Tutorial About SuperDF:
SuperDF Used in Helicopter Search and Rescue
The Applications
A helicopter is the ideal platform for Search And Rescue (SAR) or
signal tracker using the BMG Engineering, Inc. SuperDF Radio
Direction Finder (RDF). An airborne SuperDF looking down at the
ground will provide a very stable and accurate bearing on an RF
signal. There are several applications for helicopter mounted RDF
equipment:
- Rescue of firefighters trapped by brush or forest fires.
Confusion can readily exist in an emergency situation. Which ridge
are they on? Where exactly on the ridge? Smoke can make the
spotting of people on the ground difficult from a "safe" altitude.
Seconds of delay can mean the difference between life and death!
RDF can remove these problems, allowing the pilot to spiral in
directly to the firefighter's exact location. The people on the
ground do not even have to be conscious, if they have activated a
transmit lock on their radio.
- Locate downed aircraft, homing in on the Emergency Locator
Transmitter (ELT). A helicopter is much better suited to this work
than is a small fixed wing aircraft. Because the helicopters
maneuverability is so superior, the crash site can be exactly
pinpointed faster. Also, aid can be delivered within seconds or
minutes of locating the crash site.
- Boats in distress can be quickly located even in fog by
homing in on an EPIRB, marine, or HAM radio. Aid can then be
dropped, or rescue craft vectored in to the site, again by taking
RDF bearings on the rescue craft, and providing the reverse
bearing for the craft to steer.
- Police tracking of vehicles. An RDF equipped helicopter could
be used in police work to track vehicles that have been outfitted
with a radio beacon (for instance, 18 wheeler truck, a suspect's
car, or an agent's car).
The Pilot's Maneuvers
Here is a scenario of how a pilot would use our RDF for locating
exactly where to sit his machine down, even if he never sees the
rescue subject from the air. I call it the spiral-in technique,
because it results in flying in a shallow and graceful spiral
path.
- After taking off and gaining enough altitude to obtain a
steady signal, he rotates his machine to be facing directly
towards the signal source. He does this by rotating to zero a zero
center meter (or other display, to be discussed later.)
- He now flies, not directly towards the signal, but 10 or 15
degrees to one side of the actual heading, but keeping the
helicopter pointed directly at the RF heading.
- As he approaches the site, he will have to adjust his
aircraft's heading to keep it pointed at the ground site. He
should be able to do this to within 2 or 3 degrees.
- When very close (the spiral is quite tight) the pilot should
be able to identify one spot on the ground which is always in
front of his aircraft (remember, his flying task is to keep his
aircraft oriented to be directly facing the incoming RF signal,
even though he may be flying sideways at the time.
- He now knows with a high degree of certainty exactly where the
rescue subject is located, and he can then sit down as close as
the terrain will allow. Onboard rescuers also know exactly where
the person is, and can go directly to him.
Note: If done correctly, the pilot will not have to make more than
one or two "loops" around the site from only a short distance away
(50 to 500 foot distance.) Of course, if the rescue subject is
able to wave in the pilot over the last short distance, the rescue
is even quicker.
Mounting
Mounting of equipment on any aircraft can present both technical
and bureaucratic (regulatory) problems. If it modifies the airframe
in any way, a cumbersome and time consuming process is needed to
obtain approval.
It is possible (depending upon the actual helicopter) to mount the
SuperDF antenna (or one suitably modified) by clamping a cross-tube
between the skid supports, with the antenna at the center, facing
downward and slightly forward. The single Coax feed line can be taken
to the underbelly and secured with duct tape while it is being routed
to a convenient access plate location, or through the door opening.
(It is likely that the door could be closed on the coax without harm,
especially if RG174 coax is used [1/10 inch diameter].) An
access plate can be replaced with one with a coax connector on it,
and a feed line routed inside the cockpit to the RDF. with either
method, no modifications to the airframe are required, and no FAA
approval is needed.
If such a system were worked out in advance (using coax through
the door), it would take only a few minutes to attach it to any
(suitable) helicopter that was available. (Of course it would be a
very good idea to do this field setup early in a field operation,
before it might be needed!)
Display Options
I list below several display options. All have been proven in real
hardware.
- The meter mounted on the SuperDF control unit.
This requires the unit to be mounted in front of the pilot. This
meter is rather small. The pilot must switch his attention from
actual flying to reading the meter and adjusting his heading. This
is not a good solution.
- Another, larger meter mounted in the pilots view, and driven
by the control unit. Still not a good solution.
- Audio fed into the pilot's intercom. This audio can take
either of two forms.
- a. The actual RDF radio audio output, using the tone shift
display mode. The pilot can tell left from right bearing error
by the difference in tone pitch: Low pitch means rotate Left;
High pitch means rotate Right. Tone amplitude indicates about
how much heading error there is. He can hear what the rescue
subjects are telling him on the hunting frequency. He flies
"heads up" all the time. Any intercom input can be used with
the appropriate connector and circuit in the SuperDF control
unit. The pilot's eyes are free to fly. This is a better
solution.
- The tone shift comments of (above) apply, but the pilot
does not hear the radio output, but rather is listening to the
SuperDF 400 Hz oscillator directly. It does not change in
amplitude. When "On Bearing" the tone pitch is between the two
"Off Bearing" conditions. The tone stays strong so the pilot
can hear it over ambient noise. This is probably the best
solution.
Additional Comments
Because the system uses any available NBFM receiver, the system
can very easily be set up to hunt on a very wide range of
frequencies. This improves the general usefulness without incurring
the cost of a dedicated RDF receiver.
Sheriff departments may have a need for "helicopter SAR." They
often have search and rescue capability and helicopters. The
sheriff's department is likely to be available for the applications
listed earlier.
BMG Engineering Support
It is our intention to work closely with anyone wishing to make a
helicopter installation. We will review plans, make suggestions, and
design and provide interface circuitry for the intercom. We intend to
"make it fly."
George R. Andrews President
Also see...Hunting AM Signals with
SuperDF* - Hunting an ELT on
the ground - Hunting an ELT in the Mountains -
Setting up an ELT Hunting Team.
- RDF for SAR.
Contact
George R. Andrews (Russ, K6BMG)
BMG Engineering, Inc.
9935 Garibaldi Avenue
Temple City, CA
91780, USA
Voice 1(626)285-6963
Fax 1(626)285-1684 (24 hour automatic)
America OnLine: Grandrews
Web: http://users.aol.com/bmgenginc
(5 Feb 1996)
Send E-mail to grandrews@aol.com.
(A message window will open.)
Return to About SuperDF
Contents.
Return to Tutorial
Contents.
Return to TOP PAGE.