B737 MRG AND CC questions

[Raptor71]

Hello everybody,

I was reading the MRG and CC and some questions came at me:
If I can get some help on these ones:

ELECTRICAL:

==="The battery charger will not enter in the charge mode when BAT OVHT, APU START, DC1 and TFR1 unpowered, refuelling panel open."

I know that the charger has two modes ( charge and TR); I also understand that during the TR modern the charger still supplies the battery to maintain it charged.
If I understand why the charger would not charge the battery in the event of an OVHT, what about the other conditions?
I suppose that in the event of a DC1 and TFR1 failures, charger power is kept to feed the battery bus, ac and dc stay busses even if it means stopping the supply to the battery.

=== Battery OVHT: loss of hot batt and sw hot batt bus ( source: MRG and CC)...on the schematics it does not look obvious....


HYDRAULICS

===Can we assume that the 760kg fuel limitations also applies to the engine driven pumps? I mean: the fluid going to the EDP is also cooled by the heat exchanger, running this pump with low fuel in the tank could definitely damage the pump right?

===System A: two standpipes and only 1 for system B...why?

=== No OVHT light for the EDP...is these pumps not likely to OVHT?

=== Can somebody explain me the case drain the hyd pumps...where goes the fluid after cooling the components? Does it go back to the reservoir? I do not see any lines in the WW....

=== PTU: is it activated with flaps at 15? or less than 15?

=== Aileron trim INOP with loss of sys A and B....I assumed that it was electrically activated....

=== MRG schematics: if you decided to close the FLT CTRL SOV, you would loose the autopilot too ( and YD for system B)


Some more are coming most probably/

I would like to finish with some perf questions:

I did some simulations on the OPT:
In the example I took:

a full rated T/O at 22k gives N1: 93.9 and with ATM 93.0 with 33 degrees
a full rated T/O at 24k gives N1: 96.1 and with ATM 92.9 with 40 degrees

My question is: what option is better for engine life in the ATM case?
Is a decrease of 1% N1 at 22k and 24k produces the same amount of EGT decrease?

Thanks guys....

[Raptor71]

nobody knows??

[Aloha_KSA]

Very technical questions. Are you an engineer?

This site has some fantastic info for you to poke around in: The Boeing 737 Technical Site (http://www.b737.org.uk/)
Regarding Hydraulic Pumps - If one is down to less than 760 kg in a tank, you've got about 30 minutes left before you become a glider. You need the EDPs to put the gear down, power the flight controls, flaps, etc. That would not be a good time to be shutting off your EDPs, would it? Also, the mechanical pumps must have a much higher heat tolerance.

Regarding the PTU, if the flaps are anywhere more than 5 units the LEDs will all be fully extended, so the PTU is irrelevant at flap settings greater than 5.

Regarding the standpipes - those are feeds for the various systems. One of the feeds from the B system is the one that does not have a standpipe, it is the PTU. The PTU is a motor, not an actuator, and is not likely to leak. The A system, on the other hand feeds the landing gear actuators which use a LOT of hydraulic fluid and are more likely to leak, than, for example, the Flap motor powered by the B system.

For your performance question, the Assumed Temp N1 is the same (almost) for both, so there is no difference.

Maybe go over to the B737Theory page on Facebook and look for your answers. If not already addressed, you could post there and discuss with a like-minded crowd.

[Themax23]

Hello,

PTU: is it activated with flaps at 15? or less than 15?

If you read the FCOM you'll have your answer : "flaps are less than 15 but not up"

Also, on some aircraft with the short field performance package, this condition is changed to "flaps are not up".

Aileron trim INOP with loss of sys A and B....I assumed that it was electrically activated....

Yes the aileron trim is electric but it moves the feel and centering unit. If you lose all hydraulics you revert back to manual reversion. It doesn't matter where the feel and centering unit is centered as you'll have to use manual force on the whole range, and no hydraulic pressure to center your ailerons at the trim position.

[B737900er]

The MRG and CC are great study tools. If you want to understand the system better I recommend reading Boeings official documents.
FCOM 2 will answer all your questions!