
New features in XFOIL 6.1 (April 94)
------------------------------------
- An improved plot library libPlt.a is now used, courtesy of H. Youngren.
  It allows resizing of the window, and plots are not erased upon overlay
  by another window.  A minor new nuisance is that the cursor does return 
  automatically to parent window after cursor input.
  
- All LOGICAL*1 arrays have been eliminated (good riddance!).
  CHARACTER strings are used instead.  This was made possible
  by the new plot library which accepts CHARACTER variables.

- Mach number can now scale with 1/sqrt(CL) just like Reynolds number.

- Numerous improvements have been made to the GDES, MDES, and QDES
  facilities.  Cursor-input Qspec(s) in QDES and MDES will now match 
  slopes where grafted into the current Qspec(s).  Much fewer cursor
  input points are now required.  Same goes for the geometry contour 
  in GDES.  The slope-matching can be disabled to get the cruddy old 
  way of doing things.  The Qspec(s) plot in MDES and QDES now also 
  features an x/c grid overlay, making it more obvious where the 
  airfoil nose is among other things.  The Qspec(s) plot in MDES 
  can also show Qspec(s) for more than one angle of attack, showing 
  the effect of any modification on off-design pressure distributions.
  Symmetric airfoils can be much more easily designed now in MDES
  and GDES.

- Treament of non-unity airfoil chords is now much more consistent.
  Clear distinctions are made between cartesian x,y and the airfoil
  chord line-based x/c,y/c coordinates.  GDES now has more general
  airfoil positioning and scaling operations, and there is better
  graphical info on the results of flap and camber change operations.

- Cursor-selected blowups in QDES and MDES now produce exactly 
  the blowup region demarked, not some approximation thereto.
  The GDES blowups are also more faithful, but must still be
  approximate since they will not allow x/y distortion.

- A second-order treatment of the amplification equation has been
  implemented.  As expected, It makes the solution less dependent
  on the panel density.  However, it also seems to be less robust.
  For this reason, it has been implemented only as an option,
  and the old first-order treatment has been retained as the 
  standard formulation.  To switch between the two, a few labeled
  code lines in SUBROUTINES AXSET, TRCHEK (in xblsys.f) simply 
  need to be commented/uncommented.


New features in XFOIL 6.3 (Oct 94)
----------------------------------
- Nice grid overlays and axis limit set capabilities have been 
  added to the viscous variable plots (VPAR).

- GDES has a number of new options, mainly for controlling 
  individual coordinate points.

- Minor modifications have been made to the viscous formulation
  to make it very nearly the same as the MSES 2.6 formulation,
  except that XFOIL still uses a single-layer wake.


New features in XFOIL 6.4 (Dec 94)
----------------------------------
- A modification to the e^n transition criterion has been added
  to make it more reliable, especially for small Ncrit.  The
  default form for the amplification equation is now second-order.

- Limiters have been put into most of the turbulent correlations
  to make them automatically revert to their laminar form at small
  Rtheta, including the dissipation coefficient for the wake.
  As a result, XFOIL will now produce reasonable answers for
  chord Reynolds numbers down to about 1000, which approaches 
  the Stokes-flow regime.  The airfoils must be reasonably thin,
  however, else there might not be any steady solution due to
  vortex shedding.  Thin indoor-model wing airfoils can be 
  predicted reasonably well, for example.


New features in XFOIL 6.6 (March 96)
------------------------------------
- A fourth type of airfoil coordinate format is now recognized.
  This is called a "labeled coordinate file", and is the same as
  the plain format file, but includes the airfoil name string 
  on the first line, followed by the coordinates.

- A completely new plot library is now used, courtesy of H.Youngren.
  It supports color, PostScript echo on demand (instead of the arcane
  hardcopy-toggle approach of the previous plot library), lowercase
  fonts, LaTex-like math fonts (in annotation menu), etc.  This
  one plot library is used for all machines.

