Windshield Mod Phase I

[Xdot]

The following comments apply to a Parabellum Supertour. Your own results may vary.

With all these windshield threads this should go over well! And as all of you know I've made windshields and turbulence my passion because I am going deaf from the noise!

Windshield turbulence is caused by a pressure and velocity differential between the air behind the windshield and the air hitting the windshield. As the air passes over the top of the windshield the 'vacuum' behind the windshield pulls it down. An oscillation gets set up which causes vortices of air coming off the lip along the boundary between the fast and slow moving air. These vortices detach and move along the air stream, contributing to turbulence. The low frequency booming you hear is these Von Karman vortices hitting you in the head. Here's a nice little video illustrating the effect: http://en.wikipedia.org/wiki/File:Karma ... linder.ogv

My research indicates there are three ways to lessen the effects of these Von Karman vortices as regards a motorcycle windscreen.
1) Reduce the pressure differential - most easily done by cutting a hole in the front of the windshield to let some air through
2) Increase the windshield rake to reduce the compression at the top of the windscreen.
3) Move the head of the rider closer to the edge of the windscreen. (You can see in the video that the turbulence increases as you move farther from the edge.)

So, last night I performed the first step - cutting a hole in the front of my windscreen. And you know what? It made a difference. These are the steps I went through

1) Mark the size and shape of the vent on the windshield. I covered the area with masking tape so I could draw on it and to protect the plastic.


2) You have to careful cutting acrylic. If the bit or saw gets hot it will start melting instead of cutting. It is also possible to shatter or crack the material so you need to be careful. You also don't want square edges as they cause stress in the material. I chose to drill large holes at the curves using a Forstner bit as shown. It was pretty easy though the bit did heat up. I found it worked best if I used pretty good pressure but a very slow bit speed. It sort of shaved the hole but was a bit tricky as the bit tended to stick in the hole. For drilling the holes I laid the windshield front side down on a towel with some newspaper between to drill in to.






3) Next I drew lines from the curved vertices tangent to the holes.


4) Use a jigsaw with a coarse wood blade. Make sure the blade is nice and sharp so you don't crack the screen. This was not hard. The material cut easily. Of course the front of the windshield was facing up for this step.




5)This is the hole after I cut the vent out which I then cleaned up with a file and some coarse emory cloth.





6) Here's what it looked like on the bike:





All in all it was a pretty easy job. The hardest part was drilling the holes. Just go slow and make sure you have a sharp bit. For the speeds we go I don't really think it matter much what the shape of the hole is, just that it make sense.

Next is to add a diverter to direct the air up along the inside edge of the windshield and increase the rake. Increasing the rake should also move my head closer to the edge.

[ron prior]

Xdot,

Please keep us posted on the result. BTW what windshield is that?

I think that was the thinking behind the old Vetter Windjammer windshields. They had holes in them, & a cover [for rain] ? that snapped in place.

I noticed on a recent rip, that allot of turbulance comes from / off my arms. If I move one 'in' it changes everything as far as wind. @ one point [road to myself] I moved both arms 'in' behind the shield & WoW what a difference.
Which is why I'm wondering if the extra bit of width of the Parabellum might make the biggest difference? It's not so big as to look like, act like a sail,..but would likely divert air around the arms?

Ron

[Xdot]

BTW what windshield is that?

Sorry. It is a Parabellum Supertour. I added it to the top of the post.

The Supertour is pretty wide and does seem to divert the air around my arms.

[spoon]

This is good. I'm glad someone had the nerve to make the forst cut!!! I think quite a bit of turbulance comes form the bottob on the windshield and the top of the oil coolers. Someone, Aeroflow I think, makes a diverter that glues to the top of the oil cooler addresing this issue. The edges of my tank bag peramently deformed up because of this updraft. Releaving the pressure (vacuum) from the back of the windshield might address this issue. Let us know.

[gregor]

Unless my eyes have gone funny with old age or you have induced a double exposure in your pictures (remember them?) you have two windscreens/windshields fitted.

What's the point of that and why has no one else spotted it?

[Xdot]

Unless my eyes have gone funny with old age or you have induced a double exposure in your pictures (remember them?) you have two windscreens/windshields fitted.

What's the point of that and why has no one else spotted it?

LOL, yes. There is a fly screen on there too. I had hoped it would serve to divert the air up but the clearances were too tight so I just pulled it off. Unfortunately I had already taken the pics. I plan on heating a sheet of acrylic this weekend and forming a 'diverter' that will direct the air upwards along the inside edge of the windshield.

