Meus Caros,
Conforme prometido, começarei esta nossa conversa semanal com mais um pequeno
apontamento para vos dar a conhecer a modalidade desportiva que tem a designação de
Rally Aéreo.
RALLY AÉREO – Teste de Navegação
Instruções de Voo ou Rutometro
Entre um mínimo de 15 minutos e um máximo de 30 minutos antes da hora ideal de
descolagem, será entregue à tripulação um envelope contendo todas as informações
e instruções para a correcta execução do voo. Este envelope será entregue à
tripulação que deverá estar dentro/junto do avião.
Todos os pontos de controlo (check points ou CP’s) e todas as pernas devem ser
descritos dum modo claro nas Instruções de Voo. SP (starting point), iFP
(intermediate finish point), iSP (intermediate starting point) e FP (finish point) são,
para todos os efeitos, considerados pontos de controlo.
Todos os CP’s devem ser pontos perfeitamente definidos quer no mapa quer no
terreno. Por exemplo, unca seria aceitável considerar uma cidade como um CP dada a
imprecisão de sobrevoo que isso acarretaria tal a sua dimensão geográfica imprecisão de rota e imprecisão de tempo de passagem.
As instruções sobre os pontos de controlo podem ser fornecidas dos seguintes
modos:
a) Posição pré-conhecida (e.g. um aeródromo, um VOR, etc.)
b) Coordenadas geográficas (latitude e longitude)
c) Qualquer combinação de rumo e/ou distância “de” (from) ou “para” (to) pontos
definidos em a) e b).
A informação não pode ser de modo algum ambígua e nunca deverá permitir mais do
que uma única solução possível.
Na próxima semana veremos o exemplo real de um rutometro de competição.
Para mais informações visita o site da Equipa Icarus em www.icarusrallyflying.net .4
Para tema de abertura na nossa croniqueta desta semana vejamos o que é que a AOPA nos
propõe como tema de reflexão técnica. Propõe-nos uma reflexão sobre o sistema eléctrico
do avião e algumas possíveis falhas do mesmo. Vejamos a problemática do aviso de “Low
Voltage”, aquela maldita luzinha que se acende intempestivamente no nosso painel de
instrumentos. Uma luzinha que até, às vezes, se acende sem nós darmos por ela, tão
escondida costuma estar.
LOW VOLTAGE WARNING
You are in cruise flight on a daytime cross-country when a warning on the panel catches your
eye. Electrical power is being discharged and is not being replenished by the alternator. In
some aircraft, you are alerted by a low-voltage light and the ammeter showing a discharge.
In others, the total load on the alternator is displayed on the ammeter; alternator failure is
indicated by a zero load. Meanwhile, the airplane is flying along strongly, thanks to the dual
magnetos that are independent of the electrical system.
As the pilot, you have some decisions to make. "If the alternator has failed, must you land
immediately? That depends on your situation, but for visual daytime flying the answer is 'not
necessarily.' Battery life is the primary concern," Ralph Butcher explained in his "Insights"
column in the May 2001 AOPA Flight Training.
Study your aircraft's pilot's operating handbook (POH)
checklist for handling low-voltage occurrences. For
example, alternator failure in a Piper PA-28-140E is
detected by a zero reading on the ammeter. The pilot
verifies the problem by activating an electrically
powered device such as the landing light. If no
increase in ammeter reading appears, the POH gives
these steps: Reduce electrical load, check alternator
circuit breakers, switch off the "alt" switch (in many
aircraft this switch is half of the split-type master
switch), then turn it back on after a brief interval. If the
alternator remains offline, "maintain minimum
electrical load and land as soon as practical. All
electrical load is being supplied by the battery." Note
the Butcher article's suggestion for protecting avionics
from voltage spikes during this procedure.
How the pilot manages this load-shedding chore will determine whether electrical power is
available for communication and navigation until landing, writes Steven W. Ells in his
"Airframe and Powerplant" feature in the April 2003 AOPA Pilot.
On a related subject, generators once were the mainstay of light-aircraft electrical systems.
They have been supplanted by alternators, which are generally lighter and more reliable over
a broader engine-power range. The systems are compared in Chapter 5 of the Pilot's
Handbook of Aeronautical Knowledge. Know what's installed in your aircraft, and have a plan
in case the bank account that is your electrical-power supply ever threatens to become
overdrawn.
