Author Topic: General ??: Windshield design to reduce buffeting  (Read 23865 times)

Offline toaster404

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General ??: Windshield design to reduce buffeting
« on: May 27, 2016, 07:54:36 AM »
Individuals here appear to be among the most thoughtful and educated on the various fora I frequent.  So perhaps someone here has a pointer to research or some ideas that are based on physics and aerodynamics rather than on TV or magic.

I am going to make a windshield for (at least) my wife's 2009 Versys 650. 

Description: http://www.visordown.com/reviews/motorcycles/adventure/kawasaki-kle650-versys-2006---2014/361.html

The stock windscreen is minimalist.  See, e.g. http://www.totalmotorcycle.com/photos/2009models/2009-Kawasaki-Versysa.jpg  She likes this for the lower speed work, but became tired on the Interstate earlier this week after only an hour.  On the big Guzzi, I was just relaxing!  So we need a suitable screen.

The Versys fora have a variety of solutions and numerous nicely hyped commercial products exist.  However, any suggestion that there might exist wind tunnel tests or real-world evaluations without bias brings the usual cries of "heretic" - cries I am well used to!!

The aftermarket screens seem fairly pedestrian. 

Puig example: http://www.puig.tv/tuning-bikes/kawasaki-versys-650-2009/touring-screen/c171en/f213-r19-m2183/
Givi example: http://www.revzilla.com/motorcycle/givi-d405st-windscreen-kawasaki-versys-650-2006-2009

There are examples from similar bikes, e.g., the VStrom.  See, e.g. http://www.calsci.com/motorcycleinfo/VStrom1.html#Windshield

I have a VStrom with the stock screen and a laminar lip (came that way).  It's pretty tall overall, and surprisingly vertical, but I can see over the lip fine and ride at reckless driving jail time speed with my visor open.

I can cut a screen without any issues at all.  I'm just trying to figure out how to get the Karman vortex stream minimized and controlled.  Ideally, I'd have a screen that puts a fairly clean flow into her chest (stock is fair at this) and a screen that puts a fairly thin and steady stream of eddies just over the top of her helmet at speed.  That's what the VStrom screen does. 

One aspect I don't understand is the use of tapering upward screens.  Flow on a curved screen is up and out, with these edges being oblique to that flow.  The minimal and probably dangerous testing I've done by waving a stick with yarn on it around at speed (I have not yet been committed or arrested for these antics) suggests that a fairly regular, possibly spiraling vortex forms and then breaks up.  There's always some odd complex flow at the upper "corner" - at best, this just clears my shoulder.  The worst examples put some kind of mini-jackhammer into my shoulder / ear area.   I am not at all convinced that this taper does more than look good.  Were I tapering a windshield, I would put the wide at the top to minimize the amount of air moving up the windshield.

So, what departure angle to the edge of the screen is best? 

Another aspect is the rake backwards.  I can see this rake can help avoid drag lift of the front wheel.  The Versys actually has some built in ramps I suspect are there to keep the front wheel loaded at speed.  But is there some magic rake angle? 

A further consideration is control of vortex generation.  The laminar lip is one clunky method.  That's what I have on my Guzzi.  Hideous but effective enough.  Considering just making an adjustable wing, or an entirely new shield or three.  Another method is the adjustable wing, available in several incarnations.  These all work through redirection and through flow smoothing by injection of a band of air up behind the upper edge. 

I have not seen the use of simple vortex control systems.  The most obvious would be a serrated edge.  This works well - I did a test on a cruiser some time ago.  The problem is that nice row of shark teeth pointed at one's face and neck.  Another more-promising system is the Wheeler vortex generator.  See http://patentimages.storage.googleapis.com/pages/US5058837-1.png  Even small ones make a surprising difference in some turbulent spots, but I haven't worked up the edge of a windshield.  Would be interesting. 

There's also the simple vane vortex generators. 

