[Paddlewise] Flutter

While almost a novice with GP (I do own one!) I have spent
most of my youth rowing, and those effects -
the flutter and the gurgle - I remember well.

The odd gurgle is not cavitation, but air being sucked
down along the shaft, due to too enthusiastic paddling,
or rowing. Ease off a little and it disappears. It destroys power
and is annoying!

The flutter is also pretty well known - if the foil is very thin
it will bend along the edges as power is applied, and any kind
of foil that lack stiffness and is badly balanced will flutter,
no question about that. A helicopter rotor blade is a typical example:
Before carbon could create blades as stiff as you wanted, the
only cure was to add weights along the leading edge of the blades,
as with any foil (at subsonic speeds), the center of lift is at approx. 
25% chord, that is 25% of the width of the blade, so that's where
the center of gravity, and torsion, also have to be, unless brute force
and extreme stiffness can be applied. Sadly a GP can't be designed that
way, as the blade is symmetric, so it needs to be stiff, very stiff!

The thinner the blades, the more careful the design has to be to 
avoid flutter - remeber that a yuloh, the Chinese type of sculling oar,
has sharp rectangular edges, thus is fairly thick at the edges,
most likely to avoid flutter. 

I bet an advanced wing paddle also is very well balanced along the
shaft, again to avoid flutter. It is actually better to have too much
weight forward the torsional axle, as that acts as active anti-flutter
device, while perfectly balanced foils are not prone to flutter, but
if they somehow do start to flutter (say after banging them into a 
stone), the flutter will not be violent, nor accelerating.

Good Night!

Tord



-- 
Be Yourself _at_ mail.com!
Choose From 200+ Email Addresses
Get a Free Account at www.mail.com
***************************************************************************
PaddleWise Paddling Mailing List - Any opinions or suggestions expressed
here are solely those of the writer(s). You must assume the entire
responsibility for reliance upon them. All postings copyright the author.
Submissions:     PaddleWise_at_PaddleWise.net
Subscriptions:   PaddleWise-request_at_PaddleWise.net
Website:         http://www.paddlewise.net/
***************************************************************************