AN/ASQ-38(V)

[yahya]

Does anyone know what terrain avoidance radar was part of the AN/ASQ-38(V)? The available descriptions are vague and only mention a BNS radar albeit without providing any nomenclature. Could that be the AN/APS-27 or AN/APS-64, or APS-81?

That radar was connected to the small round CRT displays on the instrument panel.

https://1.bp.blogspot.com/-fNj5o1M82Co/U7RVjs9zV6I/AAAAAAAAJxs/EP9H0GuudvI/s1600/B-52B-cockpit-dashboar-double-1.jpg

https://media.defense.gov/2016/Sep/06/2001625720/2000/2000/0/160906-F-IO108-007.JPG

 

[Joe Broady]

Does anyone know what terrain avoidance radar was part of the AN/ASQ-38(V)? The available descriptions are vague and only mention a BNS radar albeit without providing any nomenclature. Could that be the AN/APS-27 or AN/APS-64, or APS-81?

I have never heard of any of the above radars. The ASB-16 in the B-52G or ASB-9A in the B-52H scanned the ground for navigation, bombing, and terrain avoidance. These variants were almost identical, the main difference being the air cooled power supplies in the latter, whereas the ASB-16 utilized legacy power supplies cooled by oil. I believe the oil had the trade name "Coolanol." Anyway, that's what we called it. The stuff was somewhat irksome for maintainers since it was tenaciously oily once it got on your hands.

Actually, I never worked on the ASB-16, just the ASB-9A with the nice air cooled power supplies. But when digital OAS (offensive avionics system) arrived in the early 80s, our B-52H aircraft with ASQ-38 were replaced by G models with the OAS. These retained the 150/300 volt power supplies with oil cooling from the old ASB-16 system, for what reason I can no longer remember.

By the time I arrived in SAC, the EVS upgrade that added low light TV and infrared scanner turrets had been accomplished years before, and the old round TA radar scopes were gone. Instead, the TA radar trace was superimposed on the EVS imagery displayed on the 9-inch monitors. They used a 975-line video format (I think), compared to the 525-line broadcast TV format in that era. Left and right on the TA display represented azimuth, while height of the trace represented the highest terrain within the selected range. Available ranges were 3 and 6 miles, and I think there was a third setting I can no longer remember. This display of height was called "profile video." The navigators in the downstairs compartment could view "plan video" on their 5- and 10-inch radar scopes. This was like a PPI display, except that only the terrain above the clearance plane would appear. For instance, if the clearance plane was set to 500 feet, only the terrain 500 feet below the aircraft, and higher, would show up.

Ordinarily, the radar antenna could do continuous rotation, or you could take the sector width knob out of detent and select anything from more than 180 degrees to a rather narrow sector. The antenna would sweep back and forth to scan that sector. However, if TA mode was selected you got a fixed scan of 90 degrees, centered on the direction of flight.

All the above is from memory. Tomorrow I'll find my old maintenance manual and check for any worthwhile corrections or additions.

 

[yahya]

Thank you for the reply. I presume that the forward and downward looking "BNS" radar, which was part of the ASB-38, was devised mainly for low level penetration. However, its nomenclature, hence the exact specs, still remain a mystery.

The B-52B/C/D was fitted with the ASQ-48 bombing system. What is clear now is that the core elements of this system were the APN-108 Doppler navigation radar and the APS-104 terrain following radar. I suppose that the small round CRT displays in the instrument panel from the first post in this thread may have belonged to the latter.

 

[Joe Broady]

Thank you for the reply. I presume that the forward and downward looking "BNS" radar, which was part of the ASB-38, was devised mainly for low level penetration. However, its nomenclature, hence the exact specs, still remain a mystery.

I have never heard of the ASB-38. My experience was with the ASB-9A BNS (bombing navigational system), which was the central component of the ASQ-38 weapon control system on the B-52H when I arrived in SAC in the early 80s. As described in technical order 1B-52G-2-26, "Organizational (Flight Line) Maintenance Instructions, Bombing-Navigational System AN/ASB-9A and AN/ASB-16," (1980), our old maintenance bible, the ASB-9A was "an advanced electronic analog-type computing and control system designed to automatically navigate an aircraft to a target area (and on the return from the target area) and compute the correct instant for bomb release based on preset information and information obtained from radar sighting. In addition to this general function, the terrain avoidance features of the system assist the pilot of the aircraft in flying at very low altitudes to avoid radar detection."

The radar portion of the ASB-9A could display " predicted radar presentation adjacent to or superimposed on top of the actual radar presentation to aid the operator in identifying a particular aimpoint in a radar complex." This was accomplished through a 35 mm film projector in the radar-navigator's 10-inch radar scope. He could view the "map match" film in a round screen about 5 inches diameter beside the radar screen, or superimpose the image via rear projection into the CRT. In addition, there was a 35 mm camera to photograph the radar presentation from the rear. That CRT must have been quite a sight, but unfortunately I never saw it. The whole scope assembly, called a "topographical comparator," was repaired at depot level only. We were not authorized to open it at base level.

