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craigyboy
16th Sep 2010, 12:33
Hiy there im currently im currently doing my first year aeronautical engineering at college and have a report to do on winglets. One of the questions i have been asked is " investigate the impact winglets have on static longitudinal and directional stability" I would be greatful for your thoughts thanks .

Terraplaneblues
16th Sep 2010, 13:48
I would suggest going to Aviation Partners Boeing (http://www.aviationpartnersboeing.com/contact.html) and contact them via the contact button. They are experts regarding all things winglets.

craigyboy
19th Sep 2010, 17:23
oki doki thanks alot mate

PBL
19th Sep 2010, 21:10
Jeff Jupp's 2001 RAeS Lanchester lecture has some insightful comments about winglets. Please remember, when you write, to cite the sources for your comments!

PBL

HarryMann
20th Sep 2010, 02:49
Static longit stab: Think along the lines the effect that higher AR would have on Longit stab e.g. Cl-Alpha curve steeper

Directional Stability: Think along the lines of increased dihedral and increased effective AR would have, as well as any changes in roll and yaw inertia.

However, this question posed in the way it is, has certain traps...

What are we comparing with what ?

Are we comparing a pre-exisiting design without winglets with bolt on winglets?

Or are we comparing an aircraft using increased straight span with one using winglets to achieve the same effective induced drag reduction (with changes in profile drag being factored in, but incidental)?

A contemporary a/c design with winglets from the initial project definition stage would have other optimisations as well... e.g. it has been said that the only beneficial effect of winglets VS increased span per se, is that the wing-root bending moment is reduced offering a wing weight saving. Perhaps keep an eye out for this benefit (the Boeing Partners link above doesn't seem to even allude to it under 'benefits')

So, lay your terms of reference out clearly first, maybe even allude to the difficulty of comparing like with like (because they are not alike :)), which should earn you a few brownie points!

I suppose the only obvious comparison today, is the more complex one, of an aircraft of identical aerodynamic performace garnered with and without winglets... raising plenty of questions, another of which is: would they have the same effective dihedral? :)


Every decoding is another encoding
David Lodge

decurion
21st Sep 2010, 15:43
Just follow the link below and you will find lots of information:

http://ntrs.nasa.gov/search.jsp?N=0&Ntk=all|all&Ntx=mode%20matchall|mode%20matchall&Ntt=winglets|stability


example report:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19800001862_1980001862.pdf

Neptunus Rex
21st Sep 2010, 17:58
So why has the B777 got such marked dihedral and no winglets?

HarryMann
22nd Sep 2010, 00:34
Because with winglets you need less dihedral, so without you need more, like in the days of yore!

bearfoil
22nd Sep 2010, 01:01
HarryMann

"Effective Dihedral" : (Current useful iteration) Boeing787.

"The Wing as Winglet"

:ok:bear

Gerz
22nd Sep 2010, 01:50
A new clean sheet aircraft being built with a winglet is an indication of a poorly designed wing.

Not just let me get ready to dodge those arrows!!!!

Neptunus Rex
22nd Sep 2010, 06:36
HarryMann
Yes, of course, but why has the 777 got such a large amount of dihedral? It is far more than any other swept wing jet airliner.

bearfoil
22nd Sep 2010, 16:47
Just a guess, but perhaps to augment stability in the roll (at cruise). This widebody can eliminate a large amount of drag in flight by making use of the "power" in an advantaged inner wing. A still and passive airframe upsets fewer air molecules.

What is the cost of one aileron cycle to "return" the wings to level at altitude? 100 bucks?