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What do you think of this idea. You make a jet engine with a centrifugal compressor, but instead of having a feed coming off to a stationary combustion chamber, why not add several small combustion chambers radially? Then cant the nozzles so that some thrust is pushed into rotating the whole device,
and you have an all rotating engine that will no longer need high speed bearings or thrust plates.
No Tail Rotor
http://www.helispot.com/images/00091.jpg
22KB image -- Hughes NOTAR. No tail rotor at all. [bristolz, Sep 12 2002, last modified Oct 04 2004]
Eclipse Jet
http://www.eclipseaviation.com
Led by ex-Microsoftie Vern Rayburn, here's an economical 4 place pure jet running the Williams International EJ22 turbofan. [bristolz, Oct 04 2002, last modified Oct 04 2004]
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I assume that if the whole device rotates, and as you require no bearings, then it is securely bolted to the aircraft. I'm afraid I'm not too keen on flying this, as usually I try to keep the airframe rotational speed close to zero. |
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Er.... no. You'll end up with the chambers spinning at 30,000 RPM and it will be a devil of a job to get power to the igniters. Plus you'll be spinning a lot more mass than just the turbine shaft in a conventional engine, causing undesireable gyroscopic effects. |
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However, it might be marginally safer than the "compulsory assisted suicide air vehicle" known as a helicopter. |
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The original rotary aircraft engines like the Gnome and the Le Rhone were a bit like this but the idea never went very far after about 1919. |
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drew: I too have a penchant for low rotational velocities in any airframe in which I am travelling. |
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Actually, thinking about it, the whole idea is baked to a crisp. It's called a rocket. |
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Hmmm... Interesting points.
Firstly, is 30000 rpm not a little to high a figure? The car turbocharger I was considering as using for the centrifuge is rated at 11000, which I considered would have workable engineering solutions for problems such as ignition and construction. Also, i reckon i would only be adding about half mass. If the device was wished to be attached to an aircraft ( I had a 1 use drone idea in view) Then the bearings could be lower grade and less hot than bearings inside a conventional jet. Cooling would not be needed, as all chambers could be air cooled by their spinning motion, much like your gnome.
Also, would be cheaper than rocket, not carrying O2.
Many apologies, you guys will know more, but I am honour bound to defend my baby :¬)~ |
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Someone with an aeronautical engineering background might be able to set me straight on this, but as I understand it: |
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1. Air cooling will be practically non-existent, unless there is a lot of air being forced through and around the combustion chambers. |
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2. This device seems (if I understand your explanation) to change the direction of the exhaust stream for some unknown reason. It is that which provides the thrust. This would retard the effect of the thing you are seeking to maximise |
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3. I would establish a pretty comprehensive product liability cover before I put this into production. It looks to be a dangerous rework of a jet engine. |
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4. The gyroscopic effect of existing aircraft jet engines results in a substantial rotational effect, hence the moving parts are made as light as possible, to reduce the rotational moment of force. This device seems to use extra parts = more weight = more rotational effect. |
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5. Aircraft powered with these engines would be horrific to control, unless you have opposite engines counter-rotating, to minimise unidirectional torque on the airframe. That would create its own problems, with a weight penalty for crossbracing. |
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si_pronto: The N1 (gas generator) stages of most turbine engines spin at that speed or higher; drew will be able to correct me, I'm sure. i'm also not sure of the figures for the original Whittle engines, but I recall it was about 20K rpm; the modern ones are much faster due to better materials. Your design sounds a bit like a whittle radial engine layout. You also need to solve the rotor/stator contrarotation proble, to stop the "fixed" portion of your vehicle whizzing round in the opposite direction.....
Car turbos tend to use oil-pressure centre-fed simple journal bearings. You'll need quite a bit of kit to provide that pressure feed, which adds mass. |
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Do i understand from your explanation that what we would think of as the rotor in a conventional jet becomes the static portion, with the "casing" containing the "fixed" compressor and tunbine blades, and the combustion chambres, spinning round it ? The problem you have there is that the larger the diameter of the rotating portion, the greater the centripetal forces at its circumference, and the stronger and hence heavier it has to be (law of dinimishing returns). A lot of effort in the design of modern turbofans goes into keeping the rotor mass down as low as possible.
