News:

Precision Simulator update 10.173 (24 February 2024) is now available.
Navburo update 13 (23 November 2022) is now available.
NG FMC and More is released.

Main Menu

Windmill driven hydraulic pump

Started by Hardy Heinlin, Tue, 26 Apr 2011 16:09

John H Watson

The ailerons might not be a good system to start with. It has two stages of hydraulic assistance.

The control wheel moves steel cables which input into hydraulically-powered Central Lateral Control Control Packages (CLCPs) in the wheel wells. These operate steel cables which run along the wing (rear spar). The cables operate levers which control valves on Power Control Packages (PCPs). These are hydraulically powered actuators which move the ailerons.

The autopilot servos input into the CLCPs, rather than into the PCPs (a la Airbus)

JHW

Jeroen Hoppenbrouwers

#21
Quote from: Hardy HeinlinH = A means: Aileron motion freezes at current position
H < A means: Aileron moves to neutral
H > A means: Aileron moves away from neutral
It is very much like your electrical power distribution grid/tree.

Pumps provide pressure, "voltage". Below a specific pressure, different per device, the device refuses to cooperate (in most cases, a device won't operate negatively, as hydraulics have two channels in antiparallel). When cooperative, depending on the device, a certain "amperage" volume flow is drawn from the pumps. Brakes require relatively little volume, flaps require an immense volume. Pressure drops little with one single firm brakes application (if there is no skidding), but nearly completely with flaps extension. When flow stops, the pumps can very quickly raise the pressure again, but a weak pump will not be able to sustain pressure even with light flows.


Jeroen

Hardy Heinlin

Exactly.

In the electrical model I have "electric adapters" (ea...), these are the interface of all electrical objects.

In my hydraulic energy model I now have "hydraulic adapters". When an object is moving, it tells the pumps via the adapter how much pressure is needed in this moment. Vice versa, the windmilling pump tells the object on the other side of the adapter how much pressure is available in this moment. Then again, the object's motion rate is adjusted according to the present pressure.

This has an interesting effect on the EICAS psi values. It feels very lively and intuitive. Like pushing on a rubber duck. The more N2 drops below idle, the softer the duck.


|-|ardy

Jeroen Hoppenbrouwers

To equal the electrics model, I think (intuitively) the pumps should tell the objects the pressure they currently provide (compare bus tension) and in response the objects tell the pumps how much volume flow they draw (compare bus current). Working with just pressure may not be the right way. In your electrics model, the objects 'know' below which supply tension (voltage) they stop working, but this does not influence the current from the bus directly.


Jeroen

Hardy Heinlin

#24
I mean the same, I just used different words.



Quote from: Jeroen HoppenbrouwersIn your electrics model, the objects 'know' below which supply tension (voltage) they stop working, but this does not influence the current from the bus directly.
Actually, it does. Every data exchange is immediately forwarded through all busses and subbusses that are part of the tree. In the hydraulics, this is simpler as there are no trees, just some parallel pairs.
Also, in the electrical model there are some objects that operate at variable voltage, e.g. the lights. When the voltage drops, the amperage drops as well. This is a bit more like the hydraulic model. When the available pressure reserves drop, the motion rate of the "consumer" will drop as well.


|-|

delcom

Quote from: Hardy HeinlinMoin,

I wonder what kind of relationship exists between N2 RPM and EDP generated hydraulic pressure.

Nice one Hardy,
As a matter of fact, there should be three different graphs, since there are three different EDP pad ratios for the three different engine types.
0.389:1 N2 PW4000
0.344:1 N2 CF6
0.3842: 1 N3 RB211

For the bird herself it is the flow, for the sim user it's the indicated pressure that matters. The indicated pressure is just the result of flow demands at a given time.

regards,
delcom

Hardy Heinlin

Thank you, Delcom.

The factors you mention, to which parameter does it refer? N2 or psi?

0.389 x 3000 psi = 1167 psi

0.389 x 60% n2 = 23.3% n2

I understand it's averaged. I'd just like to know the principle.


Cheers,

|-|ardy

delcom

I'll dig in my notes, see if I can come back with some usable info.
Available system pressure indeed can be derived from N2 and N3, however things might get a little complex even when we only focus on lateral control system. The aileron dual tandem actuators get even more complicated when only one hydraulic system is present, valve drag and airloads modify actuator rate. Blowdown...when aerodynamic load pressure exceeds available PCU supply pressure (minus return pressure). Then we have a number of spoilers, not to mention autopilot input that again will change flow demands resulting different system pressure. The formula can be looooong, so many variables and constants to plug in.

regards,
delcom

delcom

#28
No, those are EDP input shaft RPM to N2 RPM (and N3) ratios. It's a gear(down) ratio.

EDIT: This will be important later on.
Once we've figured out the EDP flow, pressure characteristics...it will be very easy to "install" the very same pump on your three different engine models,  resulting different feelings while flying on windmilling EDP's only.

delcom

Hardy Heinlin

#29
I have something like this already in my algorithm. It was essential right at the beginning because my N2/N3 idle values vary according to weather and EEC status. (In PS1 there were fixed minimum idle and fixed approach idle).

(actual N2) / (idle N2 reference) = "EDP force reserve" factor

If (actual N2) > (idle N2 reference)
-- factor always 1.0
else
-- (actual N2) / (idle N2 reference)

Example:
70% actual N2,  60% idle reference : 1.0 force reserve factor
60% actual N2,  60% idle reference : 1.0 force reserve factor
30% actual N2,  60% idle reference : 0.5 force reserve factor
00% actual N2,  60% idle reference : 0.0 force reserve factor

The lower the factor the more sluggish the controls. The psi value will always return to 3000, but the recovery time back to 3000 will increase when the factor decreases. Below a certain psi limit, there will be no recovery at all.

