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View Full Version : Engine overheat a function of throttle % and not MP?



ucanfly
12-09-2004, 01:54 PM
Lately been trying to fly certain planes more by the numbers. I've know that most planes lose manifold pressure (MP) steadily with increased altitude as IRL. I also realize (obviously) that as you gain altitude, to get the same MP you have to increase the throttle percentage (Power Percentage message). What I've come to realize is that at higher altitude, I get the engine overheat message at a much lower manifold pressure than I do when at lower altitude. This is without using any boost and keeping it at or below 100% throttle. Try in the spit VB for example.

It seems that the game [perhaps] erroneously ties engine overheat purely to throttle position instead of manifold pressure. This doesn't seem correct.

Anyone else concur or disagree?

Daiichidoku
12-09-2004, 01:57 PM
Dunno....I do notice that at certain IAS and alt and power % overheating will go away

effte
12-09-2004, 04:53 PM
To get the same MAP, the blower will be compressing the air more at a higher altitude. This will heat it more. OTOH, the air is cooler at altitude... which effect will be predominant? Beats me. http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

3.JG51_BigBear
12-09-2004, 10:13 PM
I've always thought this was the case. I just assumed they used some sort of formula like if Throttle % +/- Radiator Position +/- Air Temperature > Certain # = Overheat.

ZG77_Lignite
12-09-2004, 10:24 PM
This is actually a good question and I sure don't know the answer either, or how to test it, nor how to research it. I could (and do!) speculate wildly, however I just don't know.

ucanfly
12-09-2004, 10:29 PM
I haven't checked against all aircraft but if it happens to aircraft without supercharger (are there any?) then it definitely seems wrong to me. An aircraft wo SC would throttle itself down with rise in altitude regardless of throttle % as long as mixture is compensating as well.

Hiriyu
12-09-2004, 10:41 PM
Interesting topic. Question for ucanfly - are you using manual mixture control or automatic?

WUAF_Badsight
12-09-2004, 10:53 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by ucanfly:
It seems that the game [perhaps] erroneously ties engine overheat purely to throttle position instead of manifold pressure. This doesn't seem correct.

Anyone else concur or disagree? <HR></BLOCKQUOTE>

FB/PF doesnt do a great job of enviroment moddeling

something to do with 15 Ghz needed (or some other small , minor , annoyance)

ucanfly
12-09-2004, 11:02 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Hiriyu:
Interesting topic. Question for ucanfly - are you using manual mixture control or automatic? <HR></BLOCKQUOTE>

Well it happens in the spit (auto mixture) and in most other allied planes I tested (which are auto mixture. If you mean difficulty settings I use full difficulty.

Ugly_Kid
12-09-2004, 11:34 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by WUAF_Badsight:
something to do with 15 Ghz needed (or some other small , minor , annoyance) <HR></BLOCKQUOTE>

Don't think so. The engine power is calculated anyway for the flying part. Netto heat is more or less a function of this and ambient temperature. The information is in the game and there is some calculation there but it doesn't seem to be a correct one.

The overheating in the game is first of all function of throttle position and airspeed and not so much dependent on altitude. MAP reflects horsepower which should be first indication of the heat production not throttle position. So yes already due to ambient temperature and IAS/TAS difference you win in temperature and I think loose a bit in mass flow, the temperature is dominant change. There is already an advantage in cooling at altitude itself but if you reduce heat production (MAP) the problem should be further reduced IRL.

BBB_Hyperion
12-10-2004, 01:06 AM
Most planes doesnt model correct cooling airflow effect . Try to take a manual and reach a 30 minute or combat rating with manual given data.

The indicated temp in the manual you are always over at least in the planes i tested.

But as i only have the manual to check it its too little info in it to create a correct aircooling formular if someone know how this cooling systems work how much heat obsorbing the liquids were and how much airstream goes in and all this details it might be possible to simulate it.

ZG77_Lignite
12-10-2004, 03:38 PM
Ugly-kid, a question: Would not altitude also play a 'major' factor, in that as alitude increases (and air pressure decreases) there is less air moving over the radiator (so less heat exchange efficiency)?

It seems to me that the major factors (not necessarily in this order) are:

Engine Power (MP+RPM)
Cooling Area (radiator type/setting/effieciency)
Speed
Altitude
Ambient Temperature


In my own mind (again, wildly speculating) it seems that higher altitudes give less cooling, even though the 'effect' is offset by the lower ambient temperature.

Hiriyu
12-10-2004, 08:46 PM
To add to what Lignite says above, I believe that fuel mixture could also play a role here (hence my question to ucanfly - I'm not familiar with the Spit myself).

A lean mixture contributes to higher CHT's, while a rich mixture can [depending upon circumstances] contribute to either a higher OR lower CHT, affecting overall engine temp. There is a dynamic relationship between intake air density/air temperature and optimum fuel mix. Whether or not this is taken into account in the game engines temp formula is beyond me.

Tully__
12-10-2004, 10:40 PM
Go to the Pelican's Perch (http://www.avweb.com/news/columns/182146-1.html) column index at AvWeb and check out the engine related columns list in a panel down the right hand side. While Maddox Games have made a good start on CEM, there's still a way to go.

There are those who'll tout MS sims as superior. While they have the advantage in the detail with which the controls are managed, there are still issues with how CHT and EGT respond to these controls.

BBB_Hyperion
12-11-2004, 06:43 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by ZG77_Lignite:
Ugly-kid, a question: Would not altitude also play a 'major' factor, in that as alitude increases (and air pressure decreases) there is less air moving over the radiator (so less heat exchange efficiency)?

It seems to me that the major factors (not necessarily in this order) are:

Engine Power (MP+RPM)
Cooling Area (radiator type/setting/effieciency)
Speed
Altitude
Ambient Temperature


In my own mind (again, wildly speculating) it seems that higher altitudes give less cooling, even though the 'effect' is offset by the lower ambient temperature. <HR></BLOCKQUOTE>

The Air gets cooler and therefore air is more compressed at higher alts so cooling effect is still there . And the Plane gets faster .)

p1ngu666
12-11-2004, 08:48 AM
itis, probably, try yaks at 10k, and a damaged p47 engine that barely keeps it in the air will overheat just as easly as a full power one..