Vanity - Does the loss of both engines mean no hydraulic pressure?

freerepublic ^ | 1/16/2009 | self

[central_va]

Ok, avition question. Airbuses are fly by wire-correct? If so, is their an advantage in this over a cable/hydraulic aircraft with total engine failure, or is their hydraulic pressure without engine spin? Anyone know?

[central_va]

Looking forward to the answer.

[Squantos]

Nope but I will bump the thread up !

[Attention Surplus Disorder]

I am not expert on this, but even if both engines go out, isn’t there an APU (aux power unit) = smaller aux jet engine in the tail capabale of running all systems other than thrust? I know certain older planes had these, I guess one could see if there was a poop chute out the back of an A-320.

[xcamel]

The engines came off together when the craft it the water... perfectly.

It is exactly what the captain would have been praying for.

[SampleMan]

Generally speaking, ripped off engines mean open (unpressurized) hydraulics even in dual systems. However, if they are just shut down and an APU is running, then you are going to have hydraulics.

Additionally, electrical power from the APU would provide trim in most aircraft and you can manage to control and aircraft with just trim if nothing is too far out of wack, but you can't recover it if you make a mistake.

[omega4179]

Needs an expert answer but I suspect the fly by wires have some ability to manouver or he could not have landed perfectly.

[Ernest_at_the_Beach]

Lets drop this on the thread where people seem to be baffled as to where and how the engines might have come off the aircraft:

Both engines missing from jet ditched in Hudson ('Miracle on the Hudson' .. 'Sully' feeling fine.)

[central_va]

I am not expert on this, but even if both engines go out, isn’t there an APU (aux power unit) = smaller aux jet engine in the tail capabale of running all systems other than thrust? I know certain older planes had these, I guess one could see if there was a poop chute out the back of an A-320.

Ok so if you are in a fly by cable/hydraulic aircraft with total engine failure, then the emergency proceedure is to turn on the APU? Is that the co-pilots job?

[wyowolf]

apu is ground use. they do have some back up pressure bottles to maintain system pressure in event of both engines failing. Not sure about AB though. Some AC had ram air pumps that would deploy but i dont think AB has those. A lot of pumps are electric on the newer planes. Been awhile since i worked in Hyd shop.

[RaceBannon]

I havent worked on fixed wing aircraft, just helicopters

however, my job now is working on flight turbines that were modified for ground use to generate elctricity

there are several ports on the GG4 and GG8 engines in the main N2 gearbox for hydraulic pumps and fuel pumps

Whether these Rolls engines had these, I cant say

However, I would assume they did for hydraulic assist in powering the movement of the control surfaces

BTW, fly by wire means electronic control of the actuators for the flight controls, not wires from the yoke to control aelerons or flaps or elevators

[RaceBannon]

APU is only electrical power, it runs on jet fuel and that fuel sits in areservoir or is pumped into it from the main fuel pumps off the engine

[JRios1968]

Fly-by-wire only means that the inputs of the pilot on the control wheel and pedals are translated into electrical signals that are then sent to hydraulic cylinders, called actuators, which move the flying surfaces such as rudder, ailerons, elevators and flaps.

This hydraulic pressure is built inside hydraulic pumps which are driven by the engines.

So, the short answer is, "yes, loss of engines equals loss of hydraulic pressure."

Having said that, most modern large jets have a last-resort means of minimal hydraulic pressure and electrical power, called the Ram Air Turbine, essentially a small "windmill" connected to one of the hydraulic pumps and a generator, which pops out of the fuselage upon catastrophic loss of hydraulic pressure in flight. That will provide nominal electrical and hydraulic power as long as the airspeed remains high...at some point, though, it stops being effective.

[xcamel]

They were damaged by the birds, but didn’t detach until they hit the water. As for the hydraulics.. the APU would still have been running and supplied power all the way in.

[NormsRevenge]

Thanks,,

Somebody had to be on the Washington bridge with a camera.. or there has to be a web cam that caught this.. sounds like the engines were there ‘til impact, pretty much dead weight as they spun down,

[Oldhunk]

Here is something I read on another forum:

“Just talked to my dad who was a A320 pilot for a long time. He said if they did lose both engines the controls go into a “reduced” mode and things are not as responsive. He said roll control (ailerons) would not be too bad so he could keep the wings level. However the pitch (elevators) become sluggish where it would be very easy to over control. Also, he would have had a tailwind so he would have been going well over 150 knots. Given all of that my dad figured he did one hell of a job.”

[JRios1968]

As for the hydraulics.. the APU would still have been running and supplied power all the way in.

The APU will not produce enough hydro power to successfully steer the airplane expertly the way Sully did.

My speculation, as a former AF-trained accident investigator, is that the engines possibly retained enough integrity after sucking in geese that they could continue spinning and running the hydro pumps and generators long enough for Sully to find a suitable spot.

[Prospero]

These vehicles are pretty much Fly by Wire, these days. As I'm sure you've guessed, in the older planes, the hydraulics were closed systems. Lost here, lost everywhere. Not since the early 70’s, the Era of the 747, L-1011 and DC-10.

[Hulka]

And this former AF-trained mishap investigator agrees.

(Norton AFB, Class of ‘93)

[Ernest_at_the_Beach]

So my logic would say ,...that on a fly by wire...if you had some batteries on board they would allow a lengthy time to control the flight mechanisms...dropping the landing gear would be a heavy electrical load though I would think...

[JRios1968]

Kirtland AFB, class of 98!

Living now, very close to the old Norton!