General ??: Windshield design to reduce buffeting

[charlie b]

 




Dean

Yep, that's the one!  I didn't know JB finished 'farkling' his new rat.

[canuguzzi]

Moto Guzzi put that wind tunnel to good use with the Norge. The 8Vs fairing is very good. The heat management is outstanding to the point that few bikes do it as well.

The windscreen? There is no way to make one that suits everyone. With riders from 5'4 to 6'4" and probably more at both ends they had to find some design that hit most of the points and they accomplished that IMHO.

I rarely bother to adjust it, leaving it in the low position and I get next to nil buffeting. There is no vacuum effect to pull you forward and it doesn't act like a noise tunnel either.

The Norge fairing and windscreen? Tops in the class of STs.

[krglorioso]

The "Laminar Lip" added to my '03 Stone Touring's OEM Sport windshield has been very effective in reducing buffeting almost to nil.  Windshield "rake" experimentation also helps.  I found a more upright position worked better than more laid back, which struck me as odd, but it clearly is better upright.

Ralph

[toaster404]

The lip on my 1400 and on my DL1000 VStrom are very effective.  Unfortunately, the stock screen on the Versys does not lend itself to any kind of lip, being small and pointed.

However, the earlier Versys has a small screen.  I notice the next generation has a differently shaped screen more like the Norge.  These are similar to the Mastad.  The Versys also has a swell and notch aspect to the area below the windscreen, which may help generate a low pressure zone pulling side wash off the screen downwards.

I will make up a large, medium, and small outline based up the Calsci, Mastad, Norge, and newer Versys screens.  I will also make a rake control system.  I actually want to make the screen on my 1400 slightly more vertical.  Getting a bit more up and less out flow than I want, based on minimalist tuft experimentation. 

Thank you all for your suggestions.

[oldbike54]

 Fairly certain the wind tunnel hasn't been used in years . Yeah , I know about the Norge photo , probably staged for effect .

 Dusty

[Gliderjohn]

For what it is worth from Wiki:

It is unknown to what extent the wind tunnel is used currently. The December 2005 press release for the Norge 1200 states that the bike was "thoroughly tested" in the Mandello wind tunnel.[4] Aprilia, a company in the same group as Moto Guzzi, maintains a relationship with the aerodynamics program at the University of Perugia, where computer simulations combined with practical tests (done in smaller tunnels using scale models) can more effectively and economically provide accurate testing and feedback.

GliderJohn

[ratguzzi]

Everyone laughs but the expanded metal with house screen works amazingly well. No buffeting of any sort and I can go 70mph with a baseball cap on and sipping a pepsi. All you feel is a slight little breeze through it.
Now see the EV in the background? It has the classic barndoor on it. The WORST windshield I ever sat behind as far as super severe buffeting and weird handling if you go over 80mph. I did the same thing on a few different windshields, pump it full of holes. It drastically changes it into a great windshield like my screen. Virtually no buffeting and very quiet. I guess I am diffusing the air stream and not trying to deflect it.
JB

[alanp]

you might try one of these;  MRA x-screen

http://www.twistedthrottle.com/mra-x-creen-windshield-for-suzuki-dl650-04-11

The link is to one for a vstrom, but they make them for a variety of bikes and they just clamp on.  They are highly adjustable.  I have used them and they work well. 

[dl.allen]

I just put a national cycle street shield EX on my 850T adjusted about nose height.  It works extremely well.  It has a 2 inch gap at the bottom which curves in toward the bike.  I don't know if that has anything to do with cancelling the buffeting/stability but works great.  Looks ok ish.  I have only ran about 65mph.  $150 free shipping from Revzilla

[Madtownguzzi]

I have had good luck with Longride shields on the Harley it has a reverse curve that kicks the air up and over my helmet.
http://www.longrideshields.com/category_s/1822.htm

It still is not as good as my original Swanee Pacifico Aero Foil on my 98 V11 EV which you can still get as a reproduction from Harpers.
http://www.harpermoto.com/h-and-h-handlebar-mount-fairing.html

Longride also makes a universal shield that I have no experience with but if you were to call them I am sure they would be of help.
http://www.longrideshields.com/category_s/1826.htm

[tris]

I found with the standard MG screen on my B11 that if I had it down and only just clearing the headlight I got buffeting but if I gave it 1/2" - 3/4" clearance I didn't

[charlie b]

Here's a side view of my SPIII fairing and the MRA X visor.  The MRA X smooths the departure from the screen and moves the flow up about 2" so it just clears my helmet.  Without it the airflow 'hit' my helmet just above the visor.  The visor is adjustable for angle and also has two arms so it can be placed further up or further away from the windscreen.

I do not have any pressure reducing holes and don't feel I need any.  I think the airflow from under the fairing through the forks and such compensates for the pressure difference.

