*========================================================================*
Notes for XROTOR 6.7
HHY 6/22/98

This version started as the MIT version 6.6 and was modified to fix some 
of the compile problems.  A new Makefile was added that gives options for most
workstations (including Linux with several fortran compilers).

Work was also done to fix the interactive options for cursor input 
(for CL spec, Chord spec, Blade angle spec).  Hot keys (z,u,q) were added 
to these interactive plots to allow the user to zoom, unzoom and abort 
cursor input.  

There were also several problems with the plot library for window switching
from Landscape to Portrait.  This version of plotlib has a fix that appears
to work in the DEC Alpha and on Linux (others probably work, not tested).
*========================================================================*
*========================================================================*
Notes for XROTOR 6.80
HHY 3/13/99

This version started as a modified MIT version 6.7 and a number of changes were
made to:

 New aero model for sections based on limiter function for CL

 New option for discrete vortex wake integration of induced velocity

 Blades can optionally have constant non-zero rake angle in x,y plane (this
 requires the user to use the discrete vortex wake option)

 Structure analysis now can include correct forces for raked blades

 Options for setting # of radial stations and display increment from user
 dialog

This should be considered a developmental version of XROTOR...
*========================================================================*
*========================================================================*
Notes for XROTOR 6.9
HHY 3/13/99

This version completed a number of enhancements to the basic code

 New aero model
  Radial stations on the prop can now have assigned aerodynamic properties.
  This uses the concept of "aero sections" between which the aero properties 
  will be linearly interpolated.  

 New convergence and relaxation parameters to facilitate convergence of 
  Newton system.  

 New helicopter output quantities for cases with very low advance ratio where
  XROTOR can be used for hover analysis.
*========================================================================*
*========================================================================*
Notes for XROTOR 7.0
HHY 7/00

This version completed a number of enhancements to the basic code

 Enhancements of aero model
  Mcrit and compressibility effects can now be included with any aero section.
  The compressibility effects increase drag at Mach numbers above Mcrit.  The 
  CLmax and CLmin are also reduced by Mach number to correspond approximately
  to what is observed on real airfoils.

 Newer convergence and relaxation parameters to facilitate convergence of 
  Newton system.  

 New helicopter output quantities for cases with very low advance ratio where
  XROTOR can be used for hover analysis.
*========================================================================*
*========================================================================*
Notes for XROTOR 7.10
HHY 3/2/01

This version completed a number of enhancements to the basic code

 Mcrit and compressibility effects readjusted to improve CD(M-Mcrit) 
  correlation.

 Plotting labels and titles added to many plots

 Fixes to the induced velocity plots to correct a scaling bug
*========================================================================*
*========================================================================*
Notes for XROTOR 7.20
HHY 5/20/02

This version has several bug fixes and adds the germ of a new data plotting 
capability.  

 Fixes to the code remedy bugs in xoper.f relating to the "equivalent" prop
  which produced incorrect forces for all cases but only noticeably incorrect
  answers for ducted propellers. Don't panic, most old cases are largely 
  unaffected!  

  Also fixes include the addition of several benign but missing calls to 
   calculate body induced velocities.  

 A new set of plotting routines was added to plot blade data (like CL,CD,GAM) 
   as a function of radial station.  The presently augments the existing 
   "integrated" but very busy and terse plot output.  This option can be 
   selected through the PLOT submenu in OPER, option 10.  This capability 
   will be improved in a subsequent version of XROTOR.

 Documentation (in xrotor.doc) was updated to better describe the new AERO
   model and the discrete vortex wake model.  Not perfect, but improved...
*========================================================================*
*========================================================================*
Notes for XROTOR 7.30
HHY 7/08/02

This version has large revisions to the "equivalent" prop formulation.
The largest impact for these changes will be on ducted rotors where the 
previous formulations (including the 7.2 revision) did not properly treat 
duct effects.  

 Most of the fixes for 7.3 were to xoper.f with changes also to xrotor.f, 
  xdesi.f and xrotpl.f.  These changes concern the "equivalent" prop 
  formulation, particularly for ducted rotors.   Although the changes were
  more general and pervasive than just for duct effects open props should
  not show significant changes in thrust or performance.  

 Changes were made to the initialization code in SUBROUTINE APINIT that 
  should make XROTOR generally more robust.  The GAM circulation
  distribution is now filtered (smoothed) in APINIT and APITER when the
  Newton update is drastically underrelaxed.  This is done to eliminate wild 
  "spikes" in the circulation that upset the solution iterations.  This 
  filtering has no effect on the converged solution.

