Help wanted with bicycle wheel design
T Robinson
To: rec.bicycles.tech,sci.engr.mech
From: T.Rob...@sheffield.ac.uk (Tim Robinson)
Subject: Help needed with design project
Organization: Dept. Civ. Eng. University of Sheffield
Date: Fri, 09 Dec 94 12:21:08 gmt
X-Mailer: WinVN 0.92.1
I am posting the following for an 'A' level student in the UK. The message is
self-explanatory
I am an A-level student from Sheffield, England and am currently undertaking
a design project on an anti-crosswind front wheel for pedal cycles which
produces less drag than conventional spoked wheels. Solid disk wheels cannot
be used as front wheels on bicycles, as crosswinds cause hazardous steering
problems. The design is mainly targetted at use by time triallists, for whom
seconds of time can mean winning or losing a race.
I intend to fix a limited-angle rotatable aerofoil onto each spoke of the wheel
which would be tilted by the crosswind to allow the wind to pass through the
wheel. The aerofoils would be approximately 250mm long and 40mm wide at the top,
tapering to 10mm at the bottom.
Any relevant references or comments?
Stephen Mosley
Eckington School
Please reply by email if you can.
to: T.Rob...@Sheffield.ac.uk
or
I.W.B...@Sheffield.ac.uk
Thanks
Tim Robinson
T Robinson
: Tim Robinson
This is wrong. The correct addresses are
or
Thanks
Brent T Rowe
: a design project on an anti-crosswind front wheel for pedal cycles which
: be used as front wheels on bicycles, as crosswinds cause hazardous steering
: problems. The design is mainly targetted at use by time triallists, for whom
: seconds of time can mean winning or losing a race.
: I intend to fix a limited-angle rotatable aerofoil onto each spoke of the wheel
: which would be tilted by the crosswind to allow the wind to pass through the
: wheel. The aerofoils would be approximately 250mm long and 40mm wide at the top,
: tapering to 10mm at the bottom.
First off...is the design necessary? There are already 3 or 4 spoke
carbon-fibre wheels on the market that are lighter than a solid carbon
fibre wheel and have very little cross-wind resistance.
Another concern of mine is weight of your design...as an experienced
racer I know that weight is paramount, no matter how good your design
is, if it's heavy no one will use it.
Lastly, as to the intended benifits of this design: let's follow one
blade thru one rotation...at the top the spoke is moving 2x the speed of
the bike, usually several times the speed of any cross wind, your design
would not have much benefit here...at the bottom, the spoke isn't moving
at all, here you would have maximum benefit...and in the middle, well
your advantage is in the middle of the other cases.
Now considering that the blades will be rotating somewhat, and the wheel
is spinning at lets say 10x per second, your blades will be resonating
at that frequency and may make the wheels wobble, not to mention induce
large dynamic tensioning of the spokes wich would cause a shorter life
for the spokes as well as the bearings, and even the rider *laugh*
since the wobble would cause steering problems.
Brent.
Jim Papadopoulos
> I intend to fix a limited-angle rotatable aerofoil onto each spoke of the wheel
> which would be tilted by the crosswind to allow the wind to pass through the
> wheel. The aerofoils would be approximately 250mm long and 40mm wide at the top,
The angle should really change from top to bottom, so use segments.
I believe Hoerner's bible has a section or two on drag of
faired wires.
Even if this is a good workable solution (I haven't thought about it
practically) it's not the only possibility -- imagine
a trailing flap on a solid disk wheel, or adjustments to
steering geometry which could mitigate upset to balance and direction.
Cheers -- JP
Kerry Libberton
A friend of mine was considering making something along the lines of a three or
four spoke composite wheel with similar properties to the proposed design.
He was considering having the trailing edge of each spoke be flexible to allow
for flex due to crosswinds, however his major concern was that racing rules
state that any designs must have actual structural use. That means that if you
were to remove said aerodynamically shaped piece would the bike fall appart.
I'm not familiar with all of the regulations myself, but before spending too
much time on such a project, you might want to look at wether or not it could
be used by racers. If not, there won't be much of a market. Also Brent has a
good point, vibration could shake the bicycle to pieces.
********************************************************************************
*
KL...@uwyo.edu * Composite Engineers
Kerry Libberton * Produce
University of Wyoming * Stiffer Members
Mechanical Engineering *
*
********************************************************************************
Bill Schmidt
1. Get the book written about the bicycle wheel by
Jobst Brand. I think it is called "The Bicycle Wheel".
This will explain things like the characteristics that make
a good wheel.
