High speed oscillation - BMW Luxury Touring Community
 
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post #1 of 12 Old Jul 21st, 2007, 4:02 pm Thread Starter
 
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High speed oscillation

The other day I responded to a new rider's questions about his LT and I noted that over 100 mph I started getting an oscillation in the front end of my LT that increased with speed. If I put my windshield down, it reduced the oscillation considerably. I have ME 880's that are in really good condition at 6,500 miles,and the pressures are 47 rear, and 42 front.

I stood looking at the LT today and my eyes settled on the Euro wings I ordered with my Cee Bailey +2, -4 windshield. They stick out like bat wings and I started thinking that maybe they were causing turbulence at higher speeds.

Anyone else have any thoughts?

I probably am going to get another one without the Euro wings later this summer due to dings and chingers from rocks and debris hitting it over the last year or so.
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post #2 of 12 Old Jul 21st, 2007, 9:59 pm
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Quote:
Originally Posted by Velocityguy
The other day I responded to a new rider's questions about his LT and I noted that over 100 mph I started getting an oscillation in the front end of my LT that increased with speed. If I put my windshield down, it reduced the oscillation considerably. I have ME 880's that are in really good condition at 6,500 miles,and the pressures are 47 rear, and 42 front.

I stood looking at the LT today and my eyes settled on the Euro wings I ordered with my Cee Bailey +2, -4 windshield. They stick out like bat wings and I started thinking that maybe they were causing turbulence at higher speeds.

Anyone else have any thoughts?

I probably am going to get another one without the Euro wings later this summer due to dings and chingers from rocks and debris hitting it over the last year or so.
100+ !
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post #3 of 12 Old Jul 22nd, 2007, 11:13 am
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Yeah, that could be part of the "turbulence" generating problem.

So, remove the windscreen and ride again.. same problem?

(don't forget to use a full coverage helmet with the face screen down... and "tuck in".

also.. remove the trunk.. that brick can cause some problems at those speeds.

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post #4 of 12 Old Jul 22nd, 2007, 2:35 pm Thread Starter
 
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Smile

Yes, there are LEO's in my area but, I've been very lucky and now that I've talked about it, Murphy probably has been listening and my time could well be at hand. First offense.....traffic school on Saturdays to remove the points and record of the citation. One good Get Out of Jail card allowed every three years.
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post #5 of 12 Old Jul 22nd, 2007, 3:04 pm
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Save your saturdays and stay below 100+. That will solve your problem:-)

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Need to stay awake

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post #6 of 12 Old Jul 22nd, 2007, 5:35 pm
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What shape is the front tire??

My oscillation went away with the tire change.

David Major
Charleston, SC
-2003 LT
-2007 GS Adventure. White
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post #7 of 12 Old Jul 22nd, 2007, 7:01 pm
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I've heard of these symptoms - but only from Hayabusa pilots.

It is due to the perforations in the seat cover material.

Above 175 mph the additional airflow will cause a vortex in the time/space flux that will eventually suck your intestines out.

Not a pretty picture.


(Ditch the cheesey acrylic windshield Lee and go back to a polycarbonate OEM or V-stream. Acrylic is so flimsy it will "flutter" at high speeds.
You will also have about 25 times the impact resistance. )

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post #8 of 12 Old Jul 22nd, 2007, 7:01 pm
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Quote:
Originally Posted by Velocityguy
The other day I responded to a new rider's questions about his LT and I noted that over 100 mph I started getting an oscillation in the front end of my LT that increased with speed. If I put my windshield down, it reduced the oscillation considerably. I have ME 880's that are in really good condition at 6,500 miles,and the pressures are 47 rear, and 42 front.

I stood looking at the LT today and my eyes settled on the Euro wings I ordered with my Cee Bailey +2, -4 windshield. They stick out like bat wings and I started thinking that maybe they were causing turbulence at higher speeds.

Anyone else have any thoughts?

I probably am going to get another one without the Euro wings later this summer due to dings and chingers from rocks and debris hitting it over the last year or so.
I would guess you were experiencing a phenomenon called vortex shedding. Here is a fairly straightforward description.

http://en.wikipedia.org/wiki/Vortex_shedding

Although cylindrical objects are often shown in examples, an object does not have to be a cylinder in order to shed vortices.

Voyager
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post #9 of 12 Old Jul 22nd, 2007, 7:11 pm
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Quote:
Originally Posted by Voyager
I would guess you were experiencing a phenomenon called vortex shedding. Here is a fairly straightforward description.

http://en.wikipedia.org/wiki/Vortex_shedding

Although cylindrical objects are often shown in examples, an object does not have to be a cylinder in order to shed vortices.

Voyager
What he really needs are vortex generators - on the outside of the Cee Bailey's "wings":

http://en.wikipedia.org/wiki/Vortex_generator

Damn. Don't ya just love Wiki?
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Last edited by RonKMiller; Jul 22nd, 2007 at 7:17 pm.
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post #10 of 12 Old Jul 22nd, 2007, 7:20 pm
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Quote:
Originally Posted by RonKMiller
What he really needs are vortex generators - on the outside of the Cee Bailey's "wings":

http://en.wikipedia.org/wiki/Vortex_generator

Damn. Don't ya just love Wiki?
The only flaw in your logic is that there is no boundary layer to energize once you are past the back of the windshield!

Voyager
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post #11 of 12 Old Jul 22nd, 2007, 8:30 pm
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Quote:
Originally Posted by Voyager
The only flaw in your logic is that there is no boundary layer to energize once you are past the back of the windshield!

Voyager
There 'ya go!


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post #12 of 12 Old Jul 23rd, 2007, 8:54 am Thread Starter
 
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So let's see if I've got this right. In order to keep up with my Hayabusa riding buddies all I need to do is tape ribbons to my CB wings to disrupt the vortex as well as put duct tape over all the perforations in my KonTours seat.

Gee! That sounds like something I can do for next weekend.
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