Frequently Asked Questions - 2009/05

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format going. When
referring to already
published Q-and-As
(for follow-ups),
provide the number
as a reference.
References to addresses and Web sites are now placed in a group,
separate from the text, at the end of this column under “Sources.”
Q397: “I realize that today there are so many ARF and RTF model
aircraft available that there is little need to build a model from scratch
(with raw materials). But I still like the sense of accomplishment when
I construct a model and then go out and fly it.
“The only problem I have is cutting out all the parts. This is
especially true when it comes to the wing ribs and fuselage formers. I
hear a lot today about laser cutting of parts. How difficult is it to get
someone to laser cut certain parts of an aircraft to speed up the
assembly process?”
A397: This is an excellent question that I have been waiting for. Let’s
backtrack for a moment.
If you look inside any ARF
or RTF that is currently on the
market, it will come as no
surprise that the internal
components (structure) consist
mainly of laser-cut parts. You
can easily see the light-brown
edges that the laser creates as it
“cuts” (actually burns) through
the wood. Laser-cutting not
only accelerates the
construction process, but it also
allows the aircraft to be built
precisely time and time again.
Laser-cutting parts
May 2009 87
? Frequently Asked Questions Bob Aberle | [email protected]
Also included in this column:
• Throttle-to-elevator mixing
• Designing model aircraft
Above: Aero Craft co-owner Bill
Schaefer selects a specific grade of balsa
before cutting block material into
sheets. The sheets are sanded before
going to the laser cutter.
Right: The laser cutter produces a series
of wing ribs for the 12-foot-span Senior
Telemaster kit, which is distributed by
Hobby Lobby.
Bill holds the finished product; the ribs only have to be
removed from the balsa sheet. Just one layer of balsa
can be cut at a time.
Aero Craft’s laser cutter is capable of holding at least six sheets of balsa at a
time. The speed at which it cuts depends on the material’s thickness.
05sig3.QXD 3/25/09 9:07 AM Page 87
for laser-cutting model parts. There are
companies besides Aero Craft that provide this
kind of service, including Bob Holman Plans
in San Bernardino, California; Laser Works
Engraving and Design in Wichita Falls, Texas;
Manzano Laser Works in Tijeras, New
Mexico; Ohio Laser Engraving in Fairborn,
Ohio; and others. You can find these
companies’ contact information in the
“Sources” list.
Q398: “I have an RC scale model that has a
cowled-in engine with a large spinner. When I
built this plane I set up the engine location for
zero/zero thrust. In other words my engine has
neither side thrust nor any up or down thrust.
“The problem I have found is that as I
apply more and more power in flight, there is
a tendency for the nose to pitch up. When that
happens I have to compensate by applying
some down elevator. Going back and forth
between throttle and elevator is proving very
annoying. I realize to correct this situation I
need to add some down thrust, but that would
involve extensive motor mount and cowl
alterations. It also wouldn’t look right on this
particular scale aircraft. Can you help me
out?”
A398: The answer to this reader’s problem
came from my old friend, Nick Ziroli Sr.,
whose helpful solution may surprise you.
Most of us who fly any model of value,
such as a scale aircraft, use a transmitter with
programmable control features. That being the
case, Nick often mixes elevator control with
throttle commands at the transmitter. As he
increases the engine throttle, he adds downelevator
compensation. He does this with his
Airtronics RDS8000 digital spread spectrum
transmitter, but all RC manufacturers offer
basically the same mixing capability.
The higher the throttle-stick position on the
transmitter, the more down-elevator he applies
at the same time. As the flying speed increases
and the nose wants to pitch up, the downelevator
(that is mixed in) can compensate and
lower the nose attitude.
When you get down to it, this is an even
better solution than adding downthrust. The
message is clear: when you have these extra
features available on your RC transmitter, use
them. Great idea, Nick!
Q399: “Bob I’ve read many of your
construction articles over the years. I suspect
that you, Dick Sarpolus and Nick Ziroli, Sr.
probably have set the record for the most
have switched from die-cutting and sawcutting
wood parts to laser-cutting. Their one
machine has a large cutting area that accepts
various thicknesses of balsa and plywood. It is
powerful, which means that it can cut rapidly.
Only one layer of material may be lasercut
at a time; you can’t stack wood sheets and
slice through them on one pass. Thus it is
important that as many pieces as possible be
cut from a single sheet. That means less
waste. The layout of the parts on the cutting
surface is therefore a critical part of the
process.