So I'm all in a muddle.  Considering a shield that is, as much as feasible, a wing just below eye level of about shoulder width with vortex generators spaced along it.  A separate wing is impractical, but a heavily cut out shield with reinforcement on the verticals would do.

Another alternative could be a widening upward curved shield with a stepped edge allowing flow directly off a the steps whose edge is at right angles to flow.  Heavily ventilated in the middle, of course.  I'm used to having a bike that has good ventilation in the summer and a fair amount of gorilla tape covering vents in the winter!! Tempted sometimes to fit aircraft window vents.

Anyone who has made it this far has probably gone down this rathole before.  Any ideas? 


Offline rocker59

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Re: General ??: Windshield design to reduce buffeting
« Reply #1 on: May 27, 2016, 07:59:42 AM »

Michael T.
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Re: General ??: Windshield design to reduce buffeting
« Reply #2 on: May 27, 2016, 08:03:17 AM »
Don't underestimate the design of the helmet in reducing buffeting. Some newer designs of helmets feature anti-buffeting features, the Kabuto helmet I wear greatly reduces buffeting.

Relying on windscreen design is difficult because a small change in rider position as you move around on the seat or simply sitting up straighter can impact the benefits of windscreen effects. The helmet remains the constant factor.


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Re: General ??: Windshield design to reduce buffeting
« Reply #3 on: May 27, 2016, 08:06:02 AM »
 Here is what I think I know about air management .

 Mostly a nice still pocket of air is dependent on equalizing pressure . Proper venting seems to be the key , I experimented with airflow on a BMW airhead RT fairing , winglets , foils , lips , etc . In the end it came down to venting the windshield , had the same results with a police style windshield used on a naked beemer and a Jackal . Take a look at the Pacifica Aerofoil/Swanee/H&H fairing which is the best handlebar mount design ... EVER . The body is vented , as is the shield .

 Dusty

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Re: General ??: Windshield design to reduce buffeting
« Reply #3 on: May 27, 2016, 08:06:02 AM »

Offline kingoffleece

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Re: General ??: Windshield design to reduce buffeting
« Reply #4 on: May 27, 2016, 08:24:55 AM »
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Offline Higgins9875

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Re: General ??: Windshield design to reduce buffeting
« Reply #5 on: May 27, 2016, 08:46:06 AM »
This design worked on a Triumph 800 I had. Last time I checked they did not have one for a V7.

http://www.madstad.com/
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oldbike54

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Re: General ??: Windshield design to reduce buffeting
« Reply #6 on: May 27, 2016, 08:52:21 AM »
This design worked on a Triumph 800 I had. Last time I checked they did not have one for a V7.

http://www.madstad.com/

 Decent design , but the "unprecedented" stuff is silly .

 Dusty

Offline fotoguzzi

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Re: General ??: Windshield design to reduce buffeting
« Reply #7 on: May 27, 2016, 08:54:49 AM »
Parabellum supposedly uses a wind tunnel for design,

http://parabellum.com/Search.aspx?k=%20Versys
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Offline rocker59

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Re: General ??: Windshield design to reduce buffeting
« Reply #8 on: May 27, 2016, 08:58:35 AM »
This design worked on a Triumph 800 I had. Last time I checked they did not have one for a V7.

http://www.madstad.com/

Wish I'd had a Madstad for my Quota!

http://www.madstad.com/s.nl/sc.7/category.2335/.f

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Offline toaster404

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Re: General ??: Windshield design to reduce buffeting
« Reply #9 on: May 27, 2016, 09:46:00 AM »
Don't underestimate the design of the helmet in reducing buffeting. Some newer designs of helmets feature anti-buffeting features, the Kabuto helmet I wear greatly reduces buffeting.

Relying on windscreen design is difficult because a small change in rider position as you move around on the seat or simply sitting up straighter can impact the benefits of windscreen effects. The helmet remains the constant factor.

