Author Topic: 2007 1250s windshield (Read 7633 times)

banditone1250s · « **on:** July 02, 2007, 07:13:17 PM »

I was thinking that a lot of air got around, through, or over my windscreen and now I think something else. I think that a lot of it comes from the "hole" in the very front bottom of the screen. I wonder why that "hole" is there??? I have looked at some after market windscreens and they do not seem to have that same "hole" in the lower front. Any body have any ideas about the subject. I would appreciate any thoughts that you may have...Banditone1250s...

leedogg · « **Reply #1 on:** July 02, 2007, 07:22:03 PM »

I was wondering that myself.

ZenMan · « **Reply #2 on:** July 02, 2007, 09:31:58 PM »

My new MRA has the same hole:

So does the new Givi screen:

So does the Zero Gravity screen for older Bandits (only pic I could find):

It's there to reduce turbulence and buffeting. The air flowing through the hole up on the inside of the screen mixes with the air flowing up over the top of the screen to smooth it out. The airspeed is reduced by the time the air mixes back together. Without the hole, the air coming off the top would "tumble", and you'd get a lot of buffeting in your face.

What you have to realize is, these small fairings and sporty windscreens are not designed to give a big bubble of dead air devoid of any wind at all. They are designed to reduce air pressure to a more comfortable level.

If you want total dead air space, you'd have to have a windshield the size of a barn door.... even a convertible car has turbulence with the top down.

Here's the pamphlet I received with my Vario screen:

FUNCTIONAL DESCRIPTION

Please carefully read these instructions. You will get the most out of the adjustable spoiler if you thoroughly understand it's features.

The spoiler serves to reduce air pressure on the rider's helmet and upper body without causing disturbing air turbulence.
The spoiler has six different positions, enabling the rider to make adjustments to suit his needs.
The higher the spoiler is set, the more air will flow between the spoiler and the windscreen.
The airflow speed is reduced by means of the angle that opens in the direction of the rider, thereby providing at higher speeds the same relaxed atmosphere that a rider experiences at slow speeds.

It then goes on the explain how to adjust the spoiler.

What does the hole have to do with the spoiler? It works on the same principle, of slowing and mixing air to reduce airspeed and eliminate turbulence. I'm no expert on aerodynamics, but I understand the engineering behind these windscreens a lot better now than I did before.

I know from my V-Strom that a tall windscreen without a spoiler creates a lot of buffeting. Ask any V-Strom owner and they'll tell you it's a big problem. Go to the V-Strom forums and there are threads upon threads on the subject.

The hole helps, but the spoiler helps a lot more. That's why I bought a screen with a spoiler.

ZenMan · « **Reply #3 on:** July 02, 2007, 11:11:27 PM »

I made a crude visualization on how I think it works:

When the air curves around the screen, it slows it down. The air coming up from the vent straightens it out.

A spoiler adds more curves to slow the airspeed down even more.

That's how I understand it, anyway...

skyrider · « **Reply #4 on:** July 03, 2007, 02:13:08 AM »

I tried to make sense of it from the perspective of flaps on an airplane. Your drawings are correct in that with the slot, the turbulent air is lessened (is that a word?) or "placed" higher in the slipstream. With the curve, the air actually accelerates and the pressure drops (Bernoulli's principle) relative to that air going through the slot. I think the slot helps to place the pressure differential of the two airflows closer together and therefore reduce a ton of turbulence.

SteelD · « **Reply #5 on:** July 03, 2007, 08:57:44 AM »

ZenMan is right - the hole is there to reduce turbulence and negative pressure. The screen on my FJR was great but in the fully up position there wasn't enough air going through the front and while it deflected an awful lot of air away from me, the pressure effect felt as if there was a hand on my back pushing me forward. The air vent reduces the pressure so it's there for a reason and not a whim on the part of the designer.

ZenMan · « **Reply #6 on:** July 03, 2007, 10:41:20 AM »

Like I said, I'm no expert on aerodynamics.

I figured with the drawings at least we'd have a reference to figure it out from. Your airplane wing analogy is a good way of looking at it.

So if the curve speeds it up creating negative pressure, like lift on a wing, then the hole must be there to equalize it, thus reducing turbulence. The spoiler controls the amount of air passing over the top, thus reducing airspeed.

However it works, the result is a comfortable airspace to ride in without turbulence. Works for me.

Barbarian · « **Reply #7 on:** July 03, 2007, 05:01:01 PM »

Test! We need a test!
Somebody block the hole and see how it changes the buffeting!

(Not me, I'm still trying to find the time to adjust the handlebars and post pictures ;) )

skyrider · « **Reply #8 on:** July 04, 2007, 03:40:35 AM »

Quote from: "Barbarian"

Test! We need a test!
Somebody block the hole and see how it changes the buffeting!

Thinking the same thing. I may try to stuff a towel in there some time to test the effects. If I'm real motivated, I'll tape some strings of yarn on the outside and inside of the screen. It would be cool to see some wind tunnel/smoke visuals. Just thinking too, I wonder if a long piece of yarn from the lip of the screen would show how far the smooth slip stream extended, how high it went, and at what point it starts to burble?!

Red01 · « **Reply #9 on:** July 04, 2007, 01:46:53 PM »

I'm wondering if you stuffed a towel in there if it would stay? If the towel doesn't stay you could tape it off from the front for this experiment. Just use a tape that will peel off easily without leaving behind a bunch of residue to clean up.

ZenMan · « **Reply #10 on:** July 04, 2007, 02:25:35 PM »

Try cutting a piece of cardboard just a little bit bigger than the hole, and taping it over the hole using a clear packing tape.

The yarn I would go about 3-4", if they were too long the slipstream would grab them and pull them out too far, or they'd just flop around too much.

leedogg · « **Reply #11 on:** July 04, 2007, 04:19:07 PM »

Why do I have a new episode of mythbusters going on in my head?

skyrider · « **Reply #12 on:** July 05, 2007, 12:12:07 PM »

Quote from: "leedogg"

Why do I have a new episode of mythbusters going on in my head?

That, or someone is going to end up with a Darwin award. "Motorcyclist dies with yarn wrapped around neck, news at 11."

ZenMan · « **Reply #13 on:** July 05, 2007, 12:45:30 PM »

Quote from: "skyrider"

"Motorcyclist dies with yarn wrapped around neck, news at 11."

Barbarian · « **Reply #14 on:** July 08, 2007, 12:07:59 AM »

Oh, if people can do the Mad Bastard Scooter Rally wearing capes, a bit of yarn should be fine ;)

linky