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 Aerodynamics plus Power to weight ratio.

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les2012



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PostSubject: Aerodynamics plus Power to weight ratio.   Mon Mar 05, 2012 9:22 am

Reading the present post's I thought this might be of interest to a few people as I think it's relevant. Power to weight ratio, I
cannot give any formula as I don't know how,( but I bet J.B can). The quote I'm posting is from John Sawer's racing diary, now
Johns height about 5'10", weight 12.5stone, Mick Bridges 5'9, 9.5stone. "Cadwell 29-5-82 championship race, better place on
the grid first into hairpin, hold lead for 3-4 laps then Cashmore goes past by approx 8-10 mph extra along the straight, fortunatly
nobody close so finish 2nd,so John was losing 8-10 mph.
Race 3 Inter. Bike lent to Mike Bridges-- Mick breezes off into an immeasurable lead but pulls out to give those on Inter bikes
a chance.
Race 4 open. Mick has another good start, holds lead for 3 laps then Cashmore goes by, Mick has a go and overtakes at
Mansfield then again at the hairpin but Cashmore's bike is just a little quicker so Mick finishes a very close second, so you can see
the difference in stature and weight, same bike, same gearing, same weather, Mick had a closer race, (power to weight).
Now after those years I have the bike , before I started the rebuild I weighed the tank and seat this came to 14 pounds- thats
one stone in old money and that's not including the steel rim front wheel plus a well repaired half fairing. In my opinion be it
right or wrong one can spend a lot time on an Bantam engine ,a frame, wheels,ect but if your height and weight don't fit then
go out and enjoy it.

On another point, how to get more riders to finish on or nearly the same lap, as a suggestion, how about starting those that have
no chance of win agains't "you know who" and give a 20sec start a bit like the old 50 miler, novice, Inter, and seniors, I'm
not sure if it would work but I do think it might give the also rans a boost if they finish close to the "you know who's".

Interesting to see Rex is having a new barrel by Ron at Farhon, I wonder how long he will have to wait as Mick Bridges sent
his barrel for a reline last August 3rd and still await it's return, we are now in March.

Regards to all.
Les.













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PostSubject: JS was too big/heavy for a Bantam....   Mon Mar 05, 2012 3:20 pm

John Sawer was too big and heavy for a Bantam -- same for The Wobblyman & I -- but we got stuck in. That bluddy run and bump start was a swine! -- I´d got down from something over 15 stone to become a 12st 3lbs weakling: 3 - 5 steps pushing Icarus-1 and I collapsed. Then at the time of my very first road race it fortunately started on 3rd step otherwise I would have collapsed on the grid!!

When we crashed on Bottom Bend, Llandow (John Sawer) Scrooge and his bike were lying on top of me with my right elbow skinned to the bone. He glared at me thro his specs and said, "Why did you get in the .... way and give me back my bike."

But Bantam Racing saved my life. The two colleagues who worked with me for Simms and who liased with me at Leyland both died before 50 of excessive intake of Expenses beverages. So my dieting for Bantam reasons saved me ...

Re Power to Weight ratio -- in terms of engine max power to total weight of rider-plus-bike -- it is just the well-worn formula:-

F = ma.... where F is tractive force in pounds at the rear tyre patch, m is rider plus bike weight in lbs, W divided by g at 32.2 and a is the acceleration in ft/sec². So transposing has `a´ -- the acceleration -- equals F/m -- which will give the difference in acceleration of a 12,5 st JS and a 9.5st MB....

Tut Tut! I only got up to have a drink and take my Thyroid pill and you raise that question Les ... Its now 05.20 here in the Fatherland, so I´m going back to bed for my beauty sleep. If you don´t work out Scrooge´s (JS´s) 12.5st disadvantage re Mick Bridges 9.5st I´ll do it later ....

Cheers!
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PostSubject: I am back...   Tue Mar 06, 2012 6:50 am

I am back...

Simple, non-dimensional analysis way to look at it without bothering with `g´, rotational masses inertia or air-&-rolling resistances is as follows:-

Rider "A" with 9.5st weight compared with rider "B" of 12.5st...