INSIGHTS
Thingamajigs And Other Stuff
By Ralph L. Butcher
When evaluating a flight instructor for employment, I open an engine cowling and ask the
applicant to identify the major engine components. Many of them are unable to do this, and
that includes some who have graduated from college-level aviation training programs.
For example, they can't identify the exhaust manifold - that rusty-looking array of plumbing
that is an important preflight inspection item - and they have no idea why those dirty rubber
baffles sit atop the cylinders - a preflight item that is critical for proper engine cooling.
I feel sorry for these pilots because as a teenager, I had a deep interest in mechanical
things, and it was easy to obtain an old car, tear the motor apart, and then put it back
together and make it run. That opportunity has become almost nonexistent.
Many pilots acquire rote mechanical knowledge, but they have trouble applying it to practical
situations. When a cockpit problem occurs, they may make an assumption that results in an
incorrect course of action.
Some years ago the airlines stopped teaching the nuts and bolts of aircraft systems, and I
am glad that they did. The complexity of some modern systems had become ludicrous and
had no bearing on a pilot's ability to analyze a problem and take corrective action. Today, an
airline pilot must know how each system functions, how to deal with component failures, how
to interpret each warning light and instrument indication, and how to confirm that the desired
action did, in fact, occur when a switch was moved or a control was activated.
To acquire basic mechanical knowledge of the airplane you fly, start with the emergency
section of your pilot's operating handbook (POH). Learn everything you can about the
systems it mentions.
The electrical system is a good example. What is wrong if the alternator warning light comes
on during flight? This light is nothing more than a voltmeter. When it's off, system voltage
equals alternator voltage and all is well. When it's on, system voltage equals battery voltage,
and the alternator is not supplying power.
The POH will tell you to reduce electrical loads and turn the alternator switch off and then on,
but before you do this, be sure to turn the avionics equipment off, because a damaging
voltage spike (momentary high voltage) can occur when the alternator is turned on again.
The potential for a voltage spike exists because after you turn the alternator on it takes a
microsecond before the voltage regulator starts regulating.
If the alternator has failed, must you land immediately? That depends on your situation, but
for visual daytime flying the answer is "not necessarily." Battery life is the primary concern. A
fully charged 30-amp-hour battery will provide 30 amps for one hour. I would be pessimistic
(an important pilot trait), and I would assume that my 30-amp-hour battery is now a 15-amphour battery. If the electrical system is drawing seven amps of power, the battery should last
about 30 minutes.
On the other hand, imagine that you're flying over a desolate area. In that case, I would turn
the battery switch off in order to save the remaining battery power and have it available when
I approach a suitable destination. The engine keeps running because it's powered by
magnetos, but all electrical items in the airplane are now dead - lights, avionics, turn
coordinator, fuel gauges, oil temperature gauge, etc.
Here is an example of where a lack of system knowledge allows the pilot to make an
assumption that leads to an incorrect course of action: The alternator has failed, the pilot has
reduced electrical loads, but he has flown for almost 30 minutes. Battery life now concerns
him, so he turns off the battery switch to save battery power. When he finally approaches a
suitable destination, he turns the battery switch back on, but nothing happens. The entire
system is dead. With proper knowledge, he would have known that a relay is activated when
the battery switch is turned on, but only if enough battery voltage is available. Otherwise, the
battery relay will not activate, and the remaining battery power will be unavailable.
As pilots gain experience, they begin to realize the importance of the mechanic who twists
the wrenches, and I've never met a mechanic who wasn't interested in furthering a pilot's
knowledge of the aircraft. Therefore, if your mechanical knowledge is not up to par, I would
strongly suggest that you hire a mechanic and have him or her explain the importance of
everything that sits inside your airplane's engine cowling and on your instrument panel. It's
an investment that pays enormous dividends when you need them most.
CHARGE IT!
The magic behind alternator and generator systems
BY STEVEN W. ELLS (From AOPA Pilot, April 2003.)
With the advent of affordable integrated circuitry, today's light-airplane avionics are capable
of showing the pilot a real-time display of weather conditions, pointing out convective activity,
navigating in three dimensions with reference to satellite signals, and saving a database of
engine operating parameters. This is wonderful, but without a reliable source of electrical
power — a generator or an alternator — those wonders of the electronic age are worth little.