The radar itself, called the ACR (advanced capability radar) used "monopulse techniques to provide plan or profile display of the terrain below and in front of the aircraft and to improve ground map resolution by reducing side lobe returns while maintaining all the original capabilities of the high speed bombing radar used on earlier systems." As far as I ever saw, the radar was simply called the ACR and had no numerical designation. It was not "devised mainly for low level penetration." Its most vital functions were navigation and bombing. Without that, terrain avoidance flight is pointless.

The only B-52s I ever worked on were the G and H. When I was in SAC the D model was still in service, but its BNS was much different. The maintainers were trained in a completely separate school. I would have had no idea how to even power up a D model.

 

[yahya]

Thank you for the reply. There was my typo obviously: it should spell ASQ-38, not ASB-38.

I understand that you are acquainted with the low level attack G and H variants. I am actually interested in the older A to F variants only.

However, the old manuals suggest that the G variant was "updated" with the ASQ-38(V) bombing system, which, inter alia, consisted of the APS-81 Advanced Capabilities Radar (ACR) and the ASB-16 BNS. My understanding is that these pieces of avionics represented the analog tube technology, without any true digital content. The "processor" then could only be the crew.

By the way, its hilarious that the ARN-14 VOR, which represented the 1950s tube technology, was retained even in the contemporary BUFFs.

Check this entertaining vid, especially from 40:00.


View: https://www.youtube.com/watch?v=2sHUJnsMC2M

 

[-Hutch- 668BMS]

New to these forums, so apologize in advance.

Was B-52G nav and radar nav (bombardier) instructor, 3000 hrs total, completing tng/qual in 1978, 1st duty assignment Griffiss AFB, Rome, New York, and flew thru Griffiss' ALCM/OAS conversion (1st unit). Taught nav students inflight and classroom system instructor at Caste AFB schoolhouse for 2+yrs. Later assigned to HQ SAC staff in 1989, for early B-2 prgm.

ASQ-38 refers to overall downstairs B-52G bomb-nav sys, newer than the D-BNS system for B-52D model; before the Offensive Avionics Sys (OAS) ('mostly' digital upgrade used for ALCM's in mid-80's conversion), and lastly, was different from the B-52H model bomb nav systems of the day, ASQ-48, (primarily revolved the better heading system).

Circular pilots terrain aviodance display was gone by 1979, replaced by green monochrome milti-function displays (MFD) that showed terrain elevation sweeps back and forth as radar passed ovr selected range gates of 10, 6 and 3 miles. MFD's were part of the Electroptical Viewing System (EVS) mod....two chin bumps under the radome - one for infrared and other for B/W TV. Still seen on H's today but inop due to high maintenance and no longer needed due to high altitude operations. Infrared system was WELL advanced for it's day.

Had a few ASQ-38 sorties with the radar nav's orange 10" scope, along w/nav's 5" radar scope.... definately an acquired skill ! At that time, ASQ-38's included thumbwheel inputs to manually chg/set waypoints/turnpoints, radar aiming coordinates and targeting information, then sys was updated to the Automated Offset Unit (AOU), fed by a stack of Fortran data punch cards, B4 or during flight. For low level navigation, radar nav's job was to evaluate radar terrain 'shadows' at those selectable ranges, while pilots job was to fly left, right, or ovr terrain profiles displayed on their MFD's. Typically, terrain was called out at 10 mi, re-evaluated at 6mi, and flown ovr/around at 3 mi, depending on skill levels. Low level radar altimeter assisted in flying these low level routes at whatever altitude the particular route required.... Day VFR could be 400-600 ft, IFR and/or night could be 1000 - 1200 feet ovr the terrain. The radar altimeter and vertical velocity indicator (VVI) informed the pilots decision, at these range gate, as to when he'd start to climb ovr peaks, or just go inbetween the high points. Nav's job was to keep aircraft on track w/in a plus-minus 4 mile corridor, either side of planned centerline route, and on the specified timing, w/in 2.5 min.

B-52G DID HAVE an astrotracker, but not used for low altitude navigation. Nav's job was to program and keep astrotracker aligned to specific stars, ESP for night (or even day) star tracking, used w/out radar updates. It could update the heading system, but radar nav's aimpoint updates gave best location data, and N-1 compass was relaible enough w/out the astrotracker. Celestial tng legs were a typical tng event on every mission, training for a non-available radar system. Back then, no GPS, no cel/satallite phones, no laptops... radar aiming, nav timing, airspeed, and distance flown - dead-reckoning to a fine art.

Even fewer people will know of grid navigation, used by SAC for over-the-pole navigation, where N-1 compass was unslaved frm mag-north (due to magnetic anomolies), and hdg compas now set frm what nav had computed frm star table (HO-249) volumes. Surprisingly, same star table volumes used for celestial navigation by USS Miday in later years.... Blank white chart, w/lat/long lines, an overlay to the geographical world map. PAINFUL !

-Hutch-