13.1.C Rotary Wing Aero

Question 1

Rotary disc

Answer 1

Blade sweep area

Question 2

Plane of rotation

Answer 2

Tip path plane

Question 3

Axis of rotation

Answer 3

Axis of the blades

Question 4

Blade AOA

Answer 4

Angle between blade chord and it’s direction of motion relative to the air

Question 5

Blade angle of incidence

Answer 5

Angle between blade chord line and plane of rotation

Question 6

Total aerodynamic force TAF

Answer 6

Is generated by airflow over and under the aero foil

Question 7

Rotor disc incidence

Answer 7

Angle between rotor disc and relative airflow

Question 8

Coming angle

Answer 8

Angle formed by the spa wise axis of the blade and plane of rotation

Question 9

Twisted and tapered blades

Answer 9

Due to tip speeds being much higher than the root speeds which would cause uneven lift

To minimise this

Twist blades (washout) reducing the pitch angle spa wise

Reduce blade width spanwise (tapered blades)

Question 10

Rotor speeds and max RPM : max rotational speeds limited by tip speed
Must not go transonic or supersonic vibration issues

Answer 10

Rotor speed kept constant

To increase lift increase blade aoa

With increased aoa = increased induced drag

To maintain rotor speed with >lift = >engine power ie more torque

Question 11

Blade section

Answer 11

Long and slender (high aspect ratio)

Centre of pressure requires stability

> rigidity achieved if c of p chord wise and c of g feathering axis are all coaxial

Question 12

Metal blades

Answer 12

Twist if c of p moves chord wise

Due to this they tend to be symmetrical aerofoils = more stable cofp and less twist

Question 13

Composite blades

Answer 13

Much stiffer blades = cambered aerofoils resulting in better aerodynamic advantages

Question 14

Blade flapping

Answer 14

Movement of the blade tips in the vertical plane (high stress at blade roots)

Small two bladed helicopters can share root hinge

Large helos require individual blade hinges due to stress. (Flapping hinges)

Question 15

Flapping angle

Answer 15

Blades are flapping to tilt the rotor disc, angle is formed between the tip path plane and the horizontal plane.

Question 16

Blade feathering

Answer 16

Changing pitch angle of blades in flight. All at once (collective) individually (cyclic)

Question 17

Transition

Answer 17

Transition from hover to translational flight

Question 18

Torque reaction

Answer 18

Counteracted by use of a tail rotor (newtons third law equal opposite reaction)

Tail rotor can push or pull

Structural reasons usually a pusher

Contra-rotating (no tail rotor required - chinook)

Bleed air system - Notar no tail rotor

Question 19

Autorotation

Answer 19

Producing lift from freely turning rotor blades.

To reduce decent speed to land full collective is used to slow the decent.

Engine failure or tail rotor failure as it produces nearly zero torque

Rate of decent it’s critical
Pitch angle of the blade is critical

Question 20

Cyclic

Answer 20

Control stick - forward, backward and side to side.

Pitch up and down
Roll

Moves blades individually to control input.

Question 21

Collective

Answer 21

Control lever typically on left side of pilot.

Collectively controls all blades to produce lift, typically connected to throttle so as increased so does engine power

Question 22

Anti-torque controls

Answer 22

Foot controls to control the tail rotor. Full right reduces tail rotor pitch and allows helo to move to the right - full left is opposite