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The Boeing 777 has an optional folding wing mechanism to fit into tighter spaces, but it has never been ordered by airlines, according to Wikipedia. Why is this option so unpopular?
Now with the Boeing 777X, Boeing is again offering a smaller, less complex wing folding option. Has this been ordered, and are other airliner models planned to incorporate folding wingtips?
The folding wingtips are found mostly in naval aviation. The reason is the space constraint inside the hangar of the aircraft carrier.
"US Navy 070128-N-9712C-003 Aircraft fill the hanger bays on board USS Ronald Reagan (CVN 76) after recently embarking Carrier Air Wing One Four (CVW- 14)" by U.S. Navy Photo by Mass Communication Specialist 2nd Class John P. Curtis.
As can be seen from the photo, folding the wings offers the only practical way of fitting fighter aircraft inside the cramped hangar space. For example, the F/A-18C/D had a wing span of 11.43m; this was reduced to 8.38m with the wings folded, a 26% reduction.
However, the price to pay is an increase in complexity, weight, price and increased maintenance. The figure shows the wing folding mechanism of a F 18.
Source:polepositionimagery.com.au
The major drawbacks of folding wings are,
Source: zarco-macross.wikidot.com
As can be seen, the F/A doesn't carry fuel in the folding part of the wing. In fact, after the airlines didn't take up its folding concept in 777, Boeing added fuel tanks to that area and increased range of the 777-200/300.
There has previously been no reason for airliners to fold their wings, as airports offered enough space for operations and ground movement. However, as the size of aircraft and their aspect ratios grow (to reduce drag), designers are finding it more and more difficult to keep the wingspan below the 80m 'box' which airlines believe is the maximum they can cope up economically.
The first major program to be affected by this limitation was the A380, which limited the wingspan of the aircraft to less than 80m and reduced its aspect ratio.
"Giant planes comparison" by Clem Tillier (clem AT tillier.net) - Original Work. Licensed under CC BY-SA 2.5 via Commons.
Basically, Boeing is facing the same problem. The proposed 777x is the largest-wingspan aircraft Boeing has ever produced. However, in the case of the A380, Airbus managed to reduce induced drag through the use of wingtip fences, among other design decisions. The 777x is expected to have a raked wingtip, which is not as space effective as the wingtip fence.
Source: Flightglobal.com
As a result, Boeing is considering folding wingtips. However, there are important differences between the original plan in 777 and the proposed plan in 777x.
In the original plan, Boeing proposed to fold 21' of the wingtip. However,the new plans call for folding only 10'.
Original Wing folding plan in Boeing 777. Source:www.seattletimes.com
Image:Boeing
As can be seen from the figure, the folding plan is much more modest. This is not expected to have the drawbacks associated with the the original plan, as,
To put things into perspective, the 747-400's winglets were 6' feet tall.
Airlines have already placed orders for 777x and it is their operational record that will determine if other aviation manufacturers (Airbus, that is.) will follow suit.
why cant this apply to all airliners?
It can apply to any new or redesigned airliner. It's probably not something you'd need, want or be economically feasible to retrofit to existing in-service airliners.
Whether the manufacturer or operators want the associated disadvantages is another matter.
Reliability is critical. A 777X may be unable to vacate a runway if a wingtip fails to fold, and it has to do this in a short time (of the order of 20 seconds).
Should the wingtips not fold up and lock into place correctly after the aircraft lands, it could effectively paralyze an airport by delaying both departures and arrivals
- Liebherr-Aerospace senior executive Heiko Lütjens
Note that only the tips fold, otherwise there would be many more problems in catering for hydraulic, electrical, structural and fuel systems.
The 777X has a wingspan of 71m. Only when folded are it's wings about the same width, 64-65m, as its competitor, the A350-1000.
Wingspan matters when designing an aircraft to operate into existing terminal gates at the specific airports used by the makers' customers.
Boeing wants their 777X to be able to fit where the old 777 and its newer competitors can fit.
Aircraft Wingspan Passengers
747-400 60m 345†
777-300 61m 299†
A350-1000 65m 369
777X 71m 350‡
A380-800 80m 469†
† Most of the passenger numbers are from British Airways for 4-class operation. They don't represent anywhere near max capacity but are probably closer to typical?
‡ Typical 3-class operation.
Airbus had to put serious effort in getting airports to accommodate the A380. I guess Boeing really doesn't want the 777X to be competing with the higher-capacity superheavies for space at the bigger gates.
if the tech already exists
The notion of folding wings has been around a long time. Since before 1913
It has mostly been used on small aircraft that operate from facilities where space is severely limited.
Boeing's ideas in this area have been known since at least 2006
The B777x share most of the characteristic of B777. However, while B777 is Code E(ICAO)/Group V(FAA), due to b777x wingspan, it falls into Code F(ICAO)/Group VI(FAA) catalog.
Currently only A380 and b748 is in Code F/Group VI catalog, which the fleet size is limited (317+123), only a few airliners has such planes and not many airport can parking place and other infrastructures for those plan.
When B777x provides wing folding option, it can feet the code E/Group V parking place. The B777x can be served for most of the airport and reduce the cost.
Wing fold is not new idea.It appears after WWI, when aircraft carrier has been developed, because of the limited hangar size, most of the naval aircraft are designed as wing folded.
E-2 Hawkeye with wings folded:
F-18C with wings folded:
_after_recently_embarking_Carrier_Air_Wing_One_Four_(CVW-_14).jpg#/media/File:US_Navy_070128-N-9712C-003_Aircraft_fill_the_hanger_bays_on_board_USS_Ronald_Reagan_(CVN_76)_after_recently_embarking_Carrier_Air_Wing_One_Four_(CVW-_14).jpg){kind=link}