Assuming A´s weight to be the ideal then B/A = 1.316 which means B has 31.6% more weight than the ideal.

Which means the B rider-weight disadvantage during acceleration is roughly 32% by the formula: F = ma.

... Transposed for A as ideal unit of One, is,`à´ = F/1....

... and for B is, F/1.316 = `a´ = 0.759F.

... which says that B has only three-quarters of the tractive effort that A has -- because of B´s extra weight.

But the above is too simplistic and is wrong in leaving out the weight of bike, leathers, boots and helmet....

So let´s do it with the data above³ and get real ideas of the differences the extra weight makes to acceleration in ft/sec²; speed difference after -- say -- 5 seconds; and difference in distance covered, during a speed increase from 40mph(58.7ft/sec) to 60mph(88ft/sec)....

... that´s if you are still interested, Les? Then ³... please supply info -- doesn´t have to be exact, just near enough. -- I mean I have no idea of the weight of boots, leathers and helmet...

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PostSubject: Re: Aerodynamics plus Power to weight ratio.   Tue Mar 06, 2012 8:09 am

come on John dont stop there, it was just becomming interesting then you asked Les for details.

come on John I want to know this I already lost 9.5 kilo gramms and its killing me, well it almost did !

anyway as Iread it are you saying a rider 9.5 compared to rider 12.5 needs 32% more power to excellerate at the same rate. if you are then we have to have to add weight's to light riders of bikes or at least figure on a an average maximum combernation as if this is the case this is totally unfair!!!!

based on your clacs I need 40bhp to compete against Trevor or Ian!! I think that is a lot for a BSA Formula Bantam.

Derek

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PostSubject: NO!   Tue Mar 06, 2012 2:08 pm

No Derek -- read it again and you´ll see that the silly exercise did NOT include the weight of bike, leathers, boots and rider´s breakfast!!

THAT IS WHAT WE HEAVYWEIGHTS COMFORTED OURSELVES WITH -- DO STILL COMFORT OURSELVES WITH -- THAT WE WERE/ARE A GOOD 30% DISADVANTAGED OVER THE LIGHTWEIGHTS -- just because we were/are a bit heavier... We tend to say, "Cor! look at world champion, Casey. If he turned sideways we´d not see him and tucked in behind his fairing -- we don´t..."

When the calcs do include the total weight -- and I have NOT calculated that yet -- it would be far far less. I´d guess at less than 10%...

... say, in terms of total weight: 380lbs as compared 340lbs (roughly 3 stone!?) which is 40 on 380 -- (rapid use of ancient, Old Hat³ calculator) is 10.53...!!!????

Guessing again, I´d reckon that the difference of acceleration would only be a fraction of a ft/sec² and if it was say, 3/4... -- 0.75ft/sec² then the difference on the road would only be a few feet in say 5 seconds of accelerating.

No! Give me an example of bike, leathers, helmet and boots weight and as I told Les I´ll work out the REAL disadvantaged factual figures.

What I think slows down the heavier rider as versus the slim, skinny blokes is that the bulk is not so easilly tucked in and it is the extra cross-sectional-area presented to the wind that is the heavyweight´s major problem ....

More anon -- I only got up for a drink and a quick look at what´s new...


³... -- Just couldn´t resist that one!!
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PostSubject: Re: Aerodynamics plus Power to weight ratio.   Tue Mar 06, 2012 2:26 pm

so 10.5% disadvantage -how much weight does they represent then john 18 kg need ading to a 9.5 stone rider over a 12.5 stone rider, I hoping to be under 12 stone buy the time practice day arrives.

I would be happy to orgnise some lead to place inside tubes or make into pproper brackets "anyone"!!!!

Derek
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PostSubject: Still no weight data...   Tue Mar 06, 2012 10:11 pm

Still no weight data:-

No matter! I´ll assume 80kg as bike weight-- based on one rider here saying his bike weighed approximately that -- which is 176lbs.

Rider `A´ at 9.5st = 133lbs & Rider `B´ at 12.5 stone = 175lbs.

