On dimanche 07 décembre 2008, LeeE wrote: > On Saturday 06 December 2008, gerard robin wrote: > > On dimanche 07 décembre 2008, gerard robin wrote: > > > On samedi 06 décembre 2008, Martin Spott wrote: > > > > gerard robin wrote: > > > > > With the c172p i have included the following: > > > > > > > > [...] > > > > > > > > > To me that is perfect, [...] > > > > > > > > This is the sole point I'm talking about: Apparently, even > > > > though 'we' have "original" drawings of the entire airframe, > > > > still none of us has authoritative information at his hands > > > > how it is supposed to be properly positioned 'at level'. This > > > > is the issue which I'd was trying to sort out. > > > > > > > > Cheers, > > > > Martin. > > > > > > Yes it is a guess, how many models here are drawn with a guess > > > ? not only the landing gear :) > > > > > > Giving it a pitch of -3 deg is not so bad. > > > Or extend more the nose gear which will be ugly. > > > > AND > > The question isn't it , only: > > Which is the less stupid :) > > to keep the model floating above the ground when not in air ? > > or > > to modify the offset ? > > which won't shock anybody using that FG Reference Model. > > > > Easy to do, giving the possibility, latter on, to update, if > > somebody is able to bring the right blueprint of that Aircraft ( > > same model, same equipment .....). > > > > cheers > > Once you've aligned the reference point between the 3d model and the > FDM model you should never have to add offsets to the 3d model; if > there's a discrepancy it means that something is wrong. > > The best way, for modellers, is to make the landing gear in it's > maximum extended position - the position it would be in without any > weight upon it - and use those coordinates for the gear contact > points in the FDM. Then you vary the gear spring and compression > rates in the FDM so that the aircraft sits on the ground at the > right height and attitude, and then finally adjust the model's gear > compression animation so that the two match.
That is right but only theory. That means, too, that you include an animation compression extension of the gear (which is not the case with that c172p). With it , yes, => a drawing (blue print detailed) which gives you the right position of the gear when extended + => the know how about the right values of the landing gear ( damping_coeff , spring_coeff, pos min pos max, ) + => the right weight and force applied , on each contact point, we can do the perfect Aircraft, with a perfect FDM regarding the landing gear reactions. Unfortunately it is very rare to have all of these informations, and in many case we must be pragmatic, and the less stupid (if possible). I remember when i did the F-8E , i had some very high detailed drawing, but nothing else regarding the landing gear, but the usual position on ground. In order to get it, in a correct position when it is in air fully extended, and to get it, retracted correctly in the box without cheating , i had to calculate the size and the geometry of each components , it was a lot of work :( I had the same difficulties with an other aircraft done for a friend (SU-34). > > While it's usually impossible to get exact data on what the height > and attitude on the ground should be, with reference to photographs > etc. it should be possible to get it correct to within an inch for > small aircraft, and perhaps several inches for large aircraft. > > One of the checks that every modeller should do is to check the gear > compression under different loads. This will amount to testing > different fuel and passenger loadings, including asymmetric > loadings. Military aircraft can also be checked with different > weapon loads. Regardless of aircraft type though, once you've got > it right the gear will sit on the ground whatever the loading, even > with asymmetric loading. > > LeeE > Cheers -- Gérard http://pagesperso-orange.fr/GRTux/ J'ai décidé d'être heureux parce que c'est bon pour la santé. Voltaire ------------------------------------------------------------------------------ SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
