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What Is The New 787-9 Drag Reducing Technology?  
User currently offlineJAAlbert From United States of America, joined Jan 2006, 1491 posts, RR: 1
Posted (6 months 4 days 8 hours ago) and read 4897 times:

I watched a Boeing video on the 787-9 recently and the engineer interviewed stated that they had to find a way to reduce drag on the 787-9. Their first attempt failed, but by "leveraging a number of different disciplines" and "bringing together the best and the brightest," Boeing was able to reduce the aerodynamic drag of the 787-9. Of course this little video is just a marketing tool and doesn't provide any actual information, but it got me wondering:

1. Why is drag a bigger problem on the 787-9 vs. the 787-8?
2. Is the increased drag related to something other than the increased size of the plane?
3. What specific technologies was Boeing able to "leverage" to reduce the drag and any information by how much they were able to reduce drag? (I suppose that info is proprietary, but I might as well ask!)
4. If drag is an issue with the larger 787-9, what kind of challenges will Boeing face with the larger still 787-10 and how will they solve that problem?

Here's a link to the video - go about midway down the page to the right and click on the 787-9 Innovations link: http://www.newairplane.com/787/787-9/?v=2

10 replies: All unread, jump to last
 
User currently offlineStitch From United States of America, joined Jul 2005, 29672 posts, RR: 84
Reply 1, posted (6 months 4 days 8 hours ago) and read 4865 times:
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Boeing is implementing passive hybrid laminar flow control into the vertical stabilizer of the 787-9. This is being done to reduce stabilizer drag by upwards of 1%, which reduces fuel consumption. It is being implemented on the 787-9 because Boeing manufactures the vertical stabilizer for this model (Alenia Aeronautica builds the one used on the 787-8). I expect HLFC will also be used on the 787-10 vertical stabilizer.

Both the 787-8 and 787-9 employ natural laminar flow on the engine nacelles.

Guy Norris had a nice write-up about it in Aviation Week.

[Edited 2013-10-14 16:24:52]

User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 2, posted (6 months 4 days 7 hours ago) and read 4842 times:

Quoting JAAlbert (Thread starter):
1. Why is drag a bigger problem on the 787-9 vs. the 787-8?

Increased area means increased skin friction drag.

Increased weight means increases induced drag. Given the same wing, for a higher weight the angle of attack will be higher since the wing needs to generate more lift. More lift gives more induced drag.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineJAAlbert From United States of America, joined Jan 2006, 1491 posts, RR: 1
Reply 3, posted (6 months 4 days 3 hours ago) and read 4707 times:

Quoting Stitch (Reply 1):
Guy Norris had a nice write-up about it in Aviation Week.

Thanks for the insight. I reviewed the Aviation Week article. As I understand it, the vertical (and perhaps horizontal) stabilizers will have tiny holes on the leading edge that will suck air into the stabilizer and out an exit. The system is entirely passive. So now my questions is, isn't there a danger that these small holes can become plugged up with ice during certain flights? Much like the AF flight's pitot tubes that froze over? I don't suppose clogged intakes would interfere with the plane's ability to fly, but if they became clogged, it would cancel out the benefit of the system. Thoughts?


User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 4, posted (6 months 4 days 3 hours ago) and read 4678 times:

Quoting JAAlbert (Reply 3):
So now my questions is, isn't there a danger that these small holes can become plugged up with ice during certain flights? Much like the AF flight's pitot tubes that froze over? I don't suppose clogged intakes would interfere with the plane's ability to fly, but if they became clogged, it would cancel out the benefit of the system. Thoughts?

They could become clogged, but all you'd get is some extra drag. Also I'm assuming these holes would be quite a bit larger than a pilot tube, so less risk of icing.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently onlinemusang From United Kingdom, joined Apr 2001, 844 posts, RR: 7
Reply 5, posted (6 months 3 days 20 hours ago) and read 4544 times:

Quoting Starlionblue (Reply 4):
these holes would be quite a bit larger than a pilot tube,

Co-incidentally I was talking to a Boeing sales manager about this a few days ago. The holes are like pin-pricks.

Regards - musang


User currently offlinejetmech From Australia, joined Mar 2006, 2634 posts, RR: 53
Reply 6, posted (6 months 3 days 18 hours ago) and read 4473 times:

Quoting JAAlbert (Thread starter):

This appears to be the patent for the system;

http://www.google.co.in/patents/US7866609

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 7, posted (6 months 3 days 17 hours ago) and read 4456 times:

Quoting musang (Reply 5):
Quoting Starlionblue (Reply 4):
these holes would be quite a bit larger than a pilot tube,

Co-incidentally I was talking to a Boeing sales manager about this a few days ago. The holes are like pin-pricks.

Cool! Seems to be related to laminar flow control on the Buccaneer and such. This system is passive though.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineGAIsweetGAI From Norway, joined Jul 2006, 933 posts, RR: 7
Reply 8, posted (6 months 3 days 5 hours ago) and read 4208 times:

Quoting JAAlbert (Reply 3):
Thanks for the insight. I reviewed the Aviation Week article. As I understand it, the vertical (and perhaps horizontal) stabilizers will have tiny holes on the leading edge that will suck air into the stabilizer and out an exit. The system is entirely passive. So now my questions is, isn't there a danger that these small holes can become plugged up with ice during certain flights? Much like the AF flight's pitot tubes that froze over? I don't suppose clogged intakes would interfere with the plane's ability to fly, but if they became clogged, it would cancel out the benefit of the system. Thoughts?

I recall reading about some research Dassault had done about laminar flow - although I really don't recall where. One of the notable findings was that even with a significant fraction of the pores in the airfoil surface clogged by insects, dirt, etc., the drag of the wing was still lower than if a classic "smooth" airfoil had been used.

Does this sound familiar to anyone?



"There is an art, or rather a knack to flying. The knack lies in learning how to throw yourself at the ground and miss."
User currently offlinedynamicsguy From Australia, joined Jul 2008, 851 posts, RR: 9
Reply 9, posted (6 months 2 days 22 hours ago) and read 4075 times:

Quoting JAAlbert (Thread starter):
1. Why is drag a bigger problem on the 787-9 vs. the 787-8?

I know in discussions around the weight of the -9 during development it was stated that if it didn't hit a particular benchmark for performance then it would potentially lose half its market, so it make sense that they would also need to pull out all stops for drag. As well as keeping weight down, we made some small aerodynamic tweaks to our parts.

I'm actually not entirely sure the aerodynamic advance referred to in the video is the hybrid laminar flow control. If that was it, then why wouldn't they refer to the horizontal stabiliser in the video? The script seems to have been deliberately written to say nothing. It could be the HLFC ("deemed impractical for the past 30 years") but it could be something else.


User currently offlinenomadd22 From United States of America, joined Feb 2008, 1763 posts, RR: 0
Reply 10, posted (6 months 2 days 20 hours ago) and read 4019 times:

Quoting JAAlbert (Thread starter):
Why is drag a bigger problem on the 787-9 vs. the 787-8?

It's not "A bigger problem" They're just making a lot of improvements on the -9 now that they have all the data and knowledge from manufacturing the -8. Most of those improvements will be rolled back into the -8 eventually.



Andy Goetsch
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