What say we add 15lbs for leathers, helmet, boots, gloves and dirty underwear??

And say that the engine is producing 11ftlbs torque and the first gear ratio is 12:1 -- with Rolling Radius of Dunlop KR825 at 11.8 inches -- let´s call that one foot! -- the Tractive Effort at the rear tyre contact patch will be, TE = 12 x 11 = 132lbs force....

Total weight to be shifted:- "A" = 176 + 133+15 = 324lbs; .......... "B" = 176 + 175+15 = 366lbs.

From transpostion of TE = ma. We have, a = TE/m....

A:-- m = 324/32.2 = 10.06... a(A) = 132/10.06 = 13.1ft/sec²...

B:-- m = 366/32.2 = 11.37... a(B) = 132/11.37 = 11.6ft/sec²...

Say they were accelerating for 5 secs the speed of A would be 65.5ft/sec -- which is 44.7mph.... and the speed of B would be 58ft/sec -- which is 39.5mph --- 5.2mph slower afterr 5 seconds racing together ....

If we still had 11ftlbs of torque in Top with the gear ratio as 7:1 the Tractive Effort would be 77lbs force at the rear wheel contact patch.

Thus the acceleration whilst in Top will be less:-

For A the acceleration, a(A) = 77/10.06 = 7.65ft/sec²...

and B " " , a(B) = 77/11.37 = 6.77ft/sec²...

With those two the difference of time taken for A & B to go from 40 to 60mph --or Uh-oh! was it 40 to 80mph? can be calculated...

I have to go shopping anyway -- so I´ll come back later, look up what I said before and carry on....

Check for arithmetical errors please -- what with my forgetting what I had written before, I suspect my working-out??

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PostSubject: Re: Power to weight ratio   Wed Mar 07, 2012 1:18 am

Hi JB.
Iv'e just posted a post via post reply to Eddie so now I know I can reply post,I did post to you today at 9-10am but I had to post
new post because I didn't know then how to post reply post. I have since weighed John leathers 7.5 lb's this includes patches, I
think your estimate is right for the average rider so look forward to reading your answer. thanks again for your interest.
Regards.
Les.
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PostSubject: I galloped ahead Les...   Wed Mar 07, 2012 5:22 am

Les! I took off on the calcs not waiting for figures...

As promised I´ll do "Distance travelled by A & B in 5secs whilst in 1st gear ...

"s" is Distance travelled from "u" (intial velocity of zero) and "v" final velocity after time, t. s = ut + 1/2at². From start so u = 0 and ... s = 1/2at².

s(A) =1/2 x 13.1 x 25 = 163.8ft... s(B) 1/2 x 11.6 x 25 = 145ft.


... Distance A is ahead of B after 5 seconds is 18.8ft -- 6.3yds....

In Top gear (47 x 15) ratio 7:1 -- with 11ftlbs -- Tractive Effort at rear wheel is 77lbs force.
From previous post:-- a(A) = 7.65ft/sec² & a(B) = 6.77ft/sec²...

Time taken for "A" and "B" to go from 40mph(58.7ft/sec) to 60mph(88ft/sec)... v = u + at.

Therefore (v - u)/a = t.

.... t(A) = (88 - 58.7)/7.65 = 29.3/7.65 = 3.88secs...

.... & t(B) = 29.3/6.77 = 4.33secs...

B takes 0.45 second³ longer than A to accelerate from 40mph to 60mph....

³.... if that happens several times in accelerating from any lower speed to any higher speed during a lap -- say with an average of 1/3 second for each time of accelerating -- and the happenings were say 15 times per lap then the deficit for B would be 5 seconds but he would have 18.8 feet to make up which was lost at the start....

This is simplistic in ignoring rotational interias, air resistance to motion, inclines, rolling resistances and Drag Factor etc...--

--- but conclusive, to me, is that being 3 stone heavier is a big disadvantage when only 11 to 13ftlbs of torque is available with only 3 gears.

Hoping this has proved useful.

