How does ACM slew work?
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The silly mode that I almost never use. How does ACM slewable work? It’s “stabilized” relative to what? What does the circle and cross HUD symbology actually mean? Doesn’t the “T” symbol represent the true position of the antenna in azimuth and elevation? What coordinate system are things represented in?
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@frederf I’ve also never used it… it seems maybe obsolete, for newer blocks with HMCS and BORE mode?
(I just tried it in a TE for a few minutes.)
It seems SLEW mode does a wider scan-pattern than BORE… if the animations on the MFD are true, it looks almost like A3/4B scan pattern, roughly centered around the iron-cross symbol. (Which I assume is relative to a/c nose… [edit: no according to the manual, and a quick test, it seems to be pitch- and roll-stabilized, similar to CRM modes… weird])
I suppose maybe at night, or in cloudy weather… if one couldn’t get a lock with HMCS, but you knew the general direction of the bogey … it might be worth a try?
I can recall a couple situations like that, where I got flustered and fumbled back to CRM mode… but maybe staying in ACM mode would have been better, especially if the bogey is very high or very low (viz. instead of struggling with extremes of antenna-elevation in CRM mode).
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Read the BMS -34-1-1 manual please
but general
Slewable ACM mode allows the pilot to slew a scanning radar patch, approximately 60 deg wide and
20 deg elevation, anywhere within the radar FOV. Slewable ACM is the only available pitch and roll stabilized ACM scan pattern. SLEW is entered by slewing the cursor when in any ACM mode. Initial movement
of the cursor will command the radar scan to initialize at zero degree azimuth and elevation. Subsequent
movement of the cursor will cause the 60 deg x 20 deg patch to move about the radar FOV.
The Slewable ACM MFD symbology includes an antenna pointing symbol, ACM scan
pattern indicator, and minimum and maximum altitude coverage depictions. The ACM scan pattern indicator box graphically depicts the 60° x 20° slewable scan area. The box moves on the MFD as the scan pattern is slewed to indicate scan pattern location. The antenna pointing symbol, the cross imbedded in the scan
pattern indicator box, indicates the center of the scan pattern. Minimum and maximum slewable search altitudes are shown in the center of the ACM MFD format.
The slewable ACM HUD symbology includes a slewable ACM borecross 3 deg below the aircraft
HUD borecross. Also displayed are a min/max search altitude depiction and a search cue. The min/max altitudes are computed at one half the selected ACM range An 8 mR circle depicts the center of
the scan pattern relative to the slewable scan cross. If the center of the scan is up and left of the slewable
scan cross, the circle will be deflected up and left of the center of the cross. Minimum and maximum altitude coverage is displayed directly below and above the circle, respectively
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I understand it’s a 60x20 roll-stabilized scan volume. What I’m not getting is purely in the pitch direction, mostly about the display. For less ambiguity I’m going to break apart four concepts into four distinct words or we have no chance.
Elevation: angle in the plane perpendicular to the horizon relative to the horizon
Tilt: angle of the radar mechanism vertically relative to the nose
Azimuth: compass direction in the plane of the horizon relative to current airplane heading
Traverse: angle of the radar mechanism laterally relative to the noseFor the longest time I thought the “T” symbols on the FCR (say in RWS) left and bottom edge showed tilt and traverse, aka true antenna position in the airframe reference frame. Apparently it’s both, depending. It should be el/az in CRM modes with INS online and in tilt/traverse in ACM and/or INS offline.
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@airtex2019 - one should understand that BORE does not really “scan” at all - it’s a fixed (circular?) stare placed at the HUD optical center, for a “point and shoot” sort of scenario.
Where ACM SLEW can be useful is if you are not using HMCS and are in a close/passing situation, to get an actual off-boresight scan in the quicker ACM mode.
In general I tend get into ACM SLEW by accident and then can’t figure out how to cancel it - transitioning through BORE usually works for me…but in this case my scan volume ends up getting parked someplace other than where I want it…for a bit.