Just a thought.

With all the work going on with bikes to make them slip through the air as
efficiently as possible, particularly when they're race bikes, why has
no-one considered dimpled body work (like a golf ball) to get the desired
result. Or haave they and I just don't know about it?

I saw an episode of Miffbusters a while ago where the blokes covered a
normal car (Mondeo type) with clay/plasticine/summat and then dimpled ****
out of one and left the other smooth.

Tests were carried out for speed and fuel efficiency and interestingly, the
dimpled car won on both. Not by a massive amount, because the speed the cars
could reach was pretty useless, but enough to confirm the myth. Barnes
Wallace apparently had the same idea when he designed the bouncing bomb too,
but Bomber Harris thought it was a ridiculous idea. Seems someone was wrong.

If a golf ball can fly twice as far with a dimpled surface than it can with
a smooth surface, I can't see it *not* woking on a fairing.

So now you can rip the **** out of me for even considering it.

 

Thanks, I'll have my Ducati dimpled now please

 

bikes, in normal operation, are not spinning.

 

Dimples don't need spin to reduce drag.

 

Paging TBC. TBC to the wind tunnel telephone please.

 

<snip>

AFAIK the Fireblade had golfball-like dimples at the front of the fairing
based on that logic, so you're not the first one to consider it. Provided it
actually does work enough to make a difference, my only guess why it's not
been widely used would be stability/downforce-related, but that again would
apply more to racecars. Shouldn't be very expensive to manufacture I think,
given the non-metallic nature of motorcycle fairings.

 

<lurch>

`You called?'

Dimpling a golf ball reduces drag by making the flow over it turbulent
which helps stop separation and resulting increased drag. On a bike,
there is already massive separated flow because of the shape. Dimpling
the fairing is not going to change that.

 

IIRC, they were holes.

 

I think manufacturing would be a not insignificant problem. One, a
dimple on a mold is a bump. It takes a lot more machining time to
create a mold with all those bumps, adding cost. More important, when
making the fairing, you'd have to lay up a lot of fabric around the
dimples, or leave the spaces around the dimples empty of fabric, just
solid resin. Seems time-consuming and difficult to achieve quality
results, BICBW.

 

I was thinking more of injected plastics rather than fibre composites but I
see your point, particularly regarding molds. Still, I think that if the
benefits were significant it should be doable without really adding that
much to the cost. You make the molds once and then use them for pretty much
the entire model's production.

 

Maplin sell one of those 12V rotary tool thingies, one of the milling bits
has a ball end about 2mm or so.

 

I suspect the effect on the overall cost of the mould would be pretty
minor.

However, as was pointed out, the dimples only work by some magic means
to do with disturbing the boundary layer, which is a thin layer of air
next to the surface of the object. This magic helps the airflow
'stick' to the shape as it tapers away from the airflow at the back,
rather than break away and cause major turbulence & drag. As the main
part of a motorcycle fairing is at the fromht, dimples would have
little effect. I'm sure someone will correct my explanation.

Dimples on the tailpiece might help but by then the airflow would
probably be pretty broken.

 

'fromht' being a local dialect term for 'front', of course.

WTF that came from, I've no idea.

 

Des O'Connor in drag? Where?

 

I've only ever had one <smiles, pokes at chin> still got it. I used to
hate smiling as an early teen as I thought it made me look lopsided.

 

ISTR it's also related to the surface's Reynolds number, which
involves the chordwise length of the surface - curved or not - the
flow rate and the fluid viscosity.

 

They were/are.

 

See Stoners bike.

 

I'll get the rasps out

 

I don't think the Mondoe's used in the Mythbuster tests were either.