THE SPELLING TEST


Before there was an N73 system there was an N57 system, Like the N73, it was a strapdown system. In the simplest of terms, a strapdown system is one without gimbals. Too simple! In an ordinary Inertial Navigation System (INS), the stable platform, or instrument cluster, is kept at local level by torquing the gyros to keep the sensitive axis of one of the accelerometers pointing towards the center of the Earth. Since it is impossible to keep the  vehicle carrying the INS level at all times, a means of allowing the INS to stay level and at the same time allow the vehicle to maneuver is required. The motion of the vehicle is decoupled from the INS stable platform by a set of gimbals. A strapdown INS is one in which the entire INS is fixed to the vehicle and rotates with it. Now you know. The decoupling is done mathematically in the computer. This was the new world I was to work in until I retired. The input/output device for the N57 computer was an IBM selectronic typewriter. I never learned to type and I am very slow. That, plus the fact that instructions to the computer must Be 100 % correct every time. Bad things tend to happen otherwise. I had barely started in my new job when I was asked to input a set of instructions to a computer in order to initiate a test sequence. The instructions were typed out on a sheet of paper and I slowly and methodically typed them into the IBM typewriter. I pressed “enter” to start the process. It was the end of the workday and we left. It was expected the test would run that night and be completed when we came the following day.

I came in the next morning and found out the test had not even started. It was my fault, I was told, because I had  misspelled a word in the instruction sequence. Not good! I went and made my apology to the engineer who ordered the test and who had given me the typed instructions. He was a little miffed because he had lost a day of testing because of my mistake. I went back to my other work knowing I had not made a friend of the engineer. Later that day , I was approached by the engineer whose test I had screwed up and he began to apologize to me for incorrectly accusing me of screwing up his test. I was confused by the turn of events until he got the part where he admitted that he had misspelled the instructions he had given me for entry into the computer. I felt sorry for him as he turned himself inside out playing a part that was clearly unfamiliar to him. It was a long time before our relationship became normal. I do not know what was worse for my feelings, being the goat or the vindicated goat. Both ways, I felt bad.

 

GETTING CLOSER TO THE PICKEL BARREL


There was a period of time when I was assigned to work with the Group that had design responsibility for the G6 gyro. Ray Noar, the Manger of  the group, was an expert on the subject of the G6 gyro having been the Responsible Engineer for the gyro prior to his becoming a Manager. The G6 gyro was used on the Minuteman I, II,and III missile. I believe it is still in use on the MM III missile. We were to consider ways to improve the G6 gyro’s performance. I have a vague recollection of a larger effort to improve the accuracy of the Minuteman III missiles and we were part of that. We used the Minuteman INS error budget as a guide to rank possible improvements in gyro performance and consequently we were looking at ways to reduce gyro ‘random drift’ and ‘gas bearing model’ errors. The ‘random drift’ of the G6 gyro ensemble was well known because the random drift rate of each gyro produced was measured during the acceptance testing of the gyro, but we realized a reduction of the INS error due to gyro random drift would require a much better understanding of the mechanism of random drift within the gyro beyond a suspicion it was somehow related to gas flow inside the gyro.

The speed of the gas flowing inside the gyro was in excess of 100 mph due to the friction between the gas and the spinning rotor. Ray believed that if we could learn how this gas flow was related to the random drift rate, we could find a way to reduce the random drift rate of the gyro. The big question before him was how to the visualize and measure the turbulent effects of a gas moving ever 100 mph. Ray’s approach was simple; he slowed the process down by substituting a fluid for the gas. This fluid would have a viscosity such that when rotated at a much slower speed than 100 mph, the Reynold’s number would be the same as that of the gyro fill gas. The turbulence of the fluid was made visible by mixing powdered aluminum with the fluid. This was all done inside a clear plexiglass full scale mockup of the gyro that permitted high speed photography as the means to record the fluid flow dynamics. Using this apparatus, Ray was able to “see” the formation and subsequent history of vortices in the fluid. By studying the patterns of turbulence in the fluid, he came to the belief that controlling these vortices was the key to reducing the random drift rate. His idea for vortex control was to place channels adjacent to the locations where the vortices started forming and thus contain them. He was instrumental in the design of the channel inserts that became part of the improved gyro. I believe the addition of these channels reduced the random drift rate of the gyro, but I do not recall by how much. It was amazing to watch a vortex form, detach and dissipate adjacent to the rotor surface. As I recall, he also devised a better way to calculate random drift from the raw test data.

