Amiga Collections: MegaDisc/MegaDisc 27 (1992-03)(MegaDisc Digital Publishing)(AU)(Disk 1 of 2)[WB].zip/MegaDisc 27 (1992-03)(MegaDisc Digital Publishing)(AU)(Disk 1 of 2)[WB].adf/Flight_Sims/Flight_Sim_Theory/Flight_Sim_Theory

Text File | 1992-03-30 | 16KB | 288 lines

                   COMING TO GRIPS WITH FLIGHT SIMULATOR 11


                              by Ben Campbell


   Ed: This is the first in a series of articles by Ben on the technical
  aspects of using Flight Simulators - ie, he goes into the details of flying
  from a background of real flying, and if you follow it, you'll learn plenty
  about flying as well as get a lot more out of your digital loop-de-looping.
  Let us know if you like this piece, because it's a lot of work for Ben and
  a bit of feedback wouldn't go astray. See the accompanying graphics where
  they're referred to in the article - either by just double-clicking on the
  icons or via the menu of Fullview.


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   Are you one of the countless number of computer pilots who departed Runway
  27 only to become another Oakland Airport Crash Statistic? Whilst I don't
  claim to be any sort of expert, maybe the following observations and
  deductions might be of help, interest, or at least a catalyst for some
  thoughts of your own.

   Probably all young boys dream of flying and I was no exception. My
  childhood dreams were realised when, as a 17 year old (over 20 years ago
  now), I would make a weekly pilgrimage to Archerfield and, for one glorious
  hour or so, rise above the worries of the world to join with the sun and
  the clouds.

   In those days the cost was only $17 per hour. Still, that represented a
  goodly portion of my wage at the time. Sadly, those halcyon days are long
  past, and flying costs have not been spared from the ravages of inflation
  (Nowdays costing something more like $100 per hour). But, old aviators
  never die and I, and probably many others, owe eternal gratitude to a
  gentleman by the name of Bruce Artwick for providing a cost effective
  substitute with FS11.

   The Romance of Flight

   I imagine that aviators experience another dimension with FS2 simply
  because they can relate to what FS2 is all about. It's not just a 'go
  where you point it' device. Seemingly it has some logic of its own and
  can be unforgiving of unskilled, careless or impatient handling. Just like
  real aircraft, one has to learn its seemingly peculiar ways and work in
  harmony. Finally the reward will come when, just as with real aircraft,
  you undergo a new experience - the airplane is no longer a separate entity,
  it's simply an extension of yourself (or perhaps you become part of of it,
  a birdlike creature with the freedom of the skies.)

   So much for the romance of flight, what about the reality of all those
  aircraft that never returned safely to Runway 27!


   Training Scenario

   Let's go through a training scenario. I'll presume that you have had a
  read of the program manual and have gained a basic understanding of the
  aircraft controls and the mouse and keyboard interaction. For the purpose
  of this exercise we will rely on keyboard flight control. (Using '9' and
  '3' of the numeric keypad to control throttle and '8' and '2' to control
  nose up and nose down.)

   On commencement, FS11 defaults to Oakland Runway 27R, and the engine is
  idling over at 650RPM. For the sake of instruction, it will help if you
  open up an auxiliary window with a 'Spot Plane' view looking side on to
  your aircraft. Resize this auxiliary window smaller and move it over to
  the side of your main window so you can still get a clear view of the
  runway. Using keypad controls hold down '9' until the throttle is fully
  open at 2500RPM. So far so good, the aircraft starts to roll forward and
  progressively increases speed. Takeoff speed for a Cessna 182 is in the
  order of 65kts but to do this you will need to apply some 'nose up'
  control. Commencing at about 50kts, tap the '2' key about 15 times with a
  short interval between each tap. It doesn't matter if the speed at which
  we lift off is far in excess of 65kts, what's more important is the ongoing
  effect of the 'nose up' application after the aircraft has been given a
  chance to fully respond. Finally we become airborne, and depending on how
  much 'nose up' we applied, the airspeed should settle down somewhere about
  80kts. (It is important to note that two keystrokes applied in very rapid
  succession will register far greater that two keystrokes with a short
  interval between). Now, using the '8' and '2' keys, lets try to trim up
  for a 70kts climb. Don't be too hasty. Apply only 2 or 3 keystrokes at a
  time (with short intervals between) and then give the aircraft 15 seconds
  or so to fully respond. Remember our aircraft is operating in a 'f luid'
  medium, namely Air, and things might not happen quite as fast as, say,
  applying the brakes when driving a car. Notice how the '8' key causes a
  'nose down' reaction and this increases our airspeed. The '2' key causes
  the reverse to happen.

