Aerodynamic Forces, Lift/Drag Flashcards
When an aerofoil operates at its best lift/drag ratio, the angle between lift and total reaction is ( zero, as small as possible)
As small as possible
The total reaction ( can/can not) act at right angles to the relative airflow
Cannot
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
Improves
Closer
An airfoils lift/drag ratio is determined by its——- and ———
Shape
Angle of attack
The best lift/drag ratio is normally found when an airfoil operates at a ( large/small) angle of attack
Small
When operating at best lift/drag ratio, lift production (is/is not) at its maximum but drag is at its ( minimum/maximum)
Is not
Minimum
The axis of rotation passes through the ——- and is always at (right angles, parallel to) the plane of rotation.
Rotor head
Right angles
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.
Tip plane path
Coning
Disc loading means the ——- of the helicopter divided by the ——-.
Weight
Disc area
Flapping means the movement of blades in the ( vertical, horizontal) sense relative to the (plane of rotation, tip path plane).
Vertical
Plane of rotation
Lead lagging means the movement of the blades ( forward, aft/ up, down) in the (plane of rotation, line with the shaft axis).
Forward,aft
Plane of rotation
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.
Does not
Lead lagging
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.
Two
Lead lagging
The relative or resulting airflow that influences the rotor blade in forward flight is a combination of airflows due to ——-, ——- and ——-
Rotation
Induced flow
Aircraft’s speed
Airflow due to rotation (Vr) is (always, sometimes)in the (tip path, plane of rotation)
Always
Plane of rotation
Induced flow means the airflow forced down by rotor action ( all of which, most of which) passes through the rotor.
Most of which
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)
Increase
Decrease
Rotor thrust is a (resultant, component) of the total reaction which (can, cannot) be perpendicular to the relative flow.
Component
Cannot
Total rotor thrust always acts ( at right angles to, in line with) the ( shaft axis, axis of rotation.)
In line with
Axis of rotation
The force that overcomes the gross weight of the helicopter is ——- or a component of that force.
Total rotor thrust
Rotor drag is a force which acts in the ( plane of rotation, relative flow) and it acts to (increase, decrease) rotor rpm.
Plane of rotation
Decrease
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.
Improves
Less
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
Best
Low
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)
Greater
Worst
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.
Increase
Increase
Power
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)
Less
Easier
Less quickly
