Windshield buffeting

[Scruit]

I ride an 04 Volusia that ha a factory windshield set at the highest setting from new.. I'm 6'2 so my head it high and further back that most volusia riders.

This isn't really a question, more of a rant / documenting my thought process in hopes someone benefit from this at some point.

I've been half-heartedly chasing a wind buffeting problem caused by the windshield since I got it, but now that I'm commuting on the bike the buffeting has to stop.

The first thing I tried was putting my arm out in front of my chest and feel where the air was coming from. It was around the tank into the low pressure air behind the windshield, so I got some lowers and that fixed the problem enough that it didn't bother me too much.

Now I'm finding what's left of the buffeting to be pretty annoying. If I stay at 60-65mph for most of my commute then I wind up with my head beaten around and a nasty headache from it.

So it seems like the buffeting now is coming from the air that is going up over the windshield start off pretty clean but then get very turbulent by the time it reaches my helmet.

I've tried the following:

- Adding a laminar lip, trying everything from 5" below the top of the windshield to a high as it will go. Some positions helped a little but others made the buffeting worse.

- Found a simple mod that tilts the factory windshield more vertical. Tried that at with the windshiled at the lowest setting and found the buffeting worse, and EVEN worse with the shield mounted at the highest setting. Feels like the air becomes more turbulent the further back it gets from the windshield, so tipping the windshield away from me gives the air more time to become turbulent.

- I put the windshield back to original factory mounts but at the lowest setting. I can feel the air hitting my helmet, but it's cleaner air so up to 70mph (fastest I could test tonight) the buffeting is limited to sidewinds and when I get too close to other vehicles. The top of the windshield is now a couple inches short of my chin. This is the best setting I've found so far.

So, this weekend I'm going to give the laminar lip another try at the lwer windshield height.

If all else fails I'm going to try fabbing up some brackets that will let me tilt the windshield towards me. The turbulence seems to be at the back of the low pressure "bubble" created by the windshield, so by bringing the windshield tip closer to me should move me further forward towards the clean air.

Hopefully.

[El capitan]

i wouldn't know what to do with myself if i had a windshield. if you want to talk buffeting i got it covered.

[ReconRat]

CalSci Motorcycle Fairings and Windshields

Aerodynamics

Nearly all of our windshields have vents. These vents are part of the aerodynamic design of the shield, to reduce turbulence and noise. They are not there to make a flow of air on the rider. When you're riding on the highway, any windshield is pushing air away from the rider. This leaves a low- pressure pocket between the windshield and the rider. The air flowing past the motorcycle wants to drop into this low pressure area. If the outside air is allowed to spill into the area between the windshield and the rider, the result is turbulence, noise, and drafts. When outside air spills into the rider area, it almost always falls in a curved path, causing spinning vortices of air. These vortices are noisy and can cause the battering and hammering on your helmet reported by some riders. Our windshields and vents are designed to funnel air into the rider region to relieve this low pressure area and greatly reduce the tendency of outside air to spill in. The vents are designed so that the air coming through them is quickly dispersed, leaving almost no detectable air flow at the rider. Our goal is to produce almost completely still air on the rider with no back pressure.

I get a lot of emails, "Can you make me a windshield with a reverse flip to kick the air up over my head?" Yes, I can, but I won't. Air is a spring - there are shock absorbers made with only air as the spring. When you kick a spring, it kicks back. Putting energy into the air like this is exactly the opposite of what we're all about. Windshields with reverse flips and non-fair shapes generate semi-periodic chaotic swirls of turbulent air, called Von Karman vortices, after Theodore Von Karman. These vortices, or pockets of turbulence, grow as they move away from your windshield. If you feel your head being rocked or even slammed side to side or front to back as you ride, this is Von Karman vortices at work. Some manufacturers, to my own astonishment, actually claim to produce these vortices on purpose, apparently with the idea that some turbulence is "good" and will somehow perhaps cancel out the "bad turbulence." We work very hard with the design of the shape of our windshields and the location and size of the vents to eliminate all Von Karman vortices.