CheerS!
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PostSubject: Re: power to weignt   Wed Mar 07, 2012 7:13 am

Many thanks John for you time and knowledge.
Les.
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PostSubject: Re: Aerodynamics plus Power to weight ratio.   Wed Mar 07, 2012 8:25 am

Hi John

Your conclusion confirms my worst suspicions. Its all down to Sir Isaac and his laws of motion. What a bloke... Shocked

Chris
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PostSubject: Re: Aerodynamics plus Power to weight ratio.   Wed Mar 07, 2012 11:36 am

yes we know this John but by how much?

i think its easy 3 stone on the seay in a special seat tray made to take weight and bolted in, safe no issues.

derek
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PostSubject: The Power was ignored...   Wed Mar 07, 2012 7:48 pm

Many thanks blokes! As John in NZ said, never forget `g´ -- Sir Isaac´s discovery has always been there with us -- its when Sir Lancelot fell from his horse -- in all that armour -- that he felt he´d discovered it first and when you hit the track its when you know you´ve been ignoring `g´ the most.

At Cadwell the extra 3 stone was useful from Park to Mansfield -- even Icarus-1 went quite quickly down that slope.

Note the power was ignored and only Instant Effort (Torque) was used for calcs ... Oooh! and I forget the flywheels -- but no one has yet questioned WHY for the 5 secs from standing start 11ftlbs torque was available for the whole 5 seconds?

Well, it has only been a couple of hours since I showed off --- so I shall wait.

If I knew the 3 gear ratios and had a power curve² I could do a graph showing Tractive Effort versus Road Speed for a 125 Bantam -- which is very much like a Power to Weight picture and then get Edward to put the pic up here. My Gear Ratio chart only shows Top Gear ratios going from 8.3:1 (823mph at 10,000 revs) to 6.048:1 (112.7mph at 10,000rpm).

Interested?

²... I have 3 power curves -- it`s the gear ratios for 1st and 2nd gear -- say for Cadwell -- that I need.

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PostSubject: Re: Aerodynamics plus Power to weight ratio.   Thu Mar 08, 2012 3:56 am

Hi Derek!

bettsd wrote:
yes we know this John but by how much?

...
derek

I thought "...by how much..." was included in my last post.

The heavyweight loses ground by 18.8ft (0.63second) accelerating from zero at the start and he loses 0.45second accelerating from 40 to 60mph.

I said if you take all the times Old Chubby Chops is accelerating from any low speed to any higher speed he is going lose a FRACTION OF A SECOND each time.

No need for more calculating -- just make a guess that it might be 15 times a lap at a 1/3 of a second and you have 5-6seconds a lap Chubby is in arrears. At 6 laps a race that becomes 1/2minute to 36seconds! If Cadwell, 15 to 18 seconds because its only 3 laps -- ain´t it??!!

But in terms of actual racing ability the heavyweight might have got the other dozen-or-so things right -- one of them being handling to suit his heavier weight -- and be faster thro´corners than the fleaweight who brakes early, sits up too often and goes thro´ corners slower than Old Chubby -- because of Fleaweight braking and changing down which the Heavyweight does not do by reason of his better handling.


The playing field levels out a bit when you think of all the other things involved with racing than rider weight!!


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PostSubject: re: power to weight ratio   Thu Mar 08, 2012 5:14 am

Hi JB.
I like your last post,it shows John Sawer, coupled with his disadvantage of 3stone, what a good racer he was. Just goes to show
what can be done. End of topic (maybe)
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PostSubject: End of Topic...   Fri Mar 09, 2012 4:28 am

End of Topic, Les? No way.

I am now speaking of the very early seventies when John Sawer and I were about equal on weight & performance on the track. We had some good hard fought battles on the circuits and there were some heated arguments with him as "Scrooge" -- the club´s treasurer -- during committee meetings. I well remember our being short of marshalls and me saying we ought to pay them. John´s eyes blazed as he shouted, "What with? We have a shortfall of non-paying members and those who do pay, do so with rubber cheques."

