This web site last updated 04 April 2018
A Method of Actively, Constantly Re-Balancing a Spinning Turbine
This sub-page to www.rocketslinger.com is meant to continue off of ideas presented right before “figure 47” (use that as a search-string at the main root web page). If a turbine design (as presented there) is susceptible to becoming un-balanced in mid-flight, for any reason really, then we’d want to re-balance it with an active correction re-balancing technology. Specifically in this case we are envisioning a method of changing a jet engine (turbine) into a rocket engine at high altitudes, AKA “ variable engine geometry”, using pyrometric ceramic-containing composite turbine blades. Please refer back to the main page, of course!
As mentioned there, any automobile owner who pays a tiny bit of attention at the tire shop will realize that his or her tire, mounted on a truck or car wheel, has to be spin-mass or spin-momentum balanced by adding an appropriately-sized mass to the spinning assembly of wheel plus tire. Otherwise, destructive wobbling can set it. Now suppose (as would analogous to the case of a variable-geometry jet engine) that your wheel-plus-tire assembly is going to somewhat chaotically shed bits and pieces of itself, and/or be shifting pieces of itself to a different spin radius (different from its originally installed position), so that “angular momentum” and spin-balancing is going to start bouncing all over the place, half-way through your high-speed road trip. Constant and active re-balancing “in flight” here would be way handy, right? So let’s go there!
This sub-page here will try to focus on what I think are the BEST options, ignoring the rest. The main page mentions some other alternate options for spin-balancing. A SUMMARY of what follows below is this: For SENSING the degree and orientation of a wobble or a state of the spinning mass (turbine) being off-center, we simply rely on the fact that centrifugal force (in what engineers would call a potentially destructive run-away process of “positive feedback”) will take the off-center mass, and bend, warp, and twist the structure of the spinning mass, to allow the highest off-center mass to go yet FURTHER away from the center, aggravating the problem yet more. So we put a fluid-filled tube all around the outer perimeter of the spinning mass. The outermost (or most-off-balanced, highest-mass) part of the perimeter tube is going to gather the most fluid (and mass of the fluid)… Aggravating the problem, yes! But if we can use SENSORS to immediately, actively sense where the fluid is concentrating, then other activators and masses (on the spinning turbine blade in this case) can increase the mass concentration (or degree of pulling-outwards, centrifugal force) on the exact OPPOSITE wall of the turbine, which lacks sufficient mass, compared to where the fluid is gathering or concentrating most heavily.
What, exactly, might a simplest and most effective method of measuring such fluid distribution in a spinning tube be like? What is the fluid, what is the tube made of, and how do the sensors work? Many choices are possible… Liquid mercury would work, but is expensive and toxic. Saltwater is reasonably conductive, not horribly toxic at all, and is tolerably compatible with metals and ceramics, and so will be the choice described here. For the TUBE, metals work really nicely, but are highly conductive of electricity, and so are not compatible with electronic sensors that could be used, otherwise, to test the conductivity (or inversely, the resistance) of saltwater in the tubes. Ceramics, on the other hand (just like metals) can be high-temperatures-tolerant, for our high-temperature jet-turbine environment here… BUT, ceramics, unlike metals, are NOT conductive, and so it would be easy enough to embed a ceramic tube with saltwater conductivity sensors. Yet on the other hand, unlike metals, ceramics are not malleable or ductile, and so a ceramic tube, in such an environment, would be quite susceptible to shock and vibrations, and to temperature changes, causing it to crack or even shatter, losing its contents. A purely ceramic tube here is highly unlikely to be practical.
So what is envisioned here is a combination of metal tubing, which would comprise the majority of this spinning tube. However, PARTS of the tube (in small scattered segments spread evenly around the round “inner tube” here) would be made of ceramics, which in turn would be embedded with the sensors. A few alternate schemes for the details, mechanically and electronically, will be discussed here.
