General ??: Windshield design to reduce buffeting

[rocker59]

Who said it, by the way? Guzzi?

Moto

This question came up about ten years ago when the Norge was being shown.  People wondered if it had been done in the Guzzi wind tunnel.  I don't recall who, but someone associated with Guzzi said the tunnel was too small for the modern bikes for the reasons Seth mentioned above.

[rocker59]

A previous thread on the wind tunnel:  http://wildguzzi.com/forum/index.php?topic=60862.0

A Norge on static display inside:


V11 LeMans in the tunnel.

[Testarossa]

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

You could use a scale model, with a scale model rider, to get basic drag and stability data. But the scale model rider couldn't report on the subjective experience of buffeting behind the windscreen, and I can't imagine what instrumentation you'd need to measure the turbulence between the screen and the mini-rider's chest.

[canuguzzi]

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

Or they didn't need to put the whole bike in, just the fairings mounted on a front end. Whatever is behind that is just for looks.

[johnr]

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...

They say that do they? Last time I heard they didn't use full sized ships for tank testing....

[johnr]

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

Ah! That would imply expense! You might be onto something there Dusty.

[toaster404]

Cut a shield in rough for the Versys.  Will be interesting to see.

After all this windshield looking, raised the angle on my Cal 1400 and took off the lowers.  Terrible!  Modified the lowers to put air behind the raised angle shield, but haven't been out. 

Also on Cal 1400, screen now looks way too wide and big for summer riding.  Will make a narrower screen.  Might pull it off for summer and get handlebar mount drag fairing or fly screen to keep pressure off.  Really a lot of junk bolted onto the touring model!!

[Testarossa]

Motorcycles are not like airplanes and ships. On a motorcycle, the rider is part of the shape affecting airflow. You can't get accurate data on any shape -- including a fairing -- without both its upstream and downstream components (that is, the fork and wheel, and the rider/tank/radiator/engine). It may be counterintuitive, but the downstream shape affects what happens further forward. For instance a choke point builds a high-pressure zone ahead of itself, and by eliminating the turbulent zone behind a plate (by filling with a rider, for instance) you reduce drag (and accelerate flow) over the whole body.  Moreover, the rider's movements affect airflow over the whole system. Finally, a chief goal of wind-tunnel testing is to improve rider comfort -- which you can't measure with miniature dummies.

Thus scale model testing of motorcycles isn't a valid process.

[rboe]

If I strongly shrug my shoulders my helmet becomes very quiet. Otherwise I get a lot of noise that appears to be coming form the sides of the helmet (HJC, Bell and Bilt, all do the same, I using molded ear plugs). Noise is as bad as it was on the Quota but the helmet is not buffeted around like it was on the Quota.

Same noise with the MRA screen, or the Givi A770 (and on the other bikes).

I've used my hand to try and block air flow near the collar but nothing works like shrugging. Wondering if I should resort to wearing football pads! Or maybe a foam neck brace collar.

[Sheepdog]

Fixing the air management on my Vintage took a little time, but I have it just right. The original windshield was all wrong height-wise, so I approached Rifle about something better. I sent them my mounts and they made a taller and wider version that looks and fits like the stocker (this windshield is now part of their catalog). Leaning the shield back as far as the mounts allowed improved things a great deal, but I still experienced buffeting. I think the differential pressure between the front and back of the shield created poor laminar flow so I ordered a couple of Vetter Pop Vents to balance things a bit. The result worked very well. The vents can be rotated, opened, or closed creating lots of options. In the bargain, I have a bit more comfort in the summer. The vent's cost was very affordable (around forty bucks). This is an inexpensive, fairly stock-looking solution to correct buffeting.
http://www.craigvetter.com/pages/Online_Store/Online_Store_main.html

[/i][/i][/i][/i]

[Moto]

Motorcycles are not like airplanes and ships. On a motorcycle, the rider is part of the shape affecting airflow. You can't get accurate data on any shape -- including a fairing -- without both its upstream and downstream components (that is, the fork and wheel, and the rider/tank/radiator/engine). It may be counterintuitive, but the downstream shape affects what happens further forward. For instance a choke point builds a high-pressure zone ahead of itself, and by eliminating the turbulent zone behind a plate (by filling with a rider, for instance) you reduce drag (and accelerate flow) over the whole body.  Moreover, the rider's movements affect airflow over the whole system. Finally, a chief goal of wind-tunnel testing is to improve rider comfort -- which you can't measure with miniature dummies.

