[INVESTIGATING] Can we get the correct INS target designation behavior?

[Fri13]

 

 

 

When no Target Designation exist, the pilot is required to do so by using a Flight Path Marker as initial designator for LOS.

After initial TD is created, it is based to either barometric or radar altimeter angle.

Throught the flight toward target, pilot is required to use TDC to move the TD above target and release TDC for moment, that is called "sweetening".

The ARBS system will then re-calculate target slant range after each "sweetening" until it gets slant range properly calculated and pilot can confirm this seeing through HUD that TD diamond does stay above the target and doesn't slip away from it.

 

Higher height difference between the target and initial barometric/radar metered altitude is, then more sweetening is required.

And if the target elevation is same, then less sweetening is required.

 

At this moment we do not require any corrections. The INS mode is perfect to the target altitude as it is locked on the ground. This makes it unrealistic as target altitude is magically known.

 

The INS based TD movement is as well only possible when it is inside the HUD total field of view.

Meaning you need to be flying toward the target and have TD diamond inside HUD or otherwise TDC inputs do not move TD position, like currently happens any time you are in INS mode.

 

INS is critical part for all other sensors and target designation as without it properly done the other sensors and systems can not operate correctly.

 

 

Edited May 10, 2021 by Fri13

[lukeXIII]

On 5/11/2021 at 7:48 AM, Fri13 said:

At this moment we do not require any corrections. The INS mode is perfect to the target altitude as it is locked on the ground. This makes it unrealistic as target altitude is magically known.

 

The harrier has Digital Terrain Elevation Data (DTED) so it is possible to know the elevation using LOS angles.

 

For INS TDC behaviour, all the literature indicates it should be behaving how it is currently implemented in the F/A-18.

[Fri13]

10 hours ago, lukeXIII said:

 

The harrier has Digital Terrain Elevation Data (DTED) so it is possible to know the elevation using LOS angles.

For INS TDC behaviour, all the literature indicates it should be behaving how it is currently implemented in the F/A-18.

 

The documentation regardless with the TAMMAC says that you need to manually correct the INS target position as it calculates it based the LOS angle and BARO/RALT current alitude. 

 

Figure 1-47. Fundamental Quantities Related to Target Position NWP 3-22.5-AV8B, Vol. I 1-74

 

This is mentioned in the TAC-000 at

1.10.5.1 ARBS/LST Designation. page 1-200.

1.10.2 Concept. page 1-196.

1.10.3 ARBS Theory. page 1-196.

 

It is as well very specific that you can only move INS TD when the TD diamond is inside your HUD TFOV, not like now where you can move it when ever you want accidentally.  2.4.2 INS Designation. page 2-43 - 2-44.

 

Only way to get to know the slant range to the target (and target altitude) is either use a ARBS or then have target coordinates programmed with the altitude information like JTAC datalink or manually inputting the target altitude. But that means you need to know target coordinates in advance to program them to INS so it can use that information. 

 

The TOO function works same way, you need to overfly the target and the system use aircraft coordinates + RALT to measure the terrain altitude below the aircraft (uses only strongest return below aircraft, so not exactly "below aircraft" as if there is buildings, trees, hills etc then those are used). There is no DTED used there.

 

This is as well reason why you need to use ARBS/TV with contrast lock so the ARBS can calculate the slant range by your angle changes. It is fastest and preferred method, challenge is that you need to get a contrast lock first as it is not possible be locked on the ground like now. 

The ARBS/LST mode is only automatic locking system, where once spotting the laser it will automatically lock on it and designate the target and ARBS uses it to generate the slant range.

 

The INS targeting is the least accurate system as it requires the pilot corrections and if the height difference is too big it becomes difficult. And when you have limited time on target you don't have time to start playing with it if it requires a lot of corrections. 

 

In a AV-8B+ the radar AGR will replace the ARBS system for the slant range calculation, it is not so accurate and good as ARBS is but it is faster because pilot doesn't need to use ARBS/TV to try to acquire a target contrast to get a lock on it and be correcting it. And better than INS mode as pilot doesn't need to be correcting it based the difference of initial aircraft altitude and the target altitude. 

 

The DTED is not a system that gives target altitude and renders INS, ARBS, AGR etc obsolete because you would just get a target altitude from it when you just point "There it is". 

Edited May 12, 2021 by Fri13

[myHelljumper]

Hi we will see this with our SME to improve this behavior, thanks for the report.

[Fri13]

Figure 2-1. ARBS Height Above Target

Figure 2-14. Relationship Between Range and Angular Rate

2.2.3.2.3 HUD TD LOS Angle Ranging

Figure 2-22. Altitude Determination

Figure 2-5. Potential Radar Altimeter Error

2.2.1.6 Day and Night Attack Aircraft