Radio Control Scale Aerobatics - 2009/12

Preparing for the 2009 Tucson Aerobatic Shootout
December 2009 129
[[email protected]]
Radio Control Scale Aerobatics John Glezellis
Also included in this column:
• Weight matters
• Programming choices
• The correct propeller
choice
•When is practice enough?
Setting up the ducting on John’s DA-200-powered Extra 260 is
critical. The challenge is to direct airflow over the front, to cool
the two rear cylinders.
The Thunder Tiger Extra’s cowl is split horizontally. A duct was
added under the front intake, to direct airflow through the front
cylinder.
John’s JR 12X transmitter has specific rates and exponential
values for the DA-170-powered Extra 260. Note the low rate
exponential value.
In John’s JR 12X programming for the DA-200cc Extra 260, compare
the low rate setting on the elevator. Less elevator exponential is
used to get the same “feel” as the model with the lighter engine.
BY THE TIME you read this, the 2009
Tucson Aerobatic Shootout will be a part of
history. It will take place October 7-11. To
compete in an event of this caliber, the pilot
must devote much time and dedication.
This month, I will give you an overview of
how I prepare for this event in terms of how I
set up both my primary and backup models,
what changes I made to both airplanes during
the course of a few months of practice, and
my practice techniques. I’ll close with a few
thoughts from which I think everyone in the
giant-scale arena and the AMA can benefit.
About the Airplanes: For this competition,
I decided to fly a Thunder Tiger 40%
Extra 260. With my father, we prepared
two models; their only difference was in
power plants.
I equipped my primary model, which
was to be used for the Invitational-class
programs, with a Desert Aircraft 200cc
engine with stock mufflers. My backup
Invitational model (and primary model
for Freestyle) was powered by a Desert
Aircraft 170cc engine on KS 1090 pipes.
Oftentimes I see people set their
airplanes up as the factory recommends.
However, after a model is test-flown, the
pilot might notice that it is tail- or noseheavy.
Rather than make changes to the
aircraft in terms of moving the CG, the
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130 MODEL AVIATION
Cleanliness is a virtue. Battery packs are kept forward, near the wing
tube and CG area on the 200cc-powered model. In the 170cc Extra,
battery packs are farther forward to achieve a similar CG.
When using gas engines, add triangle stock—especially in key areas
such as the firewall. On this 200cc Extra, the entire engine box was
reinforced to make sure it would be suitable for the four-cylinder
engine’s extra weight.
Never be afraid to move battery packs around until you are fully
satisfied with the CG. The main battery pack and ignition battery are
strapped to a 37.5% Yak-54’s engine box.
flier will simply add weight to the airframe. That is not an ideal
choice.
When I built my backup model, I mounted the two JR DS8711
rudder servos in the Extra’s tail (as I also did with the 200cc primary
airplane). Although the CG was great for Freestyle, the aircraft was
too tail-heavy for sequence flying without having to add weight to the
airframe’s nose.
To correct this, I took the two rudder servos out of the tail, placed
three JR DS8711 rudder servos on an AirWild Pilot Shop servo tray,
and used pull-pull. This eliminated the need to add more than a half
pound of weight in the model’s nose.
On the subject of servos, I am using three JR DS8711s per aileron
and one JR DS8711 per elevator half on each Extra. I installed a
PowerBox Royal, from Aircraft International, in each of my
competition models. In addition, I am running two PowerBox 4000
mAh batteries to power each Extra and one PowerBox 1500 mAh
battery on the ignition.
However, the Desert Aircraft DA-200 is using two ignitions. For
their wiring, I have two ignitions plugging into one ignition battery
and switch.
Expect to get less flight time when running two ignitions off of one
battery. I can fly a total of five flights that average 10 minutes of flight
time on my DA-200, using only one 1500 mAh ignition battery,
before having to recharge.
Check your batteries before every flight. I cannot stress this notion
enough.
Difference of Programs: I’ve been flying my backup Extra 260 since
May 2009. When I finished the second model, which had the 200cc
engine, vs. the 170cc, I employed the same control-throw values (in
terms of degrees) and same exponential values. The aircraft were built
in an identical fashion, with the only exception being the rudder
servos’ placement.
When I test-flew my second airplane, it reacted slightly different in
some ways from the first model. As a result, I adjusted exponential
values, decreased throws when needed, and made all of the necessary
changes to ensure that each Extra flew similar to the other.
It is critical to fly your primary and secondary model equally, so
that if you need to use the backup, you will already feel comfortable.
It will be one less thing to worry about on the flightline.
When programming an aircraft on a computer radio, I recommend
starting with a new model. However, some people prefer to “copy” an
existing airplane in the radio into a blank model on the radio so that
they have a starting place in programming their new model.
If you decide to do this, remember to clear all subtrim values and
return all trims to their neutral position. I also recommend maxing out
all of your ATV (adjustable travel volume) values so you have every
available bit of servo movement step resolution going to the new
airplane’s control surfaces.
When Weight Matters:Weigh each of your models to see how it
compares with the manufacturer’s specifications. If it is heavier than
suggested, try to see where weight was added.
