Bomb/Nav Systems: B-47 & B-52

[Zipper730]

I started a thread about aerial bombing awhile back, and it came up that the V-bombers were using a derivative of the Mk.XIV bombsite of WWII fame. It used data fed from the INS, and radar-bombing system to improve accuracy, and during tests, seemed shockingly accurate.

I'm not sure if the results were typical of the bombing capability of the system, but the ability to put a bomb in a radius of 40-feet x 300 feet from 30,000 to 35,000 feet is remarkable

I'm curious what kind of bombing systems the USAF's B-47's had throughout it's life and the B-52 from 1955-1973, provided it's not classified.

 

[fubar57]

You might want to edit that

 

[tyrodtom]

That V-bomber drop test was one time, and it was a nuclear weapon that exploded at 500 feet in the air.
It was estimated, not measured, to be 40 feet right, and 100 yards downrange of the target. That's not 40 by100 feet.

What method of measurement is there that can estimate to the foot where a air burst nuclear explosion takes place ?

 

[Zipper730]

You might want to edit that

Already done...

That V-bomber drop test was one time, and it was a nuclear weapon that exploded at 500 feet in the air.
It was estimated, not measured, to be 40 feet right, and 100 yards downrange of the target. That's not 40 by100 feet.

Oh... I'm sorry, I didn't know it was 100 yards.

What method of measurement is there that can estimate to the foot where a air burst nuclear explosion takes place ?

Wasn't the explosion recorded on film?

 

[Graeme]

I'm curious what kind of bombing systems the USAF's B-47's had throughout it's life

I read today that the B-47's BNS (bombing-navigation system) "often went on the blink" and "while improved, never completely eliminated all of it's bugs". This of course was the vacuum-tube era.
In the mid-fifties high altitude bombing was then considered too risky, so toss-bombing and low altitude bombing was implemented. But as a result fatigue set in in the late 50's which led to project Milk Bottle. By then I think the USAF was happy to just be able to keep them in the air, let alone worry about bombing accuracy? They were retired in 1965 and "many flying officers would never trust them and were happy to see them go, and staunchly stood against their further deployment". Then it was full steam ahead for the B-52.

 

[Zipper730]

I read today that the B-47's BNS (bombing-navigation system) "often went on the blink" and "while improved, never completely eliminated all of it's bugs".

How did the V-Bomber systems compare in reliability to the B-47 and B-52?

From what I recall they used a type of radar system that operated as a pulse-doppler system to measure ground-speed and approximate wind, the H2S to map the contour of the terrain, a star-tracker device which provided more accurate course updates than the previous two could do on their own, with all this data being fed into a derivative of the old Mk.XIV bomb-sight.

I don't recall our B-47's and B-52's using a star-tracker (I know our B-58's did), though I do remember some B-47 variants using an optical sight which could be overlaid over the radar image for terrain mapping. I would assume the BNS had some form of doppler device...

 

[exradardan]

When I went through B-52 Navigator Initial Qualification in 1995 the pilot on my crew was a Lt.Col. who was requaling after a staff tour. He was a former D model Nav and he told me that they had an astrotracker that was tied into their bomb/nav system. He said it was the best heading system on the jet and better than the AHRS system we were using on the H model.

 

[Zipper730]

When I went through B-52 Navigator Initial Qualification in 1995 the pilot on my crew was a Lt.Col. who was requaling after a staff tour. He was a former D model Nav and he told me that they had an astrotracker that was tied into their bomb/nav system. He said it was the best heading system on the jet and better than the AHRS system we were using on the H model.

When did he serve on the B-52D?

 

[exradardan]

When did he serve on the B-52D?

Well we were going through the FTU in 1995 and he was a Lt. Col at that point, so I am going to guess it was in the mid to late 1970s.

 

[Joe Broady]

I don't recall our B-47's and B-52's using a star-tracker (I know our B-58's did), though I do remember some B-47 variants using an optical sight which could be overlaid over the radar image for terrain mapping. I would assume the BNS had some form of doppler device...

The B-52 (at least the H) did have an astro tracker when I arrived in SAC in 1980. Referring to my old bomb-nav maintenance manual 1B-52G-2-26, "The overall AN/ASQ-38(V) system on B-52H aircraft consists of AN/ASB-9A BNS, MD-1 automatic astrocompass, AN/APN-89A Doppler radar, and the AN/AJN-8 heading vertical reference system."

I was a BNS maintenance man, so the ASB-9A was "my" system. Other shops took care of the rest. Memories are hazy, but as I recall there was a separate Doppler shop, and Instrument/Autopilot shop was responsible for the MD-1 and AJN-8. The intricate division of labor at that time and place was remarkable. Avionics maintenance was a squadron unto itself, complete with our own commander and orderly room. The squadron occupied one whole hallway in the bomb wing building. Big shops like Bomb-Nav and ECM had a whole room to themselves.

Getting back to the MD-1, the good book says, "The MD-1 automatic astrocompass provides true heading information. The compass tracks a known celestial body by reference to the light from the body." The key word is "heading". In no wise was the MD-1 capable of generating a continuously updated position like a modern astro-inertial system.

