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Why the engine get overheat while slow speed?


MivwTaupos
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Most Fighters with non radial engines use liquid cooling to stop the engines from over heating, they achieve this by cycling the fluid through the lines to radiators which rely on air being rammed through them to achieve this effect. with less airspeed comes less airflow, with higher engine settings comes more heat. In short dont use high power settings at too low of an airspeed, this applies in most aircraft in general. as for the 109 it does also have this occure however the 109 uses MW50 water injection which helps to cool the engine and fight knock despite being at higher settings. It does still occure and i have tested this in the new damage model multiplayer servers, the mustag and spitfire also have this. Before the update for new dm testing the spitfire would pour out smoke and the mustangs engine would just fail without smoke. not the case now. as for the 190 i havent tested it however it should be fairly similar to the 109.

 

The P47 is a radial but does feater water injection and i've noticed that even with the cowl flaps fully closed that the temps still stay low despite lack of airflow.

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The P47 is a radial but does feater water injection and i've noticed that even with the cowl flaps fully closed that the temps still stay low despite lack of airflow.

 

With cowl flaps closed there is quite a lot of airflow still. Above 225mph cowl flas in p-47 must be 'closed' position but this does not mean that airflow is cut off.

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With cowl flaps closed there is quite a lot of airflow still. Above 225mph cowl flas in p-47 must be 'closed' position but this does not mean that airflow is cut off.

 

yeah i meant with respect to the flaps themselves, if you did that in a yak 52 the engine would cook faster then bacon

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Everytime when I stall, my engine come out with white smoke. is it also same with bf109k4?

 

Because at low speeds, the airflow through the radiators is reduced and they aren't big enough for adequate cooling. The solution is to throttle back so the engine survives and drop the nose to speed up. Using larger radiators would just create excess drag, slowing the aircraft down.

 

That's why the radiator in your car has fans on it--to provide enough cooling airflow even when driving at lower speeds.

 

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Main difference between cars and planes is very nature of this machines.

Let see example look at the car which is equipped with 250bhp engine, driver is not able to use this power for longer periods of time, when driving slow driver is able to use only fraction of full power or it can use full power but only for fraction of the second.

I can't imagine situation which 250bhp car with engine 100% loaded at 1st gear for couple minutes continuous can you ??

Situation in planes are completely different, pilot is able to load it's engine 100% even at 0 velocity(take off conditions), pilot is able to load engine 100% for very long periods of time, Plane's engine works in completely different environment.

If you would mount automotive engine in to plane it would perform much worst because that engine wasn't designed for that kind of application.

Plane's engine and its cooling system is not designed to perform at max power and very low speeds.

Any way imho Spitfire has the biggest radiators from all DCS warbirds and it is the slowest airplane with excellent low speed performance, it should not have problems with low speed flying, I'm not talking here about climbing vertically with almost no speed :)

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Main difference between cars and planes is very nature of this machines.

 

I can't imagine situation which 250bhp car with engine 100% loaded at 1st gear for couple minutes continuous can you ??

 

If you would mount automotive engine in to plane it would perform much worst because that engine wasn't designed for that kind of application.

 

There are examples of car engine's that have been adapted for use in aircraft, specifically ultralights and home builds and they have performed really well.

 

It doesn't mean that if you have a 250BHP car engine it can't take full throttle/load for a long period of time however. I think you would be surprised how well engineered a car engine is. They have to pass strict performance and durability checks before they are signed off to be fitted into a vehicle. I've spent the last 21 years working in R&D for road/race engines. We have had engines run at both peak power and peak torque conditions for hundreds of hours on test beds and they have survived. Ok a handful do blow up at times, but you strip it, find out what component failed, update the design and repeat the test. Modern engines are extremely robust, especially the higher performance ones. Ok running it on a test bed is cheating a bit, as we have all the cooling we need to hold a given coolant out temp and pressure, where as in the vehicle it would never see the conditions it would see on the test bed, but the engine would be fine, it's the application it's put in that causes the problems!.

