ORIGINAL: STLPilot
I have JR ES539 standard servos (not metal gear) for it (4.8kg torque) - will they be enough or should i get higher torque MG servos?
I'd put something a little stronger then a standard on the elevator on all profiles to reduce the chance of flutter. The Extra also flies a little faster then the Katana V2 due to it's slightly thinner wing which makes it track better to practice pattern and IMAC flying. It's more of a do it all plane then just low and slow 3D like the Katana.
Dion's concern should not fall on deaf ears. The 539's are stronger than standard servos though so they'll work well as a nudge up upgrade on the smaller profiles. Heck I even use them on my .60 sized fatty Yak which is a full on Freestyle. Even still with the 539's though you need to ensure that you use proper super horns on the servos and utilize the best mechanical efficiency to reduce chances of flutter. And even then still you need to use proper throttle management as with any 3D model. 539's Aren't famous for slop free operation
Their gears have lotsa backlash so make sure you use a proper mechanical setup.