Killer Incidence Meter - 2006/11

62 MODEL AVIATION
WHETHER YOU build from scratch, kits,
ARFs, or go RTF, you need a tool to set,
verify, and adjust the angle of your model’s
flying surfaces. Your airplane will never
perform to its potential if it’s not straight
and aligned, as the designer intended. I
own and have used the commercially
available incidence tools. The Killer
Incidence Meter, or KIM, goes a step
beyond.
Why should you go through the trouble
of making this incidence meter when you
could buy one?
• The KIM is simple and accurate. You can
have confidence in its readings.
• The KIM is adaptable. You can configure
it to measure in a way that makes sense to
you.
• The KIM is expandable. You can make
and install custom fixtures that enable you
to measure features that would otherwise
be difficult or impossible.
• The KIM will give you the fun and satisfaction of making a
precision instrument from materials you have in your scrap box.
The KIM’s most unique feature is that it can measure relative
angles. That means it is unnecessary to level your aircraft before taking
measurements. It saves time and eliminates a potential source of error.
The adjustable quadrant/scale allows you to “zero” the instrument on
whatever feature is convenient.
I might immobilize the airplane and zero the scale on the wing root
chord. Then I can slide the instrument outboard to detect warps.
Without changing the scale, I can measure the incidence of the
horizontal stabilizer. By swapping the tailstock and beam for the
thrustline fixture, still not touching the scale, I can measure engine
upthrust or downthrust.
The KIM consists of three major components: the headstock, the
tailstock, and the beam. The headstock and tailstock serve as bases for
the alignment and pendulum apparatus. The quadrant/scale and
pendulum are mounted to the headstock.
Both stocks slide freely along the beam to adapt to the feature being
measured. They clamp securely with thumbscrews once in position.
The KIM is “zeroed” at the wing root. The meter can then be transferred to other
parts of the model to check alignment relative to the wing.
Killer Incidence Meter
by Derek Moran
The KIM consists of a headstock unit with an adjustable quadrant
and mirrored scale, a tailstock, and a beam. All wood construction is
simple and lightweight.
11sig2.QXD 9/25/06 1:21 PM Page 62that if the beam is warped, the meter will give false readings.
I used close-grain spruce, but you may substitute any material
that meets the preceding criteria. Basswood stock will work, or
you might have an old yardstick or stirring stick that can be
milled to the right dimensions. You could also consider
laminating a sandwich of 1/32 plywood, 1/8 balsa, and 1/32 plywood.
The beam may be any convenient length, but 16-24 inches will
cover most situations. Save any scrap to make the internal
components of the headstock and tailstock.
Begin construction with the headstock and tailstock. They
share many common features, which should speed and simplify
your work.
The side plates should be made as matched pairs using doublestick
tape or clever machine setups to ensure that each pair is
identical. It is important to make the sides
parallel and the corners square (90°).
Make the ways and the gibs from
scraps of the beam material. This way the
headstock and tailstock will be just the
right width to allow the beam to slide
through smoothly. Make the bottom ways
and gibs as matched pairs.
I like to clamp each way-and-gib pair
together and pilot-drill the holes for the
guide pins and the strike/thumbscrew
blind nut. Be careful drilling the clearance
holes for the blind-nut barrels. The pilot
hole must be centered or you will break
through the wall of the way when you
enlarge the hole to fit the blind nut.
Begin assembly of the headstock and
tailstock by dry-fitting the bottom way,
guide pins, and gib. The guide pins should
project 3/8 inch above the bottom way and
the gib should slide freely up and down on
the pins. The guide pins retain the gib in
the stock. They must be long enough to
remain engaged when clamped to the
beam, but short enough to allow the gib to
be removed.
If all is well, set the gib aside and glue
the guide pins and blind nut to the bottom
way. Remember to trim the blind-nut
flanges so they will fit without
interference between the side plates.
Glue the top and bottom ways to one
side plate. The location of the top way
November 2006 63
Control surfaces must usually be removed before checking
incidence. This simple fixture (a piece of yardstick) clamped to a flat
sheet stabilizer lets you check alignment with the elevator in place.
A close-up of the headstock shows the quadrant adjustment,
mirrored scale, and pendulum. The simple pendulum
mechanism is reliable and extremely sensitive. The scale is
marked in 1/4° increments and resolution to 1/8° is possible.
The thrustline adapter measures upthrust/downthrust. The KIM can be used with
custom fixtures to check the alignment of features that are otherwise difficult or
impossible to measure.
The KIM’s construction is straightforward, and no special tools
are required. Materials are predominantly wood and standard
hardware items.
The building process will be much more efficient if you gather
all the materials before you start cutting. This is particularly true
if you intend to make material substitutions. Patience and
discipline here are rewarded because they will help clarify your
understanding of the project.
When selecting materials, pay extra attention to the beam.
