pozo
Ahh! Just passed their bike test
Tech Consultant and Graphic Designer
Posts: 43
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Post by pozo on Jan 6, 2012 18:38:14 GMT 1
Hey all, I already had a 'general' naked bike windscreen from MRA on my bike. Today I upgraded that with the MRA X-creen, after doing a test drive. The buffeting of the wind when doing 120-140 km/h on the highway was literally giving me headaches/neck problems. Probably this was caused simply by aerodynamic effect that the windscreen has combined with my height (1.89 m/6'2"), but I don't think it will be more comfortable without it. I tested the X-creen for about 15 minutes at high speed, and the effect was great Positive: - Hardly any buffeting was noticeable - which means no hernia for me so that's enough of a plus to buy it
- Easy installation (when you take the optional clamp-mounting kit as I did: I want to be able to remove it when I change bikes)
Negative: - Price: I paid €133 for a small piece of plastic (including the €19 clamp mounting set).
- View is obscured. I was always able look over my windscreen up to something 3-4 meters in front of me, now I constantly look at the X-creen. I think I'll soon get used to it but for now it feels slightly distracting.
From the riders perspective with the screen in the fully up position (as I'm using it). Note that you can also choose to mount it without the support struts, directly on your windscreen, and that you can move the screen around quite a lot. You can tilt it to be flush with or below you main screen, but I don't know the effect of that yet.
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Post by rj2para (Bisto) on Jan 6, 2012 23:12:27 GMT 1
Looks ok if it sorts your problem.
From what you say it sounds like you are looking through the new screen extender, rather than through the slot underneath it?
If so I will be interested to hear what it is like when it rains. Thinking about you looking through a wet visor and a wet screen?
Rj.
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pozo
Ahh! Just passed their bike test
Tech Consultant and Graphic Designer
Posts: 43
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Post by pozo on Jan 6, 2012 23:19:50 GMT 1
No, it's lower than you seem to be thinking - my wording was bad I'm still looking over it mostly, it sits kind of at the lower edge line between 'where you're looking' and the peripheral vision. Anything about 20 meters ahead is still 'above' the screen, but anything closer is 'behind' it. I'll try and take a picture from my riding perspective tomorrow.
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Post by McF on Jan 7, 2012 9:33:56 GMT 1
I presume the gap/height at the top is manually adjusted? I have a laminar flow screen on Mighty Pan II and it makes one hell of a difference - a lot less turbulence behind the screen and despite my shorter stature (1.74/5'9") the air flow now clears above my head rather than on my eye line. My screen is tinted and with a double edge of perspex to look through, I understand your difficulties in a clear line of sight for the road close in to your bike. Once you get used to it, the only time it will cause a concern is filtering through traffic and even then, it's not as bad as you might think (or at least not on the Mighty Pan where I have to judge width carefully)
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leslie52
Ahh! Just passed their bike test
Posts: 27
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Post by leslie52 on Jan 7, 2012 11:09:46 GMT 1
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Post by rj2para (Bisto) on Jan 7, 2012 13:09:51 GMT 1
Pozo. Your wording was fine. I just have no experience of these screens. Thinking back though, I did have a full barn door fairing on my CG125 years ago. But I must have got used to that as I do not remember it being an issue. Rj.
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pozo
Ahh! Just passed their bike test
Tech Consultant and Graphic Designer
Posts: 43
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Post by pozo on Jan 7, 2012 15:19:20 GMT 1
Updated my first post with a 'riders perspective' view to better illustrate what I mean. I took the shot in a way it closely approximates what I really see when in my riding position. Obviously this was taken when parked in front of my parent's house, so the car before me is maybe 2 meters from my front wheel.
Over the weekend I think I'll play around on the highway a bit more to find the ideal position. Maybe it'll work better if I configure it like McF's, by rotating the struts downward.
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Post by McF on Jan 7, 2012 21:02:44 GMT 1
Try the upper part fully down to begin with and then try lifting it to half way and see how the laminar air flow suits you. You may be surprised to find it will lift the turbulence over your head even at a low setting
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Post by rj2para (Bisto) on Jan 7, 2012 21:41:15 GMT 1
Can't better pictures to aid a discussion.
