mxaxai
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Posts: 1464
Joined: Sat Jun 18, 2016 7:29 am

747 vs 777 new flaps

Tue Mar 17, 2020 10:47 am

Most modern airliners since ~ 2005 use single-slotted flaps, the only exception being new variants of older models that kept their predecessor's wing like the 737max or A321neo.

However, both the 747-8 and the 777-9 seem to have received new high-lift devices compared to the 747-400 and 777-300ER, respectively. But while the 777 got modern single-slotted flaps, the 747 still has double-slotted flaps on the inner section. Is there an obvious reason why Boeing had to go with this more complex option on the 747-8? From a pure size point-of-view, even the larger A380 has single-slotted flaps.

 
mmo
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Re: 747 vs 777 new flaps

Tue Mar 17, 2020 12:29 pm

While the 747-8 inboard flaps are double slotted, all other versions had triple slotted flaps in both inboard and outboard positions. The 747-8 has double slotted, inboard and single slotted outboard. That design was chosen as it provides better low-speed handling characteristics and reduced noise on approach. Plus the 747-8 wing is a completely new wind design compared to the earlier versions.
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747classic
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Re: 747 vs 777 new flaps

Tue Mar 17, 2020 4:37 pm

mmo wrote:
While the 747-8 inboard flaps are double slotted, all other versions had triple slotted flaps in both inboard and outboard positions. The 747-8 has double slotted, inboard and single slotted outboard. That design was chosen as it provides better low-speed handling characteristics and reduced noise on approach. Plus the 747-8 wing is a completely new wind design compared to the earlier versions.


Fully correct.
I can add the following :
Wind tunnel tests showed that a single outboard en double inboard TE flap arrangement only could be used with the same approach speed target if also some of the LE flaps would be adapted.
On the 747-8 series are for that reason the inboard LE krueger flaps gapped i.s.o. sealed (747-400 series). Adding the gap showed a significant approach speed benefit.
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LH707330
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Re: 747 vs 777 new flaps

Wed Mar 18, 2020 9:55 pm

The 748 kept the same planform as the 744, and hence had more constraints than the 779, which has a completely different wing. If the 748 team had a bigger budget, they probably would have reduced the sweep angle and reimagined the whole setup.

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