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Fundamentals of Flight > Physical Laws and Principles of Airflow > Flashcards

Physical Laws and Principles of Airflow Flashcards

1
Q

What are Newtons Laws of Motion?

A

Inertia
Acceleration
Action/Reaction

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2
Q

How do Newton’s Laws explain aerodynamic lift?

A

Lift occurs when a moving flow of air is turned into a solid object. The flow is turned in one direction, and lift is generated in the opposite direction.

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3
Q

What is Bernoulli’s Principle?

A

It describes the relationship between internal fluid pressure and fluid velocity.

An example is a garden hose. If you kink the hose or decrease the diameter in a specific section, the velocity of the fluid must increase to ensure the fluid mass rate in the tube is the same

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4
Q

How does airflow relate to the airfoil?

A

As velocity of the airfoil increases, static pressure decreases above and below the airfoil. This static pressure differential produces about 75% of lift. The remain 25% is produced by action/reaction from the downward deflection of the air as it leaves the edge of the airfoil

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5
Q

What are the force vectors on an aircraft?

A

Lift, weight, thrust, drag

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6
Q

What is an airfoil?

A

Any surface such as a wing, prop, trim tab that provides an aerodynamic force when it interacts with a moving stream of air. Most often associated with providing lift.

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7
Q

What is the Angle of Incidence?

A

The angle between the chord line and rotational relative wind, usually referred to as the blade pitch angle. This is a mechanical angle. Collective input and cyclic feathering can change this.

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8
Q

What is Angle of Attack?

A

The angle between the airfoil’s chord line and relative wind. This is an aerodynamic angle.

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9
Q

What is roation?

A

The most basic movement of the rotor system. The closer to the axis of rotation, the less blade speed is produced

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10
Q

What is feathering?

A

The action that changes the pitch angle of the rotor blades by rotating them around their spanwise axis

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11
Q

What is cyclic feathering?

A

It changes the angle of incidence differentially around the rotor system by changing the AOA. This helps to control blowback and dissymmetry of lift.

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12
Q

What is flapping?

A

The vertical movement of a blade. Occurs during the response to changes in lift due to change in velocity. Helps control dissymmetry of lift.

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13
Q

What is hunting or lead/lag?

A

The fore and aft movement of the rotor blade in response to changes in angular velocity. This is to prevent undue bending stress on the blade root.

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14
Q

What is gyroscopic precession?

A

A phenomenon that occurs when rotating body has a force that manifests 90* later.

This is why rolling left or right is different. When turning right, you must compensate for the nose down tendency of the aircraft.

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15
Q

What is drag?

A

The net aerodynamic force parallel to the relative wind, usually the total of parasite and induced drag

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16
Q

How many types of drag are there?

A

Parasite, induced, profile

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17
Q

What is parasite drag?

A

Drag incurred from the nonlifting portions of the aircraft. Things like skin friction, fuselage, rotor blades, etc. It increases as airspeed increases

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18
Q

What is profile drag?

A

Frictional resistance from the blades passing through the air. Will increases rapidly with blade stall or compressibility

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19
Q

What is induced drag?

A

Drag from the production of lift. Higher angles of attack, produce more lift, generate downward velocities and vortices that increase induced drag. Decreases with increase aircraft speed

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20
Q

What is maximum range airspeed?

A

The airspeed that will allow the helicopter to fly the furthest distance. It is determined by the lowest intersecting point on the drag chart.

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21
Q

What is maximum endurance airspeed?

A

Airspeed that allows the aircraft to remain flying for the longest time.

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22
Q

How to calculate maximum rate or climb?

A

Maximum endurance airspeed combined with the maximum torque available

23
Q

Why are there high power requirements at a hover?

A

The rotor tip vortex reduces the effectiveness of the outer portion of the blade. Vortices of the preceeding blade affect the lift of the other blades. At a hover, there is a continuous creation of vortices and ingestion of existing vortices

24
Q

How is induced flow effected by the ground?

A

The ground interrupts airflow under the helicopter by altering its velocity

25
Q

How is vortex generation effected by the ground?

A

When operating close to a surface, the downward and outward flow of air tends to restrict vortex generation

26
Q

What is in ground effect?

A

At a hover near the ground, induced flow is reduced. This increased AOA requires a lower pitch angle which reduces power requirements

27
Q

What is out of grounde effect?

A

Out of IGE heights, the benefit of being near the ground is lost. Induced flow is increased, which decreases the AOA, requiring an increase in blade pitch which means more power. This also creates more drag.

28
Q

What is translating tendency?

A

At a hover, with a counterclockwise rotation, the helicopter will tend to drift leterally to the right. Translating tendemcy will result from the right lateral tail rotor thrust exerted to compensate for the main rotor.

29
Q

How is translating tendency compensated for?

A

-Aviator flight inputs
-Flight control rigging so the rotor disk is tilted to the left
-Transmission may be mounted so the mast is slightly tilted to the left
-Collective pitch control system may be designed so the rotor disk tilts slightly left when incresed collective
-SAS/FPS

30
Q

What is dissymmetry of lift?