This part must be straight, stable, and lightweight. It’s easy to see
Photos by the author
11sig2.QXD 9/25/06 1:22 PM Page 6364 MODEL AVIATION
Full-Size Plans Available—See Page 183
11sig2.QXD 9/25/06 1:23 PM Page 64November 2006 65
Full-Size Plans Available—See Page 183
11sig3.QXD 9/25/06 1:50 PM Page 6566 MODEL AVIATION
Full-Size Plans Available—See Page 183
11sig3.QXD 9/25/06 1:53 PM Page 66November 2006 67
fixes the orientation of the assembly to the
beam, so make sure the top way is parallel
to the long edge and perpendicular to the
short edge of the side plate. Once that has
set, glue on the other side plate.
Remove any glue squeeze-out on
interior surfaces because it could prevent
free movement of the beam and gib. Sand
the edges square and smooth, and radius
the corners as shown on the plans.
Each gib receives a small brad to serve
as a strike. The thumbscrew bears on the
head of the brad to prevent damage to the
wood under clamping pressure. Trim the
brad to length (1/4 inch) and glue it to the
side of the gib that faces the bottom way.
Now is a good time to sand the gib
faces so it will be .005-.010 thinner than
the top and bottom ways. This will ensure
that the gib slides freely between the side
plates. Also sand a slight chamfer or radius
on the ends to prevent the gib from
digging into the beam as the stock is
moved.
Abrade and degrease the bond area of
the two swivel shafts. The swivel shafts
are attached in two steps, the first of which
is to make a little fixture to hold the shafts
perpendicular to the bearing face of the top
way. Second, tack-glue the swivel shafts to
the back face of each stock and apply a
neat fillet of J.B. Weld or similar epoxy
with high-density filler.
Glue the quadrant mount to the back of
the headstock assembly. The quadrant
mount should be square to the bearing
surface of the top way.
Assemble the swivel mount and the Vblock
using the J.B. Weld. It is crucial for
the beveled surface of the swivel mount to
be precisely 45°.
Enlarge the plans sheet to the target
dimensions to make full-size patterns for
the quadrant, the scale, and the
antiparallax mirror. The material you
choose for the quadrant is noncritical, but
it should be flat and easy to work.
Packaged ABS and styrene sheet are
available in most hobby shops and craft
stores. Aluminized Mylar seems to be
everywhere these days, so you should have
no trouble finding a little piece for the
mirror.
I cut the outline of my quadrant on the
router, using a 1/2 plywood template and a
flush trimmer bit. I also cut the radial
clamping slot on the router. I made a
fixture to pivot the quadrant on the .063-
inch-diameter hole and swing through the
proper arc over a 1/8-inch straight cutter. If
this sounds like too much work or you
don’t have the tools, cut the quadrant
outline and slot with a hobby knife.
Spray a couple light coats of clear
lacquer or artist’s fixative on the scale to
preserve the print. Use 3M Super 77
Multipurpose Adhesive or a similar spray
contact cement to attach the scale and the
antiparallax mirror to the quadrant.
Alternately, you could make a decal or
print the scale image on adhesive-backed
label stock.
There’s nothing tricky about making
the pendulum bushing. If you have a
suitable washer in your odd-parts bin,
you’re in luck. I fabricated my washer
from thin brass stock.
When soldering, make sure the washer
is perpendicular to the axis of the bushing.
Also, try to prevent a solder fillet from
forming on the rear face of the washer. If
one does, file or scrape it away. Put a
chamfer or radius on the inside edge of the
bushing to prevent the pendulum wire
from binding.
The pendulum is also easy to make.
The only feature that needs attention is
that small-diameter hole through the nut. I
used a brass nut because it is slightly
denser than steel and is easier to crimp or
solder.
Temporarily mount the quadrant and
mark the location of the clamp screw on
the headstock. Drill and install the blind
nut on the rear side plate.
I have included plans for an optional
fixture: the thrustline adaptor. It bolts to
the engine crankshaft and enables you to
measure positive and negative shaft-line
angles. It’s an example of the sort of
custom fixtures you can devise for specific
applications.The thrustline adaptor is a simple
assembly. The only thing worth noting is
the importance of joining the beam and
shaft plate at exactly 90°.
No finish is required on the wooden
parts, but if you feel compelled you can
apply one or two coats of thinned clear
dope.
It’s time for some assembly. You’ll
need three thumbscrews; two will be 1/2
inch long and one will be 3/4 inch long.
Press the Shear-Loc knurled knobs onto
the appropriate socket-head capscrews. If
you don’t have an arbor press, you can use
your drill press. Tightly close the chuck
jaws to prevent damage to the chuck.
Install the gibs in the headstock and
tailstock. The strike faces downward,
toward the thumbscrew. Put in the
thumbscrews (the longer one goes in the
headstock) and slide the assembly onto the
beam. The beam should glide smoothly
through the stocks with little resistance
and no side play. Adjust the fit by lightly
sanding both sides of the beam.
Test the action of the clamps. They
should engage and lock with only light
torque on the thumbscrew.
Install and align the V-blocks. If you
haven’t already, drill the shaft collars to
fit on the swivel shafts. Lock the
headstock on the beam and install the
shaft collars and swivel block on its shaft.
The top of the swivel mount should be
approximately 1 inch below the headstock.
Adjust the collars so that the V-block/
swivel mount is slop-free and slightly
tight.
