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What's That Thingy Called Next To The Engine?  
User currently offlineNRT744 From Japan, joined Feb 2005, 33 posts, RR: 0
Posted (5 years 10 months 1 week 1 day 22 hours ago) and read 4603 times:

It has been bothering me since I first noticed it on a 777.
There's a small slat or a flap on the leading edge of the wing next to the 767/777 engine pylon. I suspect that it's a small Kreger flap just like the ones on the 747, but I'm not sure.
I also noticed them on the 300/310s as well.
Because it's so small, it makes you think why it's even there. Does it make significant "lift" if it's there? or is it there for other purposes?

20 replies: All unread, jump to last
 
User currently offlineGatorman96 From United States of America, joined Dec 2005, 873 posts, RR: 0
Reply 1, posted (5 years 10 months 1 week 1 day 22 hours ago) and read 4581 times:

Vortex generators....

http://en.wikipedia.org/wiki/Vortex_generator

They also occur on the wings, tails, and even inside engines a la 727

[Edited 2008-11-18 22:14:10]


Cha brro
User currently offlinePilotboi From United States of America, joined Sep 2007, 2366 posts, RR: 9
Reply 2, posted (5 years 10 months 1 week 1 day 22 hours ago) and read 4552 times:

Do you mean this?


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Photo © Alex G.-Denicourt - Contrails Aviation Photography



User currently offlineACDC8 From Canada, joined Mar 2005, 7642 posts, RR: 35
Reply 3, posted (5 years 10 months 1 week 1 day 22 hours ago) and read 4488 times:

The little spot right over the pylon or between the pylon and fuselage?


A Grumpy German Is A Sauerkraut
User currently offlineOPNLguy From , joined Dec 1969, posts, RR:
Reply 4, posted (5 years 10 months 1 week 1 day 22 hours ago) and read 4466 times:

This might be a better picture of them...


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Photo © Juan Carlos Guerra - APM



It does indeed look like a mini-Krueger flap, and since it's there, I think one can safely conclude that Boeing thought it necessary for aerodynamic reasons...


User currently offlineNRT744 From Japan, joined Feb 2005, 33 posts, RR: 0
Reply 5, posted (5 years 10 months 1 week 1 day 22 hours ago) and read 4454 times:

Not exactly. It's not on the engine, nor is it the vortex generator (which I know). It extends and retracts along the leading edge. If you look at the photo, you'll notice that there's a small piece of slat or flap next to the engine pylon and it's clearly different from the inner slat. I'm sorry, my question was not clear.

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Photo © Andrew Hunt - AirTeamImages



User currently offlineACDC8 From Canada, joined Mar 2005, 7642 posts, RR: 35
Reply 6, posted (5 years 10 months 1 week 1 day 22 hours ago) and read 4435 times:

I've never noticed those before, but I would have to agree with OPNLguy, its most likely for aerodynamic purposes.

Would be interesting to learn more about them, such as do they have the same flap/slat settings as the rest of the leading edge or do they just have one setting?



A Grumpy German Is A Sauerkraut
User currently offlineNRT744 From Japan, joined Feb 2005, 33 posts, RR: 0
Reply 7, posted (5 years 10 months 1 week 1 day 22 hours ago) and read 4407 times:

Now that the question is clear, another question pops up. Why wouldn't they extend the inner slat? It would certainly save some weight and help maintenance. Do they have to add extra weight just for a small device as that??

User currently offlineACDC8 From Canada, joined Mar 2005, 7642 posts, RR: 35
Reply 8, posted (5 years 10 months 1 week 1 day 22 hours ago) and read 4381 times:



Quoting NRT744 (Reply 7):
Why wouldn't they extend the inner slat?

Clearance over the engine cowling I would assume? If the inner slat was extended, it looks like it wouldn't be able to extend out as much due to the proximity of the cowling. Of course, this is just my assumption, I've never flown an aircraft with leading edge slats.



A Grumpy German Is A Sauerkraut
User currently offlineNRT744 From Japan, joined Feb 2005, 33 posts, RR: 0
Reply 9, posted (5 years 10 months 1 week 1 day 21 hours ago) and read 4348 times:

That would make sense only if the "thingy" was shorter than the inner slat. But it appears to me that that small piece extends closer towards the engine.

User currently offlineQF744FAN From Australia, joined Jan 2007, 121 posts, RR: 0
Reply 10, posted (5 years 10 months 1 week 1 day 21 hours ago) and read 4330 times:

I guess this is related....
also on the T7, there's a little flap that lifts up on the top of the fuselage, to one side of the tail, during taxi.

It's always down again by the time the aircraft reaches the runway, so i've always imagined it's something to do with the APU. Can anyone be more specific?


User currently offlineJohnClipper From Hong Kong, joined Aug 2005, 844 posts, RR: 0
Reply 11, posted (5 years 10 months 1 week 1 day 21 hours ago) and read 4294 times:

That's the APU intake door...