As far as the active re-balancing goes, the main page scenarios (masses on tracks or on flexible helical screws for instance, travelling under some sort of motor control around the outer perimeter of the spinning turbine) are hereby rejected as possible but not plausible. Some stubby “turbo-prop” propeller blades mounted on the outside of the spinning turbine walls, as described on the main page, would help, in the lower atmosphere, to propel our envisions jet-becomes-a-rocket vehicle here. Why not put small motors, and track or helical screws, and masses, on each (or at least on many) of these blades? In the lower atmosphere (where we want these masses out of the way of airflow) the masses would be kept close to the outer wall of the turbine. In the high atmosphere (thin air), immediately before the active (and chaotic) re-configuration of the jet-engine-becoming-a-rocket is about to begin, the masses (mounted on these outer turbo-prop, propeller blades) would all actively be re-positioned to a “middle” position (half-way between the turbine wall and the outermost extent of their ability to be positioned further out). Now when the chaotic re-configuration of the partially-melting pyrometric-ceramic-containing turbine blades starts, these outer-mounted masses are prepositioned to countervail. The actively re-positionable masses on these outer blades, that are positioned where the sense fluids have concentrated (too much pulling-outward centrifugal force) will be actively brought inwards, closer to the turbine wall. The actively powered masses on the OPPOSITE wall will be pushed further OUT, away from the center of the spinning mass of the entire assembly. This will correct the spin imbalance. As the hippies learned in the 60s, you know, the more far-out you are, on a spinning mass like our planet, the more “pull” you have (with those among your fellows who adore far-out-ness, at least; the analogy goes only so far, as you are a fellow far-out “Dude”!). J
So there you have it… A plausible sensor system, and a plausible method of actively re-distributing the centeredness (or lack of off-centeredness) of the spinning assembly, here. Now all I need to do is to spell out some more details and options or variations, and make some pretty drawings to clarify… As soon as I find some more time! Back to my day job for now… I am a C Plus Ranger by day, and a Rocketslinger by night, but only when I find some ideas, and some time…
OK, I’m back, here we go… Pressure sensors and vibration sensors might be part of the scheme(s) here, you can “Google” and “Wiki” this as well as I can, or see http://en.wikipedia.org/wiki/Pressure_sensor , http://en.wikipedia.org/wiki/Piezoelectric_sensor , etc. A fluid (like saltwater) arrayed around a tube around the periphery of the turbine, with the fluid allowed to concentrate (become deepest) at the furthest-away-from-the-center-of-the-spinning-mass would, especially under high spin speeds, have greater fluid pressure (due to centrifugal force) than the opposite side of the spinning assembly. This is obvious, and I have no special creative ideas to add here. However, I believe (I might be wrong, it HAS been known to happen!!!) that reaction speeds on such pressure sensors, and perhaps resolution as well, would leave something to be desired, for this use here. Near-instantaneous fluid-depths measurements could be gathered as described below.
First off, let’s describe a very simple method of detecting the presence or absence of electrically conductive fluid (saltwater) in a ceramic tube. A minus “-“ voltage (ground, AKA “GND”, or -12 VDC, or -48 VDC, whatever is handy) is applied to small wires filling small holes in the ceramic tube, at the “bottom” of the tube, along the length of this segment of tube. “Bottom” being the part, in this case, of the tube that is furthest away from the center of the spinning mass. Yes, our sensors here are NOT going to work until the turbine is spinning rapidly, but that shouldn’t matter much… Low spin rate means wobbles are less troublesome. … OK, so then we array more holes with more wires, and “pullup resistors”, pulled up to +12 VDC or +48 VDC or whatever DC power-supply voltage is handy. The “pulled up voltage” is then routed off to the central sensing and control computer. A solidly high sensed voltage means “high and dry”, a fluctuating one bouncing all over the place means you are on the “water line”, and a solidly low sensed voltage means your sense point if thoroughly underwater. The central computer of course “knows” where each sense point is located, and takes correcting control measures accordingly. Here is a cross-section of tubing showing the wiring as described here.
The above drawing almost definitely shows more sense points than would be needed, but hopefully get the point across. Also, the points will be spread out across the length of a tube segment as well as along the internal circumference of the tube, they would not have to be horribly densely placed as is implied in the drawing.
The above drawing hopefully clarifies that there is a hollow fluid-filled tube running around the full outer circumference of the spinning turbine, and that the fluid is free to let centrifugal force, force it to gather deepest at the most-distorted or most-off-center, outermost reaches of the spinning assembly. That is (refer back to main page), a chaotic process of transforming a turbine section of a jet engine (think “variable geometry engine”, perhaps incorporating partially-pyrometric-ceramic blades) into a rocket engine will almost inevitably lead to wobbles or asymmetries. The spinning structure will deform to allow the highest concentrations of mass to bulge outwards, the furthest away from the central spin axis. This tube is meant to sense the degree and orientation of such asymmetries or wobbles. The wobbles can then be removed by corrective actions to be described later.
In passing (with credit to my XYZ relative, person anonymous, for mentioning this), here is a possible but probably implausible idea (we DO want to fend off as many patent trolls as we can, now, don’t forget!): Like the cilia inside structures in the living ear’s sense parts (“cochlea”), we COULD even equip the turbine-mounted sense tube described here, with internal hairs or “cilia” that sense the FLOW direction (and perhaps also speed) of the sense fluid, here, as well as pressure or depth. Cilia-based sensing could provide even yet more data, and faster data, than depth alone, probably, but probably adds too much complexity, and more data than we want! However, PASSIVE (non-sensing elements) of stiff metal “hairs” (cilia-like, or, think of bristles on a VERY stiff brush, a wire brush) should almost definitely be included inside the tubes of the here-described apparatus, to “dampen” waves inside the sense tube. Otherwise, we will have waves travelling around and around the fluid surface inside the tube, constantly introducing a noise nuisance. Alternately, periodically-spaced semi-obstructions of mesh screen would perform the wave-suppression function as well.
As mentioned before, making the WHOLE tube out of ceramics alone is probably not plausible, because of the brittle nature of ceramics. Making the whole tube out of metal won’t work, because metals are better than saltwater for being electrically conductive; the sense elements of the tube have little practical choice other than to be made of ceramics. In passing, let me mention (fend off the patent trolls as usual!), it MIGHT be possible to put the ceramic elements INSIDE a sealed-metal tube, but this would be hard to do, manufacturing-wise, I suspect, and would be a maintenance nightmare as well, for lack of easy access to internal elements (lacks modularity).
So how do we manufacture the sense tube? With, say, copper tubing, or some other suitable metal… It would be nice, where the metal tube meets the ceramic tube segment, to try our best to have the “thermal coefficient of expansion” of the metal, match or almost match, that of the ceramic. The I/F (interface) between metal and ceramic may or may not be threaded, and it may or may not have a hose clamp on the outside of the metal that encloses the ceramic (the other way around would make no sense at all). I suspect that the hose clamp arrangement is probably best. Since this will be a stress point, the total thickness of the ceramic tube-wall should be thicker (stronger) here than elsewhere. The actual fluid channel should be uniform in carrying capacity, and in radial distance away from the central spin axis, throughout the entire length of the tube. BUT, the actual thicknesses of various points along the tube may vary. Also, more hose clamps, and a more complex (convoluted) surface at these pinch-points, will help reduce leakage. Some small amount of leakage at the metal-to-ceramic I/F may be inevitable… Unless we add some high-temperature-resistant gasket or sealant material in there? More on that later… But anyway, more surface area of metal mating to ceramics, under the hose clamps, may help to reduce leakage. OK, so finally, here is your drawing of the ceramic to metal tube I/F:
Notice that the metal tube-walls do not need to be as thick to have as much structural integrity as the ceramic tube-walls, AND that the ceramic tube-walls are thickened even more to withstand the “stress point” where two types of materials meet, AND the compressive forces of hose clamps are added. Hose clamps (which can be made of metal), metal tube, and ceramics are all readily available as non-toxic and high-temperature-resistant, and so this all looks to be very plausible (for use in a hot jet-engine environment). One weak spot may be at the metal to ceramic I/F, where temperature cycling and vibrations may lead to fluid leaks… We may have to add some gasket or sealant (caulking) material(s) there… Which must be high-temperature tolerant! Sounds like asbestos time to me!
