Aerodynamics of Turns, Loads, and Autos Flashcards
What are the two components of the total lift generated by a helicopter’s rotor system during a turn?
The vertical component (which holds the helicopter up) and the horizontal component (which pulls the helicopter into the turn).
What role does centrifugal force play in a helicopter turn?
Centrifugal force, or inertia, acts outward during a turn, causing any object to continue moving in a straight line unless acted upon by another force.
How does the load change when the bank angle increases?
The load becomes greater than the weight of the helicopter; at zero bank angle, load equals weight, but with a bank greater than zero, load increases.
What generates lift in a helicopter’s rotor system?
Lift is generated perpendicular to the rotor disc and is divided into a vertical component (maintaining altitude) and a horizontal component (pulling the helicopter into the turn).
What is the vertical component of lift responsible for?
It counters gravity to maintain altitude.
What does the horizontal component of lift do during a turn?
It creates a centripetal force that pulls the helicopter into the turn.
How does gravity affect a helicopter during a turn?
Gravity continues to pull down on the helicopter, requiring more lift to maintain altitude.
Define load in a helicopter turn.
Load is the total force supported by the aircraft’s lifting surfaces, which exceeds the helicopter’s weight during a turn.
What is centrifugal force in the context of helicopter turns?
It opposes the centripetal force and results from the helicopter’s inertia, which tries to keep it moving in a straight line.
How does bank angle affect load factor?
A greater bank angle increases load factor, requiring more lift to counteract gravity and centrifugal force.
What is the load factor at a 0° bank angle?
The load factor is 1, which equals the helicopter’s weight.
At what bank angle does the load factor reach 2?
At a 60° bank angle.
What happens to load factors at bank angles of 80° or higher?
Load factors rise sharply, leading to higher stress on helicopter components.
Why is it important to manage bank angles and loads in helicopter flight?
To avoid mechanical failure due to increased strain on rotor blades and other components.
What does a load factor table provide for pilots?
Load factor values at various bank angles, helping anticipate stress on the helicopter.
Describe the relationship between turbulence and load factor.
Turbulence can temporarily increase the load factor, adding strain on the helicopter, especially at higher gross weights.
How does higher gross weight affect helicopter stress?
It increases total load on the structure, leading to more stress on rotor, mast, and transmission components.
What happens to the coning angle with higher loads?
The coning angle increases, requiring more lift and resulting in a sharper coning angle.
What is the impact of increased coning angle on rotor RPM?
It may lead to higher RPM due to the coriolis effect during auto-rotation.
How does density altitude affect lift capability?
At high density altitudes, lift capability decreases due to reduced air density.
What must pilots do to compensate for reduced lift at high density altitudes?
They must raise the collective to increase the angle of attack, bringing rotor blades closer to the critical angle.
What hazards can abrupt control movements create?
They can lead to accelerated stalls or low-G situations, increasing stress on the helicopter.
What is the relationship between bank angle and power requirements?
Increasing the bank angle raises the load factor, requiring more collective pitch and power to maintain altitude and speed.
Define slips and skids in helicopter flight.
A slip occurs when horizontal lift exceeds inertia, causing the helicopter to fall into the turn. A skid occurs when inertia exceeds horizontal lift, causing the helicopter to slide outward.
How can a pilot visually identify a slip or skid?
If the tail slides outward, it’s a skid; if it falls inward, it’s a slip.
How does bank angle influence the rate and radius of turns?
More bank angle results in a higher turn rate and smaller radius.
What is auto-rotation?
A flight condition where the rotor is driven by airflow (relative wind) rather than the engine.
What is the windmill brake state?
The transition phase from engine-driven to wind-driven rotor movement during auto-rotation.
Describe airflow dynamics in powered flight.
Air flows downward through the rotor system as the helicopter moves forward.
What occurs during auto-rotative flight?
The helicopter descends, and air flows upward through the rotor, keeping the rotor blades turning.
How does entering auto-rotation from a climb differ from entering from a descent?
Entering from a climb takes longer due to upward inertia, while entering from a descent results in minimal RPM loss.
What are the three main regions of a rotor blade during auto-rotation?
Stall region, driving region, and driven region.
What happens in the stall region of a rotor blade?
Blades are at a high angle of attack, leading to a stall where they generate more drag than lift.
What is the function of the driving region?
It generates lift and thrust to maintain rotor RPM during descent.
Describe the driven region of a rotor blade.
It generates lift but with a drag that slows the blades down, moderating descent speed.
What are equilibrium points on the rotor blade?
Points where aerodynamic forces are balanced, with no net drag or thrust.
How does relative wind affect rotor aerodynamics?
It is created by rotor rotation, with profile drag acting opposite to the direction of rotation.
What impact does adjusting collective have on rotor regions?
It changes the size of the driven and stall/driven regions, affecting rotor performance.
How do aerodynamic regions shift during forward flight?
They shift towards the retreating side, with lower angles of attack on the advancing side.
What are the phases of auto-rotation?
Entry phase, glide phase (steady descent), and flare phase (approach to ground).
What controls RPM during the entry phase of auto-rotation?
Lowering the collective reduces drag and helps prevent RPM decay.
What forms of energy are available during auto-rotation?
Altitude, airspeed, and rotor RPM
What does the height-velocity diagram indicate for autorotative landings?
It shows unsafe altitude and speed combinations, highlighting risks for landing gear and tail strikes.
What does excessive landing gear stress result from?
Descending from low altitudes at high forward speeds can severely stress the landing gear.
Why is it critical to understand the height-velocity curves?
They determine safe altitude and airspeed combinations for autorotation based on conditions.
How do weight and density altitude affect shaded regions on the height-velocity diagram?
Higher weight and density altitude expand shaded areas, making autorotation recovery more difficult.
What is the recommended takeoff profile to avoid shaded areas?
Conducting a ground run at low altitude and speed, keeping under 10 feet and increasing speed before climb.
