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Everything posted by Enthalpy

  1. Quick Electric Machines

    I put thoughts in the liquid hydrogen tank because compressed hydrogen needs a tank too heavy. Also, liquid hydrogen is less dangerous than compressed one.
  2. Quick Electric Machines

    Hello, heirs of James Clerk, Nikola and the others! It is well known, but by too few people : in an electric machine, only the force means losses and heavy parts, the speed comes for free. When a motor or generator runs quickly, say 50 or 100m/s at a power plant, it is smaller than a turbine. Quick machines with rotating permanent magnets use to hold them in a tight sleeve of strong steel to counter the centrifugal force. I propose to wind a composite of graphite fibres around the magnets instead of the steel sleeve. Graphite fibres are lighter than steel and produce less eddy current losses where they cross the stator's windings; better, while the accurate diameter of a steel sleeve is difficult, fibres are commonly wound tight over varied cores, even with a pre-tension useful here. A unidirectional composite looks best here, and pre-impregnated graphite is usual at wound pressure tanks for instance - other fibres may emerge. Some thin elastic material below the magnets can prevent cracks. To run at 200m/s, 5mm thick magnets weighing 7500kg/m3 need 1.5mm of graphite composite withstanding 1000MPa - or scale both thicknesses. Neodymium magnets like Thyssen-Krupp's 300/110 still achieve 0.78T through the graphite plus 1.5mm radial gap. I already described a small electric motor turning a rocket engine pump, there http://www.scienceforums.net/topic/73571-rocket-engine-with-electric-pumps/#entry734225 and http://saposjoint.net/Forum/viewtopic.php?f=66&t=2272&start=80#p41298 the following one outputs 2083kW like the PW127M gas turbine that moves the ATR-72 and other successful planes. http://www.pwc.ca/en/engines/pw127m http://de.wikipedia.org/wiki/Pratt_%26_Whitney_Canada_PW100 http://en.wikipedia.org/wiki/ATR_72 The motor rotates at 255Hz, so a gear drives the propeller at 20Hz - but a turbofan would need none. 5mm thick magnets at D=250mm run at 200m/s. The 355mm long stator has 3 phases and 18 poles. The windings are one turn of square 5mm*5mm copper that makes 36 passes through the shared 54 slits. The induced coil voltage is 1726Vpk (reduce the length if I botched a cos30°...) and the current 804Apk, nice for an inverter supplied with 3kVdc maximum. Coil resistance is 13mohm (or a bit more as the skin depth is 1.4mm at 2292Hz) so ohmic losses are 13kW or 0.6%; core losses are small with the proper material. This electric motor weighs ~120kg, is ~400mm long and 312mm wide , while the PW127M is 660mm wide and ~1.2m long without the gear, and weighs 481kg with the gear. Direct retrofit, though we still lack proper fuel cells. Marc Schaefer, aka Enthalpy
  3. Are you an electrical engineer?

    I am. Circuit analysis tends to be very simple. Usually I need no "theorem" nor "law" at all. just currents, voltages, impedances. Exceptions are rare. Or maybe I've forgotten that the computations I make bear a name. But you shouldn't imagine that electrical engineering is only circuit analysis. Software: forget about that. Computer: no. And: if you imagine that a software or computer replaces the designer's understanding and ability to compute, you will fail. Beware: your question suggests that you imagine that software replaces knowledge, but a designer that understands his stuffs doesn't need any software. Electronic circuits are easy to compute by hand, and just a pocket calculator is faster and safer than any computer simulation. In fact, at least a friend and me often cable electronic circuits without drawing them in advance, and compute the components mentally. That's very far from needing software.
  4. How do I learn to design and make my own electronics

    You can learn from varied sources. Experiment kits are often excellent, at least as a start. Books written for (and usually by) hobbyists are an excellent way to learn. The kind of understanding they promote is much more efficient than what is taught in engineering schools and universities. Past some point, academic knowledge is necessary, but if someone has only one kind of knowledge; then the hobbyist way is superior. Journals exist for hobbyists. Elektor is excellent. I few years if you're starting now.
  5. When electronics engineer design/construct circuits?

