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Re: Aerodynamic Testing of Aero Helmets? [gymrat] [ In reply to ]
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...how often do we ride with a yaw rate??? I know we think we are fast but we are not airplanes.

.A) Will it make me :30 faster over an Olympic at 21 ave
B) How hot do they get?
C) Do you get wind noise on LG Rocket?

..


"Yaw" just means there is a slight crosswind. And there almost always is, especially for us middling folk.

A - Yes, and more.

B - Not very. I rode mine at the 91-degree Caliman IM. I didn't even notice it.

C - Quiet going straight, and it whistles in a crosswind. Kinda cool, actually.
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Re: Aerodynamic Testing of Aero Helmets? [Ashburn] [ In reply to ]
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So, which ont to get?
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Re: Aerodynamic Testing of Aero Helmets? [John Cobb] [ In reply to ]
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[reply]F Note**** helmets test a little different on different riders because of back shapes and pelvis rotation. These results are for this rider but I think they generally would have the same results.[/reply]

You are right with the first part. Aerodynamics is a tricky thing...small changes in one part can have huge impact on others... If you change your bodyposition a little, another helmet might (will!) be better. Same goes with wheels and bars and everything. There is just not such thing as a standallone best helmet, wheel, frame... The only serious approach would be: Get your most ergonomic, yet aerodynamic, position on the bike set. THEN go to the tunnel and test various equipment for your own riding position. I realize this is costly and for most (me included) no option. But i think itīs the only way to go if you want optimal results.

That doesnīt mean that almost any aerohelmet is probably better then a standard, just that data from another rider means little to nothing for yourself.

Axel
Last edited by: Axel: Aug 18, 06 4:30
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Re: Aerodynamic Testing of Aero Helmets? [roady] [ In reply to ]
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John...did I read in this data that the Rocket Tail up is quicker than the Rocket Tail down? Is this like all those short airfoils that stick upright out of the fuselage of many commercial and fighter aircraft to keep the airflow laminar?
Notice, that was only @ zero yaw
Thus clearly illustrating the importance of testing at multiple yaw angles...so once again I'm left wondering why they apparently don't normally do this in San Diego?
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Re: Aerodynamic Testing of Aero Helmets? [Ashburn] [ In reply to ]
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Ok, I did some age group speed math, I picked two avg speeds for a 40k distance that should be attainable, 24mph and 22 mph. In this model, I used a rolling hills course and Mark the rider made 300 watts avg@ 24mph. Then, I averaged the data using a bell curve I like, with more weight in the 5 - 10 degree crosswind range.

225 watts 300 watts

untaped giro 67:41 60:40

taped Giro 67:05 60:07

L.Gar. tail up 66:23 59:29

L.Gar tail dn 66:23 59:29

Bell/Walmart 67:07 60:09

Rudy Syton w/ flaps 66:50 59:54

Rudy Syto No flaps 66:52 59:55

With the avg. drag used and using the more realistic bell curve for these numbers, tail up or down doesn't matter. Not having many vents exposed [taped over] is important and race wheels are still more important than aero helmets.

New Blog - http://www.johncobbresearch.com
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Re: Aerodynamic Testing of Aero Helmets? [John Cobb] [ In reply to ]
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I wonder... Did the test rider lower his head for the tail up runs? Simply putting your head down to lift the tail up may lower drag in itself, regardless of the effect the tail has. Or was the rider's head in the same position in both runs, with tail up and tail down?
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Re: Aerodynamic Testing of Aero Helmets? [John Cobb] [ In reply to ]
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John thanks again for all this info we all appreciate it.

Could you give me/us a link to some info on correct taping of standard road helmets. I don't have an aero helmet but would like to tape my vents. Do you cover all the vents? Leave any open?



QT2 Systems

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Re: Aerodynamic Testing of Aero Helmets? [TriMike] [ In reply to ]
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I think Jordan Rapp has an article on the Timex site about aero helmets and specifically mentions the Rudy (presumably a sponsor?).

I am sure they are faster but I just can't convice myself to get one. I am afraid some old school dude will pass me and laugh. That is what I am going to do if I pass someone with an aero helmet ;-) WHY???????
Last edited by: dennis: Aug 18, 06 5:48
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Re: Aerodynamic Testing of Aero Helmets? [dennis] [ In reply to ]
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Very interesting and informative post there dennis. :)

Anyway, looking at the data for the Rocket vs the other helmets, a weighted average gives a savings of 0.3-0.5lb drag for this guy. It is very interesting that the high yaw tail up is way lower in drag than the tail down. That's very unexpected.

Jens posted some data for his CdA earlier on biketechreview, he said with the Chrono it was 0.2343 and with the Rocket it was .2172. Extrapolating this up to meet John Cobb's data (drag force proportional to CdA) this would indicate the Chrono is somewhere in the 7.7lb average drag range??? That's worse than an Atmos. There must be something else funny going on here...


