Pannier Air Flow

[S10Pilot]

Anyone heard of any modifications to the leading edge of the panniers to reduce the airflow smacking into the "square" box? I wonder if a sloped triangle "airfoil" would help reduce the drag? There's also a number of companies who are making tabs that reduce the trailing edge aerodynamic drag. I'd think a combination of the two could be effective and unobtrusive on the panniers.
I'll mess around with the idea when my Pelicans arrive.

 

[markjenn]

I'm just waving my hands here, but I doubt there is much you could do that would significantly reduce drag without being pretty visually obtrusive and structurally clumsy. You get the most benefit in drag reduction at the rear of an object. So having a long fairing in the back which keeps the airflow attached as long as possible might make a measurable difference. But who wants to add 4' of trailing fairing behind the bags? Blunting the front edge with a bubble fairing (like you see on the front of tractor-trailer boxes) would also help, but not as much as the rear. The boxes are already in pretty dirty-airflow anyway, so any benefit is further reduced.

Fooling around with little details around the box edges likely wouldn't do a thing. BTW, my undergraduate major was fluid mechanics, so I'm not completely waving my hands.

- Mark

 

[Rasher]

Waving your hands will definitely have a negative effect on airflow, you should know that from your fluid mechanics course

Looking at the rest of the bike I would guess it would make no more difference than throwing away the toolkit to save weight.

 

[S10Pilot]

I'm just waving my hands here, but I doubt there is much you could do that would significantly reduce drag without being pretty visually obtrusive and structurally clumsy. You get the most benefit in drag reduction at the rear of an object. So having a long fairing in the back which keeps the airflow attached as long as possible might make a measurable difference. But who wants to add 4' of trailing fairing behind the bags? Blunting the front edge with a bubble fairing (like you see on the front of tractor-trailer boxes) would also help, but not as much as the rear. The boxes are already in pretty dirty-airflow anyway, so any benefit is further reduced.

Fooling around with little details around the box edges likely wouldn't do a thing. BTW, my undergraduate major was fluid mechanics, so I'm not completely waving my hands.

- Mark

As long as you're "waving your hands" with ALL 5 FINGERS, I'm listening!
My Masters in Telecommunications does NOTHING to help me understand fluid dynamics (so I defer to your knowledge), but my pilot license made me aware of parasitic drag and such as that. The trailing edge airfoil is certainly out of the question, but I'm thinkin' that an interruption to the trailing edge airflow might be of some benefit. I've seen the airflow tests using smoke over pickups (for instance) and noticed that the majority of drag occurred behind the rear of the cab as opposed to that hitting the tailgate. If that drag is interrupted then some quantity of fuel savings is realized and I was curious to know if a similar setup on the panniers might be beneficial.
The Mythbusters built a "dimpled" golf ball like surface on a car and, if you can get passed the "reality TV" personalities on that show, have proven a ~11% increase in gas mileage by interrupting the laminar airflow (7 min 35 sec into this video Mythbusters Clean Car vs Dirty Car S07E14 4/4) on a car.

 

[markjenn]

Well, Mythbusters is well-known for very sloppy scientific work so I'm extremely skeptical of their result. That being said....

Changing the surface texture characteristics of an object to create a local turbulent boundary layer is a well-known way of reducing aero drag in some situations. The idea is that you want turbulence to be confined to a thin layer rather than having drag-intensive large vortex shedding, so you introduce local surface roughness to encourage the early formation of a thin turbulent boundary layer. But whether this technique works is highly dependent on a number of things - it is not a universal "fix". Boeing spends millions trying to reduce the drag of their airframes by a few percent with each new generation of airliners - if they could get a 11% reduction simply by dimpling the exterior, I would think they would have done this long, long ago. And in any case, you weren't talking about dimpling the entire exterior surface of your hardbags - you were talking about adding aerodynamic tweaks to the edges.

I'd encourage you to try some things out and see what you think. One way to assess your results would be to top-end your bike on the same deserted section of road before and after the tweaks. The extra speed would amplify the difference. But you'd have to gather a fairly large amount of data to damp out the confounding variables (e.g., wind).

If you really wanted to do this right, you'd use an instrumented wind tunnel (either physical or computationally) to do your design work. But, as I said earlier, even if you did discover a tweak that made a significant difference in drag characteristics, the fact the bags already sit in extremely "dirty" air behind the front bodywork of the bike and behind the rider's knees would likely reduce the benefit to the point where you couldn't measure it on the bike in typical conditions.

Making the overall shape of the bags radically different (e.g., giving them a long "tail" to keep the boundary layer attached for a longer period) is, IMHO, the only thing that would likely result in a measurable difference. But that's just my fluid mechanics intuition (and 2K+ hour pilot intuition) talking so take it FWIIW.

- Mark

 

[XtreemLee]

Whoa here slow down. Without a windtunnel to see what happening you have no reference point of what to do where. The general "dirty air" shape of a motorcycle and rider will be extremely difficult to make any real progress.

Ride more...

