IN THE EARLY days of this column—
let’s not discuss how many decades have
passed since that time—I wrote about
where to locate the line guide. That topic
was based on Bill Netzeband’s work
published in 1966 with the results plotted
for our three-line control systems.
The information I distributed had a
number of shortcomings, the first of
which was that my charts dealt only with
three-line control systems at normal
Carrier-model weights with Carrierspecific
line diameters and line length.
Second, each solution required a
separate plot. Third, the results were in
degrees of line sweep because that was
the only set of units that was independent
of spanwise line-guide location, but
degrees are harder to measure than
inches.
Since then we’ve progressed through
programmable calculators to computers
in most homes. Now it’s possible to write
a program that applies all the math for us
and spits out the answer in easy-to-use
terms.
Why does it matter? In high-speed
flight, drag is significantly affected by
whether or not the model is pointed in
the direction it is flying (tangent to the
flight circle). Correctly determining the
proper location of the line guide before
the first flight can simplify the trimming
process.
In the good, old days we mounted the tank, engine, and
propeller and hung the model from the leadouts. If it hung level
or slightly nose down, that was about right. That method usually
worked, but it wasn’t optimal.
Sometimes the leadout and balance-point locations published
in the plans were good, sometimes the model didn’t balance at
the designated location, and sometimes we used lines that were a
different size or length than those for which the model was
designed. The airplanes flew anyway, but maybe not as well as
they might have. With some digital help, maybe we can start out
closer to an optimum location.
There are some options on the Internet from different authors.
Each is slightly different in the assumptions used, inputs required,
and outputs provided. One of the easiest is by Bob Fogg. It
appears on the CL Speed forum at Delphi, posted originally in
Gary Hull’s new Japanese Val wasn’t ready for flight at the Nats, but it should have
been seen on the contest circles by now. Power is an O.S. .36 FSR.
A de Havilland Sea Vampire (a Bill Calkins design) in slow flight. Bob
has a new uniflow tank on this model feeding a Nelson .36 engine.
This Brewster prototype was Gary Hull’s entry in .15 Carrier. It
was a new model at last summer’s Nats.
1999. You can find the program by
searching under message number 116.1 or
you can E-mail me and I’ll send it to you.
In addition to the simple information
about leadout location, it provides data
about line drag and the power consumed
by that drag, line load, line strength (for
solid lines only), and safety factor (again,
for solid lines). The strength of stranded
lines is approximately 80% of the strength
of solid lines. Use this strength to compute
a new safety factor if you want that
information.
Other programs and comments about
this topic begin more recently at message
number 2564.1. Have fun.
The Bob Fogg program is simple to
use. It consists of a display with numerous
data blocks (line diameter, line length,
model weight, model speed, and the
location of the leadout guide in relation to
the CG). The data block is identified as
“Inboard Span.”
This latter piece of information
requires a leadout location in relation to
the CG—not the center of the fuselage or
the pivot point of the bellcrank. The
output is also in relation to the CG. There
are a few potential pitfalls in determining
the exact CG location.
The CG used as a reference for lineguide
location is the in-flight CG. It has
two dimensions that are critical to us, the
most obvious of which is the forward/aft
location we’re used to seeing. The other is
the inboard/outboard location.
Most of us determine the balance point
for our models as a routine step in
building. The problem with using that CG
location is that we carry fuel on the
model—often a significant amount—
usually forward of the empty balance
point. For the leadout position to work, the
balance point needs to be in flight
condition; i.e., with a fuel load that is
representative of the high-speed portion of
the flight.
The inboard/outboard location of the
balance point determines the input to the
program that specifies the spanwise
location of the line guide on the model.
The CG won’t be on the fuselage
centerline on most Carrier models.
Wingtip weight and line weight must be
considered. The spanwise balance point
can be measured easily without the lines.
However, the line guide must support half
the weight of the lines.
In the Fogg program there is an option
for monoline or two-line control systems.
Although that seems to be missing a
capability that is most applicable to our
Navy Carrier events, there is a simple
solution.
For three-line systems, use the
monoline option and reduce the model
weight to one-third the actual flying
weight of the airplane. For line drag and
power, multiply the program result by
three.
The dimensions determined from the
program are to the center of the line guide.
That is easy to determine if the lines exit
the same hole or are evenly spaced. If the
lines are spaced unevenly, just find the
midpoint between two lines and move
one-third the distance from that midpoint
toward the third line.
No matter how you determine initial
leadout location, the final leadout location
will probably need to be adjusted after
flight testing has determined the optimum
balance point for slow flight and stable
high speed.
I have found that the easiest way to do
that is to use colored tape that contrasts
with the model’s paint scheme. Put a piece
of tape on the inboard wingtip and a piece
of tape vertical on the fuselage side facing
the pilot at a location that is perpendicular
to the fuselage centerline from the wingtip
tape. In flight the wingtip and fuselage
marks will be aligned when the model is
tracking perfectly around the circle.
The photos this month are from the Navy
Carrier competition at the 2006 Nats.
There were several new models, some of
which I have included here. Others were
part of the coverage that was posted on the
AMA Web site at www.modelaircraft.org/
events/natsnews.asp.
