AGR in visual radar modes like DTOS
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Hello all,
I was just wondering about some nerdy bits on DTOS. I assume that AGR (Air-to-Ground Ranging) radar mode is used in conjunction with other sensors (baro/cara altitude, INS) to range a target coordinates and elevation through the HUD in the visual AG submodes. Assuming BMS has only features and no bugs two questions:
1. AGR submode means simply the FCR is used as a rangefinder? After ground stabilisation, the cursor becomes sticky, is this due to some FCR effect?
2. DTOS still works after returning to GM or GMT radar submodes. Is the FCR able to switch very quickly in and out of AGR, or is GM basically the same as AGR for the FCR?Thanks,
TwanEDIT visual radar modes in topic of course should be visual A2G modes
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1. AGR is just air to ground ranging, thus the name. It doesn’t image the ground but provides measurement. The difference between pre-designate and post-designate DTOS slew is not related to the radar specifically. In pre-designate the slew is angular in the HUD environment, being the same angle response in all directions. In post-designate slews are in reference to some assumed ground plane similar to slewing TGP in area track. This is also the case even if the radar is off. The difference is how the system determines that geometrical point and its associated plane (or maybe complex surface if DTS). At designate the system uses its best data to determine a point at some finite distance and further slews are within this geometrical ground plane.
2. DTOS and bombing in general can solve for the geometry without AGR or even radar information but it isn’t as accurate. The question of if mapping radar modes provide comparable ranging data to AGR is an interesting one. I would guess not. FTT should be equal in performance to AGR because the radar is staring at a particular spot. BMS AGR is also missing some features like a tracking diamond, range scale, moving Maltese cross, etc. My guess is that the modes which map and produce an image either result in the airplane using other data sources or very unlikely degrade radar ranging.
The clue I believe is the “B” or “F” ranging letter on the HUD. My guess is that BMS is in error showing an “F” for pre-designate DTOS because it’s exactly equal to the “B” to-steerpoint number. Post-designate should be “F” and pre-designate “B”. The “F” or “R” should only show when that sensor is priority and it’s tracking (valid data).
The fact that you can command FCR modes other than AGR in DTOS, CCIP, EO-VIS, STRAFE, and the fix modes might be a limitation of BMS anyway. It’s sort of a workaround that you go AGR-STBY and then the STBY page allows you to return to any mode instead of limiting to AGR like it might. It’s a little suspicious that if AGR-GM was possible that the system would make you go the long way AGR-STBY-GM to get there.
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Actually, with a TGP, the TGP usually ranges the TD Box or the CCIP Piper in visual delivery modes, so AGR is not always required for a precise ranging - and it usually is worse than Laser ranging anyway
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Thanks Frederf and l3crusader, I wasn’t aware that the TGP ties in to these AG-modes, those system engineers are smart people. It would explain why it is possible to get out of AGR in the first place. Although it would make the weather a factor as well…:? On question 2 I would also expect a degraded tracking performance, interesting observation regarding the missing info and hud symbology. Anyway, this gives a rough idea of how it should work, as opposite to how it is currently there in BMS I guess, which without a TGP would appear to be just a little bit too robust.
You wonder how these systems can know IRL which sensor to trust and which to mark as degraded. Anyway, no more switching to other AG radar modes without a TGP for me.