On Saturday 18 September 2004 23:40, Arnt Karlsen wrote: > On Sat, 18 Sep 2004 13:21:13 +0100, Vivian wrote in message > > <[EMAIL PROTECTED]>: > > Arnt Karlsen wrote: > > > Sent: Friday, September 17, 2004 9:47 PM > > > To: FlightGear developers discussions > > > Subject: Re: [Flightgear-devel] Problem with ballistic > > > sub-model > > > > > > > > > On Fri, 17 Sep 2004 16:09:12 +0100, Vivian wrote in > > > message > > > > > > <[EMAIL PROTECTED]>: > > > > Arnt Karlsen wrote: > > > > > Sent: Friday, September 17, 2004 10:03 AM > > > > > To: FlightGear developers discussions > > > > > Subject: Re: [Flightgear-devel] Problem with ballistic > > > > > sub-model > > > > > > > > > > On Fri, 17 Sep 2004 07:56:42 +0100, Vivian wrote in > > > > > message > > > > > > > > > > <[EMAIL PROTECTED]>: > > > > > > Ampere K. Hardraade wrote > > > > > > > > > > > > > Sent: Thursday, September 16, 2004 7:12 PM > > > > > > > To: FlightGear developers discussions > > > > > > > Subject: Re: [Flightgear-devel] Problem with > > > > > > > ballistic sub-model > > > > > > > > > > > > > > On September 16, 2004 01:08 pm, Vivian Meazza wrote: > > > > > > > > There are some other basic shortcomings as well: > > > > > > > > the submodel doesn't inherit the parent > > > > > > > > accelerations, or the velocities and > > > > > > > > accelerations due to roll, pitch and yaw. Only > > > > > > > > release droptanks when flying straight and level > > > > > > > > > > ..uh, in the real world, this is possible if not > > > > > permissible, with fun consequences like one or more > > > > > hard points releases jammed for at least a while etc. > > > > > > > > > > > > They shouldn't inherit accelerations. > > > > > > > > > > > > Quite right - they shouldn't. I was getting over > > > > > > enthusiastic there, and forgetting my Newtonian > > > > > > physics. > > > > > > > > > > ..don't worry, there is also Murphy law physics. ;-) > > > > > > > > Right, back to Newton :-). I think I've solved the > > > > problem. Mixing elevation up = positive with speed down > > > > = positive nearly made my brain blow a fuse.. ;-) > > > > > > > > I had to reverse a number of signs to get it right. I > > > > took the opportunity to add roll to the submodel so that > > > > droptanks will come off with the right orientation. I > > > > not yet added either the parent rotational speed to the > > > > submodel, or yaw, so if you release droptanks with > > > > significant roll rate or yaw angle on the aircraft the > > > > submodel will not be quite right. Straight and level, or > > > > nearly so, is fine. > > > > > > ..precisely, we will need roll rate, yaw, yaw rate, pitch > > > rate etc, > > > > I can do all of that, providing I can get at the location of > > the CofG to relate the offsets. > > > > > but no accelerations except gravity, to get it right. > > > > Not strictly true. We also need to apply aerodynamic forces. > > Drag is already applied, and wind can be applied, but no > > other. Wind is that experienced by the parent, not the > > submodel. This approximation is OK for tracer, less so for > > bombs. > > ..eh, accellerations, no, forces, yes. Both "bomber" and > "bomb" sees the same wind etc until release of child. In a > bomb bay or in a gun, the wind exposure happens as these > objects emerge outta these shielded hideouts. > > ..If either (plane or bomb etc) object passes thru say wind > shear, wing tip vortices, then the wind forces are > _different_, even if they can be approximated as "the same" as > the bomb drops thru that vortice in a millisecond. > > ..and don't forget gun recoil forces. Gun "childs" also > experience wind drift. ;-) > > > > ..also, when we get that far in the modelling; some > > > dive bombers had release rigging that threw some, say > > > centerline bombs, clear of the propeller, adding to the > > > fun we dream up here. > > > > We can already do that - just apply an appropriate initial > > velocity, and instantiate at the right offsets. > > > > > ..also keep in mind most bombs are hung by more than one > > > points, so the hardpoint mechanism and the flight > > > conditions, attitude, rates etc, act together deciding > > > which points release first, second etc on each bomb. > > > > We can probably ignore that. > > ..true, but see below. > > > > ..this too, has a major impact on the initial ballistics, > > > think bobbing bombs dropping from B-52's or B-17's, on > > > dropping out of the bomb > > > bay, some of this is sudden exposure to the airstream, > > > some is "un-even" release, asymmetric or whatever. > > > > We could probably add some randomness to account for this, > > if you think it's a significant factor, given all the other > > approximations, chief amongst which could be that the > > submodel has no inertia, and so aligns instantly with its > > trajectory. Again, OK for tracer, but for bombs? > > ..this is a design philosophy decision; how close to reality > _do_ we wanna go? My point is "do as you like, but don't > cut off future development by hardcoding stuff, leave open > hooks as bait for future developers to go berserk on." ;-)
The development philosophy behind FG seems, to me, to be: get something working, then refine it:) I'm still at the get-it-working stage:) LeeE _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d