Worth a Closer Look - 2003/06

Worth a Closer Look
14 MODEL AVIATION
In each installment of “Worth a Closer Look” we do our best
to bring you new and exciting products from our industry. These
write-ups are not press releases, but are actually minireviews
written by the Model Aviation staff. In each instance the product
or service is actually built, tested, flown, used, etc. to give you a
firsthand account of how it performs.
We have found some of these items on our own, but many have
been brought to our attention from outside sources. If you have a
product or service that you feel might be “worth a closer look,”
contact Model Aviation Aeromodeling Editor Bob Hunt at (610)
614-1747, or send an E-mail to [email protected].
46% TOC Ultimate ARF
The new Hangar 9
46% TOC Ultimate 10-
300 brings true TOC
(Tournament of
Champions) aircraft
performance to the
serious modeler who is
looking for an all-out
performance machine.
Mike McConville
designed this model for
no-holds-barred
performance.
The wings are
designed to be lightweight, yet
strong and without the need for
flying wires. The model is a true
ARF (Almost Ready-to-Fly) and
comes factory-covered in Hangar
9 UltraCote in the yellow, white,
black, and, silver trim scheme
shown. It is balsa-and-plywood
built with carbon fiber used in key areas to assure light, strong
construction. Even the carbon-fiber landing gear comes standard.
This Ultimate has a wingspan of 100 inches, a wing area of
3,310 square inches, weighs 40 pounds, and retails for $1,699.99.
Horizon Hobby Distributors: 4105 Fieldstone Rd., Champaign
IL 61822; Tel.: (800) 338-4639; Web site: www.horizonhobby.com
O.S. .91 SX-H
O.S. has introduced a special
competition version of its .91 SX-H.
This new black-case engine
incorporates features and
advancements that can
make the difference
between winning and
losing, with the largest
engine displacement
allowed in FAI (Fédération
Aéronautique
Internationale) F3C and
AMA sanctioned
helicopter
competitions.
Foremost among its
upgrades is the three-needle carburetor—for high-end, low-end,
and midrange hovering—providing the ultimate in fine-tuning. A
lighter piston and connecting rod combined with a more balanced
crankshaft significantly reduces high-rpm vibration.
The round, gold “Hyper” head with horizontal fins offers better
cooling and sharper looks. The .91 SX-H also inherits from the
standard .91 SX-H the proven push/pull throttle arm, dual ball
bearings, and ringed construction.
The .91 SX-H has a displacement of 0.912 cubic inch (14.95
cubic centimeters), a bore of 1.09 inch (27.7 millimeters), a stroke
of 0.98 inch (24.8 millimeters), and weighs 19.3 ounces (8,755
grams). The output was measured at 3.0 ps at 15,000 rpm with a
practical operating range between 2,000 and 6,000 rpm. The O.S.
.91 SX-H retails for $499.99.
Great Planes Model Distributors: Box 9021, Champaign IL
61826; Tel.: (800) 682-8948; Web site: www.hobbico.com
Biaxial Woven Fiber Tape
What? That’s a fancy
way to describe two new
woven-fiber products—
either fiberglass or
carbon fiber—from
Composite Structures
Technology.
We’ve seen woven
materials before, but
what makes these
different is that the
biaxial weave gives the
flex of a braided sleeve, but in a flat tape. These tapes are ideal for
going around corners, compound curves, and other odd shapes
because they distort easily. Once you have them formed to the
surface, a bit of epoxy is all you need to have a stronger-than-steel
bond.
This is relatively new in our industry but will become quite
popular, even though it is somewhat pricey. These tapes start at
$6.50 and go up, depending on the length and width of the
material.
Composite Structures Technology: Box 622, Tehachapi CA
DC Peak Charger
HobbyZone’s new DC Peak Charger is designed
to work with all of Horizon Hobby’s HobbyZone
aircraft.
It features peak-detection circuitry and
adjustable current so the charge rate can
be customized to suit each
battery. A red LED (lightemitting
diode) indicator shows
the charge cycle status.
The charger plugs into any
automobile 12-volt power
outlet, so it is perfect for use at
the field. Although it only
comes with a plug that
connects to Horizon’s
HobbyZone aircraft (the
Firebird, Fighterbird, and
Aerobird series), an adapter could
easily be made to allow this charger to work with any other
similar-capacity packs.
The DC Peak Charger has a street price of $18.99.
Horizon Hobby Distributors: 4105 Fieldstone Rd., Champaign
IL 61822; Tel.: (800) 338-4639; Web site: www.horizonhobby.com
June 2003 15
Profili 2.11
There are
many different
design programs
on the market that
can help you
design and build
model aircraft.