He was right, of course. With all the different classes we ran we attracted a great number of doubtful characters of very dubious machinery who could barely afford the fuel and oil to race -- much less pay their annual subs. On one occasion -- at Snetterton -- I was threatened with unimagineable discomfort by a Production racer if I mentioned his name again in The BRC Mag as being `...late with the payment of his Subscription...´ he had his own company to run, he told savagely, and his clients/customers often didn´t pay him for three months or so... Like his big bike he was a huge monster of mankind.

When I did risk it -- a mention in the mag again -- Scrooge patted me on the shoulder and said, "Good man! He´s sure to pay up now...." Ever the optimist -- was our John Sawer ....

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PostSubject: Reopen topic if you will   Fri Mar 09, 2012 7:24 am


JB, did per chance this huge monster ride a Triumph 650cc? I seem to remember a mountain on a bike but, I do remember a guy
who almost dominated the prody scene on a Triumph in them days. Yes JS was ever the optimist, I think he did a lot for the BRC
and I hope I can live up to his memory with JS2.
Les.
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PostSubject: Yes Les...   Fri Mar 09, 2012 9:22 pm

Yes, Les. Had a similar name to a Prime Minister.

But back to aerodynamics: some fairings -- and how they are used by the rider -- produce a frontal area that negates the use of any form of streamlining. One must ask how much frontal area is exposed to the wind? & how often per lap? -- WITH and WITHOUT a fairing -- how often is the sit up and beg posture adopted per lap?

To over-do the use of Dave Hunter´s avatar (on a previous posting) his exposure is so small WITHOUT the fairing that when I see him in a later picture with a fairing I have to question whether that fairing made any difference ...???

Just look at the video of Brambley v Scutt at Lydden´s Launchbury Trophy race -- both are using their fairings to full effect and only exposing themselves when braking and changing down. Look at pictures of some of the lads -- and even the pros -- sitting up behind their skirts as if going to tea at Grandma´s on a Sunday afternoon.

Yes! I know, I have been harsh about fairings yet I think I do have a point about how suitable they are to the rider and how the rider uses their own particular version....

And Power to weight -- I think Thruxton suits the heavier rider -- because it is a series of long, fast bends where the need is to keep the speed-on-in-the bends all the time and -- maybe -- handling and tyre adhesion wins over acceleration ...

We had two meetings there in 1968 (I think...?) it was.

Have any of youse raced there?

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PostSubject: Re: Aerodynamics plus Power to weight ratio.   Sat Mar 10, 2012 1:53 am

john bass wrote:
Yes, Les. Had a similar name to a Prime Minister.

What Harold Laughing

John I think you are overlooking a lot of other aspects of streamlining when you refer frontal area only. A riders legs may create less frontal area without a fairing but they will also create a lot of turbulence.
You can forget your formulas and do a simple test if you like. Lay a bike down at 80 mph and stay tucked up in the fairing. Then lay one down without a fairing at 80 mph. Let us know how you got on and if your leathers caused less drag than the slippery fairing. Laughing
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PostSubject: You are most probably right Ned....   Sat Mar 10, 2012 5:23 am

You are most probably right Ned but it has never been proved -- or has it? The air-cooled Bantam engine is relatively small and much curved in its own shape as are rider´s legs ... I look at Derek Betts pic*** on here with only the upper bit of fairing and imagine that when he is tucked in à la Dave Hunter his air drag must be quite low and that some of the fairings I have seen would present more frontal-area if not increased air-drag.

In that previous posting I said "c" -- the Drag Factor -- was the Quality of streamlining (how good the streamlining works) which was then multiplied by "A" the frontal area normal to the wind and further multiplied by "v²" -- which means the product of "c.A" is what matters -- not just "c" -- together they are the deadly factor -- and what I was getting at was the huge number of riders who don´t fit their fairings; fairings that don´t suit their rider and fairings that have sudden changes of contour that surely act as a parachute being-pulled-horizontally-forward as it were.

The fairing with the keel has the best "c.A" with air flow splitting up and over and down and under with no visor-like surfaces opposing wind but that is only subjective on my part. From the look it is as good a strealiner as one could get... Yet again the rider must get tucked in (for as much "race-time" as possible) -- for it to be effective...