I'm not saying this isn't possible, and I suspect a demonstration unit could be built fairly simply, and made to work; but I don't think that it can be scaled up to a useful (commercial) size without recourse to exotic (and hence uneconomic) materials.
Keep the ideas coming, though. |
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UnaBubba: 1. : I think he means the rotor portion turns in free air, like the early radial engines, hence adventitious cooling - but a lot of turbulence. Air passing through the combustion chambers would by definiton have to become very hot, so there is no "colling" effect to be had there. Signigifcant cooling would extinguish the combustion process. Excess air would render the mixture non-stoic and reduce efficiency. External bypass airflow cooling a la turbofan engine would be a possibility.
If the unit is not contained in a nacelle, then it is vulnerable to mechanical damge, and weather. Cold rain on red hot combustion cans owuld be "interesting". (see point 3) |
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2. Not clear on his intentions. |
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5. Not necessarily, if run in contrarotating pairs. Could be a basis for a "hammerhead" V/STOL design. But I agree the torque would be horrendous. |
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However, if you could make the engine design VERY simple you could adopt a fault-tolerant "many small engines" approach, which has attractions. |
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The Whittle engine employed centrigual compression, whereas most modern engines are turbofans, and utilise multistage axial flow compression - very different, much more efficient. 30000rpm is perfectly reasonable for a jet - 60000rpm is often used. The Whittle engine ran to about 13000rpm. |
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By the way, I suspect that car turbocharger you are looking at runs to 110,000rpm, not 11,000rpm. |
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No - many small engines isn't attractive. See just two extremely large engines nailed to B777. |
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1. I think that's the least of his problems. If I understand this correctly, the whole casing will be rotating at vast speed, possibly even fast enough to enjoy air friction heating effects. Strike that - certainly fast enough for air friction to heat it. |
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2. Not really - turbofans derive most of their thrust from the fan driven by the exhaust gases - it's about a 75/25% ratio. But that said, 25% of a lot is still, er, a lot. |
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5. If he doesn't want high-speed bearings, how does this device get attached to the airframe, without spinning it? |
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drew: What about the BAe 146 ? I think they're quite nice, actually. Every time we're over water for any length of time I am powerfully reminded of the potential benefits of multi-engine equipment. Just one extra engine would be nice. And I'm glad to hear they're using proper nails on the 777, those wretched shear bolts they were using on the pylons always made me nervous ... |
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This is going to suffer much worse design challenges than any turbine. |
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One of the most difficult challenges to designing turbofans was that the inner turbine blades had to be very light, and yet very very hard, and sustain their geometry at high temperatures and speeds. Blades made out of some of the hardest steel known still had the problem of stretching out as they spun, wearing away the edges and causing eventual catestrophic failure. So now they use some exotic ceramics to make 'em, and still they have to be replaced every so often. |
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In a nutshell, you're going to want as few rotating parts as possible, or the complexity is going to overwhelm the design from the get-go. |
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The 146 has four low-powered turbofans, because they are quiet. It's specifically designed to be a quiet aircraft, but it's not particularly economical. There's a lot to be said for having fewer engines too - a great many multi-engine aircraft simply use the remaining engines after a failure to take the aircraft to the crash site. As engines can fail quite spectacularly, like the DC10 Sioux City accident, where an engine failure caused complete loss of hydraulic power by severing all lines, they would have been much better off using just the wing mounted engines. More isn't always better. |
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See what happens when we get a *real* idea at the 'bakery? It's soooooo refreshing to have to think, for a change. |
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Too bad bris isn't around... I'd love to hear her thoughts on this one. |
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Thanks, I will have to reconsider the design. Good to have feedback on this idea though, before I lose the rest of my hair due to madness. |
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si_pronto: Hey, don't worry, just let them go ..... I lost my mind and my hair years ago, and I don't miss either of them. |
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Anyway, it's not that bad an idea; worthy of discussion. If you post sensible ideas you will get good feedback and advice. My impression is that some of the halfbakers are pretty smart people with some good specialised knowledge. |
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SteveDeGroof: It's easy for me to claim this now, but thinking about the idea later I did come up with the ide of an annular transformer around the maishaft for power and telemetry transfer. Great minds think alike, eh ? |
