Why aren't more short haul planes made extensively from composite materials as long haul planes are?

Posted by Ok-Pea3414@reddit | aviation | View on Reddit | 20 comments

World's two leading short haul planes, the 737 Max in its latest iteration and A320/321 are made from aluminum alloys. Although, they do have a significantly more proportion of composites than their previous versions, compared to long haul aircraft, the composite percentage in their construction is significantly lower. Why?

one theory is that aluminum testing is far more easier than composite testing and cheaper, for microscopic cracks and creep issues. Because of their frequent pressurization cycles, they are tested more often and thus fuselage and wings are made from aluminum alloys rather than composites.
composite manufacturing takes a lot more equipment and is more expensive. Also, it's slower. This would be fine for planes with price tags of $200M++, but for planes with tags $100M or lower, capital expenditures to have enough composite manufacturing capacity would be crazy high, and prices would need to increase substantially to accommodate composites.
composite weakening is not as well understood as aluminum. This planes which have frequent pressurization cycles and more stress of takeoffs and landings aren't made with composites.
more planes of these kind are sold, thus in repairs, you'd find these planes more too. Aluminum alloy repairs are easier than composite repairs, and less expensive and faster.
the benefit in terms of fuel savings through reduced weight is not as high as it is in larger long haul planes ?(explain why this might be so?)

Why?

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Desperate1941@reddit

A very interesting and informative article. It's just too bad that the publisher of this article does not care about grammar, spelling and context. They should be embarrassed to publish this article in its presentation state. The really confounding aspect of this publication is that the publisher apparently does not employ proof readers nor care about the very poor product.

Stoney3K@reddit

The most important factor is tooling and the necessity to certify that tooling for a specific airframe. A clean sheet re-design like the 787 or A350 means that the whole production process has to be re-approved and certified, which takes a lot of time.

That's also the reason you see a lot of commonality in aircraft manufacturing and the reason there aren't a lot of brand new aircraft types coming out yearly.

F1shermanIvan@reddit

The 737 first flew in 1967, and it uses the 707 fuselage cross sections, so it’s a 1957 design.

It’s a 68 year old fuselage.

The 737 is OLD.

That’s why.

FZ_Milkshake@reddit

The upper part is the same, but the 737 has a shallower lower lobe/baggage compartment.

747ER@reddit

OP asked about the 737 and A320, over a design feature that they both have.

Pfurzbombe@reddit

regarding your theories: 1. testing is easier and better understood, but fatigue is not really a issue for composite. Cracks dont propagate in composite. single fibers might crack, but there‘s still plenty of other fibers that take over. Unlike in aluminum, a cracked fiber doesnt affect the surrounding structure. 2. you‘re correct here. It‘s always a tradeoff between cost and benefit. 3. not quite, see my answer on 1. Fatigue (or composite weakening as you called it) is well understood and no problem. 4. correct. short haul planes spent more time on the ground, thus have higher risk of getting hit by ground vehicles, stairs, loaders, fuel trucks etc. 5. Yes correct. short haul planes usually fly for like 1-2 hours, then spent and hour in the ground unloading and then loading again. Long haul planes spent up to 19 hours in the air and one on the ground. Therefore the percentage of time spent in the air is much higher on long haul planes, therefore the gains of reduced weight are way bigger.

spacecadet2399@reddit

The 737 dates from the 1960's, the A320/321 from the 1980's.

That's why. That is literally all you need to know. You can't just change an existing design from aluminum to composite.

andrewrbat@reddit

The a220, a clean sheet design, has mostly composite wings and tail. The fuselage is mostly an alloy of aluminum and lithium. Its lighter/stronger than just regular aluminum and easier to build, and cheaper to tool than if it were all composite, as far as i understand. It seems like a good compromise as the 220 is a pretty awesome plane.

Independent-Reveal86@reddit

The biggest factor would be that they are existing designs and if major changes were made then they would have to have a new type certificate.

Isord@reddit

Yeah it's pretty safe to assume the next clean sheet from Boeing or Airbus will be carbon fiber.

RealPutin@reddit

Yup. The patent filings Boeing submitted back in ~2010 for the Y1 (canceled in favor of the MAX) showed a composite narrowbody fuselage

AckerHerron@reddit

They will be in the future. Once Boeing finally goes with a clean sheet to replace the 737. The a320 will take longer to replace with a new design as it’s much newer.

The a220 is already largely composite.

Overload4554@reddit

The A320 first flew 20 years after the 737 It’s not as young as we all think

The A220 was designed by a Canadian company, not Airbus and so it has little in common with any other plane that they offer

Appropriate-Gas-1014@reddit

The 220 has a composite wing, but isn't the fuselage still aluminum?

Designer_Buy_1650@reddit

Bunch of reasons. One not mentioned so far is cost savings by weight reduction on long haul flights are realized on a greater scale than short haul flights.

Ok-Pea3414@reddit (OP)

I would have thought otherwise. Short haul planes spend more time than long haul ones at not their cruising altitude thus weight reduction there would be more helpful than long haul planes?

ncc81701@reddit

No empty weight matters more on long haul aircraft because they are bigger to carry all the fuel it needs. If you composites saves you 10% in weight of the total aircraft, that 10% is more absolute weight on a bigger, heavier long haul aircraft than a lighter, smaller, short haul aircraft.

Separate-Fishing-361@reddit

Short-haul planes have far more takeoff/landings and pressurization cycles. If you don’t include cruising time, long-haul flights don’t incur much wear by comparison. But weight savings might pay more in cruising fuel economy and cargo capacity.

HonoraryCanadian@reddit

They're old designs that predate widespread composite use. Switching the fuselage construction from aluminum to composite would effectively be a whole new plane. We'll likely see composites when the 737 and 320 are replaced with clean sheet designs.

It's speculation, but I suspect neither Comac nor Bombardier had the manufacturing experience to risk going all in on CFRP, and Embraer probably didn't see a cost/benefit for their RJs. Your points all are valid to some degree, I think, but I believe material availability is a limiting factor, too. There's only so much aviation quality CFRP in the world, and it might take the confidence of a Boeing or Airbus product to get those suppliers to risk expanding their capacity that much.

They don’t have less composites than long-haul aircraft: compare them to the A330NEO and 747-8. The reason these aircraft aren’t made out of composites is because you can only change so much about a design before it legally has to be considered a new aircraft. Clean-sheet aircraft like the 787 and eventually A350 had the advantage of being a new aircraft type, which allows them to be built using whatever materials they want. The three clean-sheet narrowbodies of the 21st century (C-Series, C919, and MC-21) were all built by companies with no prior experience in composite materials, so they didn’t want to over-complicate the design process.