Bf-109 Radiator Drag.

[Roland_HUNter]

Greetings,

Anyone have any information on how much drag the 109's radiator causes?

 

Because that's what I'm currently experiencing in the game on a summer map:
Bf-109 F-4

0% radiator: 544 km/h

100% radiator: 481 km/h

 

63 km/h drag.

Isn't that a bit much?

 

I might add that the radiator often opens to 100%.

If I do a dive on deck at 750 km/h and then lift off to hammerhead, the radiator will open 100% at the end because the thermostat is trying to keep the engine at 100 degrees.
But it should turn on at 115, as it does on the Mustang at maximum heat: the radiator starts to open at 121 degrees.

[the_emperor]

4 hours ago, Roland_HUNter said:

But it should turn on at 115, as it does on the Mustang at maximum heat: the radiator starts to open at 121 degrees.

Nope.

102deg is the radiator automatic temperature, 115deg max for 10min.

 

 

The Merlins automatic operating temperature is 115deg and 135 for 5min

The Laggs/Yaks M-105pf operating temperature is 90-100deg with 110max for 10min

Though in game there is, for unknown reason, no time limit if you run you engine in the hot zone, though manuals clearly state those limits?‍♀️

[Charon]

The 109 radiators should certainly be draggy; Lipfert repeatedly talks about using them as air-brakes.

 

I feel like somewhere in his book he says something to the effect of "... and the mud splashed from the airfield forced us to fly with our radiators fully open, which slowed us." I don't remember if he puts numbers on how much it slowed them, and unfortunately I can't find that reference now. Maybe someone else recalls?

[357th_KW]

23 hours ago, Roland_HUNter said:

Greetings,

Anyone have any information on how much drag the 109's radiator causes?

 

Because that's what I'm currently experiencing in the game on a summer map:
Bf-109 F-4

0% radiator: 544 km/h

100% radiator: 481 km/h

 

63 km/h drag.

Isn't that a bit much?

 

I might add that the radiator often opens to 100%.

If I do a dive on deck at 750 km/h and then lift off to hammerhead, the radiator will open 100% at the end because the thermostat is trying to keep the engine at 100 degrees.
But it should turn on at 115, as it does on the Mustang at maximum heat: the radiator starts to open at 121 degrees.

 

Here's a couple tests from the 109G - the speed loss is slightly less (48 km/h) but they're also at lower speeds - max speed with rads closed on these early 109Gs was only 515 km/h. 

 

http://www.wwiiaircraftperformance.org/me109/VB-109-18-L-42.pdf

http://www.wwiiaircraftperformance.org/me109/VB-109-18-L-42.html

http://www.wwiiaircraftperformance.org/me109/me109g-perfcomp-pg33.jpg

 

Callum Douglas goes into a lot of detail about radiator design and technology in his book "The Secret Horsepower Race".  The whole reason a DB605 was transplanted in a captured Spitfire Mk V fuselage was to compare the cooling capability of the radiator on the Spitfire.  The British were essentially getting equivalent cooling from roughly half the radiator area due to the use of high temp/high pressure coolant systems. 

 

http://www.wwiiaircraftperformance.org/me109/db109g.pdf

[Kurfurst]

Effect of radiator position on flight speed, measured on a pre-series Bf 109G. 

 

Note the aircraft testbed had assymetric (copper / aluminium) radiators installed, however it should not effect the measured speeds much, if any.

 

Also note that nominal maximum speeds were understood for about 40-50 mm coolant flap openings. Climb rates were understood for radiators in 220mm open position (later in cc 1944 it was changed and the thermostat kinematics were altered for reduced opening, as it was found it boosts climb rate considerably with negligable effect on cooling capacity).

 

 

 

Edited February 8, 2024 by VO101Kurfurst

[the_emperor]

2 hours ago, VO101Kurfurst said:

(later in cc 1944 it was changed and the thermostat kinematics were altered for reduced opening, as it was found it boosts climb rate considerably with negligable effect on cooling capacity).

 

http://www.wwiiaircraftperformance.org/me109/VB-8-18-205-001.pdf

[Roland_HUNter]

On 2/8/2024 at 11:56 AM, the_emperor said:

 

http://www.wwiiaircraftperformance.org/me109/VB-8-18-205-001.pdf

I tested it.
It's exactly the same in the game.
G-6AS:
Fully opened rads:
459 km/h

Halfway opened rads:
484 km/h

Difference: 25 km/h.

Report says:
"Kühlerklappenstellung ganz auf und der vorgeschlagenen zwischenstellung bei gleicher motorleistung eine geschwingingkeitsdifferenz von 25 km/h, die sich bis zur gipfehöhe in demselben masse auswirken dürfts."

 

"Radiator flap position fully on and the suggested intermediate position with the same engine power a speed difference of 25 km/h, which should have the same effect up to the summit."

 

Very nice job developers!