Edition: Model Aviation - 2007/01
Page Numbers: 162,164
Edition: Model Aviation - 2007/01
Page Numbers: 162,164
IN THE EARLY days of this column—
let’s not discuss how many decades have
passed since that time—I wrote about
where to locate the line guide. That topic
was based on Bill Netzeband’s work
published in 1966 with the results plotted
for our three-line control systems.
The information I distributed had a
number of shortcomings, the first of
which was that my charts dealt only with
three-line control systems at normal
Carrier-model weights with Carrierspecific
line diameters and line length.
Second, each solution required a
separate plot. Third, the results were in
degrees of line sweep because that was
the only set of units that was independent
of spanwise line-guide location, but
degrees are harder to measure than
inches.
Since then we’ve progressed through
programmable calculators to computers
in most homes. Now it’s possible to write
a program that applies all the math for us
and spits out the answer in easy-to-use
terms.
Why does it matter? In high-speed
flight, drag is significantly affected by
whether or not the model is pointed in
the direction it is flying (tangent to the
flight circle). Correctly determining the
proper location of the line guide before
the first flight can simplify the trimming
process.
In the good, old days we mounted the tank, engine, and
propeller and hung the model from the leadouts. If it hung level
or slightly nose down, that was about right. That method usually
worked, but it wasn’t optimal.
Sometimes the leadout and balance-point locations published
in the plans were good, sometimes the model didn’t balance at
the designated location, and sometimes we used lines that were a
different size or length than those for which the model was
designed. The airplanes flew anyway, but maybe not as well as
they might have. With some digital help, maybe we can start out
closer to an optimum location.
There are some options on the Internet from different authors.
Each is slightly different in the assumptions used, inputs required,
and outputs provided. One of the easiest is by Bob Fogg. It
appears on the CL Speed forum at Delphi, posted originally in
Gary Hull’s new Japanese Val wasn’t ready for flight at the Nats, but it should have
been seen on the contest circles by now. Power is an O.S. .36 FSR.
A de Havilland Sea Vampire (a Bill Calkins design) in slow flight. Bob
has a new uniflow tank on this model feeding a Nelson .36 engine.
This Brewster prototype was Gary Hull’s entry in .15 Carrier. It
was a new model at last summer’s Nats.
1999. You can find the program by
searching under message number 116.1 or
you can E-mail me and I’ll send it to you.
In addition to the simple information
about leadout location, it provides data
about line drag and the power consumed
by that drag, line load, line strength (for
solid lines only), and safety factor (again,
for solid lines). The strength of stranded
lines is approximately 80% of the strength
of solid lines. Use this strength to compute
a new safety factor if you want that
information.
Other programs and comments about
this topic begin more recently at message
number 2564.1. Have fun.
The Bob Fogg program is simple to
use. It consists of a display with numerous
data blocks (line diameter, line length,
model weight, model speed, and the
location of the leadout guide in relation to
the CG). The data block is identified as
“Inboard Span.”
This latter piece of information
requires a leadout location in relation to
the CG—not the center of the fuselage or
the pivot point of the bellcrank. The
output is also in relation to the CG. There
are a few potential pitfalls in determining
the exact CG location.
The CG used as a reference for lineguide
location is the in-flight CG. It has
two dimensions that are critical to us, the
most obvious of which is the forward/aft
location we’re used to seeing. The other is
the inboard/outboard location.
Most of us determine the balance point
for our models as a routine step in
building. The problem with using that CG
location is that we carry fuel on the
model—often a significant amount—
usually forward of the empty balance
point. For the leadout position to work, the
balance point needs to be in flight
condition; i.e., with a fuel load that is
representative of the high-speed portion of
the flight.
The inboard/outboard location of the
balance point determines the input to the
program that specifies the spanwise
location of the line guide on the model.
The CG won’t be on the fuselage
centerline on most Carrier models.
Wingtip weight and line weight must be
considered. The spanwise balance point
can be measured easily without the lines.
However, the line guide must support half
the weight of the lines.
In the Fogg program there is an option
for monoline or two-line control systems.
Although that seems to be missing a
capability that is most applicable to our
Navy Carrier events, there is a simple
solution.
For three-line systems, use the
monoline option and reduce the model
weight to one-third the actual flying
weight of the airplane. For line drag and
power, multiply the program result by
three.
The dimensions determined from the
program are to the center of the line guide.
That is easy to determine if the lines exit
the same hole or are evenly spaced. If the
lines are spaced unevenly, just find the
midpoint between two lines and move
one-third the distance from that midpoint
toward the third line.
No matter how you determine initial
leadout location, the final leadout location
will probably need to be adjusted after
flight testing has determined the optimum
balance point for slow flight and stable
high speed.
I have found that the easiest way to do
that is to use colored tape that contrasts
with the model’s paint scheme. Put a piece
of tape on the inboard wingtip and a piece
of tape vertical on the fuselage side facing
the pilot at a location that is perpendicular
to the fuselage centerline from the wingtip
tape. In flight the wingtip and fuselage
marks will be aligned when the model is
tracking perfectly around the circle.
The photos this month are from the Navy
Carrier competition at the 2006 Nats.
There were several new models, some of
which I have included here. Others were
part of the coverage that was posted on the
AMA Web site at www.modelaircraft.org/
events/natsnews.asp.