# How should the maximum output force of the actuator be chosen?

If the hinge moments of the control surfaces of an aircraft are given, how should the maximum output force of the actuator be chosen? Is there any standard or reference?

• Wouldn't this depend on: a) how fast you want the surfaces to move and b) how much weight you can afford for the actuators and their fittings, which will be heavier the higher the forces involved? Commented Dec 12, 2019 at 13:48

If the largest hinge moment is known for the entire flight envelope, including that required for continued safe flight and landing after failure(s), then the actuator can be readily sized. Of course, some engineering judgement is needed to compromise between:

1. Buffering for additional unforeseen loading (i.e. factor of safety) for later stages of the design and flight test, during which swapping the actuators can be costly, and
2. Sizing down the actuators to save weight and costs.

Therefore, the more scenarios you have considered for obtaining this maximum hinge moment and the more confidence you have in your model, the better off you are. For example, for elevator, consider the following (but not limited to):

• Achieve -1g to 2.5g at Vmo/Mmo with 3 sec out-of-trim in the opposite direction (14 CFR 25.255(a) and (c))
• Achieve 1.5g at Vdf/Mdf with 3 sec out-of-trim in the opposite direction (14 CFR 25.255(a) and (f))
• Takeoff rotation with dual hydraulic failure
• Achieve 0.8g and 1.3g at Vmo/Mmo with dual hydraulic failure (or single elevator surface jam)
• Thanks for the response. Do you know a reference that i can study for this purpose? Commented Dec 12, 2019 at 13:54
• @shooschool Are you referring to the hinge moment requirements?
– JZYL
Commented Dec 12, 2019 at 13:58
• Where do the "3sec" comes from? The g load given seems to come from maximum acceptable for airliners, but i think you should develop why this values. Commented Dec 12, 2019 at 13:59
• I have the hinge moments. I need to select actuator for them. I want to know how much force should the actuator be able to provide. Commented Dec 12, 2019 at 14:01
• @ManuH Edited my response to include the sources.
– JZYL
Commented Dec 12, 2019 at 14:03