windshield

I am considering a windshield for my Hop Sing 250 for bug and weather
protection. My first thought is that the windshield would improve the
overall aerodynamics, as it seems much more streamlined than my lumpy
body. Is that right? Will a windshield result in a slight
performance improvement, or vice versa? Thanks for any replies.
Conrad "Connie" Eaton

 

It depends on:
1) How big the shield is.
2) Whether or not you mount it correctly.

Even a large shield with the proper "rake" is probably better than the wind
hitting your "lumpy body". ;-)

Even a small shield mounted too straight up will have the aero properties of
a barn door and likely be worse.

 

Well, if you want to use the term "slight", it's true that a curved
handlebar-mounted windshield is aerodynamically better than an
absolutely *flat* plate of equal area.

The aerodynamic term is "coefficient of drag". A human being isn't
flat, a human is curved, and a rider sitting upright has a 0.45
coefficent of drag.

IOW, the human body hitting the air causes 0.45 pounds of drag per
square foot of body area.

The rider cannot change his body shape, but he can reduce his frontal
area by
laying his upper body down on the gas tank.

That's why sportbikes are designed with low handlebars, and the riders
get used to riding all scrunched up like the proverbial monkey and the
football...

A sylishly curved cafe racing quarter fairing might have a coefficient
of 0.30, but only over the area covered by the front side of the
"bikini" fairing. The rest of the rider's body area is still out there
"in the wind".

And there is a huge area of turbulent air *behind* the rider,
resisting his forward progress.

One magazine articles about fully-faired sportbikes claimed that all
the stylish plastic resulted in an amazing coefficient of 0.10.

But, unlike the flat plate windshield being pushed through the air by
brute horsepower, the scientifically-designed fairings slip through
the air without a lot of turbulence on the *rear side*, they smoothly
bend the air around the motorcycle and rider, allowing the slightly
disturbed airstreams on either side to merge back together.

These scientifically designed fairings allow a very powerful sportbike
to go 200 miles per hour, with "only" 200 horsepower.

At that speed, nobody cares about *fuel economy*. The sportbike that
gets
45 miles per gallon while cruising at 60 mph might be getting only 25
miles per gallon running at full throttle.

 

That's true. Aerodynamic drag is a velocity-squared effect, IOW, if
you go twice as fast, you get four times as much drag for any given
frontal area and
shape.

But I didn't want to complicate the discussion with formulae related
to dynamic air pressure, which varies according to altitude, humidity,
and temperature, and the mass of a slug of air...

 

Nope lose mpg & performance

 

Yup, dat's it....yup, yup...
Welcome, Einstein.

 

No. Google for 'aerodynamics' in this ng, as we covered this extensively
quite recently.

 

Gee, even though I read this group regularly, I must have missed that.
If the shield results in less total drag than the rider and bike parts it is
"shielding", then there would be a slight improvement.
Are you saying that NEVER happens ??

My personal experience and sense of reason both make me believe that is
sometimes DOES happen.

 

No. Just that in this instance, it won't. Kindly do not put words into
my mouth.

Indeed it does, but far more rarely than you appear to think. Look, just
google like I suggested, and among other things, you'll find some
interesting links to bikes being tested in a wind tunnel.

Now remove those blinkers, detach yourself from your home-brewed
beliefs, and do google the thread.

 

Ooooooo.......YES SIR. THANK YOU, SIR.
Clue: I don't take orders from you.

 

Oh, the irony. Have you seen which posting you're replying to?

Nope.

 

Let me know when you get one.

 

I'm really just an interloper here, so anybody can flame if they want,
though I'll likely ignore that. I'd say that given the posts I've seen
from you (which usually seemed sensible to me, even though I'm sure I
haven't the technical experience you and the target of that comment
have) that comment is beneath you. Sorry if it sounds personal as I
think the subject of r.m.t. goes beyond the admittedly interesting
personalities here. I'm in the habit of copying pretty much everything
both of you post here, for my own private study. Both of your expertise
makes r.m.t. extremely interesting to me. I hope you both keep up your
posts but don't dilute them with too much antagonism (I think a little
antagonism is actually good for getting the thought juices running, also
sarcasm is a delightful art, but a dangerous one too). You both write
posts I find thoughtful. Just my opinion.

 

Yeah real dummy I am,retired at 45 how about you?

 

and that's what you say to a windshield!