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Post by propellanttech on Aug 19, 2011 18:20:53 GMT -5
Sure your response is good, but what is your idle speed. If there is to be use of the turbine I design, the idle will need to be quite low, to reduce the residual idle thrust. If I do make a turbine, it will be flow, in an aircraft of my design. Small of course, but large enough for a single adult. James
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Post by propellanttech on Aug 19, 2011 18:28:20 GMT -5
Hi James The throttle response does slow a bit as the rotating assembly gets heavier , unfortunately it doesn't appear to be in direct relationship to the mass flow , my bikes TV 84 seemed to accelerate better than my latter bigger builds www.youtube.com/watch?v=P-5PgWqgIJo , it could also be because of the fuel delivery method with the bike having high pressure spray (up to 750psi) vs evaporators for latter builds . You might be getting your "slow acceleration" data from Kamps book , the RC aircraft guys run very low idle power settings due to their need for minimal thrust levels to lower landing speeds , we're not restricted to such low rpm, we normally idle at ~40-45 % N1 which makes it quicker to accelerate the rotor than from say 30% N1 . Yea, and unfortunately I'm planning to use the engine on an aircraft. The thrust levels will need to be reasonable at idle. Heh heh , after 20 years of DIY turbines I'm starting to get a bit of knowledge together :-) ...........there aren't many "secrets" with our hobby , high PRs give better fuel burn and a tad more power but its efficiencies that have the biggest impact and "generally" high PRs for us mean comp efficiencies suffer due to the available components , there aren't many low trim swept back comp wheels out there . My secret is not that important, so let just say I'm working to reduce friction in the engine using true air bearings using bleed air. This is why I need such a high PR on the compressor. The bearing will probably require a lot of pressure to insure a good "float" of the shaft. The engine will be airstart with the bearings being check valved in. This will insure the bearings are at full operation when the shaft starts turning. Even without a comp map for a wheel we can make pretty close guesstimates of its performance , I never had a map for my bikes TV84 ......................maps help , but aren't strictly necessary as things will change when you fit it to a bespoke diffuser system . Cheers John The map for me is really to insure I can get the best PR to flow rate as possible. I figure for my "secret" to work, the PR is actually more important than the flow rate. James
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Post by racket on Aug 19, 2011 18:37:43 GMT -5
Hi James
Over the years there have been a number of guys wanting to make their own "jet plane" ..........heh heh me included , except I was going turboprop ,.............. though I did write an article for Pacific Flyer mag back in back in Sept 01 for a "Raggy Jet" .
150 lbs of thrust isn't a huge amount for a man sized aircraft , a 30 hp piston engine will do that and with a burn of a coupla gallons an hour , whereas a simple pure jet will be burning nearly 10 times that , very poor conversion of energy having a 2,000 ft/sec gas stream powering a vehicle at one tenth that speed .
The RC micro turbines generally have a 2-3 second acceleration ramp time , our engines can easily match that .
Cheers John
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Post by propellanttech on Aug 19, 2011 18:39:30 GMT -5
Now since my "Secret" is out, we can get down to feasibility.
I think the pressure will hold the shaft axially and radially.
The bearings will be graphite, with the shaft being nickle coated.
The bleed air should come from the T2 area, and feed the bearings through the shaft housing. The details are not drawn yet, but I do have it in my head.
The temperature of the air shouldn't matter as much as the pressure. I know there will be a pressure drop as the air cools through the passages, but it should be constant because of the feed.
The pressure will vary with speed, which is actually an advantage. Higher RPM more stable bearing ride.
There is a lot to test and figure out, but I think the idea is sound.
