166 MODEL AVIATION
Eric Conley’s innovative line “slider”
[[email protected]]
Control Line Navy Carrier Dick Perry
Also included in this column:
• Balancing issues for low and
high speed
• Nats event sponsors
• Electric-powered Carrier
• Answers to the Corsair quiz
The rotating retainer holds the lines forward
for high-speed flight. The rubber band opens
the retainer when the internal catch is
released.
Eric Conley’s Corsair’s line “slider” in the
tripped (low speed) position. This allows
the model to yaw outboard, increasing
line tension and control at low speeds.
The cable attached to the tailhook is pulled when the tailhook is extended. The cable
pulls the pin that holds the line retainer in the high-speed position.
AS IN THE April column, the photos this
month are of Eric Conley’s Corsair Profile
Carrier model. I photographed it at the
Southwest Regionals in Tucson, Arizona, in
January.
There have been many varieties of line
sliders, snappers, or other means of moving
the leadouts aft to yaw the model outboard
during slow flight. I’ve mentioned most of
them in this column through the years.
Although there are few new ideas in this
arena, Eric’s method of varying leadout
position has some new techniques.
The basics of any slider mechanism
include a guide that controls the position of
the leadouts throughout their travel and a
means of holding the lines forward for high
speed and releasing them for low speed.
Most mechanisms, including Eric’s, rely on
mounting the bellcrank aft of the model’s
balance point to generate the force to move
the lines to the rear.
The photographs provide enough detail
to allow the mechanism to be reproduced.
Dimensions are noncritical.
The line guide and retainer are made
from five-ply birch plywood, with the areas
that contact the leadouts sanded extremely
smooth. Hardening the contact surfaces with
cyanoacrylate glue would probably also be a
good idea.
As you can see from the photographs, the
retainer is pivoted inside the wing, and the
release mechanism is also internal. The
rubber band provides the force to rapidly and
positively swing the retainer from the locked
position to the open position so all three lines
are released simultaneously. The line guide
provides a slot to allow the lines to slide to the
rear and an enlarged hole at the aft end with a
rearward-facing step to trap the lines in the aft
position.
Eric uses the tailhook to release the retainer.
A brass horn is soldered to the tailhook so it
can pull an attached cable to the rear as the
hook is extended.
The cable is a standard RC flexible cable
pushrod that runs into the wing and through a
nylon sleeve that routes it to the release
mechanism at the retainer. As the cable is
pulled, it, in turn, pulls a pin from the retainer,
allowing the rubber band to rotate the retainer
and release the lines.
I’ve written about balancing Carrier models
before, including the need to determine the
balance point in flying condition; i.e., with fuel
and a flight propeller. The balance
requirements for high speed and low speed are
different enough to create difficulties if they are
not tightly controlled.
In low-speed flight the ability to hang the
model is enhanced by an aft CG (or balance
point). This improves the elevator’s
effectiveness and allows the model to maintain
a nose-high attitude without large deflections of
elevator.
That is important because a deflected
elevator, acting primarily in the propeller’s
draft, will exert a variable force if the engine
07sig6.QXD 5/22/07 1:26 PM Page 166
speed varies. Because a need to add power is
seldom accompanied by a need to increase
pitch attitude, a nose-heavy model is a
disadvantage in slow flight.
I’ve found that balancing a Carrier model
near 25% of the mean aerodynamic chord is a
good starting point for reasonable low-speed
flight characteristics. At that CG location a
reasonable-size tail and tail moment arm
provide adequate stability for most highspeed
conditions.
Certainly the model will be stable at low
power settings, even with the CG aft of 25%,
as long as the tail is large enough and the tail
moment is long enough. The potential
problem comes in high-speed flight.
Propellers mounted on the front of an
aircraft are destabilizing. A propeller facing
directly into the airflow will produce nothing
but thrust parallel to the airflow. If the
propeller axis is inclined to the airflow, a
vertical force is generated that is proportional
to the power/thrust being produced and the
distance of the propeller from the CG.
When a model is disturbed from its
normal angle of attack, the tail produces a
correcting moment to return the model to the
starting position. At the same time the
propeller tries to increase the pitch deviation
further. Moving the CG aft decreases the
stabilizing moment generated by the tail and
increases the destabilizing moment generated
by the propeller.
During takeoff and acceleration the
stabilizing aerodynamic forces build with
speed, but the propeller forces are strong from
the beginning. That makes the model
potentially less stable immediately after
takeoff.
If you adjust the CG aft to enhance lowspeed
handling, it is wise to avoid a highpower
takeoff on the next flight until you
determine that the high-speed stability has not
been adversely affected. We fly for the
excitement, but a high-power takeoff with a
marginally stable model can be a little more
than we need.
Unofficial events at the Nats include Skyray
Carrier, .15 Carrier, Nostalgia Carrier, and
Sportsman Profile Carrier. Sig Manufacturing
Company provides fuel and awards for the
Skyray Carrier event.
Gary Hull and the North Coast Control
Liners of Cleveland, Ohio, sponsor the .15
Carrier event. I sponsor the Nostalgia Carrier
events, and the Navy Carrier Society (NCS)
sponsors the Sportsman Profile Carrier
competition, the Carol Johnson Spirit of
Volunteerism Award, and the Rookie of the
Year Award.
The best thanks you could give any of
these sponsors is to come to the Nats,
compete, and take the awards home. I hope
we’ll see you there.
Peter Mazur, Bob Frogner, and others are
experimenting with electric power in a Carrier
context. Details of the developments are
appearing in the Hi-Low Landings newsletter
of the NCS.
At least three Skyray Carrier events this
year will allow electric power on an
experimental basis (not at the Nats, however).
Initial efforts are focused on determining
feasibility and gathering information. I’ll
report the results from the first contest in my
next column.
A number of designators have been used to
describe the bent-wing aircraft we recognize
as a Corsair. In addition to the familiar F4U
built by Vought, there were variants produced
by Brewster (F3A) and Goodyear (FG and
F2G).
Vought produced a variant for ground
attack that the Marines used effectively in
Korea, and it carried the AU-1 designation.
The British, with their penchant for names in
lieu of numbers, designated these aircraft
Corsair I, II, III, and IV. Before the Navy
contracted for the first XF4U, Vought called
the design the V-166B.
There were quite a few Corsair aircraft
besides the well-known F4U. More than a
decade before the first F4U was built, Vought
introduced the O2U Corsair biplane, followed
by the O3U and the XO4U, all carrying the
Corsair name.
One O2U was evaluated by the Army as an
O-28. Most O3U-2s and O3U-4s served under
the SU designation as Scout-category aircraft.
Vought reprised the name two decades after
the F4U was introduced, with the A-7 Corsair
II.
Brewster even attempted to follow the
tradition of giving its aircraft names beginning
with the letter B. Thus the F3A was referred to
by the company as the “Battler.” The name
didn’t stick!
The following is an opportunity to
demonstrate your US Navy Carrier trivia
knowledge.
As with the U designator for Vought
aircraft, there are quite a few mismatches in
the alphabet label and the first letter of the
company it represents. A year’s membership
in the NCS goes to the reader who can identify
the most mismatched designators. MA