Lee Elliott
> Sent: Saturday, September 18, 2004 3:03 PM > To: FlightGear developers discussions > Subject: Re: [Flightgear-devel] Problem with ballistic sub-model > > > On Saturday 18 September 2004 10:14, Vivian Meazza wrote: > > Lee Elliott wrote: > > > Sent: Friday, September 17, 2004 9:57 PM > > > To: FlightGear developers discussions > > > Subject: Re: [Flightgear-devel] Problem with ballistic sub-model > > > > > > On Friday 17 September 2004 16:09, Vivian Meazza wrote: > > > > 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. > > > > > > > > I've asked Erik to upload the modified files to CVS. It > looks OK > > > > on the Hunter, but perhaps Lee could give the revised > submodel a > > > > good test. > > > > > > > > Regards > > > > > > > > Vivian > > > > > > Hello Vivian, > > > > > > I just updated from cvs, including updates to the sub-model stuff > > > and while the pitch of the sub-model seems fixed ok, I'm > still not > > > able to get the > > > speed right. I tried reducing the <eda> setting to a > very low value > > > (0.0000001) and then 0 but the velocity of the sub-model > > > always seems to be > > > zero. > > > > > > As an experiment I tried setting some +ve <speed> values > i.e. 10 & > > > 1000 but still got a zero sub-model speed - I tested this by > > > 'releasing' the bomb > > > (bearing in mind I have <repeat> and unlimited models set for > > > de-bugging > > > purposes) while sitting on the runway. Instead of a stream > > > of sub-models > > > moving forward away from the stationary a/c they remain at > > > the origin. If I > > > then accelerate the a/c I leave a trail of sub-models behind me. > > > > > > There's an archive of the a/c at > > > > > > http://www.overthetop.freeserve.co.uk/EE-Canberra-20040916.tar.gz > > > > > > ...if you want to have a look. The release keyboard mapping has > > > been commented out in the ~set.xml file. > > > > Like the model: up to your usual standard. (Well, all except the > > pilot's bone dome - wrong pattern :-)) > > > > It works. The operative word is 'accelerate'. As you accelerate you > > leave bombs behind: they are instantiated with the velocity at the > > time of release, but since the aircraft is accelerating it will be > > left behind. Try the following using your original values > in submodel: > > > > Release a bomb while stationary: it turns and aligns with the > > velocity - note although the aircraft is stationary, there > are still > > some small N/E/D velocities. I'm not sure why. > > > > Accelerate down the runway: the bombs gradually align with the > > aircraft as forward motion is added, but they are left behind. > > > > Brake: the bombs shoot ahead of the aircraft, with their proper > > velocity. All those left behind now go past. Great fun - > like big fish > > swimming by. > > > > I've convinced myself, anyway - Newton's Laws of Motion at > work (see > > Arnt's comments). > > > > Regards > > > > Vivian > > Hello Vivian, > > I guess I'd better try to find some helmet 3-views;) > > I tried your suggestion of accelerating a little before > releasing and then > braking but the bombs are definitely staying in the same > place after release. > The <buoyancy> setting doesn't seem to be working either. I > was originally > using a <buoyancy> setting of 31 so that the bombs would fall slowly, > allowing me to judge the <eda> value I needed but even when I > set <buoyancy> > to 34, so that they should rise, they still stayed in the > same place, neither > moving backwards or forwards, or up or down. When I set the > <speed> to 100 I > noticed that the bombs were all aligned correctly but when I > tried re-setting > it back to 0 I could see the alignment changing, as you said it would. > > I expected though, that if I used a +ve <speed> value, the > bombs should move > forward away from the a/c if they're released while the > plane's stationary > but they don't. > > I'm just not seeing what you describe, and what I'd expect (I > agree with you > on Newton;) re the bombs catching up and overtaking the a/c > when the brakes > are put on. > > Hmm... It's just occurred to me that although my cvs is up to > date, I haven't > copied over the base package data for a couple of days - is > there anything in > there that could be causing this problem? I've got to go out > now but I'll > try copying over the latest data too, when I get back. > > LeeE > It's just occurred to me that I'm using my local version, so it's possible that I haven't asked Erik to upload one of the multitude of files it requires to alter one parameter, or there's something wrong with the files I sent in. It's definitely OK here with your model. I'll check. There's nothing in the base package. BTW negative velocities don't work, otherwise drag would cause things to run backwards. If you want submodels to move to the rear apply a +ve speed with 180 yaw offset. Bone dome is easy - there's a Mk1A in the Hunter models. Feel free to use it. There's no under-helmet right now - on my todo list. You'll need the visor as well. Regards Vivian _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
