Peck-Polymers is owed
credit for the inspiration for
this sport foamie project.
The ParkZone “brick” receiver is used to control the 100%-size version. Notice the bend
in the pushrod, to assure linear servo gear clearance.
THE ORIGINAL rubber-powered
Stringless Wonder is an intriguing, kitelike
aircraft that Bill Hannan designed and Peck-
Polymers kitted in 1973. Bill Pardoe won the
Northrop Flying Wing Contest with it, with
a five-minute flight.
This model is still available as a stickand-
tissue kit. It’s a quick build that can
provide hours of free flight fun.
The Skymasters Radio Control Club of
Michigan, in conjunction with the Romeo
Skyhawks, Greater Detroit Soaring and
Hiking Society, and Radio Control Club of
Detroit, host weekly winter indoor flying at
Above right: Ten-year-old Tim Young launches the 100%
Stringless Wonder Revisited. A high-angle toss is required. Flying
the model is fun for all ages.
Left: The 3mm carbon-fiber motor mount under heat-shrink
tubing on the motorstick allows the motor to be positioned for
optimal CG placement.
Above: A Mustang ParkZone motor
system powers the 150% version. A
scrap block of balsa is carved to
accept the mount.
Right: The larger Stringless
Wonder is higher in
performance and can be flown
slower. These aircraft turn big
and climb quickly, as did the
original FF version.
A ParkZone Ember motor system powers the 100% version. The
downthrust shown might not be everyone’s taste, so feel free to
The 100% version uses 2mm Depron, while the 150% size is built take some out.
using 3mm Cellfoam88 or equivalent. Both use a 1/4-inch
motorstick.
Photos by the author
May 2010 25
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ParkZone hardware is perfect for the Stringless Wonder. Tubing
that links the pushrod ends is glued once the control surface is
centered.
The 150% Stringless Wonder is a
great backyard flyer and can
manage light breezes. Loops and
stall turns are possible.
A CA glue fi llet is suffic ient to support the wing dihedral joint.
Hinge the surfaces b ef ore assembly. Isn’t using waxe d pap er a
good idea?
Ultimate Soccer Arenas in Pontiac, Michigan.
This phenomenal facility allows us to keep our
flying skills up and our creative juices flowing.
I started this project when I remembered
that I had a Stringless Wonder kit on the shelf.
Opening the plans got my mind in gear. I
thought that some 2mm Depron, the ParkZone
“brick” receiver/ESC/servo module (item
PKZ3351), and the Vapor motor system
should be what I needed to make an RC
version.
I cut a kit of foam pieces using the original
plans as a template. Rudder and elevator
dimensions were carefully calculated (as in
with the width of a nearby ruler). The
“motorstick” fuselage was cut from a piece of
hard 1/4 square balsa.
There are few tricks to ease assembly. I’ll
get to those in a moment.
The first flights were disappointing,
because the power from the Vapor system
barely provided a gradual descent. I knew that
a similar but stronger power system was
available, for the ParkZone Ember (item
PKZ3228 motor/gearbox and PKZ3002
propeller). That change made all the
difference.
Then I created a 150%-scale version of the
Stringless Wonder. Employing 3mm Depron
and the ParkZone Micro Mustang power
system (item PKZ3624 motor/gearbox and
item PKZ3601 propeller), flight performance is
excellent.
I have a few assembly suggestions that apply
to either size Stringless Wonder. Cut out your
kit. Actual dimensions can vary significantly, so
don’t be too concerned.
Bevel the LE of the elevator and rudder to
allow for movement of the control surfaces.
Hinge both the rudder and elevator with hinge
tape before assembling the wing. It is much
easier to decorate your aircraft before
construction, so get your felt-tip markers and
pens out now.
Attach the Du-Bro Micro Control Horns
(item 848) to the elevator and rudder with gapfilling,
foam-safe CA. The rudder control horn
is attached to the left side of the rudder. The
elevator control horn is attached on the right
side of the elevator.
Protect your building surface with waxed
paper. Attach the vertical stabilizer to the rear
wing center-section. Position the front wing
center-section on your building surface. Small
weights help hold things steady.
Attach each outer wing to the center-section
pieces. Approximately 11/4 inches of dihedral
on each wingtip is necessary. I confess that I
didn’t bevel the foam on the wing outer panels.
