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777X De-icing

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777X De-icing

Old 14th Feb 2020, 15:06
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777X De-icing

The Boeing symposium guys came around to visit a little while back and not surprisingly, were keen to discuss the 777X. They had some interesting things to say but one thing that appears to still be unanswered is for my question of how the folding wings would affect holdover time.

Holdover times at our company are reduced by 10% unless the flaps and slats are deployed as close to departure as safety allows. This is because fluid degradation is accelerated by the steeper angles of the flaps/slats in the takeoff configuration

So of course, the question is...what kind of holdover can you get with a portion of the critical surface in the vertical position. The answer was that there are ongoing discussions with the FAA. In the end, I suspect the wings will be de-iced when fully extended and then folded up for taxi and no holdover required with perhaps a few caveats.
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Old 14th Feb 2020, 17:59
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Well if itís just regular old snow, Iíd imagine you wouldnít get much accumulation on a vertical surface.

Iíd be interested to see the performance penalty if the wingtip is damaged and needs to be removed. I imagine itíll be significant.
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Old 14th Feb 2020, 19:51
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If the wings are de-iced extended that would require a lot of re-certification/surveying of de-icing stands/areas where you typically would not be/taxi alone. As the whole point of the folding wingtips is to use existing airport infrastructure without modifications, that would not seem to make sense. I'd assume it would need some testing on how fast type II/IV fluids flow off the retracted wingtips. The FAA might be less inclined to wave this through quickly these days, however.
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Old 14th Feb 2020, 21:35
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Educated guess here, but I suspect that they will simply show that wing tip icing is not critical. This is nothing new - wing anti-ice does not protect the full wing span, just the 'important' parts. The folding wing tips will not have wing anti-ice protection in-flight, so a logic extension is that they can also show that wing tip icing is not flight critical during TO.
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Old 15th Feb 2020, 12:51
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Originally Posted by Alpine Flyer View Post
I'd assume it would need some testing on how fast type II/IV fluids flow off the retracted wingtips. The FAA might be less inclined to wave this through quickly these days, however.
Surely the data is already available as we have been de-icing vertical stabilizers for decades.
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Old 15th Feb 2020, 16:16
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Snoop

Originally Posted by tdracer View Post
Educated guess here, but I suspect that they will simply show that wing tip icing is not critical. This is nothing new - wing anti-ice does not protect the full wing span, just the 'important' parts. The folding wing tips will not have wing anti-ice protection in-flight, so a logic extension is that they can also show that wing tip icing is not flight critical during TO.
And that is exactly what Boeing proposed to and approved by the FAA.
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Old 15th Feb 2020, 21:52
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Originally Posted by Check Airman View Post
Well if itís just regular old snow, Iíd imagine you wouldnít get much accumulation on a vertical surface.
See, this is where engineers in design room need to speak to operators.

Ive seen the opposite side of the representative area fail in half the time the holdover time was supposed to last, due to blowing snow in a significant crosswind. One side of the aircraft, most recently with type 2 straight, failed well before the downwind side.

Could be argued that the loss of lift on one side of the outboard folding segment is acceptable, as long as aileron can control at max contaminated crosswind limits....
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Old 19th Feb 2020, 20:16
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Another question is whether you can fold the wingtips at all after landing in icing conditions. I don't know about Boeing, but AIrbus says not to retract flaps/slats if icing is suspected. Would this also be the case for the folding wingtips? Could you risk having to de-ice before taxiing to the stand so that you can fold the wingtips in and be within the wingspan limits?
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