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

[camber]

Originally Posted by Seadog

Prior to the 12lb mod/100 octane, if you pulled the boost override you would get 18lb boost up to about 5000ft, 16 lb boost to about 7500ft, 12 lb boost to about 11000ft and 7lb boost at ~17500ft. 7lb was the maximum permissible with 87 octane so the altitude range that it would be beneficial is very restricted; below that altitude power would be reduced because detonation would occur, engine would no longer run smoothly and the engine would quickly fail altogther. The only way that the boost override would be beneficial would be if it had a mod to restrict the additional boost to ~7lb, but of course this would only result in a very modest power increase, and this mod was never done.

AFAIK, the 109E was limited to 7lb boost as well (1.4 ATA) when using 87 octane.

Exactly right as I understand it Seadog. Although I would add one proviso...the boosts you mention are at maximum throttle. There would be nothing to stop a pilot pulling the boost override and adjusting his throttle handle (which is now directly linked to the actual throttle valve) to get a desired boost. So the pilot could possibly get some more performance, say by adjusting to +7psi where before he was stuck on +61/4 psi. Boost is no longer controlled, so if he dived to a lower altitude the boost will rise on it's own and possibly damage the engine. No wonder it was not an approved way of getting combat power on 87 octane...the gain was probably modest, the risk of misuse large. Whether or not it was used unofficially is open to conjecture.

Good point about the 109E, 1.45 ata is about +6.6psi boost. So I disagree Tomcat, it appears on 87 octane both the DB601 and Merlin were restricted by the maximum usable boost avoiding fuel predetonation..not by engine design paramaters or materials.

I am still intrigued by the engine test bed report apparently stating figures of 12500 feet, ~10.5psi boost and 1300bhp. But whether these are calculated figures, an engine tested with 100 octane, whether intake pressure was actually set to 12500 ft equivalent etc. does not appear to be available. Interesting to know what would happen if in a 87 octane Spit pre BCCO mod if you pulled the cutout and progressively raised boost above 6 1/4 psi. At what boost points would:
1) predetonation be detected
2) bhp start to decrease with increased boost (due to predetonation)
3) Significant loss of engine life occur
4) High risk of rapid engine failure.

[klem]

Originally Posted by Ernst

Acctualy the SIM should be: SUPERMARINE SPITFIRE: CLIFFS OF DOVER. I almost sure the right the devs must go to BoM. At least no spitfires there. Most of data here come only from two sources: spitfireperformance.com or from Kurfurst site. I am almost sure that the DEVS had other data, maybe from URSS evaluations of the SPITS and 109s that not exactly match the data presented here.

Well a key point about the spitfireperformance website is it gives us data collected at the time in reports written at the time. It is unlikely that Russian test organisations would have got any nearer to the true performance figures than the companies building the aircraft and engines and their prime user the RAF and its test organisations.

[Al Schlageter]

Did the Russians ever get any Spitfire Mk1s and/or MkIIs? They did get Mk Vs and MkIXs.

IvanK supplied most, if not all, of the data for the DEVS.

Great posts Seadog.

[Ernst]

Originally Posted by klem

Well a key point about the spitfireperformance website is it gives us data collected at the time in reports written at the time. It is unlikely that Russian test organisations would have got any nearer to the true performance figures than the companies building the aircraft and engines and their prime user the RAF and its test organisations.

Yes, but the companies wants to sell the aircrafts. That tests were made with unique prepared aircrafts for sure. A front line fighter would perform different. Some aircraft were easier to maintain and repair and were most of time more "combat ready" and "trimmed" than others, or even the perfomance downgrade by wearing should be much less. Even the way the aircraft is painted or waxed made a big difference in performance. Do you think 30km/h or 60 km/h should be a great difference? An 110 nightfighter with 52 victories, named Martin Drewes, stated that it was possible to fly 30km/h faster if they do not wax their aircraft or even removing the camouflage. He says: Better to fly faster than have a better looking aircraft.

Conclusion: There are many variables in the performance showed in this tests. For sure that aircraft were prepared or used advantageous methods of analysis to match the performance requiriments in the contracts. Problaby if an aircraft had more difficult mainentance in front line it ll be most of time deviated from that "original" performance.

[klem]

Originally Posted by Ernst

Yes, but the companies wants to sell the aircrafts. That tests were made with unique prepared aircrafts for sure. A front line fighter would perform different. Some aircraft were easier to maintain and repair and were most of time more "combat ready" and "trimmed" than others, or even the perfomance downgrade by wearing should be much less. Even the way the aircraft is painted or waxed made a big difference in performance. Do you think 30km/h or 60 km/h should be a great difference? An 110 nightfighter with 52 victories, named Martin Drewes, stated that it was possible to fly 30km/h faster if they do not wax their aircraft or even removing the camouflage. He says: Better to fly faster than have a better looking aircraft.

Conclusion: There are many variables in the performance showed in this tests. For sure that aircraft were prepared or used advantageous methods of analysis to match the performance requiriments in the contracts. Problaby if an aircraft had more difficult mainentance in front line it ll be most of time deviated from that "original" performance.

Most of the tests were undertaken by the RAE, the bona fide testing organisation for the British Airforce testing on behalf of the government, these were not "manufacturer's tests". Manufacturer's test results were not the way aircraft gained approval. The RAF would not have accepted aircraft designs without the RAE's input and it was not in the RAF/Air Ministry's interest to generate false results when they were trying to determine the capabilities of their fighters to defend the country. These were production standard aircraft. Yes they may have been fairly new but where would you like them to have started? With clapped out front line aircraft?

As for wax/no wax/wear/trimmed etc., how would you like 1C to set up the Spitfires and Hurricanes, oh, and of course, the 109s? Worn/degraded to 90% performance? Or do you want 100% condition 109s and 85% condition RAF aircraft?

1C can only begin by assuming production standard aircraft, take data from genuine contemporary tests and use that. If they want to model in wear thats fine. For Axis aircraft too of course.

Some of these arguments are becoming ridiculous.