- Oct 15, 2010
- Reaction score
- Darling Downs
Yes, having a mixture control only allows you to adjust it, that was the point of the question. Not sure what Bird Dog is flying, but a Rotax with standard Bings at 9500 feet will be very rich as I found with the Air Fuel Ratio gauge fitted. I gets as bad as below 11:1 or richer. The mixture control allows you to get the ratio to a point where is makes more power and uses less fuel if that's a concern.Having mixture control will not tell you if you are lean or rich, all the control does is allow you to alter it.
An EGT will give an indication of how the mixture is working.
Full rich you are getting s lot of power and the excess fuel is supposed to be cooling the heads, you will have EGT readings less than maximum, or less than peak as they say. Reduce the fuel slightly and the burn will become more efficient, giving more power and also higher EGT. That is the effect of gases being hotter as they exit the cylinder. Lean some more and you will get to peak EGT. The very hottest that the gases will get and just slightly less than maximum power. As you continue leaning there will be an excess of oxygen in the mix and less fuel to burn, so EGT will drop.
Somewhere just lean of peak you will get the most efficient burn.
Running rich of peak is OK if you are lazy, or don't understand what you are doing and so long as you are not burning everything up, which is possible. Lycomings run very well way lean for taxying and they will not have so much tendency to misfiring. Run them so lean that they will cut out if you advance the throttle to take off power and you will be safe
At 9500 feet a 912 is a slug and I would suggest that running LOP, which significantly reduces power will just make it even worse.
If he's not flying behind a 912 then it's a different story, maybe there are horsepower to spare.
With a 912UL I don't care about LOP, I want all the power it can make, when I want it. Sure it runs smooth at 9500 feet, but it's rich as hell and by leaning it back to optimum power it's still smooth but has significantly more power and because of that will cruise faster and use less fuel.
I provided the graph for the O360 at post #29.