Forum: F-16 Design & Construction

Can anyone show me some photographs or diagrams of the control surface actuators in those thin wings of an F-16? I've been curious to see how they're installed and what they look like, because that wing is very thin and it amazes me that an actuator can even be installed in such a tiny space, much less that it can generate the immense forces required to control the plane.

CJ

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The Integrated Servo Actuators are in the fuselage, not the wing. Just inboard of the Flaperon.

You can see the wing detached here and where the flaperon on the wing goes into the fueslage. The hole that you see on the trailing edge is about the size of two large fists. and the hole on the leading edge is about the size of 2 or 3 fingers.

edit: Also here is a good photo of the ISA.

The leading edge flaps (LEFs) are driven by a driveshaft, connected to one PDU (primary drive unit). It's a big hydraulic motor, about the size of a keg of beer, that provides the torque for left and right LEF driveshafts equally. The single PDU is located up on the spine of the aircraft, behind the gun ammo drum bay, and just forward of the air refueling receptacle. The LEFs are mechanically interconnected, and should always move together on both wings (unless something goes way wrong -- see <a href="interviews_article28.html">Gums' recent interview</a> about the LEF that deflected only on one wing, too far up after the drive shaft came apart at the spline. Can you say "leading edge spoiler?"). Back in Torrejon days, a TJ jet also did this while up near Zaragoza (ZAB), after a lay-down bomb run. Lots of lift on one side, lots of drag on the other. Declared emergency for sure, and great piloting brought it back to ZAB though.

The flaperons on the trailing edge of each wing move independently of each other as ailerons, and move almost together as flaps (though there is no mechanical interconnect of any kind between them). The ISA (Integrated servo-actuator) for each flaperon is just inside the fuselage, where the aft wing meets the aircraft. The flaperon has a shaft that enters the ISA bay in the fuselage, and the ISA connects to it, to torque it up or down, moving the flaperon.

This is the same way the horizontal stabilizers work too. A shaft enters the fuselage, where an ISA provides the torque. And again, both are completely independent, though act together for pitch, and opposite for roll commands.

The rudder ISA is just above the rear of the engine, and is housed in the rudder island, just in front of the tail light.

Side note: All 4 of the flaperon and horizontal stab ISA's are interchangeable. The rudder ISA is slightly different, due to size restrictions in the rudder island.

Another side note that some people don't know: The rudder ISA receives a "gun fire compensation" signal whenever the M61A1 20mm gatling gun is fired. Because the gun is just left of the aircraft centerline, firing the gun would cause it to yaw to the left from the recoil. But the aircraft knows this, and compensates for it by kicking in some rudder to the right automatically so the bullets stay straight, and hopefully on target. Another benefit of the fly-by-wire flight control system.

Here's a quick cut-away drawing of the left wing flaperon, and the Inegrated Servo-actuator, that fits in the ISA bay in the fuselage.

Here's the drawing:

PDU = Power Drive Unit

Here's a few pics of an actual thing wing, compliments of the Zipper...

Forum: F-16 Design & Construction

Control surface actuators in those thin wings