suggested mods for "dog"

[Steve Lehar]

As a former commercial pilot  and  avid  aerobatic enthusiast who  has
always  had  an interest in air   combat,  I  have  received years  of
pleasure from the sgi family of flight simulators, which give a better
and more realistic feel of flying than any other simulator I have ever
flown.  Hats off to the guy who wrote this wonderful piece of code!

I have often been tempted to modify the code to fix a few  little bugs
that in  my  opinion mar the  otherwise  excellent performance of this
great program.  Well, several years have gone by and  I have never yet
had the time   to  work on  this,  so I  hope  that  if  I publish  my
suggestions  here, some  kind  soul   will   perhaps feel inclined  to
implement some of  the changes I  suggest.  Anyway, here  is a pilot's
eye view of some changes that could be made to dog and flight.

=================[ CHANGES I WOULD LIKE TO SEE ]======================

I would like to fix the few handling problems I have  encountered with
the simulator.  First, there is the tendancy for the  plane to "stick"
on due east or west headings- probably a  precision or round-off error
that could be patched relatively  easily.   Then, there is the problem
of turns- you  bank the plane to  say 15 degrees, and nothing happens.
You have to bank it more steeply and yank back a bit to "break it out"
of the straight line.  This too seems like a precision type error.  In
a real plane, as soon as you bank it a little bit,  the nose starts to
drop, and  when you pull back  to  hold it up,  then it starts to turn
automatically.  For dogfights, I would like to get an "up" view.  In a
real dogfight  (of  the  turning  kind)  you spend  more  time looking
straight up through the canopy top while pulling heavy G's than in any
other direction, just as when you do a sharp turn in your car you look
out the side  window, not the windscreen,  to see where you are going.
Besides, your opponent is often found right there at the other side of
the  circle pulling hard to get  on your tail.   Another thing I would
change is to  let you fly  harmlessly through  the  explosion  of your
opponent when you finally  get him.  In true  dogfighting it is always
better to get right  up close  to  your opponent  before  pulling  the
trigger, and in dog this is impossible because you  will  blow up when
he does.  It would also be nice to put the rudder and the throttle on
the dial and button box, so you could manipulate all the major
controls in an analog fashon.

And  finally, I would  like  to  fix the  rudder.   The rudder  is  an
interesting control on a plane- it is not used to turn the  plane, the
elevator does that when you pull back in  a bank, but  it serves three
or four various  and independant functions.  As  a flight instructor I
could  always  tell a  good  pilot  by  how   he handles  the  rudder.
Foremost, it is used to counteract  "adverse yaw", the tendancy of the
plane to yaw left when you deflect the aeleron right.   This is due to
the fact that the aeleron produces asymmetrical lift on the two wings,
and the one that is climbing "uphill" lags behind,  while the one that
is diving  "downhill" races ahead.   In a normal  airplane,  rudder is
applied  simultaneously  and proportionally with the   aeleron, not to
create a  yaw, but to  prevent one.    Technically the adverse yaw  is
proportional to the lift,  or  "G"  forces being pulled, i.e. you need
more when pulling out of a dive (while of course rolling), none at all
if pulling zero G or going straight up or down,  and you actually need
opposite rudder when  pulling  negative   G or  flying  upside   down,
although only an aerobatic pilot need know this.   In a simulator, the
adverse yaw is removed algorithmically, so that solves the problem.

