"True Negative Drag" in bicycle wheel brochure - possible?

[johnSchwaner]

Interesting in a aerodynamic expert opinion of the term.

A $3,000 bicycle wheel brochure advertises "true negative drag". "using the most difficult wind tunnel testing protocol".

Possibly these wheels don't require that I install pedals as the bike will accelerate on its own.

But seriously, possibly this is a 'term of the trade" that I am not familiar with. Or just advertising fodder.

 

[40818]

i think , without predjudice, that the term "NEGATIVE DRAG" in this ocntext is just bollo*s.
Yup, your right it all sales talk.

 

[IRstuff]

I think that the best you could hope for is "zero" drag. However, even that seems unlikely. The shuffling of air around an object still requires work to expended, hence, must be reflected as a drag.

TTFN

FAQ731-376

 

[RPstress]

Is it just possible that the wheel creates aerodynamic thrust due to its rotation? Maybe it has little features on the tire like the cups on an anemometer! Even if it did make some thrust, it seems very unlikely that it could exceed its drag.

 

[johnSchwaner]

Thankyou for your reply.

 

[btrueblood]

Does a sailboat sail produce "negative drag"?

...well, no. It can produce a lift vector if oriented properly to the the wind, and that lift vector, combined with a keel or other suitable resistance, can be directed to provide a useful thrust, usually in a direction perpendicular to the wind velocity.

Could one of those spokeless wheels act like a sail, and produce net thrust from a strong crosswind? Well, maybe. But there's no good (efficient, effective) way to counterbalance the drag force acting sideways on the bike without a third wheel, or a way to lean off one pedal and still control steering, brakes.

 

[GregLocock]

First law of thermodynmaics should cover it. Where is the energy coming from to generate this thrust?

I agree in a cross wind there may be some thrust available.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[EngineerMicah]

The 'wheel' could have a net drag in the direction of travel - but the frame would likely have more drag than normal - so the net effect may be lower overall drag. A bike and rider are a system its the whole thing, not just a component. Sounds like marketing.

 

[swearingen]

I'm curious - in a no-wind situation, how could a wheel have a net drag in the direction of travel?



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