    There are many ways to design circuits... Software replace knowledge: - NO - . That's a safe recipe for failure, not only in electrical engineering. I know quite a few people who design good circuits by experience, with limited knowledge of theory. Some hobbyist radio belong to that category, but by far not all. They are less bad than the opposite, diploma holders who have no hands-on experience. But to make good designs, especially ones that don't resemble existing ones, does require quite a bit (or sometimes a lot!) of knowledge. Computation of R, L, C circuit takes a reasonable time to learn and you can reasonably drop most developments of the theory of networks, which is too refined for all uses I met. But then, you must understand electromagnetic compatibility for instance, and this is tricky. Beyond that, electrical engineering demands many more theories and the needs evolve over time. Whether you make modulations, error-correcting codes, radio-frequencies, feedback systems... you need additional knowledge in variable amount and nature. The maths can be demanding for engineers.
  6. What Force Is Required To Bend Mild Steel?

    Hi abrogard, there is no simple answer. It depends on how your material hardens during the deformation. Usual stainless steel needs more force than mild steel. Knowing the yield strength prior to deformation does not suffice here. A first approach would compute a bending moment from the 'deformed!) yield stress and the thickness, then compare with a lever length deduced from the bending radius, and compute a force, not forgetting the symmetries and factor-of-two. Alas, this simple model is known to fail, by too much for practical purposes. So you have to use empirical knowledge. For 1m width it takes a big force, usually by hydraulic cylinders. This force suffices to deform the bending tools (matrix etc) and make the unusable when the item to be bent is narrow, so your machine needs a force limiter AND a smart operator.
  7. When putting an LED in series with a Resistor?

    The resistor serves to define a current in the LED. The current in a LED depends very (too) steeply on the voltage across it, as in any diode. The current from the voltage generator takes any value without the voltage changing, and power supplies are close to this ideal. So without any other component, the current is nearly undefined, and definitely not defined well enough. A circuit for constant current could replace the resistor. I don't grasp what convention makes the resistor more or less necessary here. And both circuits you proposed are equivalent.
  8. How fast the interactions propagate may still be an open question. I have still to think more at it, but when charges are near to an other and accelerate slowly, you can't use potentials retarded by x/c to compute the interaction. Just like the Earth-Moon interaction is much more instantaneous than delayed, as is known since the 19th century. At least common "knowledge" of electromagnetism is wrong here. How complete the understanding by experts is, I can't tell. ========== Whether an alternating current by dielectric polarisation radiates a wave, I feel it safe qualitatively. The "1" part of permittivity, equal to vacuum permittivity, does not radiate. The rest, or electric susceptibility, results from charge movement and radiates. And dielectric antennas serve in most cellular phones. But algebraically, with nice equations... That could be a remaining task, and it looks badly difficult. You know, write Maxwell's mess, and deduce logically what produces a radio wave or not. ========== This relates directly with the computation of antennas. We evaluate the far field by computing the vector potential A from the conduction current I or J but we don't include the vacuum's polarisation current e*dE/dt. This fits experiments. Though, both are equivalent to create curl(B) in Maxwell's thingy. So why only the conduction current? A direct application are vertical long-wave antennas. They get additional wires at the top to increase the capacitance there, so more current flows and the radiation increases. Though, this additional current returns to the ground through the added capacitance, and the return current compensates the additional conduction current. It works, why? ========== Does the electrostatic interaction have inertia? When, and for who? For me that's very unclear, for experts I can't tell. https://www.scienceforums.net/topic/85377-relativistic-corrections-to-hydrogen-like-atoms/?do=findComment&comment=990276 ========== The magnetic field of planets remains mysterious. For Earth we have a plausible model since the recent (!) VKS experiment https://hal.archives-ouvertes.fr/hal-00492266/document but for other planets it seems to fail. ========== As far as I know, the coherer still needs an explanation https://en.wikipedia.org/wiki/Coherer it were about time, as the effect was observed in 1835, the devices entered service around 1880 and were abandoned a century ago. Possibly more material science than pure electromagnetism, but who knows, as we ignore the explanation. ========== How does vacuum insulation (or rather the electrodes?) break down in a strong electric field? Probably not pure electromagnetism, but it would be very useful. Devices already use vacuum insulation despite we have no good models for it. Most people keep trying "field emission" again and again despite all evidence is against.
  9. Hi Aleksey, you're right almost everywhere. The rising air parcel works against its neighbours. It loses internal energy, that's why its temperature drops. Note that without any losses, energy would have to go somewhere, and the parcel isn't different from its neighbours... (Probably your next question!) The energy difference goes into kinetic energy. If the parcel was warmer than its surrounding, it becomes faster as it rises. The acceleration can happen at the bottom, the top or all along the way, depending on the profile section of the tube. In such a case, where air packets exchange no heat with anything else, the work they provide (or receive) is the variation of their enthalpy. For air, which is almost an ideal gas under usual conditions, the enthalpy is fully determined by the temperature, or by the initial temperature and the initial and current pressure. The profile section will act on the pressure indirectly by imposing a kinetic energy and so on. It's impossible to solve locally, you must consider an distribution over the full height. One funny thing: enthalpy is not fully contained in the considered air parcel. The internal energy is, but the additional P*V is stored in the surrounding. Despite this, (T, P, V) or the air parcel itself suffice to define its enthalpy. An extreme case is a liquid, say in a hydroelectric dam: as a water parcel goes down to the turbine, its temperature and internal energy keep constant, but it receives V*(P2-P1) from the neighbour water parcels, and this energy converts to speed in the injector and to work in the turbine that slows the water.
  10. Motional EMF

