1971 Experimental F750 Racer

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Rohan always relies on Wikipedia on technical matters. Their stuff is often a second hand interpretation of the work of other people, and not entirely reliable. I'd trust Phil Irving long before anything on Wiki.
 
Only in this case, Wiki is perfectly reliable, and perfectly correct.
Well, perfect for as much of the basic aero 101 stuff as I trawled through, anyway.

And providing some idiot hasn't just gone there and corrupted it, Wiki is about the most reliable source on the net these days.
Certainly better than most anything you've uttered on these hallowed pages.

BTW, I found my copy of Phil Irvings "Motorcycle Engineering", and he has NOTHING to say on Coefficients of Drag.
If I can locate where "Tuning for Speed" is, maybe its in there.
But I've only ever known, and expected, CoD to be of the order of +/- 1.0, with motorcycles typically about 0.5 unless something is different about them.
With the rider sitting bolt upright, its more like 1.0
 
In Alans defence, once you leave out out all the diversions, off topic posts, misleading statements, anti-iso rants and other extraneous material,
he does have a pretty good record.
Wiki, eat your heart out .
We do enjoy his old racing reminiscences though...

P224 in the Clymer version is 2 stroke port timings.
Nothing in the contents or index to point to anything on this subject.
You seem to be adopting the same tactics as Alan. ?
 
Speak for yourself Rohan; Clymer's came out of nowhere. Now you are truly starting to sound like one of the frayed few on this forum.

Have a look at my post above - I'll digest this for you again - I was referring to............................

Phil Irving's "Tuning for Speed"; pg. 224 or thereabouts.

Where the heck did Clymer's come into the discussion? Oh, I get it, your sense of humor.

Not taking anything away from acotrel's achievements. Hope I have his gumption when I reach his age.
 
Fair go - we are not physic visionaries like you and Alan appear to wish to be seen.
If you mean it, say it though, don't expect us to guess your meaning ?
If you just want to make up content, in the absence of knowledge, thats fine by us too...

And Clymers did many of the reprints of these books. (the vast majority, in fact ?).
I just happen to have those versions.

Nov 73 P224 of MotorCycle Engineering has "The Bottom End", and twin crankshaft versions.
Nothing in the index or contents about CoD.
Wiki is still lookin pretty good ?!
 
Rohan
Tuning for Speed by P.E. Irving
My copy is Temple Press Third impression (1965)
Chapter XX "Testing the Finished Work"
Page 272
R=A.Vsquared.C

This has got to be the most pointless of your many quibbles.
I guess if you don't have chapter XX in your copy you should ask Clymer for your money back.

Regarding the equation itself, Irving refers to it as the "drag coefficient", not the Coefficient of Drag

Page 224 in my copy is indeed about 2stroke port timing but then DWS didn't claim that his page reference was accurate.
 
Thank you SeeleyWeslake.

As stated earlier, I don't have access (nor will I for the next few weeks) to my hard bound edition of Phil Irving's Tuning for Speed but pretty sure the equation, explanations etc. were on 224 (or maybe 244) or there about.

Reading skills and intellectual curiosity of some is appalling. This particular thread has left me feeling like I am pounding the information into one ear only to stand by and sadly watch it dribble out the other.
 
Thanks - Tuning for Speed published by Mr Clymer does indeed have a Chapter XX and a page 274 (a few pages from the end of the book !).
We'll have to look into how and why a drag coefficient is different, and such a minute number with so many decimal zeros.
It does simply appear to be 1000 times smaller than the usual numbers quoted, hmmmm.
It doesn't get a mention in the index either...

You don't think that seemingly dodgy numbers and then a dodgy reference is worth a quibble ?!

Like I said, the explanations seemed good but the maths not - and it still remains to be seen why the huge variation in those values...
 
Rohan, let us know what you find out. Maybe best to pm me on this. I know that mass density of the fluid (in this case, air at some fixed value) is more than likely folded into Phil Irving's Drag Coefficient. Take a look at the terms used to define the CoD (see Wiki or published hard copy reference) as you and I are familiar with and I believe the clues is there.

Regardless, Phil Irving's formula seems to work. There is clearly a gross generalization on mass density of the fluid of interest (air) and we know that the mass density of air changes significantly with altitude and other atmospheric conditions.
 
Unread postby Rohan » Mon Jan 06, 2014 12:38 pm

Fair go - we are not physic visionaries like you and Alan appear to wish to be seen.

