Why Did Airbus Put *tiny* Engines on the A340?

if you ask an airline pilot to name the most overpowered plane flying today nearly all of them will tell you it's the Boeing 757 with extremely powerful engines for its size and a super critical Wing the plane is affectionately known as the sports car of the sky it'll Thunder Down runways get airborne quickly and reach crews in a jiffy now ask those same Pilots what the most underpowered plane is and they're just as likely to reach a consensus more likely than not they'll tell you it's the A340 specifically the A340 300 this plane is the 757's polar opposite a massive lumbering Beast that leisurely accelerates as it takes to the skies while the 757 has engines that are arguably too big the A340 300 has engines that are undeniably too small so why did Airbus stick tiny engines on this gigantic plane let me explain [Music] upping into the video I'd like to tell you about today's sponsor PayPal honey now don't skip this because honey is going to make your holiday shopping so much easier 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Boeing jet that most closely matches its range and capacity because the A340 is built from aluminum and the 787 is built from Composites the A340 weighs quite a bit more it's about 11 tons heavier when both aircraft are empty and yet the A340 puts out less thrust than the Dramliner and as a result its thrust weight ratio is about 10 percent less than the 787 okay but what does that actually translate to in real life well I ran a little experiment to find out I searched YouTube and found eight takeoff videos for the A340 and 8 for the 787 I then timed the duration of each takeoff roll and found that the A340 took on average 10 seconds longer to get off the ground of course this experiment isn't perfect and can't control for things like load Factor so let's try to control for that variable by looking at some performance charts according to 787 flight performance data the plane needs about 9100 feet of Runway to lift off at full capacity in comparison the A340 300 needs 10 200 feet and once each plane is in the air the Boeing can climb quicker than the Airbus The 787's Climb profile means that at its maximum takeoff weight it can reach a cruising altitude of 38 000 feet in about 25 minutes in comparison the A340 makes the climb in about 40 minutes now I know this is going to come as a real shock to us all but the culprit for the a340s under performance is its engines the a340300 is powered by four CFM 56s now if that name rings a bell it's probably because the cfm56 is the most popular jet engine of all time over 33 000 of them have been built to date and it Powers six different aircraft families but take a closer look at this list does anything look off to you well it seems that one of these things is not like the others the A340 is the only wide body you see the cfm56 was originally designed to power small planes and the engine itself is also fairly small at just 72 inches in diameter it's by far the smallest wide body engine in operation today for comparison the engines that power the aforementioned 787 have a fan diameter of 111 inches that's over 50 percent bigger it's no wonder then that many people think the A340 300 is severely underpowered but all of this begs the question why why did Airbus choose to stick tiny engines on such a big plane well it turns out that the cfm56 wasn't airbus's first engine of choice when the company was first designing the A340 they were hoping to power it with the iae superfan the Super Fan was truly ahead of its time Not only would it leverage Advanced composite materials and contoured titanium fan blades but it would also employ a geared turbofan architecture the geared turbofan has long been the Holy Grail of turbofan design in a normal engine the primary fan compressor and turbines are connected via a single drive shaft and as such they all spin at the same speed but for a whole bunch of complicated technical reasons this leads to inherent inefficiency a geared turbofan solves these shortcomings this type of engine adds a gearbox behind the primary fan allowing it to rotate at a different slower speed than the engine's internal components this can drastically optimize airflow through the engine increasing its bypass ratio and improving efficiency in the case of the iae superfan this would have delivered a 20 fuel burn advantage over its closest Rivals the only problem is that getting such a gearbox to work reliably has long been a challenge but even so iae convinced Airbus that it could successfully bring the technology to Market to some degree Airbus didn't have much of a choice but to believe them the A340 was envisioned to be a quad jet a design choice that allowed for greater versatility on long-haul routes but also added weight and decreased efficiency the superfan was airbus's best chance to make the design efficient unsurprisingly the Super Fan never made it to market the technical hurdles were just too great to overcome as it turns out the technology wasn't even close to being commercially viable it took 20 more years of advancement before a geared turbo fan what hit the market with Pratt Whitney debuting the technology in 2008 the super fans failure really put Airbus in a bind after all they had already promised its performance to customers so the company had to get creative and ultimately settled on the tiny cfm-56 as a stand-in its small size meant that it sipped fuel helping the A340 stay relatively efficient but it also reduced the plane's thrust by more than ten thousand pounds and leads to the lackluster takeoff performance that we see today but the cfm56 doesn't just affect takeoff performance it affects the a340s value proposition as a whole and not in a good way its inferior performance meant that Airbus had to increase the a340s wingspan by 2. 6 meters this helps generate more lift but it also adds weight to the design and worsens aerodynamic efficiency and at the end of the day this decreased the plane's range by about a thousand nautical miles the CFM 56 also makes the plane slower most wide-body aircraft Crews anywhere from Mach 0.

84 to Mach 0. 92 but the A340 300 cruises at just Mach 0. 82 and is actually most efficient at Mach 0.