Please educate me here...
While I was doing my private pilot training in a Diamond DA20 with fuel injected engine and fixed pitch prop, I was practicing engine-idle landings from various spots in the pattern -- where the instructor pulls power at some point, and you have to put the plane down nicely onto the runway. Anyway, at one point he say's "Let's say the opposite happened, your throttle cable has broken (or whatever) and you can't close the trottle at all. How are you going to land?"
Well, I justed pulled the mixture until the RPM was about where it would be if I'd reduced the throttle for landing, and then I landed normally.
So the question is "How is pulling the mixture really different from closing the throttle?" It seems like using throttle, you're restricting the flow of a fixed mixture of fuel and air. Using mixture, you're restricting the amount of fuel you mix with a constant supply of air. So if I leave my throttle wide open (like I did in my training landing), and restrict the fuel flow with mixture, I end up with a given quantity of fuel to burn, but with maybe some excess air (more than needed to burn that much fuel). If I have a properly leaned mixture, and use my throttle to restrict the flow of the fuel/air mixture into the engine, I suppose I could adjust the throttle to give me the same amount of fuel in the engine, but with just the right amount of air to burn that fuel.
Now as I understand things, common wisdom says that excessively leaning is bad, and will damage an engine. But I don't understand how this happens. It almost seems like I could almost get by with no throttle at all, and use my mixture entirely to control my engine. In some cases it would be excessively rich, and I'd be pumping excess fuel vapor out, while in others, it would be excessively lean, and I'd by pumping excess air out. Why is pumping excess air through the engine a bad thing (when I'm excessively lean)? Or is it a bad thing?
Now remember that my training was done in a fuel injected engine, as is all my current flying. I suppose that means that I might have a nicely balanced amount of fuel reaching each of the cylinders. Things may be different in non FI engines, but I've not experienced it.
I also remember reading the CAFE reports on the RV9A and RV8A. All their fuel flow / RPM / MPG reports used wide open throttle, using mixture to control fuel flow, varying it from very rich to very lean (from 10 gph to 6 gph in the first table for the RV9A). And this was with carbureted engines.
Any wisdom?
While I was doing my private pilot training in a Diamond DA20 with fuel injected engine and fixed pitch prop, I was practicing engine-idle landings from various spots in the pattern -- where the instructor pulls power at some point, and you have to put the plane down nicely onto the runway. Anyway, at one point he say's "Let's say the opposite happened, your throttle cable has broken (or whatever) and you can't close the trottle at all. How are you going to land?"
Well, I justed pulled the mixture until the RPM was about where it would be if I'd reduced the throttle for landing, and then I landed normally.
So the question is "How is pulling the mixture really different from closing the throttle?" It seems like using throttle, you're restricting the flow of a fixed mixture of fuel and air. Using mixture, you're restricting the amount of fuel you mix with a constant supply of air. So if I leave my throttle wide open (like I did in my training landing), and restrict the fuel flow with mixture, I end up with a given quantity of fuel to burn, but with maybe some excess air (more than needed to burn that much fuel). If I have a properly leaned mixture, and use my throttle to restrict the flow of the fuel/air mixture into the engine, I suppose I could adjust the throttle to give me the same amount of fuel in the engine, but with just the right amount of air to burn that fuel.
Now as I understand things, common wisdom says that excessively leaning is bad, and will damage an engine. But I don't understand how this happens. It almost seems like I could almost get by with no throttle at all, and use my mixture entirely to control my engine. In some cases it would be excessively rich, and I'd be pumping excess fuel vapor out, while in others, it would be excessively lean, and I'd by pumping excess air out. Why is pumping excess air through the engine a bad thing (when I'm excessively lean)? Or is it a bad thing?
Now remember that my training was done in a fuel injected engine, as is all my current flying. I suppose that means that I might have a nicely balanced amount of fuel reaching each of the cylinders. Things may be different in non FI engines, but I've not experienced it.
I also remember reading the CAFE reports on the RV9A and RV8A. All their fuel flow / RPM / MPG reports used wide open throttle, using mixture to control fuel flow, varying it from very rich to very lean (from 10 gph to 6 gph in the first table for the RV9A). And this was with carbureted engines.
Any wisdom?