ASCI 356 Exam 2

primary flight controls

ailerons, elevator (stabilizer), and rudder are required to control and aircraft safely during flight

secondary flight controls

wing flaps, leading edge devices, spoilers, and trim systems that improve the performance characteristics of the airplane or relieve the pilot of excessive control forces.

ailerons

control roll about the longitudinal axis, attached to the outboard trailing edge of each wing and moves in opposite directions of each other

frise-type ailerons

aileron pivots on an offset hinge, projecting the leading edge of the aileron into the airflow to help reduce adverse yaw

differential ailerons

can put each aileron in different positions

coupled ailerons and rudder

linked controls, automatically deflects rudder when airlerons are deflected to correct adverse yaw

types of flight controls: mechanical

direct linkage systems that use physical components—such as steel cables, push-pull rods, pulleys, bellcranks, and chains

simple and reliable, but does not evolve well

types of flight control: hydromechanical

combines physical mechanical linkages with hydraulic power systems to move an aircraft's control surfaces

has gust lock, can evolve, more expensive

types of flight control: fly-by-wire

replaces physical connection between pilot controls and flight control surfaces with an electrical interface

more reliable, more expensive

gust lock

a mechanical or physical device used to secure an aircraft's control surfaces (ailerons, elevators, and rudder) and controls when parked on the ground

horizontal stabilizer

small, wing-like surface located on the tail (empennage) of an aircraft that keeps the plane balanced and prevents unwanted up-and-down movement of the nose, known as pitch

C-172 flight controls

primary: elevator, ailerons, rudder, brakes

secondary: flaps, trim system

MCAS 737 Max

implemented to compensate for placing engines forward & up

Artificial feel unit (AFU)

provide feedback (as resistance) to mimic mechanical flight controls

Why do pilots need artificial feel units (AFU)

With hydraulic, and fly-by-wire systems, pilots don’t get “real” feedback like mechanical systems. Lack of ‘feel’ can cause oversteering and other problems

rudder bias system

pushes rudder towards the good engine to help decrease yaw excursion in the event of an engine failure

yaw damper

improves stability by damping out oscillations in yaw

parts of reciprocating engine

“crankshaft turns the propeller”

4 stroke cycle engine: intake stroke

(STEP 1) piston is pulled downward by the rotation of the crankshaft, increases the volume inside the cylinder, and causing air to flow through the carburetor (SUCK)

4 stroke cycle engine: compression

(STEP 2) As piston approaches TDC after being loaded, the fuel/air mixture is compressed and is fired by an electric shock (SQUEEZE)

4 stroke cycle engine: power

(STEP 3) piston is forced downward by the pressure of the burning gasses being exerted on it, downward movement of the connecting rod is changed to rotary movement by the crankshaft. This movement is then transmitted to the propeller shaft to drive the propeller (BANG)

4 stroke engine power: exhaust

(STEP 4) pushes the burned exhaust gases out of the exhaust port as it travel to the bottom dead center (BLOW)

turbo/super chargers: why do we need them?

• the fuel air mixture flowing into an aircraft engine must be relatively consistent, making a better mixture for the plane to consume

• lower air pressure higher up

turbosuperchargers

externally driven superchargers derive power from energy of engine exhaust gases directed against a turbine that drives an impeller that compresses incoming air (COMPRESSED BEFORE F/A MIXTURE)

superchargers (internally driven)

compress f/a mixture after it leaves the carburetor by using a compressor powered by the crankshaft

gasoline vs diesel engine

• has the highest effective efficiency

• can combust many different (cheaper) fuels

• very good exhaust-emmision behavior

• no high voltage system (great reliability and easy adaptation to damp environments)(no radio interference)

• can accept super or turbo charging pressure with no limits

C-172 IO-360: Engine

direct drive, horizontally opposed, 4-cylinder, overhead valve, air cooled, fuel injected engine with a wet sump lubrication system

C-172 IO-360: Fuel Lubrication System

Oil is drawn from the sump through a filter screen on the end of a pickup tube to the engine driven oil pump. Oil from the pump passes through a fuel-flow filter, with a pressure relief valve and a thermo controlled oil cooler. Oil from the remote cooler is then circulated to the left oil gallery. The engine parts are lubrictated by oil from the galleries. After lubricating the engine, the oil returns to the sump by gravity.

C-172 IO-360: Ignition and Starter System

Ignition is provided by two engine driven magnetos, and two spark plugs in each cylinder.

C-172 IO-360: Air Induction System

receives ram air through an intake covered by an air filter to remove dust and other matter in the air. Airflow then enters an air box, equipped with a spring-loaded alternate air door. If filter becomes blocked, suction will open the door and draw unfiltered air. This will result in a 10% power loss at full throttle. After passing through box, air enters the fuel.air control unit and is ducted into the cylinders.

C-172 IO-360: Fuel Injection System

After reaching the cylinders, fuel manifold evenly distributes the fuel to an air-bleed type injector nozzle in the intake valve chamber of each cylinder. A transducer between the f/a control unit and fuel distribution unit sends digital signals that display fuel flow in the cockpit.