The drift rate of the gyro changed as the acceleration of missile launch loaded the gas bearing of the gyro. A mathematical model, based on an earlier analysis by Stan Cogan, was used to predict the acceleration dependant drift rate changes and inflight real time corrections were made to the computed flight path of the missile being launched. The G6 gyro ensemble averages of the gyro’s sensitivities to acceleration and acceleration squared were the basis for the calculation of the corrections to the flight path. It was thought that if a practical method could be found to additionally measure the individual gyro’s sensitivity to acceleration to the fourth power, and if this and the individual, not the ensemble average, gyro’s measured sensitivities were used, that improvements in missile accuracy would be realized.

The gyro acceleration and acceleration squared sensitivities were already being measured during acceptance testing of each gyro. No comparable tests for higher order gyro sensitivities was available. I was working in the test laboratory developing new G6 gyro test methods that used a “linear vibrator” machine. This was a machine that imparted horizontal motion to the test gyro without rotation input. For these tests the gyro was mounted on the machine with the gyro spin axis in the horizontal plane. The angle between the test motion input axis and the rotor spin axis could be set at a predetermined  fixed angle. Gyro drift rates over a range of acceleration inputs were then measured for each of several fixture angles. These data were then used to calculate the gyro model coefficients. I had barely started to acquire test data when I was offered a position with the Group developing a new strapdown system that was based on the Autonetics Electromagnetically Suspended Gyro (ESG). I quickly accepted the offer and I turned over my G6 gyro work to others to complete. The development of test methods to measure the higher order model coefficients continued and an improved version of the G6 gyro became part of the Minuteman III INS. I was in effect starting a new career as a test engineer for strapdown systems.

 

 

 

 

 

CRUD! IF IT IS ONLY AN ACRONYM, WHY WON”T MY BEARING START?


I was introduced to crud a short while after I was introduced to the spherical gas bearing. (This bearing was the engineering tour de force at the literal and metaphorical center of the Autonetics G6 and G9 gyros.) I do not recall the exact circumstances of my first experience with a gas bearing, but it is very likely one which  involved a bearing which had failed to start rotating after power had been applied to the motor. What better way to inform a newly minted engineer about “black crud”. The term “Black crud” was the generic name given to the contaminating material often observed in failed gas bearings after disassembly. The term “black crud” had thus been inserted into my engineering lexicon where it has remained until this day. After I had decided to write of my experiences with “black crud”, I realized I did not know much about the words “black crud”. When I am faced with questions of that sort, I seek answers by entering the appropriate words into the Google search engine. After I entered the word “crud”, the search engine returned the usual avalanche of possibilities. The word “crud” is apparently completely generic in that it can range in meaning the noxious substances found in sewers to a more modern computer acronym. The word “black” has more specific meanings ranging in context from physics to psychology. I used the term “black crud” sans a definition for many years, but everyone seemed to know what I meant nonetheless. Thanks to the Google search engine, today I would say that “black crud” was the unknown substance found in failed gas bearings. It is the presumptive immediate cause for the failure of the bearing. The primary source of the “black crud” is usually not revealed by inspection of the in situ “black crud”. All bearing “crud” appears black due to the minute quantity of “crud” allowed by the very small dimensions of the gas bearing gaps. In my experience, staring at deposits of “black crud” will not reveal what it is, but trying to understand how it got there may yield clues as to origin. Even the use of marvelous machines of modern science such as the infrared spectrophotometer may not yield a satisfactory answer to the questions of origin being asked. Lifting a deposit of “black crud” and removing it without contamination is an art form mastered by only a few technicians. The first name of one such person was, very appropriately we thought, Merlin.

I was assigned the task of disassembling all G6 gyros that failed for any reason during acceptance test, determining the reason for the failure, and appearing monthly in person before the Air Force Minuteman Project Officer to present my findings for each failure. Going to Norton AFB every month was a big deal for us. Despite the serious nature of the assignment, I found it to be a lot of fun. Some of what I presented concerned gas bearing “no start” failures. I remember the times I presented Merlin’s infrared spectrophotometer charts, with their many bumps and dips, of samples of “black crud” taken from  failed bearings. I usually went through the litany of the various hydrocarbons that each bump represented and then delivered the punchline. I once showed them a chart made using a sample of hand cream. It was obvious the “black crud ” lifted from the failed bearing was hand cream. I was glad the Air Force did not have a policy of shooting the messenger or I would not be telling the story as they were not happy. However, most of the “black crud” was found to be the filler material added to epoxy resin in order to lower the thermal coefficient of expansion to a value closer to that of steel. This epoxy resin mixture was used several places inside the gyro and these could become sources of contamination.

