CONTROL LINE SPEED - 2003/07

134 MODEL AVIATION
WHEN SPEED FLIERS discuss their hunt for more speed, the
questions are usually engine related. Is my engine timed
correctly? What can I do with my Dremel tool to generate more
horsepower? Is the head deck height correct? Am I turning
enough rpm? Few modelers look at the model in their hunt for
more miles per hour, but we are going to look at a change in
model design that improved a Speed flier’s time by 6 mph!
Al Jones of Gainesville, Virginia, had been flying .21 Sport
for several years. His speeds were approximately 140 mph.
During the winter of 2001-2002, Al built a new top for his .21
Sport and made no changes to his engine, pan, or fuel-system
setup. At the Queen City Speed Meet in Cincinnati, Ohio, June
15-16, 2002, Al turned 146.16 for first place and his personal
best time in the event.
I asked Al what he had done to improve his time to such a
degree. He stated that he had moved where the wires exited the wing
in relation to the center of gravity (CG). Al had used one of those
Speed Secrets that we all hear about to improve his performance.
When a Speed flier builds a new model, one of the decisions
CONTROL LINE SPEED
Dave Mark, Box 371, Fenton MI 48430; E-mail: [email protected]
Al Jones at 1998 Nationals at Muncie IN. Chris Sackett photo.
Bob Fogg (R) prepares to start his record-holding .21 Sport
model at 1998 Nationals; Peter Brown assists. Sackett photo.
Bob Fogg (R) works on his D Speed model with his pilot George
Brown III’s help at the 1998 Nationals. Sackett photo.
that needs to be made is where the wires should exit the wingtip
in relation to the CG. When this question comes up, many refer
to past designs for guidance. Upon reviewing plans from the past
we see that many record setters had the lines exit in front of the
CG.
The Dizzy Boy series of Speed models designed by Bob
Lauderdale had the wires exiting roughly 1⁄8 inch in front of the
CG. Many others had exit points as far as 3⁄8 inch in front of the
CG. The plans for Bill Wisniewski’s record-holding Pink Lady,
printed in 1958, show the lines exiting 3⁄4 inch in front of the CG.
I am told the thinking was that this placement would allow the
model to nose in a bit in flight, thus lessening the pull on the
lines and allowing the airplane to go faster.
As you read this, think a bit about your last Control Line (CL)
flight and ask yourself how the lines looked. As you draw that
July 2003 135
image of your favorite model in your
head, you will notice that the lines were
extending out to the model in a graceful
curve behind a straight line we draw
mentally between the handle and the
model.
This curve along with the placement of
the exit point causes the model to fly with
the nose yawed inward as it pursues its
path dictated by our flying wires. The
result is an increase in drag generated by
our streamlined, carefully built model
flying sideways to the circular path we
want.
The next effect is even worse. Let’s
say we set a Speed model with a 24-inch
wingspan over a straight line on the floor
of your workshop. We line the model up
so that when viewed from the top we see
that the point of the spinner and center of
the rear of the fuselage are directly over
the line. We move the propeller so that it
is vertical. Then we reach down and move
the inboard wingtip 3⁄4 to 1 inch toward
the rear of the model.
That will demonstrate the effect the
misplacement of the line exit will have on
the model, but now look at and think
about the propeller. If we view the
propeller from the top we will see that the
extreme yaw causes the blade on top to
effectively increase in pitch and the blade
on the bottom to drop in effective pitch.
This is not a good deal! The propeller
that we spent many hours filing and
sanding so that it was identical on both
blades is now so out of position to our
flight path that we lose much of its
effectiveness.
How do we fix this? Do we guess at
the placement? Nope! We turn to a
shareware computer program that Bob
Fogg wrote. If you have been around
Speed flying much, you have heard of
Bob. If you haven’t, I would describe him
as a person who enjoys solving problems;
each problem solved produces a slightly
faster model. Bob has solved many
problems, and this is proven by his name
being on many of the records for CL
Speed and Racing classes.
To demonstrate the use of his program
we will use a Formula .40 model. It will
have a 24-inch wingspan, will weigh 26
ounces, and/or the target speed will be 162
mph.
The program is made up of two parts:
leadout.exe and leadout.dat. Both are
copied into the same directory. You start
the program by double-clicking
leadout.exe. When you do this, a window
with a green background appears along
with two data-entry boxes. The box to the
left of the screen asks you to enter the wire
diameter, line length, and select if you will
be using a monoline or two-wire
configuration.
The box to the right asks for the span
of the inboard wing. In our example it is
12 inches. The weight is next; we enter 26
ounces. The next item required is the
target speed at which we will fly; we will
use 162 mph.
As soon as these items are entered, the
program calculates the neutral leadout
position for zero yaw angle, line pull, line
yield strength based on 80% of ASTM
A228 tensile strength of an undersize
(–0.0005) wire, the wire factor of safety
(yield/load), wire Reynolds number, wire
coefficient of drag, drag load in pounds,
and wire-drag horsepower. It also includes
a feature that will notify us if the
combination of data entered is unsafe by
displaying the Factor of Safety in red.
For our example, the program tells us
that the wire should exit the wing .702 inch
or 45⁄64 inches behind the CG. If we change
the inboard length to 15 inches, the program
tells us that we can go 163.5 mph with the
same horsepower. Playing with the program
a little reveals that the line is the greatest
drag producer. That is why F2A models had
such long inboard wings in the past, just to
cover the wire. It got so out of hand that
they were regulated to roughly 30 inches.
At many contests in the past it was
common to see several models come in on
takeoff and chase the pilots around. This
was caused by forward placement of the
line. A model built with the setback
calculated by Bob’s program rolls on the
dolly with a slight nose-out attitude, thus
removing the high-anxiety element from the
launch.
This works great for the events that are
timed on the fly, but some feel that the
model’s slight outward stance works against
the .21 Proto and Formula .40 models.
Those events are timed from release for 14
laps. Many feel that a quick first lap is of
utmost importance in those events. They say
that slight outward stance slows the model
for that most important first lap.
With Speed flying, there are no perfect
solutions for all events. This is the perfect
place for a device that could be mounted in
the wing that would allow the lines to be set
at zero setback, therefore allowing the model
to take off with zero yaw during that most
important first lap. Then when our model is
up to speed, our device would be triggered
by line pull to allow the lines to move back
to the perfect setback as calculated by Bob’s
program.
Please keep in mind that Bob’s program
is shareware; if you use it, you should send a
donation to Bob as listed in the program
help file. As with all things, please note that
your mileage may vary with the use of this
information.
The program is available on the Internet
or from the North American Speed Society
(NASS) for $5 to cover the cost of mailing
and reproduction.
Modelers who are interested in plans for
models from the past should take a look at
CD-ROMs made by Tom Wilk of Duluth,
Minnesota. He offers a CD that contains
more than 200 vintage Speed models
designed from 1940 to 1958. Another CD
features more than 125 models covering
classic Speed from 1959 to the present,
and there is one with Goodyear and Team
Racing designs.
The CDs are $10 each postpaid in the
US only. Contact Steve Wilk of
Eliminator Props at (763) 531-0604 to
order.
Anyone who is interested in more
information about CL Speed should
consider joining the North American
Speed Society. Write to NASS at Box 371,
Fenton MI 48430.
That’s it for now. I’ll be back in three
months. Please send me any pictures or
requests for items you would like to see in
the column. If you’d like a reply, an SASE
would be appreciated. MA