Rear engine/motor AIR COOLING

[Winfield1990]

With a rear mounted engine or motor which would be th most efficient way of cooling , I read somewhere in a search with pros and cons that air cooling out the rear which im guessing blowing the heat away and not sucking in since its out the rear in the low pressure area.

Would be the most efficient but I am unsure , I would think radiator cooled with the radiator WAY in the front with the engine in the rear would have additional losses from pumping distance.

If air cooling through the rear is the most efficient choice would using an electric fan vs a fan ran from the motor itself be more efficient and offer adequate cooling with a temperature sensor regulating the fan.

Just slowly compiling ideas for a project cars a while down the road , I would want the car to be an economy car full electric but I may decide that I would just make it a hybrid driven only by the motor and the diesel engine just charges a supercapacitor... top speed around say 65 gears to have tons of torque to make up for the weight of the batteries..

[some_other_dave]

Unfortunately, heat does not transfer that well from metal to air, so you wind up needing lots of fins to make surface area for the transfer. Air also tends to have a real mind of its own on where it wants to go, whereas water can be pumped just about anywhere you want it to go.

As a result, air cooling tends to be more bulky and the engine pumping losses seem to be similar to, if not slightly more than, those for a water pump.

-soD

[bgd73]

you could learn from a beetle/912/914 or even the early 911 2.7-3. something flat six.

I wondered why they had air pumpin backwards through a shroud over the heads, tightly fit.... it is for homogeny. This goes way back to the orignal beetles, called tatra.
unlike liquid, air cooling needs some thought to gain the same consistent rutnime.

there is more ways than one to ship the heat out... but as air cooled goes, it needs protection at the same time, for consistent runtime.

[Bicycle Bob]

I don't think we can make a rule of thumb on this point. Long rad hoses do add a tiny bit of friction, or considerable weight if sized for truly minimal resistance. A rad in the nose is more likely to be able to get by with minimal fan use, but it can disrupt air flow over the rest of the shape. OTOH, scoops for natural air flow through the rear are another hazard to the low cd. Then you have to consider the often lower efficiency of air-cooled motors, which develop hot spots. Electric vs mechanical fan drive is affected by possibilities of variable fans and drives. Also, if your shape is streamlined and your weight is low, it pays to have batteries and or motors up front for natural stability without needing fins for balance in crosswinds. But then, you might want the sailing benefit of the fins if you have overturning resistance to spare. . . .

We can change anything, but we can never change just one thing.
Designer's Lament

[Winfield1990]

Excuse my arrange of my post , this post is just to clear up that I ment to say I read that rear air cooled was the most efficient.

So far in my design I would want to weld a frame like the flat skateboard frames that can be filled with batteries for pretty even weight distribution and improving aerodynamics , with the batteries spread through it should keep the weight distribution decently stable even with the motor and transmission being in the rear , being a rwd.

Taking from what you guys have said , I think I would need to have fan cooled , and radiator cooled , to offer adequate cooling... Generally ICE have air coole , water cooled , and exhaust which acts as a cooling function

I would love to have my radiator in the rear of the vehicle if I did both , how do you think a

transmission - motor - radiator - fan

in that positioning in the rear of the car would work... blowing through a mesh rear? With the radiator and the fan being electric.

[NeilBlanchard]

Water cooling makes it easier to preheat, and to speed up the warming up to efficient operating temp. For sophisticated air cooling in a rear engine car, check out the Tatra (T77?).

[chuckm]

Air cooling vs water cooling is also heavily dependent on engine size. Very small engines (read lawnmowers, weedeaters, etc.) can be air cooled using only unforced convection with minimal fins (I don't think wind moving at walking speed qualifies as forced). So, how big a engine are you looking at?

[dcb]

oh there's usually a bit of fan effect, even on a weed wacker. Here is one without the shroud (it needs the shroud) on a somewhat doomed project.

[Arragonis]

I think water would be better - my conclusion is based on :

- As mentioned better heat transfer from using water vs air
- You can run the radiator in the airflow, therefore only needing a fan when stopped and it gets too hot.
- If you want to go extreme you have the option of running an electric water pump too, so you could even shut off the water if the temps allowed it
- or you can use convection style coolling (water with no pump) like some bikes and older cars do.

And my wife's favourite :
- Its simple to extend the coolling system to provide heat to the passengers.

[Winfield1990]

Even though supercapacitors are heavier for the amount of stored energy Im leaning towards them because I want the least bit of maintenance as possible and quick recharging even though the weight will cut down a bit on my distance. Hopefully my weight reduction plans will keep it from being a big range problem.

I want to use a twin clutch transmission with probably 6 atleast 6 anyway. Because I would like to have each gears top speed set for cruising/driving for different circumstances with the pedal floored to my pedal governor which will keep the motor in the most efficient load. Which will also keep from pushing the motor alot keeping it cool.

example starting off and parking lot speeds I want 1st gear , and last gear highway speeds. while the gears inbetween fall onto areas speed limits or just a stepping stone gear to get to my speed more efficiently

Im not sure of how powerful of a motor I will need but I dont predict it being that powerful , im mainly relying on my gearing since my maximum speed will probably be around 60-65

Regardless of my cooling method I would do it by electrical means. I cant really give a range for the power of a motor I need you guys are more knowledgable than me. So maybe from what Ive said so far you can figure it would be if you could estimate the overall weight of the supercapacitors I plan on stuffing the frame with as many as possible or aiming for atleast 150miles with them on a charge IF POSSIBLE with them