Originally Posted by
KenV
A few points:
1. The wingtip only folds/unfolds on the ground. The flaps MUST extend and retract in flight.
2. The wingtips only have two positions. The flaps have multiple positions.
3. The wingtips each have four simple lock pins to lock them in place and are fail safe (if they fail, they fail locked). The flaps have multiple failure modes, and not all are fail safe.
4. The wingtips can fold/unfold assymetrically with no concern. The flaps MUST extend and retract symmetrically, requiring complex sensors and redundant controls to ensure this ALWAYS happens.
5. The wingtips each have a simple single rotary actuator. The flaps have multiple segments and multiple actuators
6. The wingtips have a very simple rotary motion. The flaps have a complex motion that includes translation and rotation.at constantly varying ratios which requires a complex track/link system.
7. The wingtips are structurally and aerodynamically simple and if one or both wingtips are lost in flight the aircraft remains fully controllable. The flaps are much more complex structurally and aerodynamically. Lose a flap in flight and you're screwed.
8. The wingtips only need to fold to taxi off the runway and/or fit into a gate, so the consequences of a failure to fold are minor and at most an annoyance. The flaps need to extend to land and the consequences of a failure to extend are much more serious.
9. The wingtips unfold on the ground before becoming airborne so if there's a problem you know about it well before you even commit to flight. The flaps retract AFTER takeoff and MUST retract to continue the flight. If they fail to retract the flight must be aborted.
10. There's more, but this will suffice.
I'll let the reader decide which system is "safer", "more complex", "requires more safety measures", etc
KenV: Now that is a pretty overwhelming set of arguments. I guess we will see if they all hold true in practice once the 777X is flying. But one more thing. I had heard that wing-folding was to be an option on the 777X. If this is correct, it would be interesting to hear how many frames are being ordered with, and how many without. That might indicate a bit the confidence level that airlines have in the mechanism -- or the tightness of the typical gates at which they expect to park these planes.