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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [Andrew Coggan] [ In reply to ]
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Andrew Coggan wrote:
I have also always seemed to do better relative to my (typically stockier*) competition when it is breezy instead of dead calm.

So a narrower rider is more likely to experience high yaw drag reduction... interesting.

Anyone else care to chime in on their WT data, and how well they sail?

There was one year at Moriarty since I moved to NM (11 years ago) when there was a strong 90deg crosswind. It was for most people a pretty fast year (I missed that one), but I looked at the data and compared times for people who are regulars. The impression I got was that it was a better year for the fast guys than the slower ones. At the time I thought better equipment might be the reason. I hadn't considered body shape.
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [rruff] [ In reply to ]
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rruff wrote:
The impression I got was that it was a better year for the fast guys than the slower ones.

That's every year. :)
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [Andrew Coggan] [ In reply to ]
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I've put a lot of time into testing standard (very fast) bikes vs. beam designs and the relative changes in CdA seen by a compact power rider vs. a long legged, thinner rider.

What I have observed on every beam style frame that I have gotten my hands on - Dimond, Softride Rocket TT, Softride PowerWing, Zipp 2001, and a Pearson - is that I benefit more going from a thin traditional frame to a beam frame than a shorter rider with wider (and shorter), more muscular legs. I obviously do not have enough data to say whether it might be specifically a leg length issue, or leg width.
In my experience, these frames also sail better than anything else. The Zipp especially was incredible in certain conditions...like a North/South out and back run over 15 miles doing 25mph on 190W.

I would love to just sit around and study this for days and days, but job.

...until I talk Nike into building a wind tunnel with a treadmill in the floor for testing the aerodynamics of shoes.
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [chicanery] [ In reply to ]
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I tend to think that my ‘muscular’ legs are a limiting factor in more than one way. :)

Developing aero, fit and other fun stuff at Red is Faster
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [Bio_McGeek] [ In reply to ]
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Bio_McGeek wrote:
Well, maybe that's the reason for this whole thread. That seems like a LOT of sail effect. I'd trust it if I could have the raw data and run the calculations myself.

Tom A. wrote:
Yeah...I think we're talking the same thing.

Also, seeing as how that data is from the San Diego LSWT, I'm fairly certain the "beta yaw correction" HAS been applied. Their standard reporting form us set up to automatically apply it, IIRC.

I was there for that Cervelo data, and Tom is right: it includes the cosine beta squared correction. Dave Kennedy was the one who asked them to code it into their results spreadsheet.

Sorry Jim, I don't have the raw data. :-(

Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [damon_rinard] [ In reply to ]
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damon_rinard wrote:
I was there for that Cervelo data, and Tom is right: it includes the cosine beta squared correction. Dave Kennedy was the one who asked them to code it into their results spreadsheet.
Sorry Jim, I don't have the raw data. :-(
Dave Kennedy knows a thing or two. I reckon I trust it if he was involved.
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [AeroTech] [ In reply to ]
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A bunch of half-assed assumptions and speculation follow:


Coming back to this, it seems that the laminar flow is more likely to become detached in the areas near to the rider's legs, which create dirty air.

If we hold this assumption, then a foil at the seat-tube is less likely to be effective, and it may actually be more important to create clean air in this area and allow it to reattach around the rear wheel or disc.

The other implication of this is that the rider's legs are crucial, and them being shaved will help over non-shaved, and that surface treatments or clothing that allows air to remain attached might be advantageous over bare legs.

'It never gets easier, you just get crazier.'
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [georged] [ In reply to ]
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georged wrote:
The other implication of this is that the rider's legs are crucial, and them being shaved will help over non-shaved, and that surface treatments or clothing that allows air to remain attached might be advantageous over bare legs.

Legs are a big deal. More drag than the rest of the body for a good position. The smart guys who focus on TTs have learned some tricks to deal with this, that doesn't rely on clothing (though that is used when allowed). There isn't a leg clothing restriction for Tri is there?

Surface treatments; to the skin? Maybe some strategically placed scars. Wonder how long it would take for the UCI to ban that practice...
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [rruff] [ In reply to ]
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Hello rruff and All,

Bicycle racer doing aero preparation of shoulder and neck area prior to race.

