Fan to Shroud clearance

[Alfred]

I have yet to read somewhere if the fan-top should be close to the top of the Shroud or the other way around.

So:

Fan-top close to the top of Shroud
or
Fan-bottom close to the bottom of Shroud

Which one?

[tnreefguy]

I alway set mine on my extreme with equal distances. Also I have never had any cooling issues with a ys .91 doing that. Hope this helps.

[Alfred]

Thanks

I am actually asking a more fundamental question.
I the 15+ years that I have been doing it, I have always set the fan as close as possible to the top of the Shroud with no adverse effect.
But there has got to be one position where it will give maximum air-volume being transferred down the channel.

Example: Too close to the top..might restrict airflow that needs to bend 90 degrees.

In the middle might cause air-recirculation and create a partial vacuum, who knows?

If you have ever hovered on a still morning witha rich setting and close to the ground, you can see how the exhaust smoke starts to re-circirculate by going down 1st and then in a big round arc goes all the way around back over the top and through the rotor again.

There has to be one ideal position..which one?

[DavidH]

Alfred,
I prefer the fan to be at the bottom of the shroud. That way not much air bypasses and it goes thru the vent tubing over the head. That is how I have set the fan shrouds on MA helis since 1994. The bottom of the fan is nearly flush with the bottom edge of the shroud.

David

[Alfred]

See my whole point David :D

Three pilots and three different answers so far.
I have been setting mine to the top since my 1st MA heli which was the X-Cell30 that had just arrived in Australia.

Surely we have pilots here that have a good knowledge in fluid motion and should at least in theory give us a decisive answer :?:

I am in a hot country and so is David (I think).
We both do the opposite and both of us don't have overheating issues, but there can be just one position that gives maximum effect :wink:

[tnreefguy]

Then I would think David is right. With the fan shroud positioned flush with the bottom of the fan this would create more area for the blades to strike through.

[Peter]

On the Spectra G , where the shroud height is fixed, the fan mounts as low as its possible for MA to get it ; there's approx 6mm, 1/4 inch between the top of the fan and the shroud.....

Maybe I've unknowingly been doing the right thing for many years with all my X-cells , ie keeping the shroud as high as possible !!

As Alfred said , a fluid flow experts opinion might be handy.. then again , it's human nature to disregard lots of " experts " anyway .... :wink: :wink: