Author Topic: Did real aircraft engines overheat at military power? (Read 1132 times)

BenDover · « **Reply #15 on:** May 26, 2004, 03:08:51 PM »

No they caught fire

frank3 · « **Reply #16 on:** May 26, 2004, 03:10:52 PM »

Just see how fast your engine screams down to the engine walhalla after your radiator has been bashed!

BenDover · « **Reply #17 on:** May 26, 2004, 03:14:31 PM »

valhalla?

Pyro · « **Reply #18 on:** May 26, 2004, 03:19:09 PM »

Time limits and temp limits are two different things. Games merge them together purely as a gameplay decision. I posted some info regarding the purpose of time limits in an earlier related thread.

flakbait · « **Reply #19 on:** May 26, 2004, 03:34:24 PM »

Quote

Originally posted by GScholz
There are a lot of factors. Some are engine specific others are aircraft specific. Most WEP or MIL restrictions had nothing to do with overheating the engine itself, but rather overheating specific parts in the engine, like piston heads and ball bearings. The 109s had a 30 minute restriction on the "combat and climb" setting (MIL) and a 3 to 10 minute restriction on the "emergency" setting (WEP) depending on model.

One good example of this is the P-38. Early model P-38s in Europe actually had problems with too much cooling at high altitude. They had problems keeping the engines hot enough for effective and reliable operation, while at the same time they had problems with over-revving the turbos, burning out the ball bearings.

So my conclusion is that engine cooling are rarely, if ever, a factor in restrictions on engine power settings.

You're half right. Turbochargers didn't use ball bearings, they used a thin film of oil that was circulated between the turbo shaft, turbine bucket wheel, and compressor wheel. If you overheat the oil by over-revving a turbo, the oil becomes almost like glue. As a result you'll freeze the turbo up and possibly melt the shaft or wheels at any contact points. Veeery messy. Sometimes over-revving a turbo would cause the compressor wheel to explode. Several experimental and the odd operational aircraft during WW2 suffered turbo explosions.

Overheating an engine depends on a variety of things. How close the cowl is to the engine, how big the radiators are, what the power output is, how much compression is present in each cylinder, RPM limits, radiator size and location, and a mess of other stuff. If you want a comparison: Bf-109G6 vs. C-47. The 109's DB engine was always overheating for a multitude of reasons that are still being debated today. Messerschmitt said it was because DB couldn't design a proper oil cooling loop, while DB said Messerschmitt had the cowling too close. Either way, the engine would readily cook itself if run at Mil for too long. Now look at a C-47; no power limits. You could run at Mil all day long and hardly put a dent in those bullet-proof radials. It's a combination of many factors that make an engine seize because of over-heating.

Restricting power because of cooling problems was present in the P-38 models built prior to the J. They didn't have enough control over engine temps, or over the air temp entering the engine from the turbo. As a result engine power was restricted to 1240hp. Once the J came along that restriction was lifted, allowing the J to make 1425hp at mil and 1600hp using WEP.

-----------------------
Flakbait [Delta6]
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Sled · « **Reply #20 on:** May 26, 2004, 03:44:05 PM »

Quote

There are a lot of factors. Some are engine specific others are aircraft specific. Most WEP or MIL restrictions had nothing to do with overheating the engine itself, but rather overheating specific parts in the engine, like piston heads and ball bearings.

Your right there GScholz. The main factor on engine tempature is going to be your rich and lean settings, which are going to be dialed in based on you EGT readings. You are going to be adjusting your the fuel mixture of your engine based on the ALT that you are flying and mainly on what your EGT is telling you for CLY head tempatures. The first thing that is going to burn up in an engine that is running hot, because for lean mixture, (assumeing cooling system is working properly) is the pistons and the valves. These items have no Direct contact with the cooling fluid, but are in direct contact with the hotest gasses. Running an engine too lean is going to burn it up, running an engine to rich will cool CYL temps but also leads to fowling of the combustion chamber, and reduced power. The best running engine, as far as power, is one that is about to burn up.

WEP alone should not lead to an engine overheating (again assumeing the cooling system is working properly). However it will lead to much greater wear and tear on the engine compoents, mainly (but not limited to), pistons, crankshaft bearings, wristpin bearings, and head gaskets. Mixture will cause an engine failure, but this will normaly happen before the cooling system is overheated, to the point of engine failure.

got to go for now, might add more later.

Scootter · « **Reply #21 on:** May 26, 2004, 04:10:11 PM »

Quote

Originally posted by txmx
Any gasoline engine can over heat.
But i would think the higher you go and the thinner colder air would prolong the heating process.

The thinner the air (less dense) the less heat it can absorb, so the higher you go the harder it is to keep the engine cool.
The colder air is due to the lower density more then any other factor.

The denser the medium the better the cooling it can provide.

