flapsdown40
Topic Author
Posts: 16
Joined: Thu Aug 25, 2016 11:41 am

Maximum inboard flap deflection on the 777-300

Thu May 17, 2018 12:02 pm

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!
 
User avatar
CARST
Posts: 1284
Joined: Tue Jul 25, 2006 11:00 pm

Re: Maximum inboard flap deflection on the 777-300

Thu May 17, 2018 3:07 pm

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



Also this is a nice photo:

Image
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:

Image
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:

Image
Source: https://pma27.deviantart.com/art/Boeing ... -185387592
 
LH707330
Posts: 1877
Joined: Fri Jun 15, 2012 11:27 pm

Re: Maximum inboard flap deflection on the 777-300

Thu May 17, 2018 4:20 pm

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: 4887
Joined: Fri Dec 10, 2010 6:01 pm

Re: Maximum inboard flap deflection on the 777-300

Thu May 17, 2018 7:04 pm

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



Also this is a nice photo:

Image
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:

Image
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:

Image
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: 128
Joined: Mon Jun 06, 2005 2:08 pm

Re: Maximum inboard flap deflection on the 777-300

Thu May 17, 2018 7:07 pm

LH707330 wrote:
Because the yehudi is pretty prominent


What does a Jewish violinist have to do with airplanes?
 
LH707330
Posts: 1877
Joined: Fri Jun 15, 2012 11:27 pm

Re: Maximum inboard flap deflection on the 777-300

Fri May 18, 2018 6:34 pm

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.

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