View Full Version : Fan tip clearance

17-Apr-11, 12:01 PM
I just went to line up my fan & frame and realised I have made a big mistake:o:(. Basically the frame wont bolt back on because the stators and rear cone are too far forward :(. My fault I should have checked before glassing in the stators:o "lesson learned though"! I forgot that the blade tips are narrower than the hub:o.

I am just cutting out the stators out of the duct now, but measuring the distance the fan tips are from the splitter plate I think they are going to be very close, maybe too close for comfort. I have now removed the stators and the blades do touch the slpitter plate, which is weird as the frame & splitter plate are original to the craft so must be different fan dimensions.

What would the minimum recommended distance be from the tip of the fan blade to the leading edge of the splitter plate to allow for any flexing in the fan blades?

The fan is on a rotax 503 so when looking from the rear of the craft the fan is rotating anti clockwise. Would the fan be flexing backwards or forwards under load?

Keith Oakley
17-Apr-11, 03:57 PM
I'd recommend 100mm clearance between the fan tip and the stators for noise reduction purposes. Fan tip clearance to duct should ideally be 3-5mm to reduce tip airflow turbulence and thus noise but practically with ducts and fan frames flexing under varying loads most racing folk have 8-15mm tip clearance. Non circularity of ducts is also an issue here! Tip clearance to splitter is generally 20-25mm. Blades normally pull forward under load but will whip back under some circumstances eg on bumpy transitions.

17-Apr-11, 05:00 PM
Thanks Keith