Spit IIa is now so much more inferior to the 109

[Kwiatek]

Originally Posted by 41Sqn_Banks

I don't know if you had a look at the merlin em files so far. I've looked at them a year ago, so maybe this has changed, but at that time the Merlin III and XII were very identical. The nominal rpm was 2600 RPM for both. I assume that normal rpm is the value that can be maintained without critical overheat.
My impression is that the Merlin XII - as we have it know - is modeled more like a Merlin III running 100 octane (with +8? instead of +12 emergency boost).

Hmm i didnt look at emd file for CLod yet. But if it is true like you said so there is obviously error in engine data which probably casue problem with Merlin XII power limiation in game.

Luckly i checked today spitfireperformacne site and i found interesting data for Merlin III at 87 octan fuel which i didnt see before:



So for Merlin III at 87 octan fuel we have:

max take off - +6 1/4 at 2850 RPM
climbing - +6 1/4 at 2600 RPM
All-out level flight - +6 1/4 at 3000 RPM

With 100 Octan fuel modification Merlin III power settings was rised to:



So with Merlin III at 100 Octan we have:

take off - +6 1/4 at 3000 RPM
1/2 hr climbing - +6 1/4 at 2850 RPM ( below 20 000 ft) and at 3000 RPM (above 20 000 ft)
all-out level flight - +6 1/4 at 3000 RPM ( 5 minutes)
emergency power - +12 lbs at 3000 RPM ( 5 minutes)


Of course for Merlin XII nomial RPM should be 2850 not 2600 the same like with Merlin III at 100 Octan fuel.

[Crumpp]

from 1943

Makes more sense now. July 1940 did not make any sense at all.

[Crumpp]

Most civil operating handbooks will denote a normal climb speed which is also known as Cruise Climb speed.

Very few list a cruise climb speed. Once again, it is something that changes with atmospheric conditions and the weight of the aircraft is a huge factor. That is what you are doing, climbing the plane at the optium speed as it sheds the weight of consumed fuel.

Cruise climb is calculated as it varies with conditions and is of most practical value in a turbine engine. There are two approaches. Optimum Climb speed produces the best overall fuel economy. It seeks to balance the most altitude over time using the least amount of fuel with the most distance covered over the ground. Best Economy Climb speed is the second method and it factors operating cost, maintenance, and crew cost. Neither one is applicable to a WWII piston engine fighter.

Piston engines the main benefit is engine cooling, visibility and comfort.

[Kwiatek]

Generally max climing settings could be used for level flight much more safetly beacuse there is better airflow by radiators which casue better cooling engine condition then in steady climb at the same engine settings. So if engine have 1/2 hour limit for max climbing settings it could be used even more safetly for level flight. The one thing which is imprortant here is just fuel usage. Just all.

[Igo kyu]

Originally Posted by Crumpp

Cruise climb is calculated as it varies with conditions and is of most practical value in a turbine engine. There are two approaches. Optimum Climb speed produces the best overall fuel economy. It seeks to balance the most altitude over time using the least amount of fuel with the most distance covered over the ground.

The distance covered over the ground is utterly irrelevant, the RAF used a spiral climb at the start of the BoB, it may have been a bad choice, but it proves that they weren't in the least concerned with the distance over the ground, since in a spiral climb that is effectively zero.

[Crumpp]

The distance covered over the ground is utterly irrelevant, the RAF used a spiral climb at the start of the BoB, it may have been a bad choice, but it proves that they weren't in the least concerned with the distance over the ground, since in a spiral climb that is effectively zero.

Completely irrelevant to the fact you don't cruise around at climb ratings. Even during a "cruise climb" your engine is set to a maximum continuous or below.

Generally max climing settings could be used for level flight much more safetly beacuse there is better airflow by radiators which casue better cooling engine condition then in steady climb at the same engine settings. So if engine have 1/2 hour limit for max climbing settings it could be used even more safetly for level flight. The one thing which is imprortant here is just fuel usage. Just all.

Right but completely irrelevant to the fact you don't cruise around at climb ratings. Better cooling or not, level or climb, it is an over boost condition on the engine and increased chance of failure.

[Crumpp]

Glider,

I think you asked about the Bf-109 Load factor limits. I am not sure of the specifics but I do know the engineering safety margin were higher in German aircraft. Take away being the airframes are not rated on the same scale.

[41Sqn_Banks]

Originally Posted by Kwiatek

So for Merlin III at 87 octan fuel we have:

max take off - +6 1/4 at 2850 RPM

...

So with Merlin III at 100 Octan we have:

take off - +6 1/4 at 3000 RPM

It's interesting to note that publications from 1938 and 1939 give maximum take-off engine speed of 2850 rpm for both Merlin II and III. Publications from 1940 give 2850 for Merlin II and 3000 rpm for Merlin III. The increase is not associated with the use of 100 octane fuel.

[Kwiatek]

Originally Posted by 41Sqn_Banks

It's interesting to note that publications from 1938 and 1939 give maximum take-off engine speed of 2850 rpm for both Merlin II and III. Publications from 1940 give 2850 for Merlin II and 3000 rpm for Merlin III. The increase is not associated with the use of 100 octane fuel.

Hmm interesting have you some documents with such Merlin power settings? I miss really manual ( pilot notes) for Spitfite MK1 and Hurricane MK1

[Crumpp]

from 1938 and 1939 give maximum take-off engine speed of 2850 rpm for both Merlin II and III

It also shows maximum boost at emergency power at 12,500ft as +10.55lbs at 3000 rpm for the Merlin III when you use boost override or pull the tit on 87 Octane.

Absolutely NOTHING to do with the use of 100 Octane fuel.