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What is the radiator influence on speed ? - Printable Version

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Re: What is the radiator influence on speed ? - Storebror - 20.10.2010

Serpiko Wrote:Is the "fully open" drag amount the same for every plane?
Yes.

Serpiko Wrote:Does the engine consider the drag difference?
Unfortunately no.

Best regards - Mike

Re: What is the radiator influence on speed ? - whiskey111 - 20.10.2010

The funny thing is that F-4 U Corsair is a kind of aircraft which required to fly with radiator fully opne all the time. It was even in reality in that way. The most important thing to do just after start was to open radiator. Otherwise the engine could overheat. Additionaly I haven't notice any changes of speed between radiator open and closed (for F-4 corsair)

Re: What is the radiator influence on speed ? - Storebror - 21.10.2010

whiskey111 Wrote:Additionaly I haven't notice any changes of speed between radiator open and closed (for F-4 corsair)
That's subjective perception. See this track:
http://www.filefront.com/17415473/F4U1_ ... r_Test.TRK
At 90% power, 2000m alt with radiator closed the F4U reaches 543 km/h TAS in level flight, when opening radiator the TAS decreases to 521 km/h.

Best regards - Mike

Re: What is the radiator influence on speed ? - DBG_Kabayo - 22.10.2010

~S~
I have read that the only plane who's speed increased when radiator
was fully opne was the P-51. In the D model the speed actually increased
by 5-8 mph faster. I guess the radiator was design as not to influence the
drag, when the P-51 radiator is fully open the hot gas push out the rear of the radiator which caused the increase in speed. At what altitude did
this happen I am not sure, however it must be above 18-20,000ft.

Re: What is the radiator influence on speed ? - caldrail - 22.10.2010

No, but the position of the radiator under the fuselage in the position the P51 used creates superior airflow and less drag than other positions. The Napier Heston racer of 1938 used the same configuration for the very same reason.

Re: What is the radiator influence on speed ? - {HVY-E}Jinxx - 22.10.2010

DBG_Kabayo Wrote:~S~
I have read that the only plane who's speed increased when radiator
was fully opne was the P-51. In the D model the speed actually increased
by 5-8 mph faster. I guess the radiator was design as not to influence the
drag, when the P-51 radiator is fully open the hot gas push out the rear of the radiator which caused the increase in speed. At what altitude did
this happen I am not sure, however it must be above 18-20,000ft.


The increase in speed is actually caused from a type of 'RAM AIR' effect as air enters through the intakes and is forced out the exhaust at the back of the aircraft.
There is a name for the effect, but it escapes me at the moment.
To my knowledge, it wasn't effected by alt, but by speed.

Re: What is the radiator influence on speed ? - F22-Raptor-2006 - 22.10.2010

I do air racing and basically in IL2 terms this is what the radiator does...

Open compared to closed can be up to around 70 kmh difference, this can be seen on the Mustang Mk III where you can get around 560 or so with it open and 630 or so with it closed. Depends on how you fly as well... but from my memory it's around those figures.

It doesn't matter how hot your engine gets, it's either normal or overheating. If it overheats over a set certain time then it will start loosing power etc... So if it's overheating don't bother opening the radiator slightly thinking you won't damage it as much by keeping it cool yet still overheating. So if you don't intend to cool it then keep it closed. MiG3U is around 45 seconds on overheat before it starts dying, hence cardboard engine saying. Most aircraft, such as P-51 is around 4 minutes 45 seconds, others on the other end of the scale is the p47 at around 6 minutes. Spitfire is like 9 minutes but it has auto rads.

So yes it affects you quite a bit also for climbing purposes you'd best keep it closed.

Re: What is the radiator influence on speed ? - whiskey111 - 22.10.2010

Refering to F-4U Corsair I have noticed that there is 10 mintues to demage engine since "overheating message". In my opinion it's the only way to dogfight because without this additional power the airplane is too slow.
Unfortunatley I'm not sure if 10 mintues are the proper value. Perhaps this engine demages earlier. Anyone have more detailed info ?

Re: What is the radiator influence on speed ? - F22-Raptor-2006 - 22.10.2010

whiskey111 Wrote:Refering to F-4U Corsair I have noticed that there is 10 mintues to demage engine since "overheating message". In my opinion it's the only way to dogfight because without this additional power the airplane is too slow.
Unfortunatley I'm not sure if 10 mintues are the proper value. Perhaps this engine demages earlier. Anyone have more detailed info ?

That might be when you hear the engine making noises but you'll have lost power around about after 5-6 minutes. From my experience the corsair isn't something that lasts very long. To put it simply the P47 is the longest so it won't be anything over 6 minutes or so.

