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2023-11: Warosu is now out of extended maintenance.

/diy/ - Do It Yourself

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1664969 No.1664969 [Reply] [Original]

So ive performed some new test-fires and it still isnt self-sustaining.

I suspect its either the bearings or my balancing of the shaft is not good enough so ill rebalance it. With normal steel bearings properly lubricated with oil jet using car engine oil (viscocity at 40C 82.8mm2s-1) im only getting up to speeds of 8800rpm with oil and 10500rpm without oil. Ive tried replacing the bearings and changing the blade geometries at the back but that hasnt worked.

Thinking of getting full ceramic bearings now. Probably ZrO2 with a PTFE cage. This is mainly because they have lower rolling friction and dont require much lubricant under low loads as I will be using.

Opinions on this?

>> No.1664970
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1664970

>>1664969
Heres a calculator Id made to find the friction caused by the bearings with the formulae taken from this:
https://www.skf.com/binary/68-299767/0901d1968065e9e7-The-SKF-model-for-calculating-the-frictional-movement_tcm_12-299767.pdf

Granted, it doesn't take into account aerodynamic resistance.

>> No.1664972

could you use electromagnet type setup so the shaft hovers like that maglev train? zero friction

>> No.1664973
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1664973

>>1664969
These were the calculations for the jet based on:
http://ftp.demec.ufpr.br/foguete/bibliografia/GAS%20%20TURBINE%20%20ENGINES%20%20FOR%20%20MODEL%20%20AIRCRAFT%20-%20BOOK.pdf

>> No.1664974

>>1664970
engine oil gets pretty hot when the engine is running, which reduces the viscosity. Like pretty sure the coolant in an engine runs at like 90 degrees C. Heat your oil up maybe or use an oil that is low viscosity at ambient temp.

>> No.1665052

Why are you using rolling bearings? Small turbines commonly use oil hydrodynamic bearings, which tend to self-center the shaft and have very low friction (up to the point of oil turbulance)

>> No.1665392

>>1664970
Turbine guy here...ones I work on are slightly larger though.
Have you considered a smooth bearing that floats on oil?

>> No.1665513

>>1664969
YAAAAS.


>opinions on this

Yaaaaas even moar

>> No.1665674

>>1664972
Too complex, expensive and I dont think id be able to design a system that would actually work.

>>1664974
Even without lubricant it isnt spinning fast enough. As seen in my calculator, I used the viscocity at 40C and it still predicts that it should be self sustaining.

>>1665052
>>1665392
Hmm I looked into using a system like that but that requires too much precision that I cant achieve since I dont have access to a lathe anymore.
Going to rebalance the shaft, get some ZrO2 hybrid bearings and hope for the best.

>> No.1665744

>>1665674
good luck op
I hope you get it running soon

>> No.1665811

Interesting

>> No.1665836

>>1664969
your shaft rpm numbers sound an order of magnitude too low.