- Color is now used in many of the screen plots, but only where
  it actually helps to see what's happening.  Color is NOT used
  for ornamental purposes.  Hence, many of the plots or parts
  of plots are still monochrome.  Color PostScript can be output
  by setting the IDEVRP flag appropriately (see SUBR. INIT).

- The "!" command is now understood by OPER,GDES,MDES, and QDES.
  This simply repeats the last valid command, and saves typing
  in repetitive-command situtations.


New features in XFOIL 6.8 (August 96)
-------------------------------------

- The matrix-conditioning problem which appears in sharp-TE cases
  with large TE angles has been significantly alleviated.  A more
  forgiving TE vorticity extrapolation scheme is used.

- GDES now displays useful geometric info along with the airfoil shape.

- Color is now used in most of the plots to aid visualization.
  The plot can be customized with a number of plot options set
  in the PLOP menu.  Portrait orientation plots can now be 
  generated if desired.

- Almost all commands which result in prompted input can now 
  be given arguments with the input values.  For example, 
  instead of
 
     .OPERi   c>  alfa

     Enter angle of attack (deg)   r>  3.5


  one can simply type

     .OPERi   c>  alfa 3.5


  which suppresses the prompt and just takes the "3.5" as its input.
  This also works for multiple-input commands.  For example:

     .OPERi   c>  aseq  0 10 0.5

  does the usual alpha-sequence calculation with no further prompts.
  This also works for filenames.  For example:

     XFOIL   c>  load e387.dat



New and final(!) features in XFOIL 6.9  (February 00)
----------------------------------------------------

- Finally fixed that annoying screwy behavior with sharp trailing edges.
  Instead of the vorticity extrapolation scheme, the chordwise velocity 
  at an internal point near the TE is set to zero to enforce solution 
  regularity there (this complements the Kutta condition, which controls 
  the normal velocity component).   This additional internal point is 
  placed 1/10 of the smallest panel length ahead of the TE.  The results 
  are extremely insensitive to its exact location.

- Multiple airfoil versions and associated polars can now be stored
  inside XFOIL.  The polars and airfoils are managed in OPER.
  Having the polars and airfoils online reduces the amount of 
  airfoil read/writes and mental bookkeeping which was required 
  in previous XFOIL versions which had only one airfoil stored. 
  Quite a few new commands have been added to OPER to deal with 
  this additional stuff, but everything more or less defaults to 
  the previous conventions if only one airfoil is kept stored.
  The session.txt file has a sample session with multiple polars.

- Airfoil interpolation can now be performed with the INTE
  command at top level.

- A bunch of Youngren's camber/thickness modification stuff has
  been incorporated into GDES.

- Most of the interactive modification displays now include
  "Erase" and "Done" keys in addition to the "Abort" key.
  These can also be activated just by typing "e", "d", or "a"
  rather than by clicking on the button.  The Erase key 
  deletes the previous click entry (or previous entries if done
  repeatedly).  The Done key terminates input.  In previous versions
  this was done by three identical clicks, which was sometimes 
  difficult to do.


XFOIL 6.91 (December 00) (first web release)
--------------------------------------------

- Renamed "Gamma" to "Q" in the QDES and MDES menus.  This gives
  somewhat more obvious relation to "Qspec".

- The PREM command has been added to the OPER menu.  This allows 
  removing individual points from stored polars.

- The CADD command has been added to the GDES menu.  This adds 
  new points into the buffer airfoil at excessive panel corners.  
  The new points are interpolated using a uniform-parameter spline, 
  which gives much smoother shapes near the leading edges of 
  Selig and Eppler airfoils, whose point spacing at the leading edge
  is usually not suitable for Xfoil's arclength-parameter spline.   
  For example, the load sequence...

     LOAD s6063.dat
     GDES
     CADD
        <return>  (accept default inputs)
        <return>
        <return>
     <return>
     PANE         (generate new paneling using smoother buffer airfoil)
 
  will give a much smoother paneled airfoil than the more direct...

     LOAD s6063.dat
     PANE


XFOIL 6.92 (January 01)
-----------------------

- Fixed the PSOR command.  Giving "0" for the polar index now sorts all
  the polars as advertised.  Previously, this deleted all the polars (oops).

