I have the giant scale hellcat, with 70" wingspan and century jet air retracts, what Hitec retract servo should i use for the valve, also are the air tanks re fillible and how many cycles can they go through before i should refill my air tank.

Thanks, Dave Trimmer

If they are air retracts you don't need a retract servo, just a standard one to operate the valve.

As far as "how many cycles" you'll have to experiment (On the ground) to find out how many you can safely do.