My moki 210 is pinging and making knocking sounds a bit at high rpm. But only in the air. I am worried this may damage my engine. How do I solve the problem? I am using 5% cool power fuel and a master airscrew 20X10.

The damge may have already been done? They go bye bye very easy.

Have you thought about the fact that it may be getting hot.

What about no nitro?

It is still giving power and only pings in the air at full throttle. What is causing it?

Try changing to a cooler plug.

If you mean a licht clear cracle, Your mixture may be a bit too lean, or compression ratio (CR) may be a bit too high, or a combination of both.
Check the spark plug. It should not be white (lean), or purplish (too high CR)
Just to be safe, add a head shim to reduce the CR, and set the main needle to the point that the plug just is short of turning black. In gas engines, that is the level very slightly rich of best performance. Then lean a tad. (1/32 needle turn).
To check the plug, fly at full throttle a while, then kill the engine without hesitation, so intermediate throttle will not influence the spark plug reading.

I had this same problem with my Moki 1.80. this is what I did to reduce the knocking: Reduce nitro down to 0% (use some castor). Open up the cowling for more air flow (use baffeling if needed). Use a K&B 1L plug. Run it slightly rich.

I no longer have this problem.

yes drop the nitro and run straight fai fuel in it with 3 oz extra castor oil per gallon and it will be fine