Engine overheat and altitude

[fdiron]

In space, objects are either putting out heat or drawing heat back in.

[Maverick]

Originally posted by fdiron:
My point about the air being breathable at 30k was to stress that the air is not as thin as you might think.  There have been people who have climbed Mount Everest without oxygen tanks.  In fact, I watched an IMAX documentary about a guy who climbed to the peak of everest without oxygen tanks.  It takes at least 2 weeks to get acclimated.

Last I checked, I haven't heard of any WW2 flights that lasted 2 weeks at 30k.    Certainly none that took time too acclimate the pilots for longer than that to allow them to fly without oxygen.  

 

[pbirmingham]

Originally posted by AKIron:
Take it to extreme, out of our atmosphere. Is heat unable to radiate in outer space? Personally, haven't been there, can't speak from experience.

Of course heat radiates in outer space.  It radiates at any altitude.  Radiation is a very small component of mechanism by which engines are cooled, though, which is why your computer has all those fans.

[AKIron]

Originally posted by Runny:


Of course heat radiates in outer space.  It radiates at any altitude.  Radiation is a very small component of mechanism by which engines are cooled, though, which is why your computer has all those fans.

Beg to differ Runny. Air is an insulator. The fans move away the warm air that has absorbed the heat from my cpu and the engine in my car.

If you mean that piston engined airplanes are designed to transfer heat most efficiently to a dense airflow through their radiators/cooling fins then you may be right.

However, it would seem to me that in the absence of an insulator (air in this case) heat would radiate at peak efficiency even from the fins of water radiator. I could be wrong, any engineers listening?

[ 12-24-2001: Message edited by: AKIron ]

[Furious]

Just as a side note, I think HT should model the lack of oxygen systems in those aircraft that had none.  Make the pilot act as though he/she been wounded until dead or altitude is decreased.

Also:

 

Three types of heat loss:
· Conduction
· Convection
· Radiation

Conduction of heat occurs mainly in solids. This process is where vibrating particles pass their extra vibration energy to neighbouring particles.

Convection of heat only occurs in liquids and gasses. Convection occurs when the more energetic particles move from the hotter region to the cooler region taking their energy with them.

Radiation of heat can also be called infer-red radiation. Heat radiation can travel through a vacuum. This process is different from the other two it travels in straight lines and at the speed of light. This is the only way heat can reach us from the sun. Heat radiation travels through transparent media like air, glass, and water. No particles are involved in this process it is the transfer of heat energy purely by waves.
 

F.

[pbirmingham]

Originally posted by AKIron:


Beg to differ Runny. Air is an insulator. The fans move away the warm air that has absorbed the heat from my cpu and the engine in my car.

If you mean that piston engined airplanes are designed to transfer heat most efficiently to a dense airflow through their radiators/cooling fins then you may be right.

However, it would seem to me that in the absence of an insulator (air in this case) heat would radiate at peak efficiency even from the fins of water radiator. I could be wrong, any engineers listening?

[ 12-24-2001: Message edited by: AKIron ]

Hmmm.

I'm not an engineer, really, but I have a MS in physics, so I know a little about this.

You are sort of correct.  Still air acts as an insulator, because as it heats up, according to the second law of thermodynamics no more heat can be transferred.  That is why you need some sort of breeze for a cooling effect.

The insulating effect of still air, however, doesn't affect heat transfer by radiation, as air is essentially transparent to infrared radiation.  If air interfered with this radiation, heat lamps, thermal imaging devices, and TV remotes would be useless.

Think of it this way: if your car's radiator fan gives out, it's not a problem if you're moving at highway speeds.  When you get stuck in traffic, though, your engine becomes more and more overheated.  This is because the airflow over the radiator is the most important component to the function of the cooling system.

[Pyemia]

So what you saying Runny is If I was driving my car at 30K Alt and my fan stopped working at highway speeds i'd pass out thru lack of oxygen unless aliens from outer space climbed MT Everest and erected a set of traffic lights?


Zygote?

[pbirmingham]

Originally posted by Pyemia:
So what you saying Runny is If I was driving my car at 30K Alt and my fan stopped working at highway speeds i'd pass out thru lack of oxygen unless aliens from outer space climbed MT Everest and erected a set of traffic lights?


Zygote?

No, you'd keep on driving unless you looked down and realized there was no road under you.  Then you'd fall with a whistling noise, there'd be a puff of dust at impact, and a Pyemia's-car-shaped hole in the ground where you hit.

You really mean you didn't know this?

[fdiron]

You wouldnt pass out on Mount Everest if you became acclimated.

[AKIron]

Finally realized my ignorance on the subject. Now I understand the difference between heat conduction and radiation and of course all WWII arcraft were designed to transfer heat via conduction. Good thing about being ignorant is there's always something new to learn   .

Still believe that engine temperatures would run cooler at alt but couldn't find any thing definitive on the subject. However, I did find an interesting article on the history of piston aircraft engines.

