slehar@park.bu.edu (Steve Lehar) (06/21/91)
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 -- (O)((O))(((O)))((((O))))(((((O)))))(((((O)))))((((O))))(((O)))((O))(O) (O)((O))((( slehar@park.bu.edu )))((O))(O) (O)((O))((( Steve Lehar Boston University Boston MA )))((O))(O) (O)((O))((( (617) 424-7035 (H) (617) 353-6741 (W) )))((O))(O) (O)((O))(((O)))((((O))))(((((O)))))(((((O)))))((((O))))(((O)))((O))(O)
hlo@orca.dallas.sgi.com (Howard Lo) (06/25/91)
In article <SLEHAR.91Jun21120245@park.bu.edu>, slehar@park.bu.edu (Steve Lehar) writes: |> |> 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 . . . |> 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 |> |> |> -- |> (O)((O))(((O)))((((O))))(((((O)))))(((((O)))))((((O))))(((O)))((O))(O) |> (O)((O))((( slehar@park.bu.edu )))((O))(O) |> (O)((O))((( Steve Lehar Boston University Boston MA )))((O))(O) |> (O)((O))((( (617) 424-7035 (H) (617) 353-6741 (W) )))((O))(O) |> (O)((O))(((O)))((((O))))(((((O)))))(((((O)))))((((O))))(((O)))((O))(O) Another enhancement I would like to see is in the area of ergonomics. How about using the spaceball to control the pilot's out of the window view ? This way, I can visually track another airplane for dog fighting or aerobatics by twisting the spaceball with my left hand while controlling the flight path with my right hand. Hat's off to Gary Tarolli, Rob Mace and all the contributor. -- hl