081 PoF

Principles of Flight

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Erstellt / Aktualisiert	17.08.2022 / 08.09.2022
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Where along it's airfoil is a propeller most aerodynamically efficient?

at 75% (measured from the hub/center of the propeller)

Speaking roughly, ice reduces propeller efficiency up to ...%?

20%

How is propeller efficiency calculated?

Note: On the ground and engine running, the prop efficiency is 0% There is no work done although the prop is developing a lot of thrust.

Name the items in the picture

Where is the local pitch angle higher, towards the root or tip of the propeller?

towards the root

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.