Swept wings...who can explain??
 

Hello,

I was reading an article about swept wings stall but there is something i don't understand. Who can explain a bit:

quote" A swept wing will stall at the wing tip first because the outer wing section experiences a higher aerodynamic loading (?) due to the wing taper (?), which causes a greater angle of incidence to be experienced to a degree where the airflow stalls at the wing tips"

God, what does that mean??

thx

What it means is that the author is confused.

There's no specific reason why a swept wing should have any kind of taper ratio; in fact, there's been at least one swept wing test vehicle with inverse taper (a bigger tip chord than the root) - there's a prototype at WPAFB in the R&D display of the USAFM, can't remember the aircraft name.

The tip (in this case) is experiencing a higher wing loading due to the decrease in surface area (due to the taper).

The Republic XF-91

One of Alexander Kartveli's designs - jet + rocket power.

or any number of other reasons...

A reduction in chord at the tip doesn't have to imply a higger loading at the tip. It depends on the section/camber and any washout. It's quite possible for the tip loading to be lower than the root loading. In fact swept flying wings (tail-less aircraft) are designed so that the tip loading is negative.

I think Mad Scientist had it right - the original author isn't that good.

You to take 3D-effects into account, too. At high angles of attack there is a substantial airflow parallel to the wing's leading edge. This airflow may lead a detachment of airflow on the outer wing.
Another issue is flexibility: the outer wing is more flexible than the inner wing. Especially thin wings can then experience substantial torque deformation.

The original author got two things mixed up. A wing with a straight unswept leading edge is more likely to stall outboard first the more it is tapered. This is because the local lift coefficient may be higher outboard than inboard. In this case his statement about higher loading outboard makes some sense. A wing that has a swept back leading edge is more likely to stall outboard regardless of taper due to the threedimensional flow. The boundary layer tends to increase in thickness faster outboard than inboard because some of the flow is parallel to the leading edge away from the center. This can be countered by using boundary layer fences on the leading edge, which can be found on many swept wing airplanes to improve stall characteristics. Of course a swept wing with highly tapered wings would be a bad combination for stall characteristics.

The tendency of a swept back wing to tip stal is due to the induced spanwise flow of the boundary layer from root to tip.Loss of lift at the tip move the CP foward an towards the wing root thus giving a pitch up moment.Wing fences, Vortillons or Saw tooth ( like in the F-4) help to fix this CP movement.

I agree the original author got it mixed up Tapered wing also stall at the wintips I wouldn´t like to fly an aircraft with swept back tapered wings, a bad combination I think.:eek:

Iceman, SCaro I think you have it. The best explanation I saw of this phenomenon was Davies' discussion on the superstall, (in both the 2nd and 3rd editions, Handling the Big Jets, CAA, 1975):

P119: (b) The effect of the wing planform characteristics (sweep)
In practice the whole wing does not stall at the same instant. A simple swept and tapered wing will tend to stall at the tips first because the high loading outboard, due to taper, is aggravated by sweep back. The boundary layer outlfow also resulting from sweep reduces teh lift capacity near the tips and further worsens the situation. This causes a loss of lift outboard (and therefore aft) which produces pitch up. A lot of design sophistication is needed, including the use of camber and twist, leading edge breaker strips, fences, etc., to suppress this raw quality and get an inboard section stalled first so that the initial pitching tendency is nose down.

. . . . etc

You mean a bit like the Hawker Hunter?

Once again we have a case of one man's meat being anothers poison. It will depend on what kind of aircraft and what amount of stability you wish to design into it. A fighter jet, not allot, a passenger aircraft considerably more. For stability and controllerbility it is normal that the root will stall before the tips so that the aircraft has a degree of controllerbility in a stall. ie. the alerons still work and the aircraft stalls errect without rolling on its back suddenly and emptying the toilets into the cabin. This is not without compromise and so a fighter jet my wish to forgo this stability so it can become more responsive.

So who wants to take my Swedish CAA POF test??? :sad: :sad: :sad: :hmm: :ugh: :ugh: :ugh: