Frequently Asked Questions
Please scroll down to the desired category
Where can I get urethane
Normally, you will
not find it at a building supply or small retailer of fiberglass materials.
Look in your local Yellow Pages under Plastics-Foam, Fiber Glass
Materials, or Insulation Materials. We purchase it locally
McCarther Company, 202 N. 47th Ave, Phoenix, AZ 85043. Phone: 602-272-6806. Also,
check our links page for on-line suppliers.
The foam is difficult and costly to ship. Mostly, they are
shipping air. And since the foam is easily broken, it must be well
My supplier asked what
density of foam I wanted. What should I tell him.
urethane foam sheets come in either 2- or 3-pound density. Either density will work
Can I use the
urethane foam that has foil on one side.
You can use it if
you take the foil off, but we do not recommend it. The urethane sheets that have a
foil covering are about two to three times as expensive as the plain sheets, and the foil
is sometimes difficult to remove. It's best to use the right material.
What is the brand
name of the urethane foam sheets.
Do not shop for
urethane on the basis of a brand name. The foam is usually cast in large pillows by
a local manufacturer. The manufacturer or distributor slices it into sheets according to local
needs. In this area, rigid urethane sheets
come from a company by the name of Atlas, which is located in Mesa, Arizona.
But Atlas does not sell to the end user, and there is no brand name for their
product. It's just generic urethane foam, which is the least expensive way to buy
it. If you buy it under a brand name, you could pay more, and you may not get the
Plans say that you can't
use a water-based contact cement to glue the foam together. Why not.
It just doesn't
work very well on urethane foam. Use the solvent-based contact cement made by
Weldwood or Wilhold. Coat both pieces with adhesive, let the adhesive tack off, then
press the pieces together. (Water-based cements are the non-flammable type.)
Can I use Styrofoam
instead of urethane foam.
fiberglassing resin will dissolve polystyrene foam (Styrofoam) on contact. If
you must use polystyrene foam, you'll have to switch to epoxy resin to avoid dissolving
the foam when the resin is applied. But epoxy is about three times as expensive as
polyester, and polystyrene foam is much more difficult to work with than urethane.
If you switch to Styrofoam and epoxy, you'll hate the system. If you stay with
urethane foam and polyester resin, you'll love it.
local supplier does not carry urethane foam, but he does carry polyisocyanurate foam. Can I use it?
Yes. The original urethane (technically,
"polyurethane") foam is no longer carried by many suppliers. Many
of them are now supplying polyisocyanurate foam. It's a slightly
different compound within the polyurethane foam family. Many
salesmen still call it "urethane foam" and then supply you with
polyisocyanurate foam. Others will simply say that they do
not have "urethane" foam, but they do have "polyisocyanurate" foam.
If you can locate it, the original polyurethane foam is better.
It has a tougher surface. But polyisocyanurate foam will work.
The body for our latest vehicle, the XR3 Hybrid,
was built of polyisocyanurate foam (which the company supplied when I
ordered urethane foam).
What is the
difference between laminating resin and finishing resin.
Finishing resin has wax
in it. When the resin cures, the wax comes to the surface and seals it off so the
resin fully hardens on the surface. Laminating resin has no wax, so the surface will
remain slightly tacky because it is not fully hardened. Use finishing resin only on
the last lay-up. BUT... be sure to wipe the surface with acetone (just lightly) and
sand it to remove the wax prior to applying other coatings. If the wax is not
removed, any coating applied over it may not adhere well.
Where can I get
more information on how to use fiberglass-over-urethane foam.
manual that comes with Tri-Magnum
plans is very good for general how-to information on foam core
construction. The manual is very detailed, and includes over 130 photos and
illustrations. We also have a photo-illustrated document on line that gives a
pretty good overview of how to use fiberglass over urethane foam.
But Tri-Magnum plans are far more detailed, and cover things like installing
substructures, hinges, windows, lights, upholstery, and more. The
manual that comes with our recently released XR3
plan-set may actually surpass Tri-Magnum plans in terms of detail.
And either of the two XR3 plan-sets that include the discs have a
one-hour video showing how the body is fiberglassed. If you're
interested in working with this material, the video itself is worth the
price of the plans.