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Fuel distribution is tricky because you need quite high pressures and wiping seals, unless you also use fuel as a coolant and lubricant. One idea I had was to transfer the fuel through the shaft at low pressure, then pressurise it in the rotor and use it to float the bearings. |
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Starting is another issue. You need to spin up the rotor to a high proprotion of its normal operating revs; usually done these days with compressed air from bottles or the APU (used to be done with pyrotechnic cartridges - very entertaining !!). Because this design has a lot more rotor mass it needs a lot more start power too. |
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I still think you might just about get a tiny, turbocharger sized version of this to work on a test bench, but I don't think it can be scaled up enough to be useful. |
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Everyone take note: This is what the halfbakery is *really* about. |
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Electric motors pre-spin the rotor in many small modern engines, particularly APUs - air and cartridge for old and large jets. |
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drew: I once got called in to help deal with a privately-owned Hunter on the ground at Woodford that had experienced a misfire on the pyro start system during a show. That was an "interesting" little job, and I am not unhappy to see their demise ..... dealing with a hangfire with the round jammed in the breech is no too bad on a portable weapon, but when the unit is embedded in a very valuable antique aircraft it all gets that bit more fraught. Apparently many Hunters are being converted to 'lectric start. |
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Never flown a Hunter (or indeed any cartridge starters), but I know a man who has.... |
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The cartridges are in very short supply for most engines, so lots get converted to electric start. It also means you can have as many attempts as necessary. |
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No misfire is fun. I've had a few hangfires with shotguns over the years. Breaking the breech over a waterbutt, whilst muttering obeisances to the god of gunpowder. |
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drew: You can reload them. It takes a bit of fiddling to get the slow-burn characteristics right but the physical reloading isn't that hard - no worse than a 38mm flare round.
You only get unlimited starts if you have ground power ... (actually I think the Hunters start of a trolley-acc or similar). |
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UnaBubba: If it's modern nitro powder, you're probably OK. If it doesnt' strike on the first hit, then it's not likely to go subsequently. But black powder is a different story. People bring me muzzle loaders to fix, and that's not nice, at least until the projectile is out. Not many people use BP-filled breechloading cartridges these days (thankfully) - they're just too sensetive to damp and mishandling. PS sorrt if this is OT. |
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Club rules, because most members reloaded their own, so we were never sure what was in them. |
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We took no chances. 30 seconds, relinquish the weapon to the rangemaster, eject into a 44gal drum of water. I never had one detonate, nor did I want to. |
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Anyway, surrendered the shotguns in the centrefire weapons amnesty. I miss trapshooting. |
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As for the rotary jet engine: Good grief. |
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[8th] Many helicopter pilots consider their craft to be safer than fixed wing and for some compelling reasons. Don't know that I completely agree but, given proper altitude at failure and someone who is proficient in autorotations, the landings are usually far better than the fixed wing variety in the same circumstance. |
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// Many helicopter pilots consider their craft to be safer than fixed wing // |
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Yes, and they all have the same glazed, manic grin on their faces, too. |
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// given proper altitude at failure and someone who is proficient in autorotations, the landings are usually far better than the fixed wing variety in the same circumstance. // |
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One autorotation from 300 feet into a forest clearing was enough to put me off for life. Aviation rule of survival: Take off. CLIMB HIGH. Try to stay there until you need to land. "Npa of the Earth" flying is just toooo exciting. And even from high altitude, an autorotating 'copter can't sustaim much foward airspeeed, you're trading altitude for lift ..... engine out, most fixed wing props can manage a 4 degree glideslope (at worst) and from 5000 feet that's a long time to find an open space. |
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Besides, two of the most stressed components of the 'copter are the hub/swash plate assembly, and the tail rotor. If either of them pack up, you can't autorotate - that's an engine-out option only. Modern gas turbines are far more reliable than the rest of the 'copter. |
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If other people want to ride in them, fine - I would only consider it if my life were threatened in some way and the 'copter was the only viable option. |
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An autorotation from 300 feet is indeed a very risky proposition but a fixed wing descent from that same altitude in the same location and you'd probably not be alive today to write about it, no? |