- Fixed PPLO command.  Giving multiple individual polar indices now plots only
  those polars as advertised.  Previously, all polars were always plotted.

- Added DUMP and OVER commands to the VPLO menu.  This allows comparing 
  viscous variable distributions between different airfoils and/or 
  different operating points.

- Added BLC, BLWT commands to OPER menu.  These allow plotting of boundary
  layer velocity profiles on airfoil in Cp vs x plot.  Gives more insight
  into what the flow is doing than just the displacement body shape.


XFOIL 6.93 (18 January 01) HHY
-----------------------

- Improvements to polar plotting for XFOIL and PPLOT.  Many fixes to read 
  XFOIL and non-XFOIL polar files. Routine polplt.f overhauled to eliminate 
  numerous cruftious hacks and long-standing polar plot problems.
  
- PPLOT improvements to add options and de-obfuscate menu choices. Tweaks to 
  make pplot.f work with new polplt.f changes.  More robust than previous 
  version - now reads MSES and old XFOIL format polar files.

- Fixed CAMB options for INPP and MODP.  Plotting hack for INPP fixed to 
  to properly display grid.  MODP problems (improper scaling of user points)
  fixed.  

- Changed ASKR and ASKI and all relevant calls.  Now ASKR or ASKI calls do 
  not modify variable passed in if read line is blank (i.e. user just inputs
  a <cr>).  Lines to set reasonable defaults added throughout where these
  routines read temp variables or variables not stored in globals. This affects
  mostly routines in GDES.

- Latest plotlib (version 4.44) included.  This version has several bug fixes
  and adds capability to write separate postscript files for each plot (if you
  ask for this).  Also default background color is now black.  User must now
  specifically ask for white background by setting environment variable 
  "XPLOT11_BACKGROUND white". This is done for csh/tcsh and bash using
  csh:   setenv XPLOT11_BACKGROUND white
  bash:  export XPLOT11_BACKGROUND=white

- Bug in dplot.f (LGUI declaration) and funky format (A,I) in xplots.f changed 
  to work with g77.


XFOIL 6.93 (March,April '01) MD's additions
-------------------------------------------

- Made CM axis line up with CL-axis tics in polplt.f .

- Changed Xplot11 to start cursor at previous location rather than at 
  center of plot window.  Makes repetitive mouse input much more pleasant.

- Checks for excessive panel angle in input coordinates, and prints
  suggested corrective action if indicated.


XFOIL 6.94 (Nov '01)
--------------------

- Put in alternative short versions of most commonly used commands
   Examples:  
    "ALFA" and "A" are now equivalent commands in OPER
    "EXEC" and "X" are now equivalent commands in MDES,QDES,GDES

- Added a number of minor widgets and doodads

- Fixed PostScript output semi-bug (wrong number of tokens after %%Page)


XFOIL 6.95 (Feb '03)
---------------------

- ITER command in OPER now accepts a numeric argument like the other commands

- Inviscid polar accumulation now permitted

- Improved ADDP and MOVP in GDES, allowing optional keyboard x,y entry

- Added I,O,P key functions in cursor-modifiaction windows, 
  allowing zooming and panning without exiting the window

- Added individual-frequency plotting to A/Ao plot in VPLO.
  Requires Orr-Sommerfeld database in compatible binary form.
  This is built in the new directory orrs/


XFOIL 6.96 (Jan '05)
---------------------

- Added a bunch of features to PPLOT.  
  Power coefficient polars and aircraft polars can now be plotted.

- Added graphic enable/disable flag to PLOP sub-menu.
  Allows suppression of graphics output for batch execution.

- Increased default number of panel nodes from 140 to 160

- Increased default iteration limit from 10 to 20

- Changed VACCEL logic to make it independent of airfoil size
  (previously it assumed that chord was comparable to unity)

- Added BEND command to GDES

- Airfoils are now written out in 7 significant digits using G-format.
  This should prevent introduction of noise with very fine point spacings.