Re: What is the radiator influence on speed ? - caldrail - 23.10.2010

{HVY-E}Jinxx Wrote:
DBG_Kabayo Wrote:~S~
I have read that the only plane who's speed increased when radiator
was fully opne was the P-51. In the D model the speed actually increased
by 5-8 mph faster. I guess the radiator was design as not to influence the
drag, when the P-51 radiator is fully open the hot gas push out the rear of the radiator which caused the increase in speed. At what altitude did
this happen I am not sure, however it must be above 18-20,000ft.


The increase in speed is actually caused from a type of 'RAM AIR' effect as air enters through the intakes and is forced out the exhaust at the back of the aircraft.
There is a name for the effect, but it escapes me at the moment.
To my knowledge, it wasn't effected by alt, but by speed.

Again, no. That can't happen because the the radiator impedes airflow through the channel. Therefore there is always less air coming out the back than striking the front of the radiator shroud. In other words, an aerodynamic bow wave is set up (though this doesn't become a huge problem until transonic speeds)

What does happen is two-fold. Firstly the coanda effect provides a smoother flow of air under the fuselage because it can follow the curve of the scoop (as opposed to radiators like those on Hurricanes or Yaks, that just sit in the airstream like bricks). Secondly, the air exiting the radiator scoop forms a crude boundary layer control, simply because of the arrangement, and that provides airflow around the bottom of the fuselage and rudder that is smoother and less draggy that in other aeroplane designs.

At first sight it seems a little odd - you would think the air exiting the radiator is somewhat turbulent - but the idea works. The P51 was after all a very efficient design aerodynamically for a number of reasons including this one. The Napier Heston racer, which used the same style radiator scoop as the P51 sadly never proved the point because the oil line broke on its first flight and the engine siezed, causing a crash.

Re: What is the radiator influence on speed ? - Ark-iyos - 27.10.2010

conehead Wrote:Yes, it will produces a lot of restitance and minus your speed. During WW2 the most pilots, axis or alliied using radiator flaps on the ground fully open for taxiing and during take-off. After T/O they switched to auto.

Nice!!! Thank you! I owe you one virtual-beer Wink

Re: What is the radiator influence on speed ? - KG64_Cnopicilin - 27.10.2010

Ark-iyos Wrote:
conehead Wrote:Yes, it will produces a lot of restitance and minus your speed. During WW2 the most pilots, axis or alliied using radiator flaps on the ground fully open for taxiing and during take-off. After T/O they switched to auto.

Nice!!! Thank you! I owe you one virtual-beer Wink
[Image: oktoberfest.gif]

Re: What is the radiator influence on speed ? - conehead - 27.10.2010

Hi caldrail,
watch this... I just read about the "Meredith Effect" in a german flying magazin, which was on a P-51 in 1944 in Florida.
Actually the test was made on D-Modell, which has a combined water and oil cooler system underneath the fuselage.
The hot air which comes out of that sytem compenseds the restitance from that large cooler into thrust.
Meredith, an english airplane constructor givin the name.

Re: What is the radiator influence on speed ? - ColaBen - 29.10.2010

Check out the article on the "Meredith" effect in Airpower magazine , May 1993 for the full story in massproducing The Mustang.
ColaBen

Re: What is the radiator influence on speed ? - caldrail - 29.10.2010

conehead Wrote:Hi caldrail,
watch this... I just read about the "Meredith Effect" in a german flying magazin, which was on a P-51 in 1944 in Florida.
Actually the test was made on D-Modell, which has a combined water and oil cooler system underneath the fuselage.
The hot air which comes out of that sytem compenseds the restitance from that large cooler into thrust.
Meredith, an english airplane constructor givin the name.

i knew someone would think of this. No, it doesn't. Any real increase in speed regarding the P51 radiator is due to the amount of air allowed through it. It really is all about drag. The laws of physics tell us you can't get something for nothing, so 'ram-air' effects will not produce thrust. You can't go faster by moving forward - changes in momentum still require additional impetus and energy.

Now whereas the amount of heat generated by a large V12 aero-engine is considerable, the airflow across a radiator is designed to carry that heat away, not to derive thrust from it, and in any case, since the airflow is pretty much one way, any expansion due to heat obtained is not actually impacting on the aeroplane but the airflow pushing it out the back, thus there is no significant thrust obtained, nor for that matter is the heat generated by the P51's engine sufficient to produce any thrust at all - the whole idea is cool the system down, not let it get hot, and temperature gain of air flowing through the radiator does not rise as much as might be imagined.