to member DELCOM

[luxair_ca]

hello antony

can you please send me an email or can you contact me via sms or msn or whatever....would be nice to get in touch with you again....long time not seen

marc

[delcom]

Sure thing Marc...was out on vacation for a while. No PC, no 744, no phone. Only beer and my tent for two weeks. Now everything is back to normal (with less brain cells from now on).

delcom

[Hardy Heinlin]

Hi Delcom,

I'm having a similar question. Since you have offered your help ... if you don't mind and when you have some spare time, could you email me? :-)

If it's not possible, I'll accept it also, of course.

Thank you!

Cheers,

|-|ardy

info at aerowinx.com

[Will]

Delcom, no need to email me... I have just one simple question.  Why does the animation on your signature stop before the gear doors are completely closed?

[delcom]

It's a bunch of still images put together into an animated gif. Somehow I failed to capture that part of the cycle. I had some low light, focusing problem. Didn't have a tripod...I think I shot it from the top of my toolbox. Plus I was in radio contact with my pal up in the office playing with the lever.

I've made several attempts, different angles, NLG, BLG, WLG...still have those images somewhere. Nowadays we only play with shitty mobile phone cameras, we tape them to weird places (like inside the leading edge cavity, then we retract her)...interesting little movies.

cheers,
delcom

[Avi]

... (like inside the leading edge cavity, then we retract her)...interesting little movies.

Which we all, I'm sure, love to see. Can you upload it somewhere?
Thanks,

[delcom]

Hardy,
I've made an attempt to drop you a mail, to my surprise I was missing my SEND button. Yeah, I found it weird, too. Please, do not hesitate to write any requests temporarily...let's say here. I'm on the case, to find out what's with my email thingy.

All I can say now: Hardy, at your service.

sincerely,
delcom

[Hardy Heinlin]

Good evening, Delcom,

thank you.

Do you have some approximate numbers regarding the (de-)pressurization time of the hydraulic pumps? Or perhaps even a curved graph if the timing is not linear?

Just an approximation would be fine (nanoseconds are not required).

Cheers,

|-|ardy

[delcom]

Sure thing Hardy,

"regarding the (de-)pressurization time of the hydraulic pumps?"

Are you sure you didn't mean SYSTEM depressurization? Just in case you really wanted pump depress time, it takes 1.0 sec for the EDP depressurization circuit to drop the discharge port to zero flow. A whole lot of sequenced things happen inside the pump when the solenoid gets energized....and yes it takes a second. For ACMP, ADP and AUX ACMP you can count with the spool down time of elec motor or turbine drive. No depress circuit tor these boys...since you can turn them OFF. (unlike your EDP, it runs all the time regardless of switch position)

If you meant SYSTEM pressure decay...that's an other story, and different for each hydraulic system, since the characteristics of the four hydraulic systems are totally different. Interested?

cheers,
delcom

[Hardy Heinlin]

Sorry, my question was a bit unclear. I mean the system pressure as indicated on the EICAS. I guess, how fast the pressure rises or decreases also depends on what pumps (EDP, DEM, AUX) are running and on how high the demand currently is (flaps or gear in transit etc.). Anyway, an average value would be helpful.

So, yes, I'm interested :-)

Thank you,

|-|ardy

[delcom]

HYD SYSTEM pressure decay times are the following for the four systems:
SYS 1: 20.8 sec
SYS 2: 26.3 sec
SYS 3: 25.5 sec
SYS 4: 26.2 sec

Assuming no loads, healthy hydraulic system, pump turned off at zero second. These times are from 3000 PSI down to 100 PSI. Below 100 PSI the curve is extremely shallow, takes hours to drop to reservoir head pressure. Minimum indicated system pressure equals current reservoir pressurization pressure value.

cheers,
delcom

[Hardy Heinlin]

Hi Delcom,

thank you very much.

Is it pure coincidence that Sys 1 drops faster or is it because Sys 1 incorporates an AUX pump?

...

Can I assume the pressurization from ca. 100 to 3000 psi takes about 1 to 2 seconds?


Regards,

|-|ardy

[delcom]

Hi Hardy,

"Is it pure coincidence that Sys 1 drops faster or is it because Sys 1 incorporates an AUX pump?"

I wouldn't really call that a coincidence, it's just simply the result of consuming component numbers, sizes, volumes, height etc. that is unique to each system. The system pressure decay curve is not affected by the type or number of hydraulic pumps installed on a hydraulic system. Once a fluid particle has passed the last check valve (in the pressure module) cannot flow back, so it does not matter where that particle came from. If it could, then definitely would matter what size of pump this particle needs to get squeezed back into. Remember, each pressure module has four inlet ports, but only one outlet port, (two outlets actually, but it's irrelevant now) where the system pressure transmitter is installed.

"Can I assume the pressurization from ca. 100 to 3000 psi takes about 1 to 2 seconds?"

The four hydraulic systems are different in volume (plus again different components, resistance to flow, etc), so it takes different times to pressurize each system. What's more important is what you pressurize that system with. Pressurizing the system with its tiny AUX ACMP will take a lot longer than doing it with the more powerful ACMP, or with the real big loud boys namely the ADP's. An AUX ACMP is rated at 5.7 gpm, this little pump is either OFF or rotated 5800 rpm by its little electric motor.  An ACMP is rated at 12 gpm, this big pump is either OFF or turned at 6000 (i think) rpm by its rather big electric motor. Then finally the ADP, which is even a bigger pump. Rated at a serious 32 gallons a minute. And again it's either OFF, or turned at 3200 rpm by the screaming very very loud turbine drive installed on the top of it.