Can I make a two-place
version of AquaSub.
into a two-place craft would require extensive redesign. If you enlarge the cabin to
fit two occupants, buoyancy will increase, which means the sub will have to be heavier in
order to submerge. If the sub is significantly heavier, then the substructure will
have to be strengthened. And you would have to consider the difference in the center
of buoyancy between submerged and surfaced states with the new design. So it's not
just a simple matter of making the cabin a little larger. There would be
trickle-down effects throughout the design.
Can I make AquaSub go
deeper by lengthening the outriggers.
But lengthening the outriggers will increase the loads on the hinges and the frame
inside AquaSub's hull. The pontoons are subjected to the force of wave action on the
surface, but the submerged passenger pod is not. This can translate into significant
loads on the supportive structure. And lengthening the outriggers will increase
these loads. We recommend that you do not lengthen the outriggers unless you are
qualified to do the necessary engineering.
Can AquaSub be powered
by a generator instead of batteries.
You could install
a gasoline-powered generator to power the air-circulation fan and the propulsion motors.
The generator could also power an air compressor to provide compressed air for
ballasting. Ballast air should be contained in a separate tank, rather than supplied
directly from the compressor. The necessary hardware could be housed in the
pontoons. Naturally, the pontoons would have to be enlarged to provide the necessary
room and greater buoyancy needed to account for the extra size and weight of the new
hardware. Pontoons should have enough buoyancy to prevent AquaSub from sinking (plus
a good margin of safety), even if the cabin were filled with water. Also, design the
system so there is enough compressed air to bring AquaSub to the surface should the
generator quit at any moment in the operating schedule. And locate the generator's
exhaust pipe so fumes cannot be drawn into the cabin. A fair amount of engineering
would be required to make such a system safe and reliable.
What does it cost to
build Ground Hugger.
plans give you lots of options in the selection of materials and components. So you
can build it to the level of sophistication that fits your riding needs and pocketbook.
The down side of this is that it's almost impossible to provide any meaningful
estimation of the cost to build it. It all depends on which components and materials
you select. If you use mild steel for the frame, and take parts from a used bike,
then the cost to build will be on the order of $200. But if you use aluminum or 4130
steel for the frame, and buy new, high-end bike components, then you'll end up spending
much more, depending on what you pay for parts and materials.
Where do I get the
Except for the
steering tube, seat, and frame, Ground Hugger uses standard bike parts throughout.
So you'll find most of what you need at a local bicycle shop. The universal joint at
the front of the steering tube can be machined by a local shop, or you can make it from a
tool universal joint.
What size riders does
Ground Hugger fit.
Built to the size
shown in the plans, Ground Hugger will adjust to fit riders of roughly 64 to 72 inches in
height. The seat and handlebars are adjustable. If a rider is taller or
shorter, then the frame should be lengthened or shortened accordingly.
Where do I get the
carbon fiber materials for the Ground Hugger XR2.
||A The carbon fiber
cloth and vinylester resin come from the same type of source that you'd buy conventional
fiberglass resin and cloth. Check your local Yellow Pages under "Fiber Glass
Materials." And there are a number of sources listed on the "Links" page. The material for the prototype
was purchased from Composites One in Phoenix. They have 14 outlets around the U.S,
and they'll ship to U.S. destinations.
Are any special tools
||A Tools are mostly
ordinary shop tools. You'll need paper buckets for the resin, several cheap paint
brushes, a small Surform file, a sanding block and sandpaper, ordinary scissors for
cutting the carbon fiber cloth, and a hand-held reciprocating portable saw (saber
saw). A Dremel tool will come in handy, and you'll need the wrenches used to
assemble a bicycle. A drill press is good to have, but you can use an ordinary hand
drill. Some machining is required (threading the steering tube, making the fork,
etc), but you can farm that out. The bottom bracket shells are purchased ready-made
and already threaded. The frame is built on a flat table.
How difficult is it to
build the XR2.
||A Building the frame
is pretty straightforward, and the carbon fiber and vinylester resin composite is as easy
to use as conventional fiberglass. If you're comfortable working with your
hands and building things, then you shouldn't have a problem building the XR2. In
other words, there's nothing uniquely challenging about building the carbon fiber frame,
provided you're comfortable with other types of construction projects.
I'm very large.
Can the XR2 still fit me.
The XR2 can be made to
fit someone of any height. But since it fits like a sports car, it will not be a
good candidate for someone who is significantly overweight. A person of normal
height who is 20 - 30 lbs overweight, for example, wouldn't have a problem. But if
you're 70-100 lbs overweight, you could have trouble fitting into the XR2, then it may be
difficult to pedal and steer due to the position of the handlebars and seat.
