Helicopters

Question 1

Name 4 types of Helicopters

Answer 1

Gyroplane - has a freely rotating wing supplying the aerodynamic force for lift; all forward thrust is supplied by a separate propeller as in a conventional aircraft.

Pure helicopter - Has powered rotating wings supplying all lift

Compound Helicopter - main lift supplied by rotor, supplemented by power units or stub wings

Convertible Helicopter - modifies config during flight (Vtol)

Question 2

4 Mainly used Heli configs

Answer 2

Single rotor with tail rotor
Tandem
coaxial contrarotating
NOTAR

Question 3

4 Controls used by the pilots

Answer 3

Collective Lever - Simultaneously Alter the pitch of all the blades by the same amount

Cyclic - Varied pitch of each blade cyclically

yaw pedals - Varies the force produced by the tail rotor to oppose torque reaction

throttle - Controls the throttle of RRPM

Question 4

What are the 3 ways that engine or rotor revolutions are controlled

Answer 4

Mechanical engine and rotor speed governing

Hydro mechanical engine and rotor speed governing

FADEC (Fully automatic digital engine control)

Question 5

4 Main types of rotor heads

Answer 5

Teetering Rotor
Fully articulated rotor head
Semi rigid
fully rigid

Question 6

Teetering Rotor

Answer 6

2 Blades rigidly connected to each other with a built in coning angle and gimble mounted rotor shaft

Question 7

fully articulated rotor head

Answer 7

3 hinges (3 axis)

Flapping hinge - Allows for verticle flap
Dragging hinge - Move in the plane of rotation
Feathering hinge - Allows for change in pitch

3 flapping constraints:

Droop restrainer - Limits droop of blade when rotating below normal speeds
Flapping Restrainer - Prevents flapping in gusty conditions

Question 8

Delta 3 hinges

Answer 8

Designed to improve stability of the Rotor head.

Flap hinge mounted at right angles to span of blade, pitch doesnt change during flapping instead the flapping hinge can be set at an angle, pitch angle reduced, reducing angle of attack.

Question 9

semi rigid rotor head

Answer 9

Has only feathering hinge, flapping and dragging allowed for by the flexing of the arms.

Question 10

What is the coning angle

Answer 10

The coning angle is measured between the spanwise length of the blade and the blades’ tip path plan

Will vary when the rotor RRPM and thrust from the rotor blades vary

if thrust is increased but RRPM constant, the blades will cone upwards

If RRPM is reduced but thrust stays the same, the coning angle in increase upwards due to centrifugal force

Question 11

what is wash out

Answer 11

The dispersion of root stresses throughout the rotor blade, stress increases as you move up the blade

Question 12

Verticle Movement

Answer 12

increase the pitch of each blade by the same amount at the same time, increases Angle of attack (Collective pitch change), done by raising the collective

this causes the blades to cone up increasing TR and drag. therefore more engine power will be required to maintain this rpm

Question 13

When a helicopter is hover at 200ft what state is it in?

Answer 13

HOGE -Hover outside of ground effect

Question 14

Ground descent

Answer 14

Collective pitch lever lowered, Angle of attack is reduced.

Airflow resulting will oppose induced airflow through the disc, resultant will change in direction of the RAF to the blade, increasing the AOA

When AOA reaches 4 degrees, rotor thrust will equate to the weight and downwards acceleration will be a steady rate.

Question 15

Ground effect.

Answer 15

Hovering the helicopter near the ground in still air will require less power than is required at 50ft or 100ft. this is ground effect.

Hovering near the ground creates a divergent duct causing an increase of pressure.

Question 16

4 factors that affect ground effect

Answer 16

Height
slope
nature of ground
wind

Question 17

what two components does a helicopter need to move horizontally

Answer 17

A verticle component - must be equal to the weight of the helicopter to hold the aircraft in level flight

A horizontal component - must be equal to total drag of the helicopter for constant speed in level flight

Question 18

how is horizontal movement done

Answer 18

Tilt disc, done by increasing pitch on one side, increasing AOA and Lift, causing rise on flapping hinge has the opposite effect on opposite side (decrease AOA, decrease lift) Known as cyclic pitch change, done with the cyclic pitch stick

Question 19

what is torque reaction

Answer 19

MRB Makes fuselage want to move one way, tail rotor moves it in the opposite direction. So if MRB is going CW, then Tail rotor is going ACW.

Question 20

What is tail rotor drift

Answer 20

When the helicopter has a tendency to move sideways in relation to the Tail rotor. corrected by the pilot with an opposing cyclic stick input

Question 21

How to correct for tail rotor drift

Answer 21

Mount the main rotor gearbox on the tilt

rigging the controls - set a new normal for the AC

Question 22

How to stop tail rotor roll

Answer 22

Set the tail rotor to be in line with the MRB when the helicopter is in forwards flight

Question 23

Describe flapping to equality

Answer 23

When the pilot changes the angle of the rotor disc, the blade positions change by flapping. Blades that flap down have an increase on Angle of attack and lift while reducing the acceleration. it reduces the value of the IAF

The blade that flaps up has an increased value of IAF therefore the angle of attack and lift decrease.

This creates the same values for when the rotor disc in level, providing the same results.