I agree, funny that no one else called me on it.

[iowabeakster]

I was just going to say something...then I read down the comments.

[Xdot]

Sometimes things just work out. I like it when that happens.

I pulled the SuperTour off tonight and removed the flyscreen under it. But when I did that I noticed that the flyscreen mounts looked like they were at about the right angle to lean the screen back to about where I wanted it. So, I put the SuperTour back on without the upper mounts, pushed on the top, and with virtually no pressure, the flyscreen mounts were suddenly flush with the inner, curved surface of the windscreen.

I used a plastic bit to drill four holes, inserted the original four screws, and all of a sudden I'd increased the rake angle by about 20 degrees. While the flyscreen mounts would not be strong enough if they were the only ones, with the headlight mounts the system is quite rigid. It does press on the turn signals a tad and I'll have to address that, but it's certainly fixable. Not only that, the screen looked exponentially better. I'm not sure why, but it went from looking surprised, to relaxed and... tough. I'd never liked the look of the screen but I do now.

If the weather permits I will be testing it out tomorrow and if it works, I'll post pictures. Y'all will like it.

[sstein]

Any update on this experiment Xdot?

[Xdot]

Actually, yes. Thanks for reminding me. Work has been... You get the idea.

For starters, the more sloped windshield looks a LOT better. Never really cared for the look of the SuperTour. The more angled look now follows the lines of the forks, more like a Scout fairing angle. The improvement in looks is really quite dramatic.

Noise reduction was mixed. While the slope and the cutout have pretty much eliminated the low frequency rumble, the mid and high frequency hiss is a bit more pronounced. (This is not all bad since these frequencies doen't bother me as much.) Plus, the top of the screen is now several inches lower so the airstream hits me just below the forehead. Above 60 it is pretty loud. With earplugs though it is downright quiet. Even with earplugs the low frequency tends to bother me. Ear buds don't give quite as good a result but it is still far better than either the more vertical configuration or no windscreen at all. I also noticed that with my visor opened more than a crack I get a pretty annoying vibration. It is quite pronounced as speed increases. With the visor closed or barely cracked it disappears completely.

However, if I duck down a bit it is extremely quiet. Like an RT. But it's a bit too much duck to be all that comfortable. I'm pretty sure I have the mid-height 21" screen. Going to the 23" screen would leave the edge of it a few inches under my eyes but bring it up enough for some serious noise reduction. I'm talking like 90%. I'm debating either a new 23" that I'd mod or going with a Scout.

I like the air balance vent a bit better on the Scout. The shield on the Scout also starts at a slightly different place which would seem to provide a bit better aerodynamics but I could easily be wrong about that. Moreover, the Scout fairing completely encircles the headlight and is a bit more bullet-shaped all the way around. A Scout with a K1200RS front fender might produce some pretty dramatic decreases in sound energy. Of course the lead time on a Scout is about three months!

For those not completely satisfied with the protection afforded by their SuperTour and have, or can get, a set of the curved, stock FlyScreen mounts, I would strongly recommend this mod. It is much better than the stock configuration and eliminates those large, curved brackets that run from the handlebars. If you're thinking of buying a SuperTour and doing this, by all means get the longest one available. If it is too long you can always cut it down with a jig saw. The one down side is if you make these mods and decide to do something different, you may have trouble selling the original screen cut and drilled like that.

[grwrockster]

Xdot. I just read your stuff with interest, as I've been toying with the idea of chopping a hole and wondering about making some sort of 'scoop' or airflow diverter as well. I just haven't got around to it.

I've got the screen off an FJR1300 Yam on my Rockster as an experiment (as I have 'GS handlebars so sit higher, and I got the screen cheap to play around with - it could be 'sacrificed' without it costing much, plus there aren't all that many listed screen options for Rocksters either).

I've done a lot more limited (and doubtless less scientific) stuff than you, but I've broadly noticed similar traits (i.e. you can have high-end 'hiss' or low-end fluttering and a sort of staccato drumming noise, with varying degrees of influence and annoyance). BTW, I always use plugs as my speeds on the open road in UK and Europe are regularly 80-ish, and I've not ridden anything yet with a screen that kept noise at those speeds acceptable. So my comments are all based on experiences with SNR39 ear plugs in.

Have you tried your set-up changes with a different helmet on? I've found that while my screen set-up as is has an annoying low freq vibration 'thrum' with one lid (Caberg Trip Flip Lid), it is markedly better with a spare cheapo lid (another Flip but different shape).

Also, I think that air density changes things too, as does turbulence off other traffic - have you noted this?

