The A320 Family has different fuel systems for the A318/319/320 and for the A321.
Here’s why !
The A320 has a rather complex fuel system. With both Outer and Inner tanks, similar to those found in much larger airplanes.
The A321’s rather simple design fuel system has just 1 wing tank, without needing complex systems.
The wing tanks on A320 are divided into inner and outer wing tanks.
As the fuel from inner wing fuel tanks is consumed and reaches around 750kgs, a transfer occurs and the fuel is transferred from the outer wing tanks using gravity.
The OUTER wing tanks on A320 hold only 690kg of fuel. It remains there in cruise until the Inner tank reaches 750kgs, the transfer valves then open allowing this OUTER fuel into the INNER tanks.
This was designed to reduce wing tip flutter at some high Mach Nos. & Flight Levels.
A321 does not require this feature, and only has a single tank in each wing.
The A321 (being the largest A320 family member) was designed to carry much higher weights while keeping the same wing.
This required a reinforced wing due to higher weight of the fuselage. The wing root structure is more substantial when compared to shorter versions.
Hence there was no need for outer cells to compensate wing flatter. Need for fuel as weight to relive stress was no longer required.
Did you know : This also is the reason why the A321 has a lesser capacity of the wing tanks when compared to A318/319/320.
Author – Arjun Singh ( Airline Captain A320/B737)