Exam Theory Questions Flashcards
Which of the following vehicles can be categorized as rotorcraft
A. Helicopter
B. Autogiros
C. Tiltrotor
D. Hot air balloon with fans
E. Propeller aircraft
A, B, C, E
What are the two main issues driving the multi-rotor configurations widely used in the early
rotorcraft development
Torque balance
Rolling moment in forward flight
How does the single-rotor helicopter deal with the torque balance
Tail rotor
How does the single-rotor helicopter deal with the rolling moment in forward flight?
Flapping motion
What is the difference between the helicopter and autogiros
A. The rotor powered by the engine in the cruise flight
B. Autogiros cannot take off vertically without the help of pre-rotator
C. Hover capability
D. The helicopter may be larger than the autogiros
E. Autogiros sometimes are not equipped with rotor control inputs
Why does not the autogiro need a tail rotor
The rotor of the autogiro does not connect with the engine, and it cannot transmit torque to the
vehicle.
What is the fundamental difference between the helicopter and the autogiros
The rotor powered by the engine in the cruise flight
How do single-rotor rotorcrafts provide control forces and
control moments
- Vertical force: Main rotor thrust
- Longitudinal force: Main rotor tilt fore/aft
- Lateral force: Main rotor tilt lateral
- Pitch attitude: Main rotor tilt fore/aft
- Roll attitude: Main rotor tilt lateral
- Yaw attitude: Tail rotor thrust/engine torque
How do tandem rotorcrafts provide control forces and
control moments
- Vertical force: Collective main rotor thrusts
- Longitudinal force: Main rotors tilt fore/aft
- Lateral force: Main rotors tilt lateral
- Pitch attitude: Main rotor tilt fore/aft and/or differential
main rotor thrust* - Roll attitude: Main rotor tilt lateral
- Yaw: Differential main rotor tilt in lateral directions
- *Note that differential main rotor thrust unbalances the
aircraft in yaw. There is no good alternative to differential
thrust to change aircraft pitch attitude so the pilot or the control system must cope with the coupling that results.
How do Transverse, or side-by-side rotorcrafts provide control forces and
control moments
- Vertical force: Collective main rotor thrusts
- Longitudinal force: Main rotors tilt fore/aft
- Lateral force: Main rotors tilt lateral
- Pitch attitude: Main rotors tilt fore/aft
- Roll attitude: Main rotors tilt lateral and/or differential
main rotor thrusts - Yaw: Differential main rotor tilt fore/aft
How do coaxial rotorcrafts provide control forces and
control moments
- Vertical force: Collective main rotor thrusts
- Longitudinal force: Main rotors tilt fore/aft
- Lateral force: Main rotors tilt lateral
- Pitch attitude: Main rotors tilt fore/aft
- Roll attitude: Main rotor tilt lateral
- Yaw: Differential main rotor torques
The function of the swashplate
Adjust the blade control angle at different azimuth angles.
What is the difference between the thrust and lift:
Thrust is in the rotor axial direction
Lift is normal in the inflow direction
What are the assumptions of the momentum theory
Existing a steamtube which is an axially symmetric surface passing through the rotor disc
perimeter which isolates the flow through the rotor
Incompressible flow
Velocity imparted to the fluid is constant across the disk
Far away from the disk, the air is at rest
The definition of the induced velocity
The velocity increment due to the rotor is called Induced Velocity
The condition of the momentum theory applicable to the vertical descent flight
|ð| > 2ðĢi, hover
True or False:
A figure of merit is used to evaluate the rotor performance in the vertical flight
False
It is used to evaluate rotor performance in hover
True or False:
Rotor power calculated from the momentum theory and blade element torque
is the same
False:
the power from the moment theory is the induced power (induced + parasite power in
forward flight,), and the power from the blade element theory is the all rotor power consumption.
What is the most reasonable pilot control strategy to get rid of the vortex ring state:
Push longitudinal cyclic pitch to increase forward speed
From the view of the blade element theory and considering the attack angle and the inflow
condition, indicate why the rotor needs the pre-twist angle
The pre-twist angle allows most of the blade element (especially the blade tip section) to be in the
optimal attack angle (maximise the ratio between lift and drag)
Demonstrate the function and mechanism of the pre-rotator
Function: Reduce the take-off distance of the auto-rotator and even allow the autogiro to have
vertical take-off capability.
Mechanism: Let the engine link with the rotor on the ground to make the rotor rotate, which will
disconnect with the rotor after take-off.
