Constant Speed Propeller

Ken Ryan wrote:

Seems to me that the engine, prop AND airframe are a system. They are giving you a guideline. Use that guideline to fine tune for your specific system.

Hi Ken,

I agree to some degree however no such reason was given AND I would expect each prop model to have an optimum speed range, irrespective of airframe.

Further their only unsatisfactory response (to me) were;

 # 5000 rpm(they talk in engine rpm for Rotax applications) is what most are using. Can't except this without some reason.

 # Rotax specified - Hard to believe, as Rotax consistently recomend min 5200 rpm for all "load" situations. Yes I know that there are lower  speed rpms allowable.

While it is likly that the pilot will optimise the prop for a given airframe it would be very nice to have some empirical data to start with ie not have to "reinvent the wheel".

 "Rotax consistently recomend min 5200 rpm for all "load" situations."

Sean, can you show me where they state that in writing please?

Mike

Well, SL-912-016R1 contains some guidelines/recommendations around the rev figure of 5200. For instance it does say that continuous operation at 5200 rpm or above is not limited by MAP. The SL, in my opinion, is worth reading twice and the chart in conjunction with the notes deserves some attention, too.

It also shows that with 98RON fuel (or Avgas) operation at 5000rpm is not MAP limited.

You can't use 95RON (at least in UK) because of alcohol content anyway.

In reality I wouldn't use more than about 26" at 5000 anyway, but I'm intrigued by this 5200 limitation that is so often referred to as I have yet to see it in any Rotax document.

The SL I am referring to (https://legacy.rotaxowner.com/si_tb_info/serviceletter/sl-912-016-r1.pdf) does not seem to be the one that contains the “fuel chart” and information in different types of fuel (I believe I know the one you mean, Mike).

Both, ‘yours’ and ‘mine’, are good to know for sure.