advantage of aero section bars
Simno Young
from drops,clip-ons and sti shifters to 'aero'bars with minimal brake
levers,concealed cables and bar end shifters--assuming identical
rider,frame,position etc?
Thanks
gsk
Simno Young wrote:
Believe this if you want, but in the book "High Performance Cycling" ,
John Cobb has a chapter on aerodynamics. He claims that interated airfoil
bars can make a difference of about 1:10 minutes faster than a cow horn
w/ aerobars over only 40 kms. . In this chapter Cobb makes some seemingly
wild claims such as an aero tubed frame being up to 2:26 faster over a
normal frame over 40 kms. - and that's just for the frame.
I realize John Cobb has done a lot of work in this area and has cult
status within the triathlon community. In fact I use his "big slam" bars
on my road bike and think they're great, but what makes me skeptical was
watching Stage 9 TT in this years's Tour de France where Santiago Botero
beat Lance and won riding a road bike fitted with small aerobars.
Botrnager wasn't even wearing a helmit. He did ride with his head down
which has lead some aero theorists to claim this made the difference. If
so this would suggest that rider position of the head is far more
important than is all the aero bits and pieces that tri geeks love to
spend their money on. Lots of other riders at this year's TDF TT sections
were on rebadged Cervelo P3's and couldn't get close to Botero in the
TT's. Was it the engine or is it that all these theoretical aero bits
aren't as significant as the manufacturers would like us to believe. I
dunno. But it's certainly food for thought.
Mark Hickey
>Believe this if you want, but in the book "High Performance Cycling" ,
>John Cobb has a chapter on aerodynamics. He claims that interated airfoil
>bars can make a difference of about 1:10 minutes faster than a cow horn
>w/ aerobars over only 40 kms. . In this chapter Cobb makes some seemingly
>wild claims such as an aero tubed frame being up to 2:26 faster over a
>normal frame over 40 kms. - and that's just for the frame.
I dunno about those numbers - the DO sound awfully high. If every
rider out there riding with round bars and a frame with round tubes
could improve their times by over three and a half minutes by just
changing the frame and bars... there are an awful lot of riders who
are "also rans" who should be state / country / world champions.
In just the last time trial of the TdF (stage 19), extrapolating
Cobb's number to the 50km course would indicate that the difference
would swell to four and a half minutes!
That would mean that ANY of the top 31 (!) competitors who were riding
bikes with round bars and tubes could have beat Lance by simply
changing to an aero-tubed frame and airfoil bars.
That, IMHO, is nonsense.
I suspect if you took the aero drag of JUST the frame and JUST the bar
and compared you might come up with the outlandish numbers Cobb did,
but when you try to model the very complex interrelationship between
bike and rider when it comes to aerodynamics, it all changes (that is,
it's nice that the air flows smoothly over the bars, but then it just
slams into the rider's pelvis anyway).
Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame
gsk
Mark Hickey wrote:
>
> I suspect if you took the aero drag of JUST the frame and JUST the bar
> and compared you might come up with the outlandish numbers Cobb did,
> but when you try to model the very complex interrelationship between
> bike and rider when it comes to aerodynamics, it all changes (that is,
> it's nice that the air flows smoothly over the bars, but then it just
> slams into the rider's pelvis anyway).
>
It's in black and white in chapter nine of "High Performance Cycling". I tend
to think what you suggest is what Cobb might be doing to come up with these
figures. Probably based on his windtunnel test results of the individual parts
by themselves. If they were true it would mean that Botero would be one heck
of a superior rider than Lance to be still winning Stage 9 and giving up all
that (according to Cobb) aerodynamic advantage. It's a combo of bike and rider
so I find it hard to believe that just having aero tubing, etc is going to
make a rider any where near faster what Cobb claims. I think John made a bit
of a gaff in that book and would like to hear his rational for these claims.
Andy Coggan
Martin JC, Milliken DL, Cobb JE, McFadden KL, Coggan AR. Validation of a
mathematical model for road cycling power. J Appl Biomech 1998; 14:276-291.
In this study we showed that it is possible to predict the power
requirements of outdoor cycling to w/in 1-2 W on average based on wind
tunnel measurements. (Indeed, it is this very model that John has used in
his calculations.)
If such hard science doesn't do it for you, I can offer this: my field
testing (using a PowerTap, but you need much more than just a power meter to
get good data) the indicates that I am approximately 1:20 seconds faster
over 40k when riding my full-aero TT rig than when riding my semi-aero road
bike (Trek Y-Foil). Positions (Scott Rakes on the Y-Foil), clothing/helmet,
and wheels are either identical or similar (30 mm deep 700 C rim on front of
road bike, 23 mm deep 650C rim on front of TT bike, both w/ aero cross
sections and 18 bladed spokes).
So Botero beat Armstrong - so what? That hardly disproves the influence of
aero equipment, given that we don't know A) either rider's power output, or
B) either rider's aero drag charachteristics (although 'tis interesting that
Lance is sitting up higher than he used to, and higher than Botero).
Andy Coggan
"gsk" <gr...@on.aibn.com> wrote in message
news:3D5E8349...@on.aibn.com...
Andy Coggan
one collected by Jim Martin for Project 96, the other obtained subsequently.
Hint: the difference is BIG. As the Hooker literature used to say, "round is
slow, especially on the front of the bike".
Andy Coggan
"Simno Young" <sjy...@doctors.org.uk> wrote in message
news:fe7985d9.02081...@posting.google.com...
Andy Coggan
only produced a couple hundred at best, they're pretty rare beasts.
Andy Coggan
<cle...@uicn.com> wrote in message
news:koctlug642qurq02n...@4ax.com...
> >Hint: the difference is BIG. As the Hooker literature used to say, "round
is
> >slow, especially on the front of the bike".
> >
> >Andy Coggan
>
>
> Does Hooker have a website? Hooker.com is an adult website. And
> hookerbicycles.com is not found.
>
> Thx
>
Mark Hickey
>If you doubt John's assertions, you should read this article:
>
>Martin JC, Milliken DL, Cobb JE, McFadden KL, Coggan AR. Validation of a
>mathematical model for road cycling power. J Appl Biomech 1998; 14:276-291.
>
>In this study we showed that it is possible to predict the power
>requirements of outdoor cycling to w/in 1-2 W on average based on wind
>tunnel measurements. (Indeed, it is this very model that John has used in
>his calculations.)
So you agree that any of the top 31 finishers in the Stage 19 TT in
the TdF riding non-aero frames and bars could have beaten Lance if
they would have simply switched to aero frames and bars? There were
an awful lot of them that would have qualified for the podium then,
except for poor equipment selection...
>So Botero beat Armstrong - so what? That hardly disproves the influence of
>aero equipment, given that we don't know A) either rider's power output, or
>B) either rider's aero drag charachteristics (although 'tis interesting that
>Lance is sitting up higher than he used to, and higher than Botero).
If you assume that two riders have otherwise similar position on their
bikes, and are riding the same speeds, the differences claimed by Cobb
indicate that the rider with round tubes and bars needs to generate
over 23% more power than the one on the aero bike. 23% more. That is
a HUGE number, and one that (IMHO of course) doesn't come close to
passing the ever-important common sense test.
Andy Coggan
indeed sound too large for the advantage of an aero frame, which is usually
found to be on the order of 1 min or so in a 40k. Nonetheless, I will stand
100% by wind tunnel testing and mathematical modeling as a means of
predicting performance out on the road. (Note that I'm the only one in this
debate with any quantitative data..."smell tests" don't mean much in the
scientific realm. <g>). Furthermore, I will reemphasize that my own careful
field testing (far more careful than 99.99% of what other would do, I'd
wager) indicates a 1:20 difference in a 40k between my semi-aero Trek Y-Foil
and my full aero Hooker TT bike. Presumably, the difference between the
Hooker and a round-tubed bike would be even larger, but I'm not about to
handicap my own performance by owning such a parachute. ;-)
Andy Coggan
"Mark Hickey" <ma...@habcycles.com> wrote in message
news:3d602f0d...@netnews.att.net...
gsk
Andy Coggan wrote:
> Nonetheless, I will stand
> 100% by wind tunnel testing and mathematical modeling as a means of
> predicting performance out on the road.