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The tail-rotor provides anti-torque, which is unnecessary when power is not being transmitted to the main rotor (why autogyros have no tail rotor). Not only that, if it were true that autorotations aren't possible w/o a tail rotor then autorotations would be impossible in an engine-failure, because power would be lost to the tail rotor. And we know that isn't true. |
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Granted, turbine failure is rare but transmission failure is less-rare and autorotation is possible with transmission failure (indeed, one of the basic preflight checks is to back off power quickly and make sure that rotor blade rpm and engine speed "separate," indicating that the main rotor can freewheel unfettered, a functionality that is not transmission-dependent). Also, piston helicopters seem to be making a comeback so engine failure again becomes a "more popular" failure ;-) |
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Main rotor delamination and separation are extremely rare. Alas, pilot induced catastrophic failure, such as chopping off the tail boom by suddenly pitching forward is not easily preventable (a danger of being instinctively trained for fixed wing stall recovery). |
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The trade-off of energy is, more accurately, first, altitude for rotor speed and then as you approach your cras..., er, landing site, trading rotor speed for lift. The forward, and descent, speeds are very controllable depending on how early you begin feeding in collective. The glideslope is not that bricklike. |
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The point of most rotorcraft pilots is that they'd rather have very low, or no, velocity at touchdown in a hastily chosen spot rather than lots of velocity in a slightly-less hastily chosen spot. |
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Speaking of velocity . . . if you'd rather not have rotational velocity associated with an airframe perhaps ballooning or sailplanes are better choices for your sensibilities. |
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Now and again, when we roll out to do the checks, there's a chopper sitting on the apron ( a couple of them roost in the next hangar along). Now and again, someone's got the panels open. We wander over and peer at them, and quite frankly it's terrfying. Inside it's a plumber's nightmare (worse than a Citroen) anf if you go up the ladder and look at the Jesus bolts and the swash plate and the compexity of the control gear (compared with the relative mechanical simplicity of a PA-28) then it kind of puts you off .... |
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You're quite right. I wouldn't go tree-skimming in a single engine anyway (unless it was a Spitfire) but in a twin, well, lose an engine and it's tricky and inconvenent, not rapidly fatal. See drew's remarks above. |
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I'm not too clued up on the inner gubbins of autororation, mainly because I know I'm never, ever going to be involved with it again. And kind of you to mention the problem of boom-chop caused by excessive movements of the cyclic in stall avoidance. I think the discussion about maintianing the tail rotor during transmisssion failure is so dependant on the equipment and the failure mode that one can't draw clear conclusions. |
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Be my guest; you are welcome to your airborne eggwhisk. Anything that needs its powerplany to run at 85%+ of rated output 100% of the time just to stay in the air doesn't have what I like to think of as a "margin of safety" - or much slack when you do the W&B. I like engines, preferably many of them; hence my avoidance of gliders, hanggliders, and baloons. Wilbur and Orville had it right. My own personal aircraft of choice would be a DC-3. |
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Maybe you can pick up a retired B52 to satisfy your multi-engine cravings. |
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B52 ..... Ooooooh, raw sex ........ ooooooooooh ...... Quick, Nurse, the screeens ! It's the Old Trouble again ! Ohhhhhhhhhh, the injection ! Hurry ! |
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Well, actually, the true icon of desire is a Lancaster with the Mark XXIV Merlins, but I'm never ever going to get one of those, whereas a DC-3 is juuuuust possible if all my rich relatives die at once on the same day I win the Lottery ...... |
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I had a Citroen DS some years ago, and its innards were actually quite pleasing, esthetically. However, the thought of riding a spinning jet engine juggernaut makes my tummy queasy. If one wants to design a really economical jet-powered aircraft, why not build one around the very compact Williams jet engine? They work fine in cruise misslies, should work beautifully in a sleek design like the Rutan Vari EZ. |
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The Vari-EZ would be a fluttering nightmare at the speeds a Williams turbofan could propel it. The powerplant is much better suited for an airframe designed to handle pure jet flight, like the Eclipse (see link). |
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I was thinking max speeds of 350 mph or so, nothing drastic, say cruise at 250. Of course the airframe should be beefed up. Isn't someone using a (slightly) modified Rutan design to test rocket engines? |
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I don't think anyone mentioned engine balance. Mount components symmetrically. And be careful of bolts, washers, cables, tubing, repairs, everything. For example, if you buy an ignitor from a different manufacturer, you may need to change both (or however many there are). Re-balancing for various operating speeds could take hours and much fuel -- you don't want to do that every time you change a part. Not insurmountable problems, but important to consider. |
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You have a pretty nice idea, of course I am not mechanical, aeronautical or aerospace engineer. I am a chemical engineer.
