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 Aerodynamics.

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Mick Potter

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Number of posts : 125
Age : 61
Localisation : Cheltenham
Registration date : 2007-06-09

PostSubject: Aerodynamics.   Tue Feb 21, 2012 11:43 am

Hi all.

Some posts on other subjects have been asking questions about the affects of air flow through fairings and I feel this is a better title for the subject.

All road bikes have a front mudguard. A front mudguard is not a legal requirement. Yes they are there for their looks but the primary reason is to aid air flow past the forks and into the radiator (most road bikes are water cooled).

Many years ago a motorcycle publication did an experiment to find out what one and only one bolt on accessory had the biggest increase on top speed. After they had fitted end cans, air filters, double bubble screens, dynojet kits, ECT they found that the biggest increase in top speed was produced by the cheapest accessorily. A rear wheel hugger.

Please look at the frontal images of 125 GP bikes. The widest part of the fairing aligns with the riders shoulders. When streamlining a small capacity bike it’s important to consider the rider not the bike.

Mick.
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john bass

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PostSubject: Thanks Mick...   Tue Feb 21, 2012 6:04 pm

Thanks Mick -- I still stick to the modern fairing being a `mini-skirt´ rather than a "full frock!" I agree with you on the shoulders bit and remember trying very hard to get them pulled in behind the front number plate on my Racing-On-The-Cheap Bantam.
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Derek

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PostSubject: Re: Aerodynamics.   Wed Feb 22, 2012 9:52 am

Mick what is a rear wheel hugger ? do you have a picture.

I always believed the best add on was those tiny wings built into the fairing front to hide you handle bar hands from the high pressure /air flow area at the front, I would really like to understand more about an hugger!

Derek
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Mick Potter

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PostSubject: Re: Aerodynamics.   Wed Feb 22, 2012 11:40 am

Hi Derek.

A rear wheel hugger is basically a rear mudguard that is fitted to the swing arm in close proximity to the rear tyre. The hugger separates the air flow leaving the engine bay from the rear wheel which is moving in the opposite direction. The result is less turbulent air leaving the rear of the bike. Check out Google (other search engines are available) for photos (I don’t know how to upload).

Best wishes Mick.
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johnSbantam

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PostSubject: Re: Aerodynamics.   Wed Feb 22, 2012 3:00 pm

If you want to see the worlds most beautiful and aerodynamic motorcycle, check out the Britten

This is #6, the "WaterBike" the one that did fastest IOMTT lap in 1994 and won world BEARS 95 and 96. Other versions got land speed records, won Daytona BOT etc even though less power than many big factory bikes
Not much of a fairing, but fits around the rider. Particular attention was paid to narrow frontal area and airflow behind rider.
I had the privelege of a conversation with John a few months before he died. He was asking me what had been done to build my watercooled motor !
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johnSbantam

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PostSubject: Re: Aerodynamics.   Wed Feb 22, 2012 3:05 pm

Interestingly, the first precurser of the Britten V1000; Aero de Zero had aerofoil wings in front of the handle bars, which didnt work well for the handling and stability on fast twisty circuits.
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Derek

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PostSubject: Re: Aerodynamics.   Thu Feb 23, 2012 6:15 am

Hi

Mick thank you, why didnt you say a "mud guard" I will look into this, I have a flat plate on one bike, dad is always moaning its an air brake and should be removed, but it does stop the stones that get flicked into the carb.

John sendle I agree "John Britten" was an amazing guy - We bought the video, ? well Ithink we did, "the one on his life story and the britten, but not sure its the worlds most aerodynamic motorcycle, it was a master piece, and there was certainly a lot of thought that went into every single part on it, even the trumpets, I think the electronics guy never got the recongition for the way he programmed the injectors either, he was a genius well they both were.