 A new axial rotor view plot option was added to visualize the whole prop. 
  This is probably most helpful for ducted rotors but is useful on normal
  props as well.

 Documentation (in xrotor.doc) was not updated ato better describe the new AERO
   model and the discrete vortex wake model.  Not perfect, but improved...
*========================================================================*
*========================================================================*
Notes for XROTOR 7.42
HHY 1/28/03

This version has revisions to xdesi.f and xmodi.f to treat duct cases properly
and to properly initialize before the design option is entered.  Previously
options in the DESI menu and the OPTI option in the MODI menu did not properly
initialize the circulation before the design iteration was performed.  Some 
of these problems were accentuated for near "static flow" conditions (hovering
rotor or ducted rotor).

The plotting of slipstream velocities was misleading and has been revised.  The
old induced velocity plots corresponded to the velocity induced at the rotor
plane by the vortex wake.  The slipstream swirl (downstream of the prop) is 2X 
the swirl at the rotor plane.  New plot options were added to display the 
induced velocities at the rotor plane or downstream (near the prop) in the
slipstream.  The velocities in the slipstream now include swirl derived from
the induced and viscous power (torque) to properly reflect blade drag losses 
mixing into the slipstream.  Note that the induced velocities at the rotor disk
are assumed to be vortex induced only, no viscous contribution from blade drag.
The blade data plot option (plot 12 in the PLOT menu) now can display induced
velocity on the rotor plane as well as slipstream velocities and angle. The 
plot options were rearranged to allow for the new capabilities.

The plotting options were overhauled and made more consistent between OPER,
DESI and MODI.  Now all plots are available from all three menus.

Documentation (in xrotor.doc) was revised slightly.
   Still not perfect, but improving...
*========================================================================*
*========================================================================*
Notes for XROTOR 7.5x
HHY 4/1/03

Comparison of forces from axial momentum integration with blade forces showed
that the axial induced velocity was not being set properly from the wake
advance ratio equation (in xoper.f in APITER) for ducted rotor cases.  These
cases showed that the averaged axial velocity should be set using thrust from
the equivalent prop (TWAK) rather than blade thrust (TINV).  Correcting
this bug uncovered that some of the previous fixes to calculate equivalent prop
forces (versions 7.2 and 7.3) were mis-applied - the real problem was masked 
by the incorrect average axial velocity.

Note that the thrust calculated from axial induced velocity now matches blade 
thrust forces for ducted rotors.  A check of free-tip propellers shows that 
there are mismatches between momentum forces and blade forces for highly loaded
props like the ex.prop testcase.  This does not appear to be an issue for more
lightly loaded propellers. 

Changes in this version also include a slight rework of the management of wake 
velocity calculation options (GRADED, POTENTIAL or VORTEX methods).  

The plotting of user-supplied slipstream velocities has been updated to improve
clarity.

Still a work in progress...
*========================================================================*
*========================================================================*
Notes for XROTOR 7.52
HHY 11/7/03

This version fixes a bug in the DESI mode for design. The thrust had not been
calculated for the rotor+duct but only for the rotor alone.  

The design condition for ducted rotors has been changed from the constant
induced efficiency condition used for propellers (MIL design condition) to
a constant radial circulation condition (free-vortex rotor) which is more 
appropriate for ducted rotors.

The plotting of the overall rotor disk now places the blade element chordlines
on a circle rather than on planes normal to the stacking line.

*========================================================================*
*========================================================================*
Notes for XROTOR 7.53
HHY 2/4/04

This version corrects a bug for ducted rotors where the freestream velocity
is set for the "equivalent" prop.  Previous versions set this velocity 
component to 1.0 regardless of the duct area ratio.  This produced errors in 
forces for ducted rotors (with area ratio different from 1.0) for cases with
axial velocity specified (VEL>0.0).

*========================================================================*
*========================================================================*
Notes for XROTOR 7.54
HHY 4/27/05

Buglet in xaero.f corrected (declare STALLF).  
Bug fix (perhaps not important?) in xaero.f in _W linearization.
Bug fix in xrotpl.f for scaling in VELPLT.

*========================================================================*
*========================================================================*
Notes for XROTOR 7.55
MD 2 Nov 09

Added graphics enable/disable flag to PLOP submenu at top level.

*========================================================================*

