Avionics News May 2021 - 41

of the incandescent has been a relative rarity.
Some replacement LED landing lights even offer the
option of flashing alternatively, adding an anti-collision
function to their ability to illuminate runways and taxiways
on a fraction of the current required of the old GE 4509
light common to thousands of general aviation aircraft.
Improving electrical-system reliability:
The alternator option
Older-technology generators entered aircraft
obsolescence decades ago, when aircraft OEMs embraced
a move made years earlier by the automotive industry: the
alternator. The alternator advantages are numerous - and
worth embracing for an aircraft still using a generator.
The biggest benefit of an alternator stems from its greater
power output - even when the engine is at idle. Further,
the alternator typically weighs several pounds less than
the generator it replaces. This benefit arises because the
alternator uses no heavy permanent magnet inside.
It's for these reasons that today's general aviation aircraft
depend on alternators to provide a steady, reliable source
of electrical energy to power electrical components and
recharge the battery. Many supplemental type certificates
exist for replacing generators with alternators, making
retrofits an attractive option for improving the capabilities of
the electrical system.
The typical replacement alternator can fulfill all the
electrical-system demands with the engine at idle RPMs
and, simultaneously, reduce the aircraft's empty weight -
thus improving the useful load of the plane.
Combine the alternator upgrade with a new solid-state
voltage regulator and a lighter-weight sealed recombinantgas battery can yield a weight loss of as much as 12 pounds
- maybe more depending on the weight of the old generator.
Upgrade benefits in flight instruments
The once-standard six-pack instrument stack typically
included an electrically powered turn coordinator or
turn-and-bank indicator - both using a spinning-mass
gyroscope for reference. Two other gyroscopically driven
flight instruments typically use vacuum air flow to spin
their gyroscopes, the attitude indicator and gyro compass -
commonly called a directional gyro, or DG.
Eliminating all three spinning-mass gyro instruments
may reduce electrical load only slightly but significantly
reduce the aircraft's empty weight - all while presenting
owners with an opportunity to improve the redundancy of
the electrical system.
By upgrading to a PFD for flight instruments - which
require no vacuum or pressure air flow - the electrical
system can gain a vacant drive pad on the engine's

accessory case. With no air-driven instruments, the aircraft
no longer needs a suction or pressure pump; removing the
pump opens up a mounting pad for a standby alternator.
Replacing the air pump with a suitable standby alternator
can help fulfill the need for electrical-power redundancy
when upgrading the panel to all glass. The switch to all
glass can increase the demand on the electrical system - but
all within the improved capacity of an alternator upgrade.
But going all glass means adapting the electrical system to
one with redundancy in its power supply - like a standby
alternator can provide.
Many options exist for adding a standby electrical
buss, along with the voltage regulator required to handle
a secondary buss. Again, the change to all glass may
increase the demand on the alternator - but well within
its capabilities.
The sum of the parts
The goal: reducing electrical demand versus increasing
system capacity. Both can be accomplished with existing
components.
Switching to all LEDs for inside and outside illumination
can cut more than a dozen watts off the demands on the
electrical system. LEDs can also improve the reliability of
the electrical system courtesy of the longer life span such
lights deliver.
But for older aircraft - particularly those still using old
permanent-magnet generators - upgrading to a modern
alternator delivers greater generating capacity, lighter
weight and greater reliability.
And for any owner or operator contemplating a panel
makeover to glass, the change can save weight, even though
it may increase the demand on the electrical system to drive
displays and perform all the same functions as the original
analog panel.
It warrants informing the aircraft owner when the
electrical-system demands of the new panel approaches the
limits of the generating source - an issue unlikely to be a
problem with a modern alternator supplying the current.
Ideally, reworking the electrical system should combine
steps to improve the generating source - with an alternator
in place of the generator, or a higher-capacity alternator with
a lower-power model - and steps to reduce the load on the
electrical system, such as going with LED lights in all areas.
The one thing the LED changeover won't be is
inexpensive. Many replacement options cost much more
than the incandescent units they replace.
But taking the long view, the higher costs accompanies
a longer life span of the LEDs - which can make them a
worthwhile investment in an aircraft the owner expects to
keep for a long time. q
avionics news

may

2021

Avionics News May 2021

Table of Contents for the Digital Edition of Avionics News May 2021