I sure wouldn't. A lot of airplanes that were designed in the wind tunnel never
flew.
> Furthermore, I will reemphasize that my own careful
> field testing (far more careful than 99.99% of what other would do, I'd
> wager) indicates a 1:20 difference in a 40k between my semi-aero Trek Y-Foil
> and my full aero Hooker TT bike.
I really doubt that that this could be attributed to the aero tubing alone. IMO
common sense would dictate that more than likely it has more to do with rider
positioning between the two bikes.
Stacy Hills
|
|
| Andy Coggan wrote:
|
| > Nonetheless, I will stand
| > 100% by wind tunnel testing and mathematical modeling as a means of
| > predicting performance out on the road.
|
| I sure wouldn't. A lot of airplanes that were designed in the wind tunnel
never
| flew.
|
Name some. Next, name some that didn't fly because the wind tunnel failed to
accurately measure their aerodynamic properties.
You've obviously very little clue of the design process; aircraft are not
"designed in a wind tunnel". Rigorous wind tunnel testing (hundreds upon
hundreds of hours) is used to verify and refine the mathematical models of
the aircraft that are created during the design phase. During and after the
wind tunnel tests, all those hours of data are compared with the
mathematical models. If there is some disagreement between the data and the
model that is outside the range of possible prediction error then a new,
exhaustive task is begun to determine the reason for the discrepancy. Is the
model leaving out some effect that was assumed negligible, or is there
something even more basic about the model that is in error? Or, was there
some error in either the test procedure or the recording of the test
condition? Nothing continues until the models and the data are in agreement.
Ultimately, flight test data is compared with the mathematical models to,
once again, ensure that they are correct. These tests are conducted much
like the wind tunnel tests with data points taken throughout the flight
envelope. The mathematical models are the lynch pin of the entire design
process because they are used extensively both to design the aircraft and to
determine many of the margins of safety.
Andy's posts indicate that he, Cobb, et al, have endeavored to follow this
same procedure.
stacy hills
reston, va
Brian Wagner
>
> "gsk" <gr...@on.aibn.com> wrote in message
> news:3D6160F9...@on.aibn.com...
> |
> |
> | Andy Coggan wrote:
> |
> | > Nonetheless, I will stand
> | > 100% by wind tunnel testing and mathematical modeling as a means of
> | > predicting performance out on the road.
> |
> | I sure wouldn't. A lot of airplanes that were designed in the wind tunnel
> never
> | flew.
> |
>
> Name some. Next, name some that didn't fly because the wind tunnel failed to
> accurately measure their aerodynamic properties.
Well, if you change "never flew" to "failed catastrophically" the B-70
comes to mind.
gsk
Stacy Hills wrote:You've obviously very little clue of the design process;
aircraft are not
> "designed in a wind tunnel". Rigorous wind tunnel testing (hundreds upon
> hundreds of hours) is used to verify and refine the mathematical models of
> the aircraft that are created during the design phase.
Throughout history engineers are notorious for designing things based upon their
mathematical calculations that either break or just don't work so don't give us
this b.s. Theoretical mathematical models are far when infallible once it comes
to real world testing. History has certainly demonstrated this on numerous
occassions. Remember the NASA study which the mathematical calculations
determined that bumble bees can't fly.
>
>
> Andy's posts indicate that he, Cobb, et al, have endeavored to follow this
> same procedure.
>
And I am questioning Andy as to his statement. One of his bike's bike may
certainly be faster than the other but it certainly could be other factors than
just aero tubing. If you want to believe John Cobb's statement that aero tubing
alone will make you two and a half minutes faster over forty kms then that's
your choice, but for myself, if someone is faster than me by this amount over
forty kms I'll attribute it to the engine and not the tubing. I do suggest you
read chapter nine in the book mentioned.
Mike S.
the bottom.
Riding up and down the coast here in San Diego, I see all kinds of riders.
Good riders, bad riders, pretty much the entire range. The one thing I've
noticed is that 85-90% of the people out riding on expensive tri bikes could
use help with bike fit. Since we're talking about 60% of the drag being
generated by the rider, it amazes me to see people when riding their aero
bikes. I know Steve Larsen was doing some bike fits last year down here,
(seemed to do a good job) but only a few people took the time to be fit.
My point is: it won't be the bike that wins you your next race, it'll be the
rider. Yes, an aero bike is going to be marginally faster than a non-aero
bike over 40k, but a more aero rider can make up more than that. You create
more drag than any of your parts put together.
If you haven't had a bike fit done, start there. The $100 you spend ($20 at
Supergo in O'side) on a proper fit will benefit you a lot more than an aero
bike that costs $1500+! You'll be more aero, more comfortable AND faster,
without breaking the bank. Once you've risen to your maximum potential on
the non-aero bike, THEN go get an aero bike and make sure that you are
fitted on that one too.
"gsk" <gr...@on.aibn.com> wrote in message
news:3D61839D...@on.aibn.com...
Andy Coggan
>
>
> Andy Coggan wrote:
>
> > Nonetheless, I will stand
> > 100% by wind tunnel testing and mathematical modeling as a means of
> > predicting performance out on the road.
>
> I sure wouldn't. A lot of airplanes that were designed in the wind tunnel
never
> flew.
So, you're basically questioning my scientific abilities, and with nothing
but urban legend as your basis. Do you realize how much of an insult that
truly is?
> > Furthermore, I will reemphasize that my own careful
> > field testing (far more careful than 99.99% of what other would do, I'd
> > wager) indicates a 1:20 difference in a 40k between my semi-aero Trek
Y-Foil
> > and my full aero Hooker TT bike.
>
> I really doubt that that this could be attributed to the aero tubing
alone. IMO
> common sense would dictate that more than likely it has more to do with
rider
> positioning between the two bikes.
Except that the position is essentially identical on both bikes: the Scott
Rakes allow me to get as low and as narrow as the Hooker aerobars, albeit
w/o the elbow pads to lean on. To compensate for the difference in seat tube
angle, I simply slide way up on the nose of the saddle when "hunkering down"
on the Rakes on the road bike. That's what I really like about using them:
it allows me to train in the aero position whenever it is convenient, and
not just when I drag out the TT bike.
FWIW, the usual advantage ascribed to a well-designed aero frame (which the
Hooker certainly is) over a conventional round-tubed frame (which the Y-Foil
is not) is approximately 0.3 lbs of drag at 30 mph, which translates into
about a 1 min time savings. (See the data on the Cervelo website, for
example.) The fact that I have observed a greater difference, despite using
a "semi-aero" frame as the basis for comparison, probably relates to other
equipment differences as well - in particular, the use of *very* aero
aerobars (the topic of this thread), vs. conventional drops. Nonetheless, I
believe that this is still a good example to illustrate how, if you can make
the measurements with sufficient precision, what you predict based on wind
tunnel testing is revealed in the field (as our original study showed).
Andy Coggan
doug
> |
> |
> | Andy Coggan wrote:
> |
> | > Nonetheless, I will stand
> | > 100% by wind tunnel testing and mathematical modeling as a means of
> | > predicting performance out on the road.
> |
> never
> | flew.
> |
>
> accurately measure their aerodynamic properties.
>
Well, if you change "never flew" to "failed catastrophically" the B-70
comes to mind.
----------------------------------------------------------------------------
Come on... that is like criticizing the process of wheelbuilding
because one 'failed catastrophically' when it got hit by a car! You
do know the B-70 crashed during a PR photo-op for GE when a trail
aircraft (F-104) ventured too close, got caught in the vortex and
promptly removed the B-70's vertical stabilizer, don't you? How is
this a failure to "accurattely measure their aerodynamic properties."
???
gsk
Andy Coggan wrote:
> So, you're basically questioning my scientific abilities, and with nothing
> but urban legend as your basis. Do you realize how much of an insult that
> truly is?
Sorry fella, but I don't know anything about you let alone about your scientific
abilities. Are you another of the aero gurus that us tri geeks are supposed to
follow without question just because you said it's so?
>
> (See the data on the Cervelo website, for
> example.)
