[Closed] drafting, a physics question

So my question is does the amount of energy used by A go up with B drafting and if so by how much

Energy used by A actually goes down a tad as his wake vortices go around rider B - i.e. rider A mitigates some of his own drag by having rider B behind him ( - IIRC).

Doesn't feel like that dragging a wheel sucker into a headwind on the morning commute mind!

I'm sure it's said to slightly benefit rider A too

Or is Aero Dynamic Efficiency improved for Both A and B as B breaks up A's turbulence thus reducing both riders Drag?

Edit - Beaten to it...

As above, it will definitely not go up, and may go down - but at bicycle speeds any difference will be entirely negligible.

Isn't there also a slight "bow wave" effect from the rider behind, so effectively giving the rider in front a little (very little!) push along?

As above it's a (very) slight benefit to A too.

Perhaps the most surprising conclusion from the CFD simulation is that, despite feeling the full force of the oncoming air, the lead rider experiences lower drag than if he were riding an ITT at the same speed.

The drag coefficient of the leading TTT rider is 0.277, while that of an individual rider is 0.285 [drag coeffient is measure of the force each rider experiences corrected for differences in size]. This rare example of "something for nothing" occurs because the second place rider reduces the influence of the lead rider's wake, increasing his base pressure and consequently reducing the drag force that he experiences.

http://forum.simwe.com/archiver/tid-818221.html

(stolen from bikeradar.. yes i'm lazy)

[img] [/img]

From http://www.responsesource.com/releases/rel_display.php?relid=52360 which doesn't really answer the question, but it's interesting stuff anyway.

I doubt that test on bike radar was brilliantly accurate, a difference of 0.08 could be down to anything.

In NASCAR, two cars will go faster then one, three cars will go faster then two, etc. etc. This is because if you have someone right behind you, it actually helps you go faster. In cycling, it doesn't really have any effect at all. Also, I thought the difference being behind someone was closer to 40-60%.

"[i]The drag coefficient of the leading TTT rider is 0.277, while that of an individual rider is 0.285[/i]"

3% on the Cd is a surprisingly significant difference - still not huge, but certainly not negligible if the experiment is accurate. (Though I guess we're talking pro riders, who will ride much closer and faster than plebs like me - the faster you go the larger your wake, and the closer the ride the more it's filled.)

I got a cheesy Solidworks analysis tutorial about Nascar drafting and looking at the forces/drag involved.

As above, the second car moving into close proximity reduces the drag experienced by the first car too...........

Found it, although it's not exactly a detailed explanation....

http://www.solidworks.com/includes/videovault/demo_window.cfm?docKey=C075BA75BF301C8EE7F21DBCEB09FEF9&docid=11483&CampaignHitsAllowed=0&title=Simulation+Solves+the+Stock+Car+Drafting+Quandary&language=EN&campaignID=0

Also, I thought the difference being behind someone was closer to 40-60%

27% at 25mph is what I have read. >40% sounds loads unless you are several people back.

EDIT: That's 27% reduction in Vo2, so I guess the reduction in the wattage could be a higher percentage (or would it be lower?).

Ok, maybe that's in a bunch then. Or just wishful thinking on my part.

well that's not what I was expecting.

This is implicit in the concept otherwise the peleton would not work, but it isn't news, it has been known about for a long time, I learnt it in physics in 1988. so it must be about 50 years older than that..

This is implicit in the concept otherwise the peleton would not work

As long as the total effort of all riders is reduced and everyone takes a turn on the front, the peleton would still work without the lead rider getting a benefit from the following rider.