How do linear actuators for flight controls work in fighter jets?

Question

I've built some rc planes and know that in order to control an aileron in a rc plane, that you need a servo, a control horn(sticking out of the aileron), and a pushrod. However, I was wondering how fighter jets control their ailerons. I was researching and I found that it control is via linear actuators. I was wondering how exactly it worked and tried to look for a video or an animation. However, I couldn't find anything that explains exactly how a linear actuator moves an aileron. Can you please help me understand this with a video or something like this. Thanks so much.

This is a picture of an f22 raptor someone sent me when I asked this question on Flite Test...they didnt respond after this this. You can see orange actuators in the picture but it doesn't really help me besides that. https://conceptbunny.com/lockheed-martin-f-22-raptor/

Answer 1

The working principle is surprisingly similar between the RC as you've described and most actuator powered aircraft. The linear actuator extends/retracts a pushrod, which is connected to a horn attached to the pivot point on the control surface.

Below is the zoomed-in picture from the OP. I've taken the liberty of highlighting the two rudder actuators and the left stabilator actuator. The one attached to the stabilator is the most revealing: the pushrod essentially connects to a horn, which translates the linear motion to a rotational one.

_{Ref: https://conceptbunny.com/lockheed-martin-f-22-raptor/}

Due to aerodynamic and stealth reasons, this mechanism is hidden under a smooth fairing for the F-22. But for other airplanes, you can see small blisters under their control surfaces that fair the actuator. Below is a picture of the Boeing 787 aileron. The blisters have been highlighted.

_{Ref: https://commons.wikimedia.org/wiki/File:Low-speed_aileron_of_Boeing_787.jpg}

The linear actuator itself is almost always energized via hydraulic fluid, whether it comes from a central hydraulic system or an self-contained hydraulic systems (EHA). The following diagram illustrates the working principle:

_{Ref: https://www.machinedesign.com/mechanical-motion-systems/linear-motion/article/21832047/whats-the-difference-between-pneumatic-hydraulic-and-electrical-actuators}

Answer 2

It's really not so different from your models. Due to the strength of hydraulic actuators, those horns need not stick out into the airstream. Basically, if you move the hinge into one skin, you have most of the local thickness for hiding that horn.

Here is the interesting section from the linked picture. 125 is the control unit with the valves and 126 the actuator.

However, in order to keep forces down, a small bulge is needed on the lower wing to fair over the horn that would otherwise stick out of the surface (picture source). The near one is for the aileron and the far one for the wing flap.

Below is a diagram for the F-15: Here the hydraulic actuators are controlled via pushrods and pulleys. On more modern aircraft this will be an electric line and probably even an electro-hydraulic unit so no hydraulic lines need to be strung trough the wings (picture source).

The actuators themselves consist of a cylinder, a piston, a rod connected to the piston and sticking out of the cylinder on one end and continuing to the control horn, and a couple of valves. Hydraulic fluid is pressed into the cylinder on either end of the piston, depending on the desired piston movement. The rod then transfers the piston movement to the control surface.

The valves are controlled by cables or pushrods, as can be seen in the F-15 Lateral Controls diagram. On more recent designs, electrical control is used with a central computer calculating the best valve settings several times per second.

Why hydraulics are a good choice for such actuators can be read here.