Cervelo is a good company with some seemingly innovative ideas. In fact my next
bike is going to be a Cervelo. However, while spending my money, I certainly
wonder who pays their engineers to make such statements. Unfortunately my
background is in medical science and not engineering. Even so I doubt that
anyone really knows how this data translates into real world performance. How
much of it is just marketting hype.
Read John Cobb's chapter in "High Performance Cycling". He claims the following
savings over 40 kms;
standard 36 vs rear disc/composite front 1:30
ave. racing clincher vs. high perf tubular 1:38
normal fork vs aero fork 1:16
standard barsw/clip on vs. integrated 1:10
standard frame vs aero frame 2:36
Some of this I can easily believe, particularly the wheels and tires, but the
rest of it, particualy the frame seems a bit far fetched. Botero was already
giving away the supposed aero advantage of the bars and frame to Lance when he
won the stage nine TT on his round tubed road bike at this years TDF. Didn't
seem to effect him at all which makes me a bit skeptical of Cobb's claims,
particularly since he gives more importance to the aero tubing than any of the
other things.
Andy Coggan
>
>
> Andy Coggan wrote:
>
> > So, you're basically questioning my scientific abilities, and with
nothing
> > but urban legend as your basis. Do you realize how much of an insult
that
> > truly is?
>
> Sorry fella, but I don't know anything about you let alone about your
scientific
> abilities. Are you another of the aero gurus that us tri geeks are
supposed to
> follow without question just because you said it's so?
No, but I am the senior author on that study I quoted previously, the one
that you should read before you start critiquing claims based thereon,
especially since all you have is...what? your gut instinct?
>
> >
> > (See the data on the Cervelo website, for
> > example.)
>
> Cervelo is a good company with some seemingly innovative ideas. In fact my
next
> bike is going to be a Cervelo. However, while spending my money, I
certainly
> wonder who pays their engineers to make such statements. Unfortunately my
> background is in medical science and not engineering. Even so I doubt that
> anyone really knows how this data translates into real world performance.
Au contraire, my dear fellow: we've shown directly how it translates into
"real world" performance.
> How
> much of it is just marketting hype.
>
> Read John Cobb's chapter in "High Performance Cycling". He claims the
following
> savings over 40 kms;
>
> standard 36 vs rear disc/composite front 1:30
> ave. racing clincher vs. high perf tubular 1:38
> normal fork vs aero fork 1:16
> standard barsw/clip on vs. integrated 1:10
> standard frame vs aero frame 2:36
>
> Some of this I can easily believe, particularly the wheels and tires, but
the
> rest of it, particualy the frame seems a bit far fetched. Botero was
already
> giving away the supposed aero advantage of the bars and frame to Lance
when he
> won the stage nine TT on his round tubed road bike at this years TDF.
Didn't
> seem to effect him at all which makes me a bit skeptical of Cobb's claims,
> particularly since he gives more importance to the aero tubing than any of
the
> other things.
I think it is foolish of you to try to make arguments based on the
performance of two different riders, of unknown power outputs, with
distinctly different positions.
As for the claims in the chapter, the only thing that jumps out at me as
being odd is the clincher vs. tubular comparison, unless the advantage goes
to the clincher (lower rolling resistance due lack of a "squirmy" glue bed).
The rest of it is reasonably consistent with all the wind tunnel data I've
seen over the years, although, as I said previously, the advantage ascribed
to an aero frame usually isn't quite so large (but we don't know what
particular combination John picked for this comparison).
Andy Coggan
Mark Hickey
>"gsk" <gr...@on.aibn.com> wrote in message
>news:3D6160F9...@on.aibn.com...
>| I sure wouldn't. A lot of airplanes that were designed in the wind tunnel
>never
>| flew.
>Name some. Next, name some that didn't fly because the wind tunnel failed to
>accurately measure their aerodynamic properties.
The problem with design validation in wind tunnels is that
aerodynamics don't scale very well. So, if you build a perfect 1/4
scale Belchfire X10 model, it's not necessarily going to fly anything
like its full-size sibling. I can't name a bunch of aircraft that
failed in this way off the top of my head, but that's largely because
they were never built... ;-) Perhaps the Bede BD12 (or was it 14?).
>Andy's posts indicate that he, Cobb, et al, have endeavored to follow this
>same procedure.
Perhaps so - but I can't reconcile the conclusion that there were
perhaps dozens of riders who could have taken the final TT from Lance
in the TdF with a simple change to a more aero bike frame and bars.
Would they help? I have no doubt. Would they have - by themselves -
made a 4.5 minute difference over 50km? Hard to imagine.
gsk
Andy Coggan wrote:
>
>
>
> No, but I am the senior author on that study I quoted previously, the one
> that you should read before you start critiquing claims based thereon,
> especially since all you have is...what? your gut instinct?
Here's a true story that you might find amusing.
Many years ago my parent's neighbor "Paul" was a professor in the mechanical
engineering department at the local university. He taught all academic theory
courses but in practical terms couldn't change a spark plug on his car. He
designed a large stone fireplace for his house that looked like a sort of
inverted guitar. One of the best local stone masons was a man named "Mario" who
was an immigrant from the old country. Mario had also done work on my parents
house. One day he came over and pleaded with my father to have a talk to
professor Paul about the fireplace that he was supposed to build. My dad was
also an engineer, not a PHD in academia, but more importantly a hands on kind
of guy with enough common sense to listen to Mario. Dad went over and talked to
Paul and said "look Paul, Mario has been building these things for thirty years
and he says it won't work."
Well professor Paul became very indignant and defensive. He called Mario an
uneducated ignorant tradesman and explained that he had a PHD and had done all
the mathematical calculations and this fireplace would work. It was professor
Paul's money, so Mario relunctantly built the grand stone fireplace as it had
been designed.
I was a teenager then and remember talking to dad about the fireplace and him
saying that he thought Mario was right in that the fireplace wouldn't work. I
asked dad why and he said "just a gut feeling".
The first time professor Paul lite up a fire - well you guessed it - the smoke
flowed backwards into his rec room. The fireplace didn't work just like Mario
said it wouldn't. Obviously professor Paul's calculations were wrong somewhere.
What's this got to do with your calculations? Nothing directly, but to me, the
moral of the story all these years later, is that mathematical models are quite
capable of being wrong. Or maybe it's not the mathematic models that are
infallible but sometimes rather just the people who formulate them.
Not saying you're right or wrong about your bicycle aero theories. You could
very well be right, but until I actually personally test them and see the
results for myself, based upon this fireplace experience, there will be a bit
of Missouri in me.
Andy Coggan
(amusing but largely irrelevant anecdote snipped)
> What's this got to do with your calculations? Nothing directly, but to me,
the
> moral of the story all these years later, is that mathematical models are
quite
> capable of being wrong. Or maybe it's not the mathematic models that are
> infallible but sometimes rather just the people who formulate them.
>
> Not saying you're right or wrong about your bicycle aero theories. You
could
> very well be right, but until I actually personally test them and see the
> results for myself, based upon this fireplace experience, there will be a
bit
> of Missouri in me.
See, you still don't get it. The entire purpose of the study I cited
previously was to convince skeptics such as yourself. To reiterate: we were
able to predict the power requirements of outdoor cycling to w/in 1-2 W (on
average, i.e., S.E.E.) based on wind tunnel measurements of CdA.
The reason people like yourself (and Mark Hickey, etc.) are so skeptical is
because there are so many factors that influence performance. As a result,
unless you very carefully isolate any one thing in particular (e.g.,
different clothing), the *impression* you're left with is that such things
don't work as expected. However, this isn't the case - it is simply the
inability to separate the effect from the "noise" in the data. (This is
infinitely true if your only means of testing is to simply look at pictures
of riders and their final times.)
To give but one example: remember the Tailwings skinsuit, which based on
wind tunnel testing was supposed to save around 1 min in a 40k TT? Well,
before they were banned by USA Cycling I bought one, as did several other
people I know. Their conclusion, based on the "well, I wore it, but I didn't
set a PR, so it must not work" approach, was that it was a waste of money.