C-172 IO-360: Cooling System

Ram air in for engine cooling

DA-42: Austro E4-C Engine

• Liquid Cooled, four cylinder, four stroke, with wet sump lubrication

• digital engine control with integrated propeller governor

• turbo charger with intercooler

• Each engine can only be operated with the ENGINE MASTER switch ON. Each engine has its own ECU.

• Each ECU controls their respective engine’s manifold pressure, injected fuel quantity and propeller speed

DA-42: Austro E4-C Alternate Air Lever

In the event of a power loss because of icing/blocking of the air filter, there is a way to draw air from the engine compartment. This lever serves both engines simultaneously to help air flow.

Problems needed to be solved for battery powered aircraft

• Everyday LI-ION batteries still only have 1/43 the energy density of everyday airplane fuel

• doubling the mass of the aircraft increases the power requirement 8 times

• Smaller recips are starting to become a thing but, are not equal alternatives yet

• Need batteries with much higher energy density

hydrogen fuel cells

• hydrogen and oxygen are used like positive and negatively charged halves of a battery

  • movement of electrons generates current

• problems:

  • hydrogen is 5x as expensive

  • process of making pollutes

  • still takes more energy to make than we yield

  • storing and transport require even more energy (must be super-cooled)

  • power density still too low

hydrogen combustion

• alternative to jet fuel combustion

• lower pressure ratio engines (more reactive)

hydrogen combustion problems

• H2 availability at airports and refueling

• danger with engines (can not detect leaks)

• storage

fixed-pitch propellers

• designed for best efficiency at one rotational and forward speed

• anything other than that speed is an efficiency decrease

constant-speed propeller

• pilots sets a propeller speed

• Prop governor maintains that set speed

parts of propeller

propeller governers

• governer maintains the set speed by pilot

• increase ro decrase blade pitch control

  • increase pitch = decrease RPM

DA-42 Prop

• constant speed, hydraulically regulated.feathering

• ECU sets pitch via the governer

• adding oil pressure decreases the pitch

• if feathered, oil flows back from the hub

Propeller Efficiency

• the ratio of Thrust HP : Shaft HP

• geometric pitch - effective pitch = slip

Propeller (Shaft HP)

comes from the engine

Thrust HP

Comes from the propeller

forces acting on a propeller: centrifugal force

physical force throws prop away from hub (most dominate)

detonation

an explosion, or the uncontrolled burning of the fuel air mixture inside the cylinder of a reciprocating engine

fuel system terms

REFER TO: briefing 19, slide 8

• Fuel ALWAYS goes back to reservoir

AVGAS vs Jet fuel

AVGAS:

• less viscous

• more volatile

• more flammable

• lower flash point

Jet fuel:

• all opposite

fuel lines/fittings

can be rigid/flexible

• rigid: aluminum alloy/ stainless steel

• flexible: rubber interior, then braided, then covered

• metal ones need to be grounded

fuel pump construction

• engine driven pump, mechanically driven

Types of fuel pumps: Piston Pump (Primer)

injects a fine mist or squirt of fuel directly into the engine cylinders

• centrifugal boost pump: a heavy-duty rotary machine that converts motor mechanical energy into fluid pressure using a rotating impeller

• pulsating electric pump: smaller, less expensive axillary

• vane type pump: constant displacement pump that moves a constant volume of fuel. Can be engine driven or axillary

aux/boost pump

CESSNA:

• fuel return system keeps temps lower on hot days

• can support max continuous power

• primary use: priming engine

• secondary use: vapor suppression

• continuous use enriches mixture

IN GENERAL:

• primary purpose is to deliver fuel to engine pump inlet (priming engine)

• secondary purpose is back during:

  • start

  • takeoff

  • high altitude

engine driven pump

primary fuel delivery device that can deliver fuel under pressure to the fuel metering device

Fuel Flow Meters

• many types

• simplest is pressure gauge

• modern W(f) transducer typically are installed downstream of the last fuel pump using a laser

Capacitance Type Fuel Sensing/Indicating

two concrete plates at a fixed distance and the capacitor measures the material between them. Translates fuel quantity into pounds. Compensator unit accounts for fuel temperature changes.

