Radio Control Scale Aerobatics - 2010/10

122 MODEL AVIATION
Let’s talk spins!
[[email protected]]
Radio Control Scale Aerobatics John Glezellis
Taken from a recent IMAC routine, this
Aresti diagram shows a 1-1/4 Turn Positive
Spin from upright, level flight. The model
will exit flying “cross-box” in upright, level
flight. A spin is represented by an elongated
triangle in Aresti, compared to a Snap Roll
that is shown by a normal triangle.
This JR 11X screenshot of the D/R and EXP
screen for John’s Yak-54 (as for all of his
models) employs a Flight Mode for only three
positions. Settings for “Low-Rate” position
and a corresponding graph are shown.
The author prefers to have his Flight Mode
located on the rudder switch. Choose a
switch that you feel comfortable reaching.
John normally names each Flight Mode. The
“Medium” rate is selected for both spins
and snaps. The use of Flight Modes reduces
changing control rates to a single switch.
NOT LONG AGO at the local flying
field, I saw a fellow International
Miniature Aerobatic Club (IMAC) pilot
practicing spins. Spins and snaps, and a
few other maneuvers, raise discussion
when it comes to scoring.
As I have done in the past, I will cover
the control inputs that are needed to
perform spin variants and how you can set
up a model so you will fly this maneuver
consistently. After all, consistency is the
key to winning in extreme competition.
If you are new to Aerobatics, you might
be unaware of what a spin is, by definition,
in aerobatic terms. It is performed when
the aircraft stalls and then rotates around
its CG at a constant rotation speed.
Once stalled, a wingtip drops to initiate
the spin as the wing is stalled and no
longer flying. During the spin, you will
notice that the most powerful control
surface is the rudder.
A few types of spins exist in Scale
Aerobatics. In your routine, you might see:
• A Normal Upright spin
• A Normal Inverted spin
• A Cross-Over spin
You might be asking yourself what
those terms mean. Don’t worry; after
reading this column, you will be aware of
those three spins.
Normal Upright Spin: Fly the model up
to an altitude of approximately 400 feet,
and have it travel in a manner that is
parallel to the runway and into the wind.
Decrease power.
As the airplane slows, you will need to
increase the amount of up-elevator to
maintain altitude. Then the aircraft will
either stall or mush.
10
1/4
John flies his 40% Extra 260 with smoke on at Top Gun.
During this routine he performed a Flat Spin, which is a
slight variation of this month’s column topic.
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October 2010 123
If it stalls it will drop a wingtip, which
will declare the direction of the spin.
Instantly apply up-elevator and either left
rudder and a touch of left aileron (if the
left wing dropped at the stall) or right
rudder and a touch of right aileron (if the
right wing dropped at the stall).
When you are ready to complete this
maneuver, neutralize all inputs, establish a
vertical down-line, and pull to upright,
level flight.
Normal Inverted Spin: Follow the same
procedure as for the Normal Upright Spin,
but make sure that the model is inverted
instead of upright. Then decrease power.
As the airplane slows, you will need to
increase the amount of down-elevator to
maintain altitude. Then the aircraft will
either stall or mush, which I will soon
cover.
As in the previous maneuver, once the
model stalls, a wingtip should drop; that
will show you the direction of the spin.
Keep in down-elevator input, and apply
right rudder and a touch of left aileron (if
the right wing dropped at the stall) or left
rudder and a touch of right aileron (if the
left wing dropped at the stall).
When you are ready to complete this
maneuver, neutralize all inputs, establish
a vertical down-line, and pull to upright,
level flight.
Cross-Over Spin: This is simply either
an upright spin that is performed from
inverted flight or an inverted spin that is
performed from upright flight.
Once you have performed the first
stall (as I mentioned earlier), the airplane
must stall a second time, in an opposite
direction from the first. After the second
stall, the airplane can begin proper
rotation.
If the pilot starts a spin rotation
between the first and second stall, the
entire figure should receive a zero. In all
my years of Aerobatics competition, I
have yet to see Cross-Over Spins in a
contest. However, judges have threatened
and joked with fellow pilots that they were
in various Unknown Programs. So be
prepared.
Setup Techniques for Success: When you
perform the spins I have reviewed, your
aircraft might not react as you would like.
Earlier I used the term “mush.” If you are
trying to stall your model and it mushes
(starts to descend in altitude and not stall),
it will not spin because it is not in a stalled
state.