What does it cost to
The primary expenses of
building the frame are listed on the XR2 information page.
Beyond that, it really depends on the components you select and how you purchase
them. For example, we paid $180 (new) for the combination speed-shifter and brake
lever set. And the carbon fiber wheels used on the prototype cost nearly $500.
So expenses can add up fast if you buy new top-of-the-line parts, individually.
But about five years ago, I purchased a practically-new Cannondale road bike from a
private party for $275 (the whole bicycle). Admittedly, that was a steal. But
those kinds of deals are out there if you shop around in the classified section of your
local newspaper. And that $275 bike would have supplied lots of parts
for the XR2. So it truly depends on what you buy and how you buy it.
Pressure Jet Engine
Can the Gluhareff Jet run on a different fuel, or do I have to use
The engine was designed
around the fuel, and Mr. Gluhareff was emphatic about the use of propane. But
propane is readily available. It's the same fuel used to fill barbecue tanks.
What size jet do
I need to power an ultralight.
If you know your craft's
L/D ratio, simply divide the gross weight (including your own) by the L/D ratio to obtain
the jet thrust needed for level flight.
Can I get plans
for the backpack helicopter or flying platform.
We have access to
Mr. Gluhareff's plans for these craft, but have shelved the idea of making them
available. These craft were experimental, and were never fully proven out in free
How much fuel does the
The "Specifications" table on the info page for the
jet provides specific fuel consumption in lbs/lb/hr. This means that the jet
will burn x pounds of fuel, per pound of thrust, per hour of operation. A
130-pound engine with a round intake running at full throttle for one hour, for example,
would burn about 100 pounds of fuel (0.77 x 130 x 1 = 100.10).
Propane weighs 4.23 pounds per gallon, which translates into 23.66 gallons of
How fast can a BD-5 type
plane go with two 130-pound engines.
In order to
calculate speed from thrust, you really need to have some sort of a drag curve for the
aircraft. The point at which drag equals maximum thrust determines the top speed of
the craft. Mr. Gluhareff worked up a drag/thrust curve for a hypothetical
plane that he called the MEG-600, and came up with 400 mph on two G8-2-80
engines. This info is included in the manual that comes with the
plans. But it must be stressed that the calculations are based on a
hypothetical, not an actual, aircraft. So the drag curve of your aircraft is
likely to be different.
How much will it cost me
to build a jet with 130 pounds of thrust.
There are lots of
variables that affect the cost to build the jet. If you make it from sheet metal,
there is roughly $350 to $450 worth of stainless steel and aluminum in a 130-pound thrust
engine. The jet is built mostly of 0.032-inch No. 321 stainless steel sheet.
If you farm out the welding, then the cost of welding would have to be added in.
Plans show how to spin the nose cone yourself. But if you purchase a ready-made nose
cone, then that cost would have to be considered. So if you shop for the best price
on materials and do all the fabrication yourself, $350 would be a rock-bottom estimation
of the cost to build the jet. But one could spend considerably more.
I bought the Standard
Plans package and built the 20-pound engine, but now I want to build a 130-pound
thrust engine. Do I have to buy another complete set of plans.
way to go is to upgrade to the Deluxe package. Purchasers of the Standard Plans
package can upgrade to the Deluxe Plans by paying only the different in price between the
two (plus the P&H charge). When you upgrade, you'll get the other three sets of
drawings and the CD-ROM. So you'll end up with drawings for engines in all
four thrust ratings. There is no upgrade option to select on the order form.
So send your order by mail, or phone it in, and let us know which thrust-size
you already have.
How maneuverable is HydroRunner.
maneuverable, but it turns differently than a personal watercraft. PWCs heel
(bank) into turns. HydroRunner turns flat like a hydroplane. If you let
off on the throttle, crank the handlebars to one side, then apply power again, HydroRunner
will spin around practically in its own length. But this is an extreme maneuver with
lots of skidding, and it would not be considered normal operating practice.
Can I jump wakes with
we're against the practice of jumping wakes. But HydroRunner will
operate much like a PWC in this regard. It handles jumps and rough water very
What happens if I fall
off the boat.
that you install an emergency shut-off switch, then attach the lanyard to your life jacket
while riding HydroRunner. If you should ever fall off, the lanyard pulls the rubber
cap off the shut-off switch and instantly kills the motor. We had a test-rider get
swept off during extreme maneuvers by diving through a wave, only to find HydroRunner
sitting in the water about 10 feet away. The rider heard the engine stop
almost simultaneously with having been struck by the force of the water.