OTOH, using multiple trials, collection of power data, correction for
differences in air density, etc., I was able to determine (at the P<0.05
level of confidence) that, at least one me, the Tailwings suit reduced drag
by almost the exact amount expected from the wind tunnel measurements.
So, by all means, be skeptical...all good scientists should be. But it is
more than being skeptical when you say "I don't believe it" when presented
with experimental data and you have no valid evidence to counter
with...that's simply being close-minded.
Andy Coggan
Brian Wagner
>
> Come on... that is like criticizing the process of wheelbuilding
> because one 'failed catastrophically' when it got hit by a car! You
> do know the B-70 crashed during a PR photo-op for GE when a trail
> aircraft (F-104) ventured too close, got caught in the vortex and
> promptly removed the B-70's vertical stabilizer, don't you? How is
> this a failure to "accurattely measure their aerodynamic properties."
The vortex in question is an aerodynamic quality that they failed to
predict.
Mark Hickey
>See, you still don't get it. The entire purpose of the study I cited
>previously was to convince skeptics such as yourself. To reiterate: we were
>able to predict the power requirements of outdoor cycling to w/in 1-2 W (on
>average, i.e., S.E.E.) based on wind tunnel measurements of CdA.
>
>The reason people like yourself (and Mark Hickey, etc.) are so skeptical is
>because there are so many factors that influence performance. As a result,
>unless you very carefully isolate any one thing in particular (e.g.,
>different clothing), the *impression* you're left with is that such things
>don't work as expected. However, this isn't the case - it is simply the
>inability to separate the effect from the "noise" in the data. (This is
>infinitely true if your only means of testing is to simply look at pictures
>of riders and their final times.)
The point is, 4.5 minutes is hardly "noise". That's huge - beyond
huge. Enough difference that the wind noise would be different in
your ears. Enough difference that no matter what other factors
changed, the improvement would be so obvious that no one would dare
show up at a pro TT event without the aero tubes / bars (since anyone
who tested them once would be so overwhelmingly convinced that they
couldn't dispute the enormous difference).
You still haven't said whether you actually believe that ANY of the 30
riders finishing behind Lance in the final TdF TT could have beaten
him by switching to an aero frame and aero bars (assuming of course
that doing so didn't screw up their position). Do you actually
believe that or am I missing something?
>So, by all means, be skeptical...all good scientists should be. But it is
>more than being skeptical when you say "I don't believe it" when presented
>with experimental data and you have no valid evidence to counter
>with...that's simply being close-minded.
If I did an experiment that suggested my TT speed should be 53km/h,
I'd be skeptical (heck, I'd be downright close-minded), simply because
it failed a certain common-sense test.
BTW, I'm not going to tell you whether I'd be skeptical because 53km/h
is too fast or too slow... ;-)
Stacy Hills
"Brian Wagner" <brian....@cle.philips.com> wrote in message
news:3D615496...@cle.philips.com...
| Stacy Hills wrote:
| >
| > Name some. Next, name some that didn't fly because the wind tunnel
failed to
| > accurately measure their aerodynamic properties.
|
| Well, if you change "never flew" to "failed catastrophically" the B-70
| comes to mind.
You must be thinking of some other aircraft. The XB-70 was quite successful
in testing super-sonic flight and only crashed after an F-104 took off its
vertical stabilizers.
stacy hills
reston, va
Stacy Hills
| "Stacy Hills" <hills...@hotmail.com> wrote:
|
| >Name some. Next, name some that didn't fly because the wind tunnel failed
to
| >accurately measure their aerodynamic properties.
|
| The problem with design validation in wind tunnels is that
| aerodynamics don't scale very well. So, if you build a perfect 1/4
| scale Belchfire X10 model, it's not necessarily going to fly anything
| like its full-size sibling. I can't name a bunch of aircraft that
| failed in this way off the top of my head, but that's largely because
| they were never built... ;-) Perhaps the Bede BD12 (or was it 14?).
|
Yes, that is a fair comparison...a kit plane sold by a fly-by-night
schuyster!
Scaling problems do exist but I think most of those issues have been worked
through in the last few decades.
stacy hills
reston, va
Andy Coggan
> "Andy Coggan" <aco...@earthlink.net> wrote:
>
> >See, you still don't get it. The entire purpose of the study I cited
> >previously was to convince skeptics such as yourself. To reiterate: we
were
> >able to predict the power requirements of outdoor cycling to w/in 1-2 W
(on
> >average, i.e., S.E.E.) based on wind tunnel measurements of CdA.
> >
> >The reason people like yourself (and Mark Hickey, etc.) are so skeptical
is
> >because there are so many factors that influence performance. As a
result,
> >unless you very carefully isolate any one thing in particular (e.g.,
> >different clothing), the *impression* you're left with is that such
things
> >don't work as expected. However, this isn't the case - it is simply the
> >inability to separate the effect from the "noise" in the data. (This is
> >infinitely true if your only means of testing is to simply look at
pictures
> >of riders and their final times.)
>
> The point is, 4.5 minutes is hardly "noise".
When and how did 2:26 grow to 4.5 minutes??
>That's huge - beyond
> huge. Enough difference that the wind noise would be different in
> your ears. Enough difference that no matter what other factors
> changed, the improvement would be so obvious that no one would dare
> show up at a pro TT event without the aero tubes / bars (since anyone
> who tested them once would be so overwhelmingly convinced that they
> couldn't dispute the enormous difference).
>
> You still haven't said whether you actually believe that ANY of the 30
> riders finishing behind Lance in the final TdF TT could have beaten
> him by switching to an aero frame and aero bars (assuming of course
> that doing so didn't screw up their position). Do you actually
> believe that or am I missing something?
Now hang on:
First, did 30 riders finish within 4.5 minutes of Armstrong, or did 30
riders finish within 2:26 of Armstrong? (~3 minutes, given that it was a
longer TT...but OTOH, faster riders benefit less in absolute terms from
aerodynamic improvements, so maybe ~2.5 min is still correct.)
Second, how many of those were *not* using a frame with aero tubing and
aero-shaped handlebars?
Taking #1 and #2 into consideration, I'm sure that the number would be less
than 30...but the actual number is completely irrelevant IMHO, since we
don't know the power output or aerodynamic drag characteristics of any of
the riders in question. So, rather than engage in a totally uninformed and
pointless debate, I'll stick to the data...and I seem to be the only one in
this discussion who has bothered to actually collect any.
> >So, by all means, be skeptical...all good scientists should be. But it is
> >more than being skeptical when you say "I don't believe it" when
presented
> >with experimental data and you have no valid evidence to counter
> >with...that's simply being close-minded.
>
> If I did an experiment that suggested my TT speed should be 53km/h,
> I'd be skeptical (heck, I'd be downright close-minded), simply because
> it failed a certain common-sense test.
>
> BTW, I'm not going to tell you whether I'd be skeptical because 53km/h
> is too fast or too slow... ;-)
This is a straw-man argument, because those are not the results that have
been obtained - you therefore can't criticize a prediction as being
unrealistic when no such prediction has been made. Instead, as I keep
telling you (all), the predicted and measured power requirements agreed to
w/in 1-2 W on average.
Read the study...read the study...read the study...read the study...
Andy Coggan
Andy Coggan
Actually, I'll bet you said vortex was well-anticipated. What wasn't
anticipated, apparently, was that the F-104 pilot would be so cocky as to
think that he could fly into it.
Andy Coggan
Brian Wagner
> You must be thinking of some other aircraft. The XB-70 was quite successful
> in testing super-sonic flight and only crashed after an F-104 took off its
> vertical stabilizers.
>
Stacy Hills
No, due to the F-104 pilot following the orders of the photographer who
wanted him to tuck in closer to the XB-70. The Valkyrie was designed for
operation at Mach 3 and high altitudes not for sub-sonic, formation flying.
Maybe the vortex was unknown but I'd be willing to bet that it was a
don't-care, with respect to the impact on the aircraft design, even if they
had known.
stacy hills
reston, va
doug
> "Stacy Hills" <hills...@hotmail.com> wrote:
>
> >"gsk" <gr...@on.aibn.com> wrote in message
> >news:3D6160F9...@on.aibn.com...
