JPN Fairing aero discussion

Oh come on Matt belay the absurdiums and reflex jump straight into dart like land speeders hardly anyone road races. Rohan AIr Resistance covers it all to me too and term I use anyone can feel.

I know a way we could do a real road going wind tunnel test, in foggy air with over head and side lighting. Also worth while to have a party with folks looking at your posture and help hold shape and conceal parts from the drag. That's how Rollie perfectly his naked streamlining.

Follow the flow with these...
http://www.youtube.com/results?search_q ... unnel&sm=1

Now THATS a low frontal area Norton !
Shame the article linked to didn't say more...



This appears to be connected, but much more recent ?
http://bigdcycle.com/blog/?p=408
http://bigdcycle.com/blog/wp-content/up ... 24x768.jpg
http://bigdcycle.com/blog/wp-content/up ... CN0856.JPG

Its surprising there is no fin on the tail of the yellow/Norton, there is nothing to make it stable ?

Maybe tail just not installed or they got enough mass in front so CoG leading the way and long enough tail for air pressure to always drag tail in line behind may not need one. If they waisted these dart where the wheels exit they'd gain a tad more sleek.

It's low, it's faired. I would like to see the numbers and how they stack up to a faired vintage road racer. There is more than frontal area that impacts power/speed relationship (ex. overall shape)

It could be important to use the correct type of polish on it, and keep the strokes of the rag in the same direction as the wind. - Could get a huge burst of speed that way.

Rohan said:

Reynolds numbers are another whole another level of added complexity.
At higher or lower velocities, when the flow of the fluid shifts from laminar to turbulent flow, or vice versa.
Do we really want to go there ?

Click to expand...

When Cd is measured/calculated it is usually plotted against Reynolds number, Cd is not constant with Re, Re includes a velocity term......
Unless it is a land speed stream liner you will be pretty safe to assume that it is not have flow. At speed it is likely that a stream liner is turbulent as well as it is much easier to keep the flow attached thereby reducing trailing vorticies.

Keeping the polish strokes in line of flow may not streamline-energize boundary layer as well as cross wise. I am going to tape 2-3" long pieces of yarn on Peel to see what's going on and at what speeds. Might consider same on BMW as poor man's ancient accepted wind tunnel testing. A camera mounted to view it later even better than distracted while whizzing at speeds it really matters. Btw itd the angle of attack of wing that create lift rather more than the flow speed pressure differences. Bikes create two counter swirling vortexes behind them peeling off upper area back down and around towards ground. There's some energy to get back out of them lurking. Airplanes use wing tip vanes for this.

[video]http://www.youtube.com/watch?v=9pPTuFO9HCM[/video]

[video]http://www.youtube.com/watch?v=SXwVyxorvno[/video]

[video]http://www.youtube.com/watch?v=TqTSyFz6DJc[/video]

All of this assumes that there will be controllable laminar flow around a motorcycle and rider. By controllable I mean able to be turbulent or laminar by the addition or deletion of some device, like the vortex generators in hobots video.
I believe that in most areas, on most "naked" motorcycles the airflow is largely turbulent and very umpredictable. Hence my previous story about oil droplets being carried forwards. The turbulent airflow will change with motorcycle speed, speed and relative direction of atmospheric wind and so on.
I also believe that most fairings or bodywork on modern bikes are there to reduce costs (by reducing costs of polishing stuff, and not having to have the aesthetics of cable looms etc be a concern, and to provide a forum for 14 year old graphic designers to express themselves) and keep the rider free of dead bugs.
Trying to relate the aerodynamics of an aeroplane (with largely laminar flow, and in the commercial world at least mainly constant speed and direction) travelling at aeroplane speed, with a motorcycle (with largely turbulent flow and completely irregular speed and direction)is a bit like comparing chalk and cheese.
cheers
wakeup
ps When Honda introduced the original CBR range in the late 80s, didn't they say that one of the reasons for the bodywork was to reduce costs?

Correctomundo Wakeup, but still would be educational to put yarn on just for sens of the turbulance even if nothing much can be done about it. I've seen the air flow of naked '71 taking off to about 70, around 50 mph air blasts in stirred jets out the spooks, splits around engine to slap back at air box and air past/over the pilot basically explodes in plumes of fist size vortexs the peashooters send waves into, slightly extending-preventing the slap back of each big main rear side vortex that rustles hay pieces about 6 bikes lengths back at 60 mph. I can feel peashooter puffs about 2 bike lengths behind at 60.

Pretty much all of this thread misses the OP's quest for his rpm back.....

And I sould say that we just need to read Peter Williams own discussion on the subject.

I have a copy of a JPN fairing for my Rickman build.....

OBTW, that Rickman pulled its potential 6800 at Oulton Park on gearing that indicated 150mph, in '75...with an estimated crank hp of high 70s, so lets say around that 70rwhp figure.....

Anyway, to fit my soon to be reincarnated Rickman the JPN fairing has to be extended in the belly pan and talking to the mould maker a few days back he made it at least 1" wider to try and get wider handlebars inside it...he didn't achieve enough on that one, I measured his bars at 50cm tip to tip.....I didn't get to measure a JPN yet!......

......so it is unlikely we are working with anything like the low frontal area Peter was, including his own low frontal area and ability to tuck in.....but he says got the drag down by flowing air off his back and around that big ugly seat he used. The seat fitted to your BM is a P&M style and is probably better than the smaller Ducati style one shown later....but probably still not big and ugly enough to do the job....and your backside may not even be far enough into it...experiment with moving back and forward....and tucking your toes in.....