The gyro is filled with a mixture of Hydrogen and Helium gases. This gas is caused to rotate at a speed exceeding 100 mph by frictional contact with the rotor. I always thought this high speed gas would be very effective in dislodging potential contaminants from their hiding places. The self-pressurizing property of the gas bearing required a constant flow of gas into the bearing thru small holes that led from the outer surfaces of the rotor into gas feed grooves that were located at the edge of the thrust pockets of the bearing. This arrangement of holes and grooves acted like a miniature vacuum cleaner. We sometimes observed a green powder deposited in the groove. The green color was from a dye mixed in with the calcium carbonate filler material.

I had exclusive use of a Farr bench inside the dust free instrument assembly area. This is where I did my gyro diagnostic disassembly work on failed gyros. The bench was located in an area of the room that had a direct line of sight to the managers desk on the other side of a large window in the wall between us. A failed gyro was a not a common event, but when it happened I would do my thing at my Farr bench. The Manager was well known to us as somewhat of a comedian, he was fun to be around and he had the knack of keeping tense situations from becoming worse. When I was at the bench, we would communicate using hand gestures. Like I said, he was fun to be around. His name was Gerry Sammons. The usual business of diagnostic teardown was routine and aften boring and a little horseplay at the higher levels of management helps.

The G6 gyro is sealed inside a welded, gas tight, magnetic shield can. Helium gas is added to the gyro gas mixture to permit the performance of a final mass spectrometer leak check of the gyro. I believe that Helium gas has the greatest diffusion rate of all the gases and it is notorious for being difficult to seal. The welded can was the absolute fix.  If a gyro is to be disassembled, the can must be opened by first milling the weld bead from the can. When the technician sat down a the bench, there was a gyro before him with the can weld bead removed. One time we removed the gyro from the can and I found a smashed red plastic protective cover of a fairly large round connector. I was taken aback by this turn of events and I replaced the gyro back into the can. I signaled Gerry he should put on his protective smock and come inside. After Gerry arrived at the bench and saw what I had found, he immediately suspected I was playing a practical joke on him. I finally convinced him I was not. We never did find out how that red protective cover came to be inside the welded can. If it was a case of attempted sabotage, it was a most clumsy one.

We had the use of a McCrone particle Atlas to aid us in the identification of anything we found in a gyro. With the aid of the Atlas we identified a hair from an Angora rabbit. But my all time favorite find was finding a Turkey Feather. That’s right, a whole Turkey Feather. These were duly reported to the Air Force Project Officer. I survived the ordeal without undue loss of blood as I recall.

I had moved on to other tasks when I became aware of a project to investigate the characteristic events that transpired as a coasting gas bearing contacted the stationary surface and stopped rotating. It was hoped that a “good” gas bearing could be identified and accepted and a “about to be bad” bearing would be set aside for disposition. It was an attempt,no less, to invent a “crud” finder machine. A noble endeavor indeed. I stayed in touch with Mike Albertson, the Supertech doing the work, as I was interested in the outcome.

The Instrument Test Laboratory had been for many years performing gyro drift tests using an apparatus which utilized a servo circuit to cause a single degree of freedom rotating table to constantly maintain one of the two gyro pickoffs at null. A servo circuit kept the other gyro pickoff at its null by constantly torquing the rotor. As the rotor drifted over time, the drift test table moved with it, thus the table angle was identical to the rotor drift angle. With suitable modifications, the drift table could be made to keep the drift table pickoff at null, ie, it was servoed to its own pickoff. The current flowing in table torquer was proportional to the force necessary to keep its pickoff at null.

The principle that was being exploited was simple. A gyro is mounted on a drift table such that the gyro spin axis is coaxial with the table axis. The drift test table is servoed to its self. If the gyro spin motor power is turned off and the rotor is allowed to coast, the drift table torquer current will be a measure of the drag torque acting on the rotor. If the coasting rotor contacts “crud” in the bearing as the rotor slowly looses lift, the event will leave a characteristic change in the table torquer current recording. It should be possible to reliably detect “soon to be bad” rotors! I do not remember if the machine was ever incorporated into the formal gyro acceptance tests, but I do remember it being used to diagnose rotor bearing problems for a long time thereafter. I remember being impressed by the sensitivity of the machine.

