ThIS MonTh I’ll give a short plug for a
new Cross Country race—the Canal Run.
The bulk of the column will describe some
pod-and-boom Unlimited models that were
inspired by Tom Kiesling’s Mantis.
Starting in 1976, the SOAR club of
Chicago IL ran a Cross Country Radio
Control (RC) Soaring contest called The
Great Race.
In Cross Country, the pilot steers his
glider while he or she rides in the back of a
pickup truck. The airplane alternates
between thermaling and high-speed straightline
flight. Stops on the shoulder of the road
are frequently required to concentrate on
thermaling.
The length of The Great Race course
varied slightly throughout the years; it was
usually between 42 and 50 miles.
To win this competition, pilots not only
had to complete the course, but they had to
do it faster than the other competitors. It was
a popular event, with very stiff competition
between teams.
The Great Race is no longer held, but a
replacement has appeared on the horizon:
The Canal Run, which will be held June 16,
2001 in Fort Wayne, Indiana. (June 17 is the
rain date.) The course is in the vicinity of
the old Wabash and Erie Canals.
This event will be similar to The Great
Race, and a Scale Glider class may be added
if there is sufficient interest.
The Canal Run should draw teams from
across the nation. If Joe Wurts and Skip
Miller compete, the real contest may be for
third place.
I have already sent in my entry fee!
The Web site and contact information for
the event are at the end of the column.
Variations of the Mantis: Tom Kiesling of
Johnstown, Pennsylvania first flew his
three-meter Mantis glider in 1997.
Since that time, Tom has been
refining the design and winning many
contests. Tom was the Eastern Soaring
League Expert Champion the last three
years in a row.
The Mantis has a pod-and-boom
fuselage, with pylon-mount wing and V-tail.
The gangly-looking airplane has a 122-inch
wingspan, and the three-piece bolt-on wing
Mike Garton, 506 NE 6th St., Ankeny IA 50021; E-mail: [email protected]
RADIO CONTROL SOARING
Tom Kiesling’s 3.4-meter Super Mantis (or “Superman”) glider looks similar to his
Mantis. Low wetted area (surface area) helps keep drag to a minimum.
Jerry Robertson (Flagstaff, Arizona) holds his nicely proportioned Preying Mantis,
which spans 120 inches. It has a Bird of Prey wing, Mantis-like fuselage.
The front end of Phil Barnes’ production
Mantis. This one has been modified; it
has two nose skegs instead of one.
112 M ODEL AVIATION
sports the SD7037 airfoil. Construction is
vacuum-bagged carbon-and-fiberglass
wings with a molded fuselage.
A Mantis weighs approximately 57
ounces. Its primary strengths are its light-air
floating ability and the way it lands.
With the flaps down, a Mantis slows to a
crawl. The large V-tail maintains solid
handling while landing.
Pilots report that they do not flare the
Mantis for contest landings. They just push
the nose down, and fly it at the 100-point
end of the landing tape. The Mantis’s high
strength-to-weight ratio allows it to take
these landings in stride.
If the pilot hits a wingtip on landing, the
wing pivots around a single bolt to reduce
the potential for damage. Sandpaper glued
to the wing-to-pylon interface provides
friction, and keeps the wing from pivoting
in flight.
With Tom’s permission, Phil Barnes has
been producing Mantis kits. Phil made some
internal changes for manufacturing reasons,
but the aerodynamic design of the original
Mantis has been faithfully reproduced.
One change was to replace Tom’s
custom-molded fuselage with a ready-made
carbon tube, a separate forward-fuselage
pod, and a pylon.
The pylon and the fuselage pod are made
from thick Kevlar™, around positive molds.
The parts are partially cured, slit along one
side, then pulled off the forms. The kitbuilder
rejoins the slit and reinforces it
during assembly.
This unconventional method works very
well for small composite parts.
The Mantis has built-in ballast
receptacles in the pylon.
There are more pictures of the massproduced
Mantis on the Web site; the address
and Phil Barnes’ contact information are
given at the end of the column.
Tom continues to refine the Mantis
design. In 1999, he started flying a variant
called the Super Mantis, or “Superman”
for short.
