Electric fan for engine cooling?

[Holst]

I think the main reason for can manufacturers stopping using engine driven fans were when transverse engine mounts became more common in FWD cars.
You cant put a fan in the wing of the car.
Electric fans are also cheaper and easyer to package and can be turned on and off with ease. This means that the fan can be turned off when the car is moving quickly. And also be turned on all the time when the car is stationary in traffic.

Im not sure there is any significant performance benefit on a car, there might be a small gain but I dont think this is the reason modern cars use electric fans.

Having said that.. on a heli engine the fan isnt in an ideal position as its not directly blowing onto the head. Having to route the air around the carb and onto the head using a duct isnt a pretty way of doing things.

I can definately see the advantage of using an electric fan on a heli. But 10% seems a bit optimistic to me.

Some PC cooling fans are VERY cheaply made and I wouldnt trust them on a heli. Although you can buy small 12v fans that should be properly ballraced and reliable.. panasonic make some nice fans..

[CChris]

Hi All

I have argued this may times on a car. If a electric fan is moving the same quantity of air as a mechanical fan, and the battery of the car is not discharging, an electric fan will use more energy than a mechanical fan because, the work the fans are doing is the same, but the electric fan gets its energy from a number of transfers of energy, each losing energy in the process. However and this is the big important bit (for cars anyway) the electric fan is switched based on temprature when needed, and normally car engines are under load when they are moving, and when they are moving the air is forced over the radiator anyway.

For a Heli - Don't know - Sorry

Chris.

[CChris]

Actually is does tanslate.

If the fan is moving the same volume of air over the engine as the mechanical fan, and it uses 200mAh for 8min on a 2s pack cooling, then its possible to calculate the power it used, and therefore the power gain in having the fan.


Chris.

[Holst]

Actually is does tanslate.

If the fan is moving the same volume of air over the engine as the mechanical fan, and it uses 200mAh for 8min on a 2s pack cooling, then its possible to calculate the power it used, and therefore the power gain in having the fan.


Chris.

But you dont know how much power the standard fan on the engine uses.
It may be using more than the electric fan but how much more is open to debate.

The claim earlyer in the thread is that the standard fan uses 20% of the power seems very high to me.

[unwind-protect]

The original thread I saw talked about using model aircraft ducted fans.

The thing about prop shaft driven fans is that they have to run at the same speed as the engine; what, about 10Krpm? Ducted fans can run 40Krpm and more, albeit needing some severe power. Most prop shaft fans are simple centrifugal fans; axial ducted fans at least look like there's been more though put into their design, though I've no idea if they move air more efficiently.

Also, start pushing the heli hard, and you have to richen up the mixture to keep the engine cool. If the engine can be cooled by air instead, then presumably it can be run much leaner, and so more efficiently.

(BTW, 0.2Ampere hour*8Volts/8 minutes = 12Watts. That is going to make no difference whatsoever, the efficiency gains must be somewhere else)

[electricsceadu]

my bell 222 uses the original cooling fan but has two 5cm pc fans feeding it and one 8cm pc fan drawing the hot air away due to cooling problems with a known poor cooling system on the mechanics
the lower 8cm fan doesn't last that long with the nitro getting into it
so just having a pc fan won't work long term and when it stops it will over heat and goodbye engine
my system will still cool if the pc fan fails (not as well but it does cool it)
i run off two 8.4v pp9 rechargable batteries in series giving around 18v fully charged, and i've not yet had them go flat in a days flying

[J-S-Q]

Just for the record, one of the guys in the Helifreak thread reckons he get's at least 20% longer flight time with his Odin than on his 700N or Stratus, with the same engine and fuel tank size -how much of that is down to more efficient cooling, I don't know.

[Ade_Law]

The main problem is finding a motor and fan that can cope with the vibration, Oil, dirt and gyroscopic forces.

The power gains are there. thats for sure. Im not sure its the 20% that some are saying I would love to know how they came up with this figure. It certainly has more power. As for weight if you use a normal 4000+ mah battery that would typically give 10 flights per charge on a normal 90 this drops to about 5 flights the weight stays about the same i think as you still have a fanshroud and what you loose in the mechanical fan you gain from electric cooling fan and esc.

If the fan fails the motor runs like its a couple of clicks lean. Not enough to damage it but enough that you notice. The big problem is if the fan motor goes short circuit as that shorts out the esc which shorts out the battery which if your using a single battery for the fan and rx that means you have no radio.

Ade

[unwind-protect]

The big problem is if the fan motor goes short circuit as that shorts out the esc which shorts out the battery which if your using a single battery for the fan and rx that means you have no radio.

That sounds pretty much like a theoretical problem than something you're likely to encounter in practice (don't most escs notice when the motor is stalled/ overcurrent situation occurs?); a fuse should mitigate that risk.

[andylinney]

Ok im going on my full size piloting experience here but that is not neccesarily a good thing. You could end up "shock cooling" an engine that way. This may not apply to model engines though.

A link http://en.wikipedia.org/wiki/Shock_cooling_(engines)

Still an interesting idea though.

Been a few years since I sat in the seat while I was flying but that wiki article is quite interesting...

I wonder if this application really negates the risk as the real risk on an full size engine is created by the very great temperature differences created during a prolonged descent from altitute (practice engine fail) where it's 'useful' if the engine keeps running throughout (my instructor always advocated 'warming the engine' during the descent at strategic intervals that helped position the a/c perfectly) even then, if my mind serves me correctly, the greatest risk was from carb icing and not from shock cooling.

On a single cylinder engine that was at rest the cooling rate wouldn't be massively accelerated by the presence of a fan and the pattern of cooling would remain the same, with the internals remaining hotter for longer. The instance of the fixed altitude and steady OAT would hopefully remove the major risk factors. I think it's another development that will perhaps become commonplace in time or, like so many others, die a death once it's been proved a gimmick - only time will tell...

[J-S-Q]

you still have a fanshroud.

I'm pretty sure that in the pictures of the Compass Odin that I have seen, there is no fan shroud -apologies if I'm wrong here.

[Holst]

The main problem is finding a motor and fan that can cope with the vibration, Oil, dirt and gyroscopic forces.

The power gains are there. thats for sure. Im not sure its the 20% that some are saying I would love to know how they came up with this figure. It certainly has more power. As for weight if you use a normal 4000+ mah battery that would typically give 10 flights per charge on a normal 90 this drops to about 5 flights the weight stays about the same i think as you still have a fanshroud and what you loose in the mechanical fan you gain from electric cooling fan and esc.

If the fan fails the motor runs like its a couple of clicks lean. Not enough to damage it but enough that you notice. The big problem is if the fan motor goes short circuit as that shorts out the esc which shorts out the battery which if your using a single battery for the fan and rx that means you have no radio.

Ade

If your looking for a suitable fan the Delta range are powerful and reliable
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