Mad
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Re: Aerodynamic Testing of Aero Helmets? [triguy42] [ In reply to ]
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"There must be something else funny going on here..."

That is why you cant always take the data from one individual and apply it to another. John measured the data for one particular rider, if anyone of us were going to go into the windtunnel our results could be somewhat different.

My guess is perhaps Jens benefits particularly from aero helmets, it might be due to the fact that his position is most likely more aero than the rider used for this study.

KR
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Re: Aerodynamic Testing of Aero Helmets? [Andrew Coggan] [ In reply to ]
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John...did I read in this data that the Rocket Tail up is quicker than the Rocket Tail down? Is this like all those short airfoils that stick upright out of the fuselage of many commercial and fighter aircraft to keep the airflow laminar?
Notice, that was only @ zero yaw
Thus clearly illustrating the importance of testing at multiple yaw angles...so once again I'm left wondering why they apparently don't normally do this in San Diego?


They do, it's just a question of money. When the ProTour teams come, they test at multiple yaws. For the general public, you have the option, but each change requires a few minutes to turn the splitter, which can add up to a several less runs in your alloted time.

Scott
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Re: Aerodynamic Testing of Aero Helmets? [smartin] [ In reply to ]
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so which helmet?
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Re: Aerodynamic Testing of Aero Helmets? [flying wombat] [ In reply to ]
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"There must be something else funny going on here..."

That is why you cant always take the data from one individual and apply it to another. John measured the data for one particular rider, if anyone of us were going to go into the windtunnel our results could be somewhat different.

My guess is perhaps Jens benefits particularly from aero helmets, it might be due to the fact that his position is most likely more aero than the rider used for this study.

KR


The other thing is that I used a visor with the Rocket, but not with the Chrono.



- jens
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Re: Aerodynamic Testing of Aero Helmets? [jens] [ In reply to ]
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[reply]The other thing is that I used a visor with the Rocket, but not with the Chrono. [/reply]

Ah yes that could certainly make a difference. Although I thought that a previous test on BTR showed little difference with the visor. I'll have to go searching again.

Jens, do you still have your Chrono in size M? I remember measurements you made of the width, but I had a hard time interpreting the 202mm width you stated on BTR. I wasn't sure if you meant the width was measured on *top* of the screw head, or from shell-to-shell. I measured 195mm from shell-shell on my S, and desert dude said his M was also 195mm shell-shell. I get 201.2mm wide at the top of the screw heads.


Mad
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Re: Aerodynamic Testing of Aero Helmets? [smartin] [ In reply to ]
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Would it still be beneficial to use an aero helmet while sitting up, hands on the hoods, doing a hillclimb? More specifically...

.25 miles @ -1% slope followed by 3.55 miles at 5.7% slope
17.5 mph overall average
bike + rider = 74kgs.
crr = .0042
air density = 1.18

Taped Atmos v. Untaped Atmos v. Rocket?
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Re: Aerodynamic Testing of Aero Helmets? [John Cobb] [ In reply to ]
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John.....did either the Rudy or the Rocket have the visor on? Any testing to compare with a visor vs. without?

Thanks.
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Re: Aerodynamic Testing of Aero Helmets? [smartin] [ In reply to ]
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the importance of testing at multiple yaw angles...so once again I'm left wondering why they apparently don't normally do this in San Diego?


They do, it's just a question of money. When the ProTour teams come, they test at multiple yaws. For the general public, you have the option, but each change requires a few minutes to turn the splitter
Scott[/reply]
Having experienced the whirlwind of wind tunnel testing three times (pun intended), I certainly understand that, in this setting, time definitely equals money. What I didn't realize was that the splitter platform in San Diego took so long to turn (manually??). At the TAMU tunnel, the balances are on a turntable that can be rotated to a new yaw angle in just seconds.
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Re: Aerodynamic Testing of Aero Helmets? [dvfmfidc] [ In reply to ]
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So, which ont to get?


The Zipp folks did some looking into average wind speed around the country. They concluded that most of our riding involves yaw angles of 10 to 20 degrees. However, I'm not sure if they took ground effects into account. On a day when the weather service reports 10 mph wind, the wind at 3-4' off the ground is probably more like 5-7 mph, which serves to decrease the effective yaw angle.

Look at John's data for the 5-to-10 degree yaw trials. Which helmet has the best set of values in those ranges?
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Re: Aerodynamic Testing of Aero Helmets? [Ashburn] [ In reply to ]
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In Reply To:
So, which ont to get?


The Zipp folks did some looking into average wind speed around the country. They concluded that most of our riding involves yaw angles of 10 to 20 degrees. However, I'm not sure if they took ground effects into account. On a day when the weather service reports 10 mph wind, the wind at 3-4' off the ground is probably more like 5-7 mph, which serves to decrease the effective yaw angle.

Look at John's data for the 5-to-10 degree yaw trials. Which helmet has the best set of values in those ranges?


