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Post by Deleted on Dec 16, 2014 8:46:12 GMT
Well done Simplyloco, good thread..........
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neil
Active Member
Posts: 39
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Post by neil on Dec 16, 2014 20:02:09 GMT
I built a KJ66, a long time ago, I was a member of GTBA back when it first formed. SNIP Neil Quite lovely to hear from forum members who have experience of other than steam trains. More please! John At the time I was into scale RC aircraft, WW2 and jets, I had built a few jets with an IC engine with prop, and a ducted fan, but then there was "the book from German" which showed you how to build your own jet. The GTBA was formed to share our learning, I tried to machine Inconole, which was interesting, then started to look how to get the turbine blades, guys fitted an angle grinder to the tool post of a lathe and plunged into the wheel blank, I did not want to do this, then was told of a bloke in Spain who was casting the wheel, Jesus Artez, (who is the K in KJ) so I sent him a cheque and waited, 6 Months later I got a wheel, everyone was helping each other, a mate of mine was able to get stuff laser cut, so got the combustion chamber holes cut, and we bought then off him, it was better than the drilled ones we had. This was how it progressed. From this, guys created companies started to take the designs, and make kits, and developing new designs, which was the birth of Wren Trurbines. They developed the MW54, and a powerturbine for Helicopters, these were all shared with the GBTA membership in monthly newsletters, along with other guys developments. Also at this time the big companys started to make finished engines, at more realistic prices, this I think stopped a lot of the sprite of GTBA, as a lot of the guys just wanted to fly jet aircraft. This at least is my thoughts. Flying fast aircraft is a expensive pass time, when something goes wrong it can be a mess, and expensive! It is nice to see the GTBA is still arround.
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Post by GWR 101 on Dec 16, 2014 20:35:54 GMT
Roger thanks for that, what a wonderful sight a beauty to behold. Yes it does seem that the control systems appear to be a major stumbling block, also I understand that the change over from vertical to horizontal flight is another area which has caused problems and of course this is a key part of the whole idea, not to mention viffing (oops I just have).
Thanks simplyloco great thread. Regards Paul
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jackrae
Elder Statesman
Posts: 1,333
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Post by jackrae on Dec 17, 2014 9:56:53 GMT
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Post by Roger on Dec 17, 2014 10:18:38 GMT
Roger thanks for that, what a wonderful sight a beauty to behold. Yes it does seem that the control systems appear to be a major stumbling block, also I understand that the change over from vertical to horizontal flight is another area which has caused problems and of course this is a key part of the whole idea, not to mention viffing (oops I just have).
Thanks simplyloco great thread. Regards Paul
It's possible that the only practical way to control it might be through the use of a dedicated Fuzzy Logic system to coordinate the controls. I know that modern radio control systems can include gyros and cross link controls but it might take more than that. These systems are non linear and modelling them is a nightmare. Designing a control system around Fuzzy Rules avoids a lot of the problems so I think that's the route I'd try.
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Post by GWR 101 on Dec 17, 2014 17:23:28 GMT
Interesting, I not sure if the models built up to now have a reaction control system which is present in the full size aircraft. I believe that this is vital to the stability of the aircraft and would need to be incorporated into the model system. The need to supply thrust to these nozzles is another reason why I believe an "off the shelf" gas turbine engine is difficult to adapt, my view for what it is worth is that this thrust needs to be sourced from the compressor stage. I did some 15 years ago purchase a book called Gas Turbine Engines For Model Aircraft by Kurt Schneckling and Keith Thomas, looks like I need to search it out of storage in the loft and give it another read. Regards Paul
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Post by Roger on Dec 17, 2014 17:54:47 GMT
Doesn't the Pegasus have a shaft that comes back up through the core like a Turbo fan engine? I think they extract some of the exhaust thrust to drive that additional fan at the compressor end and it's that they use for the front two thrusters. I presume they use the same source of pressure for the wing tip thrusters but I may be wrong. Either way, I don't think you'd be able to make a single shaft engine with extra compressor blades on the front. I think you would need that free running central shaft to work in the same way as the original engine. The speed of those two shafts is going to be very different I would imagine.