I have been looking into this.  She requires inexpensive helmets because they are sort of disposable on her head.  There's one in the trash right now!  However, once she stops depositing herself on the ground next to her tipped over bike, we will shop helmets. And will look at that brand.  Thank you.

Offline toaster404

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Re: General ??: Windshield design to reduce buffeting
« Reply #10 on: May 27, 2016, 09:52:23 AM »
Here is what I think I know about air management .

 Mostly a nice still pocket of air is dependent on equalizing pressure . Proper venting seems to be the key , I experimented with airflow on a BMW airhead RT fairing , winglets , foils , lips , etc . In the end it came down to venting the windshield , had the same results with a police style windshield used on a naked beemer and a Jackal . Take a look at the Pacifica Aerofoil/Swanee/H&H fairing which is the best handlebar mount design ... EVER . The body is vented , as is the shield .

 Dusty

This one? http://www.harpermoto.com/h-and-h-fairing-for-cali-1400.html  I really wish the 1400 touring had a quick release system allowing swap from winter shelter to summer flyscreen!

Venting in large measure is in my sketches.  I am also likely to put a couple of aircraft window vents into my 1400 windshield, for cooling and pressure equalization.

Offline toaster404

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Re: General ??: Windshield design to reduce buffeting
« Reply #11 on: May 27, 2016, 09:58:08 AM »
This design worked on a Triumph 800 I had. Last time I checked they did not have one for a V7.

http://www.madstad.com/

This resembles my flying wing sketch a good deal.  Up and down take extra holes.  I can make holes.   Changing tilt takes some longer machine screws and perhaps some wedged sleeves, if necessary.  The angle on the Versys is fairly decent already. 

I'll take this one for inspiration.  Still unconvinced on overall shape and wish I understood stalled trailing edge vortex generation better.  I know that my addition of vortex generators on one of my cars gave surprising slipperiness increase at Interstate speeds - obviously more quiet and mileage increased something like 5%.  Not so much at lower speeds - only at the magic 75 mph careful cop-watch speed!

Offline charlie b

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Re: General ??: Windshield design to reduce buffeting
« Reply #12 on: May 27, 2016, 10:02:27 AM »
I also do not understand the narrow windscreens.  They do really well....IF...there is no cross wind at all, which around here is a very small amount of time.  One reason I like the SPIII fairing and windscreen is how wide it is.  I suppose mfgs do it because then they can get a higher top speed out of it, and maybe because it makes the bike look 'sleeker'?

The efficiency of the screen at deflecting air is a balance.  90% of the newer bike screens are now spaced away from any fairing to allow a flow behind the windscreen as well as in front.  This relieves a lot of the pressure differential and you get a cleaner departure from the top and edges of the screen.  Think slotted or Fowler flaps.  As shown above you can do the same if your screen does not have any venting.  I use an MRA X deflector to help smooth the flow at the top of the screen.  Makes it less turbulent and can be adjusted to flow the air a little higher or lower as desired.

For an 'extreme' view of venting look at some of JB's solutions.  Two of his turned the screen into swiss cheese and one was just expanded metal screen material.  This is a solution that does not really deflect much of the air, but, it acts like a mass of turbulators for the air that is directed at the rider.
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Offline toaster404

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Re: General ??: Windshield design to reduce buffeting
« Reply #13 on: May 27, 2016, 10:11:26 AM »
Parabellum supposedly uses a wind tunnel for design,

http://parabellum.com/Search.aspx?k=%20Versys

Looking at http://parabellum.com/PARABELLUM-Replacement-Windshield-for-the-Kawasaki-Versys-2007-09-P73.aspx

The mirror cutouts are rather interesting.  Flow likely rolls over into a nice vortex at the cutout, forming a bit of a hole for the wash from the mirror.  I have noticed the mirrors really give much of the noise on my VStrom, and are a source of turbulence on Versys.  I suspect the original Versys mirrors are only good for a few more spills, then I'll replace them with something a bit lower and wider.

