How far will blades flex?

[Smithson]

How far will 8 foot pine blades flex?  Between the tips of these blades and the tower is about 12 inches.  Should I just go ahead and make counterclockwise blades?  Sorry about poor quality to the pictures.





Thank you.       Archie Smith

[Flux]

Normally I would expect 12" tip clearance to be adequate. The flex from wind pressure alone is quite modest but when you include the gyro effects things can be very different under strange conditions. So much depends on the site that you never can be sure.

It is generally considered that the worst case is when it yaws into furl during a gust. On this basis it seems to be accepted that with the offset as normally used it is actually safer for the blades to rotate the other way but I wouldn't guarantee that reversing the blades will help in every case.

If you are in doubt it will not hurt to make the blades for the other rotation but on strange sites anything can happen. If it was a guaranteed cure I am sure this reverse rotation would become standard but in reality so many machines work with clockwise rotation and the usual offset that for most sites it really is not an issue.

Flux

[birdhouse]

if you're really worried about it, you could put a layer of fiber glass on them to limit flexing.  this may make them thicker than you want, so they could be sanded a bit before the fiberglass goes on to make the end product the thickness you want. 

my 8.5' blades only has ~8" of tower clearance.  granted the blanks were laminated from multiple pieces of clear fir.  then i put one layer of 6 or 8oz (can't remember) fiberglass on them.  they are VERY stiff. 

it looks like you welding is complete, but it is also possible to tilt the entire (blade/rotor/stator) assembly back by a few degrees.  you could just drop in an angle grinder w/cut off wheel into the main connection point, bend it back a bit, then re-weld it. 

either of these ideas sound far better than carving a new set of blades! 

adam