DIY Wind Tunnel

November 1, 2017

INTRODUCTION

This document provides design drawings and materials lists for the DIY wind tunnel used in

Lectures 9 and 10 of “Do it Yourself Engineering,” taught by Professor Stephen Ressler and

produced by The Great Courses. (https://www.thegreatcourses.com/courses/do-it-yourself-

engineering.html)

Full-size templates for cutting all irregularly-shaped components are provided separately at

http://stephenjressler.com/diy-engineering/.

If you have questions about this project, please contact Steve Ressler at

http://stephenjressler.com/contact/.

PERSPECTIVE VIEW (Front)

PERSPECTIVE VIEW (Rear)

MAJOR COMPONENTS

FLOW

STRAIGHTENER CONTRACTION

SECTIONTEST

SECTION

DIFFUSER

FAN

HOUSING

LIFT MEASURING

DEVICE

LIFT MEASURING DEVICE

Component Description

A Side (2) 1/4” poplar or plywood*

B Transverse frame – lower (2) 1/4” x 3/4” x 3.5” poplar

C Transverse frame – upper 1/4” x 1-1/2” x 8”`poplar

D Axle 3/8” dia. Hardwood dowel, 9” long

E Specimen mount – side (2) 1/16” plywood*

F Specimen mount – core 1/4” poplar*

G Protractor 1/8” plywood*

H Angle of attack indicator 1/4” poplar*

I Strut 1/4” x 1/2” x 7-1/2” poplar (sanded to streamlined cross-section)

J Airfoil test specimen Balsa, dimensioned and carved as required

K Counterweight 1/4” x 1” steel bolt with nut and washers (Use enough washers to

counterbalance airfoil test specimen)

L Fastener (2) Small sheet metal screw

M Lift measurer Digital platform scale

* Full-size template available at http://stephenjressler.com/diy-engineering/.

Notes:

1. Components E, F, and H are glued to

shaft (D).

2. Shaft (D) is free to rotate in sides (A).

3. The strut (I) is glued to the airfoil test

specimen (J), but not to the specimen

mount (E and F).

TEST SECTION

Component Description

N Small flange element (16) 1/4” x 1-1/2” poplar or plywood*

O Base 1/2” x 10-3/4” x 16” plywood with 1/2” x 3” slot cut in center

P Back 3/4” x 10” x 16” plywood

Q Leg (4) 1/4” x 1/2” x 16” poplar

R Lid corner support 3/4” x 3/4” x 16” poplar

S Lid front 1/8” x 10-3/4” x 16” Plexiglas

T Lid top 1/8” x 11-5/8” x 16” Plexiglas

U Fastener (4) 1/4” x 1-1/2” steel bolt with nut

* Full-size template available at http://stephenjressler.com/diy-engineering/.

Notes:

1. Each flange is laminated from 8 elements (N), with overlapping joints at the corners. Drill the

1/4” holes in the flanges after they have been assembled.

2. Plexiglas lid front and top (S and T) are fastened to lid corner support (R) with small sheet

metal screws and washers.

CONTRACTION SECTION

Component Description

V Large flange element (8) 1/4” x 1-1/2” poplar or plywood*

W Small flange element (8) 1/4” x 1-1/2” poplar or plywood*

X Longitudinal frame element (8) 1/4” plywood*

Y Leg (2) 1/4” x 1/2” x 2-1/2” poplar

Z Shell – top & bottom (2) Lightweight cardboard*

a Shell – side (2) Lightweight cardboard*

b Fastener (4) 1/4” x 1-1/2” steel bolt with nut

* Full-size template available at http://stephenjressler.com/diy-engineering/.

Notes:

1. Each flange is laminated from 8 elements (V,W), with overlapping joints at the corners. Drill

the 1/4” holes in the flanges after they have been assembled.

2. Assemble the wooden frame (2 flanges and 4 longitudinal frame elements) before constructing

the cardboard shell.

