Performance Flashcards
What is the primary role of horsepower in helicopter performance?
It is the metric used to measure the helicopter’s performance- it’s ability to hover, climb, and maneuver.
How does altitude affect horsepower output?
Higher altitudes reduce air density, causing lower oxygen levels available for combustion and diminished horsepower.
Why does warmer air reduce engine performance?
Warmer air is less dense, lowering the available oxygen per engine stroke and reducing horsepower.
How does humidity impact helicopter performance?
Humid air is less dense, providing less oxygen for combustion and reducing engine power output.
What does ‘hover ceiling’ mean?
The maximum altitude at which a helicopter can maintain a hover. Determined for IGE and OGE.
Define ‘In Ground Effect’ (IGE) hovering.
Hovering within one rotor diameter of the ground, which enhances lift by reducing induced flow and minimizing tip vortices.
Define ‘Out of Ground Effect’ (OGE) hovering.
Hovering more than one rotor diameter from the ground, requiring more power there is more induced flow through the rotor blades and rotor tip vortices are able to grow larger.
How does weight affect hover ceiling?
Heavier loads reduce hover ceiling, requiring more power to hover at a given altitude.
What is the relationship between altitude and hovering?
At higher altitudes, the air is less dense, restricting the aircraft’s ability to hover at a certain point. A pilot must calculate hover ceilings to determine what altitude they can successfully hover at.
What is climb rate in helicopter performance?
The vertical speed at which a helicopter ascends, influenced by engine power, rotor efficiency, and air density.
How does high-density altitude affect climb rate?
It reduces lift efficiency and power output, decreasing climb rate.
How does atmospheric pressure affect performance?
Lower pressure decreases air density, reducing performance, while higher pressure increases it.
How does thermal expansion due to warm temperatures affect performance?
Warm air expands, reducing density and therefore reduces performance; cool air is denser and therefore enhances performance.
Describe the effect of humidity on air density.
When there is high humidity, the water molecules are displacing oxygen molecules and therefore decreasing air density, reducing lift and engine power.
What is density altitude?
Pressure altitude adjusted for non-standard temperature.
The altitude the aircraft “feels” like it’s at during a flight.
How does high density altitude affect takeoff distance?
It increases the required takeoff distance due to reduced air density and performance.
What is the benefit of flying in cooler parts of the day?
Cooler temperatures increase air density, improving lift and optimizing engine output.
How can high altitudes and temperatures impact rotor efficiency?
Lower air density reduces rotor lift, necessitating more power to maintain performance. There are less oxygen molecules being displaced by the airfoil which is directly affecting lift production, via the lift equation.
How can pilots use performance charts for planning?
To estimate hover ceilings, power output, airspeed restrictions under expected conditions.
How does air density influence the engine’s oxygen intake?
Lower density means fewer oxygen molecules per intake, decreasing fuel combustion efficiency.
Define pressure altitude and its purpose.
The true altitude adjusted for nonstandard pressure (29.92). It is used for performance calculations.
-set the altimeter to 29.92 and read the outcome directly
or
-mathematically: 1000 x (29.92 - reported pressure) + field elevation
How does pressure altitude vary with weather changes?
High or low-pressure systems can raise or lower the pressure altitude.
Why is manifold pressure crucial in engine management?
It shows the parameters that will keep the engine power output at 124HP at 2652rpm; exceeding limits can damage the engine.
How is VNE (Never Exceed Speed) determined in helicopters?
Determined based on altitude and temperature to prevent retreating blade stall.