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Upright Mike
human power expert

USA
3365 Posts

Posted - 11/09/2008 :  06:38:09  Show Profile  Visit Upright Mike's Homepage  Reply with Quote
Hour Record Holders - coefficient of Drag cd and frontal area A

Eddy Merckx, cd = 0.75, A = 0.34 sq meters


Francesco Moser, cd = 0.32, A = ?


Miquel Indurain, cd = 0.23, A = 0.37 sq meters


Gert-Jan, M5 Carbon highracer, cdA = 0.219?


Tony Rominger, cd = 0.20, A = 0.33 sq meters


Grame Obree, cd = 0.18, A = ?


Chris Boardman, cd = 0.165, A = 0.34 sq meters


Sean Costin, Velokraft NoCom lowracer, cdA = 0.153?

Edited by - Upright Mike on 11/09/2008 20:01:54
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Upright Mike
human power expert

USA
3365 Posts

Posted - 11/09/2008 :  06:59:05  Show Profile  Visit Upright Mike's Homepage  Reply with Quote
*These value are of special interest to me, because it is perhaps the closest to what you can get on a typical time trial bike today, ie. not an Obree Praying Mantis or the Superman position. Warren reports a value of 0.230 on the simulator page for an upright time trial bike with dual disks. This agrees closely with the value for Miquel Indurain on a similar bike. Indurain's position on the bike was not said to be good, he sat up too high and he was a big athlete. Suffice, it to say, that most "good" time trialists today will have a cdA of 0.20 to 0.23, still much less aero than a good lowracer.
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Speedbiker
human power expert

USA
2369 Posts

Posted - 11/09/2008 :  15:59:15  Show Profile  Reply with Quote
Mike,
Isn't coefficient only important when figured along with frontal area? I'm not sure I think these numbers are correct as such. Maybe my brother will chime in this topic. It seems to me that both Cd and frontal area is lower on the recumbent, but that our power outputs are lower due to ergonomics and ride ability.
Thom
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teubner
recumbent guru

783 Posts

Posted - 11/09/2008 :  17:49:38  Show Profile  Reply with Quote
Isn't cDA co-efficient of Drag times Area? Removes the area question.
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Upright Mike
human power expert

USA
3365 Posts

Posted - 11/09/2008 :  19:51:19  Show Profile  Visit Upright Mike's Homepage  Reply with Quote
Everyone, where I put cdA, I meant cd = coefficient of drag. Sorry! I've made the corrections in the above postings. The bike cult website lists both A and cd for the upright hour record holders I posted above. On the Wisil HPV simulator, I believe the term that is cdA, should be cd, but I'm not so sure. This term is effected by changing the rider height, which would make you think that it is cdA.

What doesn't make sense is if I compute out cd x A for some of the upright Hour record holders like Tony Rominger 0.20 x 0.33 = 0.066 = cdA which is too low to be believeable.

If I recall right,
Air Drag = 1/2 x p x cd x A x V^2, where
p = air density (dependent on temperature, barometric pressure and elevation above sea level)
cd = drag coefficient dependent on surface drag and pressure drag, both dependent on shape, it is a dimensionless number
A = frontal area, meters squared
V = relative velocity of the vehicle to the airstream, where head winds and tailwinds can effect. It is squared.

cdA is often calculated out, because it is assumed a constant that doesn't change for a particular vehicle-rider combination.

Edited by - Upright Mike on 11/09/2008 20:00:15
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Speedbiker
human power expert

USA
2369 Posts

Posted - 11/10/2008 :  17:02:49  Show Profile  Reply with Quote
Thanks Mike. I didn't think things added up. Especially when considering the wattages of the pros and their drag numbers.

Thom
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sean costin
human power supergeek

Lesotho
1974 Posts

Posted - 11/10/2008 :  20:11:28  Show Profile  Reply with Quote
How were these CD's calculated.or estimated? Does anyone know? This may be too inaccurate to be of value.

Sean
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Larry Lem
human power expert

South Sandwich Islands
2240 Posts

Posted - 11/11/2008 :  09:56:30  Show Profile  Reply with Quote
Mike,
Maybe start a different thread for Cd and CdA discussions.

I hope that we find that the big boys did some wind tunnel testing and that these are measured/derived values.

But then, Graeme Obree was just a regular guy who struggled to make ends meet, made his own bikes, but had great ideas and produced phenomenal power while time-trialing. I doubt that he ever went to a wind tunnel.

