Flaps, Old v New design.

[Ozgrade3]

Was asked a question the other day about old style flaps(727, 737 classic, 737-400 v new style, A380 etc. Hitting the internet has come up with all sorts of graphs, but not the answer.

Classic aircraft have 3 stage Fowler flaps that at take-off setting extend a large distance behind the trailing edge of the wing. The 727 take-off flap setting is a good example.

New aircraft, especially A380, 777, 737NG has at a guess 1/3 of the Fowler action.

Can someone explain to a simple instructor how the the new design of flap provides the same amount of lift. I have searched but there's nothign that explains the answer.

While I'm it, the A380 has a noticeably slower Vr and Vref. Is that a function of the huge wing, or wing design (airfoil tech) or am I missing something.

Take-off, flap retraction schedule. Old aircraft 727,707 it seems their acceleration during the acceleration phase (3 stage?) takes ages. Heavy takeoffs can take 7 mins to get to flaps up (watched over dozens of videos). A380 gets to clean speed in 2 mins or so. My guess better thrust to weight of new aircraft resulting in better 3rd stage segment.

https://www.youtube.com/watch?v=_l4bk2729pE&t=1s

https://www.youtube.com/watch?v=2x4pguXyo_8

[gearlever]

While I'm it, the A380 has a noticeably slower Vr and Vref. Is that a function of the huge wing, or wing design (airfoil tech) or am I missing something.



To my limited knowledge the wing of the A380 was designed for planned larger/heavier versions of the 380. So the current model has a low wing loading resulting in lower TO speeds. But stand to be corrected.

[PDR1]

IIRC in the early days of the A380 project there was a public concern over the growing noise footprints of airports, and so a design objective of the A380 was to be much quieter on approach. Analysis showed an unexpectedly large part of the noise signature of an airliner on approach was simply aerodynamic noise from the airframe. The magnitude of this noise increases with the square of airspeed, so a "simple" way to address this was simply to fly slower in the approach phase. Hence lower wing loading, stall speed etc.

ISTR hearing all of this in an RAeS lecture from airbus in the early/mid 90s - long before the design was frozen.

[MarkerInbound]

In your example videos the 727 cleans up about 1:15 after rotation, the 380 takes 2 minutes. Hard to say if both are using the same noise profile which would affect when the retraction starts.

[tdracer]

Analysis showed an unexpectedly large part of the noise signature of an airliner on approach was simply aerodynamic noise from the airframe
Not just analysis - there was a lot of testing involved as well. Supposedly Boeing did a test many years ago where they flew a 'dirty' 747 (full flaps/slats, gear down) over at TO thrust, then repeated with the engines at approach idle - it only made 3db difference. Flaps are noisy, and triple slotted flaps are far noisier than double or single slotted flaps.
The 747 went from triple slotted to double slotted flaps on the 747-8, and it was almost entirely due to noise concerns.
As for the original question of how they get the same amount of lift from double slotted, I suspect it is due to better design - computer aided design, CFD, and the like.

[Sidestick_n_Rudder]

Perhaps also the wing aerodynamics is better these days, so less complex flap is required to achieve acceptable speed on t/o and approach?

A good example would be A320 vs A321. The latter has (almost) the same wing as the former, even though it’s a heavier airplane. To keep the t/o and approach speeds in check (as well as the speeds) it has a more sophisticated, double slotted flap, compared to the original.

[vapilot2004]

On the 737, the wing area is greater by about a quarter, so right away we have more lift at our disposal. The loss of one slot increases the flaps' efficiency and the continuous span on the NG adds to the surface area and improves airflow over the old split flaps design of the classics.

With the new wing, coming down will require more boards up time if your planning is imperfect and coming over the numbers with even just a few ticks above VREF+xx will give you a lot more float than the classic ever would. The latter difference, alongside obvious training deficiencies, could be why we have seen so many overruns on the NG.

[RVF750]

NG lands far faster too. If they'd have moved the ailerons outboard and made the flaps wider the speeds would have been less, noise less and performance, especially in crosswinds a lot better.

However, the cost of certificating the new aileron system would have been far greater than Boeing would have wanted from modernising the design I guess.

[Double Back]

Most likely the triple slotted system is heavier, but definitely more complex, to build and to operate/maintain. So more expensive in all.
It took years before Boeing found a grease for those sensitive spindles that worked in an airline environment. Use anything else and you are in for an asymmetrical one of the next landings.

[Pugilistic Animus]

If you have the appropriate math and physics background then "Theory of wing sections" By Abbot and Vandoenhoff has a very good chapter on high lift devices

[krismiler]

Improved design enabled the B777 to do without winglets which were used on the earlier B744. The B727 and B737 are 1960s airframes a generation or two behind today’s B787.

The B727 was designed specifically for shorter runways which were unable to accommodate the B707, similarily the British VC10 was designed for hot and high airports in the African colonies. Lift at Low speed would have been an important factor in the design of these two types. As time progressed airports were designed with the new jet transports in mind rather than the old Dc3s and DC4s.

Basically, design improved and runways got longer.

[pattern_is_full]

Exactly - the 727 was designed as the "Twin Otter" of the early jet age, to expand jet service to smaller airports.

Which in no way negates the other improvements and changes that occurred and are mentioned above, over 50 years of development.

[Double Back]

Pugilistic Animus and others, I could download the book You meant for free on https://aeroknowledge77.files.wordpress.com/2011/09/58986488-theory-of-wing-sections-including-a-summary-of-airfoil-data.pdf

[Pugilistic Animus]

Excellent!