My bike is off-road while I service it, so not played with the screen in the current cold wet weather. But equalising pressure by adding a hole is something I've considered - what sort of size hole have you cut, and do you think in your experience I'd gain a worthwhile benefit by getting the jig saw out?

GRW.

[Gonzo49i]

Has onyone tried the laminar lip?

[Xdot]

Xdot. I just read your stuff with interest, as I've been toying with the idea of chopping a hole and wondering about making some sort of 'scoop' or airflow diverter as well. I just haven't got around to it.

I've got the screen off an FJR1300 Yam on my Rockster as an experiment (as I have 'GS handlebars so sit higher, and I got the screen cheap to play around with - it could be 'sacrificed' without it costing much, plus there aren't all that many listed screen options for Rocksters either).

I've done a lot more limited (and doubtless less scientific) stuff than you, but I've broadly noticed similar traits (i.e. you can have high-end 'hiss' or low-end fluttering and a sort of staccato drumming noise, with varying degrees of influence and annoyance). BTW, I always use plugs as my speeds on the open road in UK and Europe are regularly 80-ish, and I've not ridden anything yet with a screen that kept noise at those speeds acceptable. So my comments are all based on experiences with SNR39 ear plugs in.

Have you tried your set-up changes with a different helmet on? I've found that while my screen set-up as is has an annoying low freq vibration 'thrum' with one lid (Caberg Trip Flip Lid), it is markedly better with a spare cheapo lid (another Flip but different shape).

Also, I think that air density changes things too, as does turbulence off other traffic - have you noted this?

My bike is off-road while I service it, so not played with the screen in the current cold wet weather. But equalising pressure by adding a hole is something I've considered - what sort of size hole have you cut, and do you think in your experience I'd gain a worthwhile benefit by getting the jig saw out?

GRW.

The air balance hole helped a lot. As far as size, take a look at the pics at the top of this thread. I could provide measurements if you'd like. But the biggest difference came when I tilted the screen back. A few more inches of plexi and I'd be riding quiet. The air vent did go a long way towards shifting the sound energy from booming to hissing which I find far more tolerable. With earplugs it is down right quiet now, but I really prefer to ride with some isolating earbuds and listen to music.

As far as a scoop, I wanted to do the same thing but there's no room for one. The clock is in the way.

Laminar lip: No. Too many lines to look through.

Air density: YES. Cold, dense air seems to flow over my head better than warm, air. This makes sense as dense air would tend to follow a path better because of the greater inertia. In other words, warm air would probably get sucked into the vacuum behind the windshield a little easier.

I did ride an RT once which just seemed to get quieter as I sped up. I will eventually end up with one but haven't found anyone willing to give me one for free so I'm going to have to wait on that. I also think an R1200RT is probably the way to go which means it will be an even longer wait!

[Airman]

This is an interesting subject. I saw a post by Ricky Kuhn over on Advrider where he cut a pair of NACA ducts in the windshield of a GS with supposed excellent results in curbing the turbulance. This looks like a similar project.

[GSGeezer]

Well done post. I looked on Aeroflow's site and could not find the wind diverters for the tank. Were the ones shown in your last picture Aeroflow?
I am finally back riding after my 10/31/05 getoff. Cannot deal w/GS seat height now. The Aeroflow kept my GS relatively quiet. Have already noticed annoying turbulance on my Rockster. It came with the BMW windshield.
I diminished the 'disturbance' on the old GS by increasing the thickness of the bushings (spacers) between the top and bottom halves. Just starting the Farkling period of ownership; membership to the group and more questions to follow.
In searching for tankbag I found that Marsee has just recently discontinued their 10L 'teardrop' design. Does anyone have any connections to where I can find one. Had one with a mag mount on the GS. (Had no issues with wind below unmentionable speeds). I just like their design, shape, and quality. No affiliation or connection; just a very satisfied customer.
Bike has good provenance. Out of Robobiker's garage. 80th/943. Came w/17750mi. Soon to be lots more.

"If you can't have fun going, you're going in the wrong direction"

[Xdot]

The tanks wings were Aeroflow. I got them about a year ago. I don't know if they still sell them or not but you can probably find some for sale second had on this site.

[GSGeezer]

Thanks Xdot, I'll call them and see if they can can come up with a set.
Any ideas on how to track down a 'new' Marsee 10l Teardrop magnetic bag?
I'll try IBMWR. I guess I need to rejoin BMWMOA and BMWRA. Later.

