94 MODEL AVIATION
Model Aviation Hall of Fame member and noted model builder Larry Davidson’s
special sanding fixture uses a Dremel motor speed control and Sears drum sander.
Sanding wing dihedral and polyhedral joints
? Frequently Asked Questions Bob Aberle | [email protected]
Also included in this column:
• Du-Bro Micro Profile
Landing Gear
• Rubber-band replacement
• Expo rate control
• Battery-storage
recommendations
Notice that the wing section has been elevated to the proper angle. A couple passes
with the sanding drum results in a perfect dihedral joint.
THIS IS THE 39th monthly column in
which I try to give you the best possible
answers to questions you have written or
E-mailed to me. Each new inquiry is
given a sequential number for future
reference.
Many questions and answers have
been posted to the AMA Web site at
www.modelaircraft.org/mag/faq/index.asp.
Unfortunately that posting stopped in
August 2005 and will not continue until
this section of the AMA Web site is
revamped. In the meantime, if you can’t
find the subject matter you are interested
in, drop me an E-mail or letter and I will
try to assist you.
Q295: “I’ve been building model aircraft
for quite a long time. But I have to admit
that despite all my experience there is one
aspect of the building process that drives
me crazy and that is cutting the proper
angle for a dihedral or polyhedral wing
joints. Is there any tool or machine
available to make this job easier?”
A295: Years ago a company offered a
wing-joint sander that allowed a sanding
block to ride on rails, or a track. You
physically moved the sanding block back
and forth to sand the proper angle into
your wing-section joint. It was still a
difficult job because the wing could
easily shift position.
Recently I asked longtime friend
Larry Davidson, whom I consider to be a
master model builder, how he cuts his
dihedral joints. Several photos are
included, and I think they tell the story
best.
Larry made a track, or pair of rails,
from pieces of aluminum. He employed
an old surplus motor he powers with a
Dremel motor speed control (model 219).
06sig3.QXD 4/23/07 12:23 PM Page 94
June 2007 95
BatteryUniversity.com is a free service that is available to anyone. Recently posted
reports on battery-storage techniques are must-reads.
Du-Bro’s new Micro Profile Landing Gear assembly. Note the height and width. It is
meant for larger park flyers, such as those in the 25- to 30-ounce weight class!
Du-Bro design engineers developed this neat
attachment scheme. One screw is required
to anchor the landing gear in place.
Transmitter LCD shows channel 4 (ruddercontrol
function) set for 30% expo rate
control. This type control can help smooth
rudder application, especially when taking
off and landing.
Popular sizes of rubber bands used in our hobby. The top two
(46 and 33) typically hold wings onto fuselages.
He attached a large-diameter Sears drum sander to the motor
shaft. The speed control allows Larry to adjust the drum sander’s
speed.
The wing is placed on a flat board and elevated to the proper
dihedral or polyhedral angle. While holding the wing to the
board, Larry moves the drum sander back and forth on the metal
track. All it takes is several passes to establish a perfect-fitting
joint.
After seeing this I’m sure many modelers will be able to
duplicate Larry’s sanding device. Honestly I’m hoping that some
enterprising modeler will decide to build the device and market
it. What say?
Q296: “I’m trying to design some ‘foamie type’ E-3-D models
for the fun of it. Most likely I will employ a profile fuselage
because it is fast to build and basically a simple structure.
“But one of the items I could use is a good, lightweight
landing gear assembly that is expressly designed for use with a
profile fuselage. To your knowledge is there a product out there
that I have missed?”
A296: In the December 2006 MA on page 104 (question-andanswer
263) I showed a metal landing gear that was intended for
profile fuselages, offered by 3D Hobby Shop. This will certainly
work, but it comes in only one size.
06sig3.QXD 4/23/07 11:32 AM Page 95
I recently learned that Du-Bro came out
with a Micro Profile Landing Gear
(catalog number 943) that is made from a
plastic material. As shown, it has an
interesting mounting pad that should work
well with balsa or foam profile fuselages.
