Radio Control Scale Aerobatics-2010/08

118 MODEL AVIATION
Conquer the vertical snap
[[email protected]]
Radio Control Scale Aerobatics John Glezellis
The Aresti drawing of Maneuver 6 from the
2010 Advanced IMAC schedule includes a
pull to vertical, positive snap, Stall Turn,
then full Roll on the down-line before pulling
level to exit.
John’s JR 12X has many Flight Modes
programmed. The “Rudder D/R” switch
is assigned to select the Flight Mode in
use. The pilot can choose the switch
assignment.
The Hangar 9 Sukhoi SU-26MM is great for Aerobatics
competition, because it is affordable and promises great
flight characteristics. It’s a fun 3-D machine too.
With the 12X, more than three positions
can be used on a Flight Mode. One mode can
have the settings for normal Aerobatics and
another can have settings for hard-core 3-D.
You can actually name an individual Flight
Mode/Condition on some radios. It’s easier
to recall the assigned duty it’s named
rather than a number.
6
WITH THE 2010 flying season in full swing,
it’s time to address Snap Rolls, and in
particular, vertical snaps. Performing a typical
Snap Roll from horizontal, upright, level
flight is different from performing a vertical
snap; you might find that a model can quickly
lose airspeed and easily lose heading. As with
all aerobatic maneuvers, proper flight setup
and technique are essential.
Since this column is devoted to Scale
Aerobatics, I will discuss Maneuver 6 from
the 2010 Advanced International Miniature
Aerobatic Club (IMAC) class and highlight
one major part of it: the vertical snap.
Maneuver Six is a Stall Turn that starts
from upright, has a positive Snap Roll on the
up-line, and has a full roll on the down-line.
Let’s begin!
Keys to Success: If you have been an avid
reader of my columns, you might notice that I
stress proper airplane setup and programming.
That is because setup and programming, not
to mention control inputs, are all critical
elements to your success in Aerobatics.
A Positive Snap Roll is a stalled maneuver
that is initiated when you apply up-elevator
and the same-direction rudder and aileron
input. Depending on the model’s power-toweight
ratio, you might need to use a lot of
throttle when performing the Snap Roll on a
vertical up-line. You might also need to
change rudder deflection and/or elevator
deflection, depending on the variables.
If your model gets too “deep” in the snap
and changes heading on the z-axis (the
airplane travels quite a bit in the direction in
which you snapped), you might need to
decrease rudder rate. If you feel that your
aircraft is “tumbling” through the snap, you
might need to decrease elevator rate.
When performing a Positive Snap Roll, I
pull hard on the elevator to initiate the break
and stall the model. Immediately following, I
release elevator while adding aileron and
rudder input.
I use a program in my JR 12X radio called
“Snap Flight Mode.” Before I perform the
Snap Roll, I flip a switch that has the rates
necessary to do the maneuver.
My 37.5% Yak-54 has all of the following
values located on one switch or, as JR calls it,
“Flight Mode”:
• Aileron deflection is 40° with 55%
exponential
• Elevator deflection is 20° with 35%
exponential
• Rudder deflection is 35° with 40%
exponential
The rates for your airplane might differ,
but those numbers should serve as a starting
point.
Some radio manufacturers call a Flight
Mode a “Flight Condition.” There are a few
minor differences; please consult the
instruction manual that was supplied with
your radio system and aircraft.
Also, please keep in mind that these values
I cited are for a JR radio, on which typical
exponential is positive (+). Exponential
08sig4x.QXD_00MSTRPG.QXD 6/24/10 1:44 PM Page 118
120 MODEL AVIATION
should have a negative (-) value on Futaba
radios, to soften the stick feel around center.
In flight I prefer to have a fast-snapping
rotation rate. I use maximum, or almost
maximum, rate on aileron. Since my Yak has
a huge rudder, I found that only 35° of
deflection was needed, and so on.
However, not all aircraft perform the Snap
Roll in the same fashion. Although you might
be able to “bury the sticks” to perform a Snap
Roll on a sport model, it is impossible on a
giant-scale aerobat with “3-D size” control
surfaces.
Notice, though, that some airplanes might
increase in rotation speed depending on the
rudder input that is used. I once owned a 43%
CAP 232 that would perform a faster Snap
Roll when rudder input was increased.
Get to know your model and what inputs
it prefers to obtain the correct control rates so
it can offer the best presentation of a given
maneuver.
Performing the Maneuver: Now that you
know more about the vertical Snap Roll and
how to avoid some common errors, let’s take
a look at the Positive Snap Roll on an up-line.
Enter while traveling parallel to the
runway; increase the throttle so that it has a
setting between 75% and 100% power. It is
difficult to clearly define how much throttle is
needed on a given model, because airplanes
have different power-to-weight ratios.
Simply put, the more power the aircraft
has, the less power will be needed to establish
a vertical up-line. As the model approaches
the end of the maneuvering area, get ready to
pull gradually to a vertical up-line.
After the radius is complete and the
aircraft is traveling
straight up, leave a
line that is
approximately three
seconds in length.
Then initiate the
Snap Roll, which can
be performed in the
direction you prefer.
Once complete,
make sure there is a
line of equal length
from the first.
Decrease power and
let the airplane
decrease in speed. As
it stops, apply
enough rudder to
pivot it 180°.
When the model
is flying straight
down, perform a roll, in either direction (it’s
up to you), that is centered on the down-line.
Then pull to an upright, level exit.
This is a wind-corrected maneuver, and a
judge, if you are competing, will want the
airplane’s flight path to be vertical. This
means that if a crosswind is blowing in, you
will need to “lean” out the aircraft’s nose
slightly so that it tracks vertical despite its
orientation.
When the model performs the Stall Turn
and pivots 180°, no pendulum effect should
To prevent any loss in heading, keep the wings level before
pulling to a vertical up-line. Every IMAC maneuver enters and
exits with level wings.
occur. If you see that the tail of the airplane
oscillates, try releasing the rudder in a slower
fashion when the model nears the 180°
rotation point.
Please make sure that the aircraft
approaches a stop on the vertical up-line
before you give rudder input for the pivot. If
the model is still climbing vertically and
rudder is given, it will not pivot around its
axis point and will perform a “flyover.”
You have learned a few tricks to performing
an advanced Aerobatics maneuver, how it is
incorporated in an IMAC sequence, and a few
common errors that you could easily make
while performing it. If you want to become a
more proficient pilot, practice what you have
learned. After all, it does make perfect.
Try different control throw and
exponential settings when performing the
Snap Roll. And, ultimately, remember to
enjoy yourself at the field.
Until next time, fly hard! MA
Sources:
International Miniature Aerobatic Club
www.mini-iac.com
JR
www.jrradios.com
(800) 338-4639
Hangar 9
(800) 338-4639
www.hangar-9.com
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