'Radiator Drag Is Modelled' - Demo

[ATAG_Dutch]

I posted this video in one of the FM threads some days ago, but as the topic has arisen again, I thought it might be useful to post it in the main forum.

The video is of three vertical dives, power off, propellor as near to 'feathered' as possible.

One run with rad open, one with rad closed, one with rad at 50%. The time taken to go from 130mph to 440mph was measured using the timer in windows movie-maker, and was measured from the frame first 'unpaused' to the frame where the ASI hit 440mph in hundredths of a second.

Rad closed took just over 21seconds

Rad at 50% took 20seconds

Rad at 100% took 23 seconds.

Not only is radiator drag modelled, but causes a full 3 second difference from min to max times taken, in an aircraft travelling up to 440mph.

This is not a radiator shutter, this is a parachute.

http://www.youtube.com/watch?v=ksCmg...2&feature=plcp

[KDN]

At 50% radiator open the plane speed increased? Any possible explanation it became more aerodynamic

[ATAG_Dutch]

Yes. The fully closed position was for warming up purposes only - in reality.

Minimum drag is actually at the 35% open position, in order that air can flow freely through the radiator housing with minimum drag.

This is also true of the Bf109s in the game. Minimum radiator drag is to be found at the 35% open position.

[KDN]

Well, in that case, it is great to see this kind of autheticity.
Thank you for making it evident to us

[TomcatViP]

Didn't I say that alrdy 1 year ago (at least) ?!

Funny how I was finger pointed by some of those that complains endlessly abt the Spit/Hurri Vmax.

~S

Gallileo Tomcaternic

[hegykc]

Originally Posted by KDN

At 50% radiator open the plane speed increased? Any possible explanation it became more aerodynamic

Yes. On the P-51 the radiator, because of the hot air going out of it, didn't cause any drag at all, instead it even produced some thrust.
Saw that in a documentary.

[ATAG_Dutch]

Originally Posted by hegykc

Yes. On the P-51 the radiator, because of the hot air going out of it, didn't cause any drag at all, instead it even produced some thrust.
Saw that in a documentary.

Quite correct. This is known as 'The Meredith Effect' and the Spitfire was one of the first aircraft designed to incorporate a radiator housing designed to produce this effect.

[hegykc]

Oh thanks, didn't know the affect had a name, I thought it was by accident.
After some googleing:

"In the case of the
Mustang, this jet of heated cooling air reduced cooling drag to almost
nothing. It did not eliminate it entirely, but it reduced it to the
point where cooling drag was merely "3% of the thrust of the
propeller."

[ATAG_Dutch]

Originally Posted by hegykc

"In the case of the
Mustang, this jet of heated cooling air reduced cooling drag to almost
nothing. It did not eliminate it entirely, but it reduced it to the
point where cooling drag was merely "3% of the thrust of the
propeller."

That's very interesting information mate, thanks for posting!

Originally Posted by ATAG_Dutch

Quite correct. This is known as 'The Meredith Effect' and the Spitfire was one of the first aircraft designed to incorporate a radiator housing designed to produce this effect.

Except, at speed, the Spitfire (and 109 for that matter) had trouble with the ducts stalling and losing the effect. That's why, when the Mustang came over and proved to be so fast there was tremendous interest in the laminar wing, as it seemed the speed couldn't be due to the problematic duct effect. Real world experience, however, proved the difficulty of maintaining laminar flow in practice (Langley also doubted its field practicality). According to Lee Atwood, only two WW2 aircraft really made the Meredith effect pay off, and that was the Mustang and Mosquito and this was the biggest secret to their speeds.