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Help with DIY Gas Turbine Engine

Old 08-13-2019, 11:55 AM
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Likely not an engineer
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Question Help with DIY Gas Turbine Engine

Hello RCUniverse. Im not too familiar with forums but this seemed the best place to get advice.

So again, im currently a student (16 so I dont have a lot of money nor tools other than school ones) and am trying to get this engine ive built to self sustain. The design is mainly based on an instructable (I cant link it but just look up "homemade tin can turbine with 3D printed compressor") but ive modified the dimensions slightly for the materials I had on hand (the main body was made from a toilet brush holder 93.5mm in diameter while the one used in the instructables was 100mm). I can get up to speeds of up to 10500rpm with no oil on the bearings (using stainless steel, no shields, grease removed), with the speed dropping to 8800rpm when I start pumping lubricant (car engine oil with viscosity at 40C being 82.8mm^2s^-1) which is still not enough to self-sustain.

Ive stuck a K-type thermocouple and placed it inside the structural tube right next to the bearing and it has only gotten to a maximum of 50C (after a minute or so of running it dry with the temperature increase slowing down) so I dont believe its the steel bearings being affected by the heat. Ive also balanced the shaft and I cant feel any vibrations when I spin it up.

However, Ive discovered ceramic bearings and would like to ask how much effect they would have and if they are a worthwhile investment? Ive also heard that ceramic bearings require little to no lubrication under small loads. Additionally, is there a large difference if I get ZrO2 ceramic instead of Si3N4 ones? Would the PTFE cage cause too much friction so do I need to get cageless ones?

Attached some images of it in .pdf because this is my first post.
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Old 08-13-2019, 11:53 PM
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Jgwright
 
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I admire your desire to make an engine but fear that you will not achieve wheat you want from the way you have started this exercise. If you want to build an engine that actually works then you should buy Kurt Screcklings book
https://www.amazon.com/Turbines-Mode.../dp/1900371332
This goes through the theory and how to make the parts without special materials and inexpensively. Many years ago I made one and it did run reasonably. I have seen 2 of these engines actually powering RC model aircraft. There is a similar volume from Thomas Kamps https://www.amazon.com/Model-Jet-Eng...s=books&sr=1-1
I also made one of his designs and it successfully flew on a plane many times. It was not very reliable and a better design was one called KJ66. If you Google KJ66 you will find that parts are available for this design. However it will be expensive for you.

John
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