James
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Post by propellanttech on Aug 19, 2011 18:41:38 GMT -5
Hi James Over the years there have been a number of guys wanting to make their own "jet plane" ..........heh heh me included , except I was going turboprop ,.............. though I did write an article for Pacific Flyer mag back in back in Sept 01 for a "Raggy Jet" . 150 lbs of thrust isn't a huge amount for a man sized aircraft , a 30 hp piston engine will do that and with a burn of a coupla gallons an hour , whereas a simple pure jet will be burning nearly 10 times that , very poor conversion of energy having a 2,000 ft/sec gas stream powering a vehicle at one tenth that speed . The RC micro turbines generally have a 2-3 second acceleration ramp time , our engines can easily match that . Cheers John What you say it true, so a low (or high) bypass turbofan may be the way to go. But there is one thing a jet doesn't have that a prop does. The P factor, which is important to the craft I have designed. James
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Post by racket on Aug 19, 2011 20:32:28 GMT -5
Hi James Air bearings have their place, but what happens when you throttle back for landing , the rotor will still be spinning ~25,000 rpm but with only a few psi of P2 to support the shaft , is that enough pressure ?? Is there any reason you want/need to use air bearings rather than conventional ones ?? Have you considered using a "smaller" commercially produced RC jet engine for a gas producer and spend your energies making a "fan" powered by a freepower to produce the thrust , fuel burn rates will be much lower and the "second shaft" can be run more conventionally . Even with a very crude fan stage you'd get a far greater power conversion rate , more actual thrust for fuel burnt , but there won't be that "jet thunder" :-(( Have you looked at the engines over on the GTBA www.gtba.co.uk/ Cheers John
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wolfdragon
Senior Member
Joined: April 2011
Posts: 287
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Post by wolfdragon on Aug 19, 2011 20:45:58 GMT -5
James, the viewable combustor is Chris' creation, I have no idea what the actual speeds were
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Post by propellanttech on Aug 20, 2011 0:34:12 GMT -5
Hi James Air bearings have their place, but what happens when you throttle back for landing , the rotor will still be spinning ~25,000 rpm but with only a few psi of P2 to support the shaft , is that enough pressure ?? Is there any reason you want/need to use air bearings rather than conventional ones ?? Have you considered using a "smaller" commercially produced RC jet engine for a gas producer and spend your energies making a "fan" powered by a freepower to produce the thrust , fuel burn rates will be much lower and the "second shaft" can be run more conventionally . Even with a very crude fan stage you'd get a far greater power conversion rate , more actual thrust for fuel burnt , but there won't be that "jet thunder" :-(( Have you looked at the engines over on the GTBA www.gtba.co.uk/ Cheers John I think even at lower rpm the pressure should be enough to hold the shaft. Conventional bearings have two problems. If like a model engine, they are replaced every 25 hours, or require a 25 hour tear down. They don't last long. If like Johanssons, they create drag on the shaft, along with add additional components and weight to the unit. The way to make something more efficient is to reduce the frictional forces involved, and also insure the best energy conversion rate. Model turbines will never be more than that. I'm looking to make a small turbine that can be used without the friction of conventional bearings. I can't say it is possible, but I believe it to be. I was a member of the GTBA a few years ago, but haven't rejoined. There was little activity when I was a member, so I felt the price was a little much for what I got. The group is quite "clicky" with respects to involvement. I don't have an issue with a gas producer with a free power turbine. That is actually preferred, because the energy conversion is at a better rate. My problem, is the unit would be backwards for a low/high bypass fan design. Or the shaft configuration would be complicated. I am open to most any idea. The bearings and the use of such, is the first focal point for me. If it can be done, I'm going to do everything, I can think of, to do it. I know for a fact the Bladon Jets turbine has air bearings from bleed air. I have the international patent, and it shows. So I know it can be done, even with the low pressure ratio they are using. But I have yet to see a video of their design actually running. I have seen one they claim it is running, but it doesn't look like it to me. Looks more like half running/half air start. Think about it......no oil........and little to no friction. If the design is sound, the tear down interval would be huge (1000 hrs or so). And No, I'm not actually trying to steal their idea, but use it for a radial turbine. James
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Post by propellanttech on Aug 20, 2011 0:48:32 GMT -5
As an additional thought.........yes I spend a great amout of time thinking on the subject......