Put the shaft collars and V-block/
swivel mount on the tailstock, and slide it
onto the beam. You are going to need a
lightweight, cylindrical object measuring
roughly 1 inch in diameter and 3 inches
long; clean, undamaged PVC pipe will
work fine. Clamp this cylinder between
the V-blocks.
Adjust the tailstock swivel mount so
the cylinder is tangent to both surfaces of
each V-block. This usually takes a little
fiddling and sometimes requires more than
two hands.
Once this adjustment is perfect, the
centerline of each V-block is exactly the
same distance from the bearing surface of
the beam. Thus you can place the
headstock and tailstock anywhere on the
beam and be assured that no error will be
added to the meter display.
We’re almost finished. Install the
quadrant by pressing the pendulum
bushing into the pivot hole into the
quadrant mount. I did not glue the
pendulum bushing to the quadrant mount.
This makes it easy to remove or replace
the quadrant if necessary. Likewise, the
pendulum is not permanently attached.
The 1-inch leg of the pendulum wire is
enough to retain it during use.
The KIM is easy and intuitive to use, and,
as with any precision instrument, you
must be logical and methodical to get
valid, repeatable results. Before taking
any measurements, you must immobilize
the model.
At the very least you will need a block
under the fuselage ahead of the balance
point, a block at the tail, and a block under
each wing panel at midspan. Weight or
tape the airplane to these blocks to prevent
any movement.
Do not set the model on its landing
gear and expect to get consistent readings.
Consider making a fixture that is keyed to
the model and to your workbench. This
will allow you to check the airplane
periodically with minimum setup time.
The first thing to do when using the
KIM is to zero the scale. I like to start
with the wing and place the meter as close
as possible to the root.
Clamp the headstock on the beam in a
position that will result in roughly equal
overhang past both stocks. Hold the
headstock V-block on the LE while you
slide the tailstock V-block to meet the TE.
Align the meter parallel to the chord line.
The V-blocks will self-center on the LE
and TE and rotate to follow any taper in
the wing panel. Apply light pressure to the
tailstock V-block and clamp the tailstock.
Loosen the quadrant-clamp thumbscrewWhen the pendulum comes to rest,
adjust the quadrant so that the zero line on
the scale is collinear with the pendulum,
and tighten the clamp thumbscrew. The
antiparallax mirror will enable you to take
accurate readings.
The mirror reflects an image of the
backside of the pendulum wire. When you
are looking directly at the wire,
perpendicular to the scale, that image is
obscured by the wire itself, and the
reading you take from the scale is correct.
If you are looking at a slight angle, you
will see the reflected image of the wire
beside the wire itself. A reading taken
from this position will be incorrect.
Now is a good time to warn you that it
often takes quite awhile for the pendulum
to settle. It is quite sensitive and easily
affected by drafts and vibrations. In lieu
of a suitably simple and effective damping
device, I have decided to accept its
extreme sensitivity as a good thing. If you
are gluing a wing or stabilizer, it gives
you plenty of time to ponder the
permanence of the act you are about to
commit.
With the quadrant zeroed, the meter
can be transferred anywhere on the model
and give valid readings, as long as the
aircraft is not moved. The entire
headstock can even be removed from the
beam and installed on custom fixtures.
Credit Dan Rutherford for naming this
instrument. He has a knack for coining
clever, humorous, descriptive monikers. I
was quite flattered and the name has
stuck. Dan has made several KIMs that he
intends to give as gifts to certain
friends—but only after they finish
building their aircraft! MA

62 MODEL AVIATION
WHETHER YOU build from scratch, kits,
ARFs, or go RTF, you need a tool to set,
verify, and adjust the angle of your model’s
flying surfaces. Your airplane will never
perform to its potential if it’s not straight
and aligned, as the designer intended. I
own and have used the commercially
available incidence tools. The Killer
Incidence Meter, or KIM, goes a step
beyond.
Why should you go through the trouble
of making this incidence meter when you
could buy one?
• The KIM is simple and accurate. You can
have confidence in its readings.
• The KIM is adaptable. You can configure
it to measure in a way that makes sense to
you.
• The KIM is expandable. You can make
and install custom fixtures that enable you
to measure features that would otherwise
be difficult or impossible.
• The KIM will give you the fun and satisfaction of making a
precision instrument from materials you have in your scrap box.
The KIM’s most unique feature is that it can measure relative
angles. That means it is unnecessary to level your aircraft before taking
measurements. It saves time and eliminates a potential source of error.
The adjustable quadrant/scale allows you to “zero” the instrument on
whatever feature is convenient.
I might immobilize the airplane and zero the scale on the wing root
chord. Then I can slide the instrument outboard to detect warps.
Without changing the scale, I can measure the incidence of the
horizontal stabilizer. By swapping the tailstock and beam for the
thrustline fixture, still not touching the scale, I can measure engine
upthrust or downthrust.
The KIM consists of three major components: the headstock, the
tailstock, and the beam. The headstock and tailstock serve as bases for
the alignment and pendulum apparatus. The quadrant/scale and
pendulum are mounted to the headstock.
Both stocks slide freely along the beam to adapt to the feature being
measured. They clamp securely with thumbscrews once in position.
