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Join Date: Apr 2016 Posts: 163

TWS-Auto Track While Scan - Auto



As most know, we had a TWS-Auto implementation for the F-14 at launch, but it was quite unreliable and ended up causing more trouble than it was worth, so it was disabled. After launch of course we were kept quite busy, and it was some time before we managed to revisit and eventually rewrite the TWS-Auto system. We’re finally ready to re-release it now, and this post will summarize the functionality.



As you may remember, both TWS modes require the scan frame to be 2 seconds, and only support 2-bar ±40° or 4-bar ±20° scan volume modes (the radar gimbal moves at 80°/s, so you can see where the 2 second frame comes from in these two scan volume options). Very simply put, TWS-Auto attempts to keep the TWS pattern pointing where it is most useful in azimuth and elevation, while also controlling the optimum scan volume. TWS (and all the PD radar modes in F-14) uses ground stabilized (a.k.a. Earth fixed) patterns, so the azimuth and elevation angles are relative to a tangential plane on the surface of the earth at your present position, with azimuth further being relative to the F-14 longitudinal axis too (i.e. 0° is directly ahead on the imaginary plane, -20° is to the left, etc.).



Function of centroid



The azimuth and elevation angles are determined by a weighted centroid of targets in the scan volume. What this means is that some targets contribute more to the centroid than others, depending on a few factors outlined below. Essentially the position of each target is multiplied by its weight factor divided by the total weight of all targets, and these weighted positions are added together to give a centroid. Only sensor targets (i.e. own radar) are considered, not datalink targets.



Two separate (but somewhat related) centroids are calculated as part of the TWS-Auto update procedure: a steering centroid, and an illumination centroid. The former facilitates steering cues (on HUD, VDI, TID, DDD) to help the pilot maintain optimum target coverage, and also displays a small X on the TID indicating the steering centroid position. The illumination centroid controls the azimuth and elevation of the scan pattern center by using the angles from the aircraft to the computed illumination centroid (in TWS-Manual, these are directly controlled by the radar azimuth and elevation knobs on the RIO sensor control panel). The velocities (change in position over time) of both centroids are also calculated, used to calculate steering, and dead reckoning for a short period when all targets are lost (in an attempt to re-acquire them at their expected positions).



Weighting targets



As mentioned, a few factors influence target weighting. These differ slightly between the calculations for the steering centroid and the illumination centroid, but largely consist of the presence of a launch zone (targets marked as friendly by RIO will never get a launch zone), whether a missile is already underway to a target, and some RIO selections on targets such as DO NOT ATTK (disregards from weights completely, shows a small vertical bar over a target) and MAND ATTK (forces evaluation and raises importance, only one target may be selected for this, and mutually exclusive with DO NOT ATTK. Shows a small horizontal bar over a target).





Targets that are not displayed on the TID screen in the currently selected TID mode and range are also disregarded completely. In addition, targets which are deemed to be leaving the scannable volume are also raised in importance, if they are already deemed important by the previous criteria. For the steering centroid, the radar gimbal limits (maximum extents, basically ±65° in both azimuth and elevation) are considered, while for the illumination centroid, the current scan volume limits are considered (i.e. either 2-bar ±40° or 4-bar ±20°). This causes the illumination centroid to adjust towards important targets leaving the current pattern, and allows the steering centroid to shift towards targets that are leaving the maximum radar gimbal limits (i.e. pilot would need to steer towards that to keep them illuminated).





Engaging TWS-Auto



When TWS-Auto is first engaged, there is a period of 8 seconds where the manual controls for azimuth, elevation and the scan volume pattern are still in effect and can still be controlled by the RIO. After this period, the computer takes over. The scan volume pattern (2-bar vs 4-bar) is re-evaluated every 4 seconds, while the centroids are re-evaluated multiple times per second. The weights are updated at the end of each 2 second scan frame. The scan volume algorithm considers the future positions of all targets, and selects between which of the two options would give a greater total illumination weight. If they are equal, 4-bar ±20° is selected.



Firing an AIM-54 Phoenix while in TWS-Manual will result in automatic selection of TWS-Auto. Furthermore, when any AIM-54 missiles are deemed to still be in flight (up to 16s beyond their expected time to impact), TWS-Manual cannot be entered (the button press is ignored). Target tracks that have a missile launched at them will also behave as if Track Hold (the button to the left of the TID fishbowl) has been selected, i.e. they will continue to be extrapolated for up to 2 minutes if their radar contact is lost.



Symbology



The steering cues on HUD, VDI, TID and DDD will direct the pilot horizontally only, based on the steering centroid. By default, lead collision steering is employed. If the RIO uses the CLSN button next to the TID fishbowl, pure collision steering is instead calculated. Since both the pilot and RIO can see steering cues on their respective displays, coordination of required maneuvering is made easier. The steering cue on HUD and VDI is an upside-down T (hence called a steering tee), while on the TID and DDD the steering cue is a small square. These four displays have different steering sensitivities: TID is 40°/inch, DDD is 128.5°/inch, VDI is 25°/inch and HUD is 26.5°/inch.





In conclusion



TWS-Auto can be a handy tool for maintaining illumination on targets under attack, even while maneuvering about 60° away from the direct path to the targets. However, as pointed out by one of our RIO SMEs, good RIOs did not make exclusive use of TWS-Auto while hunting for new contacts, as it limits your overall situational awareness. RWS is still useful for scanning huge volumes, and TWS-M is still useful while maintaining the ability to control the scan volume angles. The Track Hold function (button to the left of the TID fishbowl) is also quite important, to maintain tracking (by extrapolation) on targets that would otherwise be lost in the PD filters.