A free turbine with a gas producer may be a viable option.
The gas producer would be on the front with the fan behind it. This would only complicate the fan with respect to heat. The fan would need to be able to handle the exhaust from the turbine portion.
This would be like a pusher turbofan. I don't know much about the actual turbofan arrangement with respect to stators, but I figure it is similar to turbojets.
That would definitely be a doable design. It would also reduce the size of the power section. It would add weight of the fan gearbox (if needed), and the free turbine section. It would probably increase the performance enough to offset the weight gains.
James
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Post by racket on Aug 20, 2011 2:00:14 GMT -5
Hi James I gather you've also checked out the Capstone air bearings on their machines www.capstoneturbine.com/_docs/Product%20Catalog_lowres.pdf If you want reliable bearings then brass bushes are the way to go , used on 30,000 hour between overhaul industrial turbochargers , for an aircraft you need reliability , reliability and the availability of off the shelf parts was the reasoning behind me going back to "brass" rather than balls , ..............theres not a huge amount of lost energy even with brass , if one considers how it takes a considerable amount of time to heat the oil going thru a turbo theres probably only a couple of horsepower being lost , thats only ~1% of the turbines energy in a large turbo . Heh heh , yeh the GTBA has its own "character??" , I remember spending a lot of time compiling an article for their magazine and there wasn't even one comment about it when published...............a waste of time on my part . There may be a "novel solution??" to your fan needs here .............................. www.technologie-entwicklung.de/Gasturbines/Monocopter/monocopter.html Its an interesting project you're contemplating ..............we'll try to help/guide you as best as we can , ..................it should be doable :-) Cheers John
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Post by enginewhisperer on Aug 20, 2011 3:52:52 GMT -5
I think the bearings used in turbochargers have to win on reliability, either ball bearing or plain brass bushes. There will also be large thrust loads on the shaft, which I guess are not a major issue to handle with air bearings either, but depending on where the bearings are located there might not be a massive pressure differential across them (eg using bleed air into an area behind the compressor wheel will under high pressure already)
The capstone's air bearings are very interesting, but I wonder how well they'd work under varying revs and lateral / gyroscopic loads in an aircraft.
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Post by propellanttech on Aug 20, 2011 18:53:57 GMT -5
Hi James I gather you've also checked out the Capstone air bearings on their machines www.capstoneturbine.com/_docs/Product%20Catalog_lowres.pdf If you want reliable bearings then brass bushes are the way to go , used on 30,000 hour between overhaul industrial turbochargers , for an aircraft you need reliability , reliability and the availability of off the shelf parts was the reasoning behind me going back to "brass" rather than balls , ..............theres not a huge amount of lost energy even with brass , if one considers how it takes a considerable amount of time to heat the oil going thru a turbo theres probably only a couple of horsepower being lost , thats only ~1% of the turbines energy in a large turbo . Heh heh , yeh the GTBA has its own "character??" , I remember spending a lot of time compiling an article for their magazine and there wasn't even one comment about it when published...............a waste of time on my part . There may be a "novel solution??" to your fan needs here .............................. www.technologie-entwicklung.de/Gasturbines/Monocopter/monocopter.html Its an interesting project you're contemplating ..............we'll try to help/guide you as best as we can , ..................it should be doable :-) Cheers John John, I have researched quite a few "fluid bearings", as they are called, but very few actually use bleed air. I didn't research Capstones specifics. Most air bearings do not use bleed air, but use "dynamic" air to lubricate. This has the problem of them rubbing while coming up to speed, and are design to be constant speed bearings. Bleed air should work for a turbine. I know the oil doesn't create a perceivable amount of drag, but I have seen a small rotor (1.5 inches) take over 90 seconds to stop from some one spinning it with two fingers. Even an oil bearing has much more drag on it. Also the additional parts add weight. Graphite air bearings would be easily replaced should they need to be, and wouldn't be too bad with respect to price. Also they shouldn't scar the shaft should the two touch at high speed. Graphite is a natural lubricant in powder form, and the nickle should prevent any major damage due to it's hardness(although polishing the shaft would be necessary, while building) As for the fan I was looking more toward Ewald Schuster. The one who built the true turbine Harrier model. He has a nice carbon fiber fan for the front pressure nozzles. It's a tad small, but I think it would size up nice. Interesting reference to the fan, but I don't think I'll go that route.......... I may end up with standard bearing, but I really want to bet some expensive parts to reduce the oil in the engine. I think the gamble is worth it. I may be wrong after a few compressors, and turbines. It is the price I may pay to find out. James