Larry Lem
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RollaHPV
Starting Member

USA
30 Posts

Posted - 11/11/2008 :  10:01:09  Show Profile  Visit RollaHPV's Homepage  Reply with Quote
A lot of times they do run-down tests to back-calculate CdA from the force of drag. You have to know the coefficient of rolling resistance of your tires, but that is a lot easier to find(and more readily available). Once the rolling resistance is known, it's a simple sum of forces problem. These solutions are mostly good starting values, but not super precise.

The only problem is that a lot of people assume Cd is constant through a vehicle's range of speeds, but this is very much NOT the case. Especially with faired vehicles, you have flow separation due to friction at low speeds that spikes your Cd, but as you go faster, this separation moves farther back along the vehicle and this part of Cd is reduced. The opposite is the case for the pressure component of drag. For example, the CdA of StreaMiner at 30 mph was .021, but at 60 mph the CdA was just under .018. Obviously, this is a big difference when it comes to top speed.

Cd by itself is pretty much a useless value, unless you standardize the area you are using to calculate drag force. What I mean is that with airplanes, the A is the top surface of wings and fuselage. With cars it's the frontal area of the vehicle. With boats it's the total wetted area. Really, it's apples to oranges. If you give a value of CdA, then it is a very useful variable, as anyone and their brother can figure out how much power is needed to go a given speed(Drag*V, ie P=.5*rho*V^3*CdA).

Learn to Design, Design to Build, Build to Ride, Ride to Win
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warren
human power expert

4788 Posts

Posted - 11/11/2008 :  12:14:42  Show Profile  Visit warren's Homepage  Reply with Quote
Ha. I hadn't seen this on the M5 site:

24 October 2008, 13.45 uur. Gert Jan steps off his M5 Carbon High Racer. He just managed 50,3926 km p/h for one hour. He is the new World hour record king! The old record is smashed with two and a half kilometers p/h. The crowd clapped and cheered. Observers make a deep bow.

Gert Jan! You did 54 kmh in the last lap!
"Yeah sure! I can go even faster!" says Gert Jan.

It is hard to believe that the bike that we ride to work, is the fastest bike in the world. The bike that we use for our shoppings is faster than the fastest Low Racers!

You know what: We challenge you. The first man or woman to surpass Gert Jan's WRRA unfaired record on his own shopping bike (and that can also be an M5 Carbon High Racer..) wins a set of Gold plated M5 Bram Brakes with a value of 999,- Euros. We don't think we have to wrap them up already..

Gert Jan: Congratulations!
Everybody who joined the party: Thanks!

We dare you!
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warren
human power expert

4788 Posts

Posted - 11/11/2008 :  12:44:58  Show Profile  Visit warren's Homepage  Reply with Quote
I have added Gert-Jan's record to the WRRA site with a footnote that it is not yet ratified. We are still waiting on some documentation.

Also I have received word that in December, Andreas Kaizer from Denmark will be making a WRRA 1 hour unfaired record attempt on a velokraft NoCom at the Pruszkow, Poland, national indoor wooden velodrome.

More details later.

-Warren.
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Gugi100
New Member

Netherlands
79 Posts

Posted - 11/11/2008 :  13:57:31  Show Profile  Reply with Quote

quote:
How were these CD's calculated.or estimated? Does anyone know? This may be too inaccurate to be of value.

Sean

I gues you are probably right. The data is perhaps to much based on assumptions. I found a list in this article. Though in Dutch the table (2) will be clear I think.
http://members.chello.nl/k.haan11/Tijdrijden.htm

quote:
Hi Gert-Jan,

It sounds like you are offering your 150 Euro prize to the first stock class rider to break 51.596 KPH (31.989 MPH), is that correct?

I think that the very laid-back recumbent racers probably beat the CdA of Obree's bike.


Yes the 150 Euro will go to the first rider that goes over 51.596 km.
I think that mark is in reach (though I doubt it wil be my reach)

Nice that Anreas Kaizer will take a shot!
I wonder how fast people will go on unfaired recumbents. I think pretty fast

Greetings Gert-Jan





Edited by - Gugi100 on 11/11/2008 14:00:55
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Speedbiker
human power expert

USA
2369 Posts

Posted - 11/11/2008 :  17:14:03  Show Profile  Reply with Quote
Congrats to Gert-Jan. With Sean starting the process ,it seems to have really taken off. I've often wondered how far down a serious recumbent effort could push the hour record. Now, maybe we'll see. I hope to see top efforts from Grelk, English, Whittingham and all the other guys I either can't think of (or can't spell!). Good luck.

