| I have been racing the Barracuda streamliner
for over a year, and though it's a fast and versatile design which allows me to cruise at
close to 40MPH, I STILL want to go faster!
This
page will detail the design process for a "state of the art"
streamliner, using information that I have gathered from the HPV community, and
other sources. I have learned a lot about low speed aerodynamics and laminar
flow since my first streamliner design, and I hope to pass as much of this
information on to potential HPV builders as I work my way through this
project.
6/1/01 - Basic Design goals and
initial thoughts
This new design will utilize a light weight monocoque body design, with full
suspension and front wheel drive. The body will have about 5 inches of ground
clearance to minimize ground effects and allow greater leaning
angles in the corners. It will be designed to allow the use of
fatter tires to provide more traction in the corners. I will attempt
to use 26" wheels front and rear for lower rolling resistance. |
| The new body design will
attempt to keep the airflow more laminar than the previous design, by borrowing the
ideas of some of the proven high speed HPV designs such as
those of the Edge series bikes, designed by Matt Weaver,
the Varna Mephisto, and
Varna
Diablo, designed by George Georgiev. |
|
| Older record breaking
streamliners like the the
Cheetah, designed
by Michael Selig, used NACA airfoil wing sections in their design.
Current thinking is that since the streamliner shape is not a lifting
body (and you don't want it to lift!), it should not use wing
sections in the design. |
Handling
This new "speedbike" will be raced mostly in HPRA
events, which have relatively short
tracks, sharp corners, and small bumps. Traditional streamliners (is there such
a thing?) don't utilize a suspension, and have skinny racing tires. While this
works great for straight line sprinting and bigger tracks, I have found that to
corner faster, a streamliner needs at least a front suspension and adequate
ground clearance for 45 degree leaning in the corners. Wider tires such as the
Comp Pools or Avocet Freestyles and a full suspension will be needed when short track speeds are expected to be above 40MPH. Low bike weight does help on
hills and in sprints. My goal is to make the new streamliner lighter than the 60 pounds the current
streamliner weighs.
One of many design studies for new
streamliner
Aerodynamics
The basic idea for this iteration of the
body design will be a laminar shape, with a fairly
sharp nose, and the body widening all the way to the shoulder area to keep
the boundary layer laminar as long as possible. The body will then
transition into a
mild concave shape, and end with a sharp tail. The tail section on the
existing Barracuda streamliner uses a convex tail section, which allows
the air flowing down the sides of the bike to crash back together at the
trailing edge, causing turbulence (or at least that's the picture in my
head...). The concave design is supposed to allow the air to flow straight
off the tail and "re-accelerate" the air at the back of the
streamliner. The caveat to a sharper nose section is
that it will tend to make the bike more sensitive to the wind direction
and shifts in wind direction, which can make the bike a bit of a handful in
high wind conditions. Also a shaper nose requires a custom low-Q BB
and cranks that are both short and low-Q.
The new side view design will allow more air
under the streamliner than the existing streamliner, this should be ok as
it will have more ground clearance. The net effect will be a rounder
front, which should spread the high pressure area at the front of the
fairing more evenly. Because I'll be sitting in the bottom of the
streamliner body, instead of on seat mounted on a bike frame, and I will
be using front wheel drive, the streamliner height will potentially be 3 inches less
than that of the existing Barracuda streamliner, which should punch a much
smaller hole in the air. As the total frontal area of the streamliner is
the biggest factor in it's eventual speed characteristics, I want to
keep it as small as possible.
Body Composition
This time around I'm going to try to utilize higher-tech materials.
Ideally I'll use a Nomex honeycomb core sandwiched between single layers
of carbon fiber and Kevlar weave material. This construction will be quite
rigid and able to withstand a lot of punishment.
It may look something like this
photo-retouched version of the existing 'Cuda streamliner...
Shrunken 'Cuda streamliner
8/9/01
Going back to my friend the pressure
distribution java applet, and taking into account that the transition to
the tail section should be held off for as long as possible to keep the air
laminar for as long as possible, and then adjusting the plot to get
approximately the right aspect ratio for a shape 9.5 feet long and 17 inches
wide gives the result to the right. Notice that the red pressure
distribution line remains relatively flat and low, and then drops off
more before going high at the end of the shape. |
 |
After redrawing the above
"wing" with a concave tail obtain a better
shape, and then much messing about, I finally ended up with the shape
below. This new shape looks just like Matt Weaver's Virtual Edge,
only bigger. After
some measuring, it looks like if I use a minimum Q-factor
crank, I should be able to cram myself into it.
On my previous
streamliner design page, I reasoned that any air directed under the fairing
would slow the bike down, and designed the fairing to avoid that problem to
the extreme.
