Five Manufacturers Proposing 90-Seat Turboprops

By Bradley Perrett
Source: Aviation Week & Space Technology

The exact width of the ATR five-abreast fuselage is unknown, but the company very probably intends to hold weight and drag down by staying close to its current seat-back width of 44 cm (17.3 in.). If the aircraft is optimized for relatively short flights, spacious seating would not be a great selling point. But ATR's choice of a five-abreast cross-section also offers plenty of space for an under-floor freight compartment, which could be attractive to airlines. The inevitably high-mounted wing will not obstruct it.

Drawings published by Avic suggest that its program managers aim to provide a freight compartment in the MA700 by giving its circular cross section a diameter of 3.0 meters (118 in.), unusually large for its four-abreast seating. The compartment may be shallow, but there will also be baggage stowage at the rear of the cabin.

Thanks to the MA700's great diameter, seat backs and the aisle will be 46 cm wide, and the designers have found room for 1.95 meters (6.4 ft.) of standing height in the aisle, compared with 1.91 meters in the ATR 72. Moreover, the floor is positioned for maximum width at the height of the armrests. The result is that, at the expense of fuselage weight and drag, the MA700 should offer considerable comfort for a turboprop. The design does not seem wide enough for optional five-abreast seating.

The South Korean DRA has a circular, four-abreast fuselage and an under-floor cargo compartment, suggests a published drawing. Accordingly, something very close to the MA700 may be planned. But the project seems so fluid that quite a different aircraft could appear.

In India, the RTA's designers have also provided for an under-floor cargo compartment, but have held down frontal area by adopting an egg-shaped cross section, like a traditional double bubble but with smoothly changing radius. They have thereby kept width down to 2.8 meters, not nearly as wide as the MA700's; indeed, the RTA's fuselage width is even narrower than the ATR 72's 2.87 meters, but wider than the Q400's 2.7 meters. The fuselage depth should give the cargo compartment useful height.

Bombardier's stretched Q400, if it goes ahead, will likely have the narrowest cross section and will probably be the only aircraft in the category to rely on baggage stowage at the ends of the cabin, which complicates control of the center of gravity and presents the problem of a high loading position. The narrow fuselage would offer least drag but its weight advantages would be offset by reinforcement needed to support the length. Stretching a circular fuselage of that diameter as far as 100 seats would be quite unusual.

The cross-section choices of the five development teams alone offer considerable scope for marketers to pitch the various aircraft at airlines with the most suitable business model: for example, comfort for the MA700 and freight capacity for the RTA and ATR 90-seater. The ATR aircraft should be fundamentally larger, with at least one version seating more than the others, so it will eventually appeal to carriers that want more seating. But there will be other big differentiators between the competing types: power, speed and climb (see following article).

As to structure, the RTA is planned to have a composite wing, tail and even fuselage. While Indian industry is unlikely to have the expertise to build a fully composite fuselage, such light material as can be worked into the design will offset the weight imposed by the seemingly high aspect ratio of the wing. The ATR 72 has a composite wing, and its manufacturer is probably inclined to use the material for the body of its new aircraft, too. Alenia Aermacchi's concept apparently includes a composite fuselage.

A composite fuselage is controversial not only because of the challenges in production. A turboprop airliner, operating many short flights a day, is far more likely to be banged by ground vehicles than a Boeing 787, for example, and the methods for fixing aluminum structure are well established. Also, the fuel savings from costly light materials are lower for aircraft such as turboprops that spend less time in cruise.

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