And now, please forgive me, but I have to momentarily divert to some asbestos-related ranting and raving for a few paragraphs, please skip a few if you are just after the purely engineering-related matters…
I have read that gasoline and asbestos are roughly equal as toxins (sorry, I have no search results for you on that one). We all know that gasoline is highly toxic, to say the least. Yet… Speaking of search results, check this out: I put into “Google” the phrase “asbestos toxicity” and get 11,700 hits, then I put in “asbestos toxicity” AND also “lawyer” into the same search, and I get 11,500 hits (associate between lawyers and asbestos cooties is WAY strong). Now I put in “gasoline toxicity” alone and get 7,070 hits, v/s when I add “lawyer” there, 7,070 drops WAY down to a mere 1,040 hits. What does that say to you? To me, the “Google” results-math is telling me what I already know social-political-math wise: Lawyers have taken away our asbestos because, well, because they can… And it gets them power and money. And we collectively let them get away with it, because we think only a few fat-cat special interests are at stake anyway. They have NOT taken away our gasoline away from us, only because they KNOW darn well that if they tried, we’d start turning zealous, greedy lawyers into feed-stocks for biodiesel!
What we don’t pay enough attention to, though, is “How the Health and Safety NAZIs are Killing Us”. (Someone PLEASE write a book with that title?!?!) Asbestos was NOT merely used to enrich corporate fat cats; it was used to improve health and safety for large numbers of us mere non-fat-cats (AKA low-fat cats). Forthwith, some examples for you; the Health and Safety NAZIs ARE yea verily killing us: ‘1) CFCs are bad, and so we will eliminate them EVERYWHERE, even though we could safely help a LOT of people with just a few VERY small exceptions… Like Asthma inhalers. See http://www.cbsnews.com/8301-505123_162-42849822/fdas-cfc-asthma-inhaler-ban-becomes-a-light-bulb-issue-for-conservatives/ and http://www.savecfcinhalers.org/ … Classic case of, killed by the health NAZIs! … ‘2) CFC case #2, http://www.dvorak.org/blog/2005/08/04/today-in-investors-business-daily-stock-analysis-and-business-news/ , a multi-billion dollar space shuttle, and seven astronauts, were killed by the health and safety NAZIs, because NASA had to use “politically correct foam” to insulate the fuel tanks, because one in ten trillion people might cough due to CFCs used in the older, better, politically incorrect foam insulation. ‘3) Asbestos case #1, another shuttle (and another 7 astronauts) was lost because NASA was too politically correct to use enough asbestos to properly seal the o-ring seals on Challenger. (That one may not be true according to some sources). ‘4) Asbestos case #2, the twin towers came down in NYC on 9-11 because of some evil Islamofascist killers, as primary cause, yes… But, those towers MIGHT still be standing, had they been completed as originally designed, with asbestos-insulated, TRULY “fire-proof” steel structures, not with inferior materials. Speculative, perhaps, yes… But, “Killed by the Health and Safety NAZIs” is certainly not an entirely speculative rant. I have seen the statistic that the FAA spends $100,000 to save a life, statistically speaking, while the EPA spends $6,000,000,000 (!!!) to do the same! In a rational world, we would adjust their budgets accordingly. But since preventing airplane crashes is deadly boring, un-sexy work, and “environmental toxins” sounds like a horrible boogey-monster that must be stopped at ALL costs, the politicians follow the glamor and the press coverage, and we peons all get run over by giant earth-hauling machines that are hauling “contaminated” soil from here to there, that has two molecules of cooties per each 100 tons. I am wondering… If we have to dig up and use up 2 pounds of asbestos in the effort to stop the next giant asteroid for creaming all human life on the planet, will the lawyers, and the health and safety NAZIs, allow us to do it?!!? Oh, well, back to engineering…
OK, so, then, I think we have thoroughly enough beat up the question of, HOW do we sense (quickly and fairly simply) how far out of balance are we, and, in what particular direction are we out of balance? As we are spinning our turbine assembly around, of course. Electronic wizardry can fill in the details (I volunteer if the budget and job security is superb!). Have EE, will travel!
