Let’s Talk Giant Scale
BY JOHN GLEZELLIS
T;is month, let’s discuss the importance of incidence. We’ll use two examples, the 40% ZN Line Extra 330S and the 3.1m Hangar 9 Sukhoi Su 26MM. Both are great flyers and they utilize different construc- tion methods. Unlike today’s almost ready to fly (ARF) models, the Extra 330S features a carbon and Kevlar fuselage that consists of foam and fiberglass, and wings and tail
surfaces that are foam and sheeted at the
factory with balsa. The incidence angles on
this airplane are not pre-set by the factory
and requires the builder to set it up correctly. The Sukhoi, on the other hand, is an
Important details for airframe setup
is often referred to as the centerline. Often-times, fuselage canopy hatches are made
parallel with the datum line, which is the
case with the Hangar 9 3.1M Sukhoi.
On all ARF models, the wing and stabilizer incidence are set at the factory and
very little tweaking needs to be done by
the pilot. If you are building your own
giant-scale model, you’ll need to set the
wing incidence, so always use the manufacturer’s recommended settings as a starting point.
Let’s take a look at the impact wing
incidence has on flight characteristics.
Tip of the Month
Before you begin making any
changes, I recommend that you place
a center mark on the horizontal
stabilizer at the leading edge. ;en,
place another mark on the fuselage
to mark this point. Now, no matter
what adjustments are made, you
will always be able to return to
the original starting position.
Changing the wing incidence can be
a tedious process, and should only
be performed if you have explored
all possibilities with respect to
trimming your aircraft. For example,
is the center of gravity (CG) correct?
If it isn’t, you will be in a constant
battle between the right CG and wing
incidence, and this battle will not be
Sam Filippelli’s 35% ZN Line Extra 330S awaits another flight! ;is airplane is the smaller brother to the aircraft
mentioned in this column, but each share similar building techniques. (Photo courtesy of Sam Filippelli)
0-degrees incidence relative to the stabilizer produces no upward lift to support
the airplane’s weight. As a result, trimming the airplane will only work when the
flight speed remains the same throughout
the entire flight. For example, as the speed
increases, the effectiveness of the trim will
also increase. Similarly, as speed decreases,
the pitch effectiveness decreases. You
cannot change the trim of the airplane
constantly throughout the flight so it is
important to properly adjust the incidence
of your aircraft. An airplane that has the
wrong incidence will usually hunt in pitch
throughout the flight.
ARF and has all incidence angles pre-set by
the factory. As we will see later, the Sukhoi
does have unique construction techniques
that make measuring incidence a breeze.
Let’s get down to business!
;e importance of incidence
Incidence is the angle between the chord
line of the wing where it is secured to the
fuselage and the datum line of the aircraft.
Picture the chord line as a line that goes
from the center of the leading edge to the
center of the trailing edge at the root rib.
The datum line of the airplane is a line that
all angles are measured in relation to, and
Start at a fairly high altitude and reduce
the throttle to the idle position. Perform
a gentle 90-degree push into a vertical
downline and release elevator input. If the
aircraft pulls to the canopy, you may have
to decrease the wing incidence or increase
the tail incidence. If the airplane pushes
towards the landing gear, you may have
to increase the wing incidence or decrease
the tail incidence. If there is only a slight
amount of pitch change, a bit of throttle-
to-elevator mix can be applied so that a
touch of elevator input is given when the
throttle is brought to the idle position.
It is important that you know how to measure the incidence of your aircraft. On the
Hangar 9 Sukhoi Su 26MM, the top canopy
hatch is parallel to the datum line. To measure the incidence of the wing, place a
meter, such as the Robart Incidence Meter
or the Angle Pro from Hangar 9 on the
top of the fuselage crutch. For non-digital
meters, like the Robart meter, it is necessary to place the meter on the fuselage
crutch and raise the tail until the meter
measures 0-degrees. Meters like the Angle
Pro can simply be zeroed at any relative
angle. Simply place the Angle Pro on top of