Build a
Propeller
Pitch
Gauge
May 2007 55
by Don Ogren
HAVE YOU EVER noticed that after
you break a propeller and replace it
with another propeller that is the same
brand, size, and pitch, the model
sometimes flies differently? The
reason is simple: the propellers are
different. It’s easy to verify the same
diameter when replacing a propeller,
but confirming the pitch is more
difficult.
Different propellers make a
difference in the way airplanes fly. In
RC sport flying we could seldom care
less. After a bad landing we stick on a
similar propeller and have our model
back in the air as soon as we straighten
the landing gear.
In a speed event such as Pylon
Racing or in competitive CL or RC
Aerobatics, the need for consistent and
optimum performance requires that the
propellers be consistently optimal. If
we can’t detect the differences in
propellers and select the best, we
won’t be able to predict the outcome of
our pending flights.
At the 2002 Brodak Fly-In I bought
a few wood 10 x 6 propellers and
found them (measuring on a crudely
made pitch gauge) to have pitches of
roughly 5.5 inches (at midblade).
Several of the propellers were marked
as having 6-inch pitches, but none did.
So the question arises: Where does
a manufacturer measure the pitch for
determining what numbers go on the
propeller?
When you measure the pitch of
propellers, you may come to the same
conclusion I have: Who really cares?
As long as one has the same pitch as
another at the same blade station, we
should expect consistent results in the
air, in CL lap times, and in
performance in all our models (while
other variables remain constant).
Pitch-gauge sources are few. Then
when we research the neat features and
prices, we might reason that we’ve
gotten along without one for umpteen
years, so why lay out big bucks for
such a device now? Aren’t there any
good, inexpensive pitch gauges?
I started to think about this, and
being a mechanical engineer who still
enjoys a design challenge, it didn’t
take too long for me to come up with
an idea or two. The objective was to
design a pitch gauge that would be
All the parts of the pitch gauge and the blade angle vs. blade pitch chart. Each blade station has its own graphed line.
05sig2.QXD 3/23/07 1:36 PM Page 55
56 MODEL AVIATION
A typical propeller setup. A 1/4 plywood
spacer is positioned under the propeller
hub.
The wire part of the gauge has a “dogleg” bend so it will measure the pitch angle
directly over a blade station. This allows accurate readings for tractor and reversepitch
propellers.
The heart of the pitch gauge: the angle
indicator.
The protractor scale was copied onto white paper from a regular engineer’s
protractor, cut out, and then pasted onto the 1/16 plywood.
simple to use, give accurate results, and
cost less than those available.
The usual expectation is that
something that is simple and less
expensive won’t do the job of the
expensive gadgets. I would have to be
careful to try to design this concept
away.
Pitch gauges I had seen on the
market did a great job. They indicated
the pitch angle at a radius/position on
the blade, which I’ll refer to as a
“station,” and the pitch for any given
blade station.
However, I didn’t like the common
feature of most gauges that required the
propeller to be mounted front-side up.
That meant the blade angle had to be
read from the bottom side of the
propeller, which was hard to see.
My approach to a design was to look
at the flat portion of the blade. (The
back side of the propeller would face
up.) The angle indicator would rest on
the blade and be easy to see.
What could be simpler than that?
And why should something cost more
than a few hours of shop time and a
few bucks to make, with most parts
fashioned from materials that could be
found in most modelers’ scrap boxes?
My design criteria for the pitch
gauge were to:
1) Make it small enough to store
easily.
2) Make it cover the most often
used propeller-diameter range for a
variety of sport fliers: 6-20 inches.
3) Make it so it could be
constructed in a modeler’s workshop.
4) Make it without bells and
whistles. Use a “pitch chart” plotted in
blade angle vs. pitch instead of
reading it directly on the pitch gauge
(a compromise)—a feature that could
be added later.
5) Make it easy to use.
Without describing what the
prototype gauge looked like, I’ll just
tell you that it worked and proved many
points. My objective of simplicity was
achieved in the final design, which is
presented here.
Materials and Construction: The base
is nominal 1 x 3-inch select pine—
actually 3/4 x 21/2 inch—cut to a length
of 8 inches. The slots for the angle
indicator are cut 3/16 inch deep at
locations of 2.0, 2.5, 3.0, 3.5, 4.0, 4.5,
5.0, and 5.5 inches, measured from the
Photos/drawings by the author
05sig2.QXD 3/23/07 2:22 PM Page 56
May 2007 57
The blade is shown to have a 15° angle at
the 3.0-inch station, yielding a 5-inch
The fixture under the propeller as it is pitch after the procedure.
mounted facing upward. A pusher/reverse-pitch propeller on the
pitch gauge. Turning the angle indicator
to face the opposite direction makes the
gauge usable for both types of propellers.
center of the 1/4-inch-diameter hole for
the propeller mounting screw.
I used a Dremel table saw to cut the
1/16-inch slots perpendicular to the
propeller centerline, at a constant depth.
Careful measurement and setup while
sawing resulted in accurately spaced
blade stations.
A Dremel saw blade cuts slightly
less than 1/16 inch, so I used tape on the
saw blade to make it wobble enough to
allow the 1/16 plywood to slide in the
slots. This range of stations will
accommodate 8- to 20-inch-diameter
propellers.
The propeller mounting screw is a 1/4
x 21/2-inch-long carriage bolt, pressed
into a counterbored hole in the base. A
washer and a wing nut hold the
propeller in place.
Propeller spacers measuring 3/16 and
1/4 x 1 inch in diameter are cut from
plywood to raise the propeller off the
base. In most cases this allows the angle
indicator to be moved from station to
station without having to loosen the
wing nut. The thinner spacer can be
used with lower-pitched propellers.
