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

[Seadog]

Originally Posted by Blackdog_kt

Because it's possible to change octane ratings as long as you keep to the relevant limits?

Again, cue the Blenheim Mk.IV pilot's notes where it's clearly stated that it was standard operating procedure to switch between 87 and 100 octane mid-flight: the only limitation was keeping boost within the appropriate limits for each fuel type, the engine won't suddenly explode if you just throttle back and switch to the 87 octane tanks, even though the engines were modified for 100 octane use.

P/O Art Donahue's account of using +12 boost during his first combat of 5 August 1940, whilst flying Spitfires with No. 64 Squadron out of Kenley, is typical:

“There are bandits approaching from the north” In quick response to this information, our leader sang out a command: “All Tiger aircraft, full throttle! Full Throttle!” That meant to use the emergency throttle that gave extra power to our engines. I was flying in our leader’s section, on his left. As he gave the command “Full throttle”, his plane started to draw ahead, away from me. I pushed in my emergency throttle in response to the command, the first time I had ever used it, and my engine fairly screamed with new power. I felt my plane speeding up like a high spirited horse that has been spurred. http://www.spitfireperformance.com/spit1vrs109e.html

Kinda hard to keep formation if some aircraft are using 87 octane and some 100 octane...

In a Blenheim flying a long range recon or ferry mission (which is the only time they could use the auxiliary tanks) it is quite reasonable that there will be long periods where the expectation of enemy encounters are low, and thus mixing octane types is a reasonable risk. The problem is that it will take many seconds before the change back to 100octane can be made, and during that time overboost will not be available and damage to the engine may result if overboost is applied too soon.

[Kurfürst]

Originally Posted by Seadog

Kinda hard to keep formation if some aircraft are using 87 octane and some 100 octane...

I guess not so hard as if half of them are Hurricanes and the other half are Spitfires, even if they would use the same fuel type as long as they would be both stationed at the same fighter station...

[Seadog]

Originally Posted by Kurfürst

I guess not so hard as if half of them are Hurricanes and the other half are Spitfires, even if they would use the same fuel type as long as they would be both stationed at the same fighter station...

Which is why squadrons are generally equipped with one aircraft type.

[Crumpp]

Kinda hard to keep formation if some aircraft are using 87 octane and some 100 octane...

No, at any manifold pressure and rpm setting below the knock limited performance of the fuel, the power will be the same.

Basically at any manifold pressure below +9lbs (limit for 87 Octane) in the Merlin, the power is the same for 87 Octane or 100 Octane fuels.

[CaptainDoggles]

The problem is that people think the higher octane fuels magically give more horsepower when in reality they merely allow the engine to develop higher power at higher manifold pressures without engine knock.

[VO101_Tom]

Originally Posted by CaptainDoggles

The problem is that people think the higher octane fuels magically give more horsepower when in reality they merely allow the engine to develop higher power at higher manifold pressures without engine knock.

This is totally true. To see every day on the street when the people buy it their car the expensive 100 octane "V-Power" fuel, though into the car 95 octane would be needed

[Kanalkrank]

It has been very long, interesting discussion about... FUEL and I would like to ask you guys what you propose in the next patch Flex-Fuel Spitfire or Spitfire Hybrid?

[Seadog]

Originally Posted by VO101_Tom

This is totally true. To see every day on the street when the people buy it their car the expensive 100 octane "V-Power" fuel, though into the car 95 octane would be needed

Most cars these days, especially high performance vehicles, have engine knock sensors, which sense detonation and then automatically retard the timing to prevent pinging. Depending on the car and how its CEM is setup, higher octane fuel might give better performance.

[Seadog]

Originally Posted by Crumpp

No, at any manifold pressure and rpm setting below the knock limited performance of the fuel, the power will be the same.

Basically at any manifold pressure below +9lbs (limit for 87 Octane) in the Merlin, the power is the same for 87 Octane or 100 Octane fuels.

Merlin engines were limited to 6.25lb boost when using 87 octane. At ~10,000 ft the Merlin III would produce 1310 hp at 12lb/3000rpm versus about 1000hp at 6.25lb boost. It might be possible to go past 6.25lb with 87 octane, but this leaves the engine with no safety margin since detonation is dependant on several factors, not just manifold pressure.

[TomcatViP]

Originally Posted by Seadog

Merlin engines were limited to 6.25lb boost when using 87 octane. At ~10,000 ft the Merlin III would produce 1310 hp at 12lb/3000rpm versus about 1000hp at 6.25lb boost. It might be possible to go past 6.25lb with 87 octane, but this leaves the engine with no safety margin since detonation is dependant on several factors, not just manifold pressure.

Wrong. See my post above and data pasted bellow. You need to take into account the s/c !

MerlinXX !

ALT(ft) SHP BHP (diff correspond to the power used to drive the supercharger)
15K 1267 1048
20K 1298 1073
20K+ 1362 1126
25K 1162 960
30K 945 778
35K 700 568


More over the subsequent Merlin (the XX) developed to give more power to the Hurri (what the RaF felt was more a need) was limited to 9lb at 20Kft but 12lb in T.O/Emergency


I think that you are confounding higher grade and NOS and don't forget all the cooling prob with the Merlin in the RAFFC's fighters

Quitely again as I hve said it does not fit any logics.

~S!