.....and no matter how well you do with that, those cylinders (and lever cut outs) are creating drag and turbulance that Peter never had...and they are probably defeating the whole effort. The only way you will really know is in the tunnel, send me a model, including a small bendy rider, there is one 20 metres from where I am sitting that was used to improve the Cagivas in the '90s.

In truth however, I think it is highly likely that a return to the Ducati fairing and getting some comfort back will result in overal faster lap times on all the circuits you ride!

I haven't actually started by fairing fit yet, and I have a fall back one just in case it does not work out.....I don't think those lever cut outs will please our scrutineer so I wont go there.

Nice looking bike either way

I'd consider a bit more space for the levers and then cover over with a running plastic lens.

Don't forget to ride round in varying radii circles, to eliminate atmospheric wind effects, at various speeds up to the maximum, stopping every now and then to record your observations. Please post the results!!

One of my jobs entailed observing a system on a frigate which was supposed to dowse the entire exterior surface of the ship with sea water. It required me to go round and physically watch each sprinkler to ensure that there were no dry spots, up the top of both masts, everywhere, whilst the ship was going round in circles at speeds up to the maximum (30+ knots). A very wet job! Fortunately it was what passes for Summer in the Irish Sea.
cheers
wakeup

Since the OP pertained to a BMW, JPN fairing or not, how about taking a few pages out of the Butler & Smith playbook. Maybe more frontal area is necessarily better - have a look at the top picture where the fairing bows out around the cylinders, presumable to clean the air up a bit around there.

It's a trade off of lower CoD & frontal area. Invariable, when you add a fairing you increase frontal area over an unfaired bike, yet the goal is to reduce the force at speed required to get the bike through the air mass.

We also didn't hear from the OP about whether the fairing is open in behind the front wheel there.
If some air flows through inside the fairing, it reduces the 'vacuum' thats behind the bike.

Merging it cleanly for minimum drag may take some experimentation, or wind tunnel time....

Rohan said:

We also didn't hear from the OP about whether the fairing is open in behind the front wheel there.
If some air flows through inside the fairing, it reduces the 'vacuum' thats behind the bike.

Merging it cleanly for minimum drag may take some experimentation, or wind tunnel time....

Click to expand...

Oh yeah sorry, It is open it's very like this :

wakeup said:

Don't forget to ride round in varying radii circles, to eliminate atmospheric wind effects, at various speeds up to the maximum, stopping every now and then to record your observations. Please post the results!!

One of my jobs entailed observing a system on a frigate which was supposed to dowse the entire exterior surface of the ship with sea water. It required me to go round and physically watch each sprinkler to ensure that there were no dry spots, up the top of both masts, everywhere, whilst the ship was going round in circles at speeds up to the maximum (30+ knots). A very wet job! Fortunately it was what passes for Summer in the Irish Sea.
cheers
wakeup

Click to expand...

Suddenly I realise how much I have missed in my (very) sheltered working life! :lol:

pommie john said:

Rohan said:

We also didn't hear from the OP about whether the fairing is open in behind the front wheel there.
If some air flows through inside the fairing, it reduces the 'vacuum' thats behind the bike.

Merging it cleanly for minimum drag may take some experimentation, or wind tunnel time....

Click to expand...

Oh yeah sorry, It is open it's very like this :

Click to expand...

If you go back to pictures of the JPN I think you will find that whilst visually the fairing resembles a JPN, aerodynamically it differs significantly. As does the one I have. Mine was personally made by Paul Mooney, they are now available from Spike Livingstone from the original mould, here.

http://www.raggededgeracing.com/30.html

Paul has tried to maintain good flow under the bike back to the rear wheel, and the 'air dam' of the fairing lower, rather than air inlet, which is restricted to the upper fairing. Just how this is going to work with my high level exhaust I am not yet sure. (I collect the rolling chassis with custom exhaust Monday, we will see if it ended up where I had in mind :shock: ).

Apart from the top of the fairing just about everything lower down is different. And I am pretty well convinced that the JPN used a taller screen.

John, the reduced speed could be any number of reasons, but....I had one question regarding engine cooling. The BM has consistent fins from head to barrel base, and also needs cooling air to hit the crankcase (oil reservoir), but you have external airflow to the head and at best internal airlfow to the cylinders, and probably reduced airflow to the crankcase. Does this have an effect? Have you tried local temperature measurements to see if cooling is consistent and sufficient?

Steve

Rohan said:

pommie john said:

The Guzzi listed was the 500cc V8 that had a dustbin fairing. Obviously it had good aero, but 187MPH with 70-80HP ??? I'm not convinced.

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Wherever we found that 187 mph quoted, it was mentioned that that was the speed that the dustbin faired Guzzi lapped at MIRA, (Motor Industry Research Assoc)
so if the numbers are questionable they of all people should have reliable equipment ... ?

Click to expand...

so, moto guzzi didn’t have their own wind turbine to get the fairing right :?:

http://www.youtube.com/watch?v=7wMuhucvk-Y

http://www.bing.com/images/search?q=mot ... tedIndex=2

Most of these Norton race fairing were deprived from the Peel mountain mile fairings;

http://www.bing.com/images/search?q=pee ... ORM=HDRSC2

http://www.bing.com/images/search?q=pee ... tedIndex=3