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Steve, I assumed the pulse width / manual mixture for each rotor would be different after Mode 4 balancing but I expect a consistent ratio. I will also check the voltage through the injector switches but that probably needs to be done under load. I believe the EC3 has injector dead time compensation of about 1ms. Bobby From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
Sent: Wednesday, May 10, 2017 10:10 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: F/A and EGT data Once the controller is generating different pulse widths for the two rotors as a result of balancing them with mode 4, changing both signals by the same amount with the manual mixture control will not result in both rotors receiving the same change in fuel flow unless injector dead time is taken into account. The difference in the fuel flow change will be greater when short pulse widths are being used. I have seen no indication of dead time being accounted for in the controllers that I have. I could look at the injector pulse signals behavior after mode 4 changes next week. I have always left mode 4 at default up until now.
Steve Boese I haven't considered cooling airflow. I'm also testing a new heat shield around a new exhaust header. The new header, (copy of my old one without ceramic costing), heat shield, and a suspected degraded O2 sensor were part of the reason for collecting actual F/A data for each rotor. Due to packaging, rotor 1 should have better exhaust flow and better exterior cooling. Yet rotor 1 had to be leaned to match rotor 2 at max power. The heat shield is open to the firewall and heat exchanger exits towards the prop about 12" away and inline with the header. I think another ground test to confirm actual O2 readings at the MP, RPM and F/A ratios tested in flight would be the best course of action. Then swap the injectors if the EGT delta is not consistent across the test range. Next step would be look at injector control signals when using manual mixture control. I'm assuming the injector pulse width changes and it should be consistent across all injectors? I have noticed significant changes in EGT indications depending on how cooling air passes over the exhaust headers even with the thermocouples a few inches from the exhaust ports. I'm not suggesting that this explains your observations, but it may be an additional variable.
Steve Boese I recently purchased a two channel portable wideband O2 system and installed bungs and plugs on each exhaust runner. I also have a downstream wideband that I have been using for several years. I was able to spend a very productive hour ground tuning and adjusting Mode 4 injector balance prior to my flight yesterday from Austin to Akron OH. I’m not sure what to make of the F/A EGT spread data I collect during yesterday’s flight. During the ground tuning session I balanced rotor 1 to match rotor 2 using F/A ratios for takeoff condition. This produced very close EGT readings. However at my preferred cruise settings I’m seeing a large EGT spread. I would expect a consistent EGT ratio change when adjusting the mixture knob at a steady rpm / MP. This appears not to be the case. What am I missing? Bobby Hughes
<EGT and Fuel Air data.pdf>
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