All these pumps are driven at a constant speed by pneumatic or electrical power. Unlike the EDP. Well, remove the hydraulic pump from the turbine drive and install it on the engine. These two pumps are interchangeable. One can see it straight away, that from this moment its characteristics will depend on N2 (N3 for the RR) rpm.

Ok, back to your question again. Time.
SYS 4 is unique when it comes to system pressurization for the first time. Pressurize it, depressurize it. Pressurize it again and you'll notice that 3000 psi was reached faster for the second time. Why? Because the first time the pump was fighting against the nitrogen in the parking brake accumulator. Once it is charged, the second time pressurization will take less time.

Sorry Hardy, I've gotta run right now (unexpectedly). Tomorrow I'll continue.

cheers,
delcom

[Will]

Hardy and delcom, thanks for having this discussion in public!

[Avi]

In continuation to what delcom said, while the customers of hydraulic systems 2 to 4 are in the wings and tail areas, system number 1 also has a customer in the nose (nose gear). That means there is an extra (relative long) pressure and return lines to the nose of the aircraft and it is more than possible it effects too.

[delcom]

So here is what happens on the EICAS HYD page pressurizing SYS 4 with AUX ACMP. Brake accumulator was depleted prior to turning the rotary to AUX, no flight controls were moved during the process, no brakes were applied whatsoever.

Prior to pressurization:
AUX pump full circle symbol is white with white OFF legend inside of it.
Obviously no green flow bar.
PRESS amber 70 psi. (this morning happened to be 70)
Case drain TEMP 31 deg C.

Zero second...Switch turned from OFF to AUX. Click.
PRESS increases immediately.
0.8 sec...White pump circle is replaced with amber circle, but OFF remains for an additional tenth of a second inside. PRESS reading is 290 at this moment.
0.9 sec...OFF legend is replaced with two amber vertical lines, rendering the valve symbol in the open position. Two little arcs removed from the top and bottom of the circle. PRESS is at 310 psi.
7.6 sec...1310 psi reading changes from amber to white.
7.7 sec...1400 psi green flow bar is drawn. Valve symbol changes from amber to white.
13.4 sec...3000 psi reached.
pressure changes rapidly between 3030 and 2970 up and down...then at about 16 sec it stabilizes.
Case drain temp remained 31 deg C during these 16 seconds. During the next few minutes I had my early morning coffee, and enjoyed the winter scenery from the slowly moving office. We just had to park her someplace else.

regards,
delcom

[Hardy Heinlin]

Thanks a lot, Delcom. That helps.

It's obviously much slower than I expected :-)


Regards,

|-|ardy

[delcom]

Actually it is 1300 psi when the system pressure switch logic turns the amber digits to white digits during pressurization. No time delay. I's just my camera that wasn't able to capture the color change at the exact moment.
I also found this 16 seconds a little too long. Hardy, you have an other choice...you might wanna go with the time value published by the manufacturer. They must have had the ideal setup, perfectly bled system, etc. According to those graphs an AUX pump that is installed on SYS 4 is capable of pressurizing its system (including the accumulator) in 6.8 sec. Unlike the half ready bird (D check) I did my test on the other morning. Probably it was full of air. Now, that only changes the time, not the logic of color changes.  

During depressurization it's 1200 psi + 2.0 sec delay. So you may be able to see a white value let's say 1120, depending how fast the pressure is decaying. No airline options here, nor engine type effects system low press indication logic. SYS FAULT light comes and goes (if it's not triggered by high case drain temp, or low reservoir quantity already)exactly the same moment when the digital PRESS readout changes color on the EICAS HYD page. And this applies to any of the four hydraulic systems.
ON: 1200 PSI + 2.0 sec
OFF: 1300 PSI

Things get a little more complicated with the rest of the pumps logic with all the different airline options, different engines etc.
EDP press times during engine starts, ADP press will follow shortly...I'm in the middle of a birthday party (not mine) right now. I go and have another beer instead. Cheers guys.

P.S: I'd better record times and pressures during and/or after the test flight. Those numbers will be more realistic.

take care,
delcom

[Phil Bunch]

Hardy and delcom, thanks for having this discussion in public!

I agree - it is somehow VERY interesting to read about the details of a 747-400.  I think Jeroen once characterized us as members of a religious cult, which seems correct at a superficial level...or perhaps it is correct at a deeper level!

I guess this is a sign of a hard-core PS1/PSX enthusiast.  

There Ain't No Such Thing As Too Much Information - TANSTATMI

(Patterned after the well-known slogan, "There Ain't No Such Thing As A Free Lunch" - TANSTAAFL.

[delcom]

That means there is an extra (relative long) pressure and return lines to the nose of the aircraft and it is more than possible it effects too.

Indeed, Avi

Only SYS 1 has lines routed to the nose section for nose gear and door retraction/extension plus NLG steering system. Also SYS 1 lines reach to the highest point in the tail, powering the upper rudder top actuator. Therefore the volume of SYS 1 is the largest, 227 liters of hydraulic fluid you'll need to fill it up.
Second place goes for SYS 4...volume is 193 liters.
Third in volume would be SYS 2...128 liters,
The "smallest" system is SYS 3, with 124 liters.
Total would be 672 liters, unfortunately this still will result in 0.00 EICAS quantity value. Additional 2 times 40 liters will go in the outboard reservoirs, plus 2 times 26 liters in the inboard ones in order to achieve 1.00 QTY.
She needs about 800 liters of purple fluid in total. Not bad.

Will be back soon,
d