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Guest flyclassic

Starting up with Flight Dynamics

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Hello! I've been wanting to try my FDs for a long time; so I downloaded the SDK and have been reading it along with a lot other documentation. Right now there's a thing that puzzles me to no end, and I was hoping someone could assist me.... I loaded the default C182S in FSEdit to check its variables and there is one thing that does not make sense at all, I think! The Reference Datum is 3.6 , 0.0 , 0.0 - meaning the vertical coordinate is at the FS model center. The CoG for empty weight is at -3.0 , 0.0 , 0.0 - and so the coordinate is also at the FS model center. Now... Both the Wing and HTail Apex vertical values show also as 0.0 ! Checking the model with the lights method you see that the FS model origin is where it should be... roughly at 25% MAC and at a height of pilot's seat. So how do the Wing and HTail show at zero also? ! If the Cessna was a low wing I could somewhat accept that, but that is not the case. Well, I hope I was clear enough and that someone can help me shed some light into this! Thanks a bunch,

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A simple answer to a simple question: Visual model (*.mdl file) and flight dynamics that one is editing in *.AIR file and aircraft.cfg have nothing in common. While the values in the visual model are quite descernible and obvious, that is not the case with the values in the later. Nothing to understand here - the whole structure of *.air file in such form, that "strange" values give "resonable" results and "resonable" values give "strange" results. Try to add a realistic value to the stabilator and elevator lift (should both be negative) and see what You'we got - a nonflyable design.

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Thanks guys, I'll check the mentioned sitesI can certainly relate to

"the whole structure of *.air file in such form, that "strange" values give "resonable" results and "resonable" values give "strange" results."[/endquote]I spent a lot of time collecting technical data for my model and humbly believe I came up with very reasonable numbers for the airfile. I won't say it's FSEdit fault of course, as I a complete rookie and there are other far more knowleadgeable that use it to great results. But the fact is that with data taken from, among others, the aircraft's type certificate, my model looped almost as the mains left the ground. I played with everything for a long while, distances, CoG, 25% MACs, wheels, load stations, etc. It only started working when I said "ok, let me try this... " and doubled the distance from wing to htail....! Well, the good thing is now I know how a Cessna limousine whould fly ;)FC

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Far be it from me to delve into the Mysteries of Flight Dynamics, but in addition to ACM, AA, and the 1pct Spreahsheet, I bought Jerry Beckwith's Air Wrench. Just a simple tweaking with AirWrench tamed a naughty model...

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ooo.. taming naughty models with an air wrench.... mmmmm ;)

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I must come forward and say this......just when I was about to give up, saying "ok, I'll pick the default Cessna and will tune it to at least fly like bird" ... I noticed that there was *one* parameter I had taken for granted!I had changed the reference datum and left the fuel tanks with the old values which throwed them to mid fuselage. So I added all my values again and changed that one and she flew nicely at the first take. "Out of the box" with the aircraft type certificate values and others I had to estimate within reasonable parameters. Now, still have lots to change, but FSEdit can't be that bad ;)...still my first question remains: why on earth did MS choose those apex values for their aircraft?!

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