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Old 27th Sep 2010, 21:45   #1 (permalink)
 
Join Date: Sep 2010
Location: florida
Posts: 18
sweepback wings

Hello folks. This is my first post on PPRuNe...

Here is my question.

How does sweepback wings have higher maximum speed than other rectangular wing etc..?

Why do most modern a/c use sweepback wing?

From general reading Sweepback wings tends to stall first at the tips .. But isnt't it better for a aerofoil to stall first at wing root to give pilot enough indication before the wings drop?

Please help me out with these doubts.

Thanks
Parasite
parasite tango is offline   Reply
Old 27th Sep 2010, 21:54   #2 (permalink)
 
Join Date: Jan 2008
Location: Herts, UK
Posts: 600
Yes, sweptback wings tend to load up more at the tips and stall there first, c.f. straight wings, although fortunately there are ways to prevent that becoming a serious problem.

However, they have a lower Critical Mach No.* for a given aerofoil section, which is why they are used on nearly all aircraft that fly above about M 0.65 ~ 0.7

* ...which means they have less Mach drag as the aircraft approaches the speed of sound.

The other ways Mach drag is reduced is using very thin wing sections (structurally heavy and inefficient for carrying fuel), very advanced aerofoils (super-critical sections) and careful wing/body blending at the engine pods as well as the fuselage.

Super-critical profiles are used hand in hand with sweep. As sweep is increased structural problems (more weight) start to dominate, so everything is a compromise and sophisticated optimisations are required to find the very best balance of very many factors. Fluuter, is another unwanted affect that is reduced or stabilised by sweep.

This is why so many aircraft look fundamentally similar (in fact so many twin jet airliners rear profile flying away from the observer still look like large ME 262 jets of WWII vintage, to my eye - so that must have been pretty well thought through!)

You may also notice that as engineering advances, more & more cars with the same function tend to look almost the same too...

Form follows function
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