GEM930

GEM930

Well Known Member
Friend
This is kinda a continuation of some of my past posts in reference to my climb performance, static RPM, and fuel injection tuning. I'm in the process of fine tuning the electronic fuel injection map on my O320. The system I'm using is made by Tracy Crook at Real World Solutions. The system is similar to a FADEC with the exception of a small knob (potentiometer) to control the mixture to change from a max power to best economy. According to Tracy, once the system is properly tuned you should be able to complete all aspects of flight without touching the knob if you choose to do so. The knob just allows you some flexibility. Anyway it seems to be working out okay. I'm is the process of trying to get everything fine tuned and have a few questions I hope some of the more knowledgeable people here could help me with. My 0320H2AD manual states that peak power is 100-150 degrees rich of peak EGT. I have tuned the system so that peak EGT at all phases of flight is straight up on the mixture knob (pot). What I'm seeing is that this is also the point of peak RPMs. It seems to me that peak RPM would also indicate peak power??? If I adjust the pot to 150 rich of peak I lose 50 to 75 RPM. Either way I haven't noticed much change in speed. I can certainly cool the EGT/CHT with the knob and also observe the change in fuel flow, so I know it is working. Any ideas why this is happening? Maybe it is some how related to the ghost in the system that is causing my climb RPM to be lower than my static???? On a side note. My top end has increased considerably with the new system. I see this in increased true airspeed (12KTS) and also because I'm able to over rev (+2600 RPM) my Sensenich 79 pitch prop much easier than I ever was able to before.

Any ideas????

P.S. timing still may be an issue, however I'm afraid to advance it too much as I'm terrified of detonation.
 
Last edited:
Something does not make sense here. Peak EGT should occur at stoichiometric around 14.7 to 1 AFR and max power around 12.5-13.0 to 1. You don't want to be operating that lean near max power. The difference in power between stoich and best power will be 7-10% on most engines.

Do you have 4 EGT probes and if so what is the temp spread WOT where you get max rpm?

Do you have the ignition timing varying with rpm and if so, what is the total advance at full rpm?
 
I'm not an engine guy, but I've researched this in the past.

The short answer is that if you have a fixed pitch prop, you are going to have trouble determining maximum power from just rpm.

I think that you'll find that a constant speed prop will show an increase in airspeed at 100 to 150F rich of peak EGT, indicating maximum power. Hold the rpm constant, lean to peak then enrichen to maximum power.

With a fixed pitch prop, the throttle or mixture control vary both RPM and MAP. Changing two variables at once makes it very hard to determine the output function without a calculator and the mathematical power curve of the engine.

A long time ago I published the power function for an O-320. It's lurking somewhere on VAF.

V
 
I will check my black box for the exact #s and post soon, but I don't know what WOT # are because at 8500 msl (11000 density alt I think) I could not go wide open without busting ny 2600 rpm limit. I did check the 100 degree rich of peak at several rpm/map and observed the same thing each time ... 50-75 rpm drop when I went from peak to 100 rich. I believe the egt are within 150 degrees of each other, but I'll check. As far as finding 100 ROP with a fixed pitch k just left the throttle alone and slowly turned the pot untill the temp on the hottest egt was 100 degrees cooler. As I turned the knob I observed the rpm slowly reduce about 75 rpm from where it started.
I really do appriciate all the info. This system seems to have a lot of potential. Definately making more power... Probably just needs somebody smarter than me to make it work correctly!!!
 
More rpm at WOT with a FP prop always means more power. CS props muddy tuning actually.

If you can tie down the aircraft, you should be able to do most of the tuning on the ground. If you have a proper default MAP table the mixtures should lean automatically with altitude and AFRs should stay near constant.

The part about richening from peak EGT causing an RPM loss simply does not make sense. The engine MUST make more power in this instance and this should manifest itself as an rpm increase with a FP prop.

Just throwing this out there but is the pot possibly wired backwards? Note that leaning or richening from peak will both lower EGTs.

The only other explanation is that ignition timing is changing somehow with the rpm change. This can affect both power and EGTs. Maybe check to make sure rpm and MAP timing are set to constant values under the conditions you are tuning at.
 
Have not got a chance to check the black box data yet. I know the pot is correct because I have an air fuel meter installed. Additionally, if I go rich it will smoke pretty good. The meter is just several LEDs that show a range (no numbers). Peak egt seems and rpms seem to be on the lean end of the range that is marked as stokeometric (sp?). Don't know how accurate it is, but I can usually come within a few degrees of peak egt just by adjusting the mixture to the same spot on the meter.
 
If you are just using a narrow band O2, they are not very accurate as the sensor rapidly switches at stoich around .5-.55V.

A WB meter gives a 5V linear signal which is much more accurate.

All this does not explain the loss in power as your go richer from peak EGT however.

I'm puzzled.:confused:
 
Last edited:
You must log in or register to reply here.