The second major use of the  rudder is  to  correct for torque, spiral
slipstream  and "P-factor".  Torque  is  due to  the  rotation  of the
propellor, and is experienced while  the plane is actually pitching or
yawing, so a pitch up produces a yaw right, and a yaw right produces a
pitch  down.  These forces  are so  slight  that again, they  are only
noticable to  the aerobatic pilot  when doing things like a Hammerhead
or humpty-bumps, where large pitching or  yawing motions are performed
at near zero airspeed.  P-factor  is  an effect most  noticable  in  a
helicopter- the forward speed  means  that  the advancing blade  has a
higher airspeed than the retreating blade, so the craft  tends to roll
to the left.  In a  plane,  this effect is noticed  (to a  much lesser
degree)  when  at a  high angle of  attack- i.e.   nose pointed up but
plane travelling forward, so you do get an advancing  and a retreating
blade, which produces a yaw to the left.  Again, the rudder is used to
prevent such a yaw.  Spiral  slipstream is actually the most prominent
of the three effects, and is due to the  fact that the  wash  from the
propeller comes back in a spiral corkscrew.  If the  plane  were built
symmetrically, like a  rocket with four  fins,  this would  produce  a
small but barely noticable rolling effect.  But the  ventral fin would
strike the ground on landing, so instead, the dorsal fin is made twice
as large, and  the  ventral  fin  is  usually  eliminated.  The spiral
slipstream strikes the dorsal fin on the left  side, pushing it to the
right, producing  a yaw to the left.    The  strength of this sideward
force is proportional to the power setting, and inversely proportional
to the airspeed, since at high speed the spiral  is stretched out into
a long straight  corkscrew, so in a  high power low  speed climb as on
take-off, constant right rudder is needed to hold  the plane straight.
To  relieve tired feet, the designers  put a slight left angle  to the
vertical fin, so  that at cruise  speed and power  setting no force is
needed on the rudder.  At the opposite extreme therefore, a high speed
low power dive, constant  left  rudder is  required  to hold the  nose
straight due to  the angle of the  fin.  Torque, spiral slipstream and
P-factor can all  be eliminated from  a simulatior without any loss of
performance  or controlability,  and   of  course the  latter  two are
totally absent in a jet aircraft.

Finally, the rudder is used to intentionally  yaw the plane at certain
times.  This can be done in two ways- one way is  the side slip, where
the plane is  banked to some  angle, then as  the nose starts  to yaw,
opposite  rudder is applied to hold  it straight.  The  plane  can fly
indenfintely one-wing-low like this, up to  a maximum angle determined
by the strength of the rudder  force  needed to hold her from turning.
Although  the plane  is  pointing straight,  it is   actually slipping
sideways and  downward through  the  air in the  direction  of the low
wing.  This technique is  very valuable for landing in  a crosswind to
keep the  nose  parallel  with  the  runway, and the  proper technique
requires that the upwind wheel should contact the runway in advance of
the downwind wheel.  It  is also a  useful technique for correcting  a
slight out-of-alignment on final approach, and  this technique is well
simulated  in "dog".  Say  you are on   short final, parallel   to the
runway,  but slightly off-center to  the right.  Click the right mouse
once and dip  the left wing,  and the plane  will just  slide sideways
into position without   losing its heading.    When  properly aligned,
click the middle mouse and immediately level  the wings.  Make sure to
hold    a heading  parallel   to the    runway (using the  bank angle)
throughout the maneuver.

The second way to use the rudder is not simulated at all in "dog", and
is a little-known  technique useful  only in close formation flying or
for  dogfighting.  Say  you  are on another  plane's   right wing  and
slightly astern, and you would like to tuck it  in a little closer.  A
conventional turn would require a left bank, followed immediately by a
right bank, to do a "dogleg" first left then  right.  Since such small
corrections  are constantly  required  in close formation  flying, the
result  would  be that the  wingman is constantly waggling his  wings.
The side slip, as described above, is inappropriate for this situation
because of the high airspeed, which would require a  steep bank angle.
The proper technique  is  to keep the wings  level, and kick  the left
rudder and let the side lift on the fusilage pull you in closer before
you kick the nose parallel  again.   This way,  when following another
plane through various maneuvers, all you have  to do is hold your bank
angle exactly parallel with the leader's, and use  the rudder  to pull
in or ease out.  Not only is this the most convenient way to make such
small corrections,  but it makes  for a  good looking formation, where
all the planes roll exactly in unison.  In a  dogfight, you can follow
another plane  more closely by  copying his every  wing bank,  and the
rudder is used extensively for the final pointing  of the machine guns
when you shoot.  After all this long discussion on the rudder, (please
forgive my verbosity!) this force is the one I would like to implement
in  "dog", i.e. give the vertical  surfaces of  the fusilage a certain
small aerodynamic lift.  In a high speed fighter  like  the  f-15 this
side force is easily enough to hold  the  plane level in  "knife edge"
flight- i.e.   flying straight and  steady    with the wings  vertical
instead  of horizontal,  and  the  nose yawed  up slightly above   the
horizon.  Even my old Pitts biplane could do this trick.

I would be delighted to demonstrate  these principles in actual flight
to anyone (in the Boston area) who is seriously planning to modify the
code and fix some of these little bugs.

	Steve Lehar


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