(Strategically placed bee sting welts)



Some question if the swelling will outweigh aero boundary layer gains.



If it were me I do not think I would like the group of bees forming near my eye.

Cheers, Neal

+1 mph Faster
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [Tom A.] [ In reply to ]
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I appreciate everyone's thoughtful responses. What I was trying to get at is whether achieving low drag for a bicycle or wheel at 15 degrees in the wind tunnel depends upon the wind being perfectly steady (allowing good laminar flow?) Would a slight change in the direction or speed of the wind cause the bicycle or wheel to stall (such as someone walks across the front of the bike while in the wind tunnel). The relatively minor changes to rim shape, tire shape, and frame shape that produce decently different results at 15 degrees yaw suggests that keeping the air attached and preventing stalling is difficult and that the frames and wheels are operating on an aerodynamic edge. Earlier posts indicate that riding in windy conditions that should produce some time riding at 10 to 15 degrees yaw does not result in drag savings over no wind unless the roads are pretty open and straight and the wind is steady. Related to this would be the question of whether some designs would be less sensitive to stalling. For example, would a disc be less likely to stall than a well designed 90 mm deep wheel that has a similar drag curve? Would the particularly deep tube shapes of a Felt IA or P5x allow them to avoid stalling in shifting winds that would stall an aerodynamically good 3:1 tubed bike?
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [AeroTech] [ In reply to ]
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I can see how riding down a straight, open road into a steady 15 mph 10 to 30 degree headwind could reproduce the drag savings seen in the wind tunnel. What would happen if we slowed the wind tunnel down to 15 mph, turned the bike and rider 90 degrees, and then measured the force to drag the bike and rider through that wind? Would the force required to drag the bike and rider at 25 mph through the 15 mph wind be less than the force to drag the bike and rider at 25 mph through still air?
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [wtboone] [ In reply to ]
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1. Numerous studies have demonstrated that cyclists/bicycles do not undergo any significant flow transition in the range of speeds at which people normally ride. IOW, CdA is independent of speed, such that testing at, say, 30 mph (as is routinely done to maximize precision) provides data equally valid at slower speeds.

2. Testing at realistic yaw angles is also routinely performed. Whether CdA stays the same, increases, or decreases depends upon the specific equipment, individual, and/or position being used.
Last edited by: Andrew Coggan: Mar 17, 18 5:13
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [wtboone] [ In reply to ]
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wtboone wrote:
Earlier posts indicate that riding in windy conditions that should produce some time riding at 10 to 15 degrees yaw does not result in drag savings over no wind unless the roads are pretty open and straight and the wind is steady.

No, they do not. During our field tests, the wind was both strong and gusting. Furthermore, although the venue was wide open (which would influence the relationship between wind at 10 m as normally reported and wind at ground level), wind speed (and direction) were measured at the cyclists' height.
Last edited by: Andrew Coggan: Mar 17, 18 14:31
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [Andrew Coggan] [ In reply to ]
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Your paper states: "Drag area tended to decrease slightly with increasing yaw angle, but ANOVA indicated that the differences were not significant." Were the measured differences of drag force in the wind tunnel at different yaw angles significant? For the aerodymic drag part of the equation, did the model predict SRM power based upon the drag area measured in the tunnel, the drag force measured in the tunnel, or both?

I appreciate your taking the time to discuss this.
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Re: Do the large higher yaw drag savings seen in the wind tunnel transfer to the real world? [Andrew Coggan] [ In reply to ]
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Andrew Coggan wrote:
1. Numerous studies have demonstrated that cyclists/bicycles do not undergo any significant flow transition in the range of speeds at which people normally ride. IOW, CdA is independent of speed, such that testing at, say, 30 mph (as is routinely done to maximize precision) provides data equally valid at slower speeds.

Would you be able to expand on this at all? We are now seeing lots of clothing with features designed to modulate the flow transition e.g. Endura's new skinsuit data (http://road.cc/...el.png?itok=HV_olFxz) which even reports that different skinsuits have different relative behaviours at different speeds.

Does this not mean this is no longer true, for the case of the cyclist even if not the bicycle?
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