A

The unequal lift across the rotor disk resulting from the difference in the velocity of air over the advancing blade half and retreating blade half. This is compensated by blade flapping and cyclic feathering

31
Q

What is transational lift?

A

Improved rotor efficiency from directional flight

32
Q

What occurs between 10-20kts?

A

Transverse flow effect. Air passing through the rear portion of the rotor disk has a greater downwash, which reduces the AOA. The front portion of the rotor has more horizontal air and increased AOA. This creates a difference in lift between the fore and aft portions. This is the notable vibration that you can feel at those airspeeds. Due to gyroscopic precession, this is why the aircraft wants to roll right

33
Q

What is effective translational lift?

A

Occurs between 16-24 knots, when the rotor completely outruns the recirculation of old vortices and begins operating in relatively undisturbed air. Flow of air through the rotor is more horizontal, reducing induced flow and induced drag.

34
Q

What are the 3 regions of an autorotation?

A

The driving region, the driven region, and the stall region.

The driving region is near the tip, usually 30% of the rotor disk.

The driven region is 25-70% of the disk diameter and is the area of autorotative force.

The stall region is the inboard 25% of the blade radius. This increases drag, slowing rotation of blade

35
Q

What are the phases of an autorotation?

A

Entry, steady state descent, deceleration, touchdown

36
Q

What is the cirle of action?

A

A point on the ground that has no apparent movement in the pilots field of view during a steady state autorotation. This would be the point of impact if the pilot applied no deceleration, initial pitch, or cushioning pitch during the last 100’

37
Q

What is bucket speed?

A

Airspeed range that provides the best power margin for maneuvering flight.

38
Q

What is transient torque?

A

Main rotors that turn counterclockwise, you will see a temporary rise in torque with left cyclic input and decrease with right cyclic input.

This is from downwash being greater on the aft portion of the rotor disk

39
Q

What is mushing?

A

A temporary stall condition occurring in helicopters when rapid aft cyclic is applied at high forward airspeeds, usually found in dive maneuvers.

High GW and altitude can worsen this.

Can be recognized as the aircraft failing to respond immediately but continuing on the same flight path before application of aft cyclic.

To correct for this, add forward cyclic to reduced induced flow.

To avoid all together, use smooth and progressive application of aft cyclic during high G maneuvers.

40
Q

What is the conversation of angular momentum?

A

Value of angular momentum of a rotating body will not change unless external torques are applied.

This is demonstrated with a figure skater beginning their rotation with their arms outstretched vs when they bring them in.

41
Q

What are the bank angle to increased TR percent?

A

15-3.6%
30-15.4%
45-41.4%
60-100%

42
Q

What are the aerodynamic emergencies?

A

Settling with power
Dynamic roll over
Retreating blade stall
Ground resonance
Compressibility

43
Q

What is settling with power?

A

A condition in powered flight when an aircraft settles in its own downwash, also referred to as vortex ring state

During high rates of descent, a helicopter may exceed normal downward induced flow rate in the inner blade section, causing airflow to move upward relative to disk. This produces a secondary vortex ring.

44
Q

What conditions must exist for settling with power?

A

A vertical or near vertical descent of at least 300 FPM
Slow airspeed, less than ETL
20-100% of power being used with insufficient power to arrest the rate of descent

45
Q

What flight conditions are associated with settling with power?

A

Steep approach with a high rate of descent
Downwind approach
Formation flight approach-due to turbulence
Hovering above max hover ceiling
Not maintaining constant altitude during OGE hover
Masking/unmasking

46
Q

How to recover from settling with power?

A

Initial stage: large application of collective pitch
Applying cyclic to gain directional airspeed and/or lowing collective

47
Q

What is dynamic rollover?

A

Lateral rolling tendency when there is a pivot point, exceeding the critical angle, and a rolling motion

48
Q

What are the human factors associated with dynamic rollover?

A

Inattention, inexperience, failure to make timely corrective action, inappropriate control input, loss of visual reference

49
Q

What are the physical factors of dynamic rollover?

A

main rotor thrust, CG, tail rotor thrust, crosswind component, ground surface, sloped landing area, low fuel conditions

50
Q

What are some common areas associated with dynamic rollover?

A

Failure to detect lateral motion before landing
Abrupt cyclic displacements
Large/uncoordinated antitorque pedal inputs
Slope landing/takeoff with rapid movements of collective

51
Q

What is retreating blade stall?

A

Retreating blade eventually stalling in forward flight due to different lift production in the advancing and retreating blades

Aircraft will pitch up and roll left and right

52
Q

What conditions produce a blade stall?

A

High GW
Low rotor RPM
High G maneuvers
High DA
Turbulent air

53
Q

How to recover from a blade stall?

A

Reduce collective
Reduce airspeed
Descend to lower altitude
Increase rotor RPM
Reduce severity of maneuver

54
Q

What is ground resonance?

A

Series of shocks cause the rotor blades to become positioned in a unbalanced displacement

Fundamentals of Flight (6 decks)

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