Vortex Generators (uses for topbox/panniers?)

[DeusExMachina]

You guys have seen it.

 

Those "Sonic the Hedgehog" thingies on the rear part of the roofs of those cars, like the Mitsubishi Evo. And then again, you've probably seen the stick-on/bolt-on types on wannabes (but cannot be, and cannot make it either...) like body-kitted Toyota Vios'es.

 

http://us1.webpublications.com.au/static/images/articles/i30/3058_2lo.jpg

 

Seems that the main purpose of these Vortex Generators... let's call 'em VGs, to save finger cartileges... is to reduce drag (if applied properly).

 

And the benefits? Why... increased fuel economy, of course... though the other effects might be better handling, less turbulence at high speeds, better stability at speed, better crosswind stability.... and of course every 299kph crazed favorite.... higher top speeds. *sniggers*

 

 

 

But now I'm seriously wondering, after reading these few articles.... Can VGs help reduce drag for bikes with top-boxes and panniers ??

 

Read on first. Parts 1 to 4....

 

http://www.autospeed.com/A_3058/cms/article.html

 

http://www.autospeed.com/A_3059/cms/article.html

 

http://www.autospeed.com/A_3060/cms/article.html

 

http://www.autospeed.com/A_3061/cms/article.html

 

 

And finally... their application on boxy vehicles like trucks and buses.... which is of great relevance to a bike with boxes mounted..

 

http://www.airtab.com/Images/photogallery/gallery1.htm

http://www.airtab.com/Images/photogallery/thum15full.jpghttp://www.airtab.com/Images/photogallery/thumhersh%20truck%207%20retouch.jpg

 

(These things look like those fins on the top of a Shoei helmet, don't they?)

 

Seems that when properly applied, they do work. But get it wrong, and you fcuk up your fuel economy.... and perhaps even your ride quality.

 

So with this, I've entertained the thoughts of doing something like this to the rear top end of a top box (or even the trailing edge of a pannier), but again, won't know the result unless I do some kinda wool test.

 

 

Discuss.....

[Marcheline]

The vortex generator was an idea invented for use on aeroplane wings. You see, at high speeds, air-flow changes from laminar (smooth) to turbulent (rough) as it passes through the surface (a larger surface area would create more drag, causing the air to "shear"). This turbulence or break-away from laminar air-flow occurs at the back (trailing edge) of the surfaces.

 

Now, by having vertical fins erected like that, when air flows through the fins, they become vortices (twirling air; picture a horizontal mini tornado). This "mini tornado" will blow away the turbulence and delay the change from laminar air-flow to turbulent air-flow.

 

Technically, putting it on your rear-box or panniers may work, but the increase in fuel efficiency would be very negligible. Not unless you're planning to break the sound barrier with your bike.

 

So yeah, it's like having a spoiler on a saloon car, which does not create a down-force unlike in F1 racing. Oh the vanity!

 

It's all bout aerodynamics. G'luck DeusExMachina! On the classic wool test to determine laminar and turbulent flow, that is.

[DeusExMachina]

Yes yes. I did some research into the VGs. It is indeed used on aircraft wings to reduce turbulence on the control and lift surfaces.

 

 

But for bikes with boxes, it's not about downforce... like cars.

 

How many times have powerful CL2 bikes been retrofitted with panniers or boxes.... and then find themselves unstable at speeds above 180kph on long hauls.

 

I'm wondering if these things might help with stability and drag reduction. Vanity is not an issue here.

[Marcheline]

Yes yes. I did some research into the VGs. It is indeed used on aircraft wings to reduce turbulence on the control and lift surfaces.

 

 

But for bikes with boxes, it's not about downforce... like cars.

 

How many times have powerful CL2 bikes been retrofitted with panniers or boxes.... and then find themselves unstable at speeds above 180kph on long hauls.

 

I'm wondering if these things might help with stability and drag reduction. Vanity is not an issue here.

 

No, bro. I didn't mean downforce. I quoted that as an example of a cosmetic device. The spoiler on the saloon car and vortex generators on the rear box. But I can't really comment cos' what I learnt was more for application in aviation. If it gives stability for bikes above that certain cruising speed, then hey, you've got something that works!

[DeusExMachina]

That's why I called for a discussion.

 

Ideas. Exchange them.

 

 

I really don't see use for sportbikes... unless maybe small VGs at the edge of the windscreen to smooth the flow over the rider's helmets.

 

But the main concern is for the boxes. If you care to take a look at the 5th link I posted... the Air Tabs. You'd notice that trucks and buses use those little VGs also. As I read through the stuff, I realized that truckers install them to get better mileage, and also for more stability at speeds and in X-winds.

 

Interesting. That's why I thought that perhaps bikes with boxes could benefit from something like this. After all, on tours, we need our luggage, and we definitely would like to carry some speed sometimes.

[Marcheline]

One thing you should take note is the surface area. On the truck, it's nothing short of massive. The shearing of air as it flows across the surface is very significant at speeds, causing a great deal of turbulence at the trailing edge, thereby increasing the drag as it shoots across the freeway.

[DeusExMachina]

True... a truck is sort of a long box on the move. So the air has had some distance to move before breaking up at the square end.

 

But I noticed part 3 of the article....

http://www.autospeed.com/A_3060/cms/article.html

 

The truck here (those crazy Europeans race these things... ) doesn't have too long a flow area before the rear of the cab drops off.

http://us1.webpublications.com.au/static/images/articles/i30/3060_9lo.jpg

 

Looking at proportions, the truck cab seems about the same shape as a bike's top box. I'm guessing it might be a matter of What-sized VGs to use... and where to position them?? At the railing edge? Near the trailing edge? Or additional ones at the leading edge?

 

 

 

Found something about VGs to be used on racing bikes.... but the paper's protected though.

 

http://206.160.145.240/technical/papers/2003-32-0037

[frogman]

but on aircrafts, e VGs are nearer to e leading edge..how come e trucks put them near their tail?