Anyone Played WIth A Rotax 912 Is Yet?

[Guest sunfish]

After doing the performance numbers, I'm inclining towards a Rotax 912 Is with an Airmaster Constant speed propeller for the CH750.

 

More powerful engines with fixed pitch props have to be derated because you can't pitch for 3300rpm so the peak power figure is meaningless.

 

Then there is the eternal argument about propeller pitch for cruise/climb, Hot/cold, Low/High.

 

My own view is that the less power you have, the more efficiently you need to use it.

 

Thoughts?

 

 

[David Isaac]

Interesting thought Sunfish; the argument that the more power you have the more efficiently you need to use it is also valid. Typically in aviation only the higher power engines are fitted with CSUs, usually around the 180 HP figure and above.

 

Personally I like CSUs, even though they add to the capital and maintenance costs. With the modern type electrical CSUs available it certainly makes a lot of sense to fit CSUs to the lower power engines that don't have the oil galleries for the traditional CSUs. As you say, a fixed pitch propeller is always a compromise between takeoff performance (often critical in low power installations) and cruise speed (not so critical, but important to some).

 

 

[rankamateur]

912iS which is probrably going to become the only choice from Rotax in time, to satisfy environmental targets in Europe, coupled to an Airmaster (handles upto 120Hp not 180) would be OK in a CH750 and just lovely in a Savannah S with VGs instead of wing slats, but each to there own. A 914/ Airmaster combination does very nicely in a Savannah. The stumbling block at the moment is that I understand the 912iS is not compatible with the Rotax ring mount which ICP use in their newer models to smooth out the Rotax knock at startup and shutdown, which is a great shame. I am not sure if Zenith use the ring mount or not so that would need to be clarified for your project. Edit:

 

this video shows a ring mount so maybe it is just not the same ring mount used on the regular 912ULS compatible with the ICP frames?

[facthunter]

While a CS prop will always make things better, for a plane with a low cruise speed, say below 110 Kts, I don't think I would fit one. You have cost and weight and complexity. Avoid a "toothpick prop" as they don't work well on draggy planes. A geared or low rpm engine with a good prop dia and blade area would be my aim. Has a "kiev" been considered? Nev