This month we'll take a look at charging systems.
In the same way that starting woes are most often traceable to system problems (see
"Airframe & Powerplant: Good to Go?" February Pilot), changing an alternator or voltage
regulator when charging stops is usually shortsighted. A well-educated mechanic or owner
determines the cause of the problem first. Since there are still generator-equipped airplanes
flying, let's start there.
A generator looks a lot like a black two-pound coffee can with wires connected to posts on
one end and a round wheel (pulley) on the other end. A continuous belt conducts rotation
from a bigger pulley on the engine to the generator pulley. Gear-driven alternators are bolted
directly onto the accessory case of the engine.
Generators and alternators are rated in volts (12 or 24) and amps. Common sizes for 12-volt
systems are 12, 15, 25, 38, 50, or 60 amps while 24-volt alternator ratings are typically 60 or
95 amps. The first airplane that I owned, a 1947 Piper Super Cruiser, had a 12-volt, 15-amp
Delco Remy belt-driven generator. My second airplane, a 1966 Cessna 182, supplied
electrical
power
with
a 12-volt, 60-amp alternator adapted from a Ford automotive unit.
Generators — dead at idle
Generators and alternators produce electrical energy by moving wires (conductors) through
strong electrical fields or vice versa. In the generator, the conductors are copper wires that
are wound around an armature that is bolted to the drive pulley. (As the armature rotates, the
copper wires move through a magnetic field that is produced by permanent magnets.)
Electrical power is induced in the wires and terminates in a part of the armature called the
commutator. This power is then transferred from the spinning commutator to stationary
carbon brushes that are held against the commutator segments by spring pressure.
Generators don't produce rated output until engine rpm is up in the mid-range of operation —
typically above 1,400 rpm. This liability can be a real pain in the pilot seat.
Pilots who have experienced the rapid dimming of a landing light as they reduce engine rpm
on short final will understand one of the drawbacks of a generator-powered system.
There are other drawbacks to generators. Compared to alternators, they're heavy, the
amperage ratings are lower, and because the full electrical output of a generator is
conducted across a carbon brush — commutator copper segment junction — dirt and arcing
often cause electrical noise and static that radiate to other avionics. Generators require more
maintenance than alternators. There is carbon dust to deal with, commutators to smooth and
polish, and bearings to grease and clean. Generators aren't all bad — they do have two big
advantages over alternators — they're not sensitive to errant electrical spikes or reversed
polarity, conditions that can render an alternator inoperative in a New York minute, and they
can produce electrical power even if the battery is dead.
Alternators — powerful but sensitive
Alternators are capable of producing full rated output at low engine rpm. That's important for
two reasons — because today's GA airplanes are stuffed with avionics that require electrical
power from the beginning of every flight and because systems are changing.
Twenty-first-century airplanes, such as the Lancair 350, Cirrus SR22, and Liberty XL–2,
have replaced their vacuum systems with electrically driven instruments (see "Airframe &
Powerplant: Spinning Instruments," January Pilot). This can be done in part because of the
reliability of today's alternator systems, and because the installation of a second,
independent electrical system is becoming easier. Light-aircraft alternator systems weren't
always so dependable.
An alternator can be thought of as a current multiplier because a small amount of current
(typically 1 to 4 amps) is fed into an alternator through the field terminal, and, after the magic
happens, electrical power up to the alternator rating is available at the output terminal.
The strength of the magnetic field in alternators and generators is automatically varied by an
excitement power from the voltage regulator (VR). A generator, produces electrical power
when the aircraft battery is completely discharged, because a generator creates a portion of
its output (because of residual magnetism) from the wire-through-magnetic-field interaction
that produces power. Alternators don't have permanent magnets so when the aircraft battery
is completely discharged, the alternator will not charge. Does a generator ever lose its
residual magnetism? Sort of. Occasionally a generator will need polarizing, especially after
inactivity. Flashing the field restores function. Service manuals detail this procedure.
Alternators should never be flashed.
Alternator feedback loop
If the alternator-charged system has a healthy battery and resistance-free connections, the
VR senses the aircraft electrical system voltage and varies the excitement current flow to
maintain a charging-system voltage between 13.8 and 14.2 volts in a 12-volt system and
27.1 to 28.4 volts in a 24-volt system. The electrical system voltages are higher than the
battery ratings to ensure that the battery gets fully charged. Sounds good. But alternators
have their own set of problems.
When a VR malfunctions and feeds too many amps into the alternator field circuit, the
voltage output skyrockets almost instantaneously.
If this happens, things, especially those high-cost avionics-style things,ßsignal their
displeasure by producing acrid clouds of smoke before turning out their lights and taking an
expensive nap. As electricians often say, once the smoke has escaped from those
expensive boxes, the party's over.
To prevent costly overvoltage system meltdowns, an overvoltage relay (OVR) guards against
runaway voltage outputs. Cessna started installing alternators in the mid-1960s, and OVRs
in its single-engine line around 1970. Fortunately for owners of airplanes that came out of the
factory without overvoltage protection, virtually all of today's retrofit VRs have overvoltage
protection incorporated inside the units. VRs featuring built-in overvoltage protection are
alternator control units (ACU). The OVR works like this — whenever system voltage goes
above 16 volts (for 12-volt systems) or 32 volts (for 24-volt systems), the circuit between the
bus and the ACU is automatically opened by the OVR. This cuts off the excitation current
and the alternator output drops to zero. Since transient, intermittent high-voltage spikes
occasionally fool the VR or ACU into thinking the system is in meltdown, a pilot should
attempt to reset the system by temporarily turning off the alternator switch and then turning it
back on. If the system won't reset after one or two attempts, then the pilot must shed
electrical load and evaluate his options.
Load shedding — what's that?
Since most GA airplanes don't have a backup charging system, an understanding of load
shedding is important. Here's one way of looking at it. A fully charged battery is a bank with
limited assets. Each electrical circuit is a drain on those assets. The point of load shedding is
to turn off all unnecessary drains (circuits) in order to preserve, and best use, the battery's
limited assets.
Pilots, especially those in trouble, need to keep their communication and navigation
capabilities as long as possible — so think talking and tracking when load shedding. If the
loss of charging is discovered right away, it's safe to say that an aircraft battery can power a
nav/com radio and a transponder for at least an hour. Therefore, it's important to know which
circuits are power gluttons. Any circuit that turns electrical power into heat (pitot heat) or light
is a hungry circuit. An easy way to determine how much current a circuit draws is to look at
the numbers etched on the circuit breakers. Locate the switches that control the circuits with
the big numbers, and create a plan for flying situations that would be affected by a loss of
electrical power. And remember that the regulations permit, even encourage, the pilot to
deviate from normal procedures in abnormal situations. During an abnormal situation, such
as flying instruments in the clag with no alternator, no one is going to fault the decision to
turn off the position lights. The circuit breaker trick, plus research into the airplane service
manual, enables each pilot to make informed load-shedding decisions if they ever become
necessary.
Diodes — a rectification situation
Alternators produce alternating current (AC), which is useless in GA airplane electrical
systems. To convert the AC to direct current (DC), three matched sets of silicon diodes are
paired in a solid-state device called a rectifier bridge. The alternating current output of each
leg (there are three legs) of an alternator starts at zero, climbs to a positive value, then falls
through zero to a negative value, before again returning to zero. Thus, it's called alternating
current. The rectifier removes the negative (or unusable) part of each leg's output, and
combines the three positive outputs to produce a usable DC-like output. This is important
because rectifier problems are sneaky. If one diode in a rectifier fails, the output (and bus)
voltage will not be affected, but the amount of current being produced will drop off by
approximately 20 percent. Alternators rated at 60 amps will become markedly less capable.
The loss of one diode may not be evident if the airplane isn't loaded with electrical
equipment because even the smaller well of electrical power is sufficient to power all the
circuits and keep the battery charged. But the pilot whose airplane has a full load of avionics,
ice protection, and electrical instrumentation is in trouble because the compromised
alternator can't produce enough amps for safe operation. One symptom of this malady is a
battery that won't stay charged. Another tip that the rectifier isn't hitting on all six diodes is a
high-pitched whine that varies with engine rpm — this can be heard in the radios, and if it's
bad enough it may affect ADF pointer operations.
A common system problem
The alternator on/off switch is often overlooked in alternator system troubleshooting. Taking
a few minutes to ensure that the switch is resistance-free solves all kinds of alternator
system headaches. Why? Because all it takes is a little corrosion or wear in that inexpensive
switch to completely throw the system voltage sensing function of the VR or ACU out of
whack.
This example shows why. The electrical system charging circuit consists of the alternator,
the VR or ACU, the alternator switch, and to a lesser degree, the aircraft ammeter and the
overvoltage relay.
The loop that maintains equilibrium in the electrical system starts at the aircraft electrical
bus. A bus (or buss) is simply a wire or a metal strip that the various circuits, such as
position lights and landing-gear motor, tap into to get system power for operation. It's the
central well of electrical power.
As we turn on more circuits, such as a landing light or pitot heater, each circuit's resistance is
added to the bus. This increase in resistance, because of Ohm's law, lowers the bus (and
system) voltage. Remember that voltage in a series circuit is inversely proportional to
resistance (ohms). When resistance increases, voltage decreases. The VR or ACU receives
its information on system voltage levels through the alternator switch.
Problems arise when the switch has internal resistance or is dirty. Both of these conditions
cause resistance (increase in ohms) that drops the voltage across the switch. What
happens? Even one ohm of resistance (that's not much) in the switch results in the VR or
ACU seeing a lower voltage than is actually on the bus. This causes the VR or ACU to react
to a low bus voltage reading by increasing the amperage flowing through the alternator field,
which ups the alternator output voltage. As the bus voltage increases, the voltage value
(after overcoming the resistance in the switch) sensed at the ACU rises above the "normal"
voltage parameters and the ACU, sensing that the system voltage is too high, reduces the
output of the alternator. The result is a constantly varying bus voltage that pilots first notice
as pulsating instrument lights or a pulsing ammeter needle. The ACU is chasing its tail
because the resistive switch is telling it lies.
Troubleshooting
One of the best tools for troubleshooting rectifier problems is an alternator ripple tester —
maintenance shops that are savvy about charging systems often have one.
While this technical information is of limited value to the majority of pilots, every pilot should
know the basics of his alternator system, and how to shed load in emergencies.
Many pilots with split master switches (Batt half and Alt half) have modified the owner's
manual starting procedure by leaving the alternator half of the switch in the Off position until
after the start sequence. After starting, but before turning on any other equipment such as
radios or lights, the pilot turns on the alternator half of the switch and checks for positive
movement of the ammeter needle. This verifies that the charging system is online. Engine
starting is a time when the contactors that control large current flows are opening and
closing. The potential for large voltage spikes rippling through the electrical system is very
high during this brief moment. Since rectifiers, switches, and other solid-state devices are
adversely affected by spikes, it's a good idea to isolate charging-system components during
starting — unless you have a generator on your airplane.
There are two information sources that can help pilots gain general and specific knowledge
regarding their electrical systems. Visit the Web sites www.zeftronics.com and
www.aeroelectric.com. The information from these two sources is invaluable for further
understanding of electrical systems.
Parece que valeu a pena relembrarmos alguns conceitos que estavam anestesiados no
fundo da nossa memória. 4
Há pessoas que entendem que a Segurança é, em si, um objectivo e, por isso tornam-na no
fulcro das questões. Ao longo da minha carreira profissional sempre lidei com o fenómeno
“Segurança” mas nunca o tomando como um objectivo por ele próprio. O cerne do problema
é sempre o conjunto de bens, valores e serviços que se pretendem defender. Nunca os
meios de protecção. Hiper segurança é, antes de mais, sinónimo de ineficácia.
Infelizmente, a “Segurança” em certos momentos de histeria colectiva passa a dominar tudo
e assistem-se a situações em que o custo da segurança ultrapassa, às vezes em muito, o
valor económico do objecto a segurar.
Lembro-me dum Comandante Geral da PSP que tinha segurança nos deslocamentos até
casa. Eram carros a gastar sirenes. Eram luzes azuis a piscar tudo por que é sítio. Eram
“body guards” de pistolões espalhafatosamente exibidos nas sovaqueiras. Cenas dignas da
melhor fantasia Hollywoodesca. Depois… bem, depois caia-se na normalidade e o senhor
passava a ser um pacato cidadão sem qualquer tipo de protecção especial. Percebi afinal
que a segurança da pessoa em causa só existia no horário normal de expediente. Afinal
uma situação em que a segurança se justifica a ela própria.
