From: Dale_R <dale.rog@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Tue, Aug 2, 2011 18:02:27 GMT+00:00
Subject: [FlyRotary] Re: Flywheel Machine Work

On 8/2/2011 5:05 AM, David Leonard wrote:
> ... I am starting to think that the whole science of balancing is
> just a gimmick. Despite the old balance hole being mostly drilled
> away, the new balance holes are on the opposite side of the flywheel. !??
>

Dave,

Balancing is a procedure that falls right on the edge between
science and black art. At high RPMs, changes "out of plane" can become
critical.

As an example, when I started balancing wheels all we had were
bubble (static) balancers, and - because the weights had to go on the
rim edges - we would find the amount of weight, then split it, e.g. two
half ounce weights, one on the inside and one on the outside. ~Most~ of
the time it would put give good freeway speed balance. Sometimes,
though, we'd still get an out-of-balance wobble in the wheel due to the
imbalance being off center of the c.g. plane of the wheel.

Then affordable (for a small shop) dynamic balancers came along, and
we discovered that, most of the time, less weight was required on one
side of the wheel than the other, often not even opposite each other, to
bring the center of balance the same as the center of rotation.

Drilling balance divots on only one side of something like a wheel
can create a similar situation - where the static balance is correct but
the center of balance is no longer the same as the center of rotation.
It takes sophisticated equipment and an equally sharp operator to get it
right.

BTW, FWIW ... For an average car tire with 25" diameter at the
tread, at 60 MPH, the wheel is turning ~7950 RPM.


--
Dale_R
Cozy MKIV #497


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