 

 

THE AUTONETICS G9 GYRO CASE ROTATION BEARING


The G9 gyro was an Autonetics free rotor gyro with case rotation added and it was used by the Autonetics N16 inertial navigation system. The N16 was the inertial navigation system for the FB-111 strategic bomber and a Minisins variant of the N16 was used for navigation on the Los Angeles class attack submarines of the U.S. Navy. The G9 gyro was a smaller version of the Autonetics G6 gyro which is still in use today on the Minuteman III missile.

The case rotation of the G9 gyro requires the gyro to have a case rotation bearing, a slipring capsule, a pickoff resolver, case rotation drive motor and gears, and a case rotation bearing. The gyro torquer assembly does not rotate. These items are not found on the G6 gyro. Case rotation was included in the G9 gyro design because of a requirement that the bias drift rate of the G9 be much lower than that of the G6 gyro. Case rotation has the effect of time averaging the gyro bias to zero. 

The spinning G9 rotor, like any gyro rotor, will not change its angular position in inertial space unless an external torque acts on the rotor. Assuming no torques are acting on the rotor, any changes in the magnitude of the gyro pickoff signals over the case rotation cycle will be due to the null pickoff plane not being normal to the instantaneous rotational axis of the case rotation bearing. In effect, the pickoffs are being constantly rotated away from the rotor and the pickoff signal will have a signal component with a magnitude equal to twice the non-normalcy of the pickoff null plane and frequency equal to that of the case rotation frequency. Any such signal component is a source of error to the platform gimbal servomechanisms of the system. The case rotation bearing must be of highest quality available and must be carefully designed to meet all performance requirements. For instance, the gyro is required to operate normally as the gyro is subjected to accelerations substantially greater than acceleration due to gravity. The case rotation bearing must operate normally in spite of such loads on the bearing. The bearing must be designed with an axial preload built in to preclude the bearing perfomance being degraded by externally applied loads.

The G9 gyro case rotation bearing met all of the requirements from the very beginning of the testing of the gyro. The original bearings were designed and manufactured by the New Departure Bearing Co. as I vaguely recall. The bearings were manufactured so that the bearings would be automatically set to the the proper preload value when the gap between the two pieces of the inner races was closed by the assembly screws.

We did get a big surprise at the beginning of the FB-111  program. The system environmental  tests required the system turn on and operate normally after a cold soak at -65 F. Much to our chagrin, we discovered that the bearing lubricant we used froze solid at -20 F. We obviously had a problem. Actually we had several problems on our plate. We had to find a bearing lubricant that froze at a sufficiently low temperature, had excellent lubricant properties, was available, had an adequate service life and did not evaporate at 165 F. We were very lucky because we had recently gone through the selection process for an oil for the G6 gyro stop bearing. We quickly determined that what we knew as Gyro oil D was the oil that met all requirements for the G9 bearing lubricant. It was already in use for the G6 gyro stop bearing so it had a good test history. Gyro oil D is a Pennsylvania crude “bright stock” which means the oil is not refined before its use as a lubricant. It is a rare well that produces this oil. To ensure that Autonetics always had a supply, we bought a 55 gallon drum of it. We used it by the drop, so a 55 gallon drum was a lifetime supply. Good thinking on our part, but we cold not find the 55 gallon drum when we needed to replenish our supply. Never did find that drum. I seem to remember someone commenting on the high price of the replacement oil. Gyro oil D proved to be our bearing oil never the less.

