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Strange Screen Aerodynamics CB500X
Blog Date - 26 December 2018
I'd recommend reading CB500X Screen Improvements first to make sense of this
The first step to recovery is admitting you have a problem. I am a hoarder. If I had the space I'd probably keep everything just on the slim chance that one day in the long distant future it may, possibly, perhaps just come in handy.
I have not reached the stage where I'm soon to appear on a TV program entitled "World's Greatest Hoarders". I do still have spaces on my floor. But yes, it could easily all go horribly wrong. I have to have very stern words with myself at times.
While clearing out I came across a very cheap old "bum bag" or "fanny pack" as the yanks call them. There is much lost in translation is there not? Not wishing to throw it out I decide I'll find it a space on one of the bikes. Aha! There's a suitable gap between the screen and the fairings on the 500. Here we go...
I think it was a pound from a pound shop.
Excellent. I can keep (even more) things in there.
The next day I'm off to Sharon's. As I ride I notice something is different. The screen. It is still keeping the wind off but the turbulence is, well, not as bad as it was before I fitted my extension but I'm not feeling as comfortable and cosseted as I have been. Nah. It's just me. I'm being overly sensitive. It could be the weather? Stop being a fusspot Ren.
Is, was, could, maybe? I think too much. Remember from when I was first messing with the screen I'd read that a gap between the fairing and the screen can help reduce turbulence? I've stuffed this old bum bag into that gap. Nah. Surely not.
With the bag removed normal blissful almost turbulence free comfort is returned. Wow!
Notice the bits of wood?
So when I was experimenting with the screen I installed the wood as seen above to see if the gap reduced turbulence. Without the extension it made no difference. I never removed the wood but I did fit the extension which brought comfort. Having filled the gap with the bag it seems that both the extension AND the gap are 2 parts of one solution.
I can only guess as to the why and therefore here. I come back to my original suggestion from the first post. Experiment. What works for me may not work for you but experiment. I'm still awaiting my call from Red Bull to help them perfect the aero package on their 2019 F1 car.
If you'd like to employ Ren as your aerodynamisist then you're a fool. If you'd like to sponsor Bikes And Travels however contact ren@bikesandtravels.com.
Reader's Comments
Ian Soady said :-
The purpose of the gap is to allow air to flow up the inside as well as the outside of the screen. The two airflows then join together at the top giving less turbulence.
Without the gap, the air flowing over the outside meets the static air on the inside which causes it to curl round and creates turbulence.
Having said that and with all due respect to your carpentry skills, I think chunks of 2x4 is a bit excessive. I found that spacers about 10mm thick worked fine on my V-Strom.
26/12/2018 09:54:21 UTC
Ren - The Ed said :-
2 by 4!! I'll have you know that is merely 1 by 2, I'm not a heathen you know.
I could of course have spent a half hour on ebay searching for spacers. Then a couple of days waiting for them to arrive. Then I could have fitted them. Or - as I was merely experimenting and I had a bit of wood lying around - the bits of wood went in.
Now yes, yes I could having completed my research, update the wood for something more stylish, more appropriate, more in keeping with the high standards some people set for themselves. Much to Sharon's chagrin my standards are quite low. The wood does it's job and is therefore staying where it is.
So if the gap reduces turbulence - why don't old bikes have a gap?
27/12/2018 09:54:59 UTC
Upt'North said :-
Now you've got me thinking Ed, Whurr, Whurr. I know the K1100RT adjustable screens from the mid 90's (?) sort of replicated that with the high front fairing edge. And my aftermarket MRA is of that design, although I don't know when MRA first released that design. But it definitely works dunnit. Perhaps we are just more enlightened today and barn doors we're yesterdays answer to a turbulence free ride.
Upt'North.
27/12/2018 13:38:12 UTC
Upt'North said :-
Now you've got me thinking Ed, Whurr, Whurr. I know the K1100RT adjustable screens from the mid 90's (?) sort of replicated that with the high front fairing edge. And my aftermarket MRA is of that design, although I don't know when MRA first released that design. But it definitely works dunnit. Perhaps we are just more enlightened today and barn doors we're yesterdays answer to a turbulence free ride.
Upt'North.
27/12/2018 13:38:15 UTC
Upt'North said :-
Why did I post it twice, doh.
27/12/2018 13:52:10 UTC
Ren - The Ed said :-
I often post twice Upt'North - but I have the edit button so I can avoid making myself look silly(er).
We need a real genuine aerodynamicist.
28/12/2018 09:53:04 UTC
Ian Soady said :-
Not at all, a basic understanding of Bernoulli's Equation is all we need......
28/12/2018 14:56:52 UTC
Ian Soady said :-
ps can't you remove Up t'North's duplicate post to save him embarrassment?
28/12/2018 14:57:41 UTC
Ren - The Ed said :-
I don't think Bernoulli actually understood his equations let alone us...
I would have removed Upt'North's duplicate post...then he went a commented on it.
Having seen Facebook, Amazon and many other LARGE websites having their user's data stolen I'm still very loathe to create an editable login system.
28/12/2018 15:54:25 UTC
Upt'North said :-
Who the f... Is Bernoulli?
This site is an education.
Now, only touch the button once, only touch the button once......
Upt'North.
28/12/2018 17:30:43 UTC
Ian Soady said :-
The essence of Bernoulli is that the faster a gas moves, the lower is its pressure. This of course is what keeps aeroplanes from falling out of the sky (well mostly anyway) and also allows carburetters to work. The air flow over the front is travelling at considerable speed (ie lowering the pressure), whereas if there is no airflow up the back it is relatively static (thus at higher pressure). So the lower pressure at the front will tend to pull the dead air from behind, resulting in eddies around the top edge and giving the turbulence and buffeting often encountered.
The MRA Vario mentioned by Mr North goes some way toward helping but you still get the turbulence at the top of the existing screen, although it is much reduced. I had one on my Triumph Tiger and it was much better than the standard screen.
29/12/2018 15:03:35 UTC
Ren - The Ed said :-
Yeah there's quite a lot of debate regarding how much of a plane's lift is due to Bernoulli and how much is the simpler Newtonian physics. I'd like to see a screen in a wind tunnel with smoke trails to get some sort of handle as to what is going on.
29/12/2018 18:57:21 UTC
Upt'North said :-
Ren the Ed, whilst you're out doing the Christmas shop, what about one of these. Now I know your woodworking skills are legendary, you are a leg end. But this seems a bostin bit of kit, I was expecting a price tag just some where short of a gizzillion £'s but no for around £60.00 of your hard earned £'s your screen can go up and down and with varied tilt. I'm impressed, I know I'm easily impressed, I ride a Pan after all but this seems to be a quality bit of kit. Worth checking out for other BAT'ies too as they are made for various bikes from Palmer Motorcycle Products. I'll try to attach piccie but have been having difficulties posting on here recently.
Upt'North.
05/01/2019 16:15:23 UTC
Ren - The Ed said :-
I've come across the Palmer Product page when I was researching stuff about the screen. I like it a lot, it seems like good solid basic British engineering at it's finest. I didn't want to shell out because I didn't know if it would make any difference but due to my experiences I'm thinking it might be worth it now. Hmmmm got me thinking. Remember though it is very difficult to get me to part with pennies.
06/01/2019 07:51:29 UTC
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