fixed pitch propellor

[hekokimushi]

Hi,

I hope i have placed this under the correct section.
here we go:

i am unsure the difference in performance that a 2-blade and a 3-blade prop will make to an aircraft. e.g. in C-182, 2-blade less than 2 feet ground clearance where as 3-blade, significantly more clearance, dun have the length of the props.

but can anyone highlight the difference and trade offs using the 3-blade as to 2 blade?

thanks in advance

nelson

[Genghis the Engineer]

As a rule of thumb, a 3-blade will always give greater efficiency than a 2-blade with the same mean chord, due to the greater disk density.

However, they are more expensive, heavier, require more maintenance and because of the greater propeller turning drag and inertia will tend to give slower engine response times - which are the reasons why you often see 2 blade props in preference to 3-blade.

G

[hekokimushi]

any advantageous using the 3-blade at T/O at all? and if a 3-blade is used compared to a 2-blade, would that affect the cruise speed? i would imagine it all really depends on the thrust that one prop can produce. what about the amount of vibration?
and would the 3-blade produce more thrust at the same rpm?

slower response time... so... would it be less efficient in terms of feul comsumption?

[As I See It]

Less noise is also a significant factor due to the reduced prop diameter. I remeber a Piper Pawnee that had a four blade fixed pitch prop, wooden if I recall, which had a very low noise signature. It was used for glider towing as the field had a big noise problem, the nimby's didn't like it.

[Approaching Minimums]

I have always thought too that more blades and reduced diameter of the prop will have lower noise levels. However, I was surprised that this is not always right. I found an exception from the handbook of PA-28 Turbo Arrow IV. Standard propeller for this aircraft has two blades and noise level of 69,4 dB and the optional three bladed propeller will have the noise level of 72.8 dB. The engine is same 200hp Continental with both options.

Happy new year for everyone!:ok:

Best Regards,
AM