Most cost $50 or
more, but we’d
like to show you
something that is
considerably less.
Sometimes you
get more than you
pay for!
Before we discuss Profili 2.11, we need to mention another
program: Xfoil. It was written by Mark Drela of the
Massachusetts Institute of Technology and is an interactive
program for the design and analysis of subsonic isolated airfoils.
Xfoil is a freeware program available at http://raphael.mit.edu/xfoil.
Although it’s good, it was written in the days of DOS and can be
tricky to run if you’re not used to typing in commands from a C:>
prompt.
Enter Profili 2.11, written by Stefano Duranti, which does a
masterful job of dragging Xfoil from the computer dark ages into
a modern mouse-driven, point-and-click system. The program
requires Windows 95/98/Me/XP or NT 4.0/2000 and 50MB of
free disk space. It uses the excellent basic Xfoil computations but
has added an interface that makes the program fun to use.
Profili 2.11 can be downloaded from Stefano’s Internet site,
and he is asking for a $10 fee to register the program. A CD-ROM
version can be ordered for $15, which includes shipping. Stefano
has only one fee, even if you put the program on several
computers, but he would like you to register all of them. It is a
realistic policy, and he is to be commended for his decision.
On the Profili home page there are long lists of amazing things
the program can do for you, but we can’t include them here
because of space limitations; however, following is a little of what
we found about it.
Profili has a database of more than 2,200 airfoils with
precomputed aerodynamic characteristics, which really saves time
in making airfoil comparisons. The user’s ability to easily change
the airfoils slightly (or even extremely) has been made effortless.
The program will then compute the new aerodynamics resulting
from your changes. It is interesting to watch the computations
take place; you gain a “feel” for how the pressures are distributed
over and under the airfoil.
Once you input your pet airfoil, Profili goes to work.
Depending on the complexity of the airfoil (maybe something
exotic such as a double diamond shape with a square leading edge
and ripples across the bottom), it may look as if it’s locked up.
Normally this is because Xfoil is having trouble with the pointy
edges of your pride and joy. This is not a failure in Xfoil or
Profili; there are just limits to what is possible with computational
fluid dynamics.
To help manage this, Profili has an adjustable time-out
function to keep things moving. When you try to design the
world’s most marvelous airfoil, keep in mind that nature prefers
smoothness and will reward a finesse approach to airfoil design.
You might have heard the local theorists at the flying field
discuss Reynolds numbers (Re). Profili will compute Re for you
when you input your projected flight speed and model size. The
accompanying screen shots are examples of selecting a particular
airfoil, in this case an HQ 3.0/15, and calculating the
aerodynamic characteristics at different Res. One thing we
noticed was that for the HQ airfoil, as well as many others, there
is a lot of variation in
drag coefficient (Cd)
with Re. It is one of the
reasons big models seem
to fly better than small
ones.
Did you ever wonder
what something like
tabulators did to help or
hinder an airfoil? Profili
will let you investigate
how things such as these
can help (or hinder) the
aerodynamics of any
wing, but these
examples are only
scratching the surface of
what can be learned
from using Profili.
Profili has a built-in
“Genius” that senses
when you need help and
will suggest things for
you to do to help smooth
your designing sessions.
Although you can turn
off the Genius, it is handy and accurate.
After the final aerodynamic calculations are finished and you
have refined what you need for your design, Profili is able to help
even more. It can create and print rib templates to use as guides
for foam cutting
or print standard
ribs to allow
conventional
balsa
construction. You
can even export
your final ribs as
a DXF file to
import into other
CAD software.
You can select
wing-taper ratios
or even elliptical
planforms,
leading-edge sizes, spar shapes and sizes, lightening holes,
trailing-edge widths, and skin or capstrip thicknesses.
Figure 8 is an example of the rib templates for some HQ
airfoils. The taper of the wing, the airfoil type, and the twist of
the wing were selected, and Profili produced templates that
incorporated all of them. The program can put tabs on the lower
surface of the ribs to allow the wing to be built on a flat surface,
regardless of the airfoil contours.
Profili 2.11 is a good program for its educational potential and
for the way it can ease the model-aircraft design and building
process. The fact that it automatically generates rib templates,
with just a little input from the user, can save tons of time. And
don’t forget about the bang for the buck; this program does a
great job with a minimum amount of fuss, while leaving money
in your wallet.
Duranti Stefano: Via della Casazza, 32032 Foen di Feltre
(BL), Italy; Web site: www.profili2.com/eng/default.htm MA