Charlie B's post is very interesting.  I thought of using some of the mesh around here, but it turned out to be steel.  Not friendly to riders and rather hefty!!!  I keep thinking a wider wing or highly ventilated system should work.  Of course, the obvious thing to do is an inverted version of the 727 or 747 flap system!  See, e.g., https://upload.wikimedia.org/wikipedia/commons/7/72/Undercarriage.b747.arp.jpg

Thank you all very much for your thoughts.  This is a very interesting subject.  I really wish I had access to time, equipment, and a wind tunnel.  The only wind tunnel work I ever did was documentation on a hypersonic hot shot tunnel.  I don't believe we need to worry about Mach 21!! 

I will document the trials.

Offline Chuck in Indiana

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Re: General ??: Windshield design to reduce buffeting
« Reply #14 on: May 27, 2016, 10:40:21 AM »
Airflow isn't always what you think. Airplanes are "tufted" to see what is happening. It's nothing more than pieces of yarn about 3 inches long stuck down with tape. I'm headed out to lunch, but a google search should show it.
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Re: General ??: Windshield design to reduce buffeting
« Reply #15 on: May 27, 2016, 10:42:51 AM »
Airflow isn't always what you think. Airplanes are "tufted" to see what is happening. It's nothing more than pieces of yarn about 3 inches long stuck down with tape. I'm headed out to lunch, but a google search should show it.

I did this on my Quota when chasing wind noise and turbulence.  Worked like a charm.

String, tape, and go for a ride!
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Re: General ??: Windshield design to reduce buffeting
« Reply #16 on: May 27, 2016, 10:43:23 AM »
As you know, the windshield acts like a wing through the relative wind. The idea is to get the flow to "stall or burble" at a point higher than your head. You can do this by adding a shield or stubwing on the outside, or by venting, or both. Once you have created the neutral space in the area you want, you must then decide if you want to look over or through the screen. I once added a second, taller windshield in front of an SP1000 fairing. I left an angled gap open at the bottom. It looked like crap, but it was very effective. I have seen photos of windshield on bikes in Europe where they add a second section of windshield above the original, leaving an open viewing area. The top screen looked to be adjustible in angle and height. Good luck and show us what you end up with.
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Re: General ??: Windshield design to reduce buffeting
« Reply #17 on: May 27, 2016, 11:50:51 AM »
www.calsci.com

Don't miss that calsci post from the King of Fleece! Especially this page:

http://www.calsci.com/motorcycleinfo/Fairing.html

It's about as physics-riddled as you could ask. Everything from the Wright brothers through 5th derivative fairing to Einstein's esthetics of the curvature of space.

They also make sensible-looking windscreens including one for your wife's Versys.

Way to go, King! Great post.

Moto

P.S. The page is not without fault, though. It specifies both "2 cups = 400ml" and "2 cups = 500ml" within a few lines of each other. Could be a quantum thing I guess.

M.

« Last Edit: May 27, 2016, 11:58:31 AM by Moto »

Offline mjptexas

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Re: General ??: Windshield design to reduce buffeting
« Reply #18 on: May 27, 2016, 12:19:56 PM »
As you know, the windshield acts like a wing through the relative wind. The idea is to get the flow to "stall or burble" at a point higher than your head.....

The other alternative (fly screens, etal,) is to keep your helmet in clear air to avoid buffering, but having the screen break most of the wind hitting your chest.  The result is less fatigue riding at speed.  You usually still end up with a fair amount of noise, and as stated before, the helmet really comes into play here. 
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Offline toaster404

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Re: General ??: Windshield design to reduce buffeting
« Reply #19 on: May 27, 2016, 12:29:04 PM »
Calsci:

"Wind tunnels are made to measure lift and drag, not noise and turbulence."     Incorrect.  I've seen them used to measure much much more.  A hollow sniffer will let one find the edge of turbulent flow.  Holes in surfaces can allow one to monitor detailed pressure changes which I was told can allow determination of laminar flow break away.  There are other things I've seen done, but these were not civilian tunnels.