    You can't get a voltage with that setup. But that's tricky, as electromagnetism uses to be. Essentially, the moving magnet induces zero voltage in your closed loop as is. The setup nearest to yours is a homopolar generator, see Wiki. It has moving and immobile conductors, plus (uneasy) sliding electric contacts. More generally, it takes sliding contacts to produce a DC voltage from induction. A collector for instance.
  11. capillary pump

    Sorry it won't work. Capillary action can suck water in some tube with proper filling, but the water will be equivalently harder to extract from the tube's top. It won't flow spontaneously out of the tube. Donkey, wind mill, solar cells...?
  12. How is energy stored in a field?

    You don't need two bodies to have energy stored in a field. If a star emitted light a billion years ago and you telescope catches it now, the comfortable law of energy conservation wants energy to have been stored in the vacuum in the meantime. An extreme case is when an electron-positron pair annihilates. At the time you catch a gamma ray, both particles don't exist any more. How is that energy stored? I ignore it. I don't even know what energy is.
  13. Storing Renewable Energy

    Two variations on the computation by Timo (nice to see you), which change the 45TWh figure hence the cost. Generating electricity in one country isn't necessary and does not correspond to present-day practice. If the wind doesn't blow in whole Germany, it does in Scotland, Brittany, Aquitaine or Galicia. Electricity is presently transported, typically on such distances, as the market is continent-wide. There is no need to store an amount of (Germany's mean consumption) 64GW over 29 days as the 45TWh imply. Even if the electricity came from Germany alone, wind wouldn't stop for that long. Europe-wide, you won't have more than 1 day without wind. That would be 1.5TWh storage for the country. It wastes some electricity but is globally cheaper. The Powerwall costs slightly over 340€/kWh but is a small unit for houses. It is guaranteed for 10 years so it will last rather 20 years. https://www.tesla.com/powerwall The utility-sized Powerpack is hopefully cheaper per kWh https://www.tesla.com/powerpack https://en.wikipedia.org/wiki/Tesla_Powerwall#Powerpack_specifications "should" cost 220€/kWh. 1.5TWh and 220€/kWh cost 330G€ every 20years or 16G€/year, not 1350G€/year. This is affordable and much less than what the inhabitants pay for electricity. ==================== The other point is that batteries are only one solution. It's a mature one, already in use at substantial scale, but not necessarily the cheapest one. I have good hope that flywheels are cheaper per stored kWh than batteries. The store-restore cycle is more efficient from night to day, less efficient over a week https://www.scienceforums.net/topic/59338-flywheels-store-electricity-cheap-enough/ and Prof. Seamus Garvey's underwater bags look cheap too and has been experimented https://www.offgridenergyindependence.com/articles/3358/compressed-air-energy-storage there are few more ideas.
  14. Quick Electric Machines

