LGB
27th Jan 2007, 06:50
The manual does not state this very clearly, but there are so many opinions on how to update the Delco Carousel INS.
It uses only DME, not VOR radials. Some people think it also uses the VOR, like VOR radial plus DME, like some FMS systems will.
The big question is, how smart is it? If there is a DME 150 nm ahead, 10 degrees off track, and this is enabled for a single DME updating, it has a long arc it can skate along. So even with a previous good update, you can risk the aircraft wanders several miles off track, from an otherwise good INS position. Then, when the DME comes closer and gets more abeam, the crosstrack will become more precise (but not the fore-aft). Normally, it is more desirable to have the crosstrack correct, to be on course, than to know if you are a few miles ahead or behind. If you change course drastically, it will of course change what is crosstrack and fore/aft.
In any case, the best fix you can get are two DMEs at a 90 degree angle (assuming at least two INSs are installed). Not too far away, but not too close either? So if you select two DMEs in front of you and 45 degrees of the track to each side, and leave them until they are behind you, at a 90 degree angle, and then take the update out, then you should have the best possible fix.
If you leave the update in, until they are out of reach you will first of all get a distance up to maybe 200 nm, incurring a little less DME precision, but most important, the two DME arcs will almost coincide instead of forming a perpendicular fix, and now you risk having the INS position many miles off track. I have experienced this often happens, but with nothing to check with other than the next available DME, it is hard to point out what is the cause and effect here.
Sometimes, there will only be one DME available for an update over a remote region, and you have to do a single DME update. I find that if it is enabled too early, you will just sway off course, then come back on track later on. So I prefer to wait to activate this kind of update, until it is at least at a 45 degree angle to the course. And take it out again, not too long after it passes abeam.
I have come to realize that a very good update can quickly become a bad one (if not taken out again in due time). I wish I could attach a GPS to prove what happens.
I tried to find tips and tricks like the above for the Delco INS, but I have not found anything usable yet. I hope someone can point to a page with more indepth information about this, or who cares to elaborate here.
Thank you
It uses only DME, not VOR radials. Some people think it also uses the VOR, like VOR radial plus DME, like some FMS systems will.
The big question is, how smart is it? If there is a DME 150 nm ahead, 10 degrees off track, and this is enabled for a single DME updating, it has a long arc it can skate along. So even with a previous good update, you can risk the aircraft wanders several miles off track, from an otherwise good INS position. Then, when the DME comes closer and gets more abeam, the crosstrack will become more precise (but not the fore-aft). Normally, it is more desirable to have the crosstrack correct, to be on course, than to know if you are a few miles ahead or behind. If you change course drastically, it will of course change what is crosstrack and fore/aft.
In any case, the best fix you can get are two DMEs at a 90 degree angle (assuming at least two INSs are installed). Not too far away, but not too close either? So if you select two DMEs in front of you and 45 degrees of the track to each side, and leave them until they are behind you, at a 90 degree angle, and then take the update out, then you should have the best possible fix.
If you leave the update in, until they are out of reach you will first of all get a distance up to maybe 200 nm, incurring a little less DME precision, but most important, the two DME arcs will almost coincide instead of forming a perpendicular fix, and now you risk having the INS position many miles off track. I have experienced this often happens, but with nothing to check with other than the next available DME, it is hard to point out what is the cause and effect here.
Sometimes, there will only be one DME available for an update over a remote region, and you have to do a single DME update. I find that if it is enabled too early, you will just sway off course, then come back on track later on. So I prefer to wait to activate this kind of update, until it is at least at a 45 degree angle to the course. And take it out again, not too long after it passes abeam.
I have come to realize that a very good update can quickly become a bad one (if not taken out again in due time). I wish I could attach a GPS to prove what happens.
I tried to find tips and tricks like the above for the Delco INS, but I have not found anything usable yet. I hope someone can point to a page with more indepth information about this, or who cares to elaborate here.
Thank you