3. Shell sides (a) have a 1/4” flap along both curved edges. After cutting short slits through these

flaps, as indicated on the template, fold the flaps outward. Glue the curved outer edges of the

shell top and bottom (Z) to the folded flaps on the sides (a), while also gluing the shell elements

to the wooden frame.

DIFFUSER

Component Description

c Small flange element (8) 1/4” x 1-1/2” poplar or plywood*

d Circular flange element (8) 1/4” plywood*

e Longitudinal frame element (4) 1/4” x 3/4” poplar*

f Shell (4) Lightweight cardboard*

g Fastener (4) 1/4” x 1-1/2” steel bolt with nut

* Full-size template available at http://stephenjressler.com/diy-engineering/.

Notes:

1. Each flange is laminated from 8 elements (c, d), with overlapping joints. Drill the 1/4” holes in

the flanges after they have been assembled.

2. Assemble the wooden frame (2 flanges and 4 longitudinal frame elements) before constructing

the cardboard shell.

3. Shell elements (f) should be overlapped 1/2” at their edges, glued together, and glued to the

longitudinal frame elements (e) and flanges.

FAN HOUSING

Component Description

d Circular flange element (8) 1/4” plywood*

h Circular flange element (8) 1/4” plywood*

i Longitudinal frame element (4) 1/4” x 3/8” x 4-1/2” poplar

j Fan motor mount (2) 3/8” x 1/2” x 22-1/4”

k Shell Lightweight cardboard, 4-1/2” wide

l Fan Lasko 20” household box fan with housing removed

Notes:

1. Each flange is laminated from 8 elements (d,h), with overlapping joints. Drill the 1/4” holes in

the front flange after it has been assembled.

2. Assemble the wooden frame (2 flanges, 4 longitudinal frame elements, and 2 fan motor

mounts) before constructing the cardboard shell. Drill holes in the motor mounts (j) to match the

mounting holes in the fan motor.

3. The shell element (k) is simply 4-1/2”-wide strip of cardboard fitted into the inside of the

wooden frame and glued in place.

d

d

d

d

d

d

hh

h

h

hh

h

h

i

i

i

j

j

l

FLOW STRAIGHTENER

Note: This component is optional. The wind tunnel works just fine without it, and there is no

clear improvement in the quality of measured lift data with the flow straightener installed.

Component Description

m Large frame element (8) 1/4” x 1-1/2” poplar or plywood*

n Housing element (4) 1/4” x 4” x 18-1/4” poplar or plywood

o Flow-straightener mesh 72 4”x24” strips of craft paper

72 4”x20” strips of lightweight cardboard

See Note 3 below.

Notes:

1. Flange is laminated from 8 elements (m), with overlapping joints. Drill the 1/4” holes in the

corners after the frame has been assembled.

2. Glue the flow-straightener housing (4 rectangular elements, n) to the flange before fabricating

the mesh.

3. Fabricate the flow-straightener mesh from alternating strips of craft paper and cardboard,

formed over a jig as shown on the next page.

m

m

m

m

m

m

n

n

n

n

n

o

Fabricating the Flow-Straightener Mesh

(1) Build a jig consisting of 32 1/4” dowels, each 4-1/2” long

and mounted in a board at 9/16” spacing. Clamp the jig to a

workbench as shown above.

(2) Cut a strip of craft paper 4” wide and 24” long. Weave

this paper strip over and under the dowels of the jig as shown

above. Pull the strip tight from both ends.

(3) Cut a strip of lightweight cardboard 4” wide and 20” long.

Glue it to the upper corrugations of the craft paper strip as

shown above.

(4) Clamp a board over the cardboard strip until the glue has

dried.

(5) Remove the corrugated paper-cardboard strip from the

jig. This strip will form one layer of the mesh.

(6) After trimming the strip to an 18” length, glue it inside

the flow-straightener housing as shown above. Hold each

strip in position by placing a flat board and some weights on

top of it until the glue dries.

(7) Now repeat this process 71 more times, and your flow straightener is complete!