Manifold Pressure

[Moneybox]

Hi Guys, help me out here. I've never had a manifold pressure gauge. I understand how it operates and I understand what it's reading but I don't know my best settings.

 

 

When I'm cruising I have to adjust my propeller to a high pitch to prevent the engine running over maximum revs. 

 

What I don't understand is where my best/least fuel consumption comes from when matching RPM to Manifold Pressure while maintaining cruising speed.

 

Lets say I want to keep the Rotax 912ULS spinning at 5000 revs while getting my best economical cruise speed. Do I control this with manifold pressure?

[Thruster88]

To make use of your manifold pressure gauge you would need a power chart. Such charts for say a Lycoming O-360A1A will include altitude, rpm, manifold pressure and show fuel flow for each setting. 23-23 @3500 feet is not the same power as 23-23 @5500 feet.

 

Rotax do not seem to publish such charts, good luck finding one.

 

 

[skippydiesel]

Rotax do publish the manifold pressure/expected fuel flow/ altitude/ engine rpm charts;

 

Join Rotax Owners Forum for all the Manuals/Service letters/etc https://www.rotax-owner.com/en/rotax-forum

 

I strongly advise you read the Rotax 912 ULS Operators Manual file:///C:/Users/User/Downloads/OM_912%20Series_Ed4_Rev2%20(3).pdf

 

Some downloads that may interest you;

 

https://legacy.rotaxowner.com/si_tb_info/serviceletter/sl-912-016-r1.pdf

https://aquila-aviation.de/wp-content/uploads/2021/06/SL_912_016R2_914_014R2_Rotax_Notes_engine_handling.pdf

 

A couple of excerpts;

 

 

 

 

 

Note: The figures given are nominal ie will differ due to many factors eg airframe😈