Electric fan for engine cooling?

[J-S-Q]

Has anyone looked into the idea of removing the engine fan and using an electric fan to cool the engine instead (as used on a Compass Odin)? Apparently there are significant power gains due to more efficient cooling. There's a discussion here with a guy who's trying it in his Knight 3D:-

knight 3d with esc cooling fan.... - HeliFreak

[glen_j]

not something i'd try if the battery or the esc has problems you'll destroy the engine very quickly

[Tom Burgess]

Would the power gains be enough to replace the extra weight involved in the batt and esc to control it?

[J-S-Q]

Well in the thread that I linked to, the following was posted:-

"ON the Odin the power gain is reckoned to be around 20% from not having an engine driven fan (and I believe it) - the fan is driven by a brushless motor of the same type found in miilions of PCs which have a mean time before failure of thousands of hours - in short of the dozens of things that can go wrong the fan is probably the least likely to fail - think of cars - electric driven fans replaced belt driven ones on the majority of cars years ago. THe fan draws around 200mAh for an 8 hour flight"

[J-S-Q]

Would the power gains be enough to replace the extra weight involved in the batt and esc to control it?

Yes that's clearly a valid question but don't forget that you save some weight by ditching the engine fan and (possibly) the shroud and you have less drag on the engine.

[J-S-Q]

Another benefit is that you can keep the fan running after the flight. I think that some data recorders have shown that the hottest engine temperatures can actually be registered immediately AFTER landing.

[unwind-protect]

Makes sense; the core of the engine is still hot, and you've lost your source of cooling.

I was reading about this a few days ago in a completely different application (cooling 4-strokes); someone suggested you could hack the sensor of a carbsmart, and feed the carbsmart output to the ESC for speed control.

[Tom Burgess]

Another benefit is that you can keep the fan running after the flight. I think that some data recorders have shown that the hottest engine temperatures can actually be registered immediately AFTER landing.

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.

[marktigere1]

Just bear in mind that cooling fans in computers are not subjected to high fequency vibrations.

I would be surprised if the fan bearings and even the motor would last long.

Maybe Compass have found this out?

[jamiem]

A pc fan is not subjected to the tortures of massive g forces associated with the very sudden direction changes of an rc Heli. It's also not doused with oil, nitro, dirt, dust and clutch particles. I'd be amazed if they could put up with it long term and I'm certainly not about to risk an engine to find out.

I'm sure you'd get a better power increase from going flybarless and losing all the associated parts and drag.

[SRH990]

I have to say, the experiences I've had with PC cooling fans is that they're not actually that long lived as many have plain bearings, not ball-races.

What I want to know is what sort of setup is the guy running where the cooling fan only uses 200mah in 8 hours, it must be a hell of a fuel tank

The point about engine temps rising after shutdown really isn't a problem, with existing setups as soon as you shut the engine off the fan stops anyway!

I'm sure a small brushless motor intended for model use would work quite well in this application although you'd need careful design of the fan and ductwork to give good efficiency with low current draw but would it be worth all the effort? I know Compass have gone down this route with the Odin but if it gives that big an advantage, why haven't any other manufacturers used a similar system?

[robgt]

What I want to know is what sort of setup is the guy running where the cooling fan only uses 200mah in 8 hours, it must be a hell of a fuel tank

It's an electric fan
Just hook it up on the bench and let it run for 8 hours
Cheers,
Rob

[arby]

What I want to know is what sort of setup is the guy running where the cooling fan only uses 200mah in 8 hours, it must be a hell of a fuel tank

If you go to the link that was referred to at the start of this thread it says

Actually on the Odin fan draw is 200mAh per 8 minute flight

Bob

also if you carry on reading (like wot I should have done!) it then quotes 8 hours ... confused

[SRH990]

It's interesting that they claim 20% of engine power goes in spinning the cooling fan, the estimate of the amount of power needed to spin a flybar is - you guessed - 20%, remove both and you've nearly doubled power to the main shaft.

I can understand that the gain with using an electric cooling fan is that you are actually taking the power from a battery, possibly the receiver battery. If the engine is putting out around 2.5bhp for a 90 then 20% is 0.5bhp, converting this to watts you get 368W, on a 3S lipo that's 33A! On this basis an engine driven fan must be very inefficient and using 200mah on an electric fan in 8 minutes is pulling around 0.14A.

[J-S-Q]

I know Compass have gone down this route with the Odin but if it gives that big an advantage, why haven't any other manufacturers used a similar system?

Well arguably this is a new idea in the context of rc helis -who knows, perhaps it will become more common in the future? It was pointed out on another forum that the car industry abandoned engine driven fans a long time ago -I guess that would suggest that they are less efficient.