Weather And Airfoil

Question 1

METAR

Answer 1

Meteorological Aviation Report - Testable (hourly updates, observation portion on the JET)

Zulu time is 6 hours further from Alabama time - must be converted

Winds based on true north, runways based on magnetic north

We ONLY use centigrade/celsius readings

A3004 = 30.04Hg altimeter setting

AO1 - Automated weather station (no precip discriminator)

AO2 - Automated weather station with precipitation discriminator

AO2A - Automated weather station with precipitation discriminator and a human input

SLP174 = Sea Level Pressure to be converted to Hg Mercury

TAF - Terminal Aerodrome Forecast - reports within 5 miles of location

Ex) QNH2992INS = lowest reported altimeter height

C-63 flight pub - SM meters reading to statute miles; 9999m = 7SM - Infinity miles

TX25/1219z TN05/1311z = max and min temperatures from 12 1900z to 13 1100z

Question 2

JET

Answer 2

Joint Environmental Toolkit

The weather report with the observation in the lower left corner

Question 3

Two components of an RVR report

Answer 3

Runway visual range in:

• “Hundreds of feet”
• Effective runway

Question 4

3 components of atmospheric density

Answer 4

Temperature, pressure, humidity

Question 5

What is associated with a cumulonimbus cloud?

Answer 5

Thunderstorms

Question 6

Flight control surfaces

Answer 6

Anti-torque pedals: correct for nose yaw, assist in flight trim

Cyclic: provides directional control of aircraft, produces a thrust the direction the disk is pointed

Collective: provides vertical control (ie. changes pitch collectively to all blades)

Question 7

Vectors

Answer 7

All forces are vectors (tug boat image)

4 quadrants of lifting forces (FL, FR, RL, RR)

Question 8

Newtons Laws of Motion

Answer 8

**Four forces of flight: “lift opposes weight, thrust opposes drag”

1) A body at rest will remain at rest and a body in motion will remain in motion unless a force acts upon them (lower torque in fixed velocity flight than acceleration)
2) An acceleration is a change in velocity with respect to time (pitch forward)
3) For every action there is an equal and opposite reaction (tail rotor thrust)

An example of inertia (level flight)
An example of acceleration (upward win of traffic pattern)
An example action/reaction (takeoff to a hover)

Question 9

Bernoulli’s principal

Answer 9

Within a “confined” system, total energy remains the same

Constriction causes faster speed, dynamic pressure increases and static pressure decreases and total pressure is unchanged

Question 10

Airfoil

Answer 10

An airfoil is a surface/body/structure that produces a LIFT or THRUST.

Top of airfoil - dynamic pressure increases, static pressure decreases, total pressure unchanged
Bottom of airfoil - dynamic pressure reduces, static pressure increases, total pressure unchanged.
*High STATIC pressure seeks lower pressure - lift is produced by underside of airfoil air static pressure seeking the low static pressure above the airfoil

**with an INCREASE in air speed above an airfoil, it’s dynamic pressure increases”

Question 11

Chordline

Answer 11

Line protruding from leading edge to trailing edge, where all winds and angles of forces are measured

Question 12

Chord

Answer 12

Distance from blade leading edge to trailing edge, PROVIDES longitudinal dimension of an airfoil (Self contained within airfoil)

Question 13

Airfoil sections

Answer 13

Camber - the shape or curvature of an airfoil, expressed as upper or lower camber

Upper chamber - top side of airfoil
Lower chamber - lower side of airfoil

Question 14

Span

Answer 14

Length of a rotor blade from point of rotation (root) to blade tip

Question 15

CENTER OF PRESSURE

Answer 15

Where all aerodynamic forces act on an airfoil (most critical part of an airfoil!!!)

Center of pressure is considered constant/fixed (immovable) on a symmetrical airfoil, and considered to be moveable in a non/un-symmetrical system

**Not called “asymmetrical”

What is the difference between the symmetrical and un-symmetrical blades? - their different

Question 16

Rotors

Answer 16

The blade advances into a relative wind (from 6 o’clock to 3o’clock) - flaps up due to relative velocity increase [right side advancing side]

Blade “retreats from a relative wind” (from 12o’clock to 9o’clock) and blade flaps down to to relative wind decrease [left side retreating side]

Question 17

Types of relative wind

Answer 17

Rotational relative wind as seen by a rotor blade is the relative wind coming towards the rotor blade is it rotates.

Relative wind on the advancing side is ALWAYS faster than the retreating side.

Rotor tip velocity is 394 knots. Rotor rotates at 394 rpm as well (coincidence?). Use 400 knots for exam

Question 18

Induced flow

Answer 18

The component of air flowing vertically through the rotor system

Question 19

Final wind

Answer 19

Final wind is the RESULTANT RELATIVE WIND: the rotational relative wind that is MODIFIED by induced flow.

Question 20

Induced flow in forward flight

Answer 20

The only way to reduce the effects of INDUCED FLOW is through FORWARD AIRSPEED

Question 21

Angle of incidence

Answer 21

Measured BETWEEN the CHORD-LINE and the ROTATIONAL RELATIVE WIND

Angle of Incidence (AOI) is a MECHANICAL angle

Question 22

Angle of attack

Answer 22

Measured from the CHORD-LINE to the RESULTANT RELATIVE WIND. This is the AERODYNAMIC angle

Question 23

What is the cause of all general aviation stalls?

Answer 23

*Exceeding the critical angle of attack

Question 24

Induced flow with respect to angle of attack

Answer 24

When induced flow is increase, the angle of attack decreases

This is why at hover, we dont “fly” well. Only forward speed will increase our angle of attack here

Question 25

Airspeed indicator

Answer 25

Diaphragm is vented to the pitot tube

Case is vented to the static port/pressure

Question 26

Pressures used IN a pitot static system

Answer 26

Static (static ports

Impact = dynamic (all for airspeed indicator)
Ram = dynamic
Pitot = dynamic
Total = dynamic

Question 27

True altitude

Answer 27

Altitude above mean sea level (MSL)

Question 28

Pressure altitude

Answer 28

Measured above the standard datum plane

Question 29

Indicated altitude

Answer 29

Uses current altimeter setting to indicate pressure altitude