ben1000
Senior Heliman
Location: Gilbert, Arizona
| Here's a (hopefully) layman's explanation...
Engines require 2 kinds of fuel to run, 1 is the liquid green or pink stuff that you fill your tank with, and the other is air. The fuel comes in from the tank, and the air comes in through the carb (where the throttle is). The air and fuel is mixed, and then is burnt which produces power.
Now, the amount of power that your engine produces is controlled with the throttle. It lets more or less AIR into the engine, which draws in more fuel as it's needed, but for the engine to run at its best, the correct amount of fuel and air needs to be mixed together. The amount of fuel that is mixed with the air is controlled by the needle valve.
When the valve is open more than necessary, there is too much fuel for the amount of air. The mixture is fuel-rich (more than enough fuel). This is good for breaking in the engine, because the extra fuel that doesn't burn keeps the engine cool and well lubricated and this is good treatment for a new engine.
As you close the needle value, you make the mixutre less fuel-rich, or more fuel-lean. As you lean out the mixture to the correct setting, you will notice more power out of the engine, and the engine will run hotter. As you pass the optimum fuel-air mixture (by continuing to close the needle valve), the engine will become fuel-starved, and eventually stall.
Your engine instructions should be followed to get the optimum mixture settings. Most times they tell you somthing like: Lean out the mixture untiil the engine starts to get fuel starved (engine loses power) and then richen (open) the mixture by 1/8th turn.
2 more things to remember: As the temperature increases, or as you climb in altitude, the air gets thinner, so you will need to re-adjust your needle valve setting for changes in temperature and altitude. Hotter and higher require a leaner mixture. Cooler and colder require a richer mixture. Some planes have an in-flight mixture control so you can lean out the mixture as you fly higher. Most helis don't have this.
Hope this helps.
Regards,
Ben |