[charlie b]

PS if you get the airflow to go over your helmet completely then the venting properties of your helmet are greatly reduced.  Also, rain drops do not get 'blown' off your visor.  Things to consider :)

[Moto]

Everyone laughs but the expanded metal with house screen works amazingly well. No buffeting of any sort and I can go 70mph with a baseball cap on and sipping a pepsi. All you feel is a slight little breeze through it.
Now see the EV in the background? It has the classic barndoor on it. The WORST windshield I ever sat behind as far as super severe buffeting and weird handling if you go over 80mph. I did the same thing on a few different windshields, pump it full of holes. It drastically changes it into a great windshield like my screen. Virtually no buffeting and very quiet. I guess I am diffusing the air stream and not trying to deflect it.
JB

This may be related. On the calsci website it is claimed that louvres below a certain size don't pass air above a certain speed:

"Why don't we put louvers on our vents? Air sticks to any surface; immediately at the surface the air is not moving. As you move away from the surface the air speed picks up with distance. The curve of airspeed vs. distance from the surface is called a Poisson curve. As you go to higher and higher speeds the Poisson curves from adjacent surfaces on the louvers move outwards until they touch. When they touch, that's the maximum air flow speed for that gap. Typical 1/2" louvers will choke off air flow to a maximum speed around 40 mph or so; above that speed you need more and more air flow to compensate for the growing vacuum behind the windshield, but the louvers have maxed out. So the louvered vent becomes less and less effective as your speed increases to 80 mph or beyond, and the windshield becomes more noisy and has more turbulence as you pick up speed."

In effect, your screened windscreen is made of thousands of louver openings, all operating well beyond the speed at which they can pass an air flow undisturbed. Exactly how that works out collectively for the set of them is not obvious to me.

[johnr]

Everyone laughs but the expanded metal with house screen works amazingly well. No buffeting of any sort and I can go 70mph with a baseball cap on and sipping a pepsi. All you feel is a slight little breeze through it.
Now see the EV in the background? It has the classic barndoor on it. The WORST windshield I ever sat behind as far as super severe buffeting and weird handling if you go over 80mph. I did the same thing on a few different windshields, pump it full of holes. It drastically changes it into a great windshield like my screen. Virtually no buffeting and very quiet. I guess I am diffusing the air stream and not trying to deflect it.
JB

I'm curious JB. Do you think the orientation of the expanded metal mesh makes any difference. That is to say, which way the little metal edges are pointing. The 'RAT' by the way looks more like 'UTE' to me.

[oldbike54]

Here's a side view of my SPIII fairing and the MRA X visor.  The MRA X smooths the departure from the screen and moves the flow up about 2" so it just clears my helmet.  Without it the airflow 'hit' my helmet just above the visor.  The visor is adjustable for angle and also has two arms so it can be placed further up or further away from the windscreen.

I do not have any pressure reducing holes and don't feel I need any.  I think the airflow from under the fairing through the forks and such compensates for the pressure difference.

 Charlie , doesn't the gap between the laminar lip and the main shield create a pressure
equalizer ?

 Dusty

[Rich M]

 




Dean

Hey Dean....

What type of fairing is on that California Titanium in the back ground????

Much thanks...

Rich

[charlie b]

Charlie , doesn't the gap between the laminar lip and the main shield create a pressure
equalizer ?

 Dusty

Only near the lip.  That's the reason it works is it lets the air flow over lip of the stock windscreen without turbulence.  There is still a vacuum lower behind the shield.  I can feel some of it from the air pushing me from behind.  That part is countered by the flow up under the fairing to some extent.


PS If I was really interested, I'd either put some vents low on the windscreeen, or space the windscreen out away from the fairing by a bit less than an inch.

[Testarossa]

I have an old Shoei FM5 fairing -- it looks like a smaller version of the SP fairing. Just transferred it from the T to the Mille.  Solved the pressure differential problem by removing the rubber ring that seals the headlamp rim to the fairing. That leaves about a 5mm gap all around the headlamp to equalize pressure behind the fairing and windscreen. Oddly, rain has never come through that gap.

[rocker59]

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.
 

John,

The wind tunnel in Mandello hasn't been used for developing bikes since the late '80s or early '90s. 

It wasn't used to develop the EVT fairing/windscreen of the '00s.

[johnr]

John,

The wind tunnel in Mandello hasn't been used for developing bikes since the late '80s or early '90s. 

It wasn't used to develop the EVT fairing/windscreen of the '00s.

Yes I knew it wasn't in use. That much is obvious by my standard  handlebar fairing. It's there though, so one has to wonder why not.

Think about how having an actual wind tunnel tested and developed handlebar fairing would have enhanced reputation/sales.

[Trevor G]

I just fitted an X-creen to  my Nevada Adventure Project bike and tested it over two days.

The original screen directed the air at my chest and my head was buffeted.

Last night when I rode the first time with the X-creen fitted it was a wind-free period and even on the freeway at 75mph the air was quite smooth.

Tonight there was a gusty wind blowing so I tried again, and sure enough, there was some buffeting but quite bearable.  It's a winner for me.







