081 PoF
Principles of Flight
Principles of Flight
Set of flashcards Details
| Flashcards | 60 |
|---|---|
| Language | Deutsch |
| Category | Traffic |
| Level | Other |
| Created / Updated | 17.08.2022 / 08.09.2022 |
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What happens with the propeller AoA if the RPM is decreased?
decreasing RPM, results in smaler AoA
Name the two main type of propellers:
Fixed and variable pitch.
For which flight phase does one want its propeller to be at low (or fine) pitch and for which at high (or coarse) pitch?
Low or fine: good for start and climb
High or coarse: good for cruise
What is a constant speed propeller and how does it operate?
Automatic, not selectable multi pitch position propeller:
- With a governor the pitch angle is adjusted to the actual flight attitude to keep a constant RPM
- In this way, propeller and engine work at their optimum and their best efficiency
- This allows the propeller and engine to work at there optimum.
What is propeller slipstream?
Spiral slipstream, also known as propwash, prop wash, or spiraling slipstream, is a spiral-shaped slipstream formed behind a rotating propeller on an aircraft. The most noticeable effect resulting from the formation of a spiral slipstream is the tendency to yaw nose-left at low speed and full throttle (in centerline tractor aircraft with a clockwise-rotating propeller.) This effect is caused by the slipstream acting upon the tail fin of the aircraft: The slipstream causes the air to rotate around the forward-aft axis of the aircraft, and this air flow exerts a force on the tail fin, pushing it to the right.
If Prop turns right = Yaw to the left Use right foot!
Constructive counteractions:
- Vertical stabilizer far back
- Vertical stabilizer 1-3° offset
What is propeller P-factor?
Short answer: with increasing Pitch, the down going blade has a greater AOA then the up going one.
Longer answer:
- If the AC is inclined upwards, the down going blade has a greater effective AOA than the up going blade.
- Results in more thrust on that side
- Results in a yawing moment on the other side.
- With clockwise turning props = yawing moment to the left. The asymmetrical blade effect is greatest at full power and low airspeed (= high AOA) In horizontal flight this effect is not existing.
What is propeller torque effect?
Newton’s 3rd axiom → Actio = Reactio
Right turning prop results in left turning around the longitudinal axis
On GND: left wheel is more compressed, resulting in greater download and more rolling resistance, creating yawing to the left
What is gyroscopic reaction on a propeller?
- From climb to level flight: yaw to the left
- From cruise into climb: yaw to the right
What is propeller solidity?
What are the benefits of increasing number of propeller blades?
- Higher thrust possible
- Less diameter
- Less noise
- Higher solidity
- More power absorption
What is a negative effect of increasing number of propeller blades
Decreased propeller efficiency
What happens when the chord of the propeller blade is increased?
- bigger camber
- more thrust force
- increase in pwr absorption
- more drag
What stresses act on the propeller?
- Thurst bending
- Centrifugal force
What produces more drag, a windmilling prop or a non-rotating prop?
Windmilling propeller
At which approx. blade angle does feathering a propeller result?
Blade angle at approx. 90 degrees
With regards to stability, which 2 categories of stability exist?
- Static stability
- Dynamic stability
Define statically stable for an aircraft
After displacement by a wind gust, the aircraft returns to its initial flight path.
Define statically unstable for an aircraft
After displacement by a wind gust, the aircraft continues to part from the initial flight path.
Define statically neutral (or indifferent)
After displacement by a wind gust, the aircraft continues on the newly obtained flight path
Define dynamic stability
The oscillation decreases with time
Define dynamic neutral stability
The oscillation stays the same (with time)
What is dynamic unstable?
The oscillation increases with time
Define dynamic unstable
The oscillation increases with time
Which aircraft movement is related to longitudinal stability?
Pitch
The position of the centre of gravity is denoted in % in terms of the ... ?
Mean Aerodynamic Chord (MAC)
MAC is defined as: where y is the coordinate along the wing span, S is the wing area, b is the span of the wing, and c is the chord at the coordinate y.
Related to MTOM and CG, how is an aircraft certified?
Always worst case within envelope: aircraft at MTOM and CG full forward.
Which pitching moment is created with CG ahead of CP?
The pitching moment Cm is negative -> Nose down.
How can directional and lateral stability be achieved?
- Large tail
- Dihedral wing
- Swept wing
Does the aircraft in the picture have a dihedral or anhedral wing?
Dihedral: Upward angle of wing (from root to tip).
Name all aircraft axes:
Longitudinal Axis -> X-Axis -> Roll
Lateral Axis -> Y-Axis -> Pitch
Normal or vertical axis -> Z-Axis -> Yaw
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