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Post by Deleted on Dec 17, 2014 17:58:38 GMT
Interesting, I not sure if the models built up to now have a reaction control system which is present in the full size aircraft. I believe that this is vital to the stability of the aircraft and would need to be incorporated into the model system. The need to supply thrust to these nozzles is another reason why I believe an "off the shelf" gas turbine engine is difficult to adapt, my view for what it is worth is that this thrust needs to be sourced from the compressor stage. I did some 15 years ago purchase a book called Gas Turbine Engines For Model Aircraft by Kurt Schneckling and Keith Thomas, looks like I need to search it out of storage in the loft and give it another read. Regards Paul No need to search, Paul. I just downloaded it as a perfect .pdf from here: www.ngcraft.com/doc/pdf/Gasturbine-Engines-for-Model-Aircraft.pdfBedtime reading? John
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Post by ejparrott on Dec 17, 2014 19:34:57 GMT
Could use one for a Thunderbird 2.....
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pault
Elder Statesman
Posts: 1,496
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Post by pault on Dec 17, 2014 20:44:53 GMT
One of the other big issues with the Harrier was that as you descend from the hover towards the ground you have to increase the throttle setting to increase the engine power. This is because as you get lower the engine ingests more and more of its own hot exhaust which reduces the engine power, hence the need progressively increase the throttle setting as you approach the ground.
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Post by Deleted on Dec 17, 2014 20:48:16 GMT
Uh!---- gee Mr Tracy---- do you mean like this >>>>>>>>>>>>>>> I appreciate the humour but I'd like to keep this thread focussed if at all possible. Cheers John
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Post by Deleted on Dec 17, 2014 20:50:39 GMT
One of the other big issues with the Harrier was that as you descend from the hover towards the ground you have to increase the throttle setting to increase the engine power. This is because as you get lower the engine ingests more and more of its own hot exhaust which reduces the engine power, hence the need progressively increase the throttle setting as you approach the ground. I watched a documentary covering the early years and 'nodding' close to the ground was a big problem that pilots had difficulty coping with. Apparently there were quite a few mishaps. John
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Post by Deleted on Dec 17, 2014 21:02:03 GMT
Uh!---- gee Mr Tracy---- do you mean like this >>>>>>>>>>>>>>> I have a meeting with the great man's son tomorrow morning at Henley....looks like I could be a bit busy for a while... Pete
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Post by Roger on Dec 17, 2014 21:22:34 GMT
One of the other big issues with the Harrier was that as you descend from the hover towards the ground you have to increase the throttle setting to increase the engine power. This is because as you get lower the engine ingests more and more of its own hot exhaust which reduces the engine power, hence the need progressively increase the throttle setting as you approach the ground. I'm surprised to hear that because the thrust coming from the front pair of nozzles was relatively cool since it came from a ducted fan, not the exhaust. Ok, now bear with me on this, because this is still on topic... Check out this link which shows something quite remarkable. This is an example of what can be achieved by Fuzzy Logic, and why I think it's a good candidate for a Jump Jet control. You know how hard it is to balance a pencil on your finger. Now try that with another two pencils on top of those two! That's effectivelt what this is doing albeit in one plane. Just in case it's not clear what you're looking at... each of the big black circles is a hinge point.
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Post by vulcanbomber on Dec 17, 2014 21:28:53 GMT
Doesn't the Pegasus have a shaft that comes back up through the core like a Turbo fan engine? I think they extract some of the exhaust thrust to drive that additional fan at the compressor end and it's that they use for the front two thrusters. I presume they use the same source of pressure for the wing tip thrusters but I may be wrong. Either way, I don't think you'd be able to make a single shaft engine with extra compressor blades on the front. I think you would need that free running central shaft to work in the same way as the original engine. The speed of those two shafts is going to be very different I would imagine. Nope, the Bristol Pegasus is a single spool turbo jet with the nozzles instead of a jet pipe. The "puffer Ducts" and front engine nozzels rely entirely on bleed air from the engines compressor. A turbo Fan engine is just a turbo jet with a big fan on the front which provides bypass air to reduce noise and not alot else. You are probably thinking of the Rolls Royce Trents, the first triple spool jets in the world, these have a low pressure compressor, a high pressure compressor and the front fan all driven off individual turbine stages in the engine. While my anorak is dusted off, the first twin spool turbo jet engine (and the finest sounding turbojet in its 20201 series) was again a Bristol engine, this time calles the Olympus which powered....... yep, you guessed it, the VULCAN!!!! and then after much alteration, Concorde. Now, what isnt much known is that an amount of the Low Pressure Compressor from I think the Olympus 301 series engine (late Vulcan MK2's) was mated to a Bristol Siddeley Orpheus engine, the jet pipe altered to the Nozzles and the Pegasus was born. I'm off to put my Anorak away again.
