The Recommened servos for this plane are the Hitec HS-65MG servos. They provide 31oz-in of torque when powered by six volts. This is okay, however people are experiencing blow-back because the HS-65MG lacks the torque to push and hold the big elevator reliably. Blow-back is also known as the phenomena when the servo stalls because the torque rating is being exceeded. To fix this problem, people are replacing the HS-65MG with the bigger, more powerful HS-85MG. Seems like a quick and easy fix right? Well, not so fast! The HS-85MG is bigger in physical size and modifications to the servo hole need to be made to fit the bigger servo in the airframe.
Luckily, Savox makes a servo that is perfect for this airplane, at an affordable price. The Savox SH-0255mg servo provides 54oz-in of torque on six volts. That is 23 more ounces than the HS-65MG and 5 more ounces than the HS-85MG, all in a compact size that requires no modification to the airframe. The SH-0255mg also has several ground breaking features to improve perfomance, such as the aluminum case, and Digital reliablity. Neither the HS-65MG nor the HS-85MG is Digital, or features an aluminum case for efficient cooling.
Some other brands such as Airtronics creates similar Digital servos that some people are using in the Extra. However, the Savox SH-0255mg is still cheaper, and features more torque than the Airtronics 94809 servo. Here is a quick side-by-side comparison between these four servos:
Airtronics 94809 Hitec HS-65MG Hitec HS-85MG Savox SH-0255mg
Price: $49.99 $29.49 $30.99 $32.99
Torque: 39oz-in. 30.55oz-in 48.6oz-in 54oz-in
Speed: 0.1 sec. 0.11 sec. 0.14 sec. 0.13 sec
Digital?: Yes No No Yes
As you can see, each brand has its advantage and disadvantage. But, the Savox SH-0255mg servo has the most torque, for the most practical price.
I personally used to use Hitec HS-65MG's in all my 48" planes, and was planning on using the HS-85MG for the elevator servo, and HS-65MG's the rest of the way around in my Extreme Flight Extra EXP. But after doing my research and comparing different brands of servos, I came to the conclusion that the Savox SH-0255mg is the best servo to fit my aircraft and budget.
Below is a video of my Extreme Flight Extra 300 EXP 48" in action with the Savox SH-0255mg.