User currently offlineNRT744 From Japan, joined Feb 2005, 33 posts, RR: 0
Reply 12, posted (5 years 10 months 1 week 1 day 21 hours ago) and read 4278 times:

That would be the APU air intake. It would close when the pilot turns the thing off. Obviously, they won't need it by the time it reaches the runway.

User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 13, posted (5 years 10 months 1 week 1 day 21 hours ago) and read 4212 times:



Quoting NRT744 (Thread starter):
Because it's so small, it makes you think why it's even there. Does it make significant "lift" if it's there? or is it there for other purposes?

It's sealing the gap between the flap and the pylon. Without it, you'd have a vortex trailing off the outboard end of the flap and shooting along the edge of the pylon. I don't know any specifics, but that can't be good for drag or airflow in that area. The pylon/wing interface is a very touchy area for aerodynamics and even relatively small changes (e.g. the "blisters" on the A340) can make a big difference.

Tom.


User currently offlineNRT744 From Japan, joined Feb 2005, 33 posts, RR: 0
Reply 14, posted (5 years 10 months 1 week 1 day 21 hours ago) and read 4179 times:



Quoting Tdscanuck (Reply 13):
Without it, you'd have a vortex trailing off the outboard end of the flap and shooting along the edge of the pylon.

Since you mentioned it, I can imagine that it would. Wouldn't the extension of the inner slat solve the problem (and save weight)?


User currently offlineACDC8 From Canada, joined Mar 2005, 7642 posts, RR: 35
Reply 15, posted (5 years 10 months 1 week 1 day 21 hours ago) and read 4145 times:



Quoting NRT744 (Reply 14):
Wouldn't the extension of the inner slat solve the problem (and save weight)?

Looking at the picture in reply 4, if you would just extend the inner slat, it doesn't look like it would cover enough to reduce the extra vortex/drag as per reply 13. Again, just a guess, but at least I'm trying ....  Wink



A Grumpy German Is A Sauerkraut
User currently offlineNRT744 From Japan, joined Feb 2005, 33 posts, RR: 0
Reply 16, posted (5 years 10 months 1 week 1 day 20 hours ago) and read 4109 times:



Quoting ACDC8 (Reply 15):
Again, just a guess, but at least I'm trying ....  

I appreciate it! That's what makes this post exciting!


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 17, posted (5 years 10 months 1 week 1 day 13 hours ago) and read 3925 times:

Its a "Kruger Flap" that seals off the area between the outboard end of the slat and the pylon.

Extending the slat to provide the same sealing would have required tapering the contour of the slat making manufacture and sealing of the leading edge, with the slat retracted, more difficult.


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 18, posted (5 years 10 months 1 week 1 day 3 hours ago) and read 3726 times:



Quoting NRT744 (Reply 14):
Quoting Tdscanuck (Reply 13):
Without it, you'd have a vortex trailing off the outboard end of the flap and shooting along the edge of the pylon.

Since you mentioned it, I can imagine that it would. Wouldn't the extension of the inner slat solve the problem (and save weight)?

It should solve the problem, and would save weight. However...

Quoting 474218 (Reply 17):
Extending the slat to provide the same sealing would have required tapering the contour of the slat making manufacture and sealing of the leading edge, with the slat retracted, more difficult.

This is definitely true. There's also the fact that, if you get really nice and close to the cowl (which you want to do for maximum effectiveness) you may need to have a clearance panel for the thrust reverser to translate without messing up your leading edge. On the 737NG this is a little spring-loaded flap, but I'm not sure what the 777 does.

I have to assume that somebody did the trade study and figured out that a nice 2D slat with a small Krueger flap was a cheaper (i.e. simpler overall) solution than a fancy contoured slat with some extra moving bits on one corner.

Tom.


User currently offlineNRT744 From Japan, joined Feb 2005, 33 posts, RR: 0
Reply 19, posted (5 years 10 months 1 week 18 hours ago) and read 3614 times:

I think that solves my problem. Thank you, everyone.

User currently offlineMender From United Kingdom, joined Feb 2004, 240 posts, RR: 0
Reply 20, posted (5 years 10 months 1 week 14 hours ago) and read 3534 times:

I'm not that familiar with the 777 but usually if the slat went all the way to the pylon the translating sleeve of the thrust reverser would hit the slat when the t/rev is deployed. On some aircraft part of this Kruger flap is spring loaded so it will retract when the sleeve is deployed.

I must admit from the picture there look to be enough clearance for the trans sleeve to deploy.

Additionally because the slat doesn't drive out at 90 degrees to the pylon the end of the slat would get closer to the pylon the more it extends. Using a Kruger flap allows the designers to seal this area better throughout the full range of movement of the slats.


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