    Hi Frank, thanks for your interest! Thermal engines tend to be less efficient than the fuel cells' 60%, but they improved quickly in the past two decades, and the difference is small now. As thermal engines are much lighter than fuel cells, the alternative must be considered, sure. 600kg less would sell 6 seats more, big difference. Hydrogen is difficult to bring to a combustion chamber. Injected liquid in a piston engine prior to compression, it freezes air's water vapour and possibly the carbon dioxide, and as hydrogen vaporizes, the extra volume to be compressed spoils the engine's efficiency. Injected gaseous and lukewarm in a piston engine prior to compression, the extra volume to be compressed spoils the engine's efficiency. Still bad. Injected gaseous after compression is as bad as before compression. Injected liquid after compression is the least bad option at a piston engine. Hot air components won't freeze, and this squanders the least power. However, it demands a damn strong injection pump, much worse than the difficult pump of a common Diesel engine, and the whole pump and circuit must work at 20K. Design is badly difficult AND operations get complicated, as the whole circuit must be cooled before start. In a turbomachine, hydrogen should be injected after air compression for the same reasons, but this demands a pump much more powerful than now, and again pre-cooling before starting the engine. I put there http://www.chemicalforums.com/index.php?topic=91121.msg325955#msg325955 (log in to see the drawings) and especially this message for hydrogen alone http://www.chemicalforums.com/index.php?topic=91121.msg333549#msg333549 some pumping cycles with the necessary power, and they inject the hydrogen already hot in the chamber, which helps stabilize the flame. Meant for ramjets and scramjets but fit turbomachines too. It's more rocket than aeroplane technology, and hasn't been developed for airliners up to now. Understand: long and costly. Simpler cycles are possible with turbomachines. Hot output from fuel cells: the 40% wasted energy must go somewhere, yes. My doubt is: how heavy is a heat exchanger to make use of this? Each time I tried, heat exchangers were too heavy to outperform alternative solutions. And if you can operate the fuel cell at a pressure higher than the chamber of the thermal engine that uses the waste heat, to inject the fuel cell outlet in the chamber without a heat exchanger, then you must first pump the air and the hydrogen to that pressure, which is nearly as bad and pretty complicated too. The rest is less of a problem, for instance hydrogen combustion is already known from the more difficult scramjets.
  15. Quick Electric Machines

    20 to 30 passengers, said Norway's minister, and 90 minutes electric flight. Here you are, with fuel cells, not batteries. It takes limited development, essentially the superinsulated tank I described earlier. The fuel cells exist at least for cars, the motors are nearly banal. With the main gear at the fuselage and engine nacelles under the high wing, the Dornier 328 adapts to fuel cells easily, and its size fits better than the ATR-42. de.wikipedia and (other variant) en.wikipedia Can just the nacelles be retrofitted? 2*1400kW need 2*700kg fuel cells with the Toyota Mirai's performance en.wikipedia Estimated energy needs: 262kg liquid hydrogen in two ellipsoids D=0.9m L=4.6m. 2.2MW*5400s Flight 1.0MW* 600s Taxiing 1.6MW*1000s Divert 100nm @540km/h 1.4MW*2700s Waiting to land Zero Descent compensates ascent? ---------- 17.9GJ Energy at shafts 31.4GJ Chemical energy in 130kmol *60% *95% The motor is a ring D=0.8m gap and nearly 0.2m length, because gears need maintenance, can fail and they weigh too. With some 2*30 poles and sine three-phase, each motor weighs 250kg roughly. This is the estimated mass change from kerosene to hydrogen: -800kg Two turboprops +500kg Two electric motors +1400kg Fuel cells -1300kg Kerosene +260kg Hydrogen +250kg Two hydrogen tanks ---------- +310kg Keep the airframe, take 3 or 4 passengers less. 32 had too little room anyway. The hydrogen and its tanks being so light, more range is seducing. Extra-silent propellers would make sense. Marc Schaefer, aka Enthalpy
  16. Woodwind Fingerings