   Finally we achieve a stable airspeed of 70 kts. All the while the engine
  has been operating at full throttle - 2500 RPM. Note the position of the
  horizon - about 1/5 the way up the aircraft's windscreen. A pilot gets as
  much, if not more, information from the outside world than from his
  instruments. Just the same as you don't drive around with your eyes glued
  to your car instruments, good pilots soon learn not to fly with their head
  'buried in the cockpit'. With FS11 we're a bit lucky. We don't have to
  contend with other aircraft (which can be very difficult to spot in the
  air) so we can be a little bit more indulgent until we've picked up the
  general feel of things. But, as with a real aircraft, we'll soon see the
  value of continually using the view of the outside horizon in addition to
  regularly monitoring the instruments.


   Now hopefully we're at an altitude over 1000ft - let's close (shut off)
  the throttle but DON'T change the pitch (Nose up/down) setting. Notice
  how initially our aircraft remains pointed in the same direction while the
  airspeed washes off. Then, all by itself, the nose starts to sink and the
  airspeed increases until finally the aircraft settles into a glide with the
  airspeed very close to what we had before. A similar phenomenon occurs
  when full power is applied while our aircraft is in a glide. Initially
  our aircraft will speed up, the nose subsequently rises, and finally the
  aircraft settles down to a steady climb with the airspeed close to what we
  originally had. With small incremental power changes the aircraft
  generally doesn't have any significant intermediate airspeed changes. It
  simply automatically changes pitch and maintains something close to the
  original airspeed... And this is the drill that pilots use in real
  aircraft. Aircraft are designed for optimum performance in a number of
  part icular flying configurations - climbing, cruising straight & level and
  gliding.

   PAT & PATC

   To change from one configuration to another, pilots follow a
  drill called 'PAT'. Power, Attitude and, Trim. First the POWER setting is
  changed. A slick pilot then usually momentarily adjusts the pitch so that
  the intermediate airspeed change does not occur while the aircraft is
  adopting a changed ATTITUDE. (Naturally, when close to the ground, it's
  not too healthy to apply power with the nose pointing in any way
  downwards). Finally a pilot will fine tune the T‚r‚i‚m‚ to make sure he is
  flying at the precisely intended airspeed (and then he usually checks
  things a minute or so later to see that things haven't varied.) I remember
  being taught the drill as PATC - Power, Attitude, Trim, Check. In either
  case, a tidy pilot generally keeps things 'in check' every minute or so
  anyway - And that's part of the challenge of FS11 - not just to be able
  'walk away' from every landing, but to be a 'tidy pilot', taking pride in
  being able to work with the aircraft to fly consistently and keep within
  personal tolerances. A bit like a golfer with his handicap, I guess.


   Plane's Brain - Some Theory

   But how does the aircraft have a 'brain' of its own to keep the airspeed
  so consistent? Well like all things in life, we have to bear with a little
  theory, but once learned and inwardly digested, it's amazing how much
  easier things are to understand.

   Aircraft become, and remain, airborne by utilising the movement of air
  over their wings to overcome the Force due to Gravity. This Force due to
  Gravity is commonly referred to as 'Weight'. Movement of air over the
  wings is achieved by forward movement of the aircraft. Should forward
  movement cease or fall below a critical speed, the aircraft will literally
  fall from the skies. To use the technical term, the aircraft will 'Stall".

   Forward movement can be achieved by two means:-

 1. By having the aircraft thrust forward either by a propeller or jet, or

 2. By gliding. With the nose pointed downwards, the Lift from the wings
  is inclined forwards. The Lift and the Weight oppose each other and the
  residual Force is what keeps our aircraft moving along.  The diagram (FS2
  Fig 1) shows our primary Forces and how they can be combined to produce a
  resultant.


So far I've mentioned Three Forces:-

 1. Weight. The Force due to Gravity acting upon the Mass of the Aircraft
  (This Force can be imagined to operate through one particular point called
  the 'Centre of Gravity').

 2. Lift. The Force caused by the movement of air over the wings. This
  Force, under normal sober flying practice, opposes the Weight. Lift can
  also be imagined to operate through a particular point, called the 'Centre
  of Lift'.

   As we shall see later, the Centre of Lift and the Centre of Gravity don't
  necessarily coincide.

 3. Thrust. The Force exerted by a propeller or jet. Again, we can
  imagine this Force to operate through a particular point called the 'Centre
  of Thrust'.

   Drag

   There is still one other Force to come into the equation. This one is
  called Drag. Like Weight, Drag is also provided courtesy of Mother Nature.
  However, unlike Weight, which generally remains constant (Unless we drop a
  bomb or two) Drag varies according to the Velocity of our aircraft. In
  fact, Drag varies in proportion to the Velocity squared, ie, at 140 kts
  (the cruising speed of our Cessna 182 with underecarriage retracted and
  flaps up) the Drag is 4 times greater than it is at 70 kts.  As with the
  other forces, Drag might also be considered as a Nett Force acting through
  a particular point.