Buy the way John I alread have my seat booked to your neck of the woods and "buck shee" - off her indoors Tesco point would you believe it!!! what's the chance we can look you up, it will be the end of 2013 October November possibly, or early 2014 - We are still working on Di's points, I did suggest as we only have half of them we could drop her off halfway across, but not sure its possible to parachute out of commercial air liner over the indian ocean!.

anyway John did you count the teeth on the layshaft press on and output sleve gear, (ref Mike Powell's engines photo;s) a bit of a revelation dont you think! - in terms of ratio!! its still on "I would like to get a hold of that gearbox spead sheet you did", I had it on my old P.C -not the one I drove over, but the one before that!.

regards Derek
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Ned

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PostSubject: Re: Aerodynamics.   Fri Feb 24, 2012 7:34 am

The history of the SMS fairings
Often referred to on here as “the Mike Powell , the Jimmie Gel Coat and more recently on ‘face book’ the Pete Styles fairings”

When the bikes were being designed we decided it would be good to have tailored tanks, seats and fairings as opposed to what was available and often a compromise fit for Bantams. IE Pete’s bike had an Apollo fairing that dwarfed his bike and I had an early Bultaco fairing that barely covered mine which indecently was the first bike with the SMS tag, something I put on it in appreciation for the work Mick, Tom and Pete did to improve it for me.
The construction of the seat and tank moulds was fairly simple based on measurements taken with Pete and I sat on the bare frame. However after testing Pete preferred to revert to his old style of riding with the bars further back and his elbows outside his knees.
Construction of the fairing was far more complex and to ensure a good fit the former for the mould was fabricated on the bike. Without the benefit of a wind tunnel it was designed with the thought if it looks slippery and streamlined it is. As a starting point we needed a streamlined nose that a readily available screen would fit so a wrecked TZ faring was deployed. The lower section was fabricated using stiff card and paste and smoothed off with normal household filler when it set.

That’s the basics of the fairing but here’s a couple of interesting and ironic bits you may not know. On the TZ’s the outside edge of the fairing where the screen fits was very flimsy so Yamaha fitted a metal brace between the ears and into the head stock to stop the screen flapping at speed. The Apollo fairing Pete used overcame this problem by incorporated a right angle rib inside the screen. I decided to use this idea but because TZ screens fitted inside the fairing it needed to be on the outside. By adding a blister to the handlebar area I was able to incorporate a small rib extending from it. When Pete’s bike was finished Tom and Pete took it to Brands for a practice session. After the session Pete told me they had been surrounded by Japanese mechanics taking photos of the bike. A few weeks later the Honda NR was unveiled sporting the same style rib! Coincidence ???

Jimmie Jell Coat has made a few mods to my original design but ironically retained a feature that came about as the result of a mishap. The original design was for the bottom of the fairing to go under the bike in a sharp V shape. During the final stages of making the former for the mould I put a little too much pressure on the underside and it popped in. It was such a snug fit on the bike there was no way I could get my hand in without doing more damage and pop it back out again. Try as could there was nothing I could get in there that would pop it out and keep it out. So after an hour or so of frustration, I gave up and pushed the other side in to match it. Resulting in the boat keel effect.

So now you know the history, the designer and orgional fabricator of the SMS fairings. Wink
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Derek

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PostSubject: Re: Aerodynamics.   Fri Feb 24, 2012 9:10 am

Hi Ned
what an intersting storey, anymore!
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john bass

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PostSubject: Good one Ned!   Sat Feb 25, 2012 5:33 am

Boat keel effect does look right and aerodynamic!

Cheers!
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mjpowell

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PostSubject: Re: Aerodynamics.   Sun Feb 26, 2012 4:56 am

Thanks Ned for all that info! Stuff I didn't know..
We will now refer to SMS NED Fairings Type1(Ned, Pete) and Type2(Mike) ....

Regards Mike
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john bass

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PostSubject: Good pic of you Mike...   Sun Feb 26, 2012 6:28 am

Fascinating how that keel came about -- wonder if the plot would float?

Good pic of you Mike, wheelying your avatar but you are not very aerodynamic like that.

