[net.cycle] Aerodynamics of large vehicles

gam@proper.UUCP (08/13/84)

@
My other question:

OK, you are zipping down this two-lane highway and you see this
big logging truck coming up the other lane.  You move to the
right (right?) and prepare for the hurricane.  It passes with
a moderate zephyr but no gale force winds.

Have you noticed that certain truck SHAPES may affect the air
currents you run into as they go by?  I haven't noticed this
much myself, but a friend says that logging trucks and
propane (or other gas) trucks seem to create less hazards for
motorcyclists.

Do you agree with this?  Do you have your own theory on this
matter?

[Is everyone off on vacation or what?]
-- 

Gordon A. Moffett

{ hplabs!nsc, decvax!sun!amd, ihnp4!dual } !proper!gam

marauder@fluke.UUCP (Bill Landsborough) (08/15/84)

You are right about shapes of the trucks and the turbulance they
create.  I have learned that the worst are big, tall, and square
corners all the way around, especially the back of the trailer.
The front first creates a high pressure area which pushes everything 
away from it.  Then the back, being big and square, creates a large
vacuum area which sucks everything back into it.
   The real condition which sets up the "big blast" when you are 
riding by is when the wind is blowing from your left side and the 
oncoming truck breaks that wind with a monsterous blast of pressure
then vacuum.  Your riding along leaning slightly to your left against
the normal crosswind when the truck goes by and triples the velocity.
You counteract by leaning harder to the left just as the truck gets
by and the vacuum pulls you violently to the left.  It becomes tough
to stay in your planned lane when the cross wind is around 30mph and
the trucks speed is at 70!  This is real common on two lane highways
in the deserts.  Oh well... just tuck down and hang on!

gt@hplvla.UUCP (gt) (08/16/84)

<<< LEAN WHEN YOU TURN >>>

maurader is right... especially about the prevailing winds.  I have
noticed that identical trucks will cause everything from almost no
disturbance to stomach churning excitement depending on the prevailing
winds.  

One nice thing about doing most of your riding above 5000 feet is that
the air is so much thinner.


                   George Tatge
		   ihnp4!hpfcla!hplvla!gt

Today's safety tip:
		
		When riding with no hands, always keep your foot
		ready on the brake.

an@hou2h.UUCP (A.NGUYEN) (08/16/84)

-
Riding position has a lot to do with it.  If you sit up right, you
are presenting a nice and big sail to the wind to blow on.  Ditto
large fairings.  Ditto large bikes, though their longer wheelbase
offset the effect somewhat.

I've gone places a lot on a Honda 360 (54" wheelbase) and a Kaw 550
(55" wheelbase) -- both had lower than stock handlebars (1" rise for
the 360 and 4" drop for the 550).  Neither had Windjammers or
anything of that sort.  Both had very good stability in crosswinds
and wakes of large trucks.

	Au

kar@ritcv.UUCP (Kenneth A. Reek) (08/18/84)

The prevailing wind direction has a lot to do with how much turbulence you
will feel after a truck goes by in the other lane, regardless of the shape of
the truck.

-- 
	Ken Reek, Rochester Institute of Technology
	{allegra,seismo}!rochester!ritcv!kar