We had been in production of the G9 gyro for some time and I was beginning to think that I seen everything when I received a call for help with a G9 gyro that was not failing any test but the factory test engineer was of the opinion it should be failing something, as the gyro torquer current recordings were like nothing seen before. In a normal gyro, you can see evidence of case rotation in the recordings of the magnitude of the torquer current flowing in the servo that keep the rotor pickoff angles at null. These recordings had a huge non-sinusoidal signal component that seemed to be synchronous with case rotation. I had no idea what the problem was except it was clearly related to case rotation. I found that the signal also had a component that was rotating slower than case rotation. I was not able to associate what I  was seeing with any bearing defect I could imagine so I punted. My advice to the Test Engineer was to replace the bearing and see if the problem goes away. They changed the bearing and the problem went away. We had solved a problem but I had mystery bearing on my hands. I lacked adequate equipment with which to investigate a bad bearing so I sent it back to the bearing vendor for analysis. They quickly determined that one ball of the set of balls in that bearing was larger than the others. By this time we had certified two bearing vendors and they each had their own method of adjusting the bearing preload value. One vendor set the preload by adjusting the combined height of the inner race bearing parts so that at assembly the preload is correct. All of the balls used in their bearings were of uniform size. The other vendor adjusted the preload by using ball sets of different size balls. All balls within a ball set were of uniform size. The odd bearing we had discovered in our testing had been assembled with a ball set that mistakenly included a ball larger than the others of the set. The slower than case rotating component I saw in the torquer current recording was due to the slower speed of the balls relative to the speed of the inner race. The big ball was causing the instantaneous axis of rotation of the bearing to wobble and what we observed was the servo trying to keep up with the pickoff signal. I will always remember this as the “big ball problem”.

We once had a bearing problem we brought on ourselves. I do not remember why we did so but we vacuum baked the lower assembly of the gyo with the bearings in place. Very bad decision as the bearing lubricant was almost gone after the bake was over. We ended up sending the bearings back to the vendor to be relubricated. Our experience with the bearings was good as I do not recall any problems with life or reliability. 

I AM HAVING DIFFICULTY THINKING OF A NAME FOR THIS POST!


Yesterday I went to the Orange Empire Railroad Museum (OERM) with my friend Brian. We planned to spend the day finishing the work remaining for the “noon” whistle valve assembly***. We have been working to renew the valve seat and make a new valve for the valve assembly. This has been an interesting and challenging project and we are almost done. Brian and I will most likely to be able to return the valve assembly to the owner the next time we are at the museum. Our trip to the museum was uneventful and we arrived before 10 AM. Brian unlocked the shop and we gathered our tools for the days work. While we were in the “air room” killing time, Brian was shown a non-standard screw that had been removed  from a machine that was being repaired. The screw was broken and the small delegation of volunteer mechanics that showed us the screw asked if we would make a replacement. They informed us they needed a replacement to complete the work they were doing. Brian and I determined that we could make a replacement screw easily enough and we told them we would make them one. Brian would make the screw and I would finish up the valve lapping work. As the day wore on, lunch became our priority and we decided to go to Jenny’s restaurant in Perris. At Jenny’s, as we were finishing lunch, we fell into the familiar routine of small talk, nothing of a weighty nature, but something must have been said that prompted me to tell Brian about the trips to Alaska that Patty and I had done together. As I was explaining to Brian where Patty and I had visited and something about our reasons for going to these places, I felt myself begin to lose my composure and I began to cry. I could not stop. A barrier had been breached and I just could not stop thinking about Patty and the time we had spent in Alaska. I finally stopped crying and we left for the museum leaving some nearby patrons of Jenny’s wondering what the old bearded guy was crying about.  We returned to OERM and the valve project and I started fussing with the lapping of the valve seat. Meanwhile, Brian had started making the screw using the old and slow bench lathe. There is nothing particularly wrong about using this lathe except it is slow. It was getting late in the afternoon and I began to worry that I had not brought enough pills to take me into a long evening at OERM. Brian experienced a few setbacks and misadventures as he finished the screw but he did the right things and we were OK on quitting time. We were the last persons to leave the shop so we were responsible for locking up. It looked as though I had a couple of hours leeway and I would not have any problems related to my pills. I was growing increasingly tired and my worry over my pills was replaced by concern about my fatigue and how it would effect me the next day. The trip home was unexpectedly rapid. On the return from previous OERM ventures, we had experienced traffic delays just east of Corona, on I-15, and we were pleasantly surprised when we just zipped thru without any slowing. We made it to my house in one hour and eight minutes; a distance of sixty seven miles! My previous best time was one hour and ten minutes.

I felt tired and I was hungry as we parted company at my house and, except for my loss of composure at lunch, I felt as though it had been a good day for me. We had done what we had planned on doing and more. Any thoughts about quickly going to bed were rapidly replaced by my vision of the half-rack of baby back ribs that was waiting for me in the fridge. After waiting an eternity for the thirty seconds in the microwave to be over, I ate all of the ribs and I went to bed. I slept well, waking only to pee and take my pills.