"When outside air spills into the rider area, it almost always falls in a curved path, causing spinning vortices of air"   - Part of my work on windshields has focused on reducing the size and increasing the number of vortices.  Vortex generators such as the Wheeler design interrupt the formation of large powerful vortices through the development of longitudinal  vortices.  Really quite striking.  Hideous in practice, of course!  I have a spray painted plywood shield with beer can vortex generators around here somewhere.  Worked great!!! 

"to eliminate all Von Karman vortices"  - this is a bit of a stretch, I would imagine!!   I just want a relatively thin controlled zone of mixed up flow, rather than the bang band of big whorls.

I'll pick up some material tomorrow, or maybe I have some.  Almost anything works for prototyping. 

Another thing not generally worked on is the aft end of things.  I get better mileage and less buffeting with a big bag directly behind me.  I've thought of designing front throw over bags that tie into the bike's shape a bit and come back to my knees, and rear throw over bags tapering aft that follow on the lines of the front bags and come close to my legs.  Expect there would be a reduction in drag. 

Wonder whether a tall bag close behind the rider would lift the turbulent layer a bit over the rider's head.  Not fun in cross winds, though!

Offline fotoguzzi

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Re: General ??: Windshield design to reduce buffeting
« Reply #20 on: May 27, 2016, 12:33:18 PM »
My Buell had a madstad, it was very effective and quiet
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Offline JeffOlson

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Re: General ??: Windshield design to reduce buffeting
« Reply #21 on: May 27, 2016, 12:38:33 PM »
From the CalSci website:

"Of course the quietest possible ride is when you're looking through the windshield, but only about 1% of our customers are interested in looking through a windshield."

That has been my experience, too. (The first part, not the second part.)

I have several windscreens for my Vespa and my Norge. By far, the quietest, least turbulence-causing windscreens are those that I look through, not over.

The next best option is no windscreen whatsoever. There is more wind pressure on my chest, of course, but my full-face helmet is quiet and serene as it slices through clean air.
« Last Edit: May 27, 2016, 12:40:34 PM by JeffOlson »
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Re: General ??: Windshield design to reduce buffeting
« Reply #22 on: May 27, 2016, 01:02:26 PM »




Don't know if this image will come through, but if it does, it shows the shield on my Beemer, which is the best I've used. It causes very little buffeting. The combination of about 45 degree rake, slight lift at the top, and relativel narrowness provides significant protection while smoothing the windflow around my helmet.

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Re: General ??: Windshield design to reduce buffeting
« Reply #23 on: May 27, 2016, 01:38:48 PM »
There is no one fits all solution nor a single solution that can simply be moved around to adjust for buffeting in the various riding positions someone experiences.

It's a lot of marketing.

No two riders sit with the same exact posture nor are their bodies the same (length of neck,torso etc) and all those play a significant role in where the wind or turbulence hits the helmet or head. Then consider that moat of us tend to shift our positions, sometimes leaning a bit forward, sometimes sitting up straighter and that small pocket of still air we try to create just isn't big enough to cover all those variables.

Graig Vetter (for those old enough to remember) came up with a standard in fairings and windscreen design but most of them were large. He too figured out that cutting holes in the lower part of the windscreen alleviated pressure and helped with buffeting and also the tendency for the pressure behind the windscreen to pull the rider forward. Holes in the windscreen are hardly new or something recently discovered. Might be a good read- Vetters story about hiw he created his designs. Smart guy.

When you get to smaller windscreens ala the ADV or ST styles expecting to create some still air pocket for all riding positions, even for the same rider is asking a bit much.

It is possible because some have done it to get to the happy place that reduces buffeting, usually either by cutting down the windscreen so that your head is in clean air or with a windscreen that starts to get rather large.