[grwrockster]

The air balance hole helped a lot. As far as size, take a look at the pics at the top of this thread. I could provide measurements if you'd like. But the biggest difference came when I tilted the screen back. A few more inches of plexi and I'd be riding quiet. The air vent did go a long way towards shifting the sound energy from booming to hissing which I find far more tolerable. With earplugs it is down right quiet now, but I really prefer to ride with some isolating earbuds and listen to music.

As far as a scoop, I wanted to do the same thing but there's no room for one. The clock is in the way.

Laminar lip: No. Too many lines to look through.

Air density: YES. Cold, dense air seems to flow over my head better than warm, air. This makes sense as dense air would tend to follow a path better because of the greater inertia. In other words, warm air would probably get sucked into the vacuum behind the windshield a little easier.

I did ride an RT once which just seemed to get quieter as I sped up. I will eventually end up with one but haven't found anyone willing to give me one for free so I'm going to have to wait on that. I also think an R1200RT is probably the way to go which means it will be an even longer wait!

Xdot. Have taken the plunge and cut a similar shaped hole in my screen (a bit smaller than yours I think - on the basis of I can make it larger if I want to) and taken it out in quite cold (as in maybe 2 or 3 deg C) conditions for a ride, with 2 diff helmets on to make comparison. Route varied the speed from 30-40mph to . At least some good news is that the screen doesn't upset the bike's stability at all - being bar-mounted there was always the chance it would do.

Result? The air bleed hole DOES provide an improvement. Like you - I can't rake my screen back much, as it'd then be too low to deflect air high enough.

I've also tried adding on the adjustable spoiler from my MRA Vario onto the top of my FJR screen to try. Not tested that very much yet, but I'd say at the moment the results seem mixed (again I suspect that the screen needs be be more raked back a bit more - more upright seems to equal quieter/calmer in some ways, but at the cost of some turbulence. Like you suggest, it may well be that it needs to be both higher & raked more). I think I have the scope to raise the screen a bit higher, which would then also bleed a bit more air over the instrument cowl, and which would then perhaps allow me to rake it back a degree or 2 more.

I'm still thinking also about how to experiment with a deflector to persuade the air from the new bleed hole to follow the inside face of the screen more - I think that might clean the flow up - right now if you put your hand behind the screen hole, there's a fair blast of air dissipating randomly into the space behind the screen. What to make a deflector out of, what shape, do I try for (e.g. a shallow but wide vent exit to try and force and pressurise the air from the screen bleed hole across a wide arc of the inside screen face) are all things I haven't really thought about yet.

I know what I'm doing is messing about rather then being all that scientific about it, but I plan to keep playing about and try a couple of 'what if's'. If nothing else it'll keep me amused for a while, and I might even make an improvement with a bit of luck!
Do you have any suggestions and/or sound theory that might help out my random bodgings Xdot?

[Xdot]

Do you have any suggestions and/or sound theory that might help out my random bodgings Xdot?

If you can't side-grade to an RT or RS, you might try this: http://rifle.com/Air-Balance-Windshield ... 4C541.aspx

I happen to have one that I ordered that won't fit my application. It's still in the box! I'd be willing to let it go, cheap. Not that it was all that much to start with.

John

[grwrockster]

If you can't side-grade to an RT or RS, you might try this: http://rifle.com/Air-Balance-Windshield ... 4C541.aspx

Tbh - I'm rather fond of my ugly duckling Rockster. Hardly anyone else into bikes I've met seems to like it (more the opposite), so there's no kudos to be had from ownership of one. Mine isn't spotless or lavished with care and polishing either (though I try to look after the mechanicals and I do chuck a bucket of soapy water at it now n then). I like it's basic rugged feel, and the fact that if it tips over it won't cause a grand's worth of damage, and that I've a good chance of being able to just pick it up, eye the (extra) scratches and ride off (probably one of the few genuine advantages it has over an R1200RT - along with the price). I don't mind tinkering with it, and as it's not generally considered a 'looker' then that means it's harder for me to spoil it maybe? Whatever, after 4 years I have no plans to change it for anything else - good and bad, it feels like its 'my bike'.

I have looked at the Rifle kit, and the Gold Wing adjustable vent, but got no further than looking, and then promptly chopped a different -shaped hole anyway (though it might be small enough to re-shape for a vent kit I suppose). I'm thinking more of a DIY 'suck it and see, and change it if it doesn't work' sort of process at the moment.

I'd be interested in your unbiased opinion though - what do you think of the Rifle kit, it's design and so on? Do you think it'll make a big difference over a vent hole alone?