Aero spokes, potential problems?
 

Just pondering some thoughts.

It ocurred to me today, that aero spokes in all there splendor and beauty, may actually pose some serious problems at high speed. I got to thinking about the absolute necessity of making sure they are perfectly aligned when tightened, or truing up a wheel. They are a great visual guide to help you make sure your spokes are not twisted, compared to round spokes, but if one was, the result could be catastrophic.

Suppose for instance, that one aero spoke on a wheel was ever so slightly twisted. The resulting force would be likened to a miniature propeller that would want to pull the wheel to one side or the other while spinning very fast.
My thought on this, from building airplanes myself, seems reasonable. If you had one propeller blade slightly offset with differant pitch, the result is an enormous amount of vibration which would tear the airplane apart. This would not be quite as serious on a bike, due to the small cross section of the bladed spoke itself. However, I would think that one spoke slightly out of alignment could be a contribution to noticable shimmy, when the bike frame itself seems to be the unlikely cuplrit due to it's engineering. Does this not make sense?
I suppose one could figure out the actual thrust produced by a specific spoke with a certain cross-section at a given speed of say 50mph. Those Mavic spokes are pretty wide. I wonder how much of a concern this really is, when the designers build wheels with these spokes.

ahhhh, ok, thats a good question,

I did find out that the 19.99 Db4 Wireless computer from Performance doesn't have a Aero spoke compatable magnet, that was a problem. Then when asked if they sold Aero compatable magnets I was told no, so I finished my order then googled aero spoke magnet, guess who came up first, thats right Performance, then I had to call back and amend my order which turned out to be a good thing becuase they had it on hold becuase they don't sell Size 13 booties even though the web site said 'in-stock", so I was able to cancel the said booties and order the compatable magnet ($1.95).

Did that answer your question?

mmmm, beer for lunch, but I digest.....

I think that you worry too much.

For bvfrompc, do your aero spokes go round when they reach the nipple? I have shimano wheels with bladed spokes, but the blades turn round at the nipple. I had to mount the magnet right near the rim and the magnet-picker-upper-transmitter-thingamabob just under the brake pad on the fork, but it worked. Cheapo Ascent computer, too.

For Patriot - without talking out of my a** about aeronautics and propulsion, I think there are formulae which take surface area of the blades, angle of blades, rpm's, etc which would accurately compute how much side force could be imposed by misaligned bladed spokes. However, I think that a majority of the spokes would need to be misaligned in exact wrongness in order to have any effect. If one spoke is tweaked at a 45 deg. angle and the next is only tweaked 15 deg, there's a certain turbulence that is created from one to the next.

Theoretically, I don't think (even with the wider blades) you have enough blade surface area pushing air at a fast enough rpm to generate any noticeable side force. To pull an airplane, you have 3-5 blades that are 3' +/- long and probably 6" wide, all pitched to the same angle, spinning 2-3 thousand rpm...and probably much faster...since I don't really know squat about airplane motors.

Bicycle wheels have 1/4" - 1/2" blades spokes spinning about (at most) 200 rpm on quick descents.

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I've avoided Aero Spokes precisely because I don't want to go fast enough to find out the answer to your question.

I'm switching to sharpened aero spokes after seeing the damage from that squirrel...

My thoughts are more or less with Mo'Phat. I really don't think it would be all that noticable, but was just curious. I know that on model airplanes, you're taking about blades going 10,000rpm, so if a bike wheel went that fast, you'd have bigger things to worry about, I think. :p

I agree.

At 30 mph the wheel will be turning at 400 rpm which is pretty slow for a propeller, and the propeller will be operating in the wake of the tire. The side force and the drag reduction will therefore be pretty small. The main benefit will be the avoidance of spoke twist in the build.