[imprez55]

^^ Not a bad read, might be interesting to find another windshield that might help. Otherwise I have and idea that might seem crazy to you, but if I had the problem I would use the smoke machine I have and a fan and try to see where the most turbulence is. A good place would be the garage on a calm day. Although I have never tried it (or heard of anyone trying it) it would be at the very least interesting to see. Once the problem is diagnosed I am sure there is a fix, it just might be harder to get at the root of the problem by just guesstimating what is wrong. Again, just a crazy idea, hope you fix it regardless of the path.

[Scruit]

CalSci Motorcycle Fairings and Windshields

Saw that page and looked to see if they have a windshield for my bike. Nope.

I *have* heard from other forum that people have added goldwing vents to their windshields for the same effect - to fill in the low pressure.

[ReconRat]

One possibility is to increase airflow under the windshield. Maybe moving the shield up or forward so air comes in around the lower side. Maybe. What you're looking for is creating laminar flow (smooth).

edit: I always take the edge molding off. Not sure it's a good idea, or if it helps. Some windshields that is hard to do.

Edited October 1, 2010 by ReconRat

[Slowroller]

Using the stock shield on my Concours 14 I had both buffeting and back pressure so riding at speed I left it down. With cooler temps I switched to the CalSi X-large and now buffeting gone, a large enough bubble I can listen to my GPS voice commands at highway speeds and near zero back pressure.

[Scruit]

Yeah, I wish calsi did a shield for my bike. Theirs are all unique to the bike so there's no universal fits.

[RSparky]

My wind screen is not too bad for von karman vortices. Makes me wonder about getting a double bubble like i had originally intended. That would put the windscreen further from the helmet, and possibly make a difference for the worse..

[Scruit]

I fabbed up an aluminum mount that places the shield 4" higher (at the correct height for me, level with my nose) and tilts the to edge towards me by 4". If that works out on my commute tomorrow I'll have a machine shop make me a set from stainless steel. The design allows me to loosen a quick-release and tilt the shield backwards and fowards up to 6". I can also raise/lower it by about 2".

On today's commute I had the shield at the full height but not tilted yet... As I rode any buffeting I got was "cured" by leaning forward 3" to get closer to laminar airflow right off the shield and away from the von karmans. I'm hoping that tilting the screen towards me will keep my head in laminar air in my natural seating position.

Edited October 7, 2010 by Scruit

[Scruit]

The buffeting is 90% fixed.

Here's the prototype mounting bracket in aluminum. I found a mahcine show that will fab up the brackets for me from a CAD file, so I downloaded their CAD software and I'm drawing up the design based upon this prototype with a couple of tweaks...

- The lower windshield bolt is pinched between two large washers rather than having the bolt go through the bracket. This was a the widest aluminum stock I had on hand so I improvised when I needed to go wider. In the CAD design I'm extending the bracket to have a bolt hole instead of the pinched washers.

- The holes that don't currently have bolts in are not needed and will not exist in the final version.

- The edges of the piece will be tweaked to follow the lines of the existing brackets and windshield. The bolt holes will have at least 1/2" material around them. (The top windshield mounting bolt hole in this pic does not have much material aft of the bolt - that has to be fixed.

I'm going to compare the cost of making a pair of these in 1/8" steel and chroming it, or having it made up in stainless. The company will use the CAD file to cut the plate with either water or laser, so it's going to be a professional stock-looking part when it's done.

The reason the buffeting is only 90% fixed is that by raising up the windshield so much I opened a huge gap between it and the lowers. There's air rushing through there around the tank now - I can stop it by putting my arm out in front of my belly. I'm going to adjust the lowers to compensate.

Edited October 7, 2010 by Scruit

[Scruit]

I raised up the lowers and now the buffeting is totally gone. I can ride with my visor open in the calm air behind the windshield.

From the pic above, where you can see the bolt behind the lowers... I just removed that bolt and attached it to the lowest bolt on the new bracket.

Now I need to CAD the bracket and get a pair fabbed up at the machine shop.

[ReconRat]

Yeah, I had a friend make a pair of lowers for his Star, and it was a world of difference when they were positioned right.

[Scruit]

Yeah, I had a friend make a pair of lowers for his Star, and it was a world of difference when they were positioned right.

Yeah, when they are positioned correctly they are great - but when positioned incorrectly they can make things worse. I'd rather go no-windshield than have a bad windshield.