Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
When Outboard Ailerons Act As Flaps...  
User currently offlineHappy-flier From Canada, joined Dec 1999, 299 posts, RR: 0
Posted (4 years 8 months 2 weeks 6 days 10 hours ago) and read 3411 times:

What brought about the distinct change in design philosophy that has seen airliners that routinely use the outboard ailerons to augment flap function? Examples: 777, A330/340, MD11. The use of inboard ailerons only in the same manner - as on the 767, for example - was seen a bit earlier. And, going still farther back in time, no other major jets ever used any of the ailerons (inboard or outboard) in the same way (e.g. 707, 727, DC-10, L1011, 747).

Does having the entire wing trailing edge as "one flap", even if in sections, allow you to use fewer degrees of deflection overall, thus increasing lift while decreasing drag? Is that the whole point?

As a counterexample, consider the KC-135 wing. The flaps have a large deflection, while the ailerons do not perform any flap augmentation: this causes there to be simultaneous sections of high-lift, and other sections of perfectly clean wing.

Would love to read some thoughts on this whole thing.


May the wind be always at your back . . . except during takeoff & landing.
5 replies: All unread, jump to last
 
User currently offlineRwessel From United States of America, joined Jan 2007, 2316 posts, RR: 2
Reply 1, posted (4 years 8 months 2 weeks 6 days 8 hours ago) and read 3381 times:
Support Airliners.net - become a First Class Member!

Flaperons are fairly common on sailplanes. They provide better roll performance, since the effective ailerons are now much bigger (remember that most sailplanes are pretty ponderous in roll - especially at lower speeds) - on some sailplanes essentially *entire* span* is covered by the flaperons - on others it's only the outboard half-or-so, and more effective flaps, since they're bigger too (no cutouts for the ailerons).

You do need a mixer to combine the two inputs. Presumably this is pretty straight-forward to implement on a FBW aircraft.

OTOH, you don’t see the complex flap types on gliders that you do on powered aircraft, so I’d assume it’s more treating the aileron as an additional section of simple flap to eek a few extra percent performance out of the wing at low speed.


*Although it’s not uncommon for there to be more than one segment.


User currently offlineSwiftski From Australia, joined Dec 2006, 2701 posts, RR: 2
Reply 2, posted (4 years 8 months 2 weeks 6 days 8 hours ago) and read 3378 times:



Quoting Happy-flier (Thread starter):
Does having the entire wing trailing edge as "one flap", even if in sections, allow you to use fewer degrees of deflection overall, thus increasing lift while decreasing drag? Is that the whole point?

Whenever you use flap, you increase lift (refer to lift formula if needed).

Whenever you show more of an aerofoil to the relative airflow, you increase drag.

Flaperons are designed to deploy less than flaps, not to act as a large combined flap all the way across the aerofoil.

Does that make sense? I'm not sure if I'm being clear.


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 3, posted (4 years 8 months 2 weeks 6 days 8 hours ago) and read 3367 times:



Quoting Happy-flier (Thread starter):
What brought about the distinct change in design philosophy that has seen airliners that routinely use the outboard ailerons to augment flap function? Examples: 777, A330/340, MD11.

Primarily FBW. It's not required, obviously, but it's a lot easier. Implementing aileron function, flap function, and high-speed lockout all at once in a manual or manual/hydraulic system is not trivial (and heavier). In FBW, it's just more lines of software (and no weight penalty).

Quoting Happy-flier (Thread starter):
Does having the entire wing trailing edge as "one flap", even if in sections, allow you to use fewer degrees of deflection overall, thus increasing lift while decreasing drag?

Yes. Full-span flaps have lower induced drag than the same amount of lift coming from part-span flaps.

However, I suspect the weight advantage is much larger than the drag/deflection advantage.

Tom.


User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2255 posts, RR: 15
Reply 4, posted (4 years 8 months 2 weeks 6 days ago) and read 3253 times:

We used the drooped ailerons on our MD-11 for years but they were finally deactivated due to the increased maint.

User currently onlineB777LRF From Luxembourg, joined Nov 2008, 1308 posts, RR: 3
Reply 5, posted (4 years 8 months 2 weeks 5 days 14 hours ago) and read 3104 times:

The main benefit of drooping ailerons is that it'll allow for slight lower landing speeds, thus reducing landing distance required. It may also help to lift a bit more weight off a restricted runway or, conversely, reduce the Take-off distance required with similar weights.

Though it wasn't an option for early generation FBW Airbii, it became retrofitable through nothing more than a software update, demonstrating just how clever FBW can be.



From receips and radials over straight pipes to big fans - been there, done that, got the hearing defects to prove
Top Of Page
Forum Index

Reply To This Topic When Outboard Ailerons Act As Flaps...
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
777 And 330/340 Ailerons Drooping With Flaps posted Sun Aug 29 2004 22:16:04 by Starlionblue
Inboard Versus Outboard Ailerons posted Sun Jul 28 2002 01:23:25 by Wilax
A340 Ailerons Drooping When Flaps Set posted Sat Feb 16 2008 20:15:26 by Happy-flier
When A Plane Pulls 4g What Weighs 4x As Much? posted Tue Oct 7 2008 22:37:21 by ThreeFourThree
Ailerons, Flaperons, Flaps - All On The Same Wing posted Sat Jul 7 2007 13:31:28 by TripleDelta
F/As Told When To Prepare To Land? posted Tue Apr 10 2007 00:53:35 by CanadianNorth
Why Not Fully Extend Flaps When Landing? posted Mon Feb 26 2007 03:46:10 by Theflcowboy
When To Retract Flaps During Landing Run? posted Mon Sep 13 2004 02:06:40 by Bragi
Flaps 40 The Norm When Landing On A Short Runway? posted Sun Sep 28 2003 05:13:10 by John
Modern Jetliner Exhaust - When Is It Too Dirty? posted Tue Nov 3 2009 22:00:30 by Reggaebird

Sponsor Message:
Printer friendly format