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#1
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Sidewinder engineering stoy/divide by zero
I was told by one of my college math teachers that there was an engineering
calculation in the early sidewinder days that involved a division by ZERO. No one could figure it out so they ignored it. The missile when launched destroyed itself in flight and the fix was to place a cross member in the body of the missile which then made the equation work properly Can anyone confirm or or deny this srory? Could have been sparrow but I'm pretty sure he said sidewinder. Instrucor was often freelancing as an emgineering consultant |
#2
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"leadfoot" wrote in message news:50une.14524$7p.11605@fed1read06... I was told by one of my college math teachers that there was an engineering calculation in the early sidewinder days that involved a division by ZERO. No one could figure it out so they ignored it. The missile when launched destroyed itself in flight and the fix was to place a cross member in the body of the missile which then made the equation work properly Can anyone confirm or or deny this srory? Could have been sparrow but I'm pretty sure he said sidewinder. Instrucor was often freelancing as an emgineering consultant Sounds something like the installation of the mask dead ahead in the seeker so that it essentially aims for a point where it does *not* detect the heat source. That solved a lot of problems. JK |
#3
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"Jim Knoyle" wrote in message ... "leadfoot" wrote in message news:50une.14524$7p.11605@fed1read06... I was told by one of my college math teachers that there was an engineering calculation in the early sidewinder days that involved a division by ZERO. No one could figure it out so they ignored it. The missile when launched destroyed itself in flight and the fix was to place a cross member in the body of the missile which then made the equation work properly Can anyone confirm or or deny this srory? Could have been sparrow but I'm pretty sure he said sidewinder. Instrucor was often freelancing as an emgineering consultant Sounds something like the installation of the mask dead ahead in the seeker so that it essentially aims for a point where it does *not* detect the heat source. That solved a lot of problems. Would it's abscene cause the missile to destroy itsekf in flight? JK |
#4
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leadfoot wrote: I was told by one of my college math teachers that there was an engineering calculation in the early sidewinder days that involved a division by ZERO. No one could figure it out so they ignored it. The missile when launched destroyed itself in flight and the fix was to place a cross member in the body of the missile which then made the equation work properly Can anyone confirm or or deny this srory? Could have been sparrow but I'm pretty sure he said sidewinder. Instrucor was often freelancing as an emgineering consultant Perhaps a corruption of this: http://tinyurl.com/cu3rg |
#5
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It is difficult to see where a division opperation of two variables is
needed in an early sidewinder. An analog multiplier in such a situation is likely to saturate at full output. As I understand it the early sidewinders simply followed the target and didn't solve an system of differential equations that might lead to a singularity. Do you have more data on the nature of the divide by zero? Most of the analog dividers I have seen actually produce the output Xo = (X1 x X2)/Y. In other words they are intrinsically dividers and multipliers. There are 'feedback multipliers', (that also do division), Dynameter multiplier/dividers that use two moving coils in coonected by shaft in oppostion that are blanced with a feedback circuit and photocells, electron beam multipliers (use a cathode tube with two pair of deflection plates and balance a phosphor dot on a screen by photocell, 'servo mulitpliers'(slow but accurate), 'heat trasfer multiliers' (good for 10 hertz), Simulataneous Pusle Width and Pulse Amplitude multipliers, electronic time division multipliers. (Dozens more in my copy of 'electronic analog computers by Korn and Korn of 1956). http://www.sci.fi/~fta/aim9.html Reticle Seekers - A Brief Tutorial The reticle seeker is the most common optical system design employed in conventional heat seeking missiles. Invented by the Germans during the latter phase of WW2, the reticle seeker provides a means of using a single detector element to produce an error signal in rectangular coordinates, with respect to a point target somewhere within the cone which represents the field of view of the seeker. The technique is based on the idea of mechanically chopping the light flux which impinges on a detector, in such a fashion that the characteristics of the chopped light pulses vary with the position of the light source in the field of view. Because the detector produces an electrical signal directly proportional to the impinging light flux, electronic hardware can be built to extract a positional error signal in x/y coordinates, suitable for driving a missile autopilot (or other tracking device). The simplest strategy for designing a rotating reticle seeker is the Amplitude Modulation technique, such seekers being commonly referred to as AM seekers. In an AM seeker of conventional design, the light collected by a mirror system is focussed to a spot on the detector. In between the detector and optics lies a whirling disc of optically suitable (transparent) material, which has translucent and opaque patterns etched on its surface, to interrupt the flux of infrared light. In an AM seeker, one half of the disc is translucent, and the other half covered by a spoke pattern, radiating from the centre of the disc. The result of this is pattern is an optical/electrical signal which is a series of pulses, repeating with every revolution of the reticle. The timing of these pulses with respect to the rotation of the reticle produces a phase signal which is proportional to the position in one axis, while the amplitude (size or strength) of the pulses provides an error signal proportional to the position in the other axis. The limitation of the AM seeker lies in the performance of the AM detection (here x-axis) circuits, as the average signal from the detector becomes quite weak in one direction thus producing poor tracking performance in this axis. A scheme to resolve this is what is termed frequency modulation (FM), whereby the number of spokes varies with the radial distance from the centre of the reticle. In this fashion a target closer to the centre of the reticle produces a smaller number of pulses per revolution than a target closer to the outer edge of the reticle. As a result the error signal in the radial axis of the reticle can be resolved by a frequency discrimination circuit which is locked to a