Once the windscreen gets so big you are looking through it, might as well get in the car because you've just taken your soul and character adorned motorcycle and created...

An appliance.

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Re: General ??: Windshield design to reduce buffeting
« Reply #24 on: May 27, 2016, 01:43:13 PM »
What made the Vetter windscreens work is that the pressure-relief holes were "capped" with adjustable vents. You could seal them off or open them fully or partially. That made it pretty easy to get the smooth flow you wanted without letting in the rain.

Adjustable venting is not rocket science.
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Offline toaster404

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Re: General ??: Windshield design to reduce buffeting
« Reply #25 on: May 27, 2016, 02:01:32 PM »
My former brother in law actually worked for Vetter as a test driver, until the accident! 

We're more looking for a reduction in buffeting and improvement in comfort, not some magic thing.  The closest to magic is my VStrom, which I feel like mega-tufting so I can see what's going on!

I will likely get one or more aircraft vents to have around.  Drill a hole, implant the vent, and there's your adjustable air flow.  Unlike a plane, the side windows are always open! 

I anticipate being able to scrounge around the property in a bit, maybe I have some stuff.  I need stuff for saddle bag supports, too, so it's about time I scrounge.  Outside entities have also been suggesting that my valuable raw material storage heaps are unsightly and a nuisance, so maybe I'll root around and triage some!

Offline Dean Rose

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Re: General ??: Windshield design to reduce buffeting
« Reply #26 on: May 27, 2016, 02:33:05 PM »
 

:grin:


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« Last Edit: May 27, 2016, 02:33:48 PM by Dean Rose »
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Offline lazlokovacs

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Re: General ??: Windshield design to reduce buffeting
« Reply #27 on: May 27, 2016, 06:30:50 PM »
gaffer tape, cardboard and chicken wire can make excellent prototype bits of fairing, taping bits of yarn is also very useful. The best way is to go out and experiment, I spent a whole summer trying various things on my cali. Ended up with a slightly modded swannee and its absolutely brilliant.... good luck


Offline johnr

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Re: General ??: Windshield design to reduce buffeting
« Reply #28 on: May 27, 2016, 09:44:39 PM »
Given that Moto Guzzi has a perfectly good wind tunnel it is amazing to me that the standard screen on the EVT is so bad at producing turbulence and back draft.

The back draft is such that riding in the rain with my open face helmet is almost a no go. Spray etc is blown back in such a way that I end up with water on both sides of my visor and on both sides of my glasses. Four layers of water to try to look through makes it very difficult to see!

I tried the bike without the screen altogether but found the riding position completely wrong for an unfaired bike. I was feeling the strain at as little as 50 mph.

Modification is on the "get around to it" list but in the meantime I guess I'll need to give Rainex a try.

Interesting thread! I look forward to seeing where it goes.
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Offline ITSec

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Re: General ??: Windshield design to reduce buffeting
« Reply #29 on: May 27, 2016, 09:59:09 PM »
I read quickly and maybe missed this, but something I'd consider re buffeting:

The majority of buffeting comes from airflow rising under the windshield and fairing, wrapping around the tank and upwards towards the rider's head. Three places to look to reduce it are:
  • Letting air through or under the screen using ducts/holes in the screen, space between the screen and the fairing, etc.
  • Filling the 'pocket' over the tank to change the airflow shape - most easily done with a tank bag
  • Changing the shape of the lower airflow as it starts to head upwards - this can be done with airfoils or winglets (like the Stelvio, or add-ons for the Gold Wing), with tank pannier bags (a favorite of adventure riders), lowers on the fairing, etc.

Helmet shape, windshield, and other factors are all there, but it's surprising how much can be done with these three areas.
ITSecurity
2012 Griso 8v SE - Tenni Green
2013 Stelvio NTX - Copper
2008 Norge GT - Silver

I am but mad north-northwest!
When the wind is southerly, I can tell a hawk from a handsaw...

 

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