Arnt Karlsen
> Sent: Saturday, September 18, 2004 11:41 PM > To: FlightGear developers discussions > Subject: Re: [Flightgear-devel] Problem with ballistic sub-model > > > On Sat, 18 Sep 2004 13:21:13 +0100, Vivian wrote in message > <[EMAIL PROTECTED]>: > > > ... snip ... > > > > 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. Same thing: a body changes velocity (i.e. accelerates) as the result of an applied force. Newton's 2nd Law. > 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. Not quite true. The parent is experiencing wind, so it is a good enough approximation to apply wind to the child from instantiation. Turbulent airflow around the bomb-bay doors etc. is quite another thing. Although I suspect that the tumbling that you see on films is more or less rotation of the bomb about its CofG. Any that is not can be modelled by applying a bit of randomness to the trajectory. > > ..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. Yes, and charge temperature, barrel temperature and wear, Coriolis effect, parturition effect ... . Don't think I'll bother for guns fired from an aircraft with an effective range of 400 yds. >Gun "childs" also > experience wind drift. ;-) We already apply wind drift, but the wind is that experienced by the parent, not the child. This approximation is OK for guns, but makes no allowance for the various winds experienced by bombs during their descent. > > > > ..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." ;-) > I'm afraid that it's all pretty hard stuff in C++, but if anyone wants to have a go at some of the math or coding, I'd welcome any help. As realistic as the input data will allow. I'm sure Lee wont let up on me 'till his BB bomb is right. Regards V. _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