 

[loop]

As long as you're "waving your hands" with ALL 5 FINGERS, I'm listening!
My Masters in Telecommunications does NOTHING to help me understand fluid dynamics (so I defer to your knowledge), but my pilot license made me aware of parasitic drag and such as that. The trailing edge airfoil is certainly out of the question, but I'm thinkin' that an interruption to the trailing edge airflow might be of some benefit. I've seen the airflow tests using smoke over pickups (for instance) and noticed that the majority of drag occurred behind the rear of the cab as opposed to that hitting the tailgate. If that drag is interrupted then some quantity of fuel savings is realized and I was curious to know if a similar setup on the panniers might be beneficial.
The Mythbusters built a "dimpled" golf ball like surface on a car and, if you can get passed the "reality TV" personalities on that show, have proven a ~11% increase in gas mileage by interrupting the laminar airflow (7 min 35 sec into this video Mythbusters Clean Car vs Dirty Car S07E14 4/4) on a car.

That car resembles my wife's car after shuttling four kids around for 5 years. Did not help trade-in value (a generous "fair" rating). Perhaps if I had explained the possible 11% gas mileage boost...

 

[autoteach]

No need for wind tunnel. Just attach a bunch of tell-tales to the bike all over it and have someone take pictures from a car or another bike s you pilot down the road at speed. Moving wind tunnel.

 

[toompine]

Whoa here slow down. Without a windtunnel to see what happening you have no reference point of what to do where. The general "dirty air" shape of a motorcycle and rider will be extremely difficult to make any real progress.

Ride more...

::026:: the bike is already so dirty related to airflow you are not going to make much difference

 

[Hungry Tiger]

Thot of air deflectors for leading edge of my Pelicans, but when I put a hand down there at speed (65mph) and just did not feel that much wind pressure?? Front plastic buldges seem to run pretty good interferece. Would still make great places to drop in 30 oz MSR bottle on each side.

Sent from my DROID RAZR HD using Tapatalk

 

[oKLRider]

http://www.atdynamics.com/video_trailertail.htm

 

[Ramseybella]

This is a good time for this one>> ::021::
The bike is not going to be any faster or save you gas if you don't use them all the time take them off.
Like making a 69 Ford Econoline Van aerodynamic the thing is like a wall with four wheels..

 

[Checkswrecks]

http://www.atdynamics.com/video_trailertail.htm

That can give a 5-ish percent improvement to a box that spends it's life at interstate speeds.
At less than 35 mph it's hard to get any measurable improvement.


With your leg in front of the pannier, plus the tire's outward outflow at the swing arm, the airflow between your leg and the pannier is pretty turbulent and simply rounding the edges may might only possibly-perhaps-barely make enough difference to be measurable. Especially on an adventure bike with about 90 surplus hp. (you only need something like 6 hp to get 60 mph with a human frontal area)


So I'd agree with
::021::

 

[XtreemLee]

The truck is a long flat box much different than the OVERALL shape of the motorcycle and rider. You are not getting a isolated air flow around the bags, they are just part of the dirty shape of the rider/machine.

 

[Big Blu]

Maybe someone here needs to buy a Vespa! My 300 GT get over 80mpg, it's white like a golf ball but has no dimples...... ::025::
I'm white and have dimples but I'm no golf ball...... ::021::

Paul

 

[True Grip]

In your avatar your black. Your forum name is Blu. You claim whiteness, I'm confused ;D

 

[S10Pilot]

No need for wind tunnel. Just attach a bunch of tell-tales to the bike all over it and have someone take pictures from a car or another bike s you pilot down the road at speed. Moving wind tunnel.

Hell, I could attach the tell-tales all over it and just park it on the street. Let the WY wind serve as the wind tunnels!
Caribou's for the ST will be here on Monday so we'll see how they change the riding characteristics. Have a set on the KLR, but the aero comparisons are apples and oranges between the 2 motorsickles.
Really like the MSR bottle idea. Have to adapt a bite valve/tube and just carry drinking water.

 

[Southern7]

Jesse 9.in Safaris, they are about as aero dynamic as a pannier gets.

 

[Ramseybella]

I forgot the name of the company who makes these but at one time when I owned my 2003 ZRX1200R I was thinking on buying them until I saw the price and also realized I was way to big and tall for this little bike..

 

[Dallara]

I forgot the name of the company who makes these but at one time when I owned my 2003 ZRX1200R I was thinking on buying them until I saw the price and also realized I was way to big and tall for this little bike..

Those are Corbin "Beetle Bags"...

http://www.corbin.com/kawasaki/zrx11_bags.shtml

I had a set of their "Fleetliner" bags on my Yamaha "Stratolounger"... whoops, "Stratoliner" (http://www.corbin.com/yamaha/ylnrbag.shtml), and they were pretty friggin' amazing. Beautifully crafted, great fit, paint that matched exactly, flawless function, and huge capacity. The only downside was they, and their mounts, were a bit heavier than I expected, but on the "Stratolounger" it didn't matter.

Best quality Corbin products I ever owned.

Dallara



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