3 blade or 4 blade prop for Rotax 912 100hp

[Peasant_Pilot]

Good afternoon all, looking at the bolly brolga sport props in the 3 and 4 blade for my rotax 912,

 

would be interested to hear other peoples opinions for climb performance, most of what i want to do is short, outfield stuff and the quicker i can get off the ground the better, cruise speed im happy to sacrifice for climb out performance

 

Cheers

 

Rob

[Blueadventures]

I have mates that are now running eprops  (seven in use)  and 100% happy with them.  I just received one and may get a chance to fit this weekend.  If not this weekend sometime in the next fortnight.  They are worth the money from all reports.  When your ready to fly contact Mark Kyle and you may be able to borrow a trial prop,  can't beat a try before you buy if you have any concerns about a purchase.  

[Blueadventures]

Add my preference is 3 blade an d a mate has a 4 blade on his skyranger and is fully happy with it.

[meglin]

Hello, Rob! You didn't say anything about the geometric limitation of the diameter of the propeller on your plane. For a 100 hp motor, we supplied both a 2-bladed propeller with a diameter of 1840 and 2000 m, and 3-bladed propellers with a diameter of 1750 and 1840 mm, and 4-bladed propellers with a diameter of 1720 and 1770 mm. Even a 3-blade propeller with a diameter of 1600 mm works well on this engine!

[skippydiesel]

No experience, just repeating conventional wisdom - Blade number should be kept to a minimum for best weight, aerodynamic efficiency and cost. 

 

Consideration for more blades - Propeller clearance ie two blades can not be optimum length  length due to clearance (ground/airframe) restrictions for HP available - Aesthetic/Fashion pressures

 

There is evidence that more than two blades may, during take off, deliver greater initial acceleration. There is little if any evidence to suggest this continues beyond initial ground role.  Countering this is the evidence of reduced aerodynamic efficiency and weight that will negatively impact on the aircrafts flight "envelope"

 

Some suggestion of smoother operation/noise due to more frequent & smaller "pulses" from the propeller however this perception may be as much to do with the airframe to prop relationship, as blade numbers.

 

A ground adjustable two blade propeller, optimised for climb, is likely to deliver the best result but may not meet your aesthetic expectations.

[Peasant_Pilot]

10 hours ago, skippydiesel said:

No experience, just repeating conventional wisdom - Blade number should be kept to a minimum for best weight, aerodynamic efficiency and cost. 

 

Consideration for more blades - Propeller clearance ie two blades can not be optimum length  length due to clearance (ground/airframe) restrictions for HP available - Aesthetic/Fashion pressures

 

There is evidence that more than two blades may, during take off, deliver greater initial acceleration. There is little if any evidence to suggest this continues beyond initial ground role.  Countering this is the evidence of reduced aerodynamic efficiency and weight that will negatively impact on the aircrafts flight "envelope"

 

Some suggestion of smoother operation/noise due to more frequent & smaller "pulses" from the propeller however this perception may be as much to do with the airframe to prop relationship, as blade numbers.

 

A ground adjustable two blade propeller, optimised for climb, is likely to deliver the best result but may not meet your aesthetic expectations.

Its a good point, admittedly i like the look of a 4 blade but end of the day its purpose has really nothing to do with aesthetics. the 3 blade is a good choice i feel and I'm looking predominantly for short field and climb performance. the bolly prop that the foxcon come with are on the larger side and have had a bit of history of clipping the deck if landing on rough surfaces etc

 

Thanks

 

Robert

[danny_galaga]

Wow, the debate used to be between 2 and 3 blades! I like prime numbers so for me we would have to skip 4 and go with 2,3 or 5 😊

[meglin]

The best choice is made by those customers who order a 3-blade propeller and at the same time a 2-blade hub. They get incredibly many opportunities for their own research. And they also get one spare blade in case of using a 2-blade propeller.

[RFguy]

I am ordering a four blade E-PROPS for my 912 jab.

[Blueadventures]

7 hours ago, RFguy said:

I am ordering a four blade E-PROPS for my 912 jab.

What was the performance or diameter reasons for 4 rather than the usual 3 setup? Cheers 

[RFguy]

available ground clearance (limited) (existing prop is 152cm), and performance curves.

[Thruster88]

Will the blades on the 4 be the same as a 3 for the 912, just with less pitch? 

[Blueadventures]

2 minutes ago, Thruster88 said:

Will the blades on the 4 be the same as a 3 for the 912, just with less pitch? 

E-props have difference blade lengths available.

[RFguy]

Eprop is a rather sophisticated blade, cant really compare on just pitch.  But yes, less loading per blade.

Higher low speed thrust (thrust below Vrotation) on the 4 for this diameter than the 3 for slightly large diameter

[meglin]

Great choice! Take care of the stones!