Cheers!
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Derek

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PostSubject: Re: Aerodynamics.   Sun Feb 26, 2012 5:55 pm

sorry Mike but I much prefer type 1 much more historic looking, a beautiful looking "seen Ian's new action avatar" looks the doggs" the fairing is even better.! lol

the type two is in my opinion too modern (ugly) well does not do the bike justice, this is of couse my opinion, its obviously very well thought of and made etc, but on the "Mike fairing " type 2 - did you make it then - type 2" i mean - !!!!!!! lol.

Vmcc head office chasing me on 1000, Di took a call they were not specific mike - I'm not sure what it's about! do you !!!. PM me if you do, before I return their call.

regards Derek
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mjpowell

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PostSubject: Re: Aerodynamics.   Sun Feb 26, 2012 8:59 pm

I'm a Luddite and dont like change and surprise, surprise! I prefer the SMS Ned Type1 fairing too..
After ruining my type1 and Jimmy was on the scene he re-made the fairing but with improvements?
1 More glass fibre and less screen (Ian Scutt asked for this)
2 Air scoops on the sides to flow air to the carb (to suit Ian's Roger Louis Bant) :- unfortunatly on a SMS frame the air was delivered to the engine cases.

I just run with what had been made, Jimmy later took the air scoops 'off' again

When Jimmy made a Fairing for 006 it was different again - a type 3? These fairings are used by Ian,Snowy and Michael Brown.

Alan has Norman got the mould for a Ned Type1? I think not...
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Ned

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PostSubject: Re: Aerodynamics.   Sat Mar 03, 2012 11:18 am

Bringing it back to the section it should be in Wink

Quote Derek :-
JB Ever the engineer, when you say 0.3 ref Hunter avatar could you please give an explanation on the factor this represents - drag or frontal area or a formula that includes both, please elaborate

Derek, Johns on a wined up, don't get sucked in. He has already told us he is in to aviation. So if he doesn't know the story about The spitfire and it's rivets he's the only man on this planet that doesn't.
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john bass

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PostSubject: Hey Ned!   Sat Mar 03, 2012 2:09 pm

Really!!! Hey Ned! would I -- luvverly Old JayBee*** -- wind-up anyone?

Its from a formula which includes air-density. If you want -- I´ll publish the formula.

It uses the flat plate -- normal to air-flow direction -- as the Drag Coefficient or Drag Factor, ONE. Flat front HGV Trucks being close to 1...

In the table of streamlined fairings it states that an egg shape is roughly 0.3Drag Factor and only 2 horsepower is required to maintain a 100mph ON A STRAIGHT, FLAT ROAD. Depending what the vehicle is -- a lot more horsepower is required to accelerate it to 100mp.... Racing is accelerating better than anyone else....

And I never said Dave Hunter looked like an egg ...

Cheers!

*** the starved Old German Ladies say that!!

Cheers!
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john bass

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PostSubject: Aerodynamic Drag Formula.   Sat Mar 03, 2012 7:38 pm

Aerodynamic Air Resistance formula:

Drag Coefficient --- `c´. Frontal Area -- `A´. Road Speed -- `v´.

and q is air density... The Air Resistance `R ´ -- with no wind --

R = c x A x v² x q.

So A, the frontal area for a chubby chappie is an immediate disadvantage and as Ned intinmated the flat number plate another big No-No...

With the speed being to a square law, the faster you go the more the air-resistance increases, hence you make A and C as small as possible... Hence A, with a TALL or Chubby-Chops figure has no chance of of reducing his air-resistance EXCEPT by making c smaller than everybody else´s -- and c is the streamlining factor which has to be better than anyone else´s to make up for the extra frontal area.

Examples of c:-

Open convertible -- 0.5 to 0.7; Station Wagon -- 0.5 to 0.8; Conventional car -- 0.4 to 0:6; Wedge Shape Sports Car -- 0.3 to 0.4 and the so called Optimum Streamlining -- which is egg with a long tail -- 0.15 to 0.2.

I´d estimate the Drag Factor (c) for the Keel-fairing at 0.27...