Rohan, I don't wish to be seen as a 'physic visionary' as you put it. However as it happens I have actually completed third year tertiary studies in physics and chemistry. I cannot help you get an education, however I can help exercise your stolid mind a little bit. I got a real laugh a while back when you quoted stoichiometry to me in relation to using methanol. I spent 40 years as an industrial chemist mainly in defence manufacturing, if I'm not aware of the limitations of seizing on empiricism by now, I should completely change my professional direction.
I certainly do not intend to censor my opinions to cater for your inferiority complex.
Take notice of Dances , - in every post of his that I've seen he has made good sense, and his opinions are obviously based on experience. In the past I would have agreed with everything he has said about road racing. However I don't agree that some riders are way ahead of others in ability. I suggest the fastest/competent ones have cob-webby old guys like Herb Becker with them in the pits, and at home tricking their bikes up.
 
Rohan,

'Like I said, the explanations seemed good but the maths not - and it still remains to be seen why the huge variation in those values...'

The major difference between an engineer and a scientist usually lies in the way they handle uncertainty. I think you are simply being perverse, as usual.
 
If you cannot see that modern usage and Phil Irvings usage are a THOUSAND TIMES DIFFERENT TO EACH OTHER - and call that 'perverse', then beam me up Scotty....

There has to be a reason why those numbers are sooooo far apart from each other.
Could get downright confusing if there are 2 different ways to apply what should all be the same range of numbers.

You don't often see CoD numbers applied to motorcycles, but the F1 teams throw them about all the time.
And they don't have lots of zeros attached.
Its variously quoted that the tyres alone on an F1 car produce an aero drag of about 1.0 due to the vortex created behind them.
And they have enough downforce to drive upside down on the ceiling and stay there - if they would work inverted.
Buut we diverge...

P.S. It occurs to us that maybe you don't realise when I am pointing out nonsense that has been posted here.
You instead refer to that as 'perverse'.
Google is your friend - use it to check 'facts'. ???
 
Rohan,

Just because you are in a state of confusion and cannot make sense of something does not mean it is nonsense. Consider it a puzzle and that it is puzzling.

Have you found and read the Phil Irving's reference material on drag? Others have. Have you pushed some numbers through the equation I copied from Phil Irving's text and reproduced above with units and dimensions to see how it makes sense; I have and it pasts the test of reasonableness. It's as though there's a missing dot over an "I" which prevents you from being able to read the sentence.

Did you read the forest and trees I alluded to above? Have you considered stopping the obsessing over the matter and do some digging around to answer your question?
 
No help here how to attain less drag but shows how to figure the scope of it on power vs speed attainable.
http://www.borynack.com/xr650r/Horsepower2speed.htm

1971 Experimental F750 Racer
 
Dances, I'm not 'obsessing' about it, merely pointing out that in terms of modern world reality, those numbers you and Mr Irving share seem to be somewhat archaic.
And potentially quite misleading to other readers here - note that hobots pretty colour graph shows current style coefficient numbers.
But refer to square metres - a clue ? Although CoD are supposed to be dimensionless... ?

If ever I have any need for it, will look into it.
Nothing stopping you or anyone else to do the donkeywork....
 
Rohan said:
But refer to square metres - a clue ? Although CoD are supposed to be dimensionless... ?

Look again, you are confusing things. The reference link states: "Use the line that is the closest match for the product of your projected frontal area and drag coefficient" . The curves are the power/speed relationship and the color coding relates to ones own particular cross product of Drag Coefficient and frontal area (SI). The author leaves the determination of Drag Coefficient and frontal area up to the user.

If you are the least bit inquisitive, Phil Irving's imperial coefficient of drag of 0.0008 is roughly 0.7 CoD in the SI system
Click to expand...
 
The chart must only show basic concept as not that close to reality. For instance it shows with .7 CoD it takes 50 hp to do the ton but we know we can sit bolt upright on about any C'do at 100 with less than 50 rwhp. CoD relates more to shape than frontal area so a dropped brick might hit the ground before a dropped faired cycle and rider. Also calculations of this sort are same fuzzy logic as engine power calculators.
 
hobot said:
The chart must only show basic concept as not that close to reality. For instance it shows with .7 CoD it takes 50 hp to do the ton but we know we can sit bolt upright on about any C'do at 100 with less than 50 rwhp. CoD relates more to shape than frontal area so a dropped brick might hit the ground before a dropped faired cycle and rider. Also calculations of this sort are same fuzzy logic as engine power calculators.
Click to expand...



From a quick glance that chart shows CoD per Square metre ( of frontal area)

I imagine that you have to take into account the frontal area and apply that to the graph.
 
Indeed. Which gives the clue that we are in metric territory...

Some of us just got there a little quicker.... :D :D

Rohan said:
The penny has finally dropped.
You are using all imperial figures.
Click to expand...

It did come as a surprise to find that coeff of drag has varying values, when its supposed to be a 'dimensionless' value though.
Chalk one up to the merits of discussing it, and questioning it, here....
 
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