Altitude & Drag Factor

Maintenance, accessories, operation. Anything to do with making your erg work.
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FurianXO
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Altitude & Drag Factor

Post by FurianXO » September 19th, 2019, 8:18 pm

Was wondering what others drag factor was at altitude. I'm at 8300 feet, and below are my drag factors. This is a new concept 2, with about 177k on it.

0 - 57
5 - 92
10 - 156

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Citroen
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Re: Altitude & Drag Factor

Post by Citroen » September 20th, 2019, 5:29 am

At 8,300ft (2529.84m) if the air pressure at sea-level is 1013.25hPa (standard pressure of 29.9inHg) then your air pressure is approx 744.1 hPa (21.97inHg).

The drag factor will be significantly lower at three quarters of standard pressure (I'm completely ignoring temperature to make the maths easier).

There's an online calculator (that works in your silly imperial units) at: https://www.weather.gov/epz/wxcalc_pressurealtitude

sekitori
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Re: Altitude & Drag Factor

Post by sekitori » September 20th, 2019, 8:02 pm

As long as you can get it to reach the 110-130 range with some room to spare at the high end (and you easily should), you'll be fine.

FurianXO
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Re: Altitude & Drag Factor

Post by FurianXO » September 20th, 2019, 11:30 pm

Yup, its not an issue, was just curious where others were at altitude.

dougt24
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Re: Altitude & Drag Factor

Post by dougt24 » September 22nd, 2019, 10:55 am

I'm at 5,000 ft with a max drag of 180. I exchanged emails with concept2 confirming higher altitudes does lower the drag factor.
Age: 64

Height: 5'4" (163cm)

Weight: 160#s (73kg)

echristy
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Re: Altitude & Drag Factor

Post by echristy » November 7th, 2019, 11:15 am

Being a retired engineering nerd at 5000', I just had to check the drag factors on a new model D. Data shown below are comma-separated values of "Setting-Drag". At a setting of 10, the max drag was 176. Another user reported a max of 180, which is pretty close. The whole number settings were right on the number with 1/2 number values on the lines. So my '10' value was not precisely at the max.

0.5-67, 1-67, 1.5-69, 2-67, 2.5-71, 3-75, 3.5-79, 4-84, 4.5-90, 5-95, 5.5-100, 6-107, 6.5-113, 7-120, 7.5-127, 8-135, 8.5-146, 9-155, 9.5-165, 10-176

I warned you that I was a nerd. :D Cheers.

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Ombrax
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Re: Altitude & Drag Factor

Post by Ombrax » November 7th, 2019, 10:02 pm

I'm no Aero guy, but I bet that atmospheric density is the key factor that affects the drag factor as you change altitude.

I just tried to post an image of a Std Atmosphere table but as always, got an error message. Here's a link:

https://docplayer.net/docs-images/41/15 ... page_6.jpg

The relevant number is that at 5k ft the air density is 0.8617 x the density at sea level.

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Carl Watts
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Re: Altitude & Drag Factor

Post by Carl Watts » November 7th, 2019, 10:47 pm

The most significant factor is the amount of dust in the flywheel cage blocking the holes around the outside of the cage.

A really dirty Erg will see about 90 with the damper setting on 10 so that is hopeless for most people.

As above typically in the 110-140 range is what your after except for the 500m sprint in which you need something a little higher than you normally row with.
Carl Watts.
Age:53 Weight: 104kg Height:183cm
Concept 2 Monitor Service Technician & indoor rower.
http://log.concept2.com/profile/863525/log

bmoroney
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Re: Altitude & Drag Factor

Post by bmoroney » July 19th, 2020, 2:31 pm

I live at 5000 ft (1524 M) and also noticed lower drag numbers than I expected based on the Concept 2 drag overview: https://www.concept2.com/service/monito ... rag-factor

So, using the same technique as echristy (great idea!) I measured similar values. The whole number settings were right on the number with 1/2 number values on the lines.
This was on a Model E, PM5. Just cleaned out the flywheel.

Damper -- Drag
1 -- 68
1.5 -- 71
2 -- 73.5
2.5 -- 76
3 -- 81.5
3.5 -- 85
4 -- 91
4.5 -- 96.5
5 -- 102
5.5 -- 108
6 -- 115
6.5 -- 122
7 -- 127
7.5 -- 135
8 -- 142
8.5 -- 150
9 -- 155
9.5 -- 161
10 -- 164
At far end (past 10) = 175
At easy end (past 1) = 66

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Citroen
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Re: Altitude & Drag Factor

Post by Citroen » July 19th, 2020, 2:47 pm

If the air pressure at sealevel is 1013.25 hPa then the pressure at your elevation is 843hPa.

If we assume the drag is linear and directly proportional to air pressure you can multiply each of your values by 1.2 and that brings them into a more normal range. Which is good enough for me applying the techniques I learned from https://www.youtube.com/watch?v=-_-Vg_B3nzM

bmoroney
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Re: Altitude & Drag Factor

Post by bmoroney » July 19th, 2020, 3:44 pm

That's great. Thanks.

adccl8z
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Re: Altitude & Drag Factor

Post by adccl8z » July 23rd, 2020, 5:52 am

Carl Watts wrote:
November 7th, 2019, 10:47 pm
The most significant factor is the amount of dust in the flywheel cage blocking the holes around the outside of the cage.

A really dirty Erg will see about 90 with the damper setting on 10 so that is hopeless for most people.

As above typically in the 110-140 range is what your after except for the 500m sprint in which you need something a little higher than you normally row with.
I want this to be the explanation why, about 2 years ago,my times started to gradually decline (after i thoroughly cleaned the flywheel cage),and nothing to do with hitting 50 yrs of age :D
It was the first time I'd cleaned the cage in about 10yrs, though i wouldnt say it was *that* dusty :(
52 in Jan '20. LWT. 6'3''. Best 2k 6:58 (2003) Best 5k 18:39 (2003). Last regatta: 2004. Surrey, UK

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