PROPELLER ADVICE
Posted: Wed Dec 11, 2013 12:34 pm
Hi
I know that there are some clever folk out there who know these things. I am looking for some wider opinion on this before I blow more hard-won cash on trying to fix the problem.
I have a Safari, with a 912 95 HP Rotax. It was delivered with an in-flight variable speed 2 blade prop. At 5 000 RPM, 25 inched MAP, it would cruise comfortably between 100 and 105 MPH. The ride was always a little rough, as you could expect from a 2 blade prop. I recently changed it to a 3 blade ground adjustable Arplast prop.
The ride is much smoother now, but the speed is 90 MPH at 5 000 RPM. Nothing else has changed. Climb out at the coast one-up with full tanks is still around 800 fpm. Peak revs on take off are 5 300. In level flight at full rattle, the engine peaks at 5 800 RPM and 105 MPH.
Now I am sure that 3 blades will have more drag, but a 10 - 15 % reduction in speed seems excessive.
My layman's opinion is that the Arplast has a light 'plastic' blade, which is quite flexible. Under full load, the blades will surely cone forwards and flex axially and must therefore lose efficiency.
So - will a stiff bladed Warp Drive, or a 2 bladed PPlank make for a faster cruise? Other Safaris definitely cruise faster, although their engine/prop installations differ.
Surely others have had similar issues to this? How did you solve them?
If fitting a Warp Drive, do I go for the tapered blades, or the constant width blades? What is the difference, apart from the R 9 000 price between the two models? Are there other options?
So far, I am getting to believe that the spinning technology at the front end is not so much a science, but rather a 'suck it and see' mystery of aviation?
Any opinions gladly received.
I know that there are some clever folk out there who know these things. I am looking for some wider opinion on this before I blow more hard-won cash on trying to fix the problem.
I have a Safari, with a 912 95 HP Rotax. It was delivered with an in-flight variable speed 2 blade prop. At 5 000 RPM, 25 inched MAP, it would cruise comfortably between 100 and 105 MPH. The ride was always a little rough, as you could expect from a 2 blade prop. I recently changed it to a 3 blade ground adjustable Arplast prop.
The ride is much smoother now, but the speed is 90 MPH at 5 000 RPM. Nothing else has changed. Climb out at the coast one-up with full tanks is still around 800 fpm. Peak revs on take off are 5 300. In level flight at full rattle, the engine peaks at 5 800 RPM and 105 MPH.
Now I am sure that 3 blades will have more drag, but a 10 - 15 % reduction in speed seems excessive.
My layman's opinion is that the Arplast has a light 'plastic' blade, which is quite flexible. Under full load, the blades will surely cone forwards and flex axially and must therefore lose efficiency.
So - will a stiff bladed Warp Drive, or a 2 bladed PPlank make for a faster cruise? Other Safaris definitely cruise faster, although their engine/prop installations differ.
Surely others have had similar issues to this? How did you solve them?
If fitting a Warp Drive, do I go for the tapered blades, or the constant width blades? What is the difference, apart from the R 9 000 price between the two models? Are there other options?
So far, I am getting to believe that the spinning technology at the front end is not so much a science, but rather a 'suck it and see' mystery of aviation?
Any opinions gladly received.