How much torque do I need for ailerons?

For a sport plane with 100 sq cm ailerons, 3-5 kg-cm is typical. Larger, faster models need more. Always add a 30% safety margin above calculated minimum. Digital servos provide more consistent torque than analogue servos.

Does servo speed matter?

Yes. Fast servos (under 0.1 sec/60 degrees) are essential for racing and 3D aerobatics. Moderate speed (0.12-0.17 sec) suits sport flying. Slow servos are fine for scale models and flaps. Faster servos generally cost more and draw more current.

What is the difference between analogue and digital servos?

Digital servos update their position much faster (300Hz vs 50Hz), giving better holding power, faster response and less deadband. They draw more current at idle. For primary control surfaces on anything but basic trainers, digital servos are recommended.

How does horn length affect torque requirement?

Longer servo horns give more movement (throw) but require more torque. Shorter horns need less torque but give less throw. A 15mm horn is standard. Increase to 18-20mm for more throw, or decrease to 10-12mm if you need less travel.

ModelCalcs

Servo Torque Calculator — Control Surface Sizing

Determine the servo torque needed for your control surfaces or steering.

Surface Area (sq cm)

Control surface or load area

Horn Length (mm)

Servo horn length from centre

Application

Type of control surface or linkage

Speed Requirement

Servo transit speed class

Supply Voltage

Servo power supply voltage

Servo Type

Digital has better holding power

How We Calculate This

Estimates servo torque requirements based on control surface area, horn length, hinge line, airspeed and application type.

Formula

Base torque = Surface area x 0.015 x (Horn length / 10) x Application factor
Adjusted for hinge line, deflection angle and air load
Voltage-corrected torque = Base x Voltage factor
Recommended = Adjusted torque x Safety margin

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Always verify quantities before purchasing materials.