RE: different pinions, how do they effect flight times?
By effecting Headspeed, the higher the headspeed the lower your flight time becomes.[:'(]
With a lower tooth pinion at a specified voltage, the motor doesn't have to work as hard (less load), therefore less current draw on the battery.
Think of driving a manual transmisson car with a small 4-banger, the car leaps when starting off in 1st gear (but will only take you to a certain speed). If you start off in 3rd gear, the car may "dog" off the line (if it doesn't stall), but it will take alot of load to get the car up to speed, that's is faster than you could achieve in 1st gear. The same principle applies to the motor pinion, motor Kv, battery voltage & overall headspeed.
For example: on my T-rex 500, instead of using a 6s lipo @ 22.2 volts, I'm using a 4s @ 14.8 volts. Since I cannot acheive the headspeed with the stock 12 & 13 tooth pinions the a 4 cell lipo (only 1400rpm), I geared up to a 16 tooth to start. That gave me a headspeed of around 2300rpm in ST2 @ 90% throttle, and a flight time of 18-20 minutes (all in Idle-up). When I switched to a 18 tooth pinion, I saw a slight increase in headspeed of about 20%, but flight time dropped to 12 minutes, lipo was warmer than before & motor got HOT after 1 flight. So I went back to the 16t for now.
Shadow