    The variant I sketched on Jul 30, 2017 of the even fingerings for oboe and similar http://www.scienceforums.net/topic/107427-woodwind-fingerings/?do=findComment&comment=1004315 makes simple keyworks. Experiments shall decide, but trying to imagine their use, I feel them as convenient as the other variants. So here is a fingering chart for this D variant: Register keys are not displayed. Their number and range must be experimented. Double them at left and right thumbs like the low notes. The cross-fingerings are only indicative for an oboe. This fully flexible system adapts to the instrument and extends to high modes. Marc Schaefer, aka Enthalpy ==================== This D fingering variant fits very well a bass or baritone oboe, which is a tenor written like the usual soprano oboe but sounding an octave lower, which must give it over three octaves range. Baritone oboes are presently built straight, possibly because specialized oboe luthiers don't make brass bodies. The instrument stands on the ground, and small musicians need accessory to play sitting. I prefer the older shape resembling a bass clarinet. Electrodeposition of silver, copper, nickel... alloys needs little skills and can make the boot and bell including all protruding holes. Or filament winding can make them of stiff and thick material. Usually done by a subcontractor's machine. Or plastic injection. ABS and PP are used presently for instrument bodies, polyketone should be tried, loading with choppers would make them stiffer. Needs an expensive machine at a subcontractor and an expensive mould. A separable bell can use other materials than the boot, for instance wood. The sleek folded design is as big as a tenor saxophone and fits in a smaller bag if the boot is separable. Carried with a harness, it's played sitting or standing. One or two crutches free the thumbs like on the bassoon. The boot could turn earlier and more sharply than sketched, but not as sharply as historical instruments. The bocal can replace some body length if the saved material pays the added transmissions to the register keys. Add a loop in the bocal for antique look. Instead of a pear, whose sound is boring and differs too much from the soprano oboe, I prefer a narrow bell with the extra holes added by Stowasser to the tárogató. I've sketched two stages of them. Their distance to the bell opening doesn't scale as the body length. The boot's covers have similar arms lengths and rotate around a single axis, which simplifies their synchronization as already described http://www.scienceforums.net/topic/107427-woodwind-fingerings/?do=findComment&comment=999559 For stiffness, I'd have an X, or better two pyramid frames, whose apex also holds the end of the axis. The transmissions to the boot need no big accuracy. The sketch shows the boot and bocal's side but the main joint's front. Keyworks for the thumbs were already shown on Jul 30, 2017. On this tenor, the front fingers need covers, with simple keyworks. The many transmissions between the thumbs suggest a single main joint about as long as on a bassoon: as grenadilla gets rare, filament winding is an option, or machined polymer, maybe polyketone, preferibly loaded with choppers. I dislike cocobolo's sound and suppose maple wouldn't fit here. The double-reed instrument needs narrow tone holes and chambers https://www.scienceforums.net/topic/113115-intentional-losses-in-wind-instruments/?do=findComment&comment=1035629 whose cutoff frequency doesn't scale like a tenor but stays at 3 to 4kHz https://www.scienceforums.net/topic/113243-sound-perception/?do=findComment&comment=1037471 and next Most of this applies to English horns too. Marc Schaefer, aka Enthalpy
  17. Woodwind Fingerings

    Hello dear musicians, music lovers and everyone! I'd like to describe fingerings for music instruments with tone holes (which almost means woodwinds) and the associated mechanics. My goals for these fingerings are: Open all holes below the height-defining one, at least on the two first registers; Have no difficult key nor sequence of notes; Not need to close a hole and open an other simultaneously, at least on the two first registers. That's a difficulty of the flute; Need few tone holes regularly spaced and reasonable mechanics; But I don't primarily address the ease or possibility to disassemble the instrument. 1) and 4) make the sound quality more even and let build an instrument with better intonation. To achieve that, my very own personal proposal (... other people have proposed so many!) is: Give one half-tone to the index, middle finger and ring finger of each hand, to cover the upper part of all registers; Continue lower by approximately 4 half-tones with the little fingers. Each has the full set of keys like on the Boehm clarinet; Continue even lower by approximately 5 half-tones with the thumbs. Each has the full set of keys too; Trills near a register limit are made by the little fingers or thumbs, so the registers must overlap. No extra tone hole. Have register keys at the thumbs. Preferably, each thumb has the full set of register keys. The third register and above can't be common to all instruments: an additional register key suffices for some, others need cross fingerings, still others have extra tone holes. One finger for each of the highest six holes make cross fingerings more flexible. Expect differences among the instruments at the two first registers too. The thumbs, being agile in two directions, are the best fingers to operate several keys - bassoon players can confirm. The full set of keys at right and left little fingers is very convenient on the Boehm clarinet, where musicians alternate the notes among the hands. I propose to generalize it to the thumbs, both for lower notes and register keys. Drawings to come should make it clearer. They take me a little time. Marc Schaefer, aka Enthalpy
  18. Woodwind Fingerings