Some single/dual powered motion rates are known. For the aileron it's ca. factor* 2.0 when powered by two hydraulic systems, and factor* 1.4 when it's just one. Coincidentally, 1.4 is the square root of 2.0.

* Yet another factor, for motion rate, not for force reserves.


So with the known results, I can bridge those mechanical algorithms that lie between EDP RPM and flight surface behaviour. I link the relationship directly.


Cheers,

|-|ardy

Mundyas

Hi |-| et al

Earlier I  gave you |-| the aileron figures for completeness here is the rest of the information in that book. (Re 747 Classic)

More .....
"single surfaces with a double hydraulic supply will operate effectively in the event of a single hydraulic failure. The following are the design rates for those primary services with 2 hydraulic supplies:-
(excluding aileron)

Rudders - 2 hyd systems 50 - rate (degrees / second) - I hyd system 40 rate degrees /second)
Inboard elevators - 2 hyd systems 37 down , 37 up (degrees/second) - 1 hyd system 30 down, and 26 up degrees /second "

From the book previously mentioned which is very good I think.
A

Hardy Heinlin

#31
Thank you A,

meanwhile I got mine back from the basement :-) This book is still fascinating. Whatever page I open, any page at random, I almost can't stop reading. Every statement immediately makes sense, is promptly clear, he sort of answers any question in advance, mostly within one and the same elegant sentence. I don't need to stop and wonder. The text runs directly into my neurons. I wish I could write so well.

Also interesting to rediscover all the features that the -400 and the classic have in common.


Cheers,

|-|ardy

Zinger

A side comment about hydraulic systems design. The pumps build rated pressure at RPM lower than idle, and at rated RPM a significant amount of their output is sent to the return line by the pressure regulating valve. All this while no significant use takes place by hydraulic consumers, and the flow merely cools the pumps. With increasing RPM, pump output can increase and sustain nominal pressure with hydraulic consumer demand. A common way of increasing pump output is by increasing an inner slope which increases pump valve strokes and redirects more pump valve output to the pressure line.

Quote from: Jeroen Hoppenbrouwers
Quote from: Hardy HeinlinH = A means: Aileron motion freezes at current position
H < A means: Aileron moves to neutral
H > A means: Aileron moves away from neutral
It is very much like your electrical power distribution grid/tree.

Pumps provide pressure, "voltage". Below a specific pressure, different per device, the device refuses to cooperate (in most cases, a device won't operate negatively, as hydraulics have two channels in antiparallel). When cooperative, depending on the device, a certain "amperage" volume flow is drawn from the pumps. Brakes require relatively little volume, flaps require an immense volume. Pressure drops little with one single firm brakes application (if there is no skidding), but nearly completely with flaps extension. When flow stops, the pumps can very quickly raise the pressure again, but a weak pump will not be able to sustain pressure even with light flows.


Jeroen
Regards, Zinger

dutch57

Hardy,

About hyd pumps, yes the pressure is importand, Boeing decided on 300psi, so pump is calibrated at 3000 psi, but the flow rate is important for the actuators how fast can you get the fluid where is should be.

The engine pumps and airdriven pumps are rated 3000psi at 50usg/min.
With engine in idle.

The electric pumps are rated much lower 3000psi at i thought about 12usg/min.

Lets say when cranking an engine, 20% N-2 and you use the Flaps to extend from 1 to 5 units, the hydraulic system cannot cope(no flow and pressure drop) and the flap system will revert to primary electric mode.

Same when you loose hyd-1 or hyd-4.

Also because of the high cunsumers Flaps and gear there is a priority valve in the Flap system

Hope this sheds some light in the world of hydraulics

Bob

stevejeff

#34
I wonder if in real-life, you loose all hydraulic systems, will the surfaces be locked-in place or they will be freefloating moving?

I mean either you don't have any pump working or if you have hyd leak and loose all pressure. I think these 2 situations are different.

Thank you so much!

John H Watson

#35
QuoteI wonder if in real-life, you loose all hydraulic systems, will the surfaces be locked-in place or they will be freefloating moving?

It depends on the surface. Some surfaces have hydraulic brakes. If you lose hydraulic pressure, the brakes are applied. e.g. horizontal stablizer. Surfaces like the rudders have no braking, so can be moved (by the wind, for example).

There may be differences between pressure loss and losing hydraulic fluid. Fluid under no pressure but trapped in the system may act as a dampener. The surfaces may not move as quickly if subjected to rapidly changing air forces.

Some control surfaces may be counterbalanced, so will stay in (roughly) a faired position after hydraulic pressure is lost. Some may simply droop (if not acted on by aerodynamic forces).

stevejeff

I was wondering about a total hyd loss, how surfaces gonna react regarding flutter. I know it's an extremely improbable scenario to loose all hyd systems, but if the surfaces would be freefloating, they might be prone to flutter, considering that most jets hyd actuated surfaces are not balanced.

Avi

Quote from: stevejeffI know it's an extremely improbable scenario to loose all hyd systems...
Actually there are at least 3 cases where it happened I can give you from memory: JAL123 (B747SR crashed in Japan), UA232 (DC10 crashed in Sioux City) and DHL A300 that was hit by a ground to air missile but landed safely in Baghdad.
Avi Adin
LLBG

stevejeff

Quote from: AviActually there are at least 3 cases where it happened ...
I know and that not only reinforce the doubt.