Other people in other situations describe it as useless, but I think its effectiveness will depend on how high the original screen is.  I still have some more positions to try the X-creen in but I sometimes find that there is not a lot of difference in the changes.

[toaster404]

Interesting, the large wing.  I'm trying to keep things very simple, but might well end up with a wing.  A shield that puts turbulent band into chest without wing and over head with wing might be ideal - I can make a clamp on wing without any particular trouble. 

Regardless, I made a shield that is a composite of many designs.  Will be fitting up and mounting fairly soon.  Will make a wind tunnel and tuft it, too.  Take some pictures.   Depending on how the flow works, I might fit Wheeler Y vortex generators, make mirror notches, and/or ventilate the shield in various places.

On the 1400, I mocked up a system to put the stock shield parallel to the fork rather than raked back.  If this works, I'll make some metal mount shims that look better and are more stable.  Ended up making my lowers ineffective, so they're off.

Next is to try figuring out why only my right shin gets fried.  I get turbulent buffeting and lots of heat only on the right side!!!  Doesn't make any sense to me.  Will put that bike into the processor (fan and a yarn stick sniffer), see whether I can tell what's what. 

Will also see what I can do to get the updraft under my helmet fixed on the Versys, 1400, and VStrom.  None are bad, but while I'm making aero-mods, might as well.

[rocker59]

Yes I knew it wasn't in use. That much is obvious by my standard  handlebar fairing. It's there though, so one has to wonder why not.

Think about how having an actual wind tunnel tested and developed handlebar fairing would have enhanced reputation/sales.

It's not used because it's too small for the modern behemoths.

The modern bikes are big and don't have enough clearance with the inside surface of the tunnel for good/accurate results.

That's what they say...

[oldbike54]

It's not used because it's too small for the modern behemoths.

The modern bikes are big and don't have enough clearance with the inside surface of the tunnel for good/accurate results.

That's what they say...

 Rumor has it that when the gigantic electric motor that drive the fan are started it causes a brown out in Mandello  Maybe they should go back to the Fiat aircraft engine .

 Dusty

[Wayne Orwig]

I just fitted an X-creen to  my Nevada Adventure Project bike and tested it over two days.

The original screen directed the air at my chest and my head was buffeted.

Last night when I rode the first time with the X-creen fitted it was a wind-free period and even on the freeway at 75mph the air was quite smooth.

Tonight there was a gusty wind blowing so I tried again, and sure enough, there was some buffeting but quite bearable.  It's a winner for me.

Other people in other situations describe it as useless, but I think its effectiveness will depend on how high the original screen is.  I still have some more positions to try the X-creen in but I sometimes find that there is not a lot of difference in the changes.

I put an X-creen on my Stelvio. It helped lift the "rumbling" wind noise a bit over my helmet.
Sadly, my passenger gets more wind coming up from below.
I'm still play with the positioning.

[Moto]

It's not used because it's too small for the modern behemoths.

The modern bikes are big and don't have enough clearance with the inside surface of the tunnel for good/accurate results.

That's what they say...

Makes sense. The Guzzi GP bikes were quite small in frontal area, even compared to other racers of the time, IIRC.

Thanks for posting this.

Who said it, by the way? Guzzi?

Moto

[Testarossa]

Rule of thumb for wind tunnel design: In order to avoid the effects of wall and ceiling boundary layers, the clearance has to be at least twice the dimension of the model. So if a motorcycle is 1 meter wide and 1.5 meters high, the tunnel has to be at least 5 meters wide and 4.5 meters high.  The Guzzi tunnel is less than 3 meters in diameter and I don't think this would fit, for instance, a Norge or Stelvio:

[Gliderjohn]

Quote from Testarossa:

The Guzzi tunnel is less than 3 meters in diameter and I don't think this would fit, for instance, a Norge or Stelvio:

Is there a possibility they used scaled down models, at least to test the basics?
GliderJohn

[charlie b]

I just fitted an X-creen to  my Nevada Adventure Project bike and tested it over two days.

The original screen directed the air at my chest and my head was buffeted.

Last night when I rode the first time with the X-creen fitted it was a wind-free period and even on the freeway at 75mph the air was quite smooth.

Tonight there was a gusty wind blowing so I tried again, and sure enough, there was some buffeting but quite bearable.  It's a winner for me.


Other people in other situations describe it as useless, but I think its effectiveness will depend on how high the original screen is.  I still have some more positions to try the X-creen in but I sometimes find that there is not a lot of difference in the changes.

I mounted mine without the 'arms'.  Moved the X closer to the stock screen and seemed to work a bit better that way.  I kept the arms in case I wanted to extend the X further up, but, have not needed to do that.

PS when trying to decide what to do about my screen I fabbed up a 'visor' type shield with some brass sheet.  Made 'Z' brackets to mount to the existing screen.  It seemed to work so I bought the MRA version.  FWIW, MRA sells clamp on mounts for the X so you don't have to drill holes in your screen for mounting.