Max Continuous Power

Rotax Wizard wrote: "There is no output of the CANBUS that gives power.  Power is torque (T) X RPM/5252 =HP.  The CANBUS only gives out RPM and %TPS output."

That may be the case for the 912iS, but apparently that is incorrect for the 915iS. This indicates the 915iS does indeed provide Percent Power via the CAN interface.

Further, I've been told that the percentage is based on max continuous power, not max takeoff power. So, at full throttle and 5500 RPM, it's normal for it to read 100% power. For takeoff, it will read higher than 100%, approximately 105% for the 915iS and 115% for the 916iS.

Mike,

Assuming the 915 does do a calculation to give you a %power reading, it makes me wonder what inputs the ECU would use to calculate that. To be accurate, it would require a way to read the engine torque (like a dyno) and there are no sensors for that. Possibly it could use manifold pressure, RPM, the TPS and some fancy math, but its hard to think it could be totally accurate. I’m also curious if there are flight conditions that would give you a 100% reading at 5500 RPM and WOT.  Based on what Rotax publishes, you can’t go wrong by using 5500 RPM as an indication of max continuous power.   

Jeff Blakeslee wrote:

Mike,

Assuming the 915 does do a calculation to give you a %power reading, it makes me wonder what inputs the ECU would use to calculate that. To be accurate, it would require a way to read the engine torque (like a dyno) and there are no sensors for that. Possibly it could use manifold pressure, RPM, the TPS and some fancy math, but its hard to think it could be totally accurate. I’m also curious if there are flight conditions that would give you a 100% reading at 5500 RPM and WOT.  Based on what Rotax publishes, you can’t go wrong by using 5500 RPM as an indication of max continuous power.   

My new understanding is that you should indicate 100% at 5500 RPM and WOT, because the percentage is based on max continuous, not takeoff. In the climb setting, my prop is set to 5450, just shy of 5500, so it makes sense that my power indication is just shy of 100%.

Hi all

I think there is a misunderstanding of what you are seeing.  Power (HP) is a function of torque X RPM / 5252.  The only way you get the full power is at 5800 RPM.  The display shows the throttle position not HP.  100% WOT that is limited to 5500 is very poor fuel efficiency and will give you the max continuous power and not full power.  (the engine should be set on throttle settings about 97% throttle position to get ECO power setting. 

You can refer to the performance charts in the operator's manual.  

Cheers

No, on the G3X it only shows throttle position when the engine is off, or when you go into the FADEC menu. When the engine is running it shows % power, as shown in the image from the installation manual I posted above. 

I know what ECO is, but that’s not the point of this thread.