Transcript Aerodynamics - Brown University

Controls, Systems,
Instrumentation
2 February 2005
Primary Flight Controls
Ailerons
 Control bank
 Use of ailerons requires increased
(up) elevator…why?
 Create adverse yaw
Adverse Yaw
 What happens when an airplane is banking?
 Left-bank: left aileron up, left wing down.
Right wing has more lift  more drag!
 Airplane tends to yaw in opposite direction
of desired turn.
 Primary function of the rudder is to control
yaw.
 Use rudder in the direction of the deflection
of the ailerons while banking, but not while
just banked.
Adverse Yaw
 Primary means of controlling yaw: rudder
 Engineering factors:
 Differential ailerons
 Frise-type ailerons
 Coupled ailerons and rudder
Elevator
 Controls angle of attack
 Controls pitch about the lateral axis
 Aft-movement of elevator = “up
elevator”
Miscellany
 Other (less common) airplane designs
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T-tail
Stabilator
Canard
V-tail
Secondary Flight Controls
 Primarily:
 Flaps
 Trim systems
 But also…
 Slots
 Slats
 Spoilers
Flaps
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Increase lift by increasing camber
Decrease stall speed
Increase drag
Can be deployed in increments
Used to “get down &
slow down” at the same
time
Trim systems
 Trim tabs
 Reduce workload
 Elevator trim can
maintain a constant
angle of attack
(read: airspeed)
 Rudder/aileron
trims available on
more advanced
aircraft
Aircraft Systems
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Powerplant
Propeller
Induction
Ignition
Fuel
Landing Gear
Etc.
Powerplant
 Converts chemical
energy (fuel) to
mechanical energy
(torque)
 Powers propeller and
other aircraft systems
 Reciprocating engines:
four strokes – intake,
compression, power,
exhaust (“suck, squeeze,
bang, blow.”)
Powerplant – Four Strokes
 Intake
 Intake valve opens
 Piston moves away from
top of cylinder and takes in
fuel/air mixture
Powerplant – Four Strokes
 Compression
 Intake valve closes
 Piston returns to the top
of the cylinder
 Fuel/air mixture is
compressed
Powerplant – Four Strokes
 Power
 Spark plugs spark
 Combustion of the
compressed fuel-air
mixture forces piston
down
 (This stage provides the
power for all four strokes)
Powerplant – Four Strokes
 Exhaust
 Exhaust valve opens
 Burned gases are forced
out
 Cycle complete! (Repeat
~500-2500 times a
minute)
Ignition Systems
 Magnetos
 Powered by the engine
 Electrical failures do not cause ignition failures
 Most airplanes have “dual mags” – redundancy &
engine performance
 Two spark plugs ignite
fuel from both sides of
the cylinder, creating
more even combustion
Induction Systems
 Induction systems bring in fuel and
air
 Two principal types:
 Carburetor induction
 Fuel injection
Carburetor Induction
 Air moves in through a restriction (venturi)
 Smaller area increases airspeed and
decreases air pressure (Bernoulli!)
 Decreased pressure draws fuel into
airstream; circulation mixes the two
 Manifold distributes mixture to the cylinders
Fuel injection systems
 Found on newer aircraft
 Fuel and air are mixed immediately
prior to entering the cylinder
Induction – “Mixture Control”
 Both systems must compensate for changes in
the atmosphere.
 As altitude increases (or air gets warmer), air
density decreases (Geek alert: PV = NRT)
 A given fuel/air mixture at sea level will have
too much fuel (be too “rich”) at 10,000 feet.
 A separate mixture control controls the ratio
of fuel to air. As altitude increases, the pilot
“leans” the mixture.
Engine Troubles
 Carburetor Ice
 Detonation
 Preignition
Carburetor Ice
 As air flows through the neck of the
carburetor it expands and fuel evaporates –
the “heat of evaporation” cools the air
 Solution: carburetor heat!
Air is preheated prior to
entering carburetor, either
melting or preventing ice
 Carb ice can occur between
20 and 70 deg. F when
relative humidity is high.
Carburetor Ice
 Carb heat causes intake air to be warmer, thus
less dense.
 Mixture will need to be adjusted
 Fuel-injected systems have
no carburetor, thus no
carb ice.
Temperature-Related Problems
 Detonation
 Uncontrolled & explosive ignition (rather than
combustion) during the power stroke
 Caused by:
 Too-low grade of fuel
 Too lean of a mixture
 Insufficient cooling
Temperature-Related Problems
 General temperature concerns
 Engine oil – not only lubricates, but dissipates heat
 Aviation fuel – also acts as an internal coolant
 Airflow – primary method for cooling air-cooled
engines
 When temperature is a concern:
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Reduce power
Ensure there is extra oil for greater heat dissipation
Enrich mixture (more fuel = more cooling)
Increase airflow over engine by
 lowering nose during climbs
 avoiding lengthy ground operations on hot days
Fuel systems
 Engine-driven fuel pumps
operate constantly (as
long as engine is running)
 Electric fuel pumps are
pilot-controlled – used for
priming/starting, critical
phases of flight (takeoff /
landing) and emergency
operations.
 Gravity-feed systems use
gravity alone to drive fuel
Propellers – Fixed Pitch
 Propellers have “twist”
to maintain a constant
angle of attack across
the blade
 A given RPM creates different
(linear) velocities along prop.
 Lift = airspeed x AOA and
constant lift is desired…
therefore: twist!
Propellers – Constant Speed
 Pilot controls separately power (via
manifold pressure) and RPMs.
 Avoid high MP with low RPMs
 When increasing power, advance
propeller before advancing throttle
 When decreasing power, retard throttle
before decreasing propeller
Other Systems:
 Generally airplane-specific (not on FAA
knowledge test):
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Environmental
Landing gear
Electrical
Starting
Hydraulics
 Advanced aircraft:
 Pressurization
 Oxygen
 Deicing
Next Week…
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Instrumentation
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(PHAK chap. 6)
Regulations
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(FAR/AIM & Test Prep)