I ask again, I wonder if any `Home made´ fairings have been wind-tunnel tested. I guess the GP & WSB teams have, with them being bespoke tailored as Mick Potter said so its probably OK to copy those yet ever remembering that the fairing must fit the rider ...

I certainly think it worth while to get someone to view the rider in "racing-crouch" situ before final fitting of a fairing. A photo and measurement of frontal area might be as depressing as knowing the OVERWEIGHT factor!!


*** I didn´t mean to pick on you Derek but you are the only one showing a half-fairing....


Re what you said about the smoothness of fairing compared with rider´s legs, I´d say mine were smoother -- being mostly black plastic taped plus my leathers had a very smooth surface and were very thin which meant a lot of black plastic tape was there also....

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PostSubject: Re: Aerodynamics plus Power to weight ratio.   Fri Mar 16, 2012 9:02 pm



Hi John :- I must have missed this quote below, as just looking back at my notes and history, I have to say he must have been one of the most succesfull racers never to have won the championship, his record speaks for itself, I liked John and he had a tight control on many things, but he was a wealth of help and knowledge in the Paddock, he would always make sence even when you were challenging him for speed he was still as open with his opinions and answers in the Paddock.

Hi was quite a big guy too but he was never overweight. !.


[quote="john bass"]John Sawer was too big and heavy for a Bantam -- quote]!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I dont agree with this one John Bass.

kind regards Derek

P.S we are all waiting for the spec on Kerim! "John over to you"

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PostSubject: Yes! perhaps I am WRONG again....   Fri Mar 16, 2012 11:18 pm

Nothing like good debate -- I am wrong again and surely admit it -- the heavier bklokes DO win Bantam championship titles ...

...but when John Sawer was lying on top of me at Llandow he felt more than 12 stone and his `g´ force just beforhand felt a lot heavier. Fact is I never weighed him so I was quite wrong in saying he was too heavy for Bantam racing -- because I could not have known... (That´s if I did say that??) It unfortunately sounds as if I had been maligning Scrooge by saying things about him which was not my intent -- I liked him too, but I was not too fussy about him when he lost it and brought me down...

I think my meaning was ALL HEAVIER PEOPLE -- say OVER 11 stone -- SHOULD NOT RACE BANTAMS, poor little machines!!

How we appear to others comes into this... Before getting into Bantam racing I reported sick to ask about dieting and the quack said, "Worried about your weight? Never!?"

So there is that aspect of it...???

But talking about tall blokes being Bantam Champs I seem to remember Brian White (last September sort of looking down from a great height at me along with brother John...) having won the championship and Brian must have been a reasonable weight at the time of his championship title . Don´t forget that Mike Powell says he is over 11stone and Peter Tibbitts is also tall and weighty ....

So is it not time to stop bellyaching about the extra weight disadvantage and suggestion of handicaps for lightweights ...? These champs obviously get around the difficulty by being in the "well tucked in race crouch position" and keep the throttle open longer... Re photo of Peter in front of Mike (by Lee) both well tucked in....
In my opinion riders are more Disadvantaged by their own inability to use their streamlining to the proper effect than they are by their own weight!


... that´s my theory any road-up!

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PostSubject: Re: Aerodynamics plus Power to weight ratio.   Mon Mar 26, 2012 1:07 am

[quote="john bass"]Nothing like good debate -- I am wrong again and surely admit it -- the heavier bklokes DO win Bantam championship titles ...

...but when John Sawer was lying on top of me at Llandow he felt more than 12 stone and his `g´ force just beforhand felt a lot heavier. Fact is I never weighed him so I was quite wrong in saying he was too heavy for Bantam racing -- because I could not have known... (That´s if I did say that??) It unfortunately sounds as if I had been maligning Scrooge by saying things about him which was not my intent -- I liked him too, but I was not too fussy about him when he lost it and brought me down...

I think my meaning was ALL HEAVIER PEOPLE -- say OVER 11 stone -- SHOULD NOT RACE BANTAMS, poor little machines!!

How we appear to others comes into this... Before getting into Bantam racing I reported sick to ask about dieting and the quack said, "Worried about your weight? Never!?"