Unfortunately, I created a rather high pressure area on top of the the large down turned
nose, which may have overcome any gain I would have gotten by eliminating the high
pressure zone under the bike.
Here is a side view of design exercise
#2, which considers dual 26 inch wheels, 150mm cranks and reshaped nose. The
old fairing was about 30 inches from bottom to top at it's maximum height, this
one should be 27 inches, with a 5 inch ground clearance. This picture
demonstrates that a person with a 36" inseam can use a 26" front wheel, with
short cranks and chain ring overlap.
Design prototype 2 - FWD, full susp, 26"
front and rear.
11/01/01
Currently I'm working on refining the body shape and determining that I'm going to
fit properly. Also I'm gathering parts to build a FWD lowracer mule
out of spare low grade components and muffler pipe using a 24 inch front
wheel and a 700C rear wheel. This bike will be used to troubleshoot any
geometry and handling issues that may arise. I'm planning on using the Varna
style of FWD, as it is relatively simple and fairly bulletproof.
11/26/01
After drawing and redrawing the fairing shape too many times to think about,
and measuring and re-measuring pedal box and body clearances, I have decided to create a body that is completely symmetrical from the side
view. This way I'll only need to sculpt half of the body. From the male half
plug I'll create a female mold. I'll be able to use this same mold for both
the right and left halves of the body. This will ensure that the body is
actually symmetrical, which is very hard to do with a full plug, and that it
is actually straight. My original 'Cuda mold is slightly asymmetrical, and
has a slight twist. Also, using a female mold means that the body will actually be smooth on the outside,
making finishing the surface much less of a chore.
Above are finalized top and side
views of the fairing. The side view comes fairly rapidly to pedal box
height, which will be 22" for 155mm cranks, plus a couple inches to
allow for fairing curvature. In an attempt to keep the boundary layer
attached, the fairing height continues to grow slightly until the shoulder
area is reached and then is cut off fairly rapidly.
The fairing plug will be constructed
from these drawings by building the foam up onto a plywood base for the half
mold. The plywood base will provide a fairly sturdy template to ensure that
the two halves line up properly when I try to put them together.
Using the side view plans above,
and applying head and wheel fairings, will give me
something like the scale rendition above (rendition complements of Alan
Ariail).
02/15/02
As the fairing shape and size
are not dependant on the
wheel choices, I decided to go ahead and start work on it. I'm pretty sure
now that I'll do a more traditional 406 front and 700c rear. If I could have the cranks and
chain ring overlap the front wheel like the Varna does, I'd go with a bigger
front wheel, but with the super narrow Q this bike will have, and my
requirement to be able to use fat tires for cornering, I'll need the
extra wheel clearance. Also I'm now fairly certain that the amount of
rolling resistance a larger front wheel would save is negated by the
ergonomic problems it introduces. I'm skipping the mule low racer, as I will
be using approximately the same front end geometry that the current 'Cuda
enjoys. While this bike is
designed to be useable in the HPRA races, it is mostly designed to be a high speed
Battle Mountain racer. I'm not sure at this point if it will replace or
merely augment the current 'Cuda streamliner.
7/1/04
Over the past two years that this project has been in development, I
have had plenty of time to review the design. Fortunately, it still looks
like this will be a super fast bike! Below is a profile view comparison
between the new Cuda - W and the current crop of fastest bikes in the
world.
Scale - Barracuda X is 9.5 ft long
The things I noticed were:
-
The Diablo
is way tiny! No way
am I going to get that small, but the Cuda-W should be more laminar.
-
It appears that the total
frontal area for the Cuda-W should be less than the VE and KE bikes.
-
The wheelbase is also longer
than all the other bikes. A longer wheelbase should help the 'Cuda
better handle the slight winds that can knock a streamliner over at 70+
MPH by moving the center of pressure further behind the front
wheel.
How a bike handles at high
speeds has been a real concern in the past year. As speeds reach and exceed
the 80MPH mark, the bikes become increasingly susceptible to slight gusts of
wind, so much so that some racing teams are building 3 wheeled speedbikes to
go fast without balance concerns. It has been demonstrated that the
further behind the front wheel that a pressure is applied, the less effect
it has on the vehicle. This means if the center of pressure is in front of
the wheel, the bike will be pushed around by side winds, if it's closer to
the center of the bike, the side winds won't be as noticeable. You can try
this yourself by having someone push on you while you are riding. Try (on a
recumbent) having someone push your foot, then your leg, then your seat and
observe the effects.
Now that the fairing design
has been completed, It's time to move on to:
Silly drawing
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