As do several hobby companies that use
laser-cutting, Craig and Bill sell their service
to modelers who want ribs, formers, or other
parts cut. Each company that offers this kind
of service will likely have different “input
requirements.”
At Aero Craft, the best input method is a
CADAM drawing that can be put on a disc
and mailed or transmitted via an e-mail
attachment. They, in turn, transfer the digital
image to CorelDRAW, arrange it for the most
efficient cutting sequence, and then go
directly to the laser cutter.
Craig and Bill also accept pencil sketches,
but in that case they have to scan the supplied
drawing and then convert it to a CorelDRAW
line drawing. There is a fee for that scanning
service, in addition to the laser-cutting fee.
As do so many companies in this kind of
business, Aero Craft has a large supply of
balsa and plywood at any given time. So you
can buy the wood and have the parts laser-cut
for you. I suspect that you could also send
them your own material.
I’ve given you only the basics of operation
In more recent times, the cost of goodquality,
high-output laser cutters has come
down to the point where a small company can
afford to buy one and sell the service to the
industry and the individual modeler. The cost
has come down so much that some serious
modelers have bought their own machines.
To answer this reader’s question in more
detail, I decided to pay a visit to the closest
laser-cutting facility to me: Aero Craft in
Riverhead, Long Island, New York, which
partners Craig Wagner and Bill Schaefer run.
They make kits of their own designs and kits
for the hobby industry. Aero Craft
manufactures the entire Telemaster line for
Hobby Lobby.
In the past couple of years, Craig and Bill
Downthrust could not be added without
cutting into the front of the cowl. But by
mixing throttle and elevator control at the
transmitter, the model is touched merely in
a virtual way.
Above: Making a set of plans for a new design, Bob made a
sketch by hand first. This initial step in the design process is
known in the trade as a “cartoon.”
Right: From cartoon to full-size plans to the finished model, this design netted a design that Bob calls the “Turn-Around.” Look for
it in the RC Micro World e-zine.
88 MODEL AVIATION
05sig3.QXD 3/25/09 9:08 AM Page 88
designs published. I’ve always been curious as
to how you start on a particular design project.
In other words how do you get from that first
pencil mark on the paper to the finished
aircraft?”
A399: I can’t speak for Dick or Nick, but I
released my 66th aircraft for publication in
November 2008. I started actively designing
and writing in 1973.
I worked for many years at the Grumman
Corporation, in what was known as the
“Configuration Room” (a portion of the
Advanced Systems Department). In that room
were some of the most senior Grumman
engineering designers. I was thrilled, as a
young engineer, just to be in their presence.
One of the things that all the engineers did
in that room was constantly sketch first-time
aircraft. They were usually three-views, handdrawn,
before the days of CADAM and
CATIA. The slang expression for these
sketches was “cartoons”!
As time went along and I began to design
my own model aircraft for publication, I also
drew “cartoons.” I still do! I can sit with a pad
and pencil in front of my TV set, watch a
program, and sketch all kinds of aircraft
designs at the same time.
Several weeks ago, I had in mind to do a
micro/indoor design with aileron control
instead of rudder. It was intended for
publication in John Worth’s RC Micro World
online magazine. As you can see in the photo
included with this column, I sketched the entire
model, which I named the “Turn-Around,” on a
piece of 81/2 x 11-inch paper.
I basically drew the aircraft outline,
estimated size, type of construction, and, most
important, the weight of the power and RC
equipment so I could estimate total weight and
then select the proper motor size. From that
single “cartoon,” I went to my drawing board
and prepared close to a final set of full-size
plans that would enable me to start construction.
The “cartoon” took roughly three TV
programs and the plans took close to a day. It
took three days to build the airplane, one to testfly
it, and several to write the article and
integrate the photos into it.
The Turn-Around was an original design
that started from an idea I had in mind. Many
times I will design a model based on a full-scale
aircraft. In that case, I generally start with a
three-view of the original airplane and then
work on my “cartoon” for the model. It’s the
same process.
The completed little Turn-Around ended up
at exactly 4.2 ounces—close to my original
prediction. And, yes, it flies well! MA
Sources:
Aero Craft
(631) 369-9319
www.aerocraftrc.com
Bob Holman Plans
(909) 885-3959
www.bhplans.com
Laser Works Engraving and Design
(940) 766-2667
http://lazer-works.com
Manzano Laser Works
(505) 286-2640
www.manzanolaser.com
Ohio Laser Engraving
(937) 878-5587
www.ohlaser.com
RC Micro World
www.cloud9rc.com