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 T-tail Stabilator Canard V-tail

Secondary Flight Controls  Primarily: Flaps Trim systems  But also… Slots Slats Spoilers

Flaps  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  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 ~ 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: 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): Environmental Landing gear Electrical Starting Hydraulics  Advanced aircraft: Pressurization Oxygen Deicing

Next Week… -Instrumentation -(PHAK chap. 6) -Regulations -(FAR/AIM & Test Prep)