B737 Questions

[BMM389EC]

A few questions on the 737-200.

1.Boeing says that g load effects the crossover speed(when aileron and spoilers will no longer be enough to counteract a full rudder deflection). A higher g load means a higher crossover speed. Why?

2.Aircraft have block speeds- below which we must not fly without selecting the next flap. Eg, in the 737, 210kts is the lowest clean speed, 190kts the lowest speed for flap1 etc. How is this speed determined and what protection does it give you? Is it the same for all flap settings?

3. Both the A and B system hydraulic pumps use fuel for cooling, yet the manual only states a minimum of 760kgs of fuel for the B system pumps, and says nothing about a minimum for the A system pumps. Why?

Thanks for the help.

[ 02 October 2001: Message edited by: BMM389EC ]

[avmech]

I am unqualified to answer your first 2 questions, but as far as hyd. cooling, the 737 uses two identical "radiators" one in each fuel tank for hyd SYSTEM not pump cooling. The fuel requirements should be the same for each system as the radiators are in the same place in their respective tanks.One addition point is that the left tank contains the system A cooler and the right tank the system B cooler. If you ever experience fuel migration, note the hyd. quantity, you could be "making" fuel. Not a likely scenario, but certainly not impossible.

[FuelFlow]

BMM389EC

With reference to you question on the Flap Schedule/Maneuvering Speeds, this is what boeing have to say.

" The flap maneuvering speed schedule provides the recommended maneuvering speed for various flap settings. When recommended procedures are followed, the schedule provides adequate buffet margin for an inadvertent 15 degree overshoot beyond the 30 degree bank.

The flap maneuvering speed schedule varies as a function of gross weight and will provide adequate maneuver margin above stall at all weights.

The schedule provides speeds which are close to minimum drag and in climb are close to maximum climb gradient speed. In level flight it provides relatively constant pitch attitudes and requires little change in thrust at different flap settings.

During flap retraction/extension, selecting the next flap setting should be initiated when reaching the maneuver speed for the existing flap position. Niormally the A/C should be accelerating when flaps are retracted to to the next position.
Acceptable maneuver margin is, however, retained at a speed 20 knots below the recommended speed."

With regard to the Hydraulic system

The fuel is required in the tanks to cool the Hydraulic fluid as it passes through the heat exchanger. A system, the excahnger is located in the # 1 fuel tank, while the B system exchanger is located in tank # 2.

A system pumps are engine driven pumps, while the B system are electric.
Boeing says that a minimun of 760 KGs in tank 2 for GROUND operation of B pumps.
I would think that the same limitation would be on the A system, but when would you have the engines running, to provide A system pressure with less than 760 KGs in the # tank?

Possible the B system limitation would be directed at Maintanance, while the A/C is under tow for eg.

Anyway thats my pennys thought

[Checkboard]

A system pumps are engine driven pumps, while the B system are electric.
Boeing says that a minimun of 760 KGs in tank 2 for GROUND operation of B pumps.
I would think that the same limitation would be on the A system, but when would you have the engines running, to provide A system pressure with less than 760 KGs in the # tank?

On the 737-300, the A system comproses the ENG 1 engine driven pump, and the ELEC 2 (Main Bus 2 powered) electric pump, while the B system comprises the ENG 2 engine driven pump, and the ELEC 1 (Main Bus 1 powered) electric pump. The manual requires 780 kgs in the relevant tank for electric pump ground operation - as you wouldn't taxi or take off with the electric pumps turned, off that covers engine operation as well.

Is the 737-200 THAT different?

[Jamesel]

The 737-200 uses both engine driven pumps to power the "A" system, and both electric pumps to power the "B" system. The "A" system hydraulic fluid "intercooler" is located in the #1 fuel tank (left wing), and the "B" system cooler is in the #2 fuel tank (Right wing). Our FOM says minimum of 1675 pounds in each wing tank, during ground operations. Just a wee bit different in detail. :)

[avmech]

One more minor difference, the 737-100/200 have a hydraulic ground interconnect to power A system hydraulics on the ground(requires brakes to be set). The 737-3 through 9 do not have this because they have 1 engine and 1 electrically driven pump in each system.

[GoodToGo!]

Checkboard,
Yes, as others have already pointed out, the 737-300 hydraulic system is indeed different to the 737-200. In fact the 737-200 hydraulics probably share more similarities with the 727 than with the later 737's. ie. System A uses Engine Driven Pumps, System B uses Electric Motor Driven Pumps and a Hydraulic Ground Interconnect joins the two together for ground purposes......

Cheers!

GTG! :D