Model Forum / General / Models / July 2009

"COME ON TIM!!"

    BugBear

Blu Tak.

John S.

If it was a model aeroplane prop or impeller you would use a prop balancer
which is a shaft on low-friction bearings, sometimes magnetic, and sand off
the heavy blade.  You won't find one that will do a fan blade though.

Also, it's possible and maybe likely that the noise and vibration somes
from the airflow over the blades themselves.  They're not "designed" in
any aerodynamic sense but are most likely cobbled up from whatever looked
good to the designer.  Well probably, anyhow, unless it's a very expensive
fan.  The poor airflow characteristics and the vortexes that'll be forming
all over the place at the tips and the trailing edges of the blades will
cause quite a bit of noise and vibration anyway.

On a model aeroplane the prop shape can have a marked effect on the noise
of the model - some blade shapes (and blade materials) are much quieter
than others, even when heard over the noise of an IC engine, and that's
largely for the reasons I've given above.

You can buy special "quiet" fans for electronic equipment, for instance,
which have had some effort into making good blade shapes for quieter
airflow, but the cost for doing that for a fan would be prohibitive.

Nobby

First see that the blades are not bent and are tracking in-line properly,
both front and back. If you can verify that the blade lengths are equal,
when running the heavy blade will be the first to touch a piece of chalk
moved slowly toward the outer edges.

Unless the blades are not tracking, static balance is adequate but you need
a low friction mount to do it.

Don Young (USA)