The KIM is “zeroed” at the wing root. The meter can then be transferred to other
parts of the model to check alignment relative to the wing.
Killer Incidence Meter
by Derek Moran
The KIM consists of a headstock unit with an adjustable quadrant
and mirrored scale, a tailstock, and a beam. All wood construction is
simple and lightweight.
11sig2.QXD 9/25/06 1:21 PM Page 62that if the beam is warped, the meter will give false readings.
I used close-grain spruce, but you may substitute any material
that meets the preceding criteria. Basswood stock will work, or
you might have an old yardstick or stirring stick that can be
milled to the right dimensions. You could also consider
laminating a sandwich of 1/32 plywood, 1/8 balsa, and 1/32 plywood.
The beam may be any convenient length, but 16-24 inches will
cover most situations. Save any scrap to make the internal
components of the headstock and tailstock.
Begin construction with the headstock and tailstock. They
share many common features, which should speed and simplify
your work.
The side plates should be made as matched pairs using doublestick
tape or clever machine setups to ensure that each pair is
identical. It is important to make the sides
parallel and the corners square (90°).
Make the ways and the gibs from
scraps of the beam material. This way the
headstock and tailstock will be just the
right width to allow the beam to slide
through smoothly. Make the bottom ways
and gibs as matched pairs.
I like to clamp each way-and-gib pair
together and pilot-drill the holes for the
guide pins and the strike/thumbscrew
blind nut. Be careful drilling the clearance
holes for the blind-nut barrels. The pilot
hole must be centered or you will break
through the wall of the way when you
enlarge the hole to fit the blind nut.
Begin assembly of the headstock and
tailstock by dry-fitting the bottom way,
guide pins, and gib. The guide pins should
project 3/8 inch above the bottom way and
the gib should slide freely up and down on
the pins. The guide pins retain the gib in
the stock. They must be long enough to
remain engaged when clamped to the
beam, but short enough to allow the gib to
be removed.
If all is well, set the gib aside and glue
the guide pins and blind nut to the bottom
way. Remember to trim the blind-nut
flanges so they will fit without
interference between the side plates.
Glue the top and bottom ways to one
side plate. The location of the top way
November 2006 63
Control surfaces must usually be removed before checking
incidence. This simple fixture (a piece of yardstick) clamped to a flat
sheet stabilizer lets you check alignment with the elevator in place.
A close-up of the headstock shows the quadrant adjustment,
mirrored scale, and pendulum. The simple pendulum
mechanism is reliable and extremely sensitive. The scale is
marked in 1/4° increments and resolution to 1/8° is possible.
The thrustline adapter measures upthrust/downthrust. The KIM can be used with
custom fixtures to check the alignment of features that are otherwise difficult or
impossible to measure.
The KIM’s construction is straightforward, and no special tools
are required. Materials are predominantly wood and standard
hardware items.
The building process will be much more efficient if you gather
all the materials before you start cutting. This is particularly true
if you intend to make material substitutions. Patience and
discipline here are rewarded because they will help clarify your
understanding of the project.
When selecting materials, pay extra attention to the beam.
This part must be straight, stable, and lightweight. It’s easy to see
Photos by the author
11sig2.QXD 9/25/06 1:22 PM Page 6364 MODEL AVIATION
Full-Size Plans Available—See Page 183
11sig2.QXD 9/25/06 1:23 PM Page 64November 2006 65
Full-Size Plans Available—See Page 183
11sig3.QXD 9/25/06 1:50 PM Page 6566 MODEL AVIATION
Full-Size Plans Available—See Page 183
11sig3.QXD 9/25/06 1:53 PM Page 66November 2006 67
fixes the orientation of the assembly to the
beam, so make sure the top way is parallel
to the long edge and perpendicular to the
short edge of the side plate. Once that has
set, glue on the other side plate.
Remove any glue squeeze-out on
interior surfaces because it could prevent
free movement of the beam and gib. Sand
the edges square and smooth, and radius
the corners as shown on the plans.
Each gib receives a small brad to serve
as a strike. The thumbscrew bears on the
head of the brad to prevent damage to the
wood under clamping pressure. Trim the
brad to length (1/4 inch) and glue it to the
side of the gib that faces the bottom way.
Now is a good time to sand the gib
faces so it will be .005-.010 thinner than
the top and bottom ways. This will ensure
that the gib slides freely between the side
plates. Also sand a slight chamfer or radius
on the ends to prevent the gib from
digging into the beam as the stock is
moved.
Abrade and degrease the bond area of
the two swivel shafts. The swivel shafts
are attached in two steps, the first of which
is to make a little fixture to hold the shafts
perpendicular to the bearing face of the top
way. Second, tack-glue the swivel shafts to
the back face of each stock and apply a
neat fillet of J.B. Weld or similar epoxy
with high-density filler.
Glue the quadrant mount to the back of
the headstock assembly. The quadrant
mount should be square to the bearing
surface of the top way.
Assemble the swivel mount and the Vblock
using the J.B. Weld. It is crucial for
the beveled surface of the swivel mount to
be precisely 45°.