The appearance of the Super Mantis is
similar to that of the original Mantis, but
Tom stretched the wing to 3.4 meters. He
also changed the airfoil to an MH32, which
is faster than the SD7037.
The Super Mantis provides more
penetration and range than the original Mantis.
Tom added slight polyhedral to the
Super Mantis’s wingtips; this helps
coordinate the turns while thermaling.
Jerry Robertson of Flagstaff, Arizona has
been flying a model he calls the Preying
Mantis; it’s the Bird of Prey wing on a
Mantis-like fuselage.
The Bird of Prey wing has a 120-inch
span with an SD7037 airfoil and a crescentshaped
planform. Jerry glued the two-piece
wing together and fiberglassed over the
joint. This eliminated the wingrod, and
made it lighter.
The one-piece wing should also be
stronger than the Bird of Prey’s. Jerry
reports that it eliminates the “bounce-back”
on landing. A steel or carbon wingrod can
The Preying Mantis uses a built-up conventional tail. Many pilots prefer a conventional
tail over a V-tail for handling during precision landings.
This is the machined-aluminum pylon structure of Pete Schlitzkus’ Double Barreled
Homebrew. Notice the two carbon tubes used for the main fuselage.
The nose of Pete’s Double Barreled Homebrew was vacuum-formed using
indestructible Kydex® plastic. Duct tape holds the two sides of it together.
January 2001 113
store energy during a spiked landing, and
can cause a model to bounce backward from
the point of touchdown. This is not an issue
with a one-piece wing.
The Preying Mantis also incorporates
an attractive front nose pod and a built-up
cruciform tail. A light tail allows Jerry to
use a nicely proportioned fuselage. It
appears to be 3⁄4 tailboom and 1⁄4 nose
boom.
I was surprised to see thin drafting
plastic extending behind the trailing edge of
the horizontal stabilizer. Jerry added it to
slightly increase the tail volume.
The plastic also tapers the trailing edge
to a knife-edge, which reduces drag caused
by a truncated trailing edge.
The plastic is 0.007-inch thick and 7⁄8-
inch wide. Jerry uses 1/2-inch double-stick
Scotch™ tape to adhere the two pieces,
then the sandwich is slipped onto the
trailing edge and secured with regular
Scotch™ tape.
A 3⁄16-inch gap between the original
trailing edge and the double-stick tape
allows the plastic to transition smoothly.
The Preying Mantis has winglets. I
thought it was unusual to see them on an
Unlimited-class airplane, because
aerodynamics texts teach that more
wingspan is usually chosen over winglets.
Commercial airliners use winglets when
increasing the span is not an option.
Jerry said the winglets have improved
handling; a longer wing would degrade
handling. The impact on control may be
caused by an increased effective dihedral
angle, which would help coordinate the
turns. The airplane would roll more in the
direction it was yawed.
The winglets may also increase aileron
effectiveness. Less aileron deflection
would be required. Lower deflections
mean less drag, which means less adverse
yaw, which is the tendency of the downaileron
to turn the airplane opposite of the
desired roll.
If the winglets do increase aileron
efficiency, the net effect would be morecoordinated
turns.
Jerry noted that the latest crop of
Unlimited full-scale gliders have
winglets.
Pete Schlitzkus created another Mantislike
scratch-built model; he calls his design
the Double Barreled Homebrew.
The name comes from the fact that Pete
used double-stacked carbon tubes for the
fuselage. To hold everything together, he
machined an aluminum pylon, with
receptacles for the tubes.
Is it obvious that Pete is a machinist?
A vacuum-formed plastic fairing slips
over the machined pylon, after the rest of
the airplane is assembled.
The forward fuselage of the Double
Barreled Homebrew was vacuum-formed
from Kydex®—the same durable plastic
from which luggage is made. MA
Sources:
Canal Run contact:
William Sears
8313 Beacon Ridge Pl.
Fort Wayne IN 46835
(219) 492-9261 (evening)
[email protected]
www.flyingcircuits.org/events/canalrun/in
dex.html
Mantis:
Phil Barnes
13610 Chrisbar Ct.
Germantown MD 20874
(301) 916-9574
http://pages.hotbot.com/biz/flymanti/index.html
