Project Tupolev Team :: View topic - Tu-134 Fuel System

Freddie · ÊÂÑ

The fuel system of Tu-134 consists of 3 integral tanks per wing:
root tank #1 - 4900 l/3930 kg
middle tank #2 - 2190 l/1750 kg
tip tank #3 - 1150 l/920 kg
Some aircraft are equipped with two flexible center tanks designated as #1A (that is the variant we see in FS). Each tank #1A is directly connected to the tank #1 and extends it's capacity by 750 litres (1500 litres or 1200 kg in total).

Each tank #1 includes a feed cell from which fuel is fed by two boost pumps to the engines and APU. Fuel from all tanks in the same wing is transferred to the feed cell by fuel transfer pumps. Two of them are installed in each tank.

In order to keep aircraft balance fuel in Tu-134 is transferred in so called "stages". There are 4 of them:
I - tanks #3
IIA & IIB - tanks #1/1A
III - tanks #2

Fuel system automatcally operates the transfer pumps as follows (full fuel load assumed):
1. stage I (tanks #3)
2. when 300 kg is left in tanks #3, stage IIA (tanks #1/1A) becomes active
3. when 4100 kg is left in tanks #1/1A, stage I deactivates
4. when 2200 kg is left in tanks #1/1A, stage III (tanks #2) becomes active
5. when 150 kg is left in tanks #2, stage IIB activates (in fact it's only formal as transfer pumps in tanks #1/1A just keep on going as before)
6. when 1700 kg is left in tanks #1/1A, stage III deactivates and the remaining fuel is consumed from tanks #1/1A.

When a fuel stage activates (or should be activated if manual transfer is used) a corresponding yellow light on top of the fuel panel turns on and remains lit till the end of flight. Also a triangular red warning light on captain's panel starts flashing meaning that crew shall check the fuel panel state. The red light can be extinguished by pressing on it.

Manual Fuel Transfer:
When Automatic/Manual Fuel Transfer Switch is in down position the manual fuel transfer is active. This mode is used when there's a malfunction in fuel system automatics. When a Fuel Transfer Stage yellow light turns on a corresponding transfer pump switch underneath it should be moved to the up position (on). Only stage I and III pumps can be switched manually, stage II pumps always turn on automatically. If fuel tranfer pumps do not start (as indicated by the green lights) they can be forced on using the guarded switch on the upper right side of the fuel panel. When all fuel from a stage has been consumed it's transfer pumps should be turned off.

According to the Aircraft Operation Manual 3 fuel loads are normally used:
Full - 18000 l/14400 kg total, all tanks topped off.
Medium - 12800 l/10200 kg total, 4180 l/3350 kg in tanks #1/1A, tanks #2 full, tanks #3 empty.
Minimum - 9360 l/7500 kg total, 2500 l/2000 kg in tanks #1/1A, tanks #2 full, tanks #3 empty.

Fuel System of SCS Tu-134:
In FS model fuel system somewhat differs from the real aircraft. The most notable difference is that there's one center tank instead of two #1A tanks.
Center = tanks #1A
External 1/2 = tanks #1
L/R Aux = tanks #2
L/R Tip = tanks #3

Contrary to the real aircraft where fuel from tanks #1 and #1A is consumed simultaneously as they are interconnected, in FS fuel from the center tank is used the last. There's also a bug in fuel transfer stage lights operation. When stage III activates the corresponding yellow light does not turn on while the red warning light on captain's panel starts to flash normally. Stage III yellow light comes on only when stage IIb activates. Stage IIb yellow light turns on when fuel from center tank is being used. Also the crossfeed valve is inoperable in v0.9.5.

If one wishes to have a non-standard fuel load it is recommended to use the fuel load calculator available here http://tu-134.nm.ru/files/tu-134_service.zip Otherwise if you get a wrong fuel load you may find your engines flaming out even there's plenty of fuel onboard.

Fabo · ÊÂÑ

Long, but nice Õîðîøî

KFC · ÊÂÑ