J-20 has a delta wing with leading root extensions and a trailing edge with a sweept back angle, however it can be considered a trapezoidal wing.


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Delta  wings • Advantages: • Delta  wings  have  a  long  root  chord  and  therefore  can  have  a  thick   main  spar  while  retaining  a  low  thickness-­‐to-­‐chord  ratio. • They  also  have  larger  wing  area  than  trapezoidal  wings  with  the  same   aspect  ratio.  This  means  low  wing  loading  even  during  maneuvers. • There  is  a  lot  internal  volume  for  fuel  and  landing  gear. • At  low  speed  conditions  they  can  produce  a  lot  of  additional  lift  when   placed  at  high  angle  of  attack,  thanks  to  the  leading  edge  vortices. • Delta  wing  aircraft  do  not  require  a  horizontal  tail. • Disadvantages: • Higher  viscous  drag  due  to  the  large  wing  area. • High  induced  drag  at  subsonic  conditions  due  to  low  aspect  ratio. • Bad  deep  stall. • Pitch  control  is  achieved  by  deflecting  upwards  the  trailing  edge   control  surfaces  in  order  to  produce  a  nose  up  moment.  This  reduces   the  total  amount  of  lift  generated  by  the  wing. • This  problem  can  be  overcome  by  incorporating  a  horizontal  tail  or  lifting   canards.


• The  pitch  control  and  bad  deep  stall  disadvantages  of  Delta  wings   led  to  several  variations: • Compound  Delta  or  Ogive  Delta:  the  inboard  sweep  is  generally  higher   so  as  to  create  even  stronger  leading  edge  vortices  and  delay  stall  to   even  higher  angles.   • Exception:  Saab  37  Viggen. • The  Ogive  Delta  also  reduces  supersonic  drag. • Horizontal  tail:  Provides  additionally  stability  in  pitch  and  therefore  the   wing  can  produce  more  lift.  Tail  elevator  provides  pitch  control • Canards:  They  are  usually  all-­‐moveable  and  provide  additional  pitch   control.  The  aircraft  is  usually  statically  unstable. • Note  also  that  flaps  are  difficult  to  use  with  a  tailless  Delta   configuration. • Delta  wings  are  generally  cropped.  The  pointy  wingtip  is  difficult   to  manufacture  and  structurally  weak.  Furthermore,  cropped   Delta  wings  delay  vortex  bursting. • The  centre of  lift  lies  aft  on  a  Delta  wing.  This  means  that  the   horizontal  tail  can  only  be  effective  if  it  lies  even  further  aft.   Usually  the  tail  is  highly  swept  and  can  be  placed  on  a  highly   swept  fin.

Trapezoidal  wings • In  trapezoidal  wings,  the  leading  edge  sweeps  back  but  the   trailing  edge  sweeps  forward.   • Some  Delta  wings  also  feature  a  slight  sweep  forward  angle  at  the   trailing  edge. • Advantages • Better  performance  than  Delta  wings  at  transonic  speeds  and  during   transition  to  and  from  supersonic  conditions. • They  do  not  require  upwards  deflection  of  the  trailing  edge  control   surfaces  for  pitch  control  and  therefore  do  not  lose  lift. • Their  centre of  lift  lies  further  forward  and  therefore  the  tail  must  not   lie  too  far  back  on  the  fuselage. • They  are  preferred  for  stealth  applications. • Flaps  can  be  easily  used. • Disadvantages: • High  wing  loading. • They  stall  at  much  lower  angles  of  attack  than  Delta  wings. • This  problem  is  overcome  using  Leading  Edge  (Root)  eXtensions (LEX  or  LERX)   and/or  canards


• Trapezoidal  wings  are  mostly  used  by  the  US. • They  are  nearly  always  combined  with  a   conventional  horizontal  tail  and  single  or  twin  fin. • They  are  nearly  always  combined  with  LEX. • Some  trapezoidal  wings  look  like  highly  cropped   Delta  wings  (F-­‐16  for  example). • Modern  trapezoidal  wings  have  very  highly  swept   leading  edges,  approaching  the  sweep  of  Delta   wings.

 


source  http://www.ltas-cm3.ulg.ac.be/AERO0023-1/ConceptionAeroFighter.pdf

The YF-23 has trapezoidal wings as they  stall  at  much  lower  angles  of  attack  than  Delta  wings, this  problem  is  overcome  using  Leading  Edge  (Root)  eXtensions (LEX  or  LERX)   and/or  canards, thus YF-23 has very long and sharp LERX.   The Trapezoidal wings have the centre of  lift  lies  further  forward  and  therefore  the  tail  must  not   lie  too  far  back  on  the  fuselage.  They  are  preferred  for  stealth  applications, all these features are seen on YF-23.