>
> >| I sure wouldn't. A lot of airplanes that were designed in the wind tunnel
> never
> >| flew.
>
> >Name some. Next, name some that didn't fly because the wind tunnel failed to
> >accurately measure their aerodynamic properties.
>
> The problem with design validation in wind tunnels is that
> aerodynamics don't scale very well. So, if you build a perfect 1/4
> scale Belchfire X10 model, it's not necessarily going to fly anything
> like its full-size sibling. I can't name a bunch of aircraft that
> failed in this way off the top of my head, but that's largely because
> they were never built... ;-) Perhaps the Bede BD12 (or was it 14?).
actually, basic aerodynamic data scale very well... especially if the
model is full scale (as most bicycle wind tunnel testing is). reynolds
figured out how to scale aerodynamic data about the same time the
wright brothers were making their first airplane. The majority of
flight test failures i have heard of have been human error or
oversight (i.e. installed the gyros backwards or failed to account for
aeroelasticity). Things that are not always seen in relatively simple
wind tunnel tests are vortices impinging on control surfaces in
certain flight regimes, and other flight-control related phenomena.
the equivalent for a bike would be gust response of the bike and rider
system (i.e. can a typical rider keep the bike within X ft laterally
given a Y kt ramp gust input?). proper use of a wind tunnel and
skilled data reduction should yield reliable results for drag on a
bicycle.
>
> >Andy's posts indicate that he, Cobb, et al, have endeavored to follow this
> >same procedure.
>
> Perhaps so - but I can't reconcile the conclusion that there were
> perhaps dozens of riders who could have taken the final TT from Lance
> in the TdF with a simple change to a more aero bike frame and bars.
> Would they help? I have no doubt. Would they have - by themselves -
> made a 4.5 minute difference over 50km? Hard to imagine.
>
That does seem large, especially if you take it to the other TT and
conclude botero could have won by nearly 5 minutes over the next
closest rider if he had been in full aero setup. I'd like to see what
they were comparing, and what assumptions were made... even if you
follow a proven method, if you make one invalid assumption, or
misapply the measurement equipment, the results can be skewed. I
really wish all these tests would be published in great detail in a
technical journal for all to see... have they been? having said that,
i'd be happy to review some!
doug
Having spent a fair amount of time in central Misery growing up, I'm
not all that impressed with the deductive reasoning abilities of those
in the show-me-state ;)
doug
>doug wrote:
>>
>> Come on... that is like criticizing the process of wheelbuilding
>> because one 'failed catastrophically' when it got hit by a car!
You
>> do know the B-70 crashed during a PR photo-op for GE when a trail
>> aircraft (F-104) ventured too close, got caught in the vortex and
>> promptly removed the B-70's vertical stabilizer, don't you? How is
>> this a failure to "accurattely measure their aerodynamic
properties."
>
predict.
>
Are you kidding me? You honestly believe the engineers at North
American didn't realize a 100 ft span delta wing wouldn't produce a
vortex?! Only infinite span wings do not produce vortices when
producing lift. the xb-70 was big, but not that big ;) Prandl, Glauert
and Anderson fully described this stuff back in the 1920's. If they
failed to predict a vortex on the XB-70 they had their heads up their
a**es... seeing as how the thing actually flew Mach 3 under control, I
highly doubt they were inflicted with cranial rectal inversion. a
wing producing vortices is the stuff of high school science fairs...
they all knew about it, they just screwed up... humans have a tendency
to do this sometimes.
Stacy Hills
|
|
| Stacy Hills wrote:You've obviously very little clue of the design process;
| aircraft are not
|
| > "designed in a wind tunnel". Rigorous wind tunnel testing (hundreds upon
| > hundreds of hours) is used to verify and refine the mathematical models
of
| > the aircraft that are created during the design phase.
|
| Throughout history engineers are notorious for designing things based upon
their
| mathematical calculations that either break or just don't work so don't
give us
| this b.s. Theoretical mathematical models are far when infallible once it
comes
| to real world testing. History has certainly demonstrated this on numerous
| occassions. Remember the NASA study which the mathematical calculations
| determined that bumble bees can't fly.
|
Then I suggest you "put your flat feet on the ground" because this "b.s." is
how the modern engineering world works from aircraft to automobiles to
bridges and buildings. Where, in my explanation of the basic scientific
method, did I claim the infallibility of mathematical models? If they were,
indeed, infallible then there would be no need for all the wind tunnel and
flight testing.
Bumblebees...I think that story is probably apocryphal but I'll take a walk
with you and assume it is true. Don't you suppose the people who performed
the study realized the error of their conclusion? Duh!? Then it seems to me
that would have been a humble confession of the limitations of the
aerodynamic theories of the time. An even better explanation is that
erroneous assumptions were made in modeling the bee. But, if that were the
case, then the "study" would never have been published because the engineer
or scientist would have scrapped everything and begun anew.
Check this link: http://physicsweb.org/article/news/5/10/9
I think you'd better sell all you own and move to a remote and deserted
island because that is about the only way you'll get away from all of us
evil engineers and our models and assumptions.
stacy hills
reston, va
dave thomson
<hills...@hotmail.com> wrote:
>
>Bumblebees...I think that story is probably apocryphal but I'll take a walk
>with you and assume it is true. Don't you suppose the people who performed
>the study realized the error of their conclusion? Duh!? Then it seems to me
>that would have been a humble confession of the limitations of the
>aerodynamic theories of the time. An even better explanation is that
>erroneous assumptions were made in modeling the bee. But, if that were the
>case, then the "study" would never have been published because the engineer
>or scientist would have scrapped everything and begun anew.
>
>Check this link: http://physicsweb.org/article/news/5/10/9
Check out
http://www.kav.cas.cz/~buble/text/en/TheStrangeCaseOfBumbleBeeWhichFlew.html
and http://www.maa.org/mathland/mathland_3_31.html also.
Cheers,
dt.
gsk
Stacy Hills wrote:
>
> |
>
> Then I suggest you "put your flat feet on the ground" because this "b.s." is
> how the modern engineering world works from aircraft to automobiles to
> bridges and buildings.
May I suggest you go back and read my post about our old neighbor who designed
the fireplace.
Mark Hickey
>"Mark Hickey" <ma...@habcycles.com> wrote in message
>news:3d623ebf....@netnews.att.net...
>> The point is, 4.5 minutes is hardly "noise".
>
>When and how did 2:26 grow to 4.5 minutes??
That was based on the figures that started this thread - here's the
relevant text:
> >Believe this if you want, but in the book "High Performance Cycling" ,
> >John Cobb has a chapter on aerodynamics. He claims that interated airfoil
> >bars can make a difference of about 1:10 minutes faster than a cow horn
> >w/ aerobars over only 40 kms. . In this chapter Cobb makes some seemingly
> >wild claims such as an aero tubed frame being up to 2:26 faster over a
> >normal frame over 40 kms. - and that's just for the frame.
That works out to more than three and a half minutes over 40km, which
would extrapolate to 4.5 minutes at the 50km length of the stage 19
TT.
>Now hang on:
>
>First, did 30 riders finish within 4.5 minutes of Armstrong, or did 30
>riders finish within 2:26 of Armstrong? (~3 minutes, given that it was a
>longer TT...but OTOH, faster riders benefit less in absolute terms from
>aerodynamic improvements, so maybe ~2.5 min is still correct.)
30 riders finished within 4:30 of Lance.
>Second, how many of those were *not* using a frame with aero tubing and
>aero-shaped handlebars?
>
>Taking #1 and #2 into consideration, I'm sure that the number would be less
>than 30...but the actual number is completely irrelevant IMHO, since we
>don't know the power output or aerodynamic drag characteristics of any of
>the riders in question. So, rather than engage in a totally uninformed and
>pointless debate, I'll stick to the data...and I seem to be the only one in
>this discussion who has bothered to actually collect any.
C'mon - you're dodging. If Cobb's numbers are correct, lots of the
riders could have smoked Lance in that race, whether they needed the
1:10 advantage for the integrated bars, the 2:26 for the aero frame or
both. From my recollection, only the real contenders tended to be on
really aero bikes, with the rest being on more "pedestrian steeds".