2. Understand the aerodynamics of your proposal. I think you have
an interesting idea that might be extremely hard to reduce to
practice. Like an airplane propellor, the rim end of the "spoke"
travels much faster than the hub, so for any given crosswind and
forward speed, the relative angle of incidence of the resultant
varies not only along the radius of the spoke but sinusoidally
with angle of rotation (0 forward speed at the bottom, 2X at
the top). You want the angle of attack to be zero for minimum
drag, or you want to use the crosswind to generate thrust.
Post your ideas, or send them to me. I am fascinated with the prospect.
Bill Schmidt
T Robinson
I will post any responses back here
Thanks again
Tim Robinson
Roger Barry Hertz
T Robinson <ci...@sunc.sheffield.ac.uk> wrote:
>
>I am posting the following for an 'A' level student in the UK. The message is
>self-explanatory
>
> I am an A-level student from Sheffield, England and am currently undertaking
> a design project on an anti-crosswind front wheel for pedal cycles which
> produces less drag than conventional spoked wheels. Solid disk wheels cannot
> be used as front wheels on bicycles, as crosswinds cause hazardous steering
> problems. The design is mainly targetted at use by time triallists, for whom
> seconds of time can mean winning or losing a race.
> I intend to fix a limited-angle rotatable aerofoil onto each spoke of the wheel
> which would be tilted by the crosswind to allow the wind to pass through the
> wheel. The aerofoils would be approximately 250mm long and 40mm wide at the top,
> tapering to 10mm at the bottom.
>
> Any relevant references or comments?
> Stephen Mosley
> Eckington School
>
Yes, I believe this will work quite well. Let me relate some experience that
I have with using a similar concept with super-mileage vehicles (with the
SAE).
At the University of Saskatchewan, this concept was used for developing a
body style for a small 3 wheel car, designed for very high fuel economy.
The car was designed so that it was a vertical airfoil (it had a specific
number, I believe). The airfoil was symmetric. When faced with a cross
wind, the shape of the car could produce *negative* drag. The drag is
negative because the component of lift in the direction of travel (along
the axis of the airfoil, rather then the attack angle of the wind), which
overcomes the aerodynamic drag. The angles of attack for this situation
to exist are small. I think it was something like 10 to 15 degrees from
the direction of travel.
In the specific competition (1986), the car (Canadian Challenge I think)
obtained around 5600 mp(imperial)g. The day of the competition was sunny,
and quite windy ;-).
The SAE at UofS experimented with varying the angle of attack the next year
of the competitions. They did this by introducing rear wheel steering in
the car. They found that it was quite difficult for the driver to adjust
the angle to its optimum in practice, although theoretically it gave a much
bigger range of negative drag attack angles.
Your application with the bicycle spokes is similar in many ways. If
each spoke has less drag, then the resistance of the bicycle will decrease,
and people will be able to go faster! I would recommend first selecting
an airfoil shape that works without rotation, if that is possible. One problem
is that the airfoil will usually be in choppy air, so you may not be able to avoid
separation at the best of times. A static airfoil would be able to provide
a component of thrust when hit by a cross wind in either direction.
If any one wants references, I could dig some up. I know one student did his
Masters on this concept, and also looked into applying it to heavy transport
vehicles (trucks).
Roger Hertz
--
---------------------------------------------------------------------
r...@wolverine.utias.utoronto.ca
University of Toronto Ph: (416) 667-7744
Institute for Aerospace Studies Fax: (416) 667-7799
Roger Barry Hertz
Bill Schmidt <bsch...@maybeck.engr.sgi.com> wrote:
>I suggest two things:
>
> 2. Understand the aerodynamics of your proposal. I think you have
> an interesting idea that might be extremely hard to reduce to
> practice. Like an airplane propellor, the rim end of the "spoke"
> travels much faster than the hub, so for any given crosswind and
> forward speed, the relative angle of incidence of the resultant
> varies not only along the radius of the spoke but sinusoidally
> with angle of rotation (0 forward speed at the bottom, 2X at
> the top). You want the angle of attack to be zero for minimum
> drag, or you want to use the crosswind to generate thrust.
Yes, and like I've alluded to in the previous post, some airfoils can produce
thrust with zero angle of attack. I'm definitely not very knowledgable in
this area, though. For the bicycle application, zero would be referenced to
the angle that the wheel is facing. Seems like a good comprimise for
low drag and crosswind thrust!
>
> Post your ideas, or send them to me. I am fascinated with the prospect.
> Bill Schmidt
Roger Hertz
Bernhard Graf
T Robinson wrote
TR> produces less drag than conventional spoked wheels. Solid disk wheels cannot
TR> be used as front wheels on bicycles, as crosswinds cause hazardous steering
TR> problems.
^^^^^^^^^
Make a negative steering angle (>90 deg, dont forget to adjust the fork
offset). Dont like to explain why, its so late ;-). Think about it!
Ciao
Bernhard