Avionics News December 2021 - 44

MODERNIZING ELECTRICAL SYSTEMS
Continued from page 43
For years, the rotating beacon was the only option available for
type-certified aircraft, from airliners to business aircraft and the
dominant aircraft in the general-aviation fleet.
Effective, though they were, they were heavy and maintenanceintensive.
Many used two bulbs and a current-sapping direct current
motor to rotate the beacon assembly. With two bulbs - both always
on when the beacon was powered up - and that motor, rotating
beacons could require more than 100 watts of power to function.
And strobe lights, the common alternative to those beacons,
required a powerpack to feed the flash tubes providing the bursts of
light. So they offered little in the way of weight benefit.
Today's alternative employ LEDs, which typically weigh a fraction
of the strobe systems and draw a fraction of the power required
by the strobe pack and flash tubes.
The weight advantage grows for aircraft requiring three or
more flash tubes. Similarly, the current savings also become more
substantial when the aircraft owner has to replace three or four flash
tubes.
The flash tubes aren't the only component eligible for replacement
in the name of weight saved, power saved, and greater reliability
- itself a hallmark of those solid-state LEDs.
And the anti-collision system isn't the only place where LEDs
come out on top. The same benefits apply to the wingtip-recognition
lights, as well as the white taillight.
The LED units - whether for recognition or collision avoidance
- use internal circuitry to power the lights and, for the anti-collision
beacon, the flashing rate and rhythm.
No remotely mounted power pack, no need for heavy, shielded
wire runs, while available for all three positions: aviation red for the
left wingtip, aviation green for the right wingtip, and the aviation
white taillight. And the anti-collision lights are often co-located with
the recognition lights, simplifying installation.
Off and on the ground: landing and taxi lights
Among the items carried in that 1961 Comanche as an emergency
parts kit were spare bulbs for the recognition lights - and spare
landing and taxi lights.
The Comanche used two landing lights mounted near each
wingtip - behind a clear lens. The GE 4509 - now manufactured
by Tungsram - remains the common choice because that's what so
many general-aviation aircraft used when they left the factories.
Many pilots always flew with spares as a hedge against the
100-watt bulbs' habit of failing after about 35 to 50 hours. But other
pilots and operators opted for quartz-technology alternatives to the
venerable PAR 36 GE 4509, drawn by two documented benefits.
First, the quartz bulbs produced equal or better - whiter - lighting
with half the power: 50 watts instead of 100. So a pilot of an aircraft
with dual landing lights could shave 100 watts off the full-power
44 avionics news * december 2021
demand of the aircraft electrical system and 50 watts of a system
driving a single landing light. For some aircraft, that change, alone,
would ease the load on the aircraft's electrical system.
The landing and taxi light are another watt-saving opportunity by
swapping out the old incandescent bulbs for one of the many LEDusing
options available today. And that availability pretty much
covers the spectrum of general-aviation aircraft.
A full-system changeover to LEDs - anti-collision, recognition,
landing and taxi lights, and in-the-cabin lights - can shave as much
as 200 watts off the load imposed by the incandescent originals.
The inside story
If your older aircraft is anything like mine, all the same benefits
apply at every spot where an LED source of illumination
displaces an incandescent or halogen source. From the overhead
cabin light to instrument-panel floodlights and instrument lighting,
LED solutions exist.
That also applies to those heat-generating, failure-prone post
lights. The approved options vary according to the aircraft, and
the applications can vary from model to model. But the benefits
still exist.
Current draw drops. With that decline comes lower heat generated,
making for cooler running - an issue mostly in summer and in
hot climates. With less heat generated comes far longer life.
Again, all these benefits are good things, particularly the long-life
element. The LED options aren't yet at a cost point where they can
claim to be price competitive with the old technology - until, that
is, you take into account the far-greater longevity of the LEDs. And
even then, the cost-benefit equation may not be the winning factor.
There's little doubt that incandescent-to-LED change reduces
demand on the electrical system - and where that's the goal, the
LEDs win at every front. But whether it's a change to LEDs, a move
to more-efficient starters or improving the aircraft power-producing
capabilities, the owner should understand the many ways available
to make sure a glass-cockpit upgrade doesn't overload the electrical
system and its need for a standby power source to keep those
displays running in the event of a main-electrical-power loss.
Once the changeover is complete, even a main-ship-power loss
won't be as large a crisis since the battery will last longer with the
lower demand for power.
Making standby power part of a system upgrade
We've already pointed out how modernizing the electrical system
provides an opportunity to improve reliability and reduce the
aircraft's operating empty weight. The other potential gain from an
electrical-system upgrade comes in the form of adding more depth
to the redundancy built into the aircraft.
Some pilots don't look at the main-ship battery as a redundant
power source for an emergency - that battery exists largely to
start the engine without the risks of hand-propping the powerplant.
Acknowledged: but that battery helps stabilize and absorb
Avionics News December 2021

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