premature detonation (and hence get more power out of the engine). IIRC the methanol was mainly in the mix to keep the water from freezing at altitude.

[Maverick]

Adding extra fuel to the mixture (over rich) would also help the engine stay cool and  prevent detonation.

[funkedup]

there was no mention of overheating under wep, so did the eng have unlimited wep?

Basically the answer is yes.  Overheating was only a problem at very low speeds, e.g. on the ground, or in very hot weather.  The real penalties for using too much WEP were increased fuel consumption and a shorter overhaul interval.

[Glasses]

Over rich wouldn't that foul up the spark plugs and not give any performance increase at all since the mixture would have been un even?

[senna]

>Adding extra fuel to the mixture (over rich) would also help the
>engine stay cool and prevent detonation.

True but most of the cooling is done during off throttle and to a much lesser extent during throttle open.

[senna]

>Over rich wouldn't that foul up the spark plugs and not give any
>performance increase at all since the mixture would have been
>un even?

You could use a different type or heat range spark plug to counter the fouling of plugs.

[Maverick]

You aren't going to foul the plugs to any extent using an amount of over rich mixture thast allows the engine to make power. Remember pilots have a mixture control and can tweak it to fit the altitude and power level. You can lean to max endurance, max power or richen for max cooling effect on the engine and still have power to use. If you do not fly it's a bit difficult to grasp. The mixture is not set to an absolute drowning the fire rich, just richer than max power to help cool the engine. WEP by itself also used the water to aid cooling when the engine was overboosted.

[Glasses]

I fly Maverick,that's why i brought it up because I was instructed that if the mixture is overly rich  the combustion would be uneven and would cause engine roughness,loss of power and even over consumption of fuel,that's why I brought it up and that's why I thought it was odd, that's why even if you have below the rated octane rate for the engine you have either 2 options step climb or to not utilize the full rated take off power of the engine when it was not used with the proper octane grade.

The way I understood it ,sorry I don't fly Supercharged planes yet!  is that with water added to the mix it lowered the air/fuel mixture temperature entering the combustion chamber thus lowering the  Cylinder head temperature and maintaining or slowing down the temperature increase that cause detonation and pre ignition.