Fly By Wire Electrical Question

[Autothrust Blue]

WIth the EMP scenario you're down to not a lot. On the 777 you're left with a couple of spoiler panels and the stabilizer trim levers on the console to manage an aircraft that has pushed the boundaries in terms of longitudinal stability. Not a pretty scenario at all!

Is there somewhere that I can read about exactly how relaxed the 777’s stability is? Out of sheer boredom.

 

[gotWXdagain]

From the anecdotal “I heard somewhere” file, but is it true that Boeing had to dial down the engine-out corrective inputs from the 777 fly-by-wire because pilots weren’t noticing them?

 

[🦈💜]

So, in this hypothetical situation we've had an EMP that's knocked out all electrical systems and backups? On the E175 you're a rock with zero controls. But I suspect you're a rock with zero controls on almost every aircraft these days. Lose the FADEC, lose the engines, lose all hydraulics. RAT doesn't work since it's still powering electrical pumps that are knocked out by the EMP. No hydraulics, no power, no nothing.

On the 175, you still have ailerons (hydromechanical PCUs ttbomk), flaps (they're electric, but not fbw), gear, and possibly the ability to change pitch with thrust. Generally if you lose the flight control computers, but still have bus power, you only lose the higher-level functions like thrust-lever-angle compensation, rudder speed/stroke limiting, AoA protection, YD, mach trim, and so on.

The higher-level functions on the 175 provided by the flight control computers are simple deltas that alter the control signal; that is to say, you're not a vote in the process, you're commanding it—the flight control computers can just moderate that command somewhat. Thus my understanding is:

Bus power + Computers = FBW rudder, elevator, multi-function spoilers with higher-level functions, ailerons, flaps, stab trim
Bus power = Direct mode rudder, elevator without higher-level functions or feel unit, ailerons, flaps, stab trim
No power at all = Ailerons.

Certainly not an optimal situation.

-Fox

 

[🦈💜]

So, in this hypothetical situation we've had an EMP that's knocked out all electrical systems and backups? On the E175 you're a rock with zero controls. But I suspect you're a rock with zero controls on almost every aircraft these days. Lose the FADEC, lose the engines, lose all hydraulics. RAT doesn't work since it's still powering electrical pumps that are knocked out by the EMP. No hydraulics, no power, no nothing.

Give me some backups that will continue to function in a variety of different situations and we'll discuss. But what's led to this electrical loss and what do you mean by total? So many different paths we can take on so many different aircraft.

What I meant to say, but didn't, is that a lot depends on what systems are affected by the EMP and how much. If it's just the computers, it's a very different story than if you have no power at all. Which, re-reading, I guess you actually said.

But afaik you still do have ailerons as long as you have accumulator pressure.

-Fox

 

[🦈💜]

Thanks.

"With a total loss of electrical power... you still have powered rudder and pitch trim. ...(Man Pitch Trim) in red appears on the PFD." That's a different kind of "total loss" than the one in which I'm interested. I mean, if I have no electricity, how would I get an electrically powered annunciator on an electrically powered PFD?

Let me try to be more clear about the FBW condition I'm trying to understand:
1. Electrical Power Loss
2. Total
In other words, the ship's electrical system and batteries are gone. All the backups failed. All the batteries are dead.

In that condition*, What's left as far as flight controls (aileron, elevator, rudder)?

Maybe this is easier.... In the above condition, what are you?
A rock?
A rock with thrust?
A glider?
An airplane?

In the 175, an airplane with ailerons until accumulator pressure is gone, possibly thrust at some power setting, and landing gear. Maybe you could have the passengers run from the front to the back? Remove a bin door to angle out the DV windows like a canard? Have I mentioned this is not a good situation? It's not a good situation.

-Fox

 

[shdw]

Let me try to be more clear about the FBW condition I'm trying to understand:
1. Electrical Power Loss
2. Total
In other words, the ship's electrical system and batteries are gone. All the backups failed. All the batteries are dead.

The wings still on this baby?