🦈💜
Well-Known Member
TLA compensation is cool. But you know what makes you even less smooth than direct mode?
... 27.1.
-Fox
Interview with Captain of Qantas 72 (A330 - 2008)
- Thread starter JeppUpdater
- Start date
TLA compensation is cool. But you know what makes you even less smooth than direct mode?
... 27.1.
-Fox
Epic Fail 27.1
JeppUpdater
Well-Known Member
So basically Sioux City - because nobody cares since it was just freight?
BobDDuck
Island Bus Driver
You still have hydraulic power, just not as much as normal operations.
My point was more that you are relying on a computer to translate tension to hydraulic pressure. Really no different than translating stick or yoke position to electrical current and then into hydraulic pressure. Just a shorter wire run. What it doesn't have in flight envelope protection.
If you can some time, see if you can track down the story of WHY the 170 doesn't have FBW. It involves, USAir, Mid Atlantic and a single FMS head design.
On the -9 and the #notreallyaboeing we have cables to control tabs for the ailerons and elevator full time. The rudder gets a PDU to move it, but if that fails we have a cable to a control tab. Talk about "leg day"!
Inverted
mmmmmm wine
In the bus if you get into mechanical backup you only have differential power and pitch trim. But lots of • has to go wrong for that to happen. It does make me semi nervous having zero mechanical connection to the flight controls, but then I eat my food on the giant pullout tray and forget all about it.
🦈💜
Well-Known Member
Correct me if I'm wrong, but that's what I was aiming at—aren't the aileron PCUs "dumb" PCUs that directly translate cable motion to control actuation? My impression was that there's no way the computer can disable or modify the PCU's behavior—it's slaved one for one to control input. Is that not correct?
My understanding, which could certainly be incomplete or incorrect, is that on the 170/190, the pitch and rudder movements are translated to a voltage; the flight control system can further apply a voltage differential for the higher-level functions, but the computer doesn't, itself, transduce yoke/pedal position into control input; for the ailerons, the cable runs to the PCU, which controls the surface position directly, with no capability of differential input ("computer interference").
This is not an area where training or manuals are at all specific; I've researched what I could, but I'd like to know more if you (or anyone else) knows the systems better than I.
I like that philosophy better, but as far as electronically-driven primary flight controls go, I'm relatively ok with the Embraer setup... as I understand it.
-Fox
Nick
Well-Known Member
And I like how the rudder limiter is controlled by a bellows.
Here's one in the factory in Long Beach in 1998, about to be installed in the prototype's vertical stabilizer:
BobDDuck
Island Bus Driver
Mostly, yes. That said, PCUs/PDUs are not mechanical but rather electrical and there are cards on board them that control exactly how much pressure gets applied based on a certain cable tension. They are "dumb" in the sense it's simply a scale and no logic is built in, but there is certainly the capacity for the card to short out and the PCU to go rouge.
The original design plan was to have the ailerons have a digital control architecture like the rudder and elevator, but Airways, who was the launch customer wanted the whole thing to run through only 1 FMC and either it wasn't possible or they just ran out of time trying to get it to work.
BEEF SUPREME
Well-Known Member
🦈💜
Well-Known Member
I hate it when my PCUs use makeup! ^_~
But yes, that's a failure mode I could reasonably expect. I was honestly surprised how little 'abnormal abnormal' stuff we covered in sim. If it were up to me, we'd see a lot more in that department, in this business.
</sidebar>
-Fox
BobDDuck
Island Bus Driver
Meh. Potato/pAHHHtato.
And yes, abnormal are interesting and make you feel good about your pilot skills, but may or may not translate into skill advancement. Most sims can't accurately simulate a lot of abnormals (just how WOULD the plane handle with a main cabin door open?) or the each one is different and even with the same failure your results wouldn't be the same in real life.
The rudder is mechanical(except for yaw damping, turn coordination and trim).
Inverted
mmmmmm wine
True. Except it is electronically limited until you get out of normal law.
Interesting. I've heard a story floating around that it was supposed to have a sidestick as well but I don't know how true that is.
PositionAndHold
Well-Known Member
Well look at the new Leagacy 500. Sat in one last year at NBAA. Instant side stick envy.
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learhawkerbe400
Well-Known Member
Ive been on the 190 for a while (#originalairways) and I've never heard that from any of the training department guys. They all say it was supposed to have a side stick but when Embraer got the design from Dornier it was one of the last things left that wasn't completed. The ensuing shuffle caused the side stick to get put on the back burner and ended up with the yoke.