2 blade vs 3 blade propeller

[Deano747]

Hi. Looking for opinions on fitting a 2 blade or 3 blade propeller to my Rotax 912is with a constant speed unit. Just in the ordering phase and wonder which I should go with. The airplane will be primarily used for cruising and won't be operating out of marginal strips.
I know that the old wisdom was that 3 blades were better for takeoff and 2 blades for cruise as the 3 blade was 1) heavier and 2) had more drag, but a lot of that was based on either fixed pitch or ground adjustable propellers and is the wisdom still valid for operation with a CSU (mechanical knob to a hydraulic actuator) in the age of the new composite materials (light & stiff) the blades are constructed from.

[skippydiesel]

Much will depend on your ground clearance - Airmaster CS will do you a 3 or 2 blade but recomend a 3 blade for most Rotax applications.

 

I would seriously question, the cost effectiveness of, fitting of a CS prop to any RAA class aircraft - if you configure a ground adjustable for your preferred operations (cruise for you) you will come close to the same cruise speed, as a CS, without the added cost, complexity & weight

 

I see you have "Purchasing Topaz" under your  nom de plume. Is this the aircraft you want to put a CS on? Is there more than one model? Do they come in nose/tailwheel - all information for the Forums Brains Trust, I suggest you give all details, for best advice. 

 

Edited May 7 by skippydiesel

[Thruster88]

I would also question the value of putting a CS propeller on a 100hp 100-120knot machine. It won't go 10knots faster like the sales person will say. 75% cruise power can be achieved with either propeller type.

 

Trent Palmer removed the CS prop from his bush plane and went fixed, he is in the process of fitting another propeller now, also fixed and that is a turbocharged engine which should get any benefit from a CS.

 

Fixed allows static RPM to be checked with confidence. A foolproof way to check engine health.

 

I have a hartzell CS on the RV6A, if it ever goes bad it will be getting a fixed Catto like many other RV's have.

Edited May 7 by Thruster88

[Freizeitpilot]

If you were to believe some of the marketing material from composite prop manufacturers a fixed pitch prop will deform and perform like a CS one anyhow.

Marketing aside, there may be a small amount of truth in there, but it probably amounts to about 3 kts worth.

[skippydiesel]

I thought I got great service from my two blade, ground adjustable Fitti Sport on my last aircraft.

 

Lots of interest in the E Prop range - talk to Kyle. Their CS is a light as many ground adjusts.

[Deano747]

Looking at the E-Props GLOR-3-170-C8-T.

Looked at going for a ground adjustable and still might - but I am not a 'fiddling' sort of person. Certainly will not be doing my own annual servicing etc.

It's not about the maximum speed increase, it's about operating the engine in its maximum torque range with a lower throttle setting for range increase.

I only have maybe 280 kgs to play with for useable load and 2 people my size and baggage etc eats considerably into fuel that can be carried. And yes, I know that the CS gear will weight, but the decrease in burn will more than compensate for that. 

Edited May 7 by Deano747

[Thruster88]

2 hours ago, skippydiesel said:

Much will depend on your ground clearance - Airmaster CS will do you a 3 or 2 blade but recomend a 3 blade for most Rotax applications.

 

I would seriously question, the cost effectiveness of, fitting of a CS prop to any RAA class aircraft - if you configure a ground adjustable for your preferred operations (cruise for you) you will come close to the same cruise speed, as a CS, without the added cost, complexity & weight

 

I see you have "Purchasing Topaz" under your  nom de plume. Is this the aircraft you want to put a CS on? Is there more than one model? Do they come in nose/tailwheel - all information for the Forums Brains Trust, I suggest you give all details, for best advice. 

 

Skippy a question. Some time ago you were dead keen to get a CS prop, asking for advice etc. Now that you have one on a pretty high performance aircraft you don't seem so convinced?  What has been your experience? 

[skippydiesel]

8 minutes ago, Thruster88 said:

Skippy a question. Some time ago you were dead keen to get a CS prop, asking for advice etc. Now that you have one on a pretty high performance aircraft you don't seem so convinced?  What has been your experience? 

Yeah! All true - thought I was coming into some money and wanted to see if I could maximise the performance on my Zephyr. Money was an illusion and I crashed the Zephyr. Insurance got me an almost completed Sonex Legacy/Rotax 912 ULS with Airmaster 3 blade constant speed.

 

Dont get me wrong the Armaster is great  but I am not convinced that the Sonex would not be as/almost as, good without it.

 

Short TO role,  under 100m on grass (without trying for a short field) climb out (still working on it) but I think about 2000ft/min at 80 Knots full fuel. Cruise at WOT 5450 rpm 147 knots (152 true) @ 3500ft - I usually tootle about at 130 Knots indicated, 5100-5200 rpm,  for a fuel burn of 15 L/hr (still working on the fuel consumption). All of which is great BUT I have a mate with a Sonex B/912ULS & he is getting about the same cruise speed, probably a bit longer TO role & less Climb Out but he wouldn't have an extra (say) 6 KG on the nose and would still have around $13K in his pocket.

 

There is no doubt that a constant speed will improve the performance envelope, but the cost effectiveness in these small, relativly low hp,  aircraft is ????????

[facthunter]

A fixed pitch prop  designed for the right speed can be more efficient than a CS AT THAT SPEED. CS can have reliability issues. On the fine pitch stops what airspeed will it do?   Nev