i have an avistar select with an os 40la with a zinger 10-6 prop. i was wandering if a master airscrew 9.5-6 would give my engine better performance . and are wood or plastic props better.

Depends wood will break easier then Plastic when it hits the ground on take off or landing but would doesnt flex like plastic does at high speeds so i would say plastic for beginners so you aint always replacing props and the prop size depends on what you want i dont know how preformance would be going to a lower size prop iv only been flying for a year so im still learning aswell

yeh i had heard that wood props have amore blunt leading edge than plastic and that it effects you rpms dont know if that is true or not.

You might be going the wrong direction with your prop size. Try an 11x5 prop on your .40 LA and see how you like it; it's actually the recommended prop size for the O.S. .40 LA according to the engine owner's manual. You can also buy a 9x6 or 9x7 prop and try that while you're at it, too. An 11x5 prop will move a larger column of air and provide quicker take-off thrust and more control authority at lower speeds.

Propellers are one area where pilots can safely experiment with their planes but seldom do so. Trying different lengths and pitches of propeller can result in very different performance characteristics at times. You can reduce your engine noise significantly by switch from a blunt-ended propeller to a "scimitar" style or tapered tip propeller. Running a 3-bladed 10x5 propeller versus a 2-bladed 11x5 propeller would be an interesting experiment as well. Common folklore states that 3-bladed props are less efficient, but I've run them on various engines and I've liked them quite well.

With bushed engines like the O.S. LA series or the Thunder Tiger GP series, you may see better overall performance with higher castor oil content in your fuel. The thick castor oil helps float the engines crankshaft on the bushings and provides smoother performance.

i'm running 15% nitro and 18% oil and with the 10-6 wood prop it runs really rich could it be the engine is not full broken in (only 4 tanks run)

A good glow engine tends to settle in over time, and yours will likely idle better and run smoother next year than it will this year. You have answered your own question, though, if you're looking for more performance.

If the engine is running "really rich" then it is not anywhere near optimal performance. You need to begin leaning the needle valve at full throttle a bit to increase your power output. You don't want the engine running "really rich", you want to find out where the setting is for peak rpms and then turn it back to rich just a little bit.

As the engine breaks in, you'll actually notice it on the low-end or idle setting. You will have your engine tuned nicely and then go fly it two or three times. After you get some good, solid flights in with the engine tuned in nicely, all of the sudden your engine won't idle properly anymore. It will start to "load up" while it's sitting on the ground idling and you'll have to turn in your idle screw a little more. The plane will once again idle nicely and transition to full throttle smoothly and without hesitation, but your idle speed will actually drop a little bit.

Running your engine slightly rich will protect it from friction and still offer near optimal performance. Running it really rich will provide mediochre performance and will retard the breaking-in process.