PoF Problems Part 1

[Jinkster]

Oh no not the Jinkster asking for help again you may say....I am afraid I am.

Which is one of the disadvantages of increasing the number of propeller blades?

<- answer given


1)

a) Increased noise
b) Less power can be absorbed by the propeller
c) Higher tip speed
d) Decrease propeller efficiency <-

'Surely this is wrong!!' I would suggest (a) myself but this is what my feedback is saying!

If you increase the propeller pitch during a glide with idle-power at constant IAS the lift to drag ratio will?


2)

a) increase and the rate of descent will increase
b) decrease and the rate of descent will decrease
c) decrease and the rate of descent will increase
d) increase and the rate of descent will decrease <-

SHOULD THIS QUESTION BE JUST ‘PITCH’ AS APPOSE TO PROPELLOR PITCH??

Many thanks,

Jinkster

[redsnail]

Jinks,
Not quoting from any texts but from experience.
The first one,
No, flown a 2 bladed C207, noisy as, flown a 3 bladed C207, quieter.
Second one, it's the size that can absorb the power.
Higher tip speed, no, more blades = slower = less noise.
Too many blades interfere with the airflow for the next blade.

2nd question. Someone else can answer it using far more technical language than me.
Prop blades have pitch too, not just the aircraft.
If you coarsen (or feather for twins) you certainly improve the L/D ratio because you are reducing the drag. This will also reduce the RoD.

I am sure your lecturer should be able to explain this better or someone else who's more technical than me.