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Did a search, and have gotten some conflicting results. What kind of motor actually drives the torque tubes? I've heard rotary electric, hydraulic actuator, etc... What actually powers the system, by electrical, or hydraulic means? Just looking for a little clarification. Kthx!

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Elite Joined: Oct 30, 2006 Posts: 627 Status: Offline

Electrically controlled brain (PDU) with hydraulic motor that drives torque shafts that supply mechanical energy to the LEF.

Aha. I think that's where the confusion came from. No one has ever mention that the actuator was hydraulic.

Elite Joined: Oct 30, 2006 Posts: 627 Status: Offline

The actuators you are referring are the rotary actuators, (located in leading edge of wings) which are basically a device that transmits the rotary motion from the shafts to the up/down motion of the flaps. These devices (4 per flap) are not really actuators but a simple way to join the torque shafts together, flap attach points, and provide the force to move the flaps.

dont forget those lovable AOA probes, based on how those lil guys are situated with the air flow the LEFs will adjust accordingly. High AOA and lower speed will result in the LEF's "lowering" or extending (even though on an F-16 they dont extend, but thats how some people know the terminology).... Crazy Pilot

Right, I knew that they were linked that way, but what I was fuzzy on was the actual, physical operation of the LEF itself.

Oh, one more question.... When they're locked in the 2up position on the ground, is it a metal bolt that slips into place, or it there a valve that closes and locks in the pressure, so there's no droop when the pressure bleeds off?

Veteran Joined: Sep 22, 2005 Posts: 296 Status: Offline

The command servo (electro-mechanical) receives signal from the AoA probes, DFLCC, etc... via the ECA. When the signal is received it moves a linkage assy that controls the PDU (hydro-mechanical) flow control valve.

2 degrees up os no different than any other position really...wherever the linkage is positioned (command servo' position) determines the position of the PDU flow control valve. No movement equals no positional change of the LEF's. They can be mechanically locked by the asymmetry brakes on the outboard edges of the LEF's if an asymmetrical condition occurs or electrically locked by positioning the LEF switch to "lock" as opposed to "auto."

Hope that helps some Evil or Very Mad

Ah, so it is in fact a hydraulic lock. So I take it to mean this condition is not the same for the flaperons, since they do droop when pressure is lost, parked on the ground.

Elite Joined: Apr 26, 2004 Posts: 1175 Status: Offline

Habu you are correct. The rotary actuators however are plain mechcanical.

Where does the broom handle and tie string come in to play???

(it's a "B-shop" thing..... Very Happy

)

Smitty

Rgr. So the rotary actuator is what drives the PDU, got it. Making sense now.

Veteran Joined: Sep 22, 2005 Posts: 296 Status: Offline

No... PDU drives torque shafts which drive rotary actuators. LEF's are attached to the rotary actuators.

Ah, got it now.

Veteran Joined: Mar 24, 2007 Posts: 379 Status: Offline

Habu, read what MechFromHell wrote, "electrically locked". I'm not certain, but I think the electrical lock works through the asymmetry brakes. That doesn't sound like a hydraulic lock to me. When the airplane is sitting on the ground with no hydraulics, the LEF still doesn't droop like the flaperons and horizontal tail. Why? Because the eight mechanical rotary actuators have a gear ratio of 300:1 and the small amount of friction in the system multiplied by 300 is enough to hold the LEF at 2 degrees up (or wherever it is). That gear ratio means the drive shaft must rotate 300 degrees for each degree of LEF rotation.

The flaperons and tails have linear hydraulic actuator cylinders with relatively low friction, so with pressure removed, the surfaces can droop.

On analog F-16s (below Block 40) the LEF commands are generated by the Electronic Component Assembly (ECA) which is outside the flight control computer. On digital F-16s (Block 40 and on) the LEF commands are generated in the flight control computer (DFLCC) itself.

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Ok so LEFs, how are they actually operated?