How fast you're riding has pretty big effect on yaw also.

Scott
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Re: Aerodynamic Testing of Aero Helmets? [Andrew Coggan] [ In reply to ]
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the importance of testing at multiple yaw angles...so once again I'm left wondering why they apparently don't normally do this in San Diego?


They do, it's just a question of money. When the ProTour teams come, they test at multiple yaws. For the general public, you have the option, but each change requires a few minutes to turn the splitter
Scott

Having experienced the whirlwind of wind tunnel testing three times (pun intended), I certainly understand that, in this setting, time definitely equals money. What I didn't realize was that the splitter platform in San Diego took so long to turn (manually??). At the TAMU tunnel, the balances are on a turntable that can be rotated to a new yaw angle in just seconds.[/reply]

San Diego's tunnel has an electronic splitter/turntable also. And it is only a matter of seconds to turn it. I'm not sure if you have to get off the splitter to do so or not. I am pretty sure they need to re-zero after turning it though, which means letting the tunnel wind down, then winding it back up for each yaw test (meaning it's at least as time consuming as testing an entirely different position). It would be nice if you didn't have to re-zero and could stay mounted. Then you could just keep the tunnel running and turn through the different yaws...

The behind the saddle bottle thing is interesting, but that's the first real example (besides wheels of course) where I can see the utilty of testing accross a wind yaw range. I still think that if time is limited (which it always is!), a person is likely to get more out of testing lots of things at a single, realistic yaw, than a few things at several yaws (especially since a vast majority of the time you'll see the lower yaws anyway...).

Scott
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Re: Aerodynamic Testing of Aero Helmets? [TriMike] [ In reply to ]
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I do have such an article, and Rudy IS a sponsor. I race in the Rudy helmet because that is what I am required to wear. BUT, I do find the helmet to be very comfortable and faster than my road helmet, although I couldn't give you an exact wattage number. One of these days, I'll do some TT runs with both. I hope to get a chance to do some test runs of it vs. my LG Rocket as well. The Rocket "appears" to be faster than the Rudy, just based off my loose interpretation of my SRM files. But I also would sweat like a banshee (not sure how much banshees actually sweat) in the LG (it is great in the winter, though), and I don't in the Rudy. I think that is definitely a factor given that we run after biking. Were this a bike-only sport, temperature and fluid management would be a non-issue. But it isn't.

The point of my article on the Timex site was more to encourage people to get *an* aerohelmet. The Rudy is a nice compromise for people that don't want the full dome covering. I have a friend who races in a Rocket, and he definitely notices extra strain in his neck. Maybe a bit of extra weight, but also with that big tail (which is what makes it fast) crosswinds are going to affect you more. So the Rudy is a nice balance of comfort (weight and heat) and aerodynamics. But if you want to go as fast as possible, I will readily admit that there are helmets that are going to be faster.

Even the folks at Rudy know it is not the fastest possible design. Most of the Rudy sponsored teams raced in the helmet with the carbon fairing shell in the TdF & Giro. There are pics of it somewhere. That shell will be available next spring ('07), so similar to the visor and earpieces, you can make your helmet more aero (and a bit hotter) should you choose to.

I'd love to have some real tunnel data to quote, but I don't. If I get around to doing some tests with my SRM, I'll post those, as flawed as they may be.

EDIT: I replied before seeing John's data. Certainly not suprising. I'd still like to do some runs on my own, just to see what I get out on the road, which of course will be less precise, but also unique to my position.


"Non est ad astra mollis e terris via." - Seneca | rappstar.com | Facebook - Rappstar Racing | @rappstar | I work @ Zwift

Ask me about: DiamondBack Bikes | Zipp | 1st Endurance | Normatec - $100 off RAPP2017 | Quarq | SRAM | MatchRider | Kiwami | ROKA
Last edited by: Rappstar: Aug 18, 06 16:20
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Re: Aerodynamic Testing of Aero Helmets? [smartin] [ In reply to ]
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How fast you're riding has pretty big effect on yaw also.


Yup. A 5-degree yaw for you is 10 degrees for me. ;-)
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Re: Aerodynamic Testing of Aero Helmets? [JimVance] [ In reply to ]
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I cant find a pic of the new giro aero helmet that will be coming out...anybody see it yet? I heard it is a bit different than what we have seen in the tours that some teams are wearing!
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Re: Aerodynamic Testing of Aero Helmets? [dvfmfidc] [ In reply to ]
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Bottom of the page:
http://www.cyclingnews.com/road/2006/tour06/tech/?id=/tech/2006/features/tour_giro_ionos


"Non est ad astra mollis e terris via." - Seneca | rappstar.com | Facebook - Rappstar Racing | @rappstar | I work @ Zwift

Ask me about: DiamondBack Bikes | Zipp | 1st Endurance | Normatec - $100 off RAPP2017 | Quarq | SRAM | MatchRider | Kiwami | ROKA
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