Moving on, then, the next question is, how do we efficiently, effectively, cheaply, and without torqueing off the Health, Safety, and Environmental NAZIs, go and CORRECT the spin imbalances that we have detected? Well, OK, we COULD have masses out there on the outside of the spinning turbine assembly, on the lee (downwind) side of externally-mounted “turbo-prop” blades, helical-screw-propelled, travel up and down. Further out means more angular spin momentum (more pull-out force). That’s kinda slow-reacting, boring, un-sexy, methinks, on second thought. It HAS yea verily now been mentioned, so as to fend off the patent trolls, though! On to more ideas…
The pushed-up and/or pulled-down (“up” is away from spin axis, “down” is towards spin axis) masses could be water-filled, or other-liquid-filled, with tiny little solenoids to open and close under electrical control, so as to as to shed mass (in a controlled manner) to assist with the spin-balancing act. A one-time deal… When you have “shot your load”, you are done… Hereby mentioned; patent trolls begone, deal be done…
Along similar lines, let’s mention the following: Holes in the sides of the turbine could selectively be opened, to eject hot gasses. Whichever side is bulging out too far, that is the side where we want to eject hot gasses, to counter-act against the imbalance. We could even put micro-turbines in these side / outwards micro-jets, and use them as a source of power for the control and activation electronics for this entire scheme. Speaking of power sources, how DO we power this whole sense and control scheme? OK, that particular list: Batteries, micro-turbines, micro-waved or electro-magnetically coupled energies, fuels cells, electricity-conducting contact carbon brushes from stationary onto rotating surfaces, or even vibrations, or even temperature differences across surfaces (see http://www.sciencedaily.com/releases/2013/02/130214075629.htm for example). Patent trolls are hereby further exorcised… Oh, PS, one could simply put a fairly simple electromechanical generator on the spinning part of the turbine, where it contacts the “stationary” body of the travelling jet / rocket. That’s probably your simplest and most reliable source of electrical power for the circuitry that is going to be needed, distributed around the spinning part of the turbine, for most any practical active re-balancing scheme (as here envisioned).
The masses of the components of the control circuitry, measurement tube(s), activators for the balance-restoring mass movements, etc., are all going to have to be evenly distributed through the turbine body, so that they themselves will not cause spin imbalances (with the obvious exception of the conductive fluid itself, which we have to deal with as the price of fetching our measurements). Pre-flight, before each flight, after the refurbished pyrometric-ceramics-containing turbine blades are installed, the spinning assembly would need to be pre-balanced with small counter-weights, for fine-tuning, just like they do with your wheel and tire at the tire shop. Then the aircraft / spacecraft would be properly engine-spin-balanced for low-altitude flight, all the way up till right before engine geometry starts to change.
And now just a few words about high-temperature-tolerant circuitry, as will be needed for any such scheme. See http://www.sciencedaily.com/releases/2012/06/120601103816.htm ; silicon carbide circuits can operate in temperatures up to 600 degrees Celsius. This type of circuitry should certainly help to solve at least some of the problems here. For those hopefully-small remaining parts of the circuitry that can NOT be met with silicon carbide, temperature-sensitive circuitry could be encased inside compartments that are actively cooled, via “heat pump” of some sort or another. Alternately, one active component at a time can simply be mated, heatsink-style, to a thermoelectric component (cooler). One simple choice here would be to use the “Peltier effect”; see http://en.wikipedia.org/wiki/Thermoelectric_effect ... These devices are reasonable affordable and practical. The extracted heat, extracted from the cooled chamber(s) or individual components, would be dumped onto the turbine wall, and / or the ambient environment. A drawback to these kinds of devices is that they are energy (power) hogs, but that should not be a significant drawback in a power-rich environment such as an aerospace craft.
