Radio Control Scale Aerobatics - 2010/02

The fundamentals of control linkages
February 2010 121
[[email protected]]
Radio Control Scale Aerobatics John Glezellis
Also included in this column:
• The importance of being
choosy
Peter Glezellis hovers his 50cc
Extreme Flight RC Extra 300. For a
50cc model, it has promising flight
characteristics and is a ball to fly.
Drilling a 5/64-inch pilot hole before going to
the recommended bit is important, to
provide a path for the larger bit to follow
and ensure that your control horn bolt will
be properly aligned.
After the control horn location is drilled and
tapped with 10-32 threads, wick thin CA to
harden the threads. Then you are ready to
secure the control horn bolts in place.
You must apply thread lock to any area
where a bolt or nut can loosen, such as
on this 10-32 lock nut used on a rudder
horn. Metal-to-metal contacts should
always get Loctite.
THERE IS NO doubt in my mind that
behind every great pilot is a well-built
model. In the past, I have given you
building and flying tips alike. Although
many great ARFs exist on the market
today with a great amount of
prefabrication, a few areas should never be
overlooked.
This month, I will discuss two
important building fundamentals:
mounting control horns and keeping
hardware and radio equipment constant.
Control Horns: Some airplane
manufacturers install control horns on
their aircraft. This does save a fair amount
of time. In the event that your model does
not feature preinstalled control horns, I
have some guidance to offer you.
I use threaded bolt-style control horns
on all of my Giant Scale aircraft. If a kit
does not come with control horns, I prefer
to use 10-32 Swivel Clevis Horns from
Hangar 9.
That package comes with two swivel
clevises, four 10-32 bolts, and two nuts. It
supplies everything that is needed to
complete the control horn section of the
assembly for two control horn locations.
If you are flying a model that is 35% or
larger, I advise you to use a 10-32 bolt for
your control horns. If you use bolts that
are too small, you may bend them in
flight.
I have experimented with 8-32 bolts
for the control horns on one of my 37%
airplanes. They worked for the first few
flights, but I soon found that the model
would not trim out on the aileron surface.
After I landed the aircraft, I saw that
all six aileron control horn bolts were
bent. Without further delay, I replaced
them with 10-32 hardware.
I have started assembly on a Thunder
Tiger Katana, available from Ace Hobby.
It came from one of the most recent
shipments, which included installed
hinges, an installed fuel tank, and an
installed fuel dot. Since the hinging was
already done, one of the first things I did
was install all control horns.
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122 MODEL AVIATION
To install and maintain servos deep inside a flying surface, you
can make a tool from a wood dowel fitted with a hex key
epoxied in place.
The standard connector on all Desert Aircraft ignitions is the
Anderson Powerpole. It provides excellent contact for the
necessary battery current.
Connectors can be standardized to suit the RC pilot’s needs. A
heavy-duty “pigtail” is a satisfactory substitute for most radio
electrical junctions.
John’s DA-50 ignition is ready to be plugged to the switch harness
that has a compatible UNI connector. Insulate solder joints with
heat-shrink tubing.
Sometimes people are wary when it
comes time to drill through a control surface;
it can be a bit intimidating. If you are using
10-32 hardware, you can do as I did.
1. I used a felt-tip marker to mark the
control horn plates in two places. The
Katana has light-plywood plates that can
accept traditional control horns (larger
versions of control horns that are used on
trainer and sport models) or those that were
included (bolts).
Since I used all hardware that was
supplied, I found and marked the center of
the plate and made an “X” that was 7/16 inch
back from the front of the plate. That is my
drilling location.
2. I drilled a pilot hole using a 5/64-inch
bit. Then I drilled that location with a 5/32-
inch bit, for the bolt.
3. I threaded the 10-32 bolt through the
surface (you can also tap it; either way is
acceptable), removed the bolt, and placed a
few drops of thin CA on it to harden the
threads.
4. I slightly drilled the top plate with a
1/4-inch bit, because the bolts’ heads were
cone-shaped. This ensured a flush,
professional fit with the top of the control
surface.
5. I threaded the bolt in place. On the
bottom of the control surface, I threaded the
10-32 nut that was supplied and secured it in
place using blue thread-lock compound.
6. Finally, I threaded the swivel link
assembly in place. A key point is to make
sure that the distance from the hinge line to
the center of the swivel link is the same as
the distance from the center of the servo arm
screw to the center of the ball link (or clevis
if you are using a clevis to secure the
pushrod to the servo arm).
All Things Constant: When traveling great
distances for a competition, it is important to
have spare materials. You can never have
enough equipment for your engine and radio
gear, but to simplify your build, keep bolts
the same size (if you can) and keep all servo
extensions the same. I’ll examine this notion
a bit further.
When it comes time to mount your
cowling, wheel pants, and hatch, use the
same-size bolts. On a typical Giant Scale
model, you can use 4-40 or 6-32 size. When
it comes time to assemble the airplane, you
can easily take spare bolts since you are
down to employing one size rather than
having to worry about taking various sizes to
the flying field.
As far as connectors for your batteries,
switches, and ignition, I can’t stress how
important it is to keep them the same
between models. For batteries, you can use
Deans Ultra connectors, E-flite’s EC3
Connector, or a standard JR or Futaba
02sig4.QXD_00MSTRPG.QXD 12/21/09 9:46 AM Page 122
heavy-duty servo extension connector.
I like the EC3 and Deans Ultra, because
they can handle higher amounts of current.
(Not that it is important in this application,
but it is when it comes time to use batteries
for electric-powered models.) The EC3 can
handle up to 60 continuous amps and the
Deans Ultra can handle 50 continuous amps.
I’ve been using the EC3, because that is
what the JR and Spektrum batteries come
presoldered with for either the Spektrum or
JR VR6010 voltage regulators and PowerSafe
receivers. However, all of that can be
changed. I have seen modelers use Deans
Ultra connectors off of their VR6010
regulators instead, because they have heavyduty
switches that are soldered with Deans
Ultra connectors.
In addition, I have always replaced the
connector that comes with a Desert Aircraft
ignition with a standard female Futaba or JR
heavy-duty lead. I do this as the lead plugs
into a heavy-duty switch that has a male lead.
Consistency is the key, and it will guarantee
peace of mind when it comes time to replace
the ignition or switch.
Always take time when it comes to key areas
in building your Giant Scale Aerobatics
models. As Murphy’s Law states, “Anything
that can go wrong will go wrong.”
When things do go wrong, keeping things
consistent between airframes will ensure
peace of mind and success at the field. After
all, you should be thinking about your next
flying sequence—not changing connectors at
the field.
Until next time, fly hard! MA
124 MODEL AVIATION
Sources:
Hangar 9
(800) 338-4639
www.hangar-9.com
Thunder Tiger
(949) 900-3300
www.acehobby.com
W.S. Deans Co.
(714) 828-6494
www.wsdeans.com
E-flite
(800) 338-4639
www.e-fliterc.com
Desert Aircraft
(520) 722-0607
www.desertaircraft.com
JR
(800) 338-4639
www.jrradios.com
Futaba
(800) 637-7660
www.futaba-rc.com
Spektrum
(800) 338-4639
www.spektrumrc.com
Extreme Flight RC
(770) 887-1794
www.extremeflightrc.com
International Miniature Aerobatics Club
www.mini-iac.com