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Post by propellanttech on Aug 20, 2011 19:18:05 GMT -5
I think the bearings used in turbochargers have to win on reliability, either ball bearing or plain brass bushes. There will also be large thrust loads on the shaft, which I guess are not a major issue to handle with air bearings either, but depending on where the bearings are located there might not be a massive pressure differential across them (eg using bleed air into an area behind the compressor wheel will under high pressure already) The capstone's air bearings are very interesting, but I wonder how well they'd work under varying revs and lateral / gyroscopic loads in an aircraft. You are right. The specifics about pressure drop is the key. The front bearing isn't the main issue if the shaft tunnel is sealed at the front. The rear bearing could be. This is due to the bypass air cooling the turbine disk. What are the pressure readings of a turbine at T2 and right after the NGV? The T2 would be the air bearing pressure, and the resulting pass through air would need to be reintroduced at the turbine disk (plus the remaining bypass air). You have brought up a point I haven't even considered at this point. If I can pipe the bearing flow through air to ambient, it would have a true pressure differential. I have some ideas, but I'll have to draw them out. The lateral, and gyroscopic forces will just have to be tested. It is a real unknown at this point. It may destroy the graphite bearings along with the compressor and turbine. Only testing would tell. James
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Post by racket on Aug 20, 2011 19:53:36 GMT -5
Hi James Yes , well worth a few parts to find out if it'll work ..................it might pay to find some fairly inexpensive ones initially ........................our TV94 com/turb rotor can be had for ~$500 , you'll probably find that a bespoke axial turb wheel will be a lot more expensive , I went through several rotors with my FM-1 before getting its bearings sorted ................it can be expensive when a bearing fails and the rotor gyrates :-( An interesting Paper to read .................................................... rodyn-inc.com/ISCORMA3_Gunter%26Chen_TurbochargerVer2.pdfWhat quantity of air are you considering to use ?? I can appreciate your desire to be rid of the lube system , its always a relative heavy and bulky item unless driven off the engine . Cheers John
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Post by propellanttech on Aug 20, 2011 20:14:29 GMT -5
Hi James Yes , well worth a few parts to find out if it'll work ..................it might pay to find some fairly inexpensive ones initially ........................our TV94 com/turb rotor can be had for ~$500 , you'll probably find that a bespoke axial turb wheel will be a lot more expensive , I went through several rotors with my FM-1 before getting its bearings sorted ................it can be expensive when a bearing fails and the rotor gyrates :-( An interesting Paper to read .................................................... rodyn-inc.com/ISCORMA3_Gunter%26Chen_TurbochargerVer2.pdfWhat quantity of air are you considering to use ?? I can appreciate your desire to be rid of the lube system , its always a relative heavy and bulky item unless driven off the engine . Cheers John That will take some time to decipher........wow. That would make sense. Start with a cheaper arrangement before going all out for a custom NGV and turbine. There are some different forces at work between the two, but will have some similarities as well. The quantity hasn't been calculated. It will be determined by the shaft diameter and clearance of the bearing. The Critical rotational velocity of the shaft is the first calculation. But if I can use a similar design to your FM1, then I could calculate most of that. The larger the diameter the larger the quantity, due to area ratio as you know. I think the design could actually be worth something if I could get it to work. I know ambition alone won't do it, so I hope I'm going on a path with possible success. Wow.....my brain hurts........ James
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