A few drops of gap-filling, foam-safe CA
will tack the outer wing panels to the centersection.
After the CA has kicked off, flip the
wing over and fill the gap with a bead of gapfilling
CA. The 1/4 square “fuselage” is attached
to the bottom of the wing with gap-filling,
foam-safe CA.
The receiver/ESC/servo module is attached
with double-stick foam tape. Pushrods are
created with 1mm carbon-fiber rod and .024-
inch-diameter music wire. Make the Z-bends
with small needle-nose pliers.
Notice that the music wire that attaches to
the servo is angled down, to clear the gears.
Position the wire on the carbon fiber and slide
heat-shrink tubing over the wire. Shrink the
tubing, but do not apply thin CA yet.
Remove the music wire from the servo side
of the pushrod. Slide the other Z-bend into the
flight-surface control horn. Using the forward
hole on the servo (it has a larger opening), slide
the Z-bend into the servo. Slide the wire into the
preshrunk heat-shrink tubing on the pushrod.
The fit is tight enough to allow adjustment,
including during the test flights.
After successful test flights, a drop of thin
CA will hold the wire and carbon-fiber pushrod
in place. There should be roughly 1/16 inch of
up-elevator at neutral.
The motor gearbox is adhered with CA to a
piece of 3mm-wide, flat carbon fiber. Not being
sure exactly where the motor gearbox should
be, shrink a piece of heat-shrink tubing around
the front of the 1/4 square motorstick.
Slide the 3mm carbon-fiber flat stock
underneath the heat-shrink tubing. This allows
for easy repositioning or experimentation. It
also provides for a bit of shock absorption in
case there is an “incident.”
On the original 100% version of the
Stringless Wonder, the ParkZone single-cell, 70
mAh Li-Poly battery (item PKZ3001) is
attached to the side of the fuselage with hookand-
loop fasteners in the wing opening. The CG
is close to 3/4 inch behind the wingtip.
The original version flew well with the
downthrust indicated. However, flight
perfdownthrust was removed.
Sand the bottom of the gearbox to change
the angle, and glue the gearbox to the 3mm flat
stock. The original weighs 17 grams (1/2
ounce).
It is easier to have someone else launch the
aircraft on the first flights. A light toss with
the nose pointing up approximately 20° will
reduce the altitude loss on the launch.
Adjust the battery, motor, and elevator
position to get the flight characteristics you
desire. This model will need right rudder trim
unless you set the motor with roughly 1° of
offset.
The RC Stringless Wonder is easy to fly. It
climbs easily and has a nose-up attitude, even
in a cruise.
Plan ahead for turns during flight, because
there isn’t much elevator authority to pull the
model around in a tight turn. To make a turn
as compact as possible, initiate it and add full
up-elevator while extra power is applied, to
keep the nose up.
The Stringless Wonder will not stall.
There’s enough power to fly and climb for up
to eight minutes, but looping is a challenge.
The 150% version is much better at aerobatics.
The 150% version uses all the same build
techniques. I fashioned a motor mount from a
small balsa block with approximately 7° of
downthrust.
The motor/gearbox is attached to the wood
block with CA. A ParkZone 150 mAh Li-Poly
battery (item EFLB1501S) can be used for
longer flights. On the 150% version, the Li-
Poly is attached to the wing center-section in
front of the receiver module. This iteration of
the model weighs 39 grams (slightly more
than 1 ounce).
When ordering Stringless Wonder plans
(set 1040), ask the AMA Plans Service to
provide an extra copy at 150% of the original.
You should get that copy for half price at least
for a limited time. Save the effort of having to
run to the copy center later.
The basic design allows for a great deal of
experimentation with power systems and
electronic components. Experiment with the
CG. After a dive to build speed, I have
performed loops, Immelmanns, and
Chandelles with the 150% Stringless Wonder.
Have fun! MA
Joe Hass
[email protected]
Sources:
Skymasters Radio Control Club
www.skymasters.org
Peck-Polymers/A2Z Corp
(877) 754-7465
www.a2zcorp.us/store
ParkZone
(800) 338-4639
www.parkzone.com
Spektrum RC
(800) 338-4639
www.spektrumrc.comormance improved as the excessive