So there is that aspect of it...???

But talking about tall blokes being Bantam Champs I seem to remember Brian White (last September sort of looking down from a great height at me along with brother John...) having won the championship and Brian must have been a reasonable weight at the time of his championship title . Don´t forget that Mike Powell says he is over 11stone and Peter Tibbitts is also tall and weighty ....

So is it not time to stop bellyaching about the extra weight disadvantage and suggestion of handicaps for lightweights ...? These champs obviously get around the difficulty by being in the "well tucked in race crouch position" and keep the throttle open longer... Re photo of Peter in front of Mike (by Lee) both well tucked in....
In my opinion riders are more Disadvantaged by their own inability to use their streamlining to the proper effect than they are by their own weight!


... that´s my theory any road-up! [quote]

May come in on this from a different but related point of view? Over many years I've noticed that for some unexplicable reason tall riders appear to fit their machines better than short riders, even to an extent that should really be bordering on the absurd. I've seen riders of 6' 2" (or whatever that is in new money) riding 125s, and even 50cc machines, who seem able to be able to fold themselves into their bikes. As a flyweight shorty I find this very frustrating, because when I compare photographs of me, tucked in on a bike, the entire ensemble doesn't look as streamlined as those lanky guys. Sad

Also I think it was you, John, who said something about riders not tucking in properly? Riders have dolphin fairings but seem to adopt a sit-up-and-beg posture. Now, compare photographs of riders on unfaired garden gate Nortons in the twenties and thirties, and notice how their backs are horizontal! Admittedly, some of the problem is of course full face helmets, which no longer permit the classic chin on the tank posture. However, while it wouldn't worry me if fairings were banned, I ain't proposing a return to pudding basins. No

Final point, a year or so back I bought a dustbin fairing mould from Howard White (his brother, Kevin, still holds 100cc National records from the seventies). He told me that the fairing was certainly worth 3-5mph over the standing quarter (and presumably more over a flying mile, John?). Side winds are the devil and I can see why dustbins were banned for circuit racing. Mostly okay for us sprinters, though.

Good luck to all the racers for the coming season.

Howard Smith

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PostSubject: We need a planimeter...   Mon Mar 26, 2012 5:47 am

Very good Howard!
I must admit, 42 years too late, that when I finally succumbed to fitting a fairing I did NOT do it justice. I have photos to prove that point...

It would be easy to compare how good the rider´s are at "getting the best out of their fairings" without any more than measuring the frontal area of rider-and-bike by use of a planimeter. Perhaps the club could club together and get one for Bantam riders use.

It would be easy to see the extra amount lost to sitting up (as if going to Grandma´s for Sunday afternoon tea!!) or because of elbows, legs and shoulders -- not forgetting the head -- sticking out to spoil the best of any streamlining ...

... First take a head-on picture of the fairing enshrouded bike as a baseline. Trace the area with the planimeter subracting the See-Thro´ air-spaces from the total area. This baseline could be used to compare fairing with fairing. Then take more head on pics with the rider in various modes of action during racing: sitting up for braking, sitting up to clock the birds in the gallery, in full race crouch and other times of action which could come from previous action shots.


I´d really like to do that with the photo on here of Peter Tibbitts wrapped inside his Bantam -- and of David Hunter -- as in the avatar -- among many others. It would be quite revealing. That´s because I have convinced myself that more Horsepower is lost to the POOR streamlining aspect than being heavier than 11.5 stone ...


The Air Resistance equation is, Cd.A.v² -- ignoring air density with v as the speed, A, the frontal area and Cd being the coefficient of air-drag shows how big a contribution A makes in the HP needed to overcome the air-resistance. Cd can only be obtained by wind-tunnel test but if the Cd is known for a couple of proprietary makes a reasonable estimate could be made for the home-made DIY jobs.


Ah! Maybe someone on here has a simulation programme for the above -- there seem to be so many simulation programmes available that make my waffling redundant!


How boring!? Yaaaaaawwwwnnn! Time for bed!

Just came across a wonderful saying, "Work might not kill you -- but is it worth taking the risk??"

CheerS!
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