Enlarge the plans sheet to the target
dimensions to make full-size patterns for
the quadrant, the scale, and the
antiparallax mirror. The material you
choose for the quadrant is noncritical, but
it should be flat and easy to work.
Packaged ABS and styrene sheet are
available in most hobby shops and craft
stores. Aluminized Mylar seems to be
everywhere these days, so you should have
no trouble finding a little piece for the
mirror.
I cut the outline of my quadrant on the
router, using a 1/2 plywood template and a
flush trimmer bit. I also cut the radial
clamping slot on the router. I made a
fixture to pivot the quadrant on the .063-
inch-diameter hole and swing through the
proper arc over a 1/8-inch straight cutter. If
this sounds like too much work or you
don’t have the tools, cut the quadrant
outline and slot with a hobby knife.
Spray a couple light coats of clear
lacquer or artist’s fixative on the scale to
preserve the print. Use 3M Super 77
Multipurpose Adhesive or a similar spray
contact cement to attach the scale and the
antiparallax mirror to the quadrant.
Alternately, you could make a decal or
print the scale image on adhesive-backed
label stock.
There’s nothing tricky about making
the pendulum bushing. If you have a
suitable washer in your odd-parts bin,
you’re in luck. I fabricated my washer
from thin brass stock.
When soldering, make sure the washer
is perpendicular to the axis of the bushing.
Also, try to prevent a solder fillet from
forming on the rear face of the washer. If
one does, file or scrape it away. Put a
chamfer or radius on the inside edge of the
bushing to prevent the pendulum wire
from binding.
The pendulum is also easy to make.
The only feature that needs attention is
that small-diameter hole through the nut. I
used a brass nut because it is slightly
denser than steel and is easier to crimp or
solder.
Temporarily mount the quadrant and
mark the location of the clamp screw on
the headstock. Drill and install the blind
nut on the rear side plate.
I have included plans for an optional
fixture: the thrustline adaptor. It bolts to
the engine crankshaft and enables you to
measure positive and negative shaft-line
angles. It’s an example of the sort of
custom fixtures you can devise for specific
applications.The thrustline adaptor is a simple
assembly. The only thing worth noting is
the importance of joining the beam and
shaft plate at exactly 90°.
No finish is required on the wooden
parts, but if you feel compelled you can
apply one or two coats of thinned clear
dope.
It’s time for some assembly. You’ll
need three thumbscrews; two will be 1/2
inch long and one will be 3/4 inch long.
Press the Shear-Loc knurled knobs onto
the appropriate socket-head capscrews. If
you don’t have an arbor press, you can use
your drill press. Tightly close the chuck
jaws to prevent damage to the chuck.
Install the gibs in the headstock and
tailstock. The strike faces downward,
toward the thumbscrew. Put in the
thumbscrews (the longer one goes in the
headstock) and slide the assembly onto the
beam. The beam should glide smoothly
through the stocks with little resistance
and no side play. Adjust the fit by lightly
sanding both sides of the beam.
Test the action of the clamps. They
should engage and lock with only light
torque on the thumbscrew.
Install and align the V-blocks. If you
haven’t already, drill the shaft collars to
fit on the swivel shafts. Lock the
headstock on the beam and install the
shaft collars and swivel block on its shaft.
The top of the swivel mount should be
approximately 1 inch below the headstock.
Adjust the collars so that the V-block/
swivel mount is slop-free and slightly
tight.
Put the shaft collars and V-block/
swivel mount on the tailstock, and slide it
onto the beam. You are going to need a
lightweight, cylindrical object measuring
roughly 1 inch in diameter and 3 inches
long; clean, undamaged PVC pipe will
work fine. Clamp this cylinder between
the V-blocks.
Adjust the tailstock swivel mount so
the cylinder is tangent to both surfaces of
each V-block. This usually takes a little
fiddling and sometimes requires more than
two hands.
Once this adjustment is perfect, the
centerline of each V-block is exactly the
same distance from the bearing surface of
the beam. Thus you can place the
headstock and tailstock anywhere on the
beam and be assured that no error will be
added to the meter display.
We’re almost finished. Install the
quadrant by pressing the pendulum
bushing into the pivot hole into the
quadrant mount. I did not glue the
pendulum bushing to the quadrant mount.
This makes it easy to remove or replace
the quadrant if necessary. Likewise, the
pendulum is not permanently attached.
The 1-inch leg of the pendulum wire is
enough to retain it during use.
The KIM is easy and intuitive to use, and,
as with any precision instrument, you
must be logical and methodical to get
valid, repeatable results. Before taking
any measurements, you must immobilize
the model.
At the very least you will need a block
under the fuselage ahead of the balance
point, a block at the tail, and a block under
each wing panel at midspan. Weight or
tape the airplane to these blocks to prevent
any movement.
Do not set the model on its landing
gear and expect to get consistent readings.
Consider making a fixture that is keyed to
the model and to your workbench. This
will allow you to check the airplane
periodically with minimum setup time.
The first thing to do when using the
KIM is to zero the scale. I like to start
with the wing and place the meter as close
as possible to the root.
