-400 Hyd Windmill Speed

[hymie]

Can anyone tell me the min IAS to supply adequate HYD press for the flight controls on the -400 after all eng flameout?

160 for the classic, but can't find anything definite for the 400 in the manuals.

Thx

[Intruder]

0 KIAS for Hyd systems 2 and 3 -- they are backed up by electrically-driven demand pumps.

Nothing in my FHB for 1 and 4 (air-driven demand pumps). The only figure is approx 220 KIAS for airstart with a windmilling engine. If the flaps are up, that's about minimum flaps-up maneuvering speed at light weight, anyhow.

[Cross Check]

:hmm:

-400 what exactly? It may seem like 737's rule the roost here, but it ain't a 737 Forum ... yet :}

Is Victa p.c. over here? No? Okay ... Briggs & Stratton!

[hymie]

Thx for the reply. I am talking about RR powered -400's if that makes any diff. All 4 demand pumps are ADP's on ours, so the only source of power when it all goes quiet is the step aside gear box from the core (I think)

Intruder your answer has me wondering though. I would have thought two hydraulic pumps would have put way too much drain on the batt's, mind you, one only has about 20 minutes to worry about it anyway!

X-Check Sorry, should have been clearer in the Q. Talking about the 744, but will be surprised if you tell me the 73 has 4 hydraulic systems!


5 minutes later....
Oooops, just got out the new manuals, you know, the hard to read ones, and it seems that contrary to the old manuals, some of our newer jets do have electric pumps on 2 and 3. But aren't they powered by their respective DC bus, which in turn isn't powered on STBY (batt) power?

[Intruder]

Cross Check: 747-400.

Hymie:

Ours are all GEs, so I can't address the RR installation. Also, our FHB does not tell me what bus the demand pumps are on. I don't know if they are included in the "various flight control components" powered by the Main Standby Bus or one of the battery busses.

Normally, the demand pumps are not running with the flaps up and normal hydraulic pressure available from the engine-driven pumps. We do not practice 0-engine procedures in the sim, so I can't vouch for hydraulic pressure at windmill speeds (the demand pumps would compensate during any single- or 2-engine failure). I expect, however, that the engine-driven pumps would provide adequate pressure for flight controls at 220-240 KIAS, but would probably bog down on gear or flap extension.

[mustafagander]

B744 demand pumps on #2 and #3 for QF aircraft are electric. They run on a/c, a b1oody lot of a/c. Don't even begin to imagine that the ships battery would have the grunt to energise the relays, let alone turn the pumps (through an inverter of course!!)

As far as I know, min manoeuvre speed will windmill the engine fast enough to keep the flight controls working.

[hymie]

Thanks Mustapha, had a longer look, and realised I may have been drawing a long bow to assume the pumps 2 + 3 are DC powered. Closest hard info I could get was that the "old" config, where all are ADP, has DC elect. control.
Either way, it would seem DC or AC powered, that the elec pumps on 2 and 3 would not be powered in emerg. elec config. (pls excuse airbus expression). So now it seems that the hyd power will only come from pumps 1 and 4 via windmilling step aside core gear box, providing redundant power to the flt ctls, and flaps if you are having a really bad day:(

[mustafagander]

Unless I'm badly mistaken, all 4 EDPs will supply hyd power while windmilling.

How the ADPs are controlled is merely of academic interest if all 4 engs have flamed out, there's no air or a/c power to run them anyhow.

As I understand it, with all 4 engs flamed out, all you have is batt power for lhs flt inst and radio, fire ext, igniters and windmill power for hydraulics.

[hymie]

Ahh, yep, sorry, mixing ADP power, with EDP operation. Knew what I was thinking, just didn't know what I was typing!:rolleyes:

For a simple airpcraft, it can be a little confusing!

Or am I just thick? (rhetorical thanks)

[yachtno1]

I think you still get a/c power even though the engines are windmilling. At least that's what I was told by a BA 744 P1 who really ought to know !;)

[Cornish Jack]

You need to check on engine type for the cut-in pressure for ADPs. GEs and Rollers are different.

[mustafagander]

yachtno1,
You will have no a/c from the eng driven gens - I think the underspeed switch takes them off line about 45%N3/N2. There will be none from the APU - illegal, even if it is being used to supply air. That leaves a teeny weeny bit from the stand by a/c for a few must haves.

Cornish Jack,
The cut in pressures are of academic interest only when there is no air or a/c to drive them.

[Batman]

I can't comment on the -400, but I have been involved with airtests and instructing the dual engine failure on the A320. Sufficient hydraulic pressure, to operate flaps/slats, is available down to about 190kts. Although the systems normally operate at 3000psi, the pressure has to drop to approximately 1700psi before the flight controls are effected and the ECAM caution warns. The drop from 3000-1700psi takes about 30secs, with vigorous control movement, once windmilling has stopped.

[lomapaseo]

with vigorous control movement, once windmilling has stopped.

Minor point I believe, but windmilling doesn't stopuntil you land.

I accept your point about the hyd dropping out at reduced windmill speed.

What windmill speed does the generator drop out?

[spannersatcx]

0 KIAS for Hyd systems 2 and 3 -- they are backed up by electrically-driven demand pumps

Sorry not so, electric demand pumps are optional, we have Air Driven demand pumps on 2 and 3 hyd. Some also have 1 & 4 electric aux pumps, but not all, if it's an option that you pay for then we don't take it!

As stated it's irrelivant anyway, just for info.

[*Lancer*]

mustafagander, don't forget the flight deck storm lights and whatever electronic control there is for the fuel! :)

Have seen the LHS EFIS go out with all the engines, although know the reference you talk about... Not sure if it's a 'simism' or something that might be prone to happen on some aircraft with certain electrical configurations...

[Golden Rivet]

757/767 will quite happily provide full hyd pressure(lower flow rate though) when dry motoring the engines on starters, so should provide adequate pressure when windmilling.

would imagine 747 would'nt be much different.

[Notso Fantastic]

You will not get any operation of electric hydraulic pumps when windmilling. The AC supply will fail on you- a windmilling engine will not still supply AC. The battery will just supply up to 30 minutes of emergency supply for minimal lighting and instruments. The windmilling engines at low flying speed will still supply enough hydraulic pressure through the engine driven pumps to power the control surfaces. Flaps and undercarriage should still operate through 2 of the hydraulic systems allowing flying controls to still function through the other 2 systems.
A 4-engine failure scenario is not practiced on the 747 as it is considered out of the bounds of probability. Twin jet pilots do practice total engine failure landings (and great fun they are too!)
A diagram of a 747 style hydraulic system can be found at
http://www.patprojects.org/dec98sca/av1b_2.htm
It shows the complexity and sharing out of services between the 4 systems

[HotDog]

Seems like computers have not been able to completely replace the flight engineer!;)