elevator droop

[Sponge 74]

Flaperons droop

[Vic1 3]

 

Sorry, I did actually mean flaperons, we have already established the elevators don't drop

 

Hydraulic shut of valves are on the overhead maintenance panel. Can't wait to get hold of this aircraft to test things myself, 4 weeks till I return home!

 

 

 

yes I have already tried shutting the hyd shutoff valves on the engineering maint panel..............but makes no difference

 

 

 

 

 

 

 

 

 

 

 

kav

[Mike777 163]

I think maybe there are electrical actuators that connect direct to the elevators and remain on -- although I can't get the elevators to droop even by switching all sources of electricity off and activating master battery failure.  See FCOM 2 pdf pages 606 & 611.

 

Mike

[Olympic260 415]

Elevetors drop under certain conditions, don't remeber them now and I am not on my FSX PC to check.

[Airbusman330 300]

They don't always droop and sometimes I see only one elevator droop in the real world.

[BrianW 124]

What you guys are seeing is PCU blocking mode at work, and yet another thing that makes PMDG stand out among their competition. 

 

When hydraulic power is lost to both PCUs of an elevator, and that elevator is within two degrees of neutral, blocking mode will be active.  This isolates pressure in the PCU actuator and locks the elevator to prevent flutter in flight.  Since most PC yokes and joysticks are spring centered the elevator is usually neutral during shutdown which activates this mode.  If you want to see droop you’ll need to keep the yoke forward until the system depressurizes.  For droop on both shutoff the left system last, for droop on just one elevator keep it centered until only the center or right is on, then push the yoke forward and shutoff the last system. To see blocking mode in action watch what happens when the systems are shutoff with the yoke pulled back.  I haven’t tested it, but if you hold the elevator forward at least more than two degrees (five if the flaps are down) you should see the elevators drop further as the system depressurizes.

 

Brian   

[FLEX1978 373]

Very nice Brian, Quick question before I do some research, what happens in the event of a total loss of hydraulic fluid? is pressure maintained through an accumulator?

[Airbusman330 300]

Very nice Brian, Quick question before I do some research, what happens in the event of a total loss of hydraulic fluid? is pressure maintained through an accumulator?

Then the crew will have to pull a repeat of that DHL Airbus that got hit by a missle over Iraq but I'm sure there are check valves to prevent total fluid loss.

[FLEX1978 373]

Then the crew will have to pull a repeat of that DHL Airbus that got hit by a missle over Iraq but I'm sure there are check valves to prevent total fluid loss.

I think you misunderstood I am talking about the aircraft parked on the ground.

 

According to Brains post post the aircraft has a blocking mode even if the hydraulics are depressurized.

 

Assuming that pressure is provided by the accumulators, what happens (on the ground) in an event of complete loss of hydraulic fluid? I ask because this was mentioned previously.

 

Cheers

[Flamin_Squirrel 71]

Assuming that pressure is provided by the accumulators, what happens (on the ground) in an event of complete loss of hydraulic fluid? I ask because this was mentioned previously.

 

Cheers

No, an accumulator provides a limited amount of hydraulic pressurisation. If the fluid leaks it won't be of any use. Also the 777 only has an accumulator for the brakes iirc.

[FLEX1978 373]

Ok let me try again, I understand how an accumulator works I mentioned previously that the elevators should droop if no hydraulic fluid is available. I am asking how the PMDG simulation behaves if no fluid exists. what exactly holds the elevators in place?

 

Regards

[BrianW 124]

Rob, there’s an inlet check valve that traps hydraulic fluid in the PCU.  The PCU mode selector valve has three positions, normal which allows the fluid to flow in and out of the PCU, bypass which operates as a closed loop system, and blocking which blocks all fluid from flowing in or out of the actuator thereby locking it in place.  As long as the adjacent PCU is ok, or the elevator isn’t in the neutral position the blocking solenoid on the failed PCU is energized. This keeps the mode selector in the bypass (closed loop) mode, which allows the PCU on the other hydraulic system to move the elevator.  If both PCUs fail the ACE puts them both into bypass mode and prepares to de-energize their blocking solenoids once the elevator is in the neutral position (aerodynamic forces does this in flight).  Once de-energized the blocking solenoid removes pressure to the mode selector valve and a spring in the valve moves to the blocking position which traps hydraulic fluid in the elevator actuator.

 

I hope this makes sense, it’s a somewhat complex system, and hard to explain without diagrams.

 

Brian

[jbassue 181]

Under the conditions listed in previous posts, I successfully got the droop. Though holding the yoke forward was not worth it while pressure boiled down. 

[EGLL77W 1,508]

Yeah as Brian said- if you put forward pressure whilst or straight after depressurising the hydraulics, they'll stay drooped. I've only had them droop once without forward pressure on a freighter flight. You can get some interesting combinations messing around with the hydraulics on the ground. If you've been around T5 at Heathrow - you'll often see 777's with all sorts of combinations because they have maintenance come in and do various different tests during turns.

[hopskip 253]

Ok let me try again, I understand how an accumulator works I mentioned previously that the elevators should droop if no hydraulic fluid is available. I am asking how the PMDG simulation behaves if no fluid exists. what exactly holds the elevators in place?

 

 

Why would there be "No" fluid? Did you fail the hydraulics and get them to leak?

 

Yes they would droop if there was no hydraulic fluid available. And there would be a big puddle of Hydraulic fluid somewhere on the ground nearby.