Even if only 10 or 15 of the riders were on round-tube frames with
cowhorns it's really hard to believe that their teams "gave away" an
easy advantage that would have netted them a prestigious win in the
biggest race in the world.
>> If I did an experiment that suggested my TT speed should be 53km/h,
>> I'd be skeptical (heck, I'd be downright close-minded), simply because
>> it failed a certain common-sense test.
>>
>> BTW, I'm not going to tell you whether I'd be skeptical because 53km/h
>> is too fast or too slow... ;-)
>
>This is a straw-man argument, because those are not the results that have
>been obtained - you therefore can't criticize a prediction as being
>unrealistic when no such prediction has been made. Instead, as I keep
>telling you (all), the predicted and measured power requirements agreed to
>w/in 1-2 W on average.
Normally, good testing correlates perfectly to the real world, but
when the results predict a result so dramatic, you'd expect to see the
results of that reflected in real-world results.
Let me take a different approach to this conundrum. Assume for a
moment that Cobb's right, and that a rider who rides the typical "pro
TT bike" can maintain the same speed with 75% of the effort by simply
swapping to readily available aero frames and bars. Why would any
team with a rider who is considered a contender for the overall or the
stage send him out to do a TT with anything else? The only
possibility is that they've simply never tried an aero frame and/or
integrated bar (hard to imagine...) or that their results didn't
indicate such a huge difference. How else would you explain the fact
that so many riders "gave away" an easy win to Lance?
Cobb's test results would indicate that Lance's near super-human power
output was merely "somewhere in the top 15-20% of the peloton" since
he obviously wasn't putting out relatively more power than the
competition who were handicapping themselves by up to 25% by riding
non-aero bikes with cowhorns. But somehow that doesn't correlate to
the climbing stages where he killed them all... go figure.
>Read the study...read the study...read the study...read the study...
Hey, if you can't figure out what's wrong with it, I'm not gonna stand
a chance! ;-)
Stacy Hills
If you'd like to compare your neighbor's wacky home project with industrial
scale manufacturing that includes all the ramifications of risk and
liability (not to mention profits) then you really do belong on a desert
island.
stacy hills
reston, va
Andy Coggan
> "Andy Coggan" <aco...@earthlink.net> wrote:
(points from mark's argument clarified)
> >Second, how many of those were *not* using a frame with aero tubing and
> >aero-shaped handlebars?
> >
> >Taking #1 and #2 into consideration, I'm sure that the number would be
less
> >than 30...but the actual number is completely irrelevant IMHO, since we
> >don't know the power output or aerodynamic drag characteristics of any of
> >the riders in question. So, rather than engage in a totally uninformed
and
> >pointless debate, I'll stick to the data...and I seem to be the only one
in
> >this discussion who has bothered to actually collect any.
>
> C'mon - you're dodging. If Cobb's numbers are correct, lots of the
> riders could have smoked Lance in that race, whether they needed the
> 1:10 advantage for the integrated bars, the 2:26 for the aero frame or
> both. From my recollection, only the real contenders tended to be on
> really aero bikes, with the rest being on more "pedestrian steeds".
> Even if only 10 or 15 of the riders were on round-tube frames with
> cowhorns it's really hard to believe that their teams "gave away" an
> easy advantage that would have netted them a prestigious win in the
> biggest race in the world.
You think so? Talk to John...as he describes it, most of the european pro
teams are absolutely clueless about aerodynamics, which is why, e.g.,
Rabobank paid to bring him to The Netherlands to work with their team.
(Something that won't happen again anytime soon, I gather, since I am under
the impression that John is now under some sort of exclusive contract with
USPS. Of course, that doesn't stop riders from knocking on his door late at
night, asking for help.)
> Normally, good testing correlates perfectly to the real world, but
> when the results predict a result so dramatic, you'd expect to see the
> results of that reflected in real-world results.
Let me repeat myself: the *ONLY* test that has been performed is our study,
and we found very good agreement between the wind-tunnel predicted and the
directly measured power outputs. Until and unless you have direct data to
the contrary, you're just blowing smoke.
> Let me take a different approach to this conundrum. Assume for a
> moment that Cobb's right, and that a rider who rides the typical "pro
> TT bike" can maintain the same speed with 75% of the effort by simply
> swapping to readily available aero frames and bars.
At typical pro bike rider speeds, the difference in power requirment between
riding a standard round-tubed frame and a good aero frame is only 5% - I
haven't the foggiest idea where you came up with the 25% figure.
> Why would any
> team with a rider who is considered a contender for the overall or the
> stage send him out to do a TT with anything else?
Because, as I said, they don't understand the ramifactions of their choices,
and keep making the same mistakes over and over. You only have to look at
the large number of pro riders who plow a furrow through the air with their
forearms pointing down (a horrible aerodynamic faux pas) to realize this.
> The only
> possibility is that they've simply never tried an aero frame and/or
> integrated bar (hard to imagine...) or that their results didn't
> indicate such a huge difference.
As I tried to explain before, although the difference is significant in
terms of placings/performance, it can be hard to detect against the
"background noise" created by other extraneous variables. So, unless you are
willing to get into a wind tunnel, or do repeated trials on a reasonably
flat road (or velodrome), measuring power output and accounting for changes
in air density, kinetic energy, etc., you will easily overlook it. I assume
that's what has you confused, since based on the weakness of your argument
(totally lacking in objective data) that you have never actually done any
such careful testing. (And indeed, few people have...aren't
Armstrong/Carmichael and Boardman/Keen considered unique for their careful
and quantitative approach to such issues?)
> How else would you explain the fact
> that so many riders "gave away" an easy win to Lance?
Since we have no idea how many riders were using round-tubed bikes vs.
aero-tubed bikes, nor any information as to their aerodynamic drag
characteristics or power outputs, we also have no idea how many riders "gave
away an easy win to Lance".
> Cobb's test results would indicate that Lance's near super-human power
> output was merely "somewhere in the top 15-20% of the peloton" since
See above.
> he obviously wasn't putting out relatively more power than the
> competition who were handicapping themselves by up to 25% by riding
> non-aero bikes with cowhorns.
Again, I don't know where you came up with the 25% figure.
> >Read the study...read the study...read the study...read the study...
>
> Hey, if you can't figure out what's wrong with it, I'm not gonna stand
> a chance! ;-)
Close-mindedness raises it's ugly head again.
Andy Coggan
gsk
Andy Coggan wrote:
>
>
> Close-mindedness raises it's ugly head again.
>
>
I don't doubt that a "good" aero tube may make some small degree of difference,
but is probably relatively insignificant compered to rider position. The
question really is which aero tubing really works? Cervelo supposedly makes
legitimate aero tubing but a lot of bicycles that are being marketed as being
"aero" are probably far from it. Could be the biggest bicycle industry scam
since integrated headsets.
gsk
Stacy Hills wrote:
>
>
> If you'd like to compare your neighbor's wacky home project with industrial
> scale manufacturing that includes all the ramifications of risk and
> liability (not to mention profits) then you really do belong on a desert
> island.
>
I was actually comparing it to the bicycle industry specifically. The moral of
the story went right over your head.
Stacy Hills
If that is, indeed, the case then why did you refer me to the story while in
this sub-thread about aircraft design and the engineering process?
Furthermore, the story was posted in a sub-thread about a paper authored by
Andy Coggan who is not in the bicycling industry.
And the moral of your story is that no one should be so foolish as to think
a design will work perfectly right out of the box. Why do you suppose the
aircraft industry does so much wind tunnel testing, ground vibration
testing, structural mode interaction testing and taxi testing (low and high
speed) before the plane ever leaves the ground? Because they are not foolish
enough to think that everything will work just so if they were to attempt to
fly straight away. Either your neighbor was a fool to think his design would
work without modification or he felt like spending the cash to do his own
experiment.
stacy hills
reston, va
Mark Hickey
>Mark Hickey wrote:
>
>> Let me take a different approach to this conundrum. Assume for a
>> moment that Cobb's right, and that a rider who rides the typical "pro
>> TT bike" can maintain the same speed with 75% of the effort by simply
>> swapping to readily available aero frames and bars.