What kind of tools and
skills do I need to build it.
woodworking skills and tools are all that you'll need to build HydroRunner. It's
made mostly of plywood, which is then sealed with a coating of fiberglass.
You'll need a vibrator sander, a portable circular saw, a reciprocating saw, a
screwdriver, a long straightedge, and a belt sander. A table saw is also
helpful. HydroRunner is built on a 3 x 8 foot table made from a sheet of
plywood. Imagine looking down on HydroRunner from above and tracing around the
outside profile. This silhouette is cut from a 4 by 8 foot sheet of plywood to
provide a stable foundation to build on. The top half of the boat is built on
the top surface of the plywood, and the bottom half is built on the bottom surface.
How do I get a license.
||A If you're
in the U.S., you would take your finished boat to a local office of the Department of Fish
and Game, and they'll give you a license. It's a fairly straightforward
process. For more details, see the on-line document on licensing
and insuring homebuilt vehicles.
Where do I get a
expensive route is to make your own from one of those inexpensive utility trailers sold at
building supply stores like Home Depot. Support HydroRunner on a carpet-covered
length of 1 x 10 or 1 x 12 wood down the center. Install a carpet-covered
rail (2 x 4 or 2 x 6 wood on edge) on each side to fit snuggly under the wings - the
connecting piece between each sponson and the center-hull. The weight of the
boat, however, should be supported by the bottom of the hull, not by the
wings. Purchase a winch and tie-down straps from a boat shop.
How fast does Pegasus go.
about walking speed. The speed of a hovercraft is determined by the amount of thrust
power it has. Pegasus does not have a thrust system, which means that forward thrust
comes from the lift air that spills out one side when you tilt in the opposite
direction. You can install a thrust system and get
lots more speed. But keep in mind the safety implications. A little thrust
can translate into lots of speed on a hovercraft.
Can I install a
larger engine and get more performance.
Increasing the power of
the lift engine will not have a big effect on the performance of Pegasus. Even
though Pegasus is rated for a 125-pound payload, it will actually lift close to 200 pounds
free of the ground. So it already has fairly good lifting power for its
size. The biggest improvement in performance will come from installing a thrust system. But if you're after lots of
performance, it would be better to select a high-performance design like Tri-Flyer.
Can Pegasus go over
designed for over-water operation. When a hovercraft is operating over water, it
makes a depression in the water like a boat. The thrust system has to overcome this
depression, just as a boat does when it gets onto plane. Pegasus has no thrust
system to enable it to do this. Plus, it has no flotation system and it will not
stand up to the water spray that hovercraft create over water.
I want to build Tri-Magnum, but can it be licensed for driving on the street.
build-it-yourself cars are street-legal, including Tri-Magnum. Three-wheelers are
classified as motorcycles in the U.S., and in most other parts of the world. So they
have to meet the local requirements for motorcycles. In the U.S., homebuilt cars are
licensed on a state level, and must meet requirements of your particular
state. For more information check the document entitled "Licensing
and Insuring Homebuilt Vehicles."
Since it uses a
motorcycle chassis, what do you do about a heater and defrosters.
If you use
a water-cooled motorcycle as a basis, installing a heater and defroster system is fairly
straightforward. You would use a heater core from a wrecked car, then tap into the
motorcycle cooling system and route hot coolant through the heater core. Controls
and ductwork could come from a wrecked car, or you could fabricate your own. An
air-cooled bike is more challenging, but it's still possible. You could fabricate a
heat exchanger to fit around the exhaust header and use a fan to move air through
it. That's the way heaters in small aircraft work. But take extra care
to avoid the possibility of letting exhaust gases mix with the air that's ducted into the
cabin. Carbon monoxide poisoning can be fatal. Just to play it safe, go
to a pilot shop and pick up a CO detector. It's an inexpensive device that hangs
from your key ring and turns color when carbon monoxide is present.
What about windshield
You can use the
wiper and motor assembly from the hatchback of a wrecked car. In other words, just
use a single blade to wipe the entire windshield. But you'll have to
use laminated safety plate instead of the polycarbonate windshield shown in the
plans. Windshield wipers will scratch the polycarbonate material. We've also
heard good reports from folks who have used a product called "Rain-X," which is a coating that keeps the windshield
clear even when it's raining.
