How Boeing’s 777X Folding Wingtips Actually Work

Much of the sour publicity surrounding Boeing’s 777X development has focused on delays due to the durability of the aircraft’s GE9X engines. Boeing plays down the hiccup and suggests the type’s folding wingtip system and in-cabin innovations will blow the competition away.

2 B777Xs in flight (rendering)
Folding wingtips for the B777X are Boeing’s trump card. Photo: Boeing

The 777X (777-8 and -9) was launched in November 2013. Within two years, Boeing had received 326 orders for the type. Customers included Lufthansa, Etihad Airways, ANA and Singapore Airlines.

Boeing had initially hoped to begin the 777X flight test program in March. But due to various events in the early part of the year, the target date was pushed back. In June of this year the aircraft finally made its runway debut, and showed off its famous folding wingtips.

Following ongoing re-working of the components of the GE9X, Boeing hopes to have the new variant flying by the end of 2019. Aviation Daily speculate that, “GE will require several months to develop and test fixes to the engine and first flight now looks set to be more likely in the October-November timeframe.”

The aircraft is still slated for the commencement of passenger flights in 2020. And the company expects to deliver the first twin-engine, wide-body to Emirates by 2025 (even though the UAE carrier may defer its multi-billion-dollar order.)

Why folding wingtips?

The wing of the 777X is based upon the design of the 787’s wing. It has less of the sweep of the 787 but 10% more surface area (increased from 4,702 to 5,562 sq. ft.). The re-shaping has led to a higher lift-to-drag ratio, which in turn increases usable fuel bulk from 320,863 to 350,410 lb.

As a result, the type will have a range of over 14,000 kilometers (8,699 miles).

Boeing’s motivation for its including folding wingtips within the design was not wholly steered by fuel economy. With a fully-extended wingspan of 71.8 meters, the new 777X falls within the ICAO’s aerodrome Code F. But with raked and folded wings (and a span of 64.8 meters) the type can comfortably arrive at gates designed for Code E. Aircraft in this group includes the current 777.

Are folding wingtips safe?

According to Boeing, yes! In May 2018, the FAA rubber-stamped Boeing’s new folding wingtip system. But public mistrust of the airline’s fastidiousness in respect of innovative technology is at an all-time high.

B777X in flight over clouds (rendering)
FAA rubber-stamped Boeing’s new folding wingtip system in May 2018. Photo: Boeing

In May 2018 the FAA was urged to issue special conditions in reference to the safety of the 777X’s wingtips. In the course of their deliberations the FAA demanded several assurances from Boeing.

The company was required to prove beyond doubt the load-bearing viability of the wingtips. It also needed to show how the wingtips affected ground handling in poor weather, and what alerts the crew would receive about a malfunction.

The FAA granted Boeing certification on the basis of the following provisions:

More than one means must be available to alert the flight crew that the wingtips are not properly positioned and secured prior to take-off. 

In addition to a take-off warning, a means must be provided to prevent airplane take-off if a wingtip is not properly positioned and secured for flight.

The wingtips must have means to safeguard against unlocking from the extended, flight-deployed position in flight, as a result of failures, including the failure of any single structural element.

How do they work?

The exact details of how the wingtips operate have not been made public. But Boeing states that it approached the design of the fold mechanism, locking pins and latches with the same thoroughness as it would any of its flight control systems.

B777X wingtip closeup
Can Boeing engender public trust in its innovative technologies? Photo:

On landing, the wingtips automatically fold within 20 seconds of the aircraft slowing to 50kts. The display of malfunctions and “ready” statuses will be displayed on the cockpit EICAS. Should there be a malfunction, this will be relayed to the pilots via a master caution light and audible tone.

In a statement to FlightGlobal, the company said of the wingtip safety compliance,

Boeing designs its airplanes so that redundant systems are independent, and failures or external threats cannot compromise both primary and backup systems simultaneously.

The folding wingtips are simple and highly reliable with redundant deploying, retracting and locking mechanisms. We are designing the folding wingtips like every other flight critical system so they meet safety requirements.”

  1. “The company was required to prove beyond doubt the viability of the wingtips’ load-bearing”.
    I’d really love to see how exhaustive that “proof” was. Was it just static, or also dynamic? Was it turbulence-tested (up/down movement of the wing during flight)? Was it flutter-tested? Do they know the critical resonance frequencies involved, and have they done extended load-bearing tests at those frequencies? Have they thoroughly tested the effect of large yaw angles (variable shear angles)? Have there been durability tests as a function of temperature cycle?
    If we’re to answer these questions on the basis of past MAX / 787 behavior, then we can postulate that the tests were as short and as a cheap as possible.
    I really wonder when the first of these wingtips is going to shear off in flight…potentially slamming into the tail and damaging flight surfaces/controls there, not to mention the potential damage to the wing caused by its detachment. I know that folding wings have been used on (carrier) fighter jets for ages, but these wings are a LOT bigger and heavier. It’s a neat idea, but Boeing better have done it right, or the consequences will be horrendous.

  2. “Are folding wingtips safe? According to Boeing, yes!”.
    But then Boeing said the 737 Max was safe too so that means nothing.
    1st time was when Boeing said it was safe originally with a hidden, flawed MCAS system.
    2nd time was after two crashes Boeing insisted it was safe and tried to prevent it being grounded in the US when all other countries had already grounded it.
    3rd time is now when Boeing told the FAA the flaws were corrected and the FAA found another catastrophic flaw unrelated to MCAS.
    EASA has also found new flaws.

  3. Boeing states that it approached the design… with the same thoroughness as it would any of its flight control systems. Uh oh. Based on the disastrous Boeing 737 Max control design there is likely a crash in the future. Boeing hasn’t learned anything.

  4. I wonder who programmed the folding wingtips on the new 777X? Same negligent programmer as MCAS? The wingtips are supposed to only fold on the ground. Hypothetically I can see the headline now “400 Passengers Die as Brand New 777X Spirals Into Ground”. “Passengers tweeted the wingtip on one side folded up in flight causing the plane to roll repeatedly on the way into the ground”. “Boeing and the FAA say the plane is safe and more data is needed to ground them.”

  5. “But Boeing states that it approached the design of the fold mechanism, locking pins and latches with the same thoroughness as it would any of its flight control systems.”

    “The folding wingtips are simple and highly reliable with redundant deploying, retracting and locking mechanisms. We are designing the folding wingtips like every other flight critical system so they meet safety requirements.”

    I don’t actually doubt the safety of these, but those comments from Boeing after the MAX debacle are poorly phrased. I also doubt the necessity of them. They were starting out with a clean sheet design on the wing. It’s difficult for me to believe that the added lift of the small wingtip, couldn’t have been designed into a wing. Modern designers and engineers are trying to get a bit cheeky with their designs to show their genius. Simplicity needs to be embraced more. Look at Airbus wings. They have a slightly fatter section near the fuselage. Boeing could have easily done the same. During simulations when designing the A320neo, They even discovered that the amount of possible improvement in the performance of the wing was very small, and not worth the effort. The A320 is small, and could have very easily had more narrow wings with a bigger wingspan, just like the A330neo.

  6. I find it odd that these are mandatory and the added weight and complexity is worth it. Surely airports taking a 400 seat jet have the bigger gates? At the very least, I’d have expected folding wingtips to be an optional extra since surely not every 777x will need them.

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