However, this gear is large and will
probably be best suited for larger parking
lot flyers, such as those weighing 25-30
ounces with 300 square inches of wing
area and 100-125 watts of input power. I
like this gear’s mounting design and
overall quality, but I suggest to my friends
at Du-Bro that they consider several other
smaller sizes. You can find this gear at
www.shopatron.com/product/product_id=
DUB943/101.0.
Q297: “I’m sure you can’t use rubber
bands over and over again without noting
some form of deterioration. Since we use
these rubber bands, in many cases, to hold
our wings in place, are there any
precautions that I should take?”
A297: I purchase my rubber bands mostly
in bulk packages from one of the national
stationery stores such as Staples or Office
Max. The price is certainly right.
You should select a rubber band that is
the right size for the particular application.
For my larger models, say 4 pounds and
heavier, I use the old time-honored size 64
rubber band. My smaller parking lot flyers
do better with a size 33 rubber band. For
the propeller savers on my small AXI
brushless motors, I have been using the
much smaller size 11.
When I used rubber bands on my glowfueled-
powered aircraft years ago, I
discarded the bands after each flying
session, no matter what! That is because
they had a fuel-residue coating after
several flights, and that softened the
rubber, causing them to disintegrate
quickly.
When it came to “clean” electricpowered
flight I was tempted to save or
reuse my wing hold-down rubber bands.
Don’t do it! Throw the rubber bands out
after every flight. The sun’s ultraviolet
rays cause the rubber to deteriorate
quickly. If your model’s wing falls off the
fuselage in flight, it won’t matter how
good your RC system is; the aircraft will
be history!
Q298: “A fellow club member of mine
seems to think that I can use exponential
(expo) rate control on my rudder function
to help smooth out the ground
maneuvering of my four-channel RC
aircraft.
“Will that really prove a help? It seems
that when I taxi to and from the takeoff
area and even during my takeoff run, my
aircraft zigs and zags all over the place!”
A298: I did much of my original
proportional-control flying in the late
1950s and early 1960s using a form of
single-stick RC transmitter. You held the
transmitter case with your left hand. Your
index finger worked the throttle. Your
right hand gripped a single control stick
that provided a three-axis control.
You rocked the stick left and right for
aileron control, moved it up and down for
elevator or pitch control, and rotated the
entire stick for rudder control. It felt
natural to me then.
Eventually everyone gravitated toward
dual transmitter stick control. To my
disappointment I was eventually forced to
steer the aircraft with rudder using my left
hand and bank the model with my right
hand using the ailerons. I found that my
left hand could not smoothly steer the
airplane while it was on the ground.
Then I learned about expo rate control.
It provides a nonlinear response between
the control stick and the rudder-servo
output. Moving the stick initially supplies
only a small amount of rudder control.
Hence the aircraft doesn’t jump all over
the place. It is smoothed out by virtue of
the nonlinear control output.
The smoother you want your rudder
steering control, the more rudder expo you
“dial in.” That means you increase the
percentage figure shown on your
transmitter’s LCD screen.
In the accompanying photo the expo
was set for 30%, which is a modest
amount. The higher the number, the more
desensitization you get.
I use rudder expo control on all my
four-channel-function aircraft these days. I
make sure all my RC transmitters have
expo on the rudder-control function. I
strongly recommend using that control
feature.
Q299: “I hear all kinds of suggestions for
the storage of the various batteries that we
use in our RC aircraft hobby. Is there a
good single reference that might guide me
in the right direction?”
A299: I recently found an excellent
reference for storing our batteries. It has
been mentioned many times on various
model forums and even in battery columns
such as Red Scholefield’s “The Battery
Clinic” published in MA.
BatteryUniversity.com—www.battery
university.com/partone-19.htm—was
created and is maintained by Isidor
Buchmann of Vancouver, British
Columbia, Canada. He has many
interesting suggestions for storing various
battery types. You can find other battery
subjects on the site as well.
Noted model author Greg Covey just
expanded on these battery-storage
suggestions in an article on page 100 of the
January 2007 Quiet Flyer magazine. MA
96 MODEL AVIATION
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