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Kenny L.
#14 Generic Chevy
PRC Member
Wall Scrapers Racing Team
> Hi!
> I don't really know if it's only me who has experienced or noticed this:
> When I run a race at Talladega and I am leading a train of cars my laptimes
> are much quicker than the times when I run my laps on my own. I'm not
> talking about getting bump-drafted, I tested this several times: I lead a
> pack (without getting passed or bumped) for several laps and I did 47.888,
> then I let myself drop back (in the same race!) out of range of the train,
> consequently I could do laps no faster than 48.088, no matter how many laps
> I did. It's logical that a train runs faster than a solo-car, but only when
> there are constant lead-changes in that train (like we can see in
> bicycle-races), commonly known as "working together". IMHO the train should
> *not* be faster when the leader is the same lap after lap. Is this a bug or
> are there certain aerodynamic effects from the Pos.2-car on the leader (e.g.
> the "winds" of the leader usually "break" behind him, but if he is followed
> by a car real close, then these winds break behind the 2nd car causing the
> leader to benefit from this)?
> Excuse my limited vocabulary please, but I hope I made myself
> understandable.
> Thanx for listening
> Markus
Well this is pretty much what is supposed to happen. It would seem the
physics is not that badin N3 if you can see this effect.
Constant lead changes slow the "train" and cause the second pack to
catch up. You don't watch many Nascar races on ESPN I guess :-)
They are faster when they stay in a line.
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Car A is the leader, B behind him, followed by C.
All the cars have 750 horsepower. Let's say that when you are running alone
at 185 mph, 25 horsepower (arbitrary value) is used to overcome the drag at
the front of the the car and 10 horsepower is used to overcome the drag at
the back of the car.
If car B pulls in close enough to Car A that he takes some of the drag away
from the rear of Car A, he has effectively increased the horsepower
available for propelling Car A around the track.
Another way to look at it:
Each Car is using 35 horsepower to move the air out of the way. When they
form a train, they remove some of the drag from the total system. For
instance, alone, Cars A and B use 35 horsepower each, but if Car B pulls
10'' from Car A's bumper, then Car A might have 25 units of drag, and Car B
might have 18. The whole is less than the sum of the parts.
This makes no sense, does it?
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Aaron Gillum
RDOS Director of Operations
http://www.racing-design.com/rdos Now Accepting Applications!
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"You could have been paid to read this message. www.getpaid4.com/?bargler "
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You are correct in assuming that Car B has much less total drag than Car A,
but a smart driver in Car B knows that it is best to ease up a bit and let
Car A drag you around the track.
> > The reason bike riders keep swapping the lead is because the front
> > rider
> > has more work to do...which means increased fatigue. So the bike riders
> > constantly
> > swap ends to even the work load.
> > In a Winston Cup drive, a line of two or more should always be faster,
> > not only because the lead car is breaking the wind and creating an air
> > bubble
> > for the followers. But the cars in line also help by "pushing" what air
> > is
> > left back to the front car which makes his lap times improve. constant
> > lead changes
> > disrupt the air flow and slow everyone down. A tactic at every drafting
> > track
> > is for a few drivers to try and "leave" the pack by running in single
> > file while
> > the the group behind slows down by constantly jockeying for posisiton.
> > dave henrie
Both cars see some degradations also. The rear spoiler downforce
of the leading car is reduced (changing it's handling) and
the following car is receiving less cooling air and its
downforce can be lower also. With some vehicle types,
the following car may have additional aero
performance reductions through increased turbulence
on forward aero surfaces or underbody.
A good and accessible reference for a discussion of this
is Van Valkenburgh's book (which also includes some references
to the early technical literature.)
"Race Car Engineering and Mechanics," Paul Van Valkenburgh,
Published by author: Box 3611 Seal Beach, CA 90740, 1992.
(or HP Books, NY, NY. ) ISBN 0-9617425-0-X
--
Matthew V. Jessick Motorsims
Vehicle Dynamics Engineer (972)910-8866 Ext.125, Fax: (972)910-8216
> hmmmmmm, I thought this would be the reason for a train going faster than a
> lone car, but I figured the following: The second car (B) has no air to
> break, correct, and in effect will be much faster than the leader (A)
> despite the vacuum behind him, thus he has to back off from the throttle at
> some point which in turn won't achieve faster times unless he overtakes A
> *without* backing off, which in turn desires A go *one* lane higher than he
> usually would and immediately slotting in behind B (not jockeying, working
> together). BUT, as I described initially, if A always stays up front and B
> always real close behind, aren't these two cars to be considered as *one*
> long vehicle.............duhh.......where's my thinking-error?
> Markus
Set your pedals up as a split axis so you have separate gas and
brake to do this.
--
Rich Koehler
rgkoehler(at)lucent(dot)com
killerk(at)home(dot)com
> Well this is pretty much what is supposed to happen. It would seem the
> physics is not that badin N3 if you can see this effect.
If you do this with a human driver you better both be good!
--
Rich Koehler
rgkoehler(at)lucent(dot)com
killerk(at)home(dot)com
