Home Made Aero Spin Down Test of 2 Top Wheels

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mrgray
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by mrgray

hey and after watching that video i saw another where you show a 52 spesh you're building. pretty "spesh" paint job on it. is it finished yet and if so it needs a thread. also that lawn you are running at your place looks amazing!
Bobo S&S Steel Bike - 7.5 kg
Oltre XR2- 6.6 kg
Look 585 - 6.8 kg
Look 695 SR :D

by Weenie


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cyclespeed
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by cyclespeed

mrgray wrote:hey and after watching that video i saw another where you show a 52 spesh you're building. pretty "spesh" paint job on it. is it finished yet and if so it needs a thread. also that lawn you are running at your place looks amazing!


Thanks, it's certainly very 'bling' that Sworks; I'm not sure I would have picked it if I'd bought new, but 2nd hand it was a steal. I figured if I ever got tired of those colours, I'd strip it and go bare carbon. Di2 for it should be arriving tomorrow.
And yes, if I'm not cycling, I'm mowing :)

davidalone
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by davidalone

wingguy wrote:
davidalone wrote:LOL. sure. okay. I really can't be bothered to explain online.

I think you mean you can't explain it because there is no explaining it... because you're wrong. Or at the very least you've expressed yourself so incredibly badly that what you said is the opposite of what you meant.

Draw your diagram and we'll find out. Or answer this question - according to your 'cancelling' theory, if you span one wheel in a stand with bladed spokes set correctly and one wheel with baded spokes set 90 degrees crossways, would there be a difference in total drag slowing the wheel down?

I have a master's degree in engineering,

On current evidence, that's really depressing :|


On hindsight, I realised I expressed mself rather poorly, thats the result of talking physics at 3am.

BUT nevertheless, you're abit of an arsehole, and you really do need to be cut down a notch, so here's the explanation, using a 4-spoke wheel as an illustration.

The first line shows the typical case for a rolling wheel and is not in doubt. CFD will show drag on the top being more than the bottom.

the second line shows what the OP is testing. As you can see, the Fd vectors in the direction of interest cancel each other out.
Torque about the hub caused by drag is of course non-zero.
Attachments
drag.jpg

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Rick
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by Rick

I have "pretty good qualifications" in ME and aerodynamics, an I can't understand what you are getting at either. :)

wingguy
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by wingguy

davidalone wrote:The first line shows the typical case for a rolling wheel and is not in doubt. CFD will show drag on the top being more than the bottom.

the second line shows what the OP is testing. As you can see, the Fd vectors in the direction of interest cancel each other out.
Torque about the hub caused by drag is of course non-zero.

Ok great. Just so we're clear - you've realised that when you said this "Because the wheel spins in a 360 degree circle, the minuscule amount of drag caused by the rotating spokes in the tangent direction of rotation is cancelled out by the exact same drag generated on the opposite side of the wheel." it was completely wrong, and has no relation either to the OPs test case or the real world example of a wheel rolling along? Yes?

And when you said this "Assuming our wheel is entirely symmetrical, then yes. you would get almost essentially zero rotational drag" that was also wrong, and symmetry actually has nothing at all to do with it, yes?

And when you were talking about fans having odd numbers of blades instead of even as if it made a difference that was also nonsense?

In plain english - you have realised that now, right?

(And BTW, if you think I'm an arsehole you should try explaining your original top/bottom 'cancelling out' theory to your fellow engineers. You'd be laughed out of the *f##k* building!)
Last edited by wingguy on Mon Aug 29, 2016 7:45 pm, edited 1 time in total.

PhilippCX
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by PhilippCX

davidalone wrote:..., so here's the explanation, using a 4-spoke wheel as an illustration.

The first line shows the typical case for a rolling wheel and is not in doubt. CFD will show drag on the top being more than the bottom.

the second line shows what the OP is testing. As you can see, the Fd vectors in the direction of interest cancel each other out.
Torque about the hub caused by drag is of course non-zero.