Then finally there is the electrical wiring itself to be considered; how do we insulate it? How about (if there’s nothing else that really does the job right) asbestos? Maybe we can bribe all of the lawyers and “health and safety NAZIs”… Or maybe we can get Congress to pass special laws (like they did for the small-aircraft industry) protecting this new industry here from the ravages of the lawyers. If we have to gear up to go up there & get ready to steer the next giant asteroid away from us, as I think we should… Then, an engineer’s got to do what an engineer’s got to do!
Then the next topic becomes, how do we move masses around to control spin balance (correct spin imbalances)? As previously mentioned, we can put masses on the lee (downwind) side of external “turbo-prop blades”. How? Via linear actuator; http://en.wikipedia.org/wiki/Linear_actuator has a good write-up as usual. Response rates here might be a bit slow. Here is another idea which could offer MUCH better response times, if experience in the computer industry is any guide. Use a much-larger version of the “voice coil” actuator and swing arm that positions the read / write head in a hard drive, see http://en.wikipedia.org/wiki/Hard_disk_drive .. Except in this case, we would keep the powered actuator part of it embedded in the turbine wall, and the read / write head would be replaced by a moderate-mass “hammer head” out at the end of a fairly long swing arm. Position the actuated “head” close to the turbine wall if you already have too much mass (push-out force) there, and further out if you want more “pull out force” to correct a lack of mass at that spot. This would offer extremely good response rates, but would be a power hog.
Here is what I consider to be a much better idea (the best idea): Have multiple sets of these(*) arranged around the turbine, at different orientations (different “phases” or positions on the face of a clock, if you will). (*)“These” here means that at 180 degrees out from each other, a hinged mass can swing out. Each mass is coupled, via cables, to it’s one and only partner, which sits 180 degrees out from it, on the opposite wall. For low-altitude flight (dense air and no need for spin balancing), the coupled masses are held embedded into the turbine wall (slack cable is retained, not allowing the masses to fly out, which is what they “want to do”, due to centrifugal forces). This prevents un-needed air friction. At high altitude, right before engine geometry changes begin, the slack cables are (slowly, to prevent sudden changes or shocks to the system) released. Probably also staggered release; one set of masses released at a time. The weights, masses, counter-balances, whatever you want to call them, now fly outwards, on hinges that allow them to swing freely, but not fly loose.
Now the beauties of this approach start to clarify: The two opposing weights roughly balance each other, and the cables that run between them direct the pull force of the one, against the other, providing a fairly neutral cable to pull on, one way or the other, to enable an electric (or other) motor to control one cable, which controls two masses. The two masses do the exact opposite from one another, in terms of, are they adding or subtracting from “pull-out-force”, which is exactly what we want, since they are on opposite “faces of the clock”. And no, silly person, absolutely NOT, we do NOT run the cables through the middle of the turbine, obstructing the flow of hot gasses, we detour the “pull cables” around hollow “cable guides” contoured around the outer periphery of the turbine wall. If the aerospace plane is going to come back for a conventional landing (descend back into dense air), it might be desired to add a feature enabling “slack cable” to be created again (to pull both weights back into their recessed cavities on the outside of the turbine wall).
A motor to pull the cable in on one side, pulling that weight in, now allows the opposite weight simply to keep pulling, as it always does, going further out. But a motor requires more moving parts
Which then brings us to what I believe are the REAL optimal choices for the re-balance activators: (cliff-hanger happens here; C Plus Ranger must return to my day job). Meanwhile, back at the C Plus Ranch…
Stay tuned… RocketSlinger@SBCGlobal.net
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