    The bassoon's system applies nicely to the contrabassoon. With the left hand controlling the tenor and bass joint, the right one the boot, and few transmissions between all joints, the boot can be split in narrow and large joints and easily folded upwards. With all joints nearly as long, this makes a more compact fagotto. It's one folding more than the usual Heckel system contrabassoon, whose tenor joint begins at the bottom. The four first joints stay permanently together. The bell can be bent and run downwards like on the Heckel system for a smaller instrument. Or, as depicted, it can be straight and assembled to play: More compact transport case. Contrabass taller than the bass in the orchestra, ah. Resembles more a bassoon. Needs only wood knownledge from luthier and workshops, especially if all tone holes fit on the wood sections. I believe electrodeposition can make all bends and the bocal, if needed the bell, with little skills http://www.scienceforums.net/topic/111316-woodwind-materials/?do=findComment&comment=1031427 It can also make wide stiff tubes for the keys with reasonable weight. Per carbon filament winding or of possibly reinforced polyketone, all joint walls can be single parts. Marc Schaefer, aka Enthalpy
  19. Woodwind Fingerings

    Because the soprito starts on the 2nd one and uses many higher modes, automatic cross-fingerings would be difficult. But here is a system to ease cross-fingerings for the soprito. Here 7 main holes achieve 8 notes, enough to join the modes, as these are high hence close to an other. The 7 main holes begin on C because an instrument's lowest notes tend to overblow abnormally, so the right thumb makes B and Bb. In the present system, a single front finger presses a key to move several main holes and define a note. The four upper main covers are closed at rest and the left fingers open one to four, while the three lower main covers are open at rest and the right fingers close one to three. The right index moves no main cover but can have a dummy button as sketched. The holes and the buttons are displayed separately on the sketches. Synchronisation hardware was suggested there http://www.scienceforums.net/topic/107427-woodwind-fingerings/?do=findComment&comment=999559 The musician presses only one button at a time as on a piano, excepted for the low B and Bb. This is easier than usual cross-fingerings. No alternate fingering nor trill key is foreseen. Extra buttons open one or two additional cross-fingering holes. Adjacent buttons can share the same cross-holes for different modes chosen purposely, so two sets of cross-holes suffice: Mode 1 isn't used by the Soprito. The narrow bore and the reed's size stabilize the mode 2. A register hole isn't excluded. Mode 3 reuses the same main holes as mode 3 with a register key. Mode 3 4 opens a cross-hole a fourth (5 semitones) higher than the highest open main hole. Mode 3 4 5 opens two cross-holes, a major third (4 semitones) and a major sixth (9 semitones) higher. Mode 6 isn't used. Mode 7 isn't used. Mode 5 6 8 opens two cross-holes, a fourth (5 semitones) and a minor sixth (8 semitones) higher. The system opens cross-holes 4, 5, 8 and 9 semitones higher than the highest open main hole, but adjacent main holes share cross-holes: a key for 4 and 5 is common to two adjacent main holes, a key for 8 and 9 too. The left index opens 4 main covers and 0 to 2 cross-covers. The right pinkie closes 3 main and may open 2 cross-covers. Narrow covers like at the oboe linder this drawback. The sketches show extra buttons that act on the main and cross-covers to help the musician. They need little extra local hardware. Without them, the musician would press simultaneously with the main cover 1 or 2 separate buttons linked directly with the cross-covers. Separate cross-covers ease the design of a well-tuned instrument. Register keys are not displayed. Probably at left thumb. One stabilizes mode 3, maybe an other suffices for modes 3 4 and 3 4 5, and still an other for mode 5 6 8. A sketch of the keys may come, perhaps. Marc Schaefer, aka Enthalpy
  20. Woodwind Fingerings