 

What we have here is an engine cooling problem at low airspeeds, and Merlin's were known for this for the reasons stated above, the rads were too small a surface area to give adequate cooling on the ground or low airspeed at high power settings. The same thing applies with car engines too, no forward speed and it would soon overheat.

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There are examples of car engine's that have been adapted for use in aircraft, specifically ultralights and home builds and they have performed really well.

 

It doesn't mean that if you have a 250BHP car engine it can't take full throttle/load for a long period of time however. I think you would be surprised how well engineered a car engine is. They have to pass strict performance and durability checks before they are signed off to be fitted into a vehicle. I've spent the last 21 years working in R&D for road/race engines. We have had engines run at both peak power and peak torque conditions for hundreds of hours on test beds and they have survived. Ok a handful do blow up at times, but you strip it, find out what component failed, update the design and repeat the test. Modern engines are extremely robust, especially the higher performance ones. Ok running it on a test bed is cheating a bit, as we have all the cooling we need to hold a given coolant out temp and pressure, where as in the vehicle it would never see the conditions it would see on the test bed, but the engine would be fine, it's the application it's put in that causes the problems!.

 

What we have here is an engine cooling problem at low airspeeds, and Merlin's were known for this for the reasons stated above, the rads were too small a surface area to give adequate cooling on the ground or low airspeed at high power settings. The same thing applies with car engines too, no forward speed and it would soon overheat.

 

For longer high power loads engine need different kind of care, for example oil cooler, bigger oil reservoir, 15L of oil instead 4-5L which will be sufficient for car application, etc. etc. But you need to upgrade engine and accessories for aerial use.

believe me ww2 war plane engines were robust as well, there is no harder test then combat test :)

I am just shocked how well Bf-109's cooling is performing compare to spitfire's, in bf109 you can hang plane on prop and only then you will see coolant temp rising, when spitfire's cooling problem appeared much earlier.

My main message was that both engine's aren't prepared for extremes loads at very low speeds, but the aerial application pilot can exceed limitation much easier then in car application.

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Automotive engines have been used on aircraft for a very long time, it significantly increased with home built aircraft and ultralights becoming mainstream, VW bug engines are the most common examples that can be seen in the application of homebuilts however there are also a few Cessnas flying with V8s as seen here https://youtu.be/rpZYfd0GzuQ, there are also a few kit builts flying with firewall forward CAM 100 engines which are based on the honda civic engine.

 

Additionally the most commonly used engine i can think of for ultra lights are rotax engines which have also been used in motorbike racing. most of the issues and challenges faced by using these types have already been pointed out by people above, generally car engines tend to be heavier with different tollerances that are made to be run at varying loads throughout its use where as a lot of aero engines generally cruise at one setting, climb at another and descent with a third. Not sure what the failure rate is when using such engines but i suspect its fairly low given most are run on experimantal reg and the loads should be lower unless using gear reduction to stop the prop overspeeding.

 

as for cooling issues well as stated above, not enough airflow through a radiator means not enough cooling and hence higher temps, bigger radiators generally mean more drag and hence more power needed to overcome this hence why radiators generally seem to stay fairly similar in size. a happy compromise so to speak.

 

The reason you might find temps in the 109 stay lower then the spitfire is due to MW 50 being used which uses a water methonal mixture iirc to cool the engine and prevent knock, just how effective this would be in a stall with stupidly high power settings im not sure, i do know that a 109 recently crashed at duxford due to the radiators being closed and the engine getting too hot, that being said im not sure if mw50 is used now or not. i would think unlikely.

 

edit: have also heard stories of certain aero engines being used as power plants for ground stations in remote places, might be the m14p from the yak though i could be wrong.

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Just keep in mind that we are comparing modern engines with engines designed in 1930s, back then those engines were high performance units and had no match. Now automobile engines as well as aerial engines are used in different arias but those are no longer high performance units.

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