Thursday, July 16, 2009

SWEPT WONDER

Hello guys here I am with my own aeronautics blog and it will be known the AEROGENOUS zone .Here I will come up with discussions related to various aeronautics aspects, something on which I thrive these days. My writing skills I am sure won't match up to the other regular bloggers but my motive is to put my ideas through very clearly. So here we go .............

Okay so for my first topic I thought of picking swept wings .The reason for doing this is that the advantages that the swept wings have to offer as compared to any other wings are just tremendous and have always captivated me. This is the same very reason why most of the airplanes have been using the swept wings configuration .
the grunman X-29 with forward swept wings

swept wings may be forward swept or backward swept .The sweep which you will find on most of the commercial planes is backward swept.swept wings provide wonderful static and dynamic stability and also delays critical mach numbers being reached at various parts of the plane (will be discussed later ) and thus reduce drag by preventing shock waves formation .
Let us now view the various advantages of swept wing configuration one by one:

LESS DRAG :

Now if you consider simple aerodynamic you will know that any body kept inclined to free stream velocity will offer lesser drag than the one kept normal to it .So also is the case with swept wings and thus one can save on the extra thrust due to reduced drag and also increase fuel saving along with greater flight time .

YAW STABILITY:

In the case of a crosswind coming and affecting your flight path by turning it it in the longitudinal plane in a conventional non swept wing configuration aircraft you will alter the camber of the rudder to counteract this undesirable motion .However in swept wings due its tendency of returning to its original direction (static stability) the flight will do so without the pilot having to use the rudder .The reason for this is that when you yaw the inner wings will be further inclined to the free stream of air but the outer wings will now be normal to the free stream of air thus the drag on the outer side will be more compared to that of the inner side as a result the plane will now align itself back to the original position .

ROLL STABILITY :

Just like dihedrals swept wings also give you roll stability i.e. when the plane is rotated by external undesirable forces in the along the horizontal axis by small amounts, the wings produce disproportionate lift & become horizontal again .
This actually happens because the normal flow of air over the lower wings has greater velocity than that on the upper wings this is mainly because of greater sideslip velocity of air over the upper wings (try to work it out with a vector).Thus the lower wings produce more lift than the upper wings and plane rolls back to original position .

LESS INDUCED DRAG :
Now induced drag is basically vortex formation at the wing tips which disrupts air flow . Greater the lift at the tips greater will be the magnitude of the vortex and more the drag the airplane will offer .Now most of the swept wings are formed by giving a taper like cut to the normal wing . This increase the span efficiency factor (e) . Theories suggest that greater is the span efficency factor (it basically implies to elliptical pattern of lift production wherein max lift is at root and it dies off at the tip) less will be the induced drag and hence greater will be the lift .

ADVANTAGES AT TRANSONIC SPEED :
Even when the aircraft is flying below mach 1 (say arnd 0.8-0.9 mach) there will b areas in the plane where the flow will be accelerated and shock waves will b formed offering large drag .Most of the aeronautics guide suggest that one of these areas where the flow is accelerated is around the wing tips .Now the amount by which it is accelerated is directly dependent on the chord of wing tip .Lesser the chord at the tip lesser will be the wave drag and as seen above swept wings have a samller chord at the tip as compared to that at root thus they prevent wave drag formation and allow for a proper flow to take place .

When free stream air comes under the influence of the airfoil its velocity increases continuously from the leading edge to the maximum thickness if chord and then again decreases till the trailing edge in accordance with the continuity equation .So if the flow is transonic there are chances that mach 1 speeds will be reached at max.thickness of chord and thus causing wave drag .Therefore for transonic flows the thickness of the airfoil should be reduced so that velocity at the thickest part of the chord doesn't reach sonic ranges .actually the wavedrag associated with transonic flow is directly proportional to square of chord thickness/chord length(b/l).Now swept wings is nothing but conventional wing turned through some angle therefore the length of chord is effectively increased which implies nothing but the thickness of chord has been decreased and hence swept wings offer less drag at transonic ranges .






Swept wing configuration has its fair share of disadvantages as well:
  • There is very large amount span wise flow of vortices in swept wings from the tip to the root which stalls the total wing together .this can however be prevented using wing fences which are vertical plates on wings which prevent the span wise flow of vortex.
  • The efficiency of these wings at subsonic speeds are low compared to that at transonic speeds .
  • Once the aircraft has crossed the sound barrier the efficiency's of swept wings further reduce offering large drag .
  • Many planes are under research where in you can alter the sweep angles at various stages of flight conditions and thus increase flight efficiency .Such variable sweep aircrafts have been already made but each one encountered some flaw or the other .
Well I guess thats it for my first post ...if any flaws please mention them in the comments section .....adios .......

DREAM TILL U LIVE ,CHASE TILL U DIE !!!!!

references :

  1. introduction to aerodynamics of flight
  2. From the ground up-himalayan publications
  3. www.nasa.gov
  4. www.en.wikipedia.org
  5. www.ae.metu.edu

5 comments:

  1. Nice stuff dude !

    ReplyDelete
  2. what does the spanwise flow of air do?????...

    ReplyDelete
  3. if suppose stall has occured in one part of the wing,it has tendency to flow spanwise to the other parts of the wing .Hence the turbulence(vorticity) on the other parts of the wing increases..thus causing the entire wing to stall thus reducing lift generation

    ReplyDelete
  4. thnx dude.......for a sweptback wing will the vortices(tip) spill only from the tips or all along the length of the wing....wont a sweptback wing hv a hell lot of induced drag as a result

    ReplyDelete
  5. one of the advantages of swept back wings is that the area at the tip is highly reduced as compared to that at the root hence the intensity
    of the vortex field is weaker .Also due to lesser area occupied by vortex, greater area of the wing is available for lift ...besides this aircrafts also use winglets,tiptanks etc. to reduce induced drag.

    ReplyDelete