Thus scale model testing of motorcycles isn't a valid process.

True that. One of the main uses of the Guzzi wind tunnel was to have the actual GP riders experiment to find their own most aerodynamic riding positions. Aerodynamics was Guzzi's big advantage.

[Testarossa]

And speaking of finding the most aerodynamic riding position -- wind tunnel training has become a necessary component of top-level ski racing. This is Olympic champ Daron Rahlves in the Calspan wind tunnel in Buffalo:

[johnr]

Okaaaaay... so motorcycles need to be tested full size with rider, and the Guzzi wind tunnel is too small?  Answer is obvious. Replace it with a bigger one! The advantages would be huge and seeing as how they have done it before, why not?

[atavar]

I think Guzzi did an amazin job in the wind tunnel with the Norge..  I can smoke at 50mph.. and the wind tunnel is plenty big..

[oldbike54]

Okaaaaay... so motorcycles need to be tested full size with rider, and the Guzzi wind tunnel is too small?  Answer is obvious. Replace it with a bigger one! The advantages would be huge and seeing as how they have done it before, why not?

 Well here is the problem . It would cost a lot of money and be of limited use . Computer sims have become the norm John , I don't believe even Honda uses a real wind tunnel .

 Dusty

[johnr]

Well here is the problem . It would cost a lot of money and be of limited use . Computer sims have become the norm John , I don't believe even Honda uses a real wind tunnel .

 Dusty

Well that's sort of the point I think Dusty. No one is actually using a wind tunnel and here we all are complaining about turbulent and ineffective screens and fairings. 

But here Guzzi has an actual wind tunnel and can do real world practical testing if they wish. It couldn't hurt their sales if they were to become known for having the best wind protection in the world could it?

The one above certainly looks big enough to me, but what would I know about that.

[oldbike54]

Well that's sort of the point I think Dusty. No one is actually using a wind tunnel and here we all are complaining about turbulent and ineffective screens and fairings. 

But here Guzzi has an actual wind tunnel and can do real world practical testing if they wish. It couldn't hurt their sales if they were to become known for having the best wind protection in the world could it?

The one above certainly looks big enough to me, but what would I know about that.

 All true John , the problem is aero is actually fairly well understood . Shape it like any creature than can swim fast , salmon , dolphins , Michael Phelps ,(OK maybe not him  ) , then watch as they sit on showroom floors unsold . HD spent a small fortune to develop fairings and screens that were more than just turbulence generators , and made a big production out of having done so . Problem is , all they really did was vent their screens , something Honda , BMW , and some aftermarket companies have been doing for years    MV Agusta racing fairings from the 1960's were about as low drag, low turbulence as could be W/O a full enclosure , their helicopter experience coming into play . Honda basically copied them on their gp bikes of that era , so we know what works . Hannigan built what amounted to a giant racing fairing , all round surfaces , no turbulence , and they wouldn't sell . I rode behind one on an airhead , dead calm . Problem was , everyone at that beemer gathering talked about how ugly it was . Unfortunately style trumps effectiveness .

 Dusty

[rboe]

It is my understanding the tunnel is no longer useable and it was damn expensive to use in the first place. I "think" I heard they used it on a project after the Quota - but they really really should have used it on the Quota.

[toaster404]

Kind of insane.  I like the wind tunnel designed things.  I will eventually get around to faking a tunnel here.  Calm day, stacked fans, yarn.  Really helped before on a cruiser.  Wave a piece of cardboard around until the yarn at the bad spot stops fluttering!!!!

Personally, I'd ride a trashcan if I didn't fry.  If fabbing stuff up wasn't such a pain I might be there already.

[canuguzzi]

If I strongly shrug my shoulders my helmet becomes very quiet. Otherwise I get a lot of noise that appears to be coming form the sides of the helmet (HJC, Bell and Bilt, all do the same, I using molded ear plugs). Noise is as bad as it was on the Quota but the helmet is not buffeted around like it was on the Quota.

Same noise with the MRA screen, or the Givi A770 (and on the other bikes).

I've used my hand to try and block air flow near the collar but nothing works like shrugging. Wondering if I should resort to wearing football pads! Or maybe a foam neck brace collar.

Try one of those cooling towels they sell at home improvement stores. What I use. In summer or real warm temps I soak it, wring it slightly and use it like a scarf, tucking the ends inside my shirt.

That does what you're talking about and really keeps you cool too.

[rboe]

Thanks!

[DaSwami]

Wow, I feel like a neanderthal by just sticking a DART flyscreen on and calling it good.  I put them on all my bikes.  The work great and make riding a pleasure, look good too.

I don't want the antiseptic feeling of perfect dead air in front of me while riding. 

[gentlemanjim]

Wow, I feel like a neanderthal by just sticking a DART flyscreen on and calling it good.  I put them on all my bikes.  The work great and make riding a pleasure, look good too.

I don't want the antiseptic feeling of perfect dead air in front of me while riding.

Which screen classic or Marlin?

[DaSwami]

Which screen classic or Marlin?

All classic.  I tried the Marlin once on my CB1100 with horrific results, so put the classic on and all is well.

[toaster404]

For ordinary riding, I like the small screens.  Interstate just beats me up.  Winter is COLD.  Those are the issues I have.

Wife has just this tiny screen and tires at over 50 mph.  That's my main issue. 

My VStrom gives a noisy flutter up by the bottom of my helmet.  That's another issue.

Ideal summer would be a small screen and some under chin flutter aero mods.

Really, so few bikes have good aero.  Explanation of no wind tunnel testing except for race positions makes sense!!  A nice thorough simple study of a few bikes in a tunnel would be wonderful.  There are tunnels near hear, but they're being used by the air force, so I can't just show up.  Also big.  Very big.  Some supersonic!  Loud. 

[charlie b]

There are more bikes than you think with good aero.

FJR's, Beemer RT's, ST1300 from what I hear from owners, Gold Wings.  Then there are the sport bikes that are good when you are tucked (which is what they are designed for).  For some the Norge is good and a few even like the Stelvio.

Some do better with an aftermarket screen, especially if you want a 'bubble' around your helmet.  Even the Honda Deauville was nice with an aftermarket screen, but, was pretty good with the stock screen.

[charlie b]

Forgot.

If your screen is directing the airflow where you want it and it is just a little buffeting to get rid of.....try putting a split hose around the edge of the screen, about 3/8" dia should do the trick.  It acts as a turbulator, breaking up the eddies into smaller eddies.

[Lcarlson]

Cut a shield in rough for the Versys.  Will be interesting to see.

After all this windshield looking, raised the angle on my Cal 1400 and took off the lowers.  Terrible!  Modified the lowers to put air behind the raised angle shield, but haven't been out. 

Also on Cal 1400, screen now looks way too wide and big for summer riding.  Will make a narrower screen.  Might pull it off for summer and get handlebar mount drag fairing or fly screen to keep pressure off.  Really a lot of junk bolted onto the touring model!!

I hate looking through a windshield, or having the top right in my line of vision, which was the case with my Touring windshield on the Custom. So, a couple of days ago I had two inches cut from the highest portion of the shield, while preserving the original shape as much as possible. HUGE improvement, and it doesn't look much different. Remains to be seen if it changes the buffeting I get over about 60 mph....

[oldbike54]

 


                                                         Tubulator ???????

 Dusty

[johnr]

                                                         Tubulator ???????

 Dusty

usually attached at right angles to the encabulator.

You'll learn all about it here.
https://www.youtube.com/watch?v=W9LXG7rPQfE