Take a first look at TWS-A together with Jabbers here:

As most know, we had a TWS-Auto implementation for the F-14 at launch, but it was quite unreliable and ended up causing more trouble than it was worth, so it was disabled. After launch of course we were kept quite busy, and it was some time before we managed to revisit and eventually rewrite the TWS-Auto system. We’re finally ready to re-release it now, and this post will summarize the functionality.As you may remember, both TWS modes require the scan frame to be 2 seconds, and only support 2-bar ±40° or 4-bar ±20° scan volume modes (the radar gimbal moves at 80°/s, so you can see where the 2 second frame comes from in these two scan volume options). Very simply put, TWS-Auto attempts to keep the TWS pattern pointing where it is most useful in azimuth and elevation, while also controlling the optimum scan volume. TWS (and all the PD radar modes in F-14) uses ground stabilized (a.k.a. Earth fixed) patterns, so the azimuth and elevation angles are relative to a tangential plane on the surface of the earth at your present position, with azimuth further being relative to the F-14 longitudinal axis too (i.e. 0° is directly ahead on the imaginary plane, -20° is to the left, etc.).The azimuth and elevation angles are determined by a weighted centroid of targets in the scan volume. What this means is that some targets contribute more to the centroid than others, depending on a few factors outlined below. Essentially the position of each target is multiplied by its weight factor divided by the total weight of all targets, and these weighted positions are added together to give a centroid. Only sensor targets (i.e. own radar) are considered, not datalink targets.Two separate (but somewhat related) centroids are calculated as part of the TWS-Auto update procedure: a steering centroid, and an illumination centroid. The former facilitates steering cues (on HUD, VDI, TID, DDD) to help the pilot maintain optimum target coverage, and also displays a small X on the TID indicating the steering centroid position. The illumination centroid controls the azimuth and elevation of the scan pattern center by using the angles from the aircraft to the computed illumination centroid (in TWS-Manual, these are directly controlled by the radar azimuth and elevation knobs on the RIO sensor control panel). The velocities (change in position over time) of both centroids are also calculated, used to calculate steering, and dead reckoning for a short period when all targets are lost (in an attempt to re-acquire them at their expected positions).As mentioned, a few factors influence target weighting. These differ slightly between the calculations for the steering centroid and the illumination centroid, but largely consist of the presence of a launch zone (targets marked as friendly by RIO will never get a launch zone), whether a missile is already underway to a target, and some RIO selections on targets such as DO NOT ATTK (disregards from weights completely, shows a small vertical bar over a target) and MAND ATTK (forces evaluation and raises importance, only one target may be selected for this, and mutually exclusive with DO NOT ATTK. Shows a small horizontal bar over a target).Targets that are not displayed on the TID screen in the currently selected TID mode and range are also disregarded completely. In addition, targets which are deemed to be leaving the scannable volume are also raised in importance, if they are already deemed important by the previous criteria. For the steering centroid, the radar gimbal limits (maximum extents, basically ±65° in both azimuth and elevation) are considered, while for the illumination centroid, the current scan volume limits are considered (i.e. either 2-bar ±40° or 4-bar ±20°). This causes the illumination centroid to adjust towards important targets leaving the current pattern, and allows the steering centroid to shift towards targets that are leaving the maximum radar gimbal limits (i.e. pilot would need to steer towards that to keep them illuminated).When TWS-Auto is first engaged, there is a period of 8 seconds where the manual controls for azimuth, elevation and the scan volume pattern are still in effect and can still be controlled by the RIO. After this period, the computer takes over. The scan volume pattern (2-bar vs 4-bar) is re-evaluated every 4 seconds, while the centroids are re-evaluated multiple times per second. The weights are updated at the end of each 2 second scan frame. The scan volume algorithm considers the future positions of all targets, and selects between which of the two options would give a greater total illumination weight. If they are equal, 4-bar ±20° is selected.Firing an AIM-54 Phoenix while in TWS-Manual will result in automatic selection of TWS-Auto. Furthermore, when any AIM-54 missiles are deemed to still be in flight (up to 16s beyond their expected time to impact), TWS-Manual cannot be entered (the button press is ignored). Target tracks that have a missile launched at them will also behave as if Track Hold (the button to the left of the TID fishbowl) has been selected, i.e. they will continue to be extrapolated for up to 2 minutes if their radar contact is lost.The steering cues on HUD, VDI, TID and DDD will direct the pilot horizontally only, based on the steering centroid. By default, lead collision steering is employed. If the RIO uses the CLSN button next to the TID fishbowl, pure collision steering is instead calculated. Since both the pilot and RIO can see steering cues on their respective displays, coordination of required maneuvering is made easier. The steering cue on HUD and VDI is an upside-down T (hence called a steering tee), while on the TID and DDD the steering cue is a small square. These four displays have different steering sensitivities: TID is 40°/inch, DDD is 128.5°/inch, VDI is 25°/inch and HUD is 26.5°/inch.TWS-Auto can be a handy tool for maintaining illumination on targets under attack, even while maneuvering about 60° away from the direct path to the targets. However, as pointed out by one of our RIO SMEs, good RIOs did not make exclusive use of TWS-Auto while hunting for new contacts, as it limits your overall situational awareness. RWS is still useful for scanning huge volumes, and TWS-M is still useful while maintaining the ability to control the scan volume angles. The Track Hold function (button to the left of the TID fishbowl) is also quite important, to maintain tracking (by extrapolation) on targets that would otherwise be lost in the PD filters. Attached Thumbnails





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Heatblur Simulations

______________________________Heatblur Simulations Last edited by IronMike; 04-08-2020 at 11:35 PM .