DAY 95 - 20 NOVEMBER 1990
We're doing a Phase "A" on 07, and both our Swash Plates are "high time". Wow, there's some new words probably!
Phase we've talked about enough by now, but What's a Swash Plate?
Swash plate is one of the links in the flight control chain that transmits the pilots control inputs to the rotor blades. A swash plate is actually a 2 half assembly, a top plate and a bottom plate that slide against each other, The bottom plate does not rotate, so that's where the controls are attached to. On the H-46, because we have 2 main rotors, forward and aft, all flight controls are mixed and divided between the forward and aft heads.
It takes a while to get your head around it, so let me see if I can simplify it for you. This might help, might not!
Starting at the pilots controls, you have the Cyclic control stick, which is between the pilots knees, is held in the right hand, and can be moved in a circle. The Cyclic controls Pitch, by moving the stick forward (nose down) or aft (nose up). If you move the Cyclic side to side, you Roll the aircraft in the direction you move the stick. This is pretty intuitive if you know how a regular "fixed wing" aircraft works. So far so good right?
The rudder pedals give you Yaw, basically piviting the aircraft about its vertical axis... that's a bookish answer right? Imagine you push the left rudder pedal, the nose of the aircraft would move to the left.
Collective Pitch is held in the left hand, and controls the actual vertical lift of the rotors. Pull the Collective up, the blades grab more air, and you go up. Push down, the blades flatten out and you go down. Throttles are also installed on the Collective on some helos, or in the case of the large helos, typically you have Engine Control Levers mounted on the control panel somewhere. There are also various buttons and controls on both sticks, for things like flight control trim, intercom and radio push to talk buttons, auto pilot controls, engine trims, and so on.
Ok, so the pilot has 4 controls, covering Pitch, Roll, Yaw, and Collective. These are then mixed and separated through a series of bellcranks and links into forward and aft controls.
From here, there are only actually 2 controls on each head, Pitch / Collective, and Lateral / Yaw, each with its own hydraulic actuator. One actuator, the Pitch / Collective, slides the whole Swash Plate up or down, thereby controlling the lift of all the blades uniformly on that head. The Lateral / Yaw actuator tilts the swash plate, so that for example blades on the left side are lifting more, then as they rotate toward the right side, they lift less.
By combining the forward and aft controls, you can do any combination of movement you need.
Need to lift off? The Pilot pulls up the Collective. That sends a Collective up to both heads, all the blades increase their angle, which generates more lift.
Want to slide sideways? The Pilot moves the Cyclic to the side. At both rotor heads, the Lateral controls tilt both swash plates the same way, and the helo moves sideways.
Want to Yaw, or basically pivot in place? Push one of the rudder pedals, and the forward Lateral control would tilt left, and the aft Lateral control would tilt right. Instant turn around. Nice!
So, that wasn't so bad right? You should try to answer that question on a timed exam sometime!
Ok, with all that said... what were we talking about? Oh now I remember, we're removing both Swash Plates, because they're "high time". High Time means they've been in use their maximum expected safe life time. So we remove them, send them back and install a new set of Swash Plates. Now of course to remove the Swash plate, we need to pull the Blades, Rotor Heads, and disconnect all the flight control inputs. And remove the rain shields, the fairings... you get the idea!
That's why we are doing it now, during a Phase inspection. The people up in Maintenance Control are always looking at the log books and upcoming inspections, and do their best to work it so we can do these big things when it makes the most sense.
Oh, all the above, was actually done in one work shift. The blades pulled, heads pulled, flight controls disconnected, swash plates removed, new swash plates installed, and the heads back on, all today. Almost takes longer to explain it than it does to do it when you're working with a great team!
While all that was going on, I also spent about 7 hours on another exfoliation corrosion gripe, this time inside the helo, back in the cabin area, down near the decking. There was a small angle bracket that joins between a rib and a stringer that was corroded nearly in half. First I had to drill out the rivets that held the bracket in place, then inspect the area behind where this bracket was mounted. Corrosion tends to spread, so of course once I had the bad piece out, I had to clean all the surfaces it was attached to. Then I set about trying to replace the bracket. This normally would be a simple job, but we don't seem to have any aluminum that we can bend with out breaking. There is different grades of aluminum, some is very strong but brittle, others are quite easy to bend and shape, but not nearly as strong, and so on. I'd get a piece cut to size, drill the holes, go to bend it, and snap. Damn! I'll have to look next shift to see if we can find some other sheet stock around the ship, if not, I'll just make a splice patch to reinforce the area and write a MAF to replace it when proper materials are available.
Secured ato 0730, ate some breakfast and to bed around 0900. I was wide awake, so read some magazines, tried to go to sleep a few times, finally passed out around noon.
