Misleading information about the BF109?

[MarkusZeller]

Various sources claim how late Bf 109s (K4) are suppossed to climb at 4300ft/m at sea level (1.8 ata).
According to this document dated back in 1943 a Bf 109 G1 achieved already 4100ft/m at sea level, this was not calculated but a real test with a pilot sitting in a cockpit.
BF109 G1 6600lb 1310hp 0,198hp/lb
BF109 K4 7500lb 1850hp 0,247hp/lb
Both AC have a very similar wingloading but the Kurfurst trumps the Gustav in terms of power to weight. 200ft/m seems very weird? So why is there such a miniscule difference?
[CLOSED] Climb rate appears to be to high, even for 109k
Dora climb rates
The guy who is responsible for flight models in DCS claimed how exhaust trust, prop efficiency etc. was not taken into account by Focke Wulf and Messerschmitt. Currently the BF109 K4 (full takeoff weight 1.8 ata) climbs at 5100ft/m at sea level which seems to be very plausible given how the plane has an insane powerloading.

Has anyone here access to "erflogene Werte" aka real tests? I've already searched on Kurfurst's website, but he has only calculated stuff. Calum Douglas?

 

[drgondog]

Various sources claim how late Bf 109s (K4) are suppossed to climb at 4300ft/m at sea level (1.8 ata).
According to this document dated back in 1943 a Bf 109 G1 achieved already 4100ft/m at sea level, this was not calculated but a real test with a pilot sitting in a cockpit.
BF109 G1 6600lb 1310hp 0,198hp/lb
BF109 K4 7500lb 1850hp 0,247hp/lb
Both AC have a very similar wingloading but the Kurfurst trumps the Gustav in terms of power to weight. 200ft/m seems very weird? So why is there such a miniscule difference?
[CLOSED] Climb rate appears to be to high, even for 109k
Dora climb rates
The guy who is responsible for flight models in DCS claimed how exhaust trust, prop efficiency etc. was not taken into account by Focke Wulf and Messerschmitt. Currently the BF109 K4 (full takeoff weight 1.8 ata) climbs at 5100ft/m at sea level which seems to be very plausible given how the plane has an insane powerloading.

Has anyone here access to "erflogene Werte" aka real tests? I've already searched on Kurfurst's website, but he has only calculated stuff. Calum Douglas?

ROC calcs stress Available HP and GW. Available HP = (TV-DV)/W The drag between the two versions would have emphasized the Induced Drag difference between the two ships. The delta for K4 over G1 is 1.13 for GW, and (1.13^2) for Induced Drag delta. The HP Available would be reduced accordingly assuming the same climb speed (actual - not ROC). Seems reasonable to me without having all the data to calculate true ROC.

 

[ThomasP]

There are actual tests for the K-4 model on the same site as the G model you reference above.

"Kurfürst - Performance of 8 - 109 K4 and K6 with DB 605 ASCM/DCM"

This graph shows the K model with the DB 605 D engine having a SL ROC of ~4800 ft/min.

"http://kurfurst.org/Performance_tests/109K_PBLeistungen/files/5026-19_DCSonder_MW_steig.jpg"

 

[thunderbird]

One of the interesting problems in evaluating airplane climb performance is the problem of low speed propellor efficiency. Propellors approach 85% efficiency at a certain pitch angle and propellor advance ratio. Variable pitch props increase the range of advance ratios where the prop reaches peak efficiency, but efficiency drops as speed decreases, and best climb speeds are generally just a bit faster than takeoff speeds.

Incidentally, propellor efficiency is zero at zero airspeeds, because power is force times velocity. Doesn't mean the prop isn't developing thrust.

It seems prop design was somewhat an art in WWII. I developed a mathcad program that would calculate the prop efficiency based on published performance data, and as i recall, propellor efficiency at best climb speed varied somewhat from one aircraft to another. Of course i made assumptions. I didn't have any real propelle data.

One would have to have actual propellor geometry and propeller performance data to do the analysis more completely.

But climb performance is actually even more complicated than that. The K outweighs the G significantly, but has the same wing. At climb speeds, the drag of the airplane is mostly induced drag, drag due to lift. That K wing has to produce more lift, more lift means more induced drag, which by itself, might wipe out a significant part of that excess power advantage.