In some cases, pounds, not ounces, can be saved by using:
• Lighter battery packs (either Li-Poly or Li-Ion)
• Carbon-fiber landing gear
• Carbon-fiber wing tube
• Carbon-fiber horizontal stabilizer tube
On some models, you can save more than a pound by changing a
landing gear from aluminum to carbon fiber. The same applies to
carbon wing tubes and different battery packs.
Good carbon wing tubes are those from PBG Composites. They
are available in the US from Desert Aircraft. The nice thing about
carbon-fiber spar tubes is that they won’t bend as time goes by, as
aluminum will.
Ace Hobby has a carbon-fiber landing gear I’ve used on both Extra
260s and that my father has used on his 37.5% Yak-54. They hold up
well and are much lighter than the same size of aluminum gear. Your
airplane’s manufacturer might offer carbon-fiber “upgrades.”
See what the maker of your aircraft has in terms of carbon
accessories. Remember that ounces do add up in the end. And
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when flying at a higher elevation, you will
benefit greatly from a lighter airplane.
Props, Props, Props: I tried many different
propellers throughout the course of the
summer. I tested the following two-blade
varieties on both my 170- and 200-powered
models.
• Mejzlik 30 x 12
• Mejzlik 30 x 13
• Mejzlik 32 x 10
• Menz 32 x 12
• Menz 32 x 10
• Menz 30 x 12
• Air Models 31 x 12
Each of those propellers offered a different
set of performance values, which is the benefit
of testing. Also, each brand had a different
design. The Menz types have a fairly wide
blade when compared to the Air Models.
On my DA-200, I can spin an Air Models
31 x 12 at 6,700 rpm and turn a Menz 30 x 12
at 6,500 rpm. It was interesting to see that a
larger propeller actually spun at a higher rpm
than the smaller one.
After I tried the propellers I listed, it was no
surprise that each had a different “feel”
throughout the flight. By “feel,” I mean that in
some maneuvers you will notice the airplane
reacting quicker in terms of roll rate, throttle
response, etc.
Don’t be afraid to try different propellers
when you build a new model. If you are unsure
of what propeller to use, start with the aircraft
manufacturer’s recommendation and talk with
either the company or fellow modelers.
When using the 170cc and 200cc engines,
I prefer the 32-inch-diameter propellers when
flying close to sea level. They do not turn the
highest rpm, but they provide a lot of pull for
my model and do not overheat the engine.
However, when flying at higher altitudes, I
prefer to use either the 31- or 30-inchdiameter
propellers, to have a similar feel and
performance that I have when using the 32-
inch-diameter propeller at sea level.
When is Practice Enough? To make the
answer simple, you can never practice
enough. Weather permitting, I generally fly
roughly five sessions a week and prefer to
practice in all types of conditions. Flying in
extreme weather is necessary so that a pilot
will know how a model reacts in 35 mph
winds and in mere 5 mph winds.
It might be necessary to change
propellers in high winds. You could find
that in high winds, your airplane flies
slower going into the wind and might have
less power on vertical up-lines. As a result,
you might need to use a smaller propeller
to turn higher rpm.
I like using a 32-inch propeller on the DA-
170 at sea level. But if I am flying in winds
that are approximately 35 mph, I go to either
31 or 30 inches, depending on how extreme
the winds are that day.
There is a lot to learn with new aerobatic
schedules. When I practice alone, I break
sequences into sections. If it has 10
maneuvers, I practice the first three or four in
the first flight and work my way up from
there.
When practicing a complex program, it is
frequently easier to memorize the program
when practicing it in parts rather than trying to
perform the entire routine from memory in the
first attempt.
It is important to have a caller at times
during practice and definitely on the
competition flightline. Sometimes it is
impossible to have a caller for each practice
session; with that, patience is a virtue.
Also, don’t be afraid to change a dualrate
value, exponential value, or whatever
adjustment you need to get your aircraft
flying the way you like it.
You have just learned about some of the
dedication it takes to prepare for a large
competition and some of the changes you
can make to get your aircraft to perform
better.
Never hesitate to make a change to
your model. You will never know what it
is fully capable of until you try different
dual rate and exponential settings,
propellers, techniques to lighten your
airplane, etc.
Last, remember to respect those around
you. Through the years, I have seen clubs
encounter issues with people who fly
Giant Scale models.
This hobby is made up of many types
of aircraft; people are interested in gliders,
aerobatic models, warbirds, jets, and
electric-powered airplanes, to name a few.
Proper consideration must be made so that
everyone at the flying field can coexist.
Please take into account that this is not
directed toward the Giant Scale crowd, but
rather everyone who makes up our great
hobby. Welcome others at the flying field,
and treat others as you would like to be
treated. MA
Sources:
DA engines, air Models, Mejzlik, Menz, PBG
Composites:
Desert Aircraft
(520) 722-0607
www.desertaircraft.com
AirWild Pilot Shop
(949) 699-1059
www.airwildpilotshop.com
JR
(800) 338-4639
www.jrradios.com
Aircraft International
(732) 761-0997
www.aircraftinternational.com
Ace Hobby Distributors
(866) 322-7121
www.acehobby.com
International Miniature Aerobatic Club
www.mini-iac.com