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Paveway LGB




Laser Guided Bomb


In this Fall 1998 photograph, while on the Moody Air Force Base flightline, USAF Capt. Kevin Raybine checks out the training variant of the GBU-10 Paveway laser guided bomb loaded on his A-10A -- Photo by Shelby G. Spires 



  Polaroid Film and laser beams:




    "We didn't know enough about lasers at all ..." -- Weldon Word

     Although certainly not a new  discovery to science by 1965, the laser was virgin territory for the TI engineers.  At first, they didn't  know how to read if the machine was on or off. It was a simple problem with a simple solution, Word remembers.  "We got this thing and we were out on the outskirts of  Dallas on about a three story building.  We were shooting the laser at a Plano, Texas water tower about a mile away.  That was the only thing sticking out of the ground. We didn't know anything about safety.  We didn't know enough about lasers at all.  We were using wet emulsion Polaroid film.  The only way we could tell the laser worked was to take the Polaroid film, hold it with your finger tips and stick it front of the laser.  We knew it was on and working if it blew a hole through the film about the size of a penny right through the film," Word recalls.
       The laser may have presented a unique set of detection problems, but at least it was a tangible device.  The seeker was designed and built from a concept which had been drawn out on a sheet of paper.  There was no such device.  A challenge, the seeker was the part of the system the team had to develop on their own. Seeker Head on a GBU-10
       The engineers figured out that a silicon material could be used to detect the light, they fashioned a thin wafer of the silicon and placed it in the front of the seeker. The material detected the laser light. The next challenge was the aerodynamics of the sensor.  After running through a few mathematical analog computer simulations on machines that required programming in terms of turning gears and cogs, TI aeronautical engineer Dick Johnson struck upon the idea to use an aircraft probe. Johnson thought that a probe device, which is used to measure air flow around leading edges of aircraft, would work aerodynamically as a seeker.
       "We struck on the idea of lets put the seeker in a Geanini Probe," Word said. "What that will do is put the seeker, the instrument that is looking for the spot the instrument that is giving guidance directions." The probe resembled a badminton birdie, and from then on it was dubbed the "Birdie Head."
       The engineers couldn't just slap the probe on the end of the bomb, and brand it a guided weapon, though.  It had to be aerodynamic.  There was no funding to test the aerodynamics of the laser guided bomb shapes in a wind tunnel.  A back yard swimming pool held the answer. Johnson made several scale models of the fat shaped World War II bombs and used a swimming pool to test their aerodynamic wind flow.
       "About a month into this, Dick came in with a little model he had made at home.  It was about 10-inches long.  We took that model, went out to the swimming pool and dropped it.  He had different size control surfaces and he was trying to get the dart to have stability with the smallest size fins we could make.  We had to get it under the wing of the airplane, and if you couldn't get it going outwards you had to go radially," Word recalls.The seeker head on an LGB hangs limp.
       The lack of  money in late 1965 also meant the team had to be creative in the test approach used at Eglin Air Force Base, Florida.  With no funds for large data collection devices and expensive machinery, the key word in the test program was "improvise," Nick Baker recalls.
       "When we did the first tests, well, we didn't have enough money to go put a nice telemetry system on the weapon.  We had a high resistance tape recorder that you just screwed in the fuse well.  That bomb would go down and burrow down and it may go off to the side, and we had to find it to recover this tape recorder.  It looked like we were digging up half the county down there to find the things.  You had great big cranes out there digging up all these holes to recover that data.  You normally think of test programs with big telemetry systems, and we did not have a wealth of data.  If you had to stand out there for a week digging, then it was worthwhile to do that.  You just had to have that information.  No matter what the result was that created the hole in the ground, you had to have the information to judge the performance of it."
       Digging in the sand and clay of west Florida was worth the trouble to the TI team.  Out of ten bombs tested on the Florida ranges, eight were deemed a success, coming within thirty feet or closer to the target.   The Air Force began combat trials of the bombs in 1968, and based on those, the Paveway was redesigned and mated in the summer to the "slick" shaped or (for an explanation of aerodynamic shaped bomb click here) Mark-80 series of bombs

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All Text and Design Copyright (c) 2005 Shelby G. Spires. All rights reserved.