A Flight Dynamics Critique of FS2004

[nudata 10]

The following link goes to an interesting exposition of the authors view of some of the FLIGHT simulation characteristics of FS2004. I was wondering if anyone here believes that he carries some validity in his discussion?http://www.flightsim.com/cgi/kds?$=main/op-ed/ed316.htmDick KLBE

[Guest Birdie]

He does have some good points being a real world pilot myself.especialy about the vertial movement of air which would be a great improvement. The rudder in flight sim I noticed is pretty much only useful to center yourself in a crosswind on takeoff and landing. But it is a computer program.A very realistic one at that. If you want perfection go flying in a real airplane.

[nudata 10]

I have a question. The author mentions induced drag when the airlerons are displaced. He says that the airleron that riases the wing has the induced drag while the one that lowers the other wing has the opposite effect. Doesn't the lower wing also have induced drag by virtue of the airleron sticking up into to the wind?In another section he speaks of the adverse yaw. I am not an engineer but my impression is that the aircraft is actually trying to pivot on the lower wing (up arileron). It does not do this very efficiently so it actually tilts to the side begins to turn but also slips, moves, or yaws in the direction of the high wing (down airleron). I would call this adverse yaw. The pivoting is on the slower element - up airleron wing. It is actually similar to a car going into a broadside slide while negotiating a turn. To correct this the rudder is used to actually yaw/point the aircraft in the desired direction resulting in a shaper turn.This is my backyard mechanic view of the process. Please let me know where there is error, and there probably is. Using the RealAir Cessna 172 I always found that the action of the inclinometer seemed to follow the proper scenario as outlined by the author. Hpwever, the MS Cessna 172 acts as if the inclinometer ball is being pulled back toward the center by magnets. It rarely travels fully beyond the two vertical lines. It does not appear to react to speed changes as well. The effectiveness of the rudder noticeably increases in the RealAir Cessna 172 as speed increases. FPS =25 2D panel.Dick KLBE

[Guest Fabio Miguez]

Hello Dick,Regarding the higher induced drag on the wing that moves up, it is caused by the simple fact that only this wing is producing more lift than at straight and level. By moving the aileron up, the wing that moves down produces less lift than straight and level flight. Induce drag is proportional to lift created, therefore it becomes clearer why when starting a turn, adverse yaw is encountered. It is nothing more than higher drag on one side of the plane, which by virtue of momentum tends to yaw the craft, on an opposing way to the desired direction.I hope I helped you more than I confused you ;-).Best regards.

[nudata 10]

Could I say that induced drag is the sum of drag and lift?? Probably a little bit of induced drag then in the high wing since nothing is perfect. The low wing is, of course, a big contributor of induced drag in this case.Thanks,Dick KLBE

[Guest Tom Goodrick]

Sorry, you could not say that induced drag is the sum of drag and lift. In fact it is the sum of the parasite or 'zero lift drga' plus a term shere the lift coefficient is squared and then divided by the aspect ratio and constants. Induced drag is drag induced by lift.With this differential drag applied to the wings, the aircraft tends to pivot AWAY from the turn. Thus, in a real plane, the rudder pedal is pressed on the side going into the turn as soon as the ailerons are moved to roll into the turn. When riding around the turn, the rudder pedals are generally close to neutral, especially in high-bank turns.The article you link to on flightsim.com is indeed correct. These are very big flaws in FS that have always been there. As a former pilot - now inactive - I had developed a rudder pedal technique that quickly became second nature. It was just a natural thing to combine some foot action with the stick or wheel action (I flew both.) The one time you do not use much rudder is in a fast sewpt-wing jet like the F-86. I embarassed myself as a 14-year-old J-3 Cub pilot getting into an F-86 simulator at an Air Force base when the instructor told me to make a left turn. I whipped the stick over and stabbed the rudder pedal and the aircraft went quickly into a violent spin. That was a simulator that was attended, in 1958, by a room full of computers. The sim was a cockpit with a solid gray canopy that lowered so you were always in the soup. The vertical wind problem in FS is a much bigger problem although both can kill you if you get in an aircraft and think you can fly it like in FS. I have recently been flying in FS9 in the Alps where you must frequently ride down the sides of mountains. Vertical winds can mess you up big time in such cases.FS can still be very helpful at teaching many things about flying such as basic maneuvers for landing and taking off and navigation. The scenery makes things more interesting. When a person experienced in FS flying takes real flying lessons, he will have to unlearn a few things but most of what was learned in FS will help and will cut the time needed to complete training.

[nudata 10]

Thanks Tom - I bet that there is lawsuit fodder there when someone is killed because they used FS2004 technique!Ok I understand the "induced drag". It relates to lifting force products that are used to raise the wing. But isn't there an induced drag, perhaps of another name, from the lowered wing with a negative lifting coefficent squared? As is often the case in technical realms the process is not that complicated it is the termininology that was developed to explain itthat bogs you down. Think that I will stick to playing with scenery (Ground2K) as the pretense of flight continues to elude Microsoft.Dick KLBE

[Guest]

The lower wing isn't at a negative lift coefficient, it's just at a lift coefficient a little closer to zero than the upper wing. The wing contributes most to the lift coefficient, with the ailerons making small changes +/- to it. So raising an aileron just decreases lift coefficient a wee bit, but it doesn't go negative.

[Guest Tom Goodrick]

Sorry guys, you both have it wrong. In a standard, steady turn while the aircraft is flying a circular path at a constant altitude, both wings are developing equal lift that counters the vector sum of the weight plus the centripetal force component. When you first deflect the ailerons, during the resulting roll, there is more lift and drag on the section of the upper wing containing the aileron. The added lift makes you roll. Since that drag is not balanced by an opposite force on the lower wing's aileron section, there is a torque tending to turn the plane out of the turn. It is called adverse yaw and it exists both in reality and in FS if the stability derivatives are set right.I have fixed the Cessna 182 RG, the 182S and the 172SP so that they exhibit the proper amount of adverse yaw. To make a good turn, you must apply rudder with the stick rolling into the turn, neutralize the stick - but holding back pressure - and hold just a little rudder to keep the ball centered while riding around the turn. To roll out you tap the opposite rudder a bit as you roll out. Failure to do it right will be evident just looking out the window at scenery ahead of the aircraft. But I also developed an xml gauge that reads the sideslip angle (beta) and displays it on the panel. Flying these aircraft is a little bit harder until you master the rudder-aileron coordination. If you do not have rudder pedals, do not bother with the download.To download these files go tohttp://home.hiwaay.net/~goodrick/Downloads.htmlThere are several other aircraft listed. While these fly well in FS9, they have not been 'fixed' for adverse yaw. I will be working on that over the next few weeks.

[nudata 10]

Tom,I see that you have published an article on Flight Simulator flight dynamics. I went to Abacus site but it is no longer available. Perhaps you could point us toward a location where we can get a copy.Downloaded you file (above) and need time to try it.Thanks,Dick KLBE