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Post by Roger on Dec 17, 2014 21:38:34 GMT
Very interesting Dave, and that makes it a lot simpler to construct and more compact too. So there's a big fan stage ahead to the main turbine compressor and presumably the output turbine has to have the equivalent to the extra stages that it would require if it was a 2-shaft engine. Come to think of it, I guess this is probably more stable in terms of generating the same amount of thrust from the front and rear nozzles at all throttle settings. If it was done in as a 2 shaft engine, the lag on the front nozzles picking up speed would be catastrophic.
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Post by vulcanbomber on Dec 17, 2014 21:48:32 GMT
Very interesting Dave, and that makes it a lot simpler to construct and more compact too. So there's a big fan stage ahead to the main turbine compressor and presumably the output turbine has to have the equivalent to the extra stages that it would require if it was a 2-shaft engine. Come to think of it, I guess this is probably more stable in terms of generating the same amount of thrust from the front and rear nozzles at all throttle settings. If it was done in as a 2 shaft engine, the lag on the front nozzles picking up speed would be catastrophic. Dont get your terminology mixed up.... you dont compress with a turbine.... And the tubine is there ONLY to drive the compressor, just the same as the turbo on a car. My knowledge of Gas Turbines isnt enough to say if a twin spool engine is a good idea for vectored thrust. However, if you read/speak/listen to a Vulcan Pilot (and there is 5 in the world Current on a Vulcan) and a Victor Pilot they will all say that the Olympus was the Better engine for responsiveness due to its twin spool design. the Victor was powered by a single spool, low bypass turbo fan made by Rolls Royce and called the Conway..... The Conway was slightly more powerful but nothing like as responsive as an Olympus.... and believe me, when your trying to fly a 4 inch diameter tube into a 12 inch diameter basket, 30 feet from a 111 foot wide plane carrying 50 tons of Jet A1 while doing 250+ MPH.... you want responsive engines!!!!
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Post by GWR 101 on Dec 17, 2014 22:44:34 GMT
John yes that's the one many thanks, saved me visiting the loft !. I found it most interesting and also amusing how he had utilised an EMPTY camping gas cylinder to make the body, not sure his method of twisting the rotor blades would go down well with some engineers, but give the man credit this was some 20 odd years ago. Regards Paul
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jma1009
Elder Statesman
Posts: 5,901
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Post by jma1009 on Dec 17, 2014 23:23:35 GMT
there was a 'jet' train tried out in south wales at the heads of the valleys - it was one of the very cold winters in the late 1940s or 50s and the jet engine was supposed to blow away all the snow drifts on the track that were blocking the lines.
the jet engine quickly removed the snow - plus all the track ballast! it also melted the snow which quickly turned to ice which was impossible to remove by shovel. so the 'jet' train was abandoned.
cheers, julian
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Post by Roger on Dec 18, 2014 8:11:06 GMT
Very interesting Dave, and that makes it a lot simpler to construct and more compact too. So there's a big fan stage ahead to the main turbine compressor and presumably the output turbine has to have the equivalent to the extra stages that it would require if it was a 2-shaft engine. Come to think of it, I guess this is probably more stable in terms of generating the same amount of thrust from the front and rear nozzles at all throttle settings. If it was done in as a 2 shaft engine, the lag on the front nozzles picking up speed would be catastrophic. Dont get your terminology mixed up.... you dont compress with a turbine.... And the tubine is there ONLY to drive the compressor, just the same as the turbo on a car. Fair comment, but it's also called a Fan on a TurboFan engine, so that first stage is arguably a fan and not a compressor. I wonder what Bristol called that front set of blades.
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