Fuel Filtration

• Filter: fine mesh that can trap contaminates on the micron level

• strainer: relatively coarse wire mesh fuel flows through by the help of gravity

• typically multiple:

  • fuel tank

  • between tank and inlet to engine driven pump

  • between engine driven pump and fuel metering device

Fuel Indicating

IN GENERAL:

• electronic quantity indicating is most common

  • gauge face does not matter

  • convert variable resistance into a digital signal to be processed by the computer

CESSNA:

• 1 fuel quantity sensor in each wing tank

• 0 gals indicated, means 1.5 gals (unusable) remain

• sensor management range is 24 gal

• “low level” at 5 gal

• not accurate in slips/skids

• indicator will flash red at 0 gal

• fuel flow indicates:

  • turbine type transducer

  • located between FCU and flow divider

fuel vent system (C172)

• complete blockage of the fuel vent system will result in decreasing fuel flow and eventually engine stoppage

• selector valve: operate in “left”, “right”, or “both” for fuel flow to the engines

• when ¼ tank or less, prolonged uncoordinated flight may result in fuel tank outlets being uncovered and start to starve the engine

fixed v retractable gear pros/cons

retractable:

• eliminates the added drag penalty from fixed landing gear

• used only when the drag is higher than the weight penalty (drag>weight penalty)

fixed:

• avoids the added weight penalty that is not worth it in smaller GA aircraft

shock absorbing landing gear

• transfer shock energy from landing on the ground and distributes it throughout the airframe

• can be converted into heat

shock struts

• most common method of shock dissipation

• uses compressed air & hydraulic fluid

• compression forces fluid to be passed through a small orifice to the top of the strut

  • building pressure and the passage of the fluid through the orifice causes heat

  • this pressure creates the resistance needed when landing a heavy piece of machinery which causes the aircraft to begin moving upward farther from the ground after landing

large aircraft landing system

• most commonly use a hydraulic pump from the accessory drive

• all small gear components and:

  • door actuators: opening and closing the doors of the landing gear bay during takeoff and landing sequences

  • sequencing valves: valve that ensures landing gear components (such as the gear legs and wheel well doors) deploy or retract in a strict, predetermined order

  • uplocks / downlocks: mechanical safety and securing mechanisms used in an aircraft's retractable landing gear system to hold the wheels safely in place during flight and upon landing

• almost always has a backup electrical hydraulic pump

Small airplane landing gear systems

self-contained, electrically driven (reversable) hydraulic pump that pressurizes fluid to raise and lower the landing gear

landing gear safety (squat) switch

• switch positioned to open and close depending on the extension or compression of the main landing gear strut

• wired into any number of system operating circuits

• circuit prevents gear from being retracted while the aircraft is on the ground, creating a “lock-out”

aircraft wheels (material)

• two-piece rims to prevent tire stretching

• made out of forged aluminum or alloy halves

• sealed o-ring at mating surface

aircraft wheels (construction)

• inboard wheel half has to host brakes

• inner half often hosts the thermal and overinflation plugs (melt if wheels/brakes are too hot to avoid and explosion by deflating the tires)

• outer half often hosts the wheels speed transducer:

DA-42 Retractable Gear

• hydraulic pressure via electric pump

• hydraulic pressure keeps the gear in the retracted positon

• warning horn with less than 20 % power on aircraft

• squat switch prevents unwanted gear retraction

• emergency gear extension releases the pressure holding the gear in the retracted position

forces acting on a propeller: Torque bending force

bends prop in opposite direction of rotation

forces acting on a propeller: Thrust bending force

bends the prop blades forward

forces acting on a propeller: Aerodynamic twisting force

turns blades to high blade angle

forces acting on a propeller: centrifugal twisting force

forces blades towards a low blade angle

Types of fuel pumps: Centrifugal boost pump

a heavy-duty rotary machine that converts motor mechanical energy into fluid pressure using a rotating impeller

Types of fuel pumps: Piston Pulsating electric pump

smaller, less expensive axillary

Types of fuel pumps: Vane type pump

constant displacement pump that moves a constant volume of fuel. Can be engine driven or axillary

brakes

Converts the kinetic energy of aircraft in motion to heat energy through the creation of friction.

common aircraft brake designs

• independant of hydraulic system (non-hydraulic)

• hydraulic system boost (light aircraft)

• Hydraulic System Powered (airliners)

large aircraft brake system

segmented rotor-disk brakes are multiple disc breaks. a disk rotates with the turning wheel assembly, along with a sttionary caliper. When pressure is applied by the hydraulic system, this caliper resists the rotation of the wheels.

large aircraft brake system components

carbon brakes

• carbon fiber materials

• 40 percent lighter

• newer, more advanced

• withstand higher temps

• dissipate heat faster

• longer service life

• expensive

anti skid system (how it works)

• detects imminent skid by seeing how fast the wheel is turning compared to how fast it SHOULD be turning

  • all wheels should be turning the same speed, if not a skid is occurring

• modulates break pressure

anti-skid components: wheel sensor

• built like a transducer

• RPMs is produced by the wheel speed

• output is fed to control unit

anti-skid components: control unit

• the brain of the system

• looks for changes in voltage/wheel speed

• compares aircraft speed to wheel speed

• compares wheels sped to other wheels

anti-skid components: control valve

• fast-acting, electronically controlled hydraulic valve

• adjusts pressure to the brakes

Skid v anti-skid performance

skid:

• longer stopping distances

• high risk of flat tire/blowout

• carefully pump brakes

C-172 Brakes

• single disc brake on each MLG

• pilot (only) has set of master cylinders attached

• parking brake sets both wheels

• minimize brake usage during taxi and landings