Small electric household fan, about 8"– 12"
preferably strong and multispeed
Lexan panel, 0.220"× 30"× 36" at some Home
Depot stores, $34. Similar polycarbonate
plastics can be found at TAP Plastics,
tapplastics.com. Acrylic is cheaper, but
not as easy to cut.
Cen-Tech digital pocket scale Harbor Freight
Tools part #93543, $15, harborfreight.com
Brass hinges, ¾" ( 2) with screws
Utility hinges, 1½" ( 4) with screws
Stiff steel wire, 15"-long such as fiberglass
insulation support wire
Insulated hook-up wire
4" plywood pieces, 8"× 40" and 12"× 40" or
equivalent in 1× 8, 1× 12, and/or 1× 4 boards
Scrap ¼" plywood and lumber pieces
Wood screws ( 30)
Wood glue and plastic epoxy
Transparent tape and duct tape
Scrap cardboard or thin plastic
White LED 10 strand (optional) for lighting,
$2 from IKEA
Box of drinking straws (optional) for flow
Drill and drill bits
Dremel tool with cutting disks
Hot glue gun and glue
2. Build the test stand.
The upper surface of the test stand must be flush C
with the floor of the tunnel, and the hinged struts
should pivot easily and balance just aft of vertical.
All other connections must be rigid; minute movements of the stand must be applied to the force
beam rather than absorbed in any joints.
Using scrap ¼" plywood, cut two 2"-square vertical struts and a 2¾"× 6½" test section floor. Cut the
back plate 2"× 2½" tall, and lighten it with a large
cutout, because weight not centered in the pivoting
mechanism will tend to fall backward and inflate
very small measurements. Glue a ½"×¾" block to
the lower-center-back of the plate; this spacer is
what presses against the force beam.
Mount the underside of the test section floor to D
the struts, using two 1½" hinges. Glue the back plate
Photography by Doug Desrochers
144 Make: Volume 15