Thom
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Auré
Starting Member

France
48 Posts

Posted - 10/23/2009 :  15:43:52  Show Profile  Reply with Quote
quote:
Originally posted by Gugi100


quote:
How were these CD's calculated.or estimated? Does anyone know? This may be too inaccurate to be of value.

Sean

I gues you are probably right. The data is perhaps to much based on assumptions. I found a list in this article. Though in Dutch the table (2) will be clear I think.
http://members.chello.nl/k.haan11/Tijdrijden.htm

quote:
Hi Gert-Jan,

It sounds like you are offering your 150 Euro prize to the first stock class rider to break 51.596 KPH (31.989 MPH), is that correct?

I think that the very laid-back recumbent racers probably beat the CdA of Obree's bike.


Yes the 150 Euro will go to the first rider that goes over 51.596 km.
I think that mark is in reach (though I doubt it wil be my reach)

Nice that Anreas Kaizer will take a shot!
I wonder how fast people will go on unfaired recumbents. I think pretty fast

Greetings Gert-Jan








Done yet
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WillStewart
Starting Member

USA
47 Posts

Posted - 02/23/2011 :  08:58:09  Show Profile  Reply with Quote
quote:
Originally posted by Upright Mike

Be careful to distinguish between cd and cdA below:

This site: http://www.bikecult.com/bikecultbook/sports_recordsHour.html
1972 Eddy Merxcx "UCI traditional" drop handlebar, round tubes, 28/32 spoked wheels, leather strap helmet, shorts+jersey, cd = 0.750
1984 Francesco Moser, cow-horn bar, aero tubes, dual disk wheels, round helmet no tail, one-piece skinsuit, cd = 0.320
1994 Miquel Indurain, triathlon bar, carbon monocoque aero frame, dual disk wheels, Aero helmet, skinsuit, cd = 0.230*
1994 Tony Rominger, triathlon bar, oval steel tubes, dual disk wheels, aero helmet, one-piece skinsuit, cd = 0.200*
1993 Graeme Obree, praying mantis bar, aero tubes, Specialized tri-spoke wheels, Giro aero helmet, skinsuit cd = 0.180
1996 Chris Boardman [Obree] superman bar, carbon monocoque aero frame, 5-spoke carbon, disk rear wheels, Bell aero helmet, skinsuit, cdA = 0.165

The HPV Simulator created by Warren: http://www.wisil.recumbents.com/wisil/simul/HPV_Simul.asp

For Gert-Jan, I plugged in his provided values of 197 cm (6 foot 5.5 inch height), 88 kg (193.6 lbs), assummed 10.9 kg (24 lb) M5 Carbon weight, 23 deg seat angle, narrow tires. Based on HPV simulator, this gives cdA = 0.219 !

For Sean, I plugged in assummed values of 181 cm (5 foot 11 inch height), 74.9 kg (165 lbs), assummed 10.9 kg (24 lb) NoCom weight, 23 deg seat angle, narrow tires. Based on HPV simulator, this gives cdA = 0.153

Additional values for comparison. All simulations assume narrow racing tires and rider height of 1.8 meters (5 foot - 11 inches), and weight of 143 lbs, 65 kg
Recumbent High-racer, 30 deg seat angle, rear wheel disk, cdA = 0.207
Recumbent High-racer, 23 deg seat angle, rear wheel disk, cdA = 0.193
Recumbent Low-racer, 30 deg seat angle, rear wheel disk, CdA = 0.157
Recumbent Low-racer, 23 deg seat angle, rear wheel disk, CdA = 0.144
Recumbent Low-racer with added tailbox, 23 deg seat angle, rear wheel disk, cdA = 0.128

So I'm sure a debate may begin about the assumptions or accuracy in all this data,


Yes, my first question as an engineer is "what is the verified source of this information?" Were there wind tunnel tests performed under identical (or very similar) aerodynamic conditions? Were these estimated, and if so, what were the estimation assumptions, what was the source for them, and were they applied identically to all Cd values?

We have to make sure we are comparing apples to apples, and if not, at least have a full understanding of what the variations are.
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