How does Tri-Magnum back
Tri-Magnum did not have a reverse. The best option for a reverse is to
build Tri-Magnum around a Honda Gold Wing. The Special Edition and Aspencade models are factory equipped with an electric reverse. And the Honda
Gold Wing is about the best choice possible for Tri-Magnum. Another
option is to install a friction wheel that can swing against the rear tire, then power it
with a car starter motor. We've used electric reverse systems on other
vehicles, and they work quite well.
plans specify a Briggs & Stratton 16 hp twin, but the same engine comes in higher
power ratings. Can I use a more powerful engine.
Stratton makes this aluminum-case opposed twin-cylinder engine in higher horsepower
ratings, and any engine in this series may be used. In fact, other
manufacturers make similar engines. So you do not have to stay with Briggs &
Stratton. But avoid any engine that has a cast iron block because of the
increased weight. Trimuter's engine sits on top of the final drive
housing. So a significantly heavier engine would increase the height of the
vehicle's center of gravity, which would affect it's stability in high-speed
turns. For more information on the importance of center of gravity location,
go to our on-line document on three-wheeler handling stability.
Can I used a VW
engine and transaxle and give Trimuter lots more performance.
We've seen it
done, but do not recommend it. Trimuter was designed around the idea of a sort
of in-town commuter car, and speeds above 60 mph were not considered when it was
designed. Trimuter's top speed on 16 hp is about 63 mph. We installed a
30-hp rotary engine in the prototype and drove it up to 80 mph, where it began to feel
light in the front end. Notice that Trimuter's front end is angled slightly
upward on the bottom. This creates aerodynamic lift at higher speeds.
Since there isn't much weight on the front wheel, aerodynamic lift could cause control
problems at very high speeds. So if you're making a high-speed version of
Trimuter, the body should be angled downward at the front to get downward pressure from
aerodynamic effects. And the cg should be lowered for a greater margin of
safety against rollover. For a really high-performance three-wheeler, take a
look at Tri-Magnum.
What kind of
transmission does Trimuter use and where do I get it.
Trimuter uses a Salsbury
CVT, like the type used in snowmobiles. You do not have to shift gears. It's
done automatically by the transmission. Salsbury sold off rights to their CVTs
to Hoffco/Comet Industries. The Salsbury transmission used in Trimuter
is available from them.
What skills and
tools are needed to build Tri-Flyer.
Tri-Flyer is made
much like a wooden boat. It has station formers that are made mainly of 1 x
3-inch wood. Wood stringer are then placed to run lengthwise across the
station formers, then this framework is covered with 1/8-inch plywood. Seams
are sealed with a single lay-up of fiberglass. The duct for the thrust prop is
made of foam and fiberglass. But basically, building Tri-Flyer is a woodworking
project. So you'll need basic woodworking skills, and ordinary shop tools like
a circular saw, belt sander, hammer, straightedge, square, and similar kinds of tools.
What happens if the lift
engine quits while you're going fast over the water.
When I was taking
flying lessons, I asked my flight instructor what happens if the engine quits.
He said: "We land!" That's what happens when Tri-Flyer's lift engine
quits. You settle to the surface. But the bottom of Tri-Flyer's hull is
sealed, and it's angled upward around the edges so it will not dive into the
water. Instead, it would plane across the surface then quickly settle into the
water and float like a boat.
Where do I get the
Plans provide a
source for the lift fan and thrust prop. You can also get skirt material from
the same source. The wood can be purchased from a local supplier.
But sometimes you'll have to shop a bit to locate the 1/8-inch plywood used for the
skin. Not every lumberyard will carry it. And it's best to use Marine
grade plywood for the skin.
How do you stop
Tri-Flyer. There aren't any brakes.
To reduce speed, you
just back off on thrust power. Aerodynamic drag and the drag of the skirt
occasionally contacting the surface will bleed off speed fairly quickly - especially over
water. But to stop a hovercraft quickly while going fast, use the rudders in
the propwash to spin the craft around on its axis so it is traveling
backwards. You then apply thrust power to slow it down. A
hovercraft can yaw, or spin around on its axis, without changing its direction of travel.
