Aerodynamic Forces, Lift/Drag

Question 1

When an aerofoil operates at its best lift/drag ratio, the angle between lift and total reaction is ( zero, as small as possible)

Answer 1

As small as possible

Question 2

The total reaction ( can/can not) act at right angles to the relative airflow

Answer 2

Cannot

Question 3

If lift remains constant but drag is reduced, the lift/drag ratio ( improves/ gets worse) and the total reaction leans ( closer/further away from) lift

Answer 3

Improves
Closer

Question 4

An airfoils lift/drag ratio is determined by its——- and ———

Answer 4

Shape
Angle of attack

Question 5

The best lift/drag ratio is normally found when an airfoil operates at a ( large/small) angle of attack

Answer 5

Small

Question 6

When operating at best lift/drag ratio, lift production (is/is not) at its maximum but drag is at its ( minimum/maximum)

Answer 6

Is not
Minimum

Question 7

The axis of rotation passes through the ——- and is always at (right angles, parallel to) the plane of rotation.

Answer 7

Rotor head
Right angles

Question 8

The disc area is the area contained with the ——- and in flight, the area (is, is not) constant because it is affected by the ——- angle.

Answer 8

Tip plane path
Coning

Question 9

Disc loading means the ——- of the helicopter divided by the ——-.

Answer 9

Weight
Disc area

Question 10

Flapping means the movement of blades in the ( vertical, horizontal) sense relative to the (plane of rotation, tip path plane).

Answer 10

Vertical
Plane of rotation

Question 11

Lead lagging means the movement of the blades ( forward, aft/ up, down) in the (plane of rotation, line with the shaft axis).

Answer 11

Forward,aft
Plane of rotation

Question 12

The difference between a fully articulated rotor and a semi rigid rotor is that the latter (does, does not) allow for (feathering, lead lagging) through hinges.

Answer 12

Does not
Lead lagging

Question 13

The semi rigid rotor system is common with (two, more than two)bladed rotors and (lead lagging, flapping) is generally taken up within the blades or the blade components.

Answer 13

Two
Lead lagging

Question 14

The relative or resulting airflow that influences the rotor blade in forward flight is a combination of airflows due to ——-, ——- and ——-

Answer 14

Rotation
Induced flow
Aircraft’s speed

Question 15

Airflow due to rotation (Vr) is (always, sometimes)in the (tip path, plane of rotation)

Answer 15

Always
Plane of rotation

Question 16

Induced flow means the airflow forced down by rotor action ( all of which, most of which) passes through the rotor.

Answer 16

Most of which

Question 17

When the induced flow increases, the inflow angle (increases, decreases) and for a given blade angle and rotor rpm, the angle of attach will (increase,decrease)

Answer 17

Increase
Decrease

Question 18

Rotor thrust is a (resultant, component) of the total reaction which (can, cannot) be perpendicular to the relative flow.

Answer 18

Component
Cannot

Question 19

Total rotor thrust always acts ( at right angles to, in line with) the ( shaft axis, axis of rotation.)

Answer 19

In line with
Axis of rotation

Question 20

The force that overcomes the gross weight of the helicopter is ——- or a component of that force.

Answer 20

Total rotor thrust

Question 21

Rotor drag is a force which acts in the ( plane of rotation, relative flow) and it acts to (increase, decrease) rotor rpm.

Answer 21

Plane of rotation
Decrease

Question 22

Assuming constant rotor rpm, when the inflow angle decreases and the collective is lowered proportionally , the total rotor thrust /drag ratio ( improves, worsens) so that (more, less) power is required to maintain rotor rpm.

Answer 22

Improves
Less

Question 23

A rotor operates at its most efficient when the total rotor thrust/ drag ratio is at the (best, worst) and the collective lever is as (high, low )as practically possible

Answer 23

Best
Low

Question 24

Compared to a cool dry day, on a hot and humid day the blades angle of attack needs to be ( greater, smaller, the same) and the total rotor thrust / drag ratio is at its (best, worst)

Answer 24

Greater
Worst

Question 25

With a constant rotor rpm, raising the collective will (increase, decrease) the coning angle, rotor drag will (increase, decrease) and the requirement for —— goes up.

Answer 25

Increase
Increase
Power

Question 26

The advantage of the high inertia rotor over the low inertia rotor is that rotor rpm tends to fluctuate (more, less) and the flare is ( easier, more difficult) to execute but recovery from low rpm is achieved (quicker, less quickly)

Answer 26

Less
Easier
Less quickly