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 a new member and new builder plus progress so far

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john bass

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Number of posts : 1729
Age : 88
Localisation : Bensberg, Germany
Registration date : 2006-12-06

PostSubject: Exhaust pipes...   Thu Mar 03, 2016 5:20 am

John C,  I can understand the feeling of awe...
I  spent a lot of time at Brands testing different pipes on Bantam and the AB 250 and proved the practical  outcome doesn´t always follow the theory exactly, which can be frustrating particularly when a `new´ pipe has the engine burbling with no power...

And when it has been got right the difference is awsome
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dansofield550

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Number of posts : 362
Localisation : gravesend kent
Registration date : 2011-10-23

PostSubject: Re: a new member and new builder plus progress so far    Thu Mar 03, 2016 9:39 pm

heres a brain teaser for you john , whats the merits draw backs etc of a pair of cranks weighing the same (3kg)
but one is larger diameter say 96mm and 118mm
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john bass

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Number of posts : 1729
Age : 88
Localisation : Bensberg, Germany
Registration date : 2006-12-06

PostSubject: Hi Danso...   Fri Mar 04, 2016 2:48 am

Hi Danso...!

Unfortunately I did the exercise with the 125 having 96mm dia and weight at 2.4kg and the 175 with 136mm dia and 3.8kg which meant the difference of inertia between the 125 and the 175 was BIG.


There was a diffference according to my calcs...*** in the 175´s acceleration being a bit sluggish but that may be made up for by the tendency to rev on in the four gears with TE - TE**  always being ample enough for acceletaion before the next up-gear change....

I assumed there´d be no great disadvantage in road performance but an advantage in heavy flywheels amoothing the cyclic speed variations and aiding the revving-on...

** Tractive Effort minus Tractive Resistance = Acceleration .... I have in Edward Pickering´s Library a diagram of the 125´s TE-TR which might be useful in understanding what I am driving at...

With only the dia difference there will still be a fair-sized difference but obviously not as much as my brain exercise.

***  I cannot stay on here too long because my PC is still an upgraded 95, 98,2000 and XP Woíndows and I keep getting my blogs  chopped off...

I´ll come back with my accelerations figures ASAP....
Cheers!
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john bass

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Number of posts : 1729
Age : 88
Localisation : Bensberg, Germany
Registration date : 2006-12-06

PostSubject: Was cut off....   Fri Mar 04, 2016 3:32 am

Hi Danso...!

Immediately after posting that,  I was cut off.**

This treatise I did is 30 boring pages long -- I think I must have been overcome by brain-fever. Mike Powell said he didn´t understand it and that was only the graph of moments of inertia.

I'll try sending you a PM e-Mail and if you really want to read this missive I´ll copy it and send...

My conclusion -- as i read it again -- does not ring as true as it did 1st time round...The flywheel stored power increases with speed much more in the 175 (this exercise with bigger flywhees)and I am sure that although  this makes for sluggish acceleration it is of advantage when Tractive resistance increases -- exponentially as it does -- at higher speeds ....?????
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john bass

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Number of posts : 1729
Age : 88
Localisation : Bensberg, Germany
Registration date : 2006-12-06

PostSubject: Hi Danso...   Fri Mar 04, 2016 4:29 am

I tried sending a PM and don´t think it went and found one from Keith Webb in the In-Box -- sorry Keith I couldn´t open it...


b.... computer ,,, this the third of going completely out and starting all over agin...

I really do believe the large flywheels in the 175 are an advantage and not sure of the 125. The slipping of the clutch -- with high revs -- stores a lot of energy .... Hmmmm??? eh...?

My reference to Mike Powell referred to -- I think it was -- last Cadwell of 2012 when he was very busy with something looking unusual with oil into his gearbox so he probably wanted to get rid of me and was too polite to say so....s

John.
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john bass

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Number of posts : 1729
Age : 88
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Registration date : 2006-12-06

PostSubject: Continuation for Danso...   Fri Mar 04, 2016 5:54 am

If the rider is slipping the clutch with the revs in the Useful power band  where the resonant exhaust pipe is working the power engine output is at its optimum  and the clutch-slip acts as a torque converter (á la fliud flywheel) and the stored flywheel energy assists acceleration during the lower road speeds where tractive resistance is less than it is at the higher road speeds....

What must be remebered is that body-weight plus bike weight (ie Total Weight -- TW) is the curse of accelerating force for  such as me who could never get his body weight low enough for the 125 with the formula ever being:-

    Force, F   =  Mass x  Acceleration  which is F  =   TW/g x a

which transposed is  a  =  g/TW x F  which has the acceleration as  exoressed in ratio of g as

   F/TW.g  = acceleration -- F/TW being the ratio of g as acceleration -....

So lay off the cream cakes and beer ...!
Cheers!

JayBee.
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john bass

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Number of posts : 1729
Age : 88
Localisation : Bensberg, Germany
Registration date : 2006-12-06

PostSubject: Just to finish for the moment...   Sat Mar 05, 2016 5:10 am

Just to finish for the moment, Danso,

I looked up my treatise (is on A4 longhand -- not on computer) on heavier flywheels and had plotted curves for two flywheels of same weight with double dia -- not Bantam, of course  -- in with the 125 & 175. As expected the larger flywheels with their `k´, radius of gyration larger -- twice as large -- proves the point in the curves. I´ll get the curves to you somehow -- my PM to you didn´t go.... Could you try PM´ ing me with your address and I send otherwise it might be that Edward or Trevor could help out with this ....


BUT the amount of stored energy is small relative the torque to the the rear wheel which suggests the large flywheels do not contribute as much as the small ...

What I think is a bigger advantage with the 175 -- pushing aside the total weight issue -- is that with its four gears :- Bottom (1st) can be very low (which the 125 cannot afford to do). This would allow the 175 racer to get off the line quicker ands then get into the close ratio range similar the 125....

Cheers!

JayBee.
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