If this happens, you might need to add
more elevator throw. Another option is to
change the CG. Add a slight amount of
tail weight and see if the aircraft will stall.
Once the model is spinning, pay
special attention to ensure that it is not
“spiraling” downward at a fairly moderate
descent rate. If it is, you might need to add
more rudder throw and/or elevator throw
to the rates you employ to perform the
spin.
Recently I have put in a fair amount of
stick time on a 35% and 37.5% Yak-54.
Both are great overall Giant Scale aircraft,
which means that they can perform
precision and extreme 3-D maneuvers.
However, when an airplane has what I call
“3-D-sized” control surfaces and surface
deflection, it is critical to use dual or triple
rates to pilot it with the utmost consistency.
If you have been an avid reader of my
columns, you might be aware that I use
Left: Flying into the wind, John’s father (Peter)
decreases throttle and applies enough up-elevator to
maintain altitude in preparation for a correct spin
entry.
Below: Once the model stalls and a wingtip drops,
apply necessary inputs. Here, the right wing has
dropped. Resulting, full up-elevator and right rudder
are applied, as is a touch of right aileron (for a positive
spin to the right).
Below: Exit your spin at the typical “base altitude,” and
make sure your airplane’s wings are level so that the judges
know that the maneuver is complete and scorable.
10sig4.QXD_00MSTRPG.QXD 8/20/10 12:43 PM Page 123
three “Flight Modes” on all of my
Aerobatics models. Flight Mode 1 covers
all basic flight and Rolling Circles. (I am
unable to perform a Snap Roll on this
mode because of limited control surface
deflection.) Flight Mode 2 covers Snap
Rolls and Spins. Flight Mode 3 is for 3-D
flying or performing Tailslides.
To guide you in the right direction, take
a look at the Snap/Spin Flight Mode on my
35% Yak.
• Aileron deflection is 35° with 60%
exponential.
• Elevator deflection is 17° with 20%
exponential.
• Rudder deflection is 35° with 40%
exponential.
Different airplanes will require
different adjustments when it comes to
control surface deflection and exponential
settings. All aircraft fly differently, and
you must cater to the needs of each one.
If you think that your model might be
set up improperly, use the preceding
control surface deflections and exponential
settings as a base. Then make corrections
as necessary to cater to your preferences,
using some of the techniques I have
mentioned throughout this column.
Scoring Tips: In the more advanced
IMAC classes, a roll segment can follow a
spin. If that is the case, make sure that a
brief line exists between the spin and the
roll. And if you use only aileron to
complete the spin, a penalty of 1 point per
5° will apply.
Let’s say that you have to perform a 1-
1/4 Turn Positive (Upright) Spin and
aileron (roll) the last 20°. You will receive
a maximum score of 8—and that’s if the
rest of the maneuver is perfect. If flying in
an extreme crosswind, the entry line into
the spin and the line after the spin must be
wind-corrected as a model’s flight path is
judged, not the actual heading of the
airplane.
Let’s say that we are performing a 1-1/4
Turn Positive (Upright) Spin and we are
“crabbing” the aircraft into the wind 20° in
heading. Resulting, a full 1-1/4 Turn Spin
will be impossible to perform (if the model
stalls into the wind), because the fuselage
is leaning before the spin starts.
That is not a downgrade. However,
make sure that the airplane is stalled
throughout the maneuver; when rotating, it
might drift with the wind.
Judges look to see that the aircraft
performs a clean break and a fully stalled
autorotation, stops on a prestated heading,
and executes a 90° down-line before it
pulls, or pushes, to exit the maneuver. In
addition, rotation speed and pitch attitude
during autorotation are not downgrades,
because all models spin differently.
Now that you have learned about types of
spins you could encounter, always take
time to properly tune your airplane to meet
your needs. It will pay off on the
flightline.
Last, avoid some of the common
mistakes I mentioned to ensure maximum
points for your flight scores. Keep
practicing, and practice flying in various
weather conditions. After all, you don’t
know what the weather will be on
competition day.
Until next time, fly hard. MA
Sources:
International Miniature Aerobatic Club
www.mini-iac.com
Futaba
(800) 637-7660
www.futaba-rc.com
JR
(800) 338-4639
www.jrradios.com
Thunder Tiger:
Ace Hobby
(866) 322-7121
www.acehobby.com