The Russian MS-21 narrow body airliner is first use of non-autoclaved composites in the primary structure of a commercial aircraft:

As Russian aircraft manufacturer Irkut Corp. (Irkutsk, Russia) rolled out its narrow-body MS-21 (132-211 passengers) today (June 8), it’s time to recognize again the novelty of this plane. The MS-21 will carry into the air a major aerospace and composites industry milestone: The first out-of-autoclave (OOA) composite wing and wing box on a commercial aircraft.

As CW reported in early 2014, the MS-21 wing and wing box represent a major and hard-won accomplishment in aerospace composites manufacturing. Never before has such a large, complex and important aerostructure been made OOA. So, it’s worth reviewing now how it was made.

The OOA parts— the wing box, integrated stringers and skins, and spars — are fabricated by AeroComposit (Moscow, Russia), a sister company of Irkut (both are owned by Moscow-based United Aircraft Corp.). The materials used come from Solvay (Cytec when plane development was begun; Woodland Park, NJ, US). The layup is done via placement of unidirectional dry fiber with automated tape laying (ATL) equipment provided by MTorres (Torres de Elorz, Navarra, Spain) and Coriolis (Queven, France).

Lance Parcell, new business development director at Solvay, provided development assistance to AeroComposit starting in 2008 and says the material used, EP 2400, is “a unique product that is toughened and infusible without having to introduce tougheners in other forms like films or polymer fibers.” Further, the resin offers a long window for the infusion process, which provides more than adequate time for large primary structures such as wings. The result, says Parcell, is very low porosity in the final part that “is equal to or less than in an autoclave.”

In a conventional aviation composites, an autoclave, which applies both heat and pressure.

The pressure is used to push the resin in between the fibers to prevent voids.

An autoclave is both an oven and a pressure vessel, and at larger sizes they are expensive and finicky items.

Another option is to make smaller pieces and fasten them together, but that creates a whole new set of issues 

If you can infuse the resin without voids, then you can just cure the resin in an ordinary oven, which is cheaper and easier.

This has been done in marine composites for years, but in those applications, you are not trying to use an absolute minimum of material.

In the weight conscious aviation field, adding margin is not an option.

It’s a pretty impressive technical feat.