Engine History

 

Originally posted by Runny:


Hmmm.

I'm not an engineer, really, but I have a MS in physics, so I know a little about this.

You are sort of correct.  Still air acts as an insulator, because as it heats up, according to the second law of thermodynamics no more heat can be transferred.  That is why you need some sort of breeze for a cooling effect.

The insulating effect of still air, however, doesn't affect heat transfer by radiation, as air is essentially transparent to infrared radiation.  If air interfered with this radiation, heat lamps, thermal imaging devices, and TV remotes would be useless.

Think of it this way: if your car's radiator fan gives out, it's not a problem if you're moving at highway speeds.  When you get stuck in traffic, though, your engine becomes more and more overheated.  This is because the airflow over the radiator is the most important component to the function of the cooling system.

[pbirmingham]

Originally posted by AKIron:
Good thing about being ignorant is there's always something new to learn   .

Also, you get to learn about cooler and cooler stuff.

The link was great stuff.

I can't really say that engines will run hotter or cooler at high altitudes, actually. The maximum amount of heat that can be carried off by the air that sweeps past an engine at a given TAS is lower at 10 km than at sea level; the temperature drop isn't enough to make up for the density drop.  This theoretical maximum isn't the whole story, though, and there
could be inefficiencies that are greater at sea level than at altitude.  This is to say that the whole question is a little complicated, and I would be suspicious of anybody who says "engines will run hotter/cooler" at altitude, unless they spoke from experience or gave some rigorous explanation.

[Blue Mako]

Originally posted by AKIron:
However, it would seem to me that in the absence of an insulator (air in this case) heat would radiate at peak efficiency even from the fins of water radiator. I could be wrong, any engineers listening?

Yeah, I'm listening but I think I was sleeping through most of my Thermodynamics classes.  

As I understand it, heat will radiate away from anything given the chance but conducting heat away is the most efficient method.  Air is a poor conductor.  Water conducts 10x better than air which is why radiators need so much surface area and a large amount of air flow to cool the liquid coolant effectively.

The peak efficiency of a cooling system is acheived when the temperature difference of the object being cooled and the conductor is greatest.  Thus a hot engine will cool quicker in cool air then hot air (obvious I know).

Having said that, the lower density of the air at altitude means that for the cooling to be efficient, the flow rate(ie. the volume of air passing through the cooling system) of air must be higher than the air at sea level, even though the temperature is lower.

All told I think that the cooling would be better at high alt due to the difference in temp being more effective than the lower density decreasing efficiency.

Then again, I could be wrong, just an uninformed opinion.  

[ 12-26-2001: Message edited by: Blue Mako ]

[Beegerite]

I have the distinct impression that everybody missed the operative word in this question, "MODELS"

I personally don't think there is as much being modeled in AH as should be to make our aircraft actually act and react like their real life counterparts would.  The game, and let's not forget that that's what is is, can't be expected to attempt to attempt the level of simulation that a simulator along the lines of the ones the airlines use would.

I for one would really like to have the HTC folks give us the facts and nothing but the facts about the detailed performance figures being modeled in each aircraft including lift, drag, airfoils etc. etc.  Then all the aeronautical engineering and physics types in here could really have a field day.  Unfortunately, I suspect that without a dark room, lamp and truth serum we're never going to hear anything from them on this subject.

Skeptically Yours,
Beeg
 

 

Originally posted by Tyro48:
Dale/Doug:

    I was wondering if the FM in Aces High models the adiabatic temp change over altitude and the relation that would have on how fast the engine temperature overheat would drop off as altitude is acquired. Seems to me the time it takes for the engine to return to a normal temperature is the same at sea level as it is at 25k, at an altitude of 25k the outside air temp must be somewhere on the order of -30 deg below zero and therefore the eng should cool much faster, agree or disagree?  

[Wlfgng]

hehe   'bout time  

[Rude]

Let me preface the following by saying that I have not flown above 12k personally, yet to understand aircraft performance, be it flight dynamics or cooling dynamics, you must first understand air density at altitude.

The idea of density altitude begins with the standard atmosphere, a table of air temperature, pressure and density at various altitudes. The actual values of all of these change with the weather. But, the standard atmosphere figures can be used to calculate for various altitudes how much lift a wing should produce, how much power will come from the engine or engines and how much thrust will push the aircraft along and how much drag should be produced.

Pilots need to adjust these theoretical values of lift, power and thrust to take account of differences between the standard atmosphere and the real atmosphere at a particular time and place. They use charts or aviation computers to say that the real atmosphere at a particular time has the density of the standard atmosphere at a certain altitude, which is likely to be different from the true altitude. The aircraft performs as though it were at the density altitude.

To say that a air-cooled piston engine would cool faster at a higher altitude than at sea-level just because it is colder at higher alt, is incorrect. The demands put on this engine at each alt in addition to many other factors will impact that cooling as well.

Toad...jump in here pls