I have experienced these meltdowns before and I have been thinking of ways I can work toward my desire to become able to talk about my life with Patty without becoming a basketcase. The next morning I asked David to bring my slides and negatives in from storage in our garage. These images are largely about our Alaskan adventures. I plan to get them organized so we may enjoy looking at them and perhaps lessen my propensity towards sadness and crying.

I went to Alaska for the first time in 1983. I was a member of a six man expedition with the shared goal of climbing Denali. I was not successful in reaching the summit of Denali, but I returned with many images and stories to tell about my time in Alaska and these stories  provided the impetus for Patty becoming interested in our going there and learning more about Alaska. As Patty and I talked about a trip to Alaska, it became clear to us that we did not want to go there with any groups or guides. We wanted to do our own thing and we did just that. This proved to be good decision for us. I had sent for a State of Alaska tourist guide book and Patty and I planned a trip to our liking. I spoke to the proprietors of the places we wanted to visit and I made reservations at locally owned establishments the year before we went. I paid in advance and never once in our several trips was I disappointed at what I received in return. We did our own thing, met some very nice people, and we very much got our money’s worth. It is the memories of those times with patty that I find so hard to talk about. I am hopeful that the memory activation that goes with the organization of my images into sensible groupings will lessen my tendency to becoming very sad when thinking of her. I have time working on my behalf, or so I am led to believe. I will know soon enough.

*** “noon” is my name for the large steam whistle that was located at the SPRR Taylor Yard shop in Los Angeles.

WHISTLE VALVE REPAIR IN THE OERM SHOP


One of the members of OERM is an avid collector of steam whistles and one day he brought some of the whistles from his collection to OREM and showed them to us. I made the comment that one of the whistles seemed too large for use on a steam locomotive. I was told the whistle used to be the  “noon” whistle at the SPRR Taylor yard shop. The whistle’s owner told me the whistle was not in working condition and asked me if I would make a new valve stem and renew the seat for the whistle. I said I would give it a try if we could figure out how to do it. The major uncertainty was about the method we could use to refinish the valve seat. I knew we had the equipment in the OERM shop that we would need and the job did look interesting. I also was sure we did not have any bar stock large enough to make the new valve stem, but I knew where to purchase bar stock of the size required. It was a done deal, or so I thought.

  What I did not know at the time I made the original agreement was that I would become unable to complete the job personally. I have Parkinson’s disease and the symptoms have progressed to the point that I no longer am able to operate machinery in a safe and responsible way. Also, I recently voluntarily stopped driving because I am not sure my reflexes are up to the driving challenges. Brian kindly offered to come to my Lakewood home and drive me to OERM for an occasional work session. There I would instruct him on what has to be done to complete this and future jobs. We decided to try the plan and see how it went. 

We have done this twice and it seems to be working out for us. I arrive back at home in the early evening tired but pleased that I am able to remain a working member of OERM. It is all to easy for a person with a chronic debilitating disease to become homebound. I am very fortunate to have a supportive family and friends like Brian in my life. What more could a person want.

Later, Brian began the work by setting the valve body up in the lathe. Because the seat is located deep inside the cast bronze valve body and hard to reach with a lathe cutting tool, I decided to have Brian chuck the body up in the Axelson’s four jaw independent chuck to maintain a secure grip on the casting and use a boring bar arrangement to extend the cutting tool to the valve face so we could make the cuts. The process worked perfectly.

I previously had purchased a piece of brass stock for the valve stem and, after settling the account, I found myself with a renewed commitment to saving brass cuttings.* After a little bit of preliminary lathe work, Brian setup the brass stock in a dividing head mounted in the Bridgeport milling machine. He machined the three flutes of the stem and we moved to the the  Axelson lathe for the remainder of the work. We reviewed the dimensions of the new valve stem to make sure we understood them, Brian finished the lathe work.

The lever that was used to blow the whistle is attached to the valve body by a bolt that had seen better days so we replaced it with a new one. For the whistle to work properly, it is necessary to lap the new valve stem face to the valve seat in the valve body. To do this properly, we had to make a tool to keep the valve stem straight while  lapping the seat. A piece of scrap aluminum was found that met our needs and the tool was made.

The lapping operation went without a hitch. After rough lapping, the valve seat was finished with 320 grit lapping compound. An air driven hand grinder head and a carbide burr was used to deburr the valve stem. The valve was assembled.

All that remains to  be done is deliver the refurbished valve assembly to the collector.

I wonder if we will get to hear this very large whistle.

