flapsdown40
Topic Author
Posts: 47
Joined: Thu Aug 25, 2016 11:41 am

### Maximum inboard flap deflection on the 777-300

While watching many plane-spotting videos on YouTube, I'd like to know what the maximum inboard flap deflection is on the 777-300 series of aircraft. The inboard flaps seem to be deflected downwards at about a 60-65 degree angle, but I'm sure it's just an optical illusion caused by a variety of factors- aircraft attitude, location of the vlogger vs location of the plane, etc. I'm thinking the inboard flaps deflect to about 40 degrees or so. If they did, in fact, deflect down to 60 degrees, the engines would probably be howling at 90% N1 just to keep the plane flying and not pancaking into the ground with the inboard flaps at 60 degrees.

TIA for any responses.
I'm already insane but I'm not crazy!

CARST
Posts: 1370
Joined: Tue Jul 25, 2006 11:00 pm

### Re: Maximum inboard flap deflection on the 777-300

If you watch these photos you see that it is no optical illusion:

Also this is a nice photo:

Source: https://www.decodedscience.org/wing-fla ... ft/11831/2

The source for the phot above is worth a read anyway, because it gives some nice explanation about the lift-increase of different flap-systems used in the past decades...

flapsdown40 wrote:
If they did, in fact, deflect down to 60 degrees, the engines would probably be howling at 90% N1 just to keep the plane flying and not pancaking into the ground with the inboard flaps at 60 degrees.

I think you must understand of how a wing works to understand that this is wrong. While engine thrust has to be added to counter-act against the "breaking action" from the extended flaps, they also add massively to the lift created and thus less power is needed to keep the aircraft flying at low speeds. So the real power increase might be just 30-40%...

This is from Wikipedia about how aircraft "wings" work:

Source: https://en.wikipedia.org/wiki/Wing

And that (see how similar it is) is how the 777 wing looks with the flaps extended fully:

Source: https://pma27.deviantart.com/art/Boeing ... -185387592

LH707330
Posts: 1932
Joined: Fri Jun 15, 2012 11:27 pm

### Re: Maximum inboard flap deflection on the 777-300

I've noticed that too on the 777, and I imagine that the inboard flaps do create quite a bit of induced drag. I think the tradeoff that Boeing went for was more lift and drag inboard with the double slot to allow single slot outboard, and keeping the thrust gate for the inner flaperon to make the outboard wing thinner. Because the yehudi is pretty prominent on the 777, they probably get quite a decent amount of lift from that setup, and they have enough thrust to pull it all along.

BoeingGuy
Posts: 5266
Joined: Fri Dec 10, 2010 6:01 pm

### Re: Maximum inboard flap deflection on the 777-300

CARST wrote:
If you watch these photos you see that it is no optical illusion:

Also this is a nice photo:

Source: https://www.decodedscience.org/wing-fla ... ft/11831/2

The source for the phot above is worth a read anyway, because it gives some nice explanation about the lift-increase of different flap-systems used in the past decades...

flapsdown40 wrote:
If they did, in fact, deflect down to 60 degrees, the engines would probably be howling at 90% N1 just to keep the plane flying and not pancaking into the ground with the inboard flaps at 60 degrees.

I think you must understand of how a wing works to understand that this is wrong. While engine thrust has to be added to counter-act against the "breaking action" from the extended flaps, they also add massively to the lift created and thus less power is needed to keep the aircraft flying at low speeds. So the real power increase might be just 30-40%...

This is from Wikipedia about how aircraft "wings" work:

Source: https://en.wikipedia.org/wiki/Wing

And that (see how similar it is) is how the 777 wing looks with the flaps extended fully:

Source: https://pma27.deviantart.com/art/Boeing ... -185387592

There is one error in those graphics. In Landing Flap configuration (25, 30), the slats are in the "gapped" position. That is depicted there. Air can flow between the wing and slat up over the airfoil.

For Takeoff and Climb settings (1, 5, 20), the slats are in the "sealed" position so air cannot flow between the slat and wing as incorrectly show in the second graphic.

aeropix
Posts: 159
Joined: Mon Jun 06, 2005 2:08 pm

### Re: Maximum inboard flap deflection on the 777-300

LH707330 wrote:
Because the yehudi is pretty prominent

What does a Jewish violinist have to do with airplanes?

LH707330
Posts: 1932
Joined: Fri Jun 15, 2012 11:27 pm

### Re: Maximum inboard flap deflection on the 777-300

aeropix wrote:
LH707330 wrote:
Because the yehudi is pretty prominent

What does a Jewish violinist have to do with airplanes?

Here's the story I heard for that: When the DC-8 was first designed, they had straight trailing edges, and designers found that they wanted more lift inboard, someone decided to fiddle around and add a triangular section inboard to increase root chord. When the inevitable question "what do we call this thing" arose, they said, "Well, we fiddled with it, so let's name it after a famous fiddler." It could be apocryphal, but I've seen it elsewhere.

flapsdown40
Topic Author
Posts: 47
Joined: Thu Aug 25, 2016 11:41 am

### Re: Maximum inboard flap deflection on the 777-300

Thanks to all who replied to my post, especially the ones with the pictures and the diagrams. Glad to know that what I was seeing was not, in fact, an optical illusion, but an inboard flap that was deflected downwards further than I had expected them to be. They must give the 777 a *lot* of extra lift at landing speeds, not to mention a lot of drag to help slow the plane once it has landed.
I'm already insane but I'm not crazy!

767333ER
Posts: 866
Joined: Wed Jun 15, 2016 5:14 am

### Re: Maximum inboard flap deflection on the 777-300

The 767 uses a similar configuration as well where the double slotted inboard flaps go much steeper than the outboard. The 787 is again similar, but less so since the inboard flaps are single slotted.
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Faro
Posts: 1783
Joined: Sun Aug 12, 2007 1:08 am

### Re: Maximum inboard flap deflection on the 777-300

You want unbelievable inboard flap deflection angles? Have a look at some of the Comet IV landing pics in the database...80+ degrees, almost perpendicular...absolutely crazy deflections...

Faro
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