Clamp the headstock on the beam in a
position that will result in roughly equal
overhang past both stocks. Hold the
headstock V-block on the LE while you
slide the tailstock V-block to meet the TE.
Align the meter parallel to the chord line.
The V-blocks will self-center on the LE
and TE and rotate to follow any taper in
the wing panel. Apply light pressure to the
tailstock V-block and clamp the tailstock.
Loosen the quadrant-clamp thumbscrewWhen the pendulum comes to rest,
adjust the quadrant so that the zero line on
the scale is collinear with the pendulum,
and tighten the clamp thumbscrew. The
antiparallax mirror will enable you to take
accurate readings.
The mirror reflects an image of the
backside of the pendulum wire. When you
are looking directly at the wire,
perpendicular to the scale, that image is
obscured by the wire itself, and the
reading you take from the scale is correct.
If you are looking at a slight angle, you
will see the reflected image of the wire
beside the wire itself. A reading taken
from this position will be incorrect.
Now is a good time to warn you that it
often takes quite awhile for the pendulum
to settle. It is quite sensitive and easily
affected by drafts and vibrations. In lieu
of a suitably simple and effective damping
device, I have decided to accept its
extreme sensitivity as a good thing. If you
are gluing a wing or stabilizer, it gives
you plenty of time to ponder the
permanence of the act you are about to
commit.
With the quadrant zeroed, the meter
can be transferred anywhere on the model
and give valid readings, as long as the
aircraft is not moved. The entire
headstock can even be removed from the
beam and installed on custom fixtures.
Credit Dan Rutherford for naming this
instrument. He has a knack for coining
clever, humorous, descriptive monikers. I
was quite flattered and the name has
stuck. Dan has made several KIMs that he
intends to give as gifts to certain
friends—but only after they finish
building their aircraft! MA

62 MODEL AVIATION
WHETHER YOU build from scratch, kits,
ARFs, or go RTF, you need a tool to set,
verify, and adjust the angle of your model’s
flying surfaces. Your airplane will never
perform to its potential if it’s not straight
and aligned, as the designer intended. I
own and have used the commercially
available incidence tools. The Killer
Incidence Meter, or KIM, goes a step
beyond.
Why should you go through the trouble
of making this incidence meter when you
could buy one?
• The KIM is simple and accurate. You can
have confidence in its readings.
• The KIM is adaptable. You can configure
it to measure in a way that makes sense to
you.
• The KIM is expandable. You can make
and install custom fixtures that enable you
to measure features that would otherwise
be difficult or impossible.
• The KIM will give you the fun and satisfaction of making a
precision instrument from materials you have in your scrap box.
The KIM’s most unique feature is that it can measure relative
angles. That means it is unnecessary to level your aircraft before taking
measurements. It saves time and eliminates a potential source of error.
The adjustable quadrant/scale allows you to “zero” the instrument on
whatever feature is convenient.
I might immobilize the airplane and zero the scale on the wing root
chord. Then I can slide the instrument outboard to detect warps.
Without changing the scale, I can measure the incidence of the
horizontal stabilizer. By swapping the tailstock and beam for the
thrustline fixture, still not touching the scale, I can measure engine
upthrust or downthrust.
The KIM consists of three major components: the headstock, the
tailstock, and the beam. The headstock and tailstock serve as bases for
the alignment and pendulum apparatus. The quadrant/scale and
pendulum are mounted to the headstock.
Both stocks slide freely along the beam to adapt to the feature being
measured. They clamp securely with thumbscrews once in position.
The KIM is “zeroed” at the wing root. The meter can then be transferred to other
parts of the model to check alignment relative to the wing.
Killer Incidence Meter
by Derek Moran
The KIM consists of a headstock unit with an adjustable quadrant
and mirrored scale, a tailstock, and a beam. All wood construction is
simple and lightweight.
11sig2.QXD 9/25/06 1:21 PM Page 62that if the beam is warped, the meter will give false readings.
I used close-grain spruce, but you may substitute any material
that meets the preceding criteria. Basswood stock will work, or
you might have an old yardstick or stirring stick that can be
milled to the right dimensions. You could also consider
laminating a sandwich of 1/32 plywood, 1/8 balsa, and 1/32 plywood.
The beam may be any convenient length, but 16-24 inches will
cover most situations. Save any scrap to make the internal
components of the headstock and tailstock.
Begin construction with the headstock and tailstock. They
share many common features, which should speed and simplify
your work.
The side plates should be made as matched pairs using doublestick
tape or clever machine setups to ensure that each pair is
identical. It is important to make the sides
parallel and the corners square (90°).
Make the ways and the gibs from
scraps of the beam material. This way the
headstock and tailstock will be just the
right width to allow the beam to slide
through smoothly. Make the bottom ways
and gibs as matched pairs.
I like to clamp each way-and-gib pair
together and pilot-drill the holes for the
guide pins and the strike/thumbscrew
blind nut. Be careful drilling the clearance
holes for the blind-nut barrels. The pilot
hole must be centered or you will break
through the wall of the way when you
enlarge the hole to fit the blind nut.