>
>At typical pro bike rider speeds, the difference in power requirment between
>riding a standard round-tubed frame and a good aero frame is only 5% - I
>haven't the foggiest idea where you came up with the 25% figure.
Are you suggesting I can shave two and a half minutes off my 40k TT
with only 5% more power? Wooo hoo! I ran the numbers on the
analyticcycling.com website to arrive at the 25% number, and it sounds
about right.
Again... (are you getting tired of this yet?) ... extrapolating Cobb's
(wild) claim of 2:26 reduction for an aero frame and 1:10 for
integrated aero bars over a 40k TT, that nets a 4:30 delta over 50km.
Tell me where I'm misinterpreting Cobb's claims. Or how I can trim
2:26 from my next TT with an increase of only 5% in power!
>> Why would any
>> team with a rider who is considered a contender for the overall or the
>> stage send him out to do a TT with anything else?
>> How else would you explain the fact
>> that so many riders "gave away" an easy win to Lance?
>
>Since we have no idea how many riders were using round-tubed bikes vs.
>aero-tubed bikes, nor any information as to their aerodynamic drag
>characteristics or power outputs, we also have no idea how many riders "gave
>away an easy win to Lance".
It's easy enough to check - but I erased the tape with stage 19 on it.
(anyone with the tape feel like helping out here?) But I do recall
that full-on aero bikes were very much the exception.
Even so, I'm confused why the riders' power output is so important to
determining whether they gave away the win - Cobb's numbers weren't
referenced to a "400-watt rider", and his claims were that the aero
frame and integrated bars together would shave over three and a half
minutes off a 40km TT. If those numbers aren't valid for pro riders,
who ARE they valid for?
>> >Read the study...read the study...read the study...read the study...
>>
>> Hey, if you can't figure out what's wrong with it, I'm not gonna stand
>> a chance! ;-)
>
>Close-mindedness raises it's ugly head again.
Explain to me how I can go 2:26 faster with 5% more power and I'll
open my mind (and kick some serious butt at states this year now that
I'm racing the "old farts"!). Heck, I'll just plan on upping my
output by 10% and knock off five minutes! ;-)
Andy Coggan
> "Andy Coggan" <aco...@earthlink.net> wrote:
>
> >Mark Hickey wrote:
> >
> >> Let me take a different approach to this conundrum. Assume for a
> >> moment that Cobb's right, and that a rider who rides the typical "pro
> >> TT bike" can maintain the same speed with 75% of the effort by simply
> >> swapping to readily available aero frames and bars.
> >
> >At typical pro bike rider speeds, the difference in power requirment
between
> >riding a standard round-tubed frame and a good aero frame is only 5% - I
> >haven't the foggiest idea where you came up with the 25% figure.
>
> Are you suggesting I can shave two and a half minutes off my 40k TT
> with only 5% more power? Wooo hoo! I ran the numbers on the
> analyticcycling.com website to arrive at the 25% number, and it sounds
> about right.
You made an error in logic:
Considering aerodynamic drag alone:
power = 0.5 * air density * CdA* velocity^3
therefore velocity = (power/0.5 * air density * CdA)^0.33
Thus, as the above equations demonstrate, it is incorrect to equate the
percentage increase in power needed to achieve a certain velocity with a
similar reduction in the power required to travel at that velocity due to
the same percentage reduction in drag. In the first case, the relationship
is a cubic one, whereas in the second case, the relationship is a linear
(and inverse) one.
> Again... (are you getting tired of this yet?) ... extrapolating Cobb's
> (wild) claim of 2:26 reduction for an aero frame and 1:10 for
> integrated aero bars over a 40k TT, that nets a 4:30 delta over 50km.
In addition to being tested in the wind tunnel aboard my Hooker TT bike, I
was also tested on a Wynn TT bike belonging to Team EDS. This bike was built
primarily of Reynold Speedstream tubing, and had some nice aerodynamic
features, such as an aero seatpost and a really nice fairing around the
whole headtube/downtube/toptube juncture. It wasn't, though, a Hooker..in
particular, the downtube was more round than anything else (to satisfy this
track team's desire for stiffness), and it used standard round cowhorns and
clip-ons. The results? A difference in drag of 0.7 lbs at 30 mph, enough to
account for a 2:20 difference in 40k time. That is less than the 2:26 + 1:10
= 3:36 reported in the book, but the Wynn bike was far from standard as
well.
But you don't like wind tunnel data, so let's go back to the field
experiments I've done comparing my Y-Foil and my Hooker. I do these in an
office park, with 4 laps coming out to 8.3 miles. For 6 such trials, my
average time aboard the Hooker is 19:12, at an average power of 282+/-8 W.
By comparison, the average of 8 trials on the Y-Foil is 19:40, at an average
power of 289+/-7 W. That's a difference of 28 seconds in 8.3 miles, or 1:24
in a 40k. Again, not as much as John reported, but the Y-Foil also isn't of
standard design.
> Tell me where I'm misinterpreting Cobb's claims.
You're not - you're just refusing to believe it, even though you have no
objective data to the contrary.
> Or how I can trim
> 2:26 from my next TT with an increase of only 5% in power!
Buy a Cervelo. ;-)
> Even so, I'm confused why the riders' power output is so important to
> determining whether they gave away the win - Cobb's numbers weren't
> referenced to a "400-watt rider", and his claims were that the aero
> frame and integrated bars together would shave over three and a half
> minutes off a 40km TT. If those numbers aren't valid for pro riders,
> who ARE they valid for?
The more power you generate, the faster you go. The faster you go, the less
time you spend covering a given course. The less time you're out on the
road, the less time you have to benefit from a reduction in aero drag.
Consquently, in terms of absolute time savings it is the *slower* riders
that benefit the most.
> Explain to me how I can go 2:26 faster with 5% more power and I'll
> open my mind (and kick some serious butt at states this year now that
> I'm racing the "old farts"!).
See above - you made a mathematical error.
Andy Coggan
MJuric
<aco...@earthlink.net> wrote:
>
>> Even so, I'm confused why the riders' power output is so important to
>> determining whether they gave away the win - Cobb's numbers weren't
>> referenced to a "400-watt rider", and his claims were that the aero
>> frame and integrated bars together would shave over three and a half
>> minutes off a 40km TT. If those numbers aren't valid for pro riders,
>> who ARE they valid for?
>
>The more power you generate, the faster you go. The faster you go, the less
>time you spend covering a given course. The less time you're out on the
>road, the less time you have to benefit from a reduction in aero drag.
>Consquently, in terms of absolute time savings it is the *slower* riders
>that benefit the most.
>
Is it not also true that drag follows more of a geometric
rather than a linear line. Thus the faster you go the drag increases
geometrically so a faster/higher output rider would benefit more from
the decrease in drag than a slower rider?
~Matt
Andy Coggan
I *thought* I was being clear...
The answer is, no, at least not if you're taking in terms of absolute time
savings in the speed range that cyclists typically average. (See the Cervelo
website for sample calculations illustrating this somewhat counterintuitive
result.)
Andy Coggan
Cleveland Steamer
"Andy Coggan" <aco...@earthlink.net> wrote in message
news:Rgc99.1088$ld4.1...@newsread2.prod.itd.earthlink.net...
> <MJuric> wrote in message news:3d654519....@news.choiceone.net...
> > On Thu, 22 Aug 2002 18:47:15 GMT, "Andy Coggan"
> > <aco...@earthlink.net> wrote:
>
.
> > >
> >
> > Is it not also true that drag follows more of a geometric
> > rather than a linear line. Thus the faster you go the drag increases
> > geometrically so a faster/higher output rider would benefit more from
> > the decrease in drag than a slower rider?
>
Drag is a velocity squared relationship. i.e To increase your speed form 20
mph to 25 mph (25% increase) requires greater than a 50% increase in power
output.
>
>
Andy Coggan
news:ak41l0$bvr$1...@eeyore.INS.cwru.edu...
First, you've screwed up the attributions, and made it appear that I posed
that question - I did not.
Second, the increase in power is much more that 50%...it's 95%, to be exact.
That's assuming, of course, that flow transition doesn't occur, and that
wind resistance is the only form of resistance to be overcome - which it is
not.