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pozo
Ahh! Just passed their bike test
Tech Consultant and Graphic Designer
Posts: 43
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Post by pozo on Jan 8, 2012 22:46:35 GMT 1
You were 100% correct McF, I flipped the unit down, went down a more or less deserted highway fast enough to leave no possible doubt (which is probably as clear as I can be without directly incriminating myself ) and had virtually no buffeting. Thanks! I'll play around a bit more to fine tune it tomorrow night I think - it's a bit of a slow process as you have to go off and on the highway while finding a place to safely stop and adjust the screen in between runs. Here's a dark picture that I edited to be slightly better visible, this is how I have it now:
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Post by McF on Jan 8, 2012 23:02:59 GMT 1
You were 100% correct McF, I hope I haven't peaked this early in the year It's reassuring to know when you're on the right track. Good luck with the tweaking I cannot explain how it works, but I think it's similar to a lift dynamic we often used in gliding called "Wave Lift" (or less commonly - Lee Wave) en.wikipedia.org/wiki/Lee_wavesWhich enable unpowered fixed wing aircraft to achieve record heights in excess of 50,000 feet (yep, that's right!). The UK records are set from Aboyne in Scotland (West of Aberdeen) with nearly 39,000 feet achieved (as someone still learning, my personal best to date is only circa 5,000 having started from a 2000 foot aero tow from sea level.
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pozo
Ahh! Just passed their bike test
Tech Consultant and Graphic Designer
Posts: 43
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Post by pozo on Jan 9, 2012 1:07:59 GMT 1
Haha let's hope so Cool that you're leaning to fly! I hope to get my license some day as well, preferable for micro/ultralight aircraft Actually, I'm and aerospace engineer so I can kind of understand how it works. Kind of depressing that I didn't think of it myself, but I'm still having my Christmas holiday so I can still live with myself The way I had it up first (all the way up) worked, but that was more or less a brute force technique - it was simply extending the wind screen. This way it works better, and it's indeed aerodynamic forces doing it - but I don't think the Lee Waves is quite the right model to explain this - it's more straightforward than that if I'm correct. I'll explain it 'to you' but in a way non-flying people understand it as well I would rather explain it using 'laminar flow' (hence the name of your windscreen) A motorcycle windscreen is similar to a wing at a high angle of attack (angle with respect to the wind direction). The air smashing into my 'main' wind screen without X-creen gets forced up and over it with very high pressure. When the wind screen abruptly stops (or similar: when the flow reaches the trailing edge of a wing), the there is a low pressure area right behind the screen (/wing). The high speed air gets sucked down hard, and because the flow is not 100% perfect this causes turbulence in the flow. At the very least this causes noise. At high speeds however, you'll even get 'vortex shedding', which is the flow basically doing the same as in the next video, which feels like someone is repeatedly hitting you in the head and what bikers usually refer to as either turbulence or buffeting: www.youtube.com/watch?v=2ghBUcQG1lQ&feature=relatedYou can see this happening to a wind screen analogue at the end of this short video at the lower end of the wing (think of it as an upside down windscreen . youtu.be/bTcXGQ78cHM Now when we stick on an extra screen, like on your Pan and my X-creen, and drive at high speeds. This changes that dynamic. The small gap between the two screens allows a small portion of the air smashed up against the main screen to go through, but certainly not all of it. The rest will pass up and over the X-creen as it simply cannot compress fast enough to squeeze through the small gap. The gap widens up right after its start (you can vary how much with my screen) which gives the air room to expand gracefully - the volume of the air increases so the pressure drops. This way, the air flowing through the gap forms a layer of 'medium pressure' air, that will still tend to be sucked down into the low pressure area but not hard enough to severely disrupt its streamlines and cause buffeting - it behaves more like the air flow you'd have without the X-creen at maybe half the speed you're actually going. The high pressure layer of air still exists, but as it passes the upper edge of the screen it does not encounter the very low pressure area but rather the medium pressure area created by our double screens. Again the flow will be sucked down, but less hard. The combination of screens has caused the flow to remain laminar (flowing in locally parallel layers without turbulence), for long enough to pass right over our heads. Hence no air smashing into our heads at high frequencies, but just one steady stream of air. I can't find a good vid of that, but if you look at this you can see that the upper and lower sides have nice laminar flow: the flow gracefully goes around the object up to 'three lines away' from the object, there the turbulence/vortex shedding starts. Again, what the extra screen does is keeping the flow laminar like that at least up to the point it hits our helmets. www.youtube.com/watch?v=0H63n8M79T8&feature=related
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Post by McF on Jan 9, 2012 1:56:51 GMT 1
Some extreme Angle of Attack going on there
I'm doing quite a lot of research at present into theories of flight - induced, interference drag, transition and stagnation points etc etc
a huge amount to take in and balance against all of the potential theory areas
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pozo
Ahh! Just passed their bike test
Tech Consultant and Graphic Designer
Posts: 43
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Post by pozo on Jan 9, 2012 13:11:27 GMT 1
Ghehe I know, I've been doing it for 3 years in my BSc period If you're interested in knowing more than you'd have to for piloting, I can recommend Fundamentals of Aerodynamics by Anderson - should you not yet have that one.
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Post by De Graaf van Salland on Jan 9, 2012 21:36:42 GMT 1
Impressive, Gentlemen
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