View Full Version : Need "how to use radiator flaps" 101 course

10-19-2004, 05:06 PM
I would very much appreciate a quick primer on the use of radiator flaps. Do I open prior to takeoff, close mid-flight, open as needed after that? I fly without the hudlog text messages - are the cockpit temperature gauges accurate? Why the intermediate positions (2,4,6,8) between open and closed? I noticed USAAF aircaft (and Yak-3) have a closed/auto position which RAF aircraft do not have. How does this function as opposed to the RAF equipment? As you can see, I'm quite inexperiened on this point. Any help is much appreciated.

10-19-2004, 05:18 PM
They are useless in the game, leave them open at all times to keep engine cooler so you can squeeze more power out of your engine. At least it works this way in the BF-109. The amount of drag is maximum 5-10 km/h if anything at all.

10-19-2004, 05:25 PM
Mmmm, well, to me, there is a drag versus cooling efficiency trade off.

Are you sure there's no benefit, H_D? Seems to me there is.

I can use the radiator "flaps" on a P-51D for example at "4" and fly around for a pretty long time and not overheat at ~95% throttle. With the reduced drag, I feel I can maintain a top speed only slightly less than if the rad 'flaps' were open all the way and I was using full power, and without fear of overheating.

10-19-2004, 05:25 PM
I don't think it has anything to do with power.
Open them for extra engine cooling in cases where you ask a lot of it; e.g. take-off, dogfights, etc. to minimize engine overheat or even fire chances.

Close them during cruise, when you're running on economy setting or any other case where there's a relatively low engine setting.
You don't need the extra cooling then.

Use your brain to calculate the intermediate settings (e.g. between open and closed).

The power issue is too small to be of any positive effect in this case.

However, opening the cowl flaps does extend something out of the airframe so remember you will be flying with increased drag!

10-19-2004, 05:27 PM
Tecnically, an IC engine is most efficient when hot. But closing the rad "flaps" or "doors" doesn't create more power, it reduces drag caused by opening the "flaps" or "doors"

10-19-2004, 05:28 PM
Yes the radiator functions are different for different aircraft and you will have to learn your plane.

As far as use of the radiator flaps goes, I try to run the plane so they will not be needed. In past patches of this sim there has been a noticable decrease in the speed of the aircraft at any throttle setting when the radiator or cowl flaps are open.

If the engine is overheated there is a good chance you will lose performance also. So I take off with them closed, run the throttle full and climb to alt as far as I can with this setting, when the overheat warning comes on I throttle back to a setting my particular plane can run at without overheating and with the radiator closed. I finish climbing to the desired altitude at this setting and then throttle her back even more when not climbing to whatever will maintain my alt an speed around 325 or so km/hr.

Now your engine is nice and fresh for combat and you are ready to use your alt and not the engine for getting speed. After a dive and firing pass use full throttle for a little bit to regain alt.
In an emergency when you are saving your butt and you overheat the engine, then you will pop open the cowl flaps just to keep the engine from blowing up and to give youself a better chance of making it back over the line or home.

To summarize, if you fly right your engine should not overheat much at all. When you fly around with the cowl flaps open you use more fuel to go slower and will not be able to attain or keep as much speed as you would with them closed and the plane cleaner aerodynamically. S!


My advice above is what works better on servers and missions with realistic settings and might be closer to how things were done in the day. Of course on an arcade server with the airfields close together you can run the engine throttle and cowling wide open, because with a big colored arrow pointing to your plane, and an identifying tag, you will probably not be around long enough for it to overheat anyway.

10-19-2004, 05:34 PM
What I meant by "so you can squeeze more power out of your engine" is that you'll be able to fly at a higher power setting for a much, MUCH longer time with them open. Power over time becomes much increased, not maximum power.

Drag does not seem to be modeled to any significance in the game. (I have no clue how much drag it even produces in real life). In a 109 rad flaps does not appear to protect the engine any better from bullets either.

10-19-2004, 05:43 PM
In that case, my fellow pilot, you are correct!

In real life cowl flaps don't produce much drag at all, to be honest their effect on aerodynamics might very well be neglected at all I guess... For civil airplanes that is, don't know about the WWII fighters, that's why I put the warning there.

10-19-2004, 05:46 PM
Yes, it's modelled pretty significant.