There are three major problem with your reasoning. i) You are assuming a stationary state, ii) you are mixing up scalars and vectors, and iii) you are confusing force and velocity.

In line two you are drawing velocity vectors which in fact cancel each other. All that tells you is that the whole wheel is going nowhere (or to be more precise there are no net forces on the whole wheel). But there is of course an angular velocity which is a vector which - by definition - is pointing into the drawing plane.
Then instead of v you write F_D somehow indicating that speed is force. But force is a function of acceleration, i.e. change in speed over time. And somehow you draw only two force vectors along the x-axis and they are somehow supposed to be 0. What really happens is due to symmetry (same argument as above) the whole wheel is not seeing any net force. But what you have is torque, i.e. angular force. By definition torque is the cross product of distance from center and force and again by definition of handedness it is pointing out of the drawing plane. We see that it is in fact in the opposite direction of the angular velocity and thus slowing the wheel down.
And with this definition of torque it is not 4*F_D at all (neither in terms of absolute value, nor direction).

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kgt
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by kgt

That's what happens when members of a cycling forum give lessons on Physics...

PhilippCX
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by PhilippCX

kgt wrote:That's what happens when members of a cycling forum give lessons on Physics...


That's what happens when people have nothing to contribute but do it anyways...

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cyclespeed
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by cyclespeed

kgt wrote:That's what happens when members of a cycling forum give lessons on Physics...


I'm amazed that anyone with an engineering degree would suggest that you can spin a wheel 'for free' with no aero energy loss, but hey.....

On a lighter note, another short vid with more aero testing on the road, that again gives a small advantage to the LW's over the Corimas.

https://www.youtube.com/watch?v=F1S4muZVeZs

I hasten to add, before any vicious critiques, that this is just a fun day out, not atomically calibrated testing......!

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corky
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by corky

cyclespeed wrote:
kgt wrote:That's what happens when members of a cycling forum give lessons on Physics...


I'm amazed that anyone with an engineering degree would suggest that you can spin a wheel 'for free' with no aero energy loss, but hey.....

On a lighter note, another short vid with more aero testing on the road, that again gives a small advantage to the LW's over the Corimas.

https://www.youtube.com/watch?v=F1S4muZVeZs

I hasten to add, before any vicious critiques, that this is just a fun day out, not atomically calibrated testing......!


Oh no Mr. Cyclespeed.. you're not getting away with a disclaimer like 'fun day out' ....this is serious business for basement dwellers..........I have a cycling proficiency badge issued by the Scouts I'll have you know.....

sawyer
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by sawyer

There is no such thing a fun day out where methodologically flawed aero tests and WWs are involved! :wink:

Even if there is noise in the test the conclusion that those fat Corima spokes are more draggy is absolutely consistent with plenty of other tests across the years

BTW I suspect the LW's spokes are a bit draggy vs CX-Ray type spokes also
----------------------------------------
Stiff, Light, Aero - Pick Three!! :thumbup:

mbrider
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by mbrider

@cyclespeed - by chance, can you do your test with a traditional spoked wheel that is similar in depth etc to these wheels?

It also would be interesting to see how a pair of Rolf wheels would do. They have even less spokes, that are paired and most are aero spoke too. I swear that my Rolf Vigor clinchers (32mm deep traditional v) are pretty aero due to the spokes. The downside is they are squirly in crosswinds, but in a low wind / low wind angle, they are really fast.

RyanH
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by RyanH

Out of curiosity, I spun the Reynolds RZRs by hand with mild effort and it took 2:10 to get to the last full revolution and then 48s to come to a standstill, so a total moving time of 2:58. I then did the same with the Zipp 404s and it came out to 1:00 for the last full revolution then 13s to come to a stop. Mind you, the 404s are significantly heavier at the rim than the RZRs.


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RChevalier
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by RChevalier

You guys should get angry.

Oh and also, I did some tests as well, it was pointless and proved nothing, but I know what I'm talking about and I too have an illustration to help explain.
Attachments
home made aero spoke test
home made aero spoke test

by Weenie


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