Begin assembly of the headstock and
tailstock by dry-fitting the bottom way,
guide pins, and gib. The guide pins should
project 3/8 inch above the bottom way and
the gib should slide freely up and down on
the pins. The guide pins retain the gib in
the stock. They must be long enough to
remain engaged when clamped to the
beam, but short enough to allow the gib to
be removed.
If all is well, set the gib aside and glue
the guide pins and blind nut to the bottom
way. Remember to trim the blind-nut
flanges so they will fit without
interference between the side plates.
Glue the top and bottom ways to one
side plate. The location of the top way
November 2006 63
Control surfaces must usually be removed before checking
incidence. This simple fixture (a piece of yardstick) clamped to a flat
sheet stabilizer lets you check alignment with the elevator in place.
A close-up of the headstock shows the quadrant adjustment,
mirrored scale, and pendulum. The simple pendulum
mechanism is reliable and extremely sensitive. The scale is
marked in 1/4° increments and resolution to 1/8° is possible.
The thrustline adapter measures upthrust/downthrust. The KIM can be used with
custom fixtures to check the alignment of features that are otherwise difficult or
impossible to measure.
The KIM’s construction is straightforward, and no special tools
are required. Materials are predominantly wood and standard
hardware items.
The building process will be much more efficient if you gather
all the materials before you start cutting. This is particularly true
if you intend to make material substitutions. Patience and
discipline here are rewarded because they will help clarify your
understanding of the project.
When selecting materials, pay extra attention to the beam.
This part must be straight, stable, and lightweight. It’s easy to see
Photos by the author
11sig2.QXD 9/25/06 1:22 PM Page 6364 MODEL AVIATION
Full-Size Plans Available—See Page 183
11sig2.QXD 9/25/06 1:23 PM Page 64November 2006 65
Full-Size Plans Available—See Page 183
11sig3.QXD 9/25/06 1:50 PM Page 6566 MODEL AVIATION
Full-Size Plans Available—See Page 183
11sig3.QXD 9/25/06 1:53 PM Page 66November 2006 67
fixes the orientation of the assembly to the
beam, so make sure the top way is parallel
to the long edge and perpendicular to the
short edge of the side plate. Once that has
set, glue on the other side plate.
Remove any glue squeeze-out on
interior surfaces because it could prevent
free movement of the beam and gib. Sand
the edges square and smooth, and radius
the corners as shown on the plans.
Each gib receives a small brad to serve
as a strike. The thumbscrew bears on the
head of the brad to prevent damage to the
wood under clamping pressure. Trim the
brad to length (1/4 inch) and glue it to the
side of the gib that faces the bottom way.
Now is a good time to sand the gib
faces so it will be .005-.010 thinner than
the top and bottom ways. This will ensure
that the gib slides freely between the side
plates. Also sand a slight chamfer or radius
on the ends to prevent the gib from
digging into the beam as the stock is
moved.
Abrade and degrease the bond area of
the two swivel shafts. The swivel shafts
are attached in two steps, the first of which
is to make a little fixture to hold the shafts
perpendicular to the bearing face of the top
way. Second, tack-glue the swivel shafts to
the back face of each stock and apply a
neat fillet of J.B. Weld or similar epoxy
with high-density filler.
Glue the quadrant mount to the back of
the headstock assembly. The quadrant
mount should be square to the bearing
surface of the top way.
Assemble the swivel mount and the Vblock
using the J.B. Weld. It is crucial for
the beveled surface of the swivel mount to
be precisely 45°.
Enlarge the plans sheet to the target
dimensions to make full-size patterns for
the quadrant, the scale, and the
antiparallax mirror. The material you
choose for the quadrant is noncritical, but
it should be flat and easy to work.
Packaged ABS and styrene sheet are
available in most hobby shops and craft
stores. Aluminized Mylar seems to be
everywhere these days, so you should have
no trouble finding a little piece for the
mirror.
I cut the outline of my quadrant on the
router, using a 1/2 plywood template and a
flush trimmer bit. I also cut the radial
clamping slot on the router. I made a
fixture to pivot the quadrant on the .063-
inch-diameter hole and swing through the
proper arc over a 1/8-inch straight cutter. If
this sounds like too much work or you
don’t have the tools, cut the quadrant
outline and slot with a hobby knife.
Spray a couple light coats of clear
lacquer or artist’s fixative on the scale to
preserve the print. Use 3M Super 77
Multipurpose Adhesive or a similar spray
contact cement to attach the scale and the
antiparallax mirror to the quadrant.
Alternately, you could make a decal or
print the scale image on adhesive-backed
label stock.
There’s nothing tricky about making
the pendulum bushing. If you have a
suitable washer in your odd-parts bin,
you’re in luck. I fabricated my washer
from thin brass stock.
When soldering, make sure the washer
is perpendicular to the axis of the bushing.
Also, try to prevent a solder fillet from
forming on the rear face of the washer. If
one does, file or scrape it away. Put a
chamfer or radius on the inside edge of the
bushing to prevent the pendulum wire
from binding.
The pendulum is also easy to make.
The only feature that needs attention is
that small-diameter hole through the nut. I
used a brass nut because it is slightly
denser than steel and is easier to crimp or
solder.