So as far as the hovercraft is concerned, there is nothing unusual about
What does it cost to
The cost of the
materials is not very high - about $700 - maybe a little more. The biggest
expense variable will be the amount you pay for engines. Tri-Flyer uses an
aluminum-case, two-cycle engine for thrust, and it takes engines of 40 hp to 80
hp. If you buy a brand new engine in one of the higher power ratings, the cost
can be quit high - perhaps as much as $5,000. But if you locate a used one, or
even a run-out snowmobile from which the engine can be salvaged, then you could end up
with a thrust engine for as little as $1,000, or maybe even less. For lift power,
Tri-Flyer uses a single-cylinder, aluminum-case, vertical-shaft engine of the type used on
riding lawnmowers and other lawn and garden equipment. If you can find a used
engine, expect to pay $200 or so. New, they cost about twice that amount.
So with prudent shopping, the minimum estimated total cost to build Tri-Flyer would
be on the order of $3,000 - $3,500. But much depends on the engines you
purchase and what you pay for them.
buy printed plans now, then want the CD-ROM when it becomes
If you buy the printed plans
and then later decide you want the CD-ROM, you can upgrade and get the CD by paying only the difference in
price between the two plans packages.
have a CAD system. Can I still view the CAD files.
||A You don't need a
CAD or 3D modeling program to view the electronic drawings and 3D models.
The CD-ROM provides a link where you can download a free viewer.
printed plans, why do I need the 2D CAD drawings that come on the CD-ROM.
||A The 2D CAD
files let you print out extra copies of the plan sheets and close-up views of
individual parts and work from them so the original plans stay clean. Also, a local
plotting service can make new prints from the CAD files, should the originals become
damaged or lost. And if a part was shown in scale on the original prints, you have
the option of printing full-size templates if you need them. Also, lots of people
like to modify the original design. So if you have a CAD system, you can import the
CAD files and make changes to see how it works out on "paper" before going
ahead. You can then produce working drawings of your new design and have a
personalized set of plans.
the advantages of having the 3D electronic models that comes on the CD-ROM.
There are lots of
advantages in having a 3D model. One of the biggest benefits to the average person
is the ability to see how something is built from any angle, and see what's inside and how
it fits together. Remember, the 3D models are full-size, fully-detailed electronic
representations of the actual item. You can strip off the skin, individually hide or
display the parts, and take measurements in three-dimensional space to an accuracy of
one-thousandth of an inch (or one hundredth of a millimeter). If machining is needed, you can use the 3D
files for CNC work (computerized machining). This saves time
(money), and it produces a much more accurate part.
the advantages of having the construction manual in electronic format.
all, your kids can't use it for a coloring book. But even if that would never happen
in your household, there are plenty of other advantages. The electronic manual
is in color, and the printed manual is in black & white. And the electronic
format makes it possible to provide much larger images. We've formatted the
electronic manual to look like the printed one, but when you click on an image, a
high-resolution version of the picture pops up and fills your entire screen.
So you can see things in much greater detail. And if you're connected to the
Internet, links on the CD provide seamless access to on-line updates, revisions, addenda,
and technical support. And if your printed manual does get used as a coloring
book, you can print out a new one. The electronic format makes it possible to
provide features that are impossible to provide in a printed manual.
Considering the benefits of the electronic format and CAD
systems, why are you still offering printed plans.
Like the issue of
American versus SI units (see below), this is a tough issue because
there is no way to generalize an answer that applies universally to DIY
hobbyists. Many hobbyists still prefer hard copies, and there are
still consumers that do not have ready access to a computer. But
we are migrating to electronic format in all our projects.
Looking to the future, the practice of shipping electronic files on
CD-ROM will likely become outmoded too. Technology is moving
rapidly, people are adapting to it, and we are continuously
re-evaluating the alternatives.
you make plans available in SI or metric units.
This is a
tough one. Over 80 percent of our sales are to U.S. residents, and the U.S.
has been slow to convert to SI units - at least on a consumer level. In
the U.S., common sizes for steel tubing and other ordinary building materials are still
mostly in inches and feet. And metric tubing, for example, is much
more costly than similar tubing in inch-sizes. So we design to common material sizes and use the units
that the majority of our customers are familiar with. Once a
product has been designed , it's impractical
to simply switch dimensions over to SI units.
Specifications for bearings, fasteners and other components do not match up, and
dimensions end up looking nonsensical. In order to use SI units,
the product has to be designed in SI.
NOTE: As of July, 2011 our new
solar-assist recumbent bicycle, the XR2 HP,
is in SI units. We will continue to reconsider the issue of units
with new and/or updated plan-sets.