Third, how does your response address M Juric's misbelief that because of
this non-linear relationship, faster riders benefit more from a decrease in
drag?
Andy Coggan
Mark Hickey
Cobb: Aero frame reduces your 40k TT by 2:26.
Coggan: Aero frame reduces power requirement by only 5% at a given
speed.
Analyticcycling: Reducing a 40k TT time by 2:26 requires about 25%
more power.
Hickey: one or more of the above have to be wrong.
Cobb's assertion includes the assumption that power is constant and
aerodynamics and the "cubic relationship" between power and speed are
factored in (unless he sends along high-performance legs or tickets to
a high-altitude velodrome with that frame).
I used the calculator at analyticcycling to determine how much more
power (aerodynamics remaining unchanged) the TT rider would need to
make to net a 2:26 improvement - it was around 25%.
I ran the following numbers at analyticcycling to test the effect of a
5% reduction in aero drag:
Power 300 watts Frontal Area 0.5 m2 Coefficient Wind Drag 0.5
Dimensionless Air Density 1.226 kg/m3 Weight Rider & Bike 75 kg
Coefficient of Rolling 0.002 Dimensionless Slope of Hill 0.000.
That predicts a speed of 12.25m/s (or 44.1km/h).
Reducing my frontal area by 5% the speed changes to 12.46m/s
(or 44.856km/h). That's a 1.7% increase in speed - certainly
worthwhile - but still well under a minute total delta. This
calculation assumes that nothing changes but the aero drag (rider's
output stays the same, and the cubic relationship between speed and
power requirements is factored in to all the above).
To knock 2:26 off my 12.25m/s starting point requires a velocity of
12.84m/s, which (using the same parameters and changing only the
frontal area) requires a drag reduction from 0.5 to 0.433, or a 13.4%
reduction in frontal area. That seems to be an unrealistic number to
attribute to JUST the frame, no matter what you did to make it aero
(including removing it altogether).
What am I missing?
Sam Bean
How is the IMH training going?
and what bars are you riding?
Cheers!
Sam
Andy Coggan
> Here it is again, in its simplest form:
>
> Cobb: Aero frame reduces your 40k TT by 2:26.
> Coggan: Aero frame reduces power requirement by only 5% at a given
> speed.
> Analyticcycling: Reducing a 40k TT time by 2:26 requires about 25%
> more power.
> Hickey: one or more of the above have to be wrong.
That is an incorrect summary of our current difference of opinion.
Specifically, what I took exception to was your claim that because it takes
25% more power to go 2:26 faster (a figure that is incorrect - see below),
then a reduction in aero drag that would allow you to go 2:26 faster at the
same power output would reduce your power requirement by 25% at the initial
velocity.
> I used the calculator at analyticcycling to determine how much more
> power (aerodynamics remaining unchanged) the TT rider would need to
> make to net a 2:26 improvement - it was around 25%.
That's odd - when I ran the calculations using the values you suggested
below, I find that it only requires a 14% increase in power. Maybe you
should try running the numbers again.
> I ran the following numbers at analyticcycling to test the effect of a
> 5% reduction in aero drag:
>
> Power 300 watts Frontal Area 0.5 m2 Coefficient Wind Drag 0.5
> Dimensionless Air Density 1.226 kg/m3 Weight Rider & Bike 75 kg
> Coefficient of Rolling 0.002 Dimensionless Slope of Hill 0.000.
>
> That predicts a speed of 12.25m/s (or 44.1km/h).
>
> Reducing my frontal area by 5% the speed changes to 12.46m/s
> (or 44.856km/h). That's a 1.7% increase in speed - certainly
> worthwhile - but still well under a minute total delta. This
> calculation assumes that nothing changes but the aero drag (rider's
> output stays the same, and the cubic relationship between speed and
> power requirements is factored in to all the above).
This result is entirely as expected, but has absolutely nothing to do with
what I said. Read your own summary above: I estimated (based on the wind
tunnel data I have available to me) that an aero frame would reduce the
POWER REQUIREMENT at a given velocity by about 5% - not that it would reduce
frontal area by about 5%.
>
> To knock 2:26 off my 12.25m/s starting point requires a velocity of
> 12.84m/s, which (using the same parameters and changing only the
> frontal area) requires a drag reduction from 0.5 to 0.433, or a 13.4%
> reduction in frontal area. That seems to be an unrealistic number to
> attribute to JUST the frame, no matter what you did to make it aero
> (including removing it altogether).
See my previous posts: as measured in the wind tunnel, my drag is 0.7 lbs
(at 30 mph) less on my Hooker TT bike than on a less-optimized Wynn TT bike.
That's 0.7 lbs out of 5.2 lbs total, or 13.5%. Again, that's with a bike
(the Wynn) that is probably better than a standard round-tubed frame.
Andy Coggan
Andy Coggan
news:rGq99.2523$ob2.2...@newsread1.prod.itd.earthlink.net...
> Andy,
> How is the IMH training going?
> and what bars are you riding?
1) You have me confused with somebody else - I don't compete in triathlons.
2) I use Hooker aero bars, but to others I usually recommend VisionTech or
Scott 100k bars mated to a Look Ergostem, depending on their bike, position,
and event. However, for a triathlete who can't fit themselves to VisionTech
bars, the Profile Carbon X or Cinelli Angel bars might be a better
alternative.
Andy Coggan
Mark Hickey
>"Mark Hickey" <ma...@habcycles.com> wrote in message
>news:3d65b1fd....@netnews.att.net...
Uh oh, I think we're getting closer to mutually admitting Cobb is
wrong... ;-)
>> I used the calculator at analyticcycling to determine how much more
>> power (aerodynamics remaining unchanged) the TT rider would need to
>> make to net a 2:26 improvement - it was around 25%.
>
>That's odd - when I ran the calculations using the values you suggested
>below, I find that it only requires a 14% increase in power. Maybe you
>should try running the numbers again.
<snip>
>I estimated (based on the wind
>tunnel data I have available to me) that an aero frame would reduce the
>POWER REQUIREMENT at a given velocity by about 5% <snip>
So, to summarize your position:
* To go 2:26 faster I'd need 14% more power.
* At that new faster velocity, that aero frame only reduces my power
requirement by 5%.
So WHO or WHAT is making up the missing 9%?
gsk
Stacy Hills wrote:
>
> Then I suggest you "put your flat feet on the ground" because this "b.s." is
> how the modern engineering world works
Watched a fascinating show on TV tonight with a bunch of different engineering
teams trying to figure out how the Egyptian pyramids were made. All had their
wonderful theories and solutions based upon mathematical models but when put
into actual demonstration all these engineering teams failed miserably. Not one
team was successful. Obviously the Egyptians were able to build these structures
without the use of modern engineering techniques. They obviously had some
knowledge of mathematics but I would assume their results were largely achieved
thru trial and error and common sense. Just like my story about our PHD engineer
neighbor failing to build a fireplace when a stone mason told him it would never
work.
My point is that there is practical engineers(who don't necessarily have an
engineering degree) and the theorists. That's why I'm a bit skeptical of Andy et
al. aero theories. Show me the actual road test results.
doug
>
> My point is that there is practical engineers(who don't necessarily have an
> engineering degree) and the theorists. That's why I'm a bit skeptical of Andy et
> al. aero theories. Show me the actual road test results.
practice vs. theory... all depends on what you consider adequate
proof. my guess would be that 99% of those involved in aerodynamics
would consider wind tunnel testing a practice, and not a theoretical
exercise. just as you say 'show me the actual road test results', an
program manager in the boeing commercial aircraft group would tell a
conceptual design engineer to 'show me the tunnel data' prior to
making an important decision. wind tunel testing is just one step in
the design process (albeit a relatively new one in the bicycle
industry). i think you underestimate the amount of work that has gone
into validating wind tunnel testing methods and data reduction... the
only question, is did the engineers make valid assumptions in their
test processes (the questions you asked about how they tested). my
guess is that if they were able to predict necessary power to the
precision they claim, that their assumptions were dead on. how someone
else takes these assumptions and applies them is beyond the control of
the original work (i.e. andy can't control how cobb applies his test
results).