Radiator drag

[Kurfürst]

Thx ivank.

109 data.

I. For what it's worth, French trials of 109E suggest the following figures:

http://kurfurst.org/Performance_test...formanceT.html

Bf 109E-3 at 5000m, OPEN radiators, 2400 rpm and 870mm Hg boost: 520 km/h
Bf 109E-3 at 5000m, CLOSED radiators, 2400 rpm and 880mm Hg boost: 570 km/h

II. As per the V15a trials.

the 570 km/h speed was understood with the coolant radiator flaps 1/4 open (radiator flaps in streamlined position) and closed (I guess minimum) oil flaps position.
This was sufficient to maintain a constant, optimal 90° Celsius coolant and 62/82° Celsius oil temperature, at +5 ° Celsius external temperature during level speeds.

Maschine Bf 109 V 15 a D-ITPD W.-Nr. 1774
Motor DB 601 A W.-Nr. 140
Schraube 3 fl. VDM Verstellschraube 9-11081 W.-Nr.17459
Wasserkühler 1/4 geöffnet (Klappe in Straak)
Wassertemperatur konstant = 90°
bei +5° Außenlufttemperatur

Ölkühler Klappe geschlossen
Öltemperatur 62/82°; Öldruck 3,2 kg/cm2
bei +5° Außenlufttemperatur

http://kurfurst.org/Performance_test...w_109V15a.html

III. Somewhat related are the figures for Bf 109 G radiator drag.

It should be noted that the top speed of 109's were understood for a condition where the raditor was very slightly open (1/4 open in 109E, 50 mm open on 109F-K) compared to it's minimum opening position, ie. not 'fully' closed (which I believe was impossible to do on 109E anyway). This was usually referred to as 'schnellflugstellung', ie. fast speed setting. Top speed data refer to this setting.

See: http://kurfurst.org/Performance_test...cton_speed.jpg

CONLCUSION

Therefore, IMHO and based the data in a good and realistic 109E radiator drag setting should look as the following:

Raditor closed: ca. + 5 km/h faster speed (negative drag)
Radiator 1/4 open: no drag = top speed achiavable
radiator 100% open: ca. -35 km/h speed loss at SL, ca. -50 km/h speed loss at 5000m (since drag has greater effect at higher speeds/at full throttle heights)

I am looking forward to see the specs for other aircraft as well.

Picture of 109E coolant radiator in presumably fully open condition.