   We've seen how these forces operate on an aircraft in a glide. Let's now
  see what the situation is when we're cruising along flying straight and
  level.  (Refer FS2 Fig 2)

   Just a Moment

   Notice in the above Fig 2 I've chosen to show the Forces of Lift and
  Weight being of equal magnitude but operating through different points such
  that an anticlockwise Couple (or Bending Moment) results. I've also chosen
  to show Thrust and Drag with much smaller but again equal magnitudes but
  with points of application which cause a clockwise Moment. Without getting
  into complex mathematics, let's imagine that the clockwise and
  anticlockwise Moments cancel each other out. In summary, no residual (ie
  unbalanced) Forces or Moments. This particular state of affairs is
  referred to as 'Equilibrium'. Now Isaac Newton was a man who knew his
  apples (including what happens when the influence of gravity on them is
  unopposed). Long before the days of Cessna 182s and FS11, Sir Isaac gave
  deep thought to this blissful state of affairs called Equilibrium and
  thence proclaimed his First Law of Motion - 'A body continues in its state
  of rest or uniform motion unless an unbalanced force acts on it'. Our
  airplane is not at rest but it is in a state of uniform motion. ie It is
  moving with constant velocity - no acceleration - the airspeed is steady.
  Why do I refer to Equilibrium as a state of bliss? Well basically when we
  and Mother Nature sort out our differences and establish Equilibrium, we
  can sit back, relax and our airplane will fly itself. (Until a gust of
  wind or something else comes along to upset the applecart.)

   Decreasing Power

   Now imagine the situation we have when we reduce power. First the Thrust
  is reduced. For the present, Inertia keeps our aircraft going. The Drag
  Force (a product of Velocity) still remains, and the imbalance between Drag
  and Thrust causes our airplane to decelerate. (The airspeed 'washes off'
  and, when Drag and Thrust are again in balance, we we will get back to a
  situation of flying at constant velocity). As a result of power being
  reduced, there also occurs a significant rearrangement of things due to an
  inbalance in the Moments. The Clockwise Moments caused by Drag & Thrust
  are considerably reduced because the magnitude of both these Forces was
  reduced. The Weight Moment remains unchanged and the Moment produced by
  the Lift Force is in fact reduced slightly (for reasons I won't pursue
  here), but overall the combined Anticlockwise Moments of Weight and Lift
  'overpower' the Clockwise Moments of Thrust and Drag. So the nose sinks
  until a point is reached where, once again, the Moments balance. Due to
  the resulting change in attitude, the airspeed is affected (it increases
  back to roughly where it was originally) and guess what happens as a
  result? Yes, finally the imbalance between Thrust and Drag, and Lift and
  Weight as well as the Moments pr oduced by these Forces gets sorted out,
  and we settle back to Equilibrium.

   Increasing Power

   Naturally,the reverse happens when we increase power - initially airspeed
  is increased and subsequently the nose will rise and the airspeed will
  finally settle down near to what it was originally.... Now it all starts
  to add up.... and we can only sit back and marvel at the aeronautical
  engineer who spent countless hours over a slide rule (probably all that was
  around when Cessna 182s first came off the drawing board) and came up with
  such a finely balanced work of art - and also marvel how Bruce Art wick has
  faithfully incorporated this behavior in FS2.

   Real Life Situations

   Let's imagine some real life situations. We've carefully trimmed our
  aircraft cruising along say at 2000RPM in Straight & Level flight.
  Suddenly without warning we have an engine failure. Yes, the aircraft is
  naturally sinking into a slightly nose down g lide, and all by itself
  avoiding a dreaded 'Stall' while we desperately try to locate the source of
  the power failure, put out a 'Mayday' call, quoting Greenwich Mean Time by
  the way, and hopefully spot and line up a suitable paddock to put down in.
  I well remember those 'fun days', cruising at 3000ft over Loganlea,
  savoring my $17 an hour worth, when unexpectedly my flying instructor would
  rip off the throttle and gleefully announce a simulated engine
  failure!!!*#@&.

   When doing landing approaches you also appreciate a bit of assistance
  while you're very busy looking out for other aircraft on the ground and in
  the air, as well as judging your approach hoping to come in over the
  threshold at the right height despite variable headwinds and pockets of
  rising and decending air.

   So, aircraft are not such uncontrollable brutes after all. In fact they
  can be downright friendly when you have a little patience to come to a
  working arrangement to share some of the jobs between you!

   Good luck & happy landings.


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