MET Flashcards
What does the ISA assume?
1013 hPa, decreasing at 1 hPa / 30ft
1.225 kg/m3
MSL temp of +15 C, decreasing at 2 C / 1000ft
Air Density is affected by what?
Gravity
Temperature
Humidity
Air Pressure
How does pressure effect density?
Air Pressure increases, Density increases
Air Pressure decreases, Density decreases
How does temperature effect Density?
Air Temp increases, Density decreases.
Air temp decreases, Density increases.
What is the DA calculation?
DA = PA +/- 120t
What does t stand for in the DA equation?
T is the difference between actual air temperature and ISA temperature for that PA.
What is Low Density?
When atmospheric pressure is low, or air temperature is high, the density of the air is reduced and the DA at sea level becomes high.
What is high density?
When low air temperatures are combined with high atmospheric pressure, the density of the air increases, this gives rise to low DA at sea level.
A lower than usual air density effects helicopter performance in 4 important ways. What are they?
Power available reduces
Power required increases
Stabilty reduces
Handling deteriorates
How do rotors perform at high altitude?
More collective pitch required to increase the AoA in order to generate the required lift.
More power required to overcome the extra rotor drag resulting from the increase in pitch.
How to rotors perform at low altitude?
Less collective pitch required to generate lift, therefore reduced AoA and less rotor drag.
As density decreases and collective pitch angle increases, what will happen?
Reduction in max speed.
Reduction in control response.
Rotor blades approach stalling speed.
In a low DA what is engine power normally limited by?
Torque
In a high DA what is engine power normally limited by?
Max TOT or Max N1
What errors does IAS suffer from?
Pressure error
Instrument error
