Inaccurate performance data for BOB fighters in COD comparing to RL data

[Crumpp]

So even with 100 octane fuel being the common fuel in January 1942, the "All out" limit remained +6 1/4. So obviously there is no relation between introduction of 100 octane fuel and the fact that the "All out" limit remained +6 1/4.

Yes!!

Read the instructions for using +12lbs boost. First you have to override the normal controls and it emphasized that it is a very overloaded condition.

+12lbs is almost 3 times more pressure than the engine was designed to handle.

The modifications to the cylinder heads changes the frequency harmonics in order to reduce the incidence of cylinder head cracking. It does not increase the design strength of the engine.

BMW did the same thing when attempting to raise the motor to 1.8ata in the BMW801D2. The service trials resulted in a high incidence of cylinder cracks so they changed the cylinder barrel liners to ones that conformed harmonically under the new load.

Think of a tuning fork, if you want to change the frequency you adjust the length of the tines. To change the frequency in the merlin III, they added .020 inches to the spigot.

[Robo.]

Originally Posted by Crumpp

Yes!!

Read the instructions for using +12lbs boost. First you have to override the normal controls and it emphasized that it is a very overloaded condition.

Yes of course, but it was possible therefore it should be possible in the sim, too. No matter how you look at it, I really try hard to see your point, but you're wrong on so many levels I am afraid. Why are you doing this anyway?

Originally Posted by Crumpp

+12lbs is almost 3 times more pressure than the engine was designed to handle.

It is approximately 2 times more than original nominal rating. And the RR engineers have had slightly different approach to getting more power from their designs - testing, breaking and consequently reinforcing what breaks first, hence so many mods and pilot notes amendmets that seem to confuse you.

+16lbs was 3 times more pressure and it was still used on Sea Hurricanes on the very same engine for obvious reason - no problem except drastically limited lifespan of the engine.

Honestly, Crumpp

[41Sqn_Banks]

Crumpp is right that +12 boost is about 3 times higher than the maximum continuous rating (+ 4 1/2), which is the highest rating that is not considered a overload condition (see attachment). I don't know if this was the rating the engine was designed for.

IIRC we know that +12 boost reduced the life-time to about 20 hours instead of 100 hours at maximum continuous rating.

[Al Schlageter]

The 12lb boost was a reduction from the 17lb boost that there normally would be. Yes there are references to this boost of 17lb. The boost was cut back to 12lb for reliability.

Crumpp still is evading identifying the 16 squadron that he claims were the only squadrons that used 100 octane fuel.

[Robo.]

Originally Posted by 41Sqn_Banks

Crumpp is right that +12 boost is about 3 times higher than the maximum continuous rating (+ 4 1/2), which is the highest rating that is not considered a overload condition (see attachment). I don't know if this was the rating the engine was designed for.

I see what he means now, thank you. It doesn't make much sense though - engines are designed for certain HP and that was never achieved at max. continuous rating as far I can tell.

[41Sqn_Banks]

Originally Posted by Robo.

I see what he means now, thank you. It doesn't make much sense though - engines are designed for certain HP and that was never achieved at max. continuous rating as far I can tell.

Rolls Royce gives 990 b.h.p as "international power rating" (+ 6 1/4 Boost with 2,600 RPM at 12,250 feet), see http://forum.1cpublishing.eu/attachm...8&d=1334724563.

Don't we have to convert the boost values to ata before we compare them make a statement about the factor between them? Otherwise the atmospheric pressure offset is not eliminated.

[Robo.]

Originally Posted by 41Sqn_Banks

Rolls Royce gives 990 b.h.p as "international power rating" (+ 6 1/4 Boost with 2,600 RPM at 12,250 feet), see http://forum.1cpublishing.eu/attachm...8&d=1334724563.

Don't we have to convert the boost values to ata before we compare them make a statement about the factor between them? Otherwise the atmospheric pressure offset is not eliminated.

My point is that early Merlin were not designed to operate at 4.5lbs. boost max. I am aware of the conversion issues and I only tried to point out that Crumpps assumtion was wrong.

[41Sqn_Banks]

Originally Posted by Robo.

My point is that early Merlin were not designed to operate at 4.5lbs. boost max. I am aware of the conversion issues and I only tried to point out that Crumpps assumtion was wrong.

According to this article the Merlin was designed as "1,100 hp-class" engine to fill the gap between the 700 hp Peregrine and the 1,500 hp Vulture.

However I don't think Crumpp claims that the Merlin was limited to +4 1/2 boost at any time, if he does he will certainly provide a document to support this claim. I think he consider the "maximum continuous rating" of every engine as the design goal and uses this value to compare different engines. He's free to do so. Others consider the maximum power, and some may use the takeoff power. It doesn't matter, the engine remains the same.

[Seadog]

Originally Posted by Robo.

I see what he means now, thank you. It doesn't make much sense though - engines are designed for certain HP and that was never achieved at max. continuous rating as far I can tell.

Actually 12lbs of boost is not "three times" what the engine was designed for; 4lbs of boost = 15psi (1 atmosphere) + 4psi = 19psi while 12lbs = 15psi (1 atmosphere) + 12psi = 27 psi, so 12lb of boost is actually about 1.5x the pressure level.

This can be more easily seen by using inches of mercury instead of lbs of boost:

inches of mercury (inHg)or absolute pressure = Pounds per square inch of boost or gauge pressure.
80 inHg= +25 lbf/in² boost
67 inHg= +18 lbf/in² boost
61 inHg= +15 lbf/in² boost
46 inHg= +8 lbf/in² boost
44.5 inHg= +6 lbf/in² boost