The angle indicator is cut from 1/16
plywood, which fits the base slots. I
selected .047-inch-diameter wire simply
because it fit the E-Z adjust connector I
found in my collection of parts.
Probably the most common size of
connector will have larger holes for
pushrod-size wire. That size connector
would be okay to use, but I recommend
using wire that is smaller than 1/16 inch
in diameter for bending ease. I filed a
point on the end to the wire for a more
precise reading.
Also, the pivot point of the
connector, the wire, and the protractor’s
“0” need to be in horizontal alignment
with the reference slots and base.
The pitch chart has a graphed line for
each blade station. I made calculations
and then plotted the “y” coordinates for
every 2° of pitch for each station. This
isn’t as much work as it looks because
the circular (one revolution) distance of
each station is a constant and is simply
multiplied by the tangent of the angles.
Using the Pitch Gauge: After a propeller
has been centered on the base and
secured with the wing nut, place the
angle indicator at the blade station to be
measured. I start at midblade or the
station nearest the maximum blade
width. You can slide the gauge in the
slot so the wire comes to rest on the flat
of the blade.
Some propellers have a camber on the
underside, making it more difficult to
measure. But once you’ve chosen the
flattest part of the blade for
measurement, you should use this same
relative position for all your
measurements.
Your best guess may have to work
here, as with any pitch gauge. But, as
you can see, having a good view of the
angle-detection part of the gauge on the
flat side of the propeller makes the
device a cinch to use.
As the wire rests on the propeller,
read the angle from the protractor. Go to
the chart, find the angle on the “x” axis,
and go up the chart to the line that is
labeled for that blade station. Then go to
the left “y” axis and read the pitch.
As you use the pitch gauge more,
you’ll want to jot down your readings at
different stations for comparison and
future reference. I did this on a propeller,
which came with an engine I purchased
on eBay, that was marked as an “Aldrich
Custom” 10 x 61/2—a brand I had never
seen. (Yes, the late George Aldrich also
designed and marketed propellers.)
While observing the propeller I
noticed that the blades had a nice twist
to them, departing from most
propellers’ nearly “flat paddle.” I
measured this propeller and found it to
be extremely close to a constant 6-inch
pitch from the hub to the tip (but not the
61/2-inch pitch)!
Most propellers are not pitched as
constant as this. This constant pitch
indicated to me that the propeller’s
pulling power was more uniformly
distributed along the blade.
At this point I began to realize that
propellers are interesting things to
study. And the more we can learn about
the equipment we fly, the better we will
fly.
A Bolly 111/4 x 4 propeller wasn’t
pulling well for me—my CL lap times
were high—so I decided to repitch it to
5 inches. The chart shows that 15° will
yield a pitch of 5 inches at the 3.0-inch
station, so I made a “fixture” of 15°
with which to work.
This has been an interesting project for
me, and I hope you’ll enjoy making a
gauge for your personal use. If you want
a pitch gauge and don’t want to make
one, contact me in May. I’ll be set up
for production by then, and I’ll put your
name and pitch gauge on hold until I
can ship to you. The cost will be $25
plus $5 shipping and handling (in the
continental US).
Have fun and fly safely! MA
Don Ogren
6172 Prestwick Ct.
Spring Hill FL 34606
(352) 666-2901
[email protected]
05sig2.QXD 3/23/07 2:24 PM Page 57
3/8
45/8
35/8
27/16
215/16 R (Ref.)
1/4
1/16
5
6
7
Dia.
Pitch Indictor
(full-size pattern)
Angle
Scale
(full size)
58 MODEL AVIATION
Pitch Gauge
Designed by: Don Ogren
Date: Nov.10, 2006
31/8
21/8
1/2
1/2
Indicating Wire
.047 inch diameter
(full-size pattern)
* See photographs for assembly and use.
Notes: *
Dimensions + 1/64 inch, all from
center of propeller mounting hole.
Slots every 1/2 inch up to 51/2 inches.
Drill 1/4 inch diameter through. Countersink
bottom side for carriage bolt head
Slots 3/16 inch deep x 1/16 inch wide
for pitch indicator
Chamfer corners 1/4 inch x 1/4 inch optional
1/16 inch aircraft plywood
Zero reference
Attach angle scale with
glue stick. Cover
with clear tape
for protection.
1
2
3
4
5
6
7
21/2
11/2
21/2
8
3/4
2
3
1
Clear Pine
Base
(half size)
4
05sig2.QXD 3/23/07 2:26 PM Page 58
3/8
45/8
35/8
27/16
215/16 R (Ref.)
1/4
1/16
5
6
7
Dia.
Pitch Indictor
(full-size pattern)
Angle
Scale
(full size)
58 MODEL AVIATION
Pitch Gauge
Designed by: Don Ogren
Date: Nov.10, 2006
31/8
21/8
1/2
1/2
Indicating Wire
.047 inch diameter
(full-size pattern)
* See photographs for assembly and use.
Notes: *
Dimensions + 1/64 inch, all from
center of propeller mounting hole.
Slots every 1/2 inch up to 51/2 inches.
Drill 1/4 inch diameter through. Countersink
bottom side for carriage bolt head
Slots 3/16 inch deep x 1/16 inch wide
for pitch indicator
Chamfer corners 1/4 inch x 1/4 inch optional
1/16 inch aircraft plywood
Zero reference
Attach angle scale with
glue stick. Cover
with clear tape
for protection.
1
2
3
4
5
6
7
21/2
11/2
21/2
8
3/4
2
3
1
Clear Pine
Base
(half size)
4
05sig2.QXD 3/23/07 2:26 PM Page 58