Temporarily mount the quadrant and
mark the location of the clamp screw on
the headstock. Drill and install the blind
nut on the rear side plate.
I have included plans for an optional
fixture: the thrustline adaptor. It bolts to
the engine crankshaft and enables you to
measure positive and negative shaft-line
angles. It’s an example of the sort of
custom fixtures you can devise for specific
applications.The thrustline adaptor is a simple
assembly. The only thing worth noting is
the importance of joining the beam and
shaft plate at exactly 90°.
No finish is required on the wooden
parts, but if you feel compelled you can
apply one or two coats of thinned clear
dope.
It’s time for some assembly. You’ll
need three thumbscrews; two will be 1/2
inch long and one will be 3/4 inch long.
Press the Shear-Loc knurled knobs onto
the appropriate socket-head capscrews. If
you don’t have an arbor press, you can use
your drill press. Tightly close the chuck
jaws to prevent damage to the chuck.
Install the gibs in the headstock and
tailstock. The strike faces downward,
toward the thumbscrew. Put in the
thumbscrews (the longer one goes in the
headstock) and slide the assembly onto the
beam. The beam should glide smoothly
through the stocks with little resistance
and no side play. Adjust the fit by lightly
sanding both sides of the beam.
Test the action of the clamps. They
should engage and lock with only light
torque on the thumbscrew.
Install and align the V-blocks. If you
haven’t already, drill the shaft collars to
fit on the swivel shafts. Lock the
headstock on the beam and install the
shaft collars and swivel block on its shaft.
The top of the swivel mount should be
approximately 1 inch below the headstock.
Adjust the collars so that the V-block/
swivel mount is slop-free and slightly
tight.
Put the shaft collars and V-block/
swivel mount on the tailstock, and slide it
onto the beam. You are going to need a
lightweight, cylindrical object measuring
roughly 1 inch in diameter and 3 inches
long; clean, undamaged PVC pipe will
work fine. Clamp this cylinder between
the V-blocks.
Adjust the tailstock swivel mount so
the cylinder is tangent to both surfaces of
each V-block. This usually takes a little
fiddling and sometimes requires more than
two hands.
Once this adjustment is perfect, the
centerline of each V-block is exactly the
same distance from the bearing surface of
the beam. Thus you can place the
headstock and tailstock anywhere on the
beam and be assured that no error will be
added to the meter display.
We’re almost finished. Install the
quadrant by pressing the pendulum
bushing into the pivot hole into the
quadrant mount. I did not glue the
pendulum bushing to the quadrant mount.
This makes it easy to remove or replace
the quadrant if necessary. Likewise, the
pendulum is not permanently attached.
The 1-inch leg of the pendulum wire is
enough to retain it during use.
The KIM is easy and intuitive to use, and,
as with any precision instrument, you
must be logical and methodical to get
valid, repeatable results. Before taking
any measurements, you must immobilize
the model.
At the very least you will need a block
under the fuselage ahead of the balance
point, a block at the tail, and a block under
each wing panel at midspan. Weight or
tape the airplane to these blocks to prevent
any movement.
Do not set the model on its landing
gear and expect to get consistent readings.
Consider making a fixture that is keyed to
the model and to your workbench. This
will allow you to check the airplane
periodically with minimum setup time.
The first thing to do when using the
KIM is to zero the scale. I like to start
with the wing and place the meter as close
as possible to the root.
Clamp the headstock on the beam in a
position that will result in roughly equal
overhang past both stocks. Hold the
headstock V-block on the LE while you
slide the tailstock V-block to meet the TE.
Align the meter parallel to the chord line.
The V-blocks will self-center on the LE
and TE and rotate to follow any taper in
the wing panel. Apply light pressure to the
tailstock V-block and clamp the tailstock.
Loosen the quadrant-clamp thumbscrewWhen the pendulum comes to rest,
adjust the quadrant so that the zero line on
the scale is collinear with the pendulum,
and tighten the clamp thumbscrew. The
antiparallax mirror will enable you to take
accurate readings.
The mirror reflects an image of the
backside of the pendulum wire. When you
are looking directly at the wire,
perpendicular to the scale, that image is
obscured by the wire itself, and the
reading you take from the scale is correct.
If you are looking at a slight angle, you
will see the reflected image of the wire
beside the wire itself. A reading taken
from this position will be incorrect.
Now is a good time to warn you that it
often takes quite awhile for the pendulum
to settle. It is quite sensitive and easily
affected by drafts and vibrations. In lieu
of a suitably simple and effective damping
device, I have decided to accept its
extreme sensitivity as a good thing. If you
are gluing a wing or stabilizer, it gives
you plenty of time to ponder the
permanence of the act you are about to
commit.
With the quadrant zeroed, the meter
can be transferred anywhere on the model
and give valid readings, as long as the
aircraft is not moved. The entire
headstock can even be removed from the
beam and installed on custom fixtures.
Credit Dan Rutherford for naming this
instrument. He has a knack for coining
clever, humorous, descriptive monikers. I
was quite flattered and the name has
stuck. Dan has made several KIMs that he
intends to give as gifts to certain
friends—but only after they finish
building their aircraft! MA