O quadro seguinte é, dalguma maneira, um conjunto de situações que são corolário do que
acabo de referir. Afinal certas medidas de segurança só servem para prejudicar o cidadão
comum e nunca para criar barreiras defensivas eficazes contra aquelas pessoas que
pretendem, dalguma maneira, causar danos à comunidade. A história mostra que esses são
espertos de mais para verem os seus passos maléficos tolhidos por profissionais da
segurança. Afinal os primeiros estão sempre um passo à frente.
A história recente dos USA é um bom exemplo disso: dois presidentes baleados apesar da
super segurança que os rodeia.
ADIZ PUNISHES PILOTS BUT WON'T STOP TERRORISTS, PILOTS SAY
The frustration pilots and air traffic controllers feel with the Washington, D.C., Air Defense
Identification Zone (ADIZ) came through loud and clear in the more than 18,200 comments
filed to date in response to the FAA's proposal to make the restrictions permanent. One
resounding theme: The ADIZ punishes law-abiding pilots but does nothing to protect
against terrorism. "I am a member of the Army National Guard currently deployed in Iraq
and I am civilian pilot," wrote one commenter. "Ostensibly, I am in Iraq to protect the freedom
of the American people, and I find the imposition of regulations such as the D.C.-area ADIZ
personally offensive because they abolish the very freedoms I have given up a year of my life
defending, yet do nothing to enhance the public's safety." Other pilots pointed out the
numerous measures already in place to protect the nation's capital—measures that make the
ADIZ an unnecessary burden. "We already have the proper solution in place with the 15-mile
no-fly zone around the Capitol, missile systems, and fighters flown by pilots such as my son
(a USAF F-16 pilot) on alert," wrote one airline pilot. "Little slow Cessnas are not a viable
terror threat to the Capitol, and have never been used as such."
Entretanto, piloto sofre...
4
O micro jactinho da Eclipse vai estando cada vez mais pronto.
ECLIPSE ACHIEVES HIGH-SPEED MILESTONE
Eclipse Aviation President and CEO Vern Raburn arrived at AOPA Expo Wednesday behind
the controls of his dream machine: N506EA. Raburn landed the Eclipse 500 jet in Tampa
after a 1,300-nautical-mile flight at 33,000 feet from the company's home in Albuquerque,
New Mexico. "This aircraft is a complete pleasure to fly," he said. Eclipse revealed that a test
aircraft, N502EA, recently reached a true airspeed of 452 knots, achieving the maximum
speed required for FAA certification (16 percent past redline). Raburn said the jet performed
well and didn't experience any flutter or other aerodynamic challenges at that speed. 4
A Cessna vai prometendo. Esta é a segunda notícia que nos chega no espaço de pouco
mais de um mês. Será que há mesmo intenções de mudar a linha base da Cessna ou
estamos perante especulações para ir entretendo a comunidade da Aviação Geral? O futuro
nos dirá.
CESSNA LOOKS AT NEW PISTON AIRCRAFT MODELS
Cessna Aircraft President and CEO Jack Pelton reconfirmed at AOPA Expo that Cessna is
looking at building new piston aircraft models. "We have been conducting market studies and
assessing new technologies to ensure our next generation piston family is responsive to
market requirements and provides significant improvements in safety, performance, comfort,
and economics. We are currently in the process of listening to what our stakeholders have to
say about our possible designs," he said. To date, no decisions have been made regarding
configuration, specifications, or timetable. "We plan to make an announcement once those
decisions are made," Pelton said. In the meantime, Cessna continues to add capability to the
aircraft it presently builds. 4
Por esta semana é tudo ou quase tudo. Não me despeço sem o meu conselho habitual:
visita o site da Equipa Icarus em www.icarusrallyflying.net. Há sempre novidades. Mas,
acima de tudo decide-te e resolve, duma vez por todas, praticar Rally Aéreo. Praticando
Rally Aéreo serás muito melhor piloto.
Um abração do
Fernando