Remember in space no-one can hear you scream (no air = no sound)

Scootter · « **Reply #22 on:** May 26, 2004, 04:19:42 PM »

Quote

Originally posted by SLED
Your right there GScholz. The main factor on engine tempature is going to be your rich and lean settings, which are going to be dialed in based on you EGT readings. You are going to be adjusting your the fuel mixture of your engine based on the ALT that you are flying and mainly on what your EGT is telling you for CLY head tempatures. The first thing that is going to burn up in an engine that is running hot, because for lean mixture, (assumeing cooling system is working properly) is the pistons and the valves. These items have no Direct contact with the cooling fluid, but are in direct contact with the hotest gasses. Running an engine too lean is going to burn it up, running an engine to rich will cool CYL temps but also leads to fowling of the combustion chamber, and reduced power. The best running engine, as far as power, is one that is about to burn up.

WEP alone should not lead to an engine overheating (again assumeing the cooling system is working properly). However it will lead to much greater wear and tear on the engine compoents, mainly (but not limited to), pistons, crankshaft bearings, wristpin bearings, and head gaskets. Mixture will cause an engine failure, but this will normaly happen before the cooling system is overheated, to the point of engine failure.

got to go for now, might add more later.

To a point, if you keep leaning, things get cool again (less fuel to make heat) power falls off and depending on the intake system and fuel distrubution the engine may get rough.

http://www.avweb.com/news/columns/182135-1.html#engine

http://www.avweb.com/news/columns/182084-1.html

If you want to learn how to run an aircraft engine look here folks..

This guy is an AIRCRAFT GOD IMHO

http://www.avweb.com/news/columns/182146-1.html

GScholz · « **Reply #23 on:** May 26, 2004, 05:16:55 PM »

Quote

Originally posted by Scootter
The thinner the air (less dense) the less heat it can absorb, so the higher you go the harder it is to keep the engine cool.
The colder air is due to the lower density more then any other factor.

The denser the medium the better the cooling it can provide.

Remember in space no-one can hear you scream (no air = no sound)

This is wrong. The air is cooler at altitude because the only thing heating the air is the earth and particles in low altitudes. Ambient temperature more than anything dictates how well the air can cool your engine. At 30K and -50C the air has much a better cooling effect than at SL and +20C, even if the air is denser at SL.

GScholz · « **Reply #24 on:** May 26, 2004, 05:18:03 PM »

Flakbait, I stand corrected on the P-38 turbo.

Scootter · « **Reply #25 on:** May 26, 2004, 06:18:29 PM »

Quote

Originally posted by GScholz
This is wrong. The air is cooler at altitude because the only thing heating the air is the earth and particles in low altitudes. Ambient temperature more than anything dictates how well the air can cool your engine. At 30K and -50C the air has much a better cooling effect than at SL and +20C, even if the air is denser at SL.

Sorry I don't agree

Airplanes engines (not turbine) run hot at high alt. due to less air flow (less dense air) just like a wing looses lift.

Read the operating man. on a Turbo Charged air-cooled sometime.

DRY ADIABATIC LAPSE RATE.? If a par-cel of air is lifted, its pressure is DECREASED, since pressure decreases with height, and its temperature falls due to the expansion. If the air is dry and the process is adiabatic, the rate of temperature fall is 1?C per 100 meters of lift (10?C per Km), or 5 1/2?F per 1,000 feet of lift. If that parcel descends again to higher pressure, its temperature then INCREASES at the rate of 1?C

http://www.infodotinc.com/weather2/2-18.htm

Regards:

GScholz · « **Reply #26 on:** May 26, 2004, 06:26:44 PM »

P-38s ran too cool at high alts, while they didn't have any difficulty at low alts.

Sled · « **Reply #27 on:** May 26, 2004, 06:31:41 PM »

Quote

To a point, if you keep leaning, things get cool again (less fuel to make heat) power falls off and depending on the intake system and fuel distrubution the engine may get rough.

Well yes of course, if you turn your mixture down far enough, the engine quits. no fuel means no go.

I was only speaking of mixture rates where the engine will run and produce usable power.

Also keep in mind I am being VERY general here, I am not trying to tell people how to run their engine on their plane. I was just speaking basic therory, on engine operations, and the effect of mixture.

Sled

Scootter · « **Reply #28 on:** May 26, 2004, 06:53:39 PM »

Quote

Originally posted by SLED
Well yes of course, if you turn your mixture down far enough, the engine quits. no fuel means no go.

I was only speaking of mixture rates where the engine will run and produce usable power.

Also keep in mind I am being VERY general here, I am not trying to tell people how to run their engine on their plane. I was just speaking basic therory, on engine operations, and the effect of mixture.

Sled

True, but Lean of Peak LOP operation will produce usable power and quite a fuel savings.

You can have your cake and eat it too.

Scootter · « **Reply #29 on:** May 26, 2004, 06:59:16 PM »

Quote

Originally posted by GScholz
P-38s ran too cool at high alts, while they didn't have any difficulty at low alts.

I have read that the pilots of 38 froze there butts off, using an electrical heater or some such. But not that the engines ran too cold, if true it may have a lot to due with the hi alt interceptor design and liquid cooling with large coolers (but they should have been fine at lower alt then).