Searching for Free Flight - 2004/05

40 MODEL AVIATION
FOR MANY YEARS we Free Flighters have been wandering
around trying to find our airplanes on foot or atop small dirt bikes,
following what we hope are the “lines” the models took during their
flights. Most of the time we try to get visual lines or fixes on the
directions our airplanes take by sighting in on a mountain, a tree, or,
here in Arizona, a cactus. We are usually successful, and we get our
models back to fly again.
However, sometimes we get off-course because we have to cross
obstacles such as ditches or highways, or because we just plain don’t
walk too straight. If we waste a bunch of time searching and can’t
find our models quickly, it affects how many flights we can put up
at a contest. The best time to fly on any given contest day is usually
fairly short. The ultimate nightmare is losing models that really
should be easy to find.
This article will explore a simple way to locate a model based on
knowledge of wind speed to calculate flight distance and wind
direction to predict a point where the model should be sitting using a
Global Positioning System (GPS). It is a relatively inexpensive yet
high-tech approach to getting our models out of the corn! By
knowing the amount of time the airplane is in the air and the
accurate wind speed and direction, we can easily go right to the
model.
A Free Flight model is set up to glide in circles as it follows the
Multitime World
Champion F1C flier
Randy Archer and son
Ryan show GPS
receiver with wind
speed and direction
station. They like using
GPS to locate models
after long flights.
Sometimes flyoff flights
get far away, and it is
helpful to have a way to
find where they land
using wind information
and GPS receiver.
by John Patton
May 2004 41
Wind-speed meter shows current, average wind speeds. Unit logs max wind speed too.
Wind direction is measured on protractor.
wind to its (it is hoped) max flight. The
aircraft drifts downwind in this circle for as
long as you have set the timer for the
dethermalizer device. This is a known time
and is used for your calculations with a fudge
factor for how long it takes your airplane to
lose altitude when dethermalized.
It is good if you can see the model and
time it until it reaches earth. This reduces any
time-related errors. Even if the flight is not a
max, you can accurately follow the aircraft’s
path straight downwind with GPS
information. This is difficult to do with only a
compass if you are not an expert.
There are some nice marine binoculars
available with built-in electronic compasses
that can give you an accurate heading as you
follow the model’s flight path. You need to
know wind speed and direction accurately for
the next part of the equation. The old wet
finger up in the air ain’t gonna do it!
Several inexpensive wind-speed meters on
the market (some even advertised in this
magazine) should be within any club fund’s
or most serious modeler’s reach. You can be
in business for way less than $100.
Commercial wind-direction meters are more
Photos courtesy the author
42 MODEL AVIATION
complex (read expensive). In this article I’ll
refer to a simple yet extremely accurate winddirection
meter.
You can use the time of flight and the
wind speed to predict how far the model has
traveled since launch; that is the distance
traveled. Then you can use the GPS to
navigate to the point where the airplane
should be by using the distance traveled and
wind-direction information.
You can easily calculate the distance the
model has traveled by multiplying the time of
flight in minutes by the wind speed in miles
per hour and dividing by 60. For a fourminute
flight in a 6 mph breeze, the airplane
should travel 6 x 4 ÷ 60 = .40 mile. During a
seven-minute flight in an 8 mph breeze, the
airplane will travel 7 x 8 ÷ 60 = .93 mile. The
chart gives you some numbers to use.
Now that you know the distance, you can get
to the high-tech stuff; for that you need a GPS
unit. Don’t let these things scare you. There
are as many options/features on these things
as there are bumps on a pickle. You don’t
really need all the fancy maps for your use.
The simplest unit (inexpensive) is the
Garmin eTrex personal navigator (the yellow
one). You can find these for $100 in sportinggoods
places and on the Internet. Any GPS
will do the trick, and if you really need a
moving map, go for it!
You will be using the “Projecting a
Waypoint” feature, which is common to all
the GPS units. It is outside the scope of this
article to explain how to navigate to a point
using all the different brands, so I will confine
the instructions to the Garmin eTrex.
In GPS terminology, a “waypoint” is
anyplace you choose for the unit to remember.
The waypoint you are going to project to is
the point on earth where you have calculated
that your model has landed. You also need to
know where you are coming from, so you
must create a waypoint at the launch site.
Turn the unit on and let it find its satellites
per the instruction manual. This gets the unit
to figure out where it is on earth. To mark a
waypoint at the launch site, press and hold the
“Enter” button until the “Mark Waypoints”
page appears. This page shows where you are
on earth and allows you to name the launchsite
waypoint something such as “field.”
When the launch site is named—field—
use the “Down” button to go to “OK,” and
then press “Enter.” Use the “Page” button to
go to the “Menu” page. Select and enter
“Waypoints.” Find and select the “field”
waypoint. This will open the “Review
Waypoints” page with “field” as the waypoint.
Next, project to a waypoint at the distance
and bearing as calculated. Select and enter
“Project” on the “Review Waypoints” page.
This will open the “Project Waypoint” page.
The unit will assign a number—which you
should remember—to the projected waypoint
or you can name it yourself.
Enter the distance and angle we arrived at
earlier in the number and angle fields, and the
GPS will have a place to go to. After the “Edit
Number” and “Edit Angle” features are
entered, you will return to the “Review
Waypoint” page.
Scroll to the “Go To” function and hit
“Enter”; that will activate with the selected
waypoint as the destination. It will also
activate the “Pointer” page, which will steer
you to the waypoint where your model is
resting.
Since the GPS unit won’t let you put in a
number smaller than .1 mile for distance,
remember that .01 mile is 52.8 feet. If you
need to travel .34 mile to your model, enter .3
mile in the GPS and go another 211 feet (as
measured on the GPS readout) with the pointer
indicating that you are going straight away
from your waypoint. It may be easier to use the
“Map” page to follow the line to the model.
A basic and accurate anemometer to
measure wind speed and direction is shown in
the illustrations. A wind-speed meter—the
Vortex Pro-1200—is mounted on one end of a
bar. Wind direction is measured at the other
end of the bar by a weathervane device that
indicates the bearing in compass degrees as
measured on a protractor.
Mount the whole rig on a tripod to get it
high off of the ground. Orient the bar to
magnetic north, and read the wind direction on
the protractor scale that increases numerically
clockwise.
It seems as though you have just gone back
to school, doesn’t it? Enough with the
lessons—let’s go fly! MA
John Patton
4228 N. 35 Pl.
Phoenix AZ 85018
Sources:
Vortex Pro-1200:
ItWorks (Innovative Tech Works)
527 Flume St.
Chico CA 95928
www.itworks.com
www.weathershop.com