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Question On Wing Design...  
User currently offlineKhenleyDIA From Sweden, joined Feb 2005, 425 posts, RR: 0
Posted (6 years 4 months 2 days 20 hours ago) and read 3117 times:

I have wondered about this for a long time and I decided to actually post my question. Not sure of the right words or ways to explain it, so it makes it hard to look for duplicates too.

Examples:


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Photo © Duncan Monk
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Photo © Artur Jarosz - Warsaw Aviation Photography



Two different planes, but I want to focus on a certain part of the wing. Looking at where the Engine Mount (?) attaches to the wing... The question is this. With the KC-10, there is a rather large 'lip' that sticks out over the Engine Mount. The 757 has one too, but not as big. Thinking of airflow, why not smooth that design so air passes over it easier? I understand you want air under the wing, but I would imagine that these 'lips' disrupt the airflow a bit. Good or bad??

Thanks,

KhenleyDIA

Missed an 'N' in the title. Bad keyboard.

[Edited 2008-03-30 01:16:26]


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8 replies: All unread, jump to last
 
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 1, posted (6 years 4 months 2 days 19 hours ago) and read 3107 times:

When the leading edge slats (the moveable surfaces you see deflected downwards in the pictures) come up, that lip will be perfectly integrated with the rest of the wing. Redesigning it to be smooth with the slats extended would mean it would not be smooth with the slats retracted and hence hamper the aerodynamics in the region of flight where it will really cost you.

Rgds,
/Fred



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User currently offlineSpencer From United Kingdom, joined Apr 2004, 1635 posts, RR: 17
Reply 2, posted (6 years 4 months 2 days 16 hours ago) and read 3090 times:



Quoting KhenleyDIA (Thread starter):
I understand you want air under the wing, but I would imagine that these 'lips' disrupt the airflow a bit.

In fact most of the lift, or a great percentage of it, comes from air passing over the upper surface of the wing. The greater distance the airflow has to travel over the top surface, as opposed to the lower surface (due to the shape of the wing) results in a faster airflow on top, leading to a lower pressure region, producing lift. From the images you've linked there looks to be a greater area above the "lip" than below.
Spencer.



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User currently offlineJetMech From Australia, joined Mar 2006, 2684 posts, RR: 53
Reply 3, posted (6 years 4 months 2 days 16 hours ago) and read 3082 times:



Quoting KhenleyDIA (Thread starter):
but I would imagine that these 'lips' disrupt the airflow a bit. Good or bad??

I think the engine pod and pylon in general will disrupt the airflow around that region of the wing. Many commercial airlines have strakes on the sides of the engine cowls to help remedy this situation. You can see these strakes on the picture of the DC-10.

IIRC, these strakes general powerful vortices which help to re-enrgise the sluggish flow around this region. This makes it much more likely that the airflow will remain attached to the region of the wing behind the pylon. I believe that this is most important for high angle of attack operations such as rotation on take off. I'm not too sure of the importance of the strakes for cruise conditions.

You can just see the vortice coming off the cowl strake upon rotation in these videos.





They are much clearer in these photos.


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Photo © Lasse Kaila
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Photo © Belgium Air Force Sgt. Dirk Voortmans




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Photo © Tim de Groot - AirTeamImages
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Photo © Javier Guerrero - AirTeamImages



Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 4, posted (6 years 4 months 2 days 9 hours ago) and read 3030 times:



Quoting KhenleyDIA (Thread starter):
Thinking of airflow, why not smooth that design so air passes over it easier? I understand you want air under the wing, but I would imagine that these 'lips' disrupt the airflow a bit. Good or bad??

You're always going to have some airflow disturbance where the pylon joins the wing because of the abrupt changes in surface normals. So the question becomes...where do you want your disturbed air going? The top surface of the airfoil is far more sensitive to separation and disturbed flow than the bottom, so you want to keep you "dirty" airflow under the wing, not over it. I suspect that's why the slight overhang on the leading edge. In cruise, that probably puts your stagnation point entirely above the pylon and your dirty air would all go under the wing.

The 777, which was done with considerably more advanced CFD codes than the DC-10 or 757 has the same thing, so I would guess that it's not worth smoothing it out:

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Photo © Andrew Hunt - AirTeamImages



The 737, interestingly, does not, but I suspect that's due to the very tight ground clearance requirement:

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Photo © Matthew Wallman



Tom


User currently offlineEx52tech From United States of America, joined Dec 2006, 559 posts, RR: 1
Reply 5, posted (6 years 4 months 2 days 7 hours ago) and read 3002 times:



Quoting JetMech (Reply 3):
I'm not too sure of the importance of the strakes for cruise conditions.

Because the nose cowls are interchangeable on the DC10, if you mount the strake in the wrong place, especially on the inboard side of the nose cowl it will cause a vibration, and oscillation that gets worse with speed. So they do effect more than low speed high angle of attack on a DC10 anyway.



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User currently offlineJetMech From Australia, joined Mar 2006, 2684 posts, RR: 53
Reply 6, posted (6 years 4 months 2 days 3 hours ago) and read 2961 times:



Quoting Ex52tech (Reply 5):

I see. I actually remember one of the boys having to remove a strake from the cowling of a 767. Perhaps it was for the same reason? Do you know if it is possible for the DC-10 to operate without one or both of the strakes?

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineKhenleyDIA From Sweden, joined Feb 2005, 425 posts, RR: 0
Reply 7, posted (6 years 4 months 1 day 21 hours ago) and read 2928 times:

Thank you all for your answers! They were very helpful!

JetMech, thanks for the pictures and the videos. I have seen that first hand, but still always good to have it explained, at least so I can say I have some idea, even if I can't say that I 'know' all about it.

Again, thanks!!

KhenleyDIA



Why sit at home and do nothing when you can travel the world.
User currently offlineEx52tech From United States of America, joined Dec 2006, 559 posts, RR: 1
Reply 8, posted (6 years 4 months 1 day 12 hours ago) and read 2869 times:



Quoting JetMech (Reply 6):
Do you know if it is possible for the DC-10 to operate without one or both of the strakes?

I would think that they could continue on if they lost one, I don't have access to the MEL anymore to check. I do know that they cause a lot of raised eyebrows if placed wrong.



"Saddest thing I ever witnessed....an airplane being scrapped"
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