Note: the air density has been ignored -- in my opinion it only makes a big differences when driving in dense fog ...!!!??

Has anyone on here ever had a wind tunnel test? I mean with elbows tucked well in....?
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mjpowell

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PostSubject: Re: Aerodynamics.   Sun Mar 04, 2012 7:09 am

This is for Alan as he's asked for pic's of fairings/tanks for recognition purposes, matching moulds to fairings etc. but we can all have a look. Alan knows a Lauchbury but does not know the various SMS Ned/Jimmy fairings
which are availible to all. I know others have different types of tanks etc- PhilBetty Ian Scutt but I haven't got any of them...

SMS Ned type 1


SMS Ned type 2 - also without side scoops


SMS Jimmy type 3


SMS tanks Ned type



SMS Ned type with sunken underside



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Derek

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PostSubject: Re: Aerodynamics.   Sun Mar 04, 2012 10:24 am

Hi Mike some great infomation photo" I feel photo 2 apitermisers! real Bantam racing ,what a great shot!, obviously Cadwell "may the good times roll"

best regards Derek.
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Derek

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PostSubject: Re: Aerodynamics.   Sun Mar 04, 2012 10:24 am

bettsd wrote:
Hi Mike some great information photo" I feel photo 2 apitermisers! real Bantam racing ,what a great shot!, obviously Cadwell "may the good times roll"

best regards Derek.
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Derek

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PostSubject: Re: Aerodynamics.   Sun Mar 04, 2012 10:30 am

my gooodness just spotted another Mike what does AM stand for ?????

kind regards Derek
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john bass

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PostSubject: Error -- Error --- Error....   Sun Mar 04, 2012 6:07 pm

Massive error in the formula -- should have been halved... Sorry!

Air Resitance, R = c.A.v²/2 . (I left out the ".../2...")-

c is the Drag Factor which is how good the streamlining is, and A is the projected frontal area....

"A" can be obtained by using a planimeter on a photograph taken from the front. This is the most difficult bit for tall bulky blokes because getting balled-up in the marvellous manner Mike has done is frequently not physically possible.

Not to be forgotten is that A is the large factor in the formula. Some fairings actually INCREASE `A´. Look at Derek´s avatar and see that when tucked in his frontal area might be less than if he had a `bottom-half´ on as his `skirt´!

Didn´t mean to pick on you Derek -- just that yours was the only example of top-half-of-a-fairing!

Cheers!
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mjpowell

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PostSubject: Re: Aerodynamics.   Sun Mar 04, 2012 7:51 pm

As requested and to stop folk getting eye strain here a blow up of the sticker on my tank -
posted by the technical inspector following a crash at coppice - which proves they have a
sence of humour too ...

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john bass

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PostSubject: No boring calcs...   Mon Mar 05, 2012 12:23 am

No boring calculations on here, right!

-- I just worked out that an unstreamlined -- `Naked´-- rider with 5.25ft² frontal area and 0.3 air-drag-factor would need 4 more horsepower to keep alongside a rider whose frontal area, A was = 3.75ft² and Drag Factor `c´ (SMS fairing, guess) = 0.27 -- with them travelling at 60mph....

The latter was based on a GUESS that the SMS Fairing has a "c" of 0.27 and where the rider well tucked in has an "A" which would fit into a rectangle 3.0ft high and 1,25ft wide. Which I made equal to 7.13horsepower needed to break wind at 60mph.

So that rather blows a quote to the winds that I made earlier --

-- which I had taken from Google that said "Only 2 HP was needed to travel at 100mph on a flat, straight road..." -- which seems to suggest that NOT all stated on Google can be trusted. Perhaps the writer was referring to the tractive resistance from wheel bearings and transmision friction...? I must take another look.

Cheers!
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john bass

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PostSubject: Wonderful pictures...   Mon Mar 05, 2012 12:32 am

Wonderful pictures Mike but #2 pic: -- wheelying at Cadwell -- increases the frontal area and hence increases Air-Resistance to forward motion....!!

CheerS!
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