Could an NMA be made good enough, Part 3?

Discussion
Fuselage

In Part 2 of the series, we designed an NMA cabin. The cabin resembles a longer Boeing 767-200 cabin, Figure 2.

Figure 2. Example of an NMA cabin in two classes with 227 seats. Source: Leeham Co.

Capacity is 227 seats in a Domestic two-class configuration. This is the cabin for the smaller NMA variant. The larger variant would add around 30-40 seats, making the cabin four meters longer.

Once the cabin is settled, the fuselage dimensions follow. There are rules for the taper of a front and rear fuselage. These determine the length of the front fuselage containing the cockpit and the tail fuselage holding the horizontal and vertical tail.

A resulting fuselage is shown in Figure 3. It would be 49m long and 4.9m wide. The fuselage for the Airbus A321LR is shown as a reference.

Figure 3. NMA and A321LR fuselage comparison. Source: Leeham Co.

The NMA fuselage is reminiscent of a Boeing 767-200 fuselage, but it’s 2m longer and has a very different cross section, Figure 4.

Figure 4. Fuselage cross sections for A321LR, Boeing 767 and an NMA. Source: Leeham Co.

The tighter cross section reduces the dominant drag component per seat (skin friction drag) by 16% compared with the 767 fuselage. Compared with the A321LR, the NMA fuselage would have a 6% higher skin friction drag per seat, as the front and rear overhangs grow larger with a wider fuselage.

Fuselage weight

The idea behind a tighter fuselage cross section for an NMA, compared to a 767, is to gain both drag and weight advantages. To enable an elliptical cross section, the NMA fuselage is made with Carbon Fiber Reinforced Polymers (CFRP) for skins, stringers and frames. This makes the wider fuselage weight competitive with the single aisle fuselage.

The weight per seat would be the same between the NMA and an A321LR fuselage. Both are 35% lighter than the 767 on a per seat basis.

Summary

A twin aisle fuselage can be made competitive with a single aisle fuselage on a weight and drag basis. This requires a carefully chosen cross section and the use of the smaller container from the single aisle market, the LD3-45.

The weight on a per seat basis would be the same as the single aisle A321LR, whereas the drag would be fractionally higher, as the fuselage overhangs get larger with a wider fuselage.

In the next part we will look at the wing required to achieve the target efficiency for the NMA.

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