posted 4/22/2008 by Dave Gamble
other articles by Dave Gamble
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Another aspect of X-Plane that enables it to provide a realistic enough flight environment to be used for actual flight training is its physics engine. If all you are going to do is try to immerse yourself in the illusion of flight ala FSX (and don’t get me wrong, there is nothing at all wrong with that), you don’t need a whole lot of fidelity to actual flight physics. In fact, too much realism would be detrimental in that it would make it much harder for novices to successfully fly (witness my experience with trying to fly helicopters!) and it could also have a negative impact on system performance. Calculating physics takes CPU time, as does animating the fountains at the Bellagio. These operations are quite likely to be handled by separate sub-systems in the modern gaming PC, but then again, maybe not completely. In any event, if you want (or have the need for) the most accurate flight physics available, X-Plane is the proper choice for you.

I’m not an aeronautical engineer by any stretch of the imagination, so I’ll borrow heavily from X-Plane’s web site to provide an explanation as to why X-Plane is the more accurate flight model. First and foremost, “X-Plane reads in the geometric shape of any aircraft and then figures out how that aircraft will fly. It does this by an engineering process called ‘blade element theory’, which involves breaking the aircraft down into many small elements and then finding the forces on each little element many times per second. These forces are then converted into accelerations which are then integrated to velocities and positions.” Wow, sounds complicated! Fortunately, it’s a lot like a heart defibrillator – you really don’t care how it works, as long as it works when you need it to! It’s important to note the part that says that it ‘finds the forces on each element many times per second’ because that is what allows the flight characteristics to respond correctly to ever-changing conditions ranging from up and down drafts, angle of attack on the wing (a complex calculation that involves a whole heck of a lot of things), control inputs, drag from the air on the airplane itself, momentum, and a host of even more complex things.

That’s a heck of a lot of math going on, but the net result has both positive and negative outcomes. On the positive side, real-world pilots or pilots-in-training are going to find a simulated airplane that behaves similarly to a real airplane, which will in turn make their simulated flight more beneficial to their competency level. On the negative side, it can cause somewhat exotic behavior if a ham-handed pilot gets the airplane into a situation where the math gets into boundary conditions. It is possible to get the airplane into modes of flight that don’t exist in the real world, and at that point the staunch adherence to the math and physics of the flight model no longer has any grounding in the real world and, in a word, gets a bit wacky. In essence, X-Plane flight physics adhere to a fundamental and immutable computing tenet: Garbage in, garbage out. Fly it like you’d fly a real plane and it will respond like a real plane. Throw it into conditions in which a real airplane cannot and will not fly, and all bets are off. It’s standard medical advice that I offer here: if it hurts to do it, stop doing it. Treat X-Plane like the professional tool that it is, and you will get professional results. Treat it like a toy, and a toy is what you will have.

Another thing that you absolutely have to be aware of is another application of the ‘garbage in, garbage out’ principle: the quality of your controller(s) will have a very large influence on the performance of X-Plane. You will not be able to fly it with a mouse and/or keyboard. I’m not sure you would even be very satisfied with a cheapy joystick. I’m using two different control set-ups, depending on the type of plane I’m flying. For fighters and other stick-controlled aircraft, I’m using the Saitek X52 Pro Flight System. For the yoke-controlled planes, I’m using the Saitek Pro Flight Yoke System with an additional quadrant. For both types, I use the Saitek rudder pedals.

These are quality controllers, but even so they exhibit a few inherent weaknesses with a high-fidelity program like X-Plane. Like all controllers, they have to have centering springs. In almost all flight, but especially in high-response airplanes such as my RV-6, the majority of control inputs happen in a very small area around the center of the control. Unfortunately, this is exactly the area where the breakout forces of the controller centering springs are the highest. This is noticeable in both pitch and roll on the joystick airplanes, but it is at its absolute worst in the pitch axis of the yoke-controlled airplanes. Note that this is not unique to X-Plane; I have the same problem with FSX. It ends up causing over-controlling, which often results to PIO, or ‘Pilot Induced Oscillations.’

Both X-Plane and FSX provide configuration screens to help address control customization issues like this, though, and it possible to mitigate these problems to some degree. This does bring to light a significant difference between X-Plane and FSX, however: configuring X-Plane requires quite a bit more attention to detail and willingness to learn the system than FSX does. In a word, configuring X-Plane is complicated. A lot of power is put in your hands when it comes to setting every facet of X-Plane, including display parameters, weather conditions, control configuration, possible simulated system failures, etc. With that power comes, in the words of Peter Parker’s very dead Uncle Ben, great responsibility. Expect to devote some time to learning how to set up X-Plane for your mission. The first few times you bring up configuration screens can be somewhat daunting, but once you learn your way around you will appreciate the level of control you have over the environment. Even fundamental things like setting the action associated with a button or keyboard key are completely different from what you may be used to. In FSX, for example, you select the action and then press the button you want to trigger that action. In X-Plane it’s the exact opposite: you click the button then select the action it should perform. Neither way is better or worse; they’re just different. You’ll run into a lot of that.
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