I don't have any personal experience with the MD-1 since it was the responsibility of "those other guys" in the shop next door. However, we in Bomb-Nav did utilize it as a reference to align our stuff. You would go up on top of the B-52 to the little glass astro tracker dome, and fasten a fixture on top of the dome. This fixture had a flat surface where you could set a clinometer. This provided the official pitch and roll attitude of the plane. When our own vertical gyro needed alignment, it was adjusted to match this "gold standard." Also, a telescopic sight attached to the fixture gave you the official centerline of the fuselage. By reference to the scope, a test transmitter could be positioned accurately ahead of the aircraft in order to boresight the radar antenna.

As for that "BNS Doppler device", no such thing. As already noted, the B-52 Doppler in that era was a separate dedicated system. However, the BNS could "dope" the wind with a mode called "Memory Point". You set the radar crosshairs on some distinct return from the ground, press the Memory Point button, and wait for the MP light to come on. When it does, move the crosshairs back to the same return (if they drifted off) with the crosshair control (joystick), then press the button on top of the crosshair control to exit the mode.

The act of moving the crosshairs causes the north and east wind counters (like mechanical odometer counters) to drive. The more the crosshair movement, the greater the change in the wind counters. When they were correct, the radar crosshairs would track a point on the ground, same as a Norden bombsight would track if the speed and drift were set properly.

Sorry about the 2 years late reply. I was browsing old threads and noticed, oh wow, they're talking about a topic where I have some first hand knowledge.

 

[Zipper730]

Referring to my old bomb-nav maintenance manual 1B-52G-2-26, "The overall AN/ASQ-38(V) system on B-52H aircraft consists of AN/ASB-9A BNS, MD-1 automatic astrocompass, AN/APN-89A Doppler radar, and the AN/AJN-8 heading vertical reference system."

The heading vertical reference combines pitch with heading?

This fixture had a flat surface where you could set a clinometer. This provided the official pitch and roll attitude of the plane. When our own vertical gyro needed alignment, it was adjusted to match this "gold standard."

So you set the vertical gyro to match the clinometer, so it gets an exact read of where up/down is? And by extension left/right?

Also, a telescopic sight attached to the fixture gave you the official centerline of the fuselage. By reference to the scope, a test transmitter could be positioned accurately ahead of the aircraft in order to boresight the radar antenna.

And the telescopic sight helped you ensure the radar antenna is lined up the way it's supposed to be?

the BNS could "dope" the wind with a mode called "Memory Point". You set the radar crosshairs on some distinct return from the ground, press the Memory Point button, and wait for the MP light to come on. When it does, move the crosshairs back to the same return (if they drifted off) with the crosshair control (joystick), then press the button on top of the crosshair control to exit the mode.

I'd almost swear there was some kind of device the B-36 had, which served a function. It mentioned something about moving the reticle to correct for the airplane movement or something.

Sorry about the 2 years late reply. I was browsing old threads and noticed, oh wow, they're talking about a topic where I have some first hand knowledge.

Don't worry

 

[Joe Broady]

I don't have any personal experience with the MD-1 since it was the responsibility of "those other guys" in the shop next door. However, we in Bomb-Nav did utilize it as a reference to align our stuff. You would go up on top of the B-52 to the little glass astro tracker dome, and fasten a fixture on top of the dome. This fixture had a flat surface where you could set a clinometer. This provided the official pitch and roll attitude of the plane. When our own vertical gyro needed alignment, it was adjusted to match this "gold standard." Also, a telescopic sight attached to the fixture gave you the official centerline of the fuselage. By reference to the scope, a test transmitter could be positioned accurately ahead of the aircraft in order to boresight the radar antenna.

My description of that fixture may give the impression it was attached to the astro compass dome, but it didn't touch the glass. In fact, the thing was called a "3-star simulator." Judging from the name, I guess it generated synthetic stars to check out the astro compass. What we in Bomb-Nav used was the top part, with the flat plate and scope. The plate provided an accurate surface parallel to the B-52 "waterline" to measure its attitude.

Attitude is just the orientation of an aircraft with respect to the direction of gravity. It has two components. There's pitch, the measure of how much the fuselage centerline departs from the horizontal (nose high or nose low). At right angles to that is roll, which expresses the departure from a wings level orientation.

Both angles could be measured with the aforementioned plate and a clinometer. The latter was a contrivance with a sensitive bubble level in a rotatable cell which could be adjusted with a knob. Its position could be read to a single minute of angle (1/60 of a degree). To measure pitch, you oriented the clinometer to a fore and aft position, centered the bubble, and read the angle. Roll was similar, except that the clinometer was oriented crossways to the fuselage. (Years later, in the B-2 test program, we had digital clinometers, but on the B-52 it was a totally mechanical device.)

The pitch and roll angles measured thereby were the basis for leveling the bomb nav system's "stabilization data generator," which was a gyro which remained accurately vertical and supplied pitch and roll signals during flight. On the ground, a piece of test equipment could be connected to read the pitch and roll outputs. If necessary, the stab data generator mount was adjusted so the electrical outputs matched the pitch and roll measured via the clinometer.

The other part on the 3-star simulator that we used was the telescopic sight. It was mounted on pillars which elevated it above the flat plate. The sight had freedom to tilt up and down but could not move left or right. Thus, it provided a reference to position something on the ramp precisely ahead of the plane. That "something" was a test set antenna used to boresight the antenna of our bombing radar, same as you'd adjust a rifle sight so it doesn't shoot to the left or right. I'm sure the Fire Control (tail gun) people had a similar operation, but that was a different shop and the other end of the B-52!