reference frequency signal produced by the reticle motor. Practical seekers use a range of variations on these two themes, with various schemes using fixed cassegrainian mirrors and moving reticles, or rotating secondary mirrors and fixed reticles, the latter arrangement used in the Sidewinder family. Other design issues in reticle seekers revolve about the detector element, its supporting optics and cooling system employed. The detector is a small piece of semiconductor material with suitable photo-electric properties, ie it changes its electrical resistance or produces an electrical current or voltage when illuminated. The key design parameters in choosing a detector are sensitivity, a measure of how faint a light signal will generate a useful electrical response, and colour sensitivity, a measure of which visible or infrared wavelengths will or will not produce a response. Most semiconductors used for the purpose have some characteristic longest wavelength to which they respond, while producing output for all shorter (hotter) wavelengths. Therefore some detector materials can see only hot objects like tailpipes, whereas others can see the whole aircraft. Because all hot objects, such as the sun or flares, emit infrared blackbody radiation, a missile seeker must have means of reducing or removing such sources of infrared light to prevent seeker seduction. Therefore optical filters are used. These filters are typically made of a rare earth doped glass, with a multiple layer interference filter deposited on the surface. Such filters are essentially transparent over a narrow range of colours and opaque to all others, therefore passing only the desired infrared colour through to the detector. Cooling the detector is a means of improving its sensitivity. Even the meagre amount of heat in a detector at room temperature will produce a response in a good material, resulting in thermal noise which would mask the target, therefore the detector must be cooled to prevent this. Two strategies are typically used for this purpose, thermoelectric cooling with a Peltier device or gas cooling. A Peltier is a thermocouple which acts as a heat pump, albeit very inefficient, when electrical current is passed through it. Gas cooling relies on the expansion of compressed gas, and while lighter than Peltier schemes, usually imposes a limit on total seeker cooling time when the gas bottle is exhausted. The evolution of heatseeking missiles over the last four decades has seen almost every one of these schemes, or combinations thereof employed. The Sidewinder is a good instance. |
#6
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An unlikely story. The early sidewinder was developed by the Navy at
China Lake, CA by a couple of desert rats. An infra-red sensor was essentially attached to a piece of 5 inch pipe, the old HVAR rocket tube. The control system aimed for the highest heat source, hopefully a jet tail pipe, and tried to continuosly correct to that source. The dead center of the seeker did have a mask which gave a zero audio tone or nul. The sinous flight path to targets inspired the desert snake name, "Sidewinder". First operational test was a couple of missiles fired by Chinat's against a couple of Chicom Migs, resulting in first Sidewinder Mig kills. Later version had a radar dectector for exclusive use on Navy F-8 Crusaders in an attempt to give that airplane some modicum of all-weather missile capability. It was a miserable failure but did have the unique ability to self-destruct if it lost target return. This self-destruction would occur right after it's safe and arm time, about 3 sec. A very reliable source of mine had one of these sidewinders (Aim-9C) go off in his face one night leading to a less that hoped for operator acceptance. Perhaps this characteristic spawned the Math teacher's story, likely told to emphasize the supreme importance of that science. leadfoot wrote: I was told by one of my college math teachers that there was an engineering calculation in the early sidewinder days that involved a division by ZERO. No one could figure it out so they ignored it. The missile when launched destroyed itself in flight and the fix was to place a cross member in the body of the missile which then made the equation work properly Can anyone confirm or or deny this srory? Could have been sparrow but I'm pretty sure he said sidewinder. Instrucor was often freelancing as an emgineering consultant |
#7
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What idiot would attempt to divide by zero?
There is no "figure it out" as its not definable. Every high school student is taught that. "leadfoot" wrote in message news:50une.14524$7p.11605@fed1read06... I was told by one of my college math teachers that there was an engineering calculation in the early sidewinder days that involved a division by ZERO. No one could figure it out so they ignored it. The missile when launched destroyed itself in flight and the fix was to place a cross member in the body of the missile which then made the equation work properly Can anyone confirm or or deny this srory? Could have been sparrow but I'm pretty sure he said sidewinder. Instrucor was often freelancing as an emgineering consultant |
#8
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niceguy wrote:
What idiot would attempt to divide by zero? There is no "figure it out" as its not definable. Every high school student is taught that. You can be pretty sure it wasn't intentional. When you're programming with variables, it can happen that one of them becomes zero due to unforseen conditions. Of course, a wizardly programmer will both forsee the possibility of those conditions and also include tests to trap errors (like zeros in embarrassing places), but sometimes in the old days memory was extremely tight, not permitting such "luxuries," and then not all programmers are wizards. -- Noah |
#9
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You don't have to be a wizard.
Any programmer should ensure that a zero denominator can "never" happen. Whoever did that should have been fired as well as whomever was contracted to review and test the code. "Noah Little" wrote in message ... niceguy wrote: What idiot would attempt to divide by zero? There is no "figure it out" as its not definable. Every high school student is taught that. You can be pretty sure it wasn't intentional. When you're programming with variables, it can happen that one of them becomes zero due to unforseen conditions. Of course, a wizardly programmer will both forsee the possibility of those conditions and also include tests to trap errors (like zeros in embarrassing places), but sometimes in the old days memory was extremely tight, not permitting such "luxuries," and then not all programmers are wizards. -- Noah |
#10
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niceguy wrote:
What idiot would attempt to divide by zero? God. That's how we get black holes. |
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