Flight Training - July 2013 - 48
CAREER PILOT»
TECH TALK
GIMME POWER
Relying on the APU
» By Jared Dirkmaat
ON LARGER, COMPLEX aircraft, powering
all the equipment, lighting, and amenities
can present a challenge to designers and
manufacturers. Powering all that equipment and electronics can be difficult using
batteries, and the added weight of extra
batteries could reduce payload capabilities. Many aircraft designs include an
auxiliary power unit, or APU.
The APU is a small gas turbine engine
that provides electrical and pneumatic
power for aircraft systems either independently or with aircraft engines and
engine-driven generators. Often, aircraft
designers place the APU in or near the tail
cone of the aircraft.
An APU provides an easy way to transition from ground power to independent
aircraft power. While the aircraft is parked
at the gate a ground power unit (GPU)
is often used to supplement or replace
the use of aircraft batteries for powering the avionics, cabin electrical lighting,
and other essential items. This allows the
aircraft to be boarded with lights on; the
lavatory operational; and the avionics programmable, set up, and ready for flight.
Once ready for gate departure, or
immediately prior to, the APU is started to
transition away from the GPU. APU start-
48 /
FLIGHTTRAINING.AOPA.ORG
ing, operation, and shutdown is controlled
with the FADEC (full-authority digital
engine control). Once up and running
at a stabilized turbine rotation speed,
the APU is capable of providing electrical power to aircraft systems as well as
pneumatic power for engine starting and
air conditioning.
Now that the aircraft can be powered
independently, gate pushback occurs and
the engines can be started for taxi. Bleed
air is supplied by the APU compressor and
is used to power the pneumatic starter on
either aircraft engine. Once at least one
engine is up and running the APU can be
shut down, or left running to start other
engines. By design, most aircraft bleed air
systems are designed to allow cross-bleed
engine starts, either to facilitate an inoperative APU or fuel savings by shutting
down the APU immediately following the
first engine start.
The APU is a versatile piece of equipment that not only enhances operational
flexibility, but also reliability, systems
redundancy, passenger comfort, and convenience. Welcoming passengers aboard
an aircraft that is well lit, air-conditioned,
and ready for flight is a competitive advantage as well as an operational one.
http://www.airsafetyinstitute.org/firc
http://FLIGHTTRAINING.AOPA.ORG
Flight Training - July 2013
Table of Contents for the Digital Edition of Flight Training - July 2013
Flight Training - July 2013
Contents
Member Benefits
Right Seat
Centerline
Letters
Spin Doctor
Success Story News
How It Works
News
After the Checkride
Asi News
Training Products
Final Exam
Flight Lesson
Checkride
Flying Carpet
Weigh In
Just Like the Real Thing
Glider Pilot for a Day
Technique
Weather
Go or No/go?
Career Advisor
Tech Talk
Two Touchdown Techniques
Keep Your Distance
Talk to Yourself
Advertiser Index
Debrief
Flight Training - July 2013 - Flight Training - July 2013
Flight Training - July 2013 - Cover2
Flight Training - July 2013 - Contents
Flight Training - July 2013 - 2
Flight Training - July 2013 - 3
Flight Training - July 2013 - Member Benefits
Flight Training - July 2013 - 5
Flight Training - July 2013 - Right Seat
Flight Training - July 2013 - 7
Flight Training - July 2013 - Centerline
Flight Training - July 2013 - 9
Flight Training - July 2013 - Letters
Flight Training - July 2013 - 11
Flight Training - July 2013 - Spin Doctor
Flight Training - July 2013 - 13
Flight Training - July 2013 - Success Story News
Flight Training - July 2013 - How It Works
Flight Training - July 2013 - News
Flight Training - July 2013 - After the Checkride
Flight Training - July 2013 - Asi News
Flight Training - July 2013 - 19
Flight Training - July 2013 - Training Products
Flight Training - July 2013 - 21
Flight Training - July 2013 - Final Exam
Flight Training - July 2013 - Flight Lesson
Flight Training - July 2013 - 24
Flight Training - July 2013 - Checkride
Flight Training - July 2013 - Flying Carpet
Flight Training - July 2013 - 27
Flight Training - July 2013 - Weigh In
Flight Training - July 2013 - 29
Flight Training - July 2013 - 30
Flight Training - July 2013 - 31
Flight Training - July 2013 - Just Like the Real Thing
Flight Training - July 2013 - 33
Flight Training - July 2013 - 34
Flight Training - July 2013 - 35
Flight Training - July 2013 - Glider Pilot for a Day
Flight Training - July 2013 - 37
Flight Training - July 2013 - 38
Flight Training - July 2013 - 39
Flight Training - July 2013 - Technique
Flight Training - July 2013 - 41
Flight Training - July 2013 - Weather
Flight Training - July 2013 - 43
Flight Training - July 2013 - 44
Flight Training - July 2013 - Go or No/go?
Flight Training - July 2013 - Career Advisor
Flight Training - July 2013 - 47
Flight Training - July 2013 - Tech Talk
Flight Training - July 2013 - Two Touchdown Techniques
Flight Training - July 2013 - Keep Your Distance
Flight Training - July 2013 - Talk to Yourself
Flight Training - July 2013 - 52
Flight Training - July 2013 - Advertiser Index
Flight Training - July 2013 - 54
Flight Training - July 2013 - 55
Flight Training - July 2013 - Debrief
Flight Training - July 2013 - Cover3
Flight Training - July 2013 - Cover4
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