Aerodynamics Question.

Probably a dumb question, but if you're driving along, slipstreaming
behind a van[1], does your presence have any effect on the van, e.g.
increased drag?

[1] Several feet away rather than inches.

 

Reduced, if any.

 

No idea about a bike but for cars it can actually decrease the drag on
the leading vehicle.

 

Does that mean that "tailgating"[1] is more fuel-efficient for both
vehicles?


[1] In quotes as what I mean is following at a certain distance, where
certain distance is less than the 2 second rule, for example.

 

Now that does surprise me. So it's win, win then.

 

In theory, yes. Close enough and the two bodies act as one much longer
one, which will generate less drag. One reason why speed record
vehicles are usually very long.

 

If you're close enough, yes.

 

A slight acceleration boost for the van when you ram into the back of
it.

 

Where's WUN when you need him?

 

What about a staggered formation - it works for geese?

 

Ain't that interesting. So, and I'm just ruminating aloud here, a ukrm
French Run is likely to be 'faster' if we all stick together....

 

Depends on the shapes of the van and car. No significant effect unless
you're within the first vortex off the back of the van (about 2ft), then
you both get a decrease in drag. You'd have to do this for at least 2
percent of your total driving time to see a statistically significant
change in fuel consumption.

Crash repairs and fines would cancel that out though....

 

Different physics.

 

Certainly the case in my experience.

 

For anyone who cares to try it...
I had to do a long m'way trip in shitty cold weather, with inadequate
winter gear and no fairing. After being pulled by a copper for being too
close to the truck in front (tailgating for some weather protection), I
discovered there was a secondary low pressure area about fifty or sixty
feet behind most full-sized wagons that were travelling at or around
their max speed of the day (early 80s). Result: I was able to tailgate
and remain legal.

 

Goosix.

 

Yes, really! I know that controlling the airflow off the rear of a
vehicle is very important, & assumed that another vehicle following
close behind would upset that flow, making it less effient. Which I
realise probably isn't an issue with a van, but I'm still surprised it
makes it /more/ efficient.

I'm a bit fick, me.

 

Yes, sort of. Bernoulli found all this shit out hundreds of years ago
which is about when a fashion for longer thinner ships came about.

The aerodynamic efficiency of a body is increased in proportion to its
length. So, if you are close enough that you can be considered the same
body as the vehicle in front from the perspective of the medium through
which it is traveling you will both be a little more efficient.

 

It's also why fast jets are generally "waisted" along the fuselage. Starting
"fat" at the front and getting slimmer before putting the weight back on at
the arse end.

Probably

 

Kinda: it keeps the cross-sectional area more or less the same as a
Sears Haack body over the length of the aircraft (Whitcomb area rule).