The A321 was developed from the A320 about 30 years ago. The A321 kept the A320’s base wing with a 5% enlarged wing area by extending the trailing edge devices of the wing. The flaps were also changed to give the A321 a more nose down landing attitude.
The fuselage was stretched by inserting two plugs fore and aft of the wing, 14A and 16A in Figure 1.
With the longer fuselage came more passenger capacity but also higher weights. With a wing which is the same except for a 5% increase in wing area the aerodynamic loading of the wing increases.
The so-called Wingloading at Maximum Take-Off Weight (MTOW) goes from 640kg/m2 for an A320 to 750kg/m2 for the A321LR. A higher Wingloading means longer take-off distances and lower cruise flight levels. Lower cruise flight levels mean less ideal routing when crossing the Atlantic for example.
The other problem with the A321 wing is the fuel volume stayed the same between the A320 and the A321. Normal for airliners is to house the fuel in the wingbox of the wing, Figure 2.
The tank volume in the wing for A320 and A321 is 23,800l. For the A321LR to fly to its maximum range this is not enough.
When an A321LR is loaded full with passengers and the wing tanks are filled, there is still about 7 tonnes of fuel which could have been added if the tanks were larger. With full wing tanks, the A321LR can fly 3,000nm.
To fly further, more tank space must be found. Figure 2 shows how extra Additional Center Tanks (ACTs) can be installed in the aft and forward cargo compartments. The figure shows two ACTs placed in the aft compartment.
The A321LR is normally equipped with three ACTs, where the last tank is placed ahead of the wing in the forward cargo compartment. With three ACTs the A321LR can fly the advertised 4,000nm but not longer. To fly further we need more tank space and a higher Max Take-Off Weight (MTOW) than the present 97 tonnes.
Requirements to take away market from the NMA
The NMA specification talks about a 797-6X which flies 225 passengers 5,000nm and a larger 797-7X which flies 265 passengers 4,200nm. An improved A321LR would target to shave off as much of the 797-6X market as possible.
The A321LR is labelled as a two-class 206-seater by Airbus, flying these passengers 4,000nm. The 225 seats in the smaller NMA and the 206 seats in the A321LR don’t have the same seating standard. The NMA is specified with 32-inch seat row pitch in Economy whereas the A321LR has a 30-inch Economy pitch in the 206-seat configuration. So a 30-inch Economy section 797-6X cabin would hold more passengers than 225.
Airbus has played with adding two seat rows to the A321XLR by enlarging the A321 fuselage plugs, but this would take longer to implement. The market wants a more capable A321XLR within the next two to three years. Airbus main track is, therefore, to increase the range of the present A321LR and leave the seating capacity intact in a first step, according to Aviation Week.
To get more range, more fuel space is needed and a higher MTOW to allow this fuel to be filled before take-off. How this can be achieved without resorting to a new larger wing is the subject of next week’s article.