I had the same idea as you few nights ago and many can be done but not for planes. Cars, trucks and all the industry need a ROTARY MULTISTAGE INTERNAL COMBUSTION ENGINE (RMICE) but many problems must be solved.
Here are few of my ideas: |
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The engine must have 3 sections(inlet, combustion chamber and outlet) all of them mounted in de same shaft. |
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Inlet must be an axial compressor. A similar design than use actual gas turbines but much simpler. This is for forcing the air inside the engine. |
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Combustion chamber must have the geometry of a centrifugal compresson with much more blades (check the number of blades of regenerative blowers). Spaces between blades will be small combustion chambers. |
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Outlet must be same as inlet for helping the engine to exaust combustion gases but in contrary position. This is just for generation some vacum. |
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The RMICE will have the following characteristics: |
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1) Completelly rotary and no cavitating or reciprocating parts. |
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2) Will not rotate to high speeds because are not necesary. |
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3) With the propper geometry, You can increase the RPM of the engine if you sincronize the explossions for torque generation or you can reduce RPM inmediatelly just sincronizing the different chambers to works against rotation. |
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5) You dont need exotic expensive materials as aeronautical or space industry needs. |
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6)RMICE will not need inlet or outlet valves and fuel injection is automatically solved. |
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7) Special seals are not necesary because explosion are small. |
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8) Lubrication is simple. |
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9) Cooling system must be solved during development. |
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Here the VERY BIG PROBLEM is the electronics for controlling the explosions inside the RMICE. My younger brother is an elecronic engineer and automatic control specialist. He think all the necesary electronic exist at these times. Just need putting all parts together. |
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I like to talk about the RMICE, please reach me at foreigner_44@yahoo.com |
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I think much people will be really surprised with these exotic and rare ideas. Please free your mind and remember that "We can do all We can think" |
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Wow alot of naysayers. I had this idea some time ago and I am contemplating building one because it's relatively simple since you need one rotating piece. |
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I think I understand his intentions.
Imagine a car turbo centrifugal compressor. If the entire housing rotated you could ad small combustion chambers at the periphery slanted to give the whole thing some spin. That'd work wouldn't it? |
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Basicly I figured I'd need a old Garret turbocharger compressor and some Iconel machine parts. the idea is the rotating assembly includes a cylindrical combustion chamber mounted on the shaft, and exhaust exits through radial slots with variable vanes to assist spool up and control thrust and overspin. |
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1. Spinning ~100,000rpm unenclosed provides all the cooling necessary, infact rather too much heat will be lost through the combustion chamber walls. |
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2. Ignition gear is entirely encluded in the rotating spindle and provided by the rotating motion, sparking is constant with rotation. |
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3. Overspeed is controled by centrifugal force and a linkage that tilts the slats back in the direction of axial thrust. This would also help the engine spool up as fast as possible from low speed - a problem with conventional turbojets. |
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4. Rotating mass might be much less than an existing jet. Your also eliminating all that non rotating mass. |
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As for comparission to a rocket? Comparable to a poor performing rocket yes. However efficiency and no need for O2 closes up the gap. If you could make these jets weigh as little as I think you might be able to you could easily package enough of them to make some VTOL rocket vehicle. |
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