    I have doubts now that the piccolo woodwind can have a single reed as depicted on Nov 06, 2017 http://www.scienceforums.net/topic/107427-woodwind-fingerings/?do=findComment&comment=1021947 because the reed's susceptance destimated as on Dec 03, 2017 http://www.scienceforums.net/topic/112039-woodwind-reed-susceptance/?do=findComment&comment=1026941 remains big even with an Ab clarinet reed. The clarinet's cylindrical bore is wide near the reed, whose susceptance shortens the air column reasonably. A saxophone (soprillo) is wide and plays the high notes only by the second mode, so hole positioning can correct the intonation. A single reed would shorten a narrow conical bore possibly too much, more than a quarter wavelength. Only a double reed, uncomfortably small, would fit. I may provide figures some day.
  21. Percussion Instruments

    Bartók died over 70 years ago so all his compositions are in the public domain in Europe. This differs in the US, where property can last 100 years under some conditions.
  22. Percussion Instruments

    Hello dear music lovers! Church bells are still made today like in the Middle Age: Cu80Sn20Pb0 bronze cast in a one-way clay mould. One batch of varied middle-sized bells takes six weeks of hard work to ten persons. I propose instead to electroform them. A well-developed technology, electroforming can deposit varied metals and alloys, from ultra-thin to thick, on diversely shaped mandrels, bulk conductive or not, and separate the created item from the mandrel. Here bronze and the bell shape are easy. Maybe the mandrel can be of wax on wood, or talcum-loaded paraffin... In one interesting option, the mandrel itself would be obtained by electroforming on the inner face of a good existing bell. For the parting film, ask a specialist. The current density varies with the rest, let's take 500A/m2 as an example. This grows 11mm/week copper and slightly more bronze, faster than traditional mould making. The current in copper and tin electrodes, and initially the electrolyte composition, control the alloy composition; I ignore if the electrodes can be bronze. A D=0.8m bell has around 1.2m2 surface, needing 600A (or less since some parts are thinner) and roughly 3V and 1.8kW only. The anodes are closer to the created item than depicted, their shape and number is not representative. Maximum 30mm thickness take 3 weeks, mean 25mm just 700kWh costing 150€. Upsizing is easy. Schottky diodes could provide the DC current, but I prefer MOS to reduce the losses and regulate the current, for instance by pulse swallowing. Electronics can produce a square single phase around 24V (safer than 500V) distributed to local transformers, at 400Hz for laminated iron cores or higher for iron powder or ferrite. Some processor can distribute the swallowed pulses smartly. The currents must be monitored automatically, the thickness could be measured manually from time to time but is better monitored automatically too. The bath needs limited cooling. Rotating the electrodes (or the bell) during the growth may achieve a rounder shape. Then, the transformers better rotate with the electrodes, so fewer contacts pass less current. I've no opinion about the internal stress of electrodeposited bell bronze nor its acoustic qualities. It can be heat-treated afterwards. Titanium parts are isostatically hot-pressed (in silicone) after casting, this may apply here too. Impurities from the mandrel or parting agent must be removed from the bell. Marc Schaefer, aka Enthalpy
  23. Quick Electric Machines

    The Norwegian government wants electric airliners for all flights under 90min in 2040 bbc.com and dailymail.co.uk In 2018, I see how to fly for 90min with batteries, but to divert to an airport 100nm away then wait 45min in the air, as safety demands, a plane doesn't resemble a profitable airliner. With liquid hydrogen and fuel cells, such a design is easy. The Atr42-72 modification I described on Apr 18, 2013 scienceforums.net does much more than that.
  24. Percussion Instruments

    I haven't checked what notes composers specified. Could be a challenge, sure. Worse than a grand piano. Taking a symphonic orchestra on tour is already a headache. Not just the visas for 150 people. Most airlines ignore if one can take a violin in the cabin, but musicians don't want their instrument in the cold nor at low pressure, even less lost. And what about the materials? Violins use Pernambouc wood (Pau Brasil) and blackwood, both being prohibited to export or import in many countries. Woodwind use grenadilla and rosewood, same story. Then you have flutes of silver and gold not pure enough for France, whose law doesn't consider musical uses. Other funny laws may impose to fumigate all wood that enters a country as a protection against insects. Pssch pssch on the cello. Then you have the scores. Intellectual property differs among the countries, and a score acquired lawfully in Europe can bring you trouble in the US. I say: headache.
  25. HELP! Infrasound detector antenna

    For infrasound, you may prefer a pressure sensor over a microphone. Possibly an array of sensors.