If closed, engine gets overheat much faster at high power.
If opened, it drags your plane significantly (subjectively) in high speed.

But if you just want to keep it open and sacrifice your speed, it's your choice.

10-19-2004, 05:58 PM
Usually on late 109's I have them open since before take of (turning on wep system too), then I switch to auto during a dogfight (also use power over 100% only in this case thus enabling wep). I've found that there is a slight speed diference, and maybe It's my mind, but it seems like doesn't bleed so much when turning. While in a dogfight if I dive (and I'm in relative advantage position), i quickly throttle back to 80-90% and open rads, swithing 'em back to auto and 110 as soon as I start leveling, this gives some extra wep time. I only close them in an emergency like following someone on a very step and short climb. Maybe I do it all wrong but seems the most logical to me.

10-19-2004, 06:28 PM
No it DOES NOT drag your aircraft significantly (in the GAME). You are wrong. I am right. Go test it! Top speed seems almost unchanged! Acceleration is the same. It pays off to fly with it open at all times. You can push your engine harder and thus get more performance.

10-21-2004, 06:36 AM
Thank you to all who took the time to post. responses to my question. I have learned a lot.

10-21-2004, 06:47 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by HART_dreyer:
They are useless in the game, leave them open at all times to keep engine cooler so you can squeeze more power out of your engine. At least it works this way in the BF-109. The amount of drag is maximum 5-10 km/h if anything at all. <HR></BLOCKQUOTE>

Not 100% true HART. The speed difference varies from plane to plane. Some reach 20 km/h. Some change nothing (like P51)

Also acceleration improves with flaps closed (already measured that) specially above 400 km/h.

I usually leave them Full open until I nedd to jump on somebody or make a fast escape, moments where 15 km/h more at max speed and a shorter time to reach that speed are very welcome.

Of course is not a ALL or NOTHING feature, so do not expect HUGE performance difference.

10-21-2004, 07:05 AM
Rads open and closed do about 20 km/h Topspeed difference depending on planetype tho.

10-21-2004, 07:13 AM
One of the first things I do in a P39 (or most of the planes) is set the radiator full open.

I found early on that the 'Cobra would eventually overheat in combat if I left them in the closed/auto position, and once it had overheated, it was a real PITA to get back down into normal ranges unless you were free of combat.

However, by opening them prior to going into combat, I discovered that it will never overheat under "average" combat conditions.

Since I flew the P39-N1 almost exclusively for about a year, and then spent many months flying the Q1, opening the radiator immediately just became something I do without thinking.

Lately I've been giving some of the 'auto' settings a try, since it seems like later versions of the game are much more forgiving of heat than the original IL-2.

As for real life operations, that gets a bit easier, since there are often specified times when they should be open or closed. If nothing else, it's fairly easy to just watch the temp gauge and then manage the heat with pitch/mixture/power/cowl flaps depending on what you're doing and how you want to cool down.

Sometimes the extra drag from the cowl flaps is actually useful. I found it was a nice help during engine out operations in a twin. Close the cowl flaps on the dead engine to reduce the drag, and open the flaps on the working engine to increase cooling.

The nice side effect was that it helped balance out the plane a lot more and noticably decreased the amount of rudder input (or trim) required to keep the plane flying directly into the relative wind.

That could be really useful in FB/AEP/PF if there were any amount of accurate engine out modeling in the sim, but since a Lightning with an engine physically missing is far tamer than a Seminole with an engine out, it's not of much use.

Now, I'll admit that I've never flown a P38, let alone one with an engine missing, but I suspect it's safe to say that a twin with over 1,000HP available on one side and the massive drag penalty of a bare firewall exposed on the other would be darn near uncontrollable. In AEP, it's merely an "Oops, guess I should RTB" event.

Not that I'm really complaining, it's just a limitation of the current sim and I accept it.

I guess to sum it all up:

Use them as they best fit to your current situation. Sometimes the extra drag is a pain, sometimes it's a bonus. Prolonged high power ops will probably require them to be open. Hot maps will need them open more than cold maps.

Oh, if your engine is on fire and you're trying to put it out, close the cowl flaps.

That's about all I can think of.

10-21-2004, 08:41 AM
There is still no way to see your radiator setting (cokpit view) with screen text disabeld?

Or has this changed?

That is the main reason why I do not use it!