Constant Speed Propeller

I have 914 and MT cs. I don't see the value in maximum speed when travelling, but in endurance, which means that I set the propeller speed and Manifold pressure after the flow meter. I therefore usually fly around 4600 rpm 26" it gives me 100-104 kts / 13.5-14 l/h

The engine has been flown like this for over 1000 hours so it has not been overloaded

Hi Johan,

Thank you for your thought provoking experince.

What is the aircraft?

Have you arrived at this engine/prop setting, taking trip time into account?

My last aircraft, ATEC Zephyr/912ULS/Fiti Ground Adjust, cruised at 100-105 knots at around 5200 rpm. With full fuel & just me, I usually had  under 13L/hr. With a passenger 14L/hr. I flight planned at a conservative 15L/hr.

My current aircraft, Sonex Legacy/912ULS/Airmaster CS, my target cruise is 130 knots. As this discussion aludes I am still fine tuning the prop/MAP settings however am fairly confident of 14L/hr. Currently flight planning at 15L/hr. The 130 knot cruise is giving me a much reduced trip time, meaning that overall fuel consumption is similar to the Zephyr (especially in head winds).😈

Up Date!

Airmaster still being resistant over why they recomend Auto Cruise 5000 rpm for 912ULS. 

I have now asked directly, at least thris, for their reasoning on this topic - they just repeat the 5000 rpm and say, as pilot I can set the system to whatever I want, subject to Rotax advice (4300-5500 rpm)

It seems to me that they:

 # Have just gone with the majority setting  - not good - hoped for better.

 # Have not done their own testing - empirical evidence - as above.

I am awaiting the response to my fourth request, this time asking for the most efficient (converting engine power to forward motion) prop speed.

I fail to understand why Airmaster is not being more open with the reasons why they recomend Auto Cruise setting of 5000 rpm / 912ULS.

Airmaster have a great reputation. The quality of my prop is second to none. They seem friendly. Their responses to enquiries is commendable rapid. What is the problem?

Am I being unreasonable in expecting evidence based/reasoned recommendations for optimum prop speed/engine rpm, a recommended speed or a range of rpm's, with empirical results on fuel consumption/ engine load/etc?

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.