 

*I have been saving copper alloy waste (chips) in a container for a considerable time and it has become to heavy to move easily.  Waste not and thus want not are words to live by.

 

THE FUZZ BUTTON FOLLIES


I have been trying to remember as much as I can about my work at Autonetics. I am doing this at the encouragement of two long time collectors of aerospace memorabilia. We met(sort of, they live on the east coast) when they commented on some of my posts to this Blog. Their encouraging words resonated with my need to write. I have been trying to remember the details of the Electronics Module of the Autonetics G9 gyro. That is how I came to recall the “fuzz button”. The “fuzz button” a small bit of compressed wire that has been knited on a machine used to make socks. Stay with me, this is not a joke story. These little, pill like, pieces of wire made the G9 gyro electronics module a practical way to solve some tough packaging problems that must have arose during the G9 gyro design process. I did not have any part to play in the original design of the G9, but I was the Senior Responsible Engineer for the gyro for ten years and my memories of the “fuzz button” are my personal ones.

The G9 gyro was a small, case rotated version of the Autonetics G6 gyro. The fact that that the G9 gyro, except for the stationary torquer assembly, was rotated continuously made it not practical to use the very reliable pickoff transformer used on the G6 gyro. It was way too big. The G9 pickoff circuit was designed around an Autonetics current amplifier instead. The amplifier required wiring for power and the G6 transformer did not. The case rotation feature of the G9 brought with it the need for a resolver to “derotate” the gyro pickoff signals as well as a slipring assembly. All of this was required to be packaged in the electronics module. Space for the electronics module was limited by the requirement the module must fit inside the case rotation bearing. The electronics module was to plug and unplug into the gyro case quickly and easily without special tools. This must have seemed an impossible situation to the designer because there was no space in the electronics module for standard design connectors. A new G9 gyro specific connector would introduce more complexity and higher cost into an already tough situation. I do not know the circumstances, but the designer became aware of the “fuzz button” and like magic his problems with connectivity of the module melted away. The heart of any ordinary connector is a metal pin inserted into a metal spring – like split sleeve that makes electrical contact between the pin and sleeve. A connector assembly is an array of the pin and sleeve devices. The pin and sleeve devices are held in  fixed positions by insulating blocks. The pin and sleeve arrays are known as male and female connectors respectively. The force necessary to make or break the electrical connection is the sum of the force necessary insert or withdraw a single pin. A greater number of pins and sleeves equates to a greater force for connector insertion and withdrawal. To avoid damage to the connector assembly, the connectors must be well aligned as the connection is made. So, how does a “fuzz button” work and why did it enable he designer of the electronics module to make a successful module design?

The “fuzz button” is a pill – like compressed piece of knitted wire. The amount of knitted wire in a given pill size is carefully controlled so that after the wire pill is inserted into a cup – like holder it will remain compliant. Connection is made when a rounded end pin is inserted into the metal mesh pill. Since the diameter of the metal pill is substantially larger than the pin, only nominal alignment is required at insertion. The force necessary to make contact is the force necessary to compress the pill. This force is less than the insertion  force for an ordinary pin and sleeve connector. There is no withdrawal force associated with the “fuzz button”. Think of the implications of what is stated above. The use of the “fuzz button” makes it possible to design an module that only needs to be nominally aligned, requires virtually no insertion force and has no withdrawal force. The “fuzz button” is held in place by a simple  cup – like hoder that is easy to manufacture. Bulky ordinary connectors are replaced by a simple unobtrusive array of cup – like holders that can be arranged in the most advantageous pattern. It is my assertion that the use of the “fuzz button” green lighted the design of the G9 gyro in the  form we knew it.

So, if the “fuzz button” was so beneficial to the design of the G9 gyro, why do I harbor mixed feelings about my experiences with it? It is simple really. The “fuzz button”, as seemingly simple as it seemed to be, required the customer to be ever vigilant concerning errors in the manufacturing process. For instance, the compliance of the “fuzz button” was dependant on having the precise amount of knitted wire before compression into the pill. We developed a method of measuring the density of each pill before use to guard against too much or too little mesh in each pill. We learned the hard way to not allow the “fuzz buttons” to shipped in envelopes the allowed commingling. We were once  forced to untangle a batch with tweezers to avoid a delay in the production of modules. There were some unhappy technicians during that episode. I must concede that the availability of the “fuzz button” was a positive factor in the success of the Autonetics G9 gyro.

 

 

 

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