Aerobatics Made Easy
By John Glezellis Illustration by FX Models
Horizontal Knife-Edge Square
with a Positive Snap Roll
An advanced move that combines
three basic elements
EN TER the maneuver
straight and level,
parallel to the runway.
The nature behind advanced aerobatics is the fact that each aerobatic element is built upon another. For example, when you start out, a simple roll is one of the first stunts you probably
attempted. As you built both experience
and confidence, you transitioned to inverted
flight, a hesitation roll, and knife-edge flight.
;e maneuver of the month is no di;erent
and will require that you’re familiar with the
traditional knife-edge and the positive snap roll,
and performing negative 90-degree pushes.
Combining these three basic elements while
flying a geometric shape is a sight to behold.
We will begin by looking at the aircraft design
recommended as well as a few programming
and setup fundamentals to ensure success.
We will then transition into an overview of this
exciting figure and the required control inputs.
Without further delay, let’s get started!
BEFORE WE BEGIN
For the aerobatic newcomer, it is important to
understand that success can be broken down
into two areas: the ability of the pilot, and the
design and setup of the airplane. For instance,
while you can fly knife-edge with a trainer-type
model that features dihedral and a flat bottom
airfoil, mid- or low-wing models with fully
symmetrical airfoils will decrease pilot workload
and keep corrective inputs to a minimum.
Always read the instruction manual
provided with a given aircraft and use the
factory-recommended control-surface rate
settings and exponential amounts as a starting
point. After you are familiar with the flight
characteristics, you can make changes to
customize the aircraft.
For illustrative purposes, we will use the
E-flite Slick 3D 480 ARF as our sample aircraft.
For a model like this, I prefer to use the low-rate setting for both precise rolling maneuvers
and snap rolls. On this rate, I have about
30 degrees of aileron deflection, 25 degrees
of elevator deflection, and 30 degrees of
rudder deflection, with about 20% of
exponential across all surfaces. Again, these
settings only serve as a basis because pilots
have di;erent personal preferences. You might
ask about the proper deflection required and
how to test di;erent amounts. I recommend
using a rate that requires about 60 to 70%
rudder to sustain altitude while in knife-edge
flight. ;en, once fully deflected, the aircraft
should begin to perform a slow and gradual
With the control-deflection amounts
complete, the aircraft will be sensitive to any
input if you don’t use exponential. Exponential
will soften how the airplane will respond to
certain control inputs around neutral, but
maximum travel can be obtained by moving the
control stick to the maximum amount. If your
model has some form of flight stabilization,
refer to the instruction manual provided with
the flight-stabilization hardware to ensure
proper exponential implementation. In the most
basic form, though, always add exponential in
increments of 5 or 10% and note the impact it
has on the flight characteristics of the aircraft
until you’re satisfied.
To begin this maneuver as it is shown, the
airplane should fly upright, level and parallel to
the runway, into the wind, and at a moderate
flight speed. For this particular example, the
maneuver will be flown from the left side of
the field to the right. When the aircraft is about
75 feet away, roll 90 degrees to knife-edge
flight and apply top rudder to maintain altitude.
Rolling to the right to see the top of the airplane,
one should apply left “top” rudder to maintain
altitude. As soon as the airplane passes you by
about 50 feet, apply down-elevator to perform
a 90-degree radius. Once the aircraft flies
100 feet, perform another 90-degree radius.
As the airplane approaches the halfw ay
point, which will be directly in front of you
but at a significant distance away, execute a
positive snap roll. Holding the same rudder
deflection, increase the deflection amount
while simultaneously applying left aileron
and up-elevator. Release all inputs with the
exception of rudder and continue with the
knife-edge circle. Performing two more radii
and focusing on the geometry in accomplishing
a horizontal square with constant radii, roll the
airplane to upright level flight.
Let’s simplify matters and divide this stunt
into four separate steps:
Step 1: Begin by lining up to the runway so that
the plane is traveling into the wind at a fairly
high altitude and at a moderate flight speed.
For an aircraft like the E-flite Slick 3D 480 ARF,
I prefer 75% throttle, but this aircraft is highly
overpowered. Adjust the throttle setting as
needed for your aircraft. As you approach the
runway, roll 90 degrees and establish knife-
edge flight. Rolling to the right, apply left rudder
to keep a constant altitude. Remember, smooth
control inputs are the key to gracefulness!
Step 2: Push ever so slightly on the elevator
control surface to initiate the figure. A constant
90-degree radius should exist, and once
accomplished, you can release elevator input.
Continue to apply rudder to sustain altitude.
Note, though, that the size of the first radius
performed must match the three following radii
that will be performed throughout the figure,
and no change in altitude should exist. Minor
corrections in rudder, elevator, and aileron will be
needed so that the aircraft is in the proper knife-edge attitude throughout the maneuver. After
you’ve flown a line segment that’s twice as long
6 Push down- elevator to make
the fourth 90-degree
Remove the down-elevator so that the
new segment is in line
with and at the same
altitude as the entry