Buffetting and physics, random musings - Kawasaki Versys Forum
  • 2 Post By Fly-Sig
  • 2 Post By webmost
LinkBack Thread Tools Display Modes
post #1 of 3 (permalink) Old 07-03-2019, 09:48 AM Thread Starter
Fly-Sig's Avatar
Join Date: Jun 2015
Location: Salt Lake City
Posts: 1,013
Mentioned: 3 Post(s)
Buffetting and physics, random musings

I noticed the other day on the highway above about 75mph a significant subsonic buffet hitting my helmet. Something like 4 cycles per second. The faster I went the stronger it got. It was minimal at 60 but was there. Once I had felt it at the higher speeds I could detect it at lower speeds, but mixed in with the other random turbulence.

Putting my hand in different places I was able to determine it was riding up the back side (rider's side) of the windshield, then separating close to the top and moving towards my helmet.

I had adjusted the windshield on an earlier ride to maximum tilt towards me. This is a Madstad windshield, but the physics would apply to all brands. Previously I kept it adjusted at mid tilt. It seemed to work well mid tilt and I liked the visual line the best.

We've all made noise blowing over the top of a soda bottle (at least those of us over a certain age) and know the frequency doesn't change with how hard we blow, just the magnitude changes. But changing the dimensions (fluid level in the bottle) changes the frequency.

Eureka! There must be a dimension somewhere involving the windshield with a natural frequency of about 4 Hz. At this maximum tilt angle the gap between the instrument cowling and the windshield is large and fairly constant.

Adjusting the windshield to more upright killed the 4 hz buffet without creating a different one. At the more vertical angle the gap is much narrower at the bottom and opens up. The gap is not at all constant either laterally or vertically, so there is no natural frequency.

I guess the moral of the story is that buffeting isn't merely whether the windshield deflects the air away from the rider. The aerodynamics are important, and the gap is actually a pretty sophisticated application of the slotted flap/slat found on aircraft. But there is the simple Coke Bottle effect happening too.

If you're getting buffeted, moving the windshield can make a bigger difference than might be expected.
16VGTIDave and brwster like this.
Fly-Sig is offline  
Sponsored Links
post #2 of 3 (permalink) Old 07-03-2019, 02:25 PM
webmost's Avatar
Join Date: Jan 2018
Location: Dull-Aware
Posts: 165
Mentioned: 0 Post(s)
If you're getting buffeted, removing the windshield can make a bigger difference than might be expected.
There... fixed it for ya

Fastoman and Fly-Sig like this.

Unmitigated risk aversion is the new Puritanism; complete with witch hunts funny outfits and humorless preachers thundering doom. The Deity is Safety; Satan is a Lawyer; but the object is the same: to suck the life out of life and tell you how to live it.

Last edited by webmost; 07-03-2019 at 02:27 PM.
webmost is offline  
post #3 of 3 (permalink) Old 07-03-2019, 08:56 PM
Super Moderator
Fastoman's Avatar
Join Date: Sep 2009
Location: Ipoh.Perak.Malaysia
Posts: 6,958
Mentioned: 6 Post(s)
Thanks for sharing.
Fastoman is offline  
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Kawasaki Versys Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome