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T Rex motor problems Empty2019-03-03, 23:44 by Charles E Cornes

Saturday 7/7/18

2018-07-07, 21:07 by Gary M Jones

I was at the field today between 14:00 & 15:00 all on my own , good flying too. There is a dead sheep along the fence line towards the gate from the pits, I saw the farmer so reported this to her. I hope no one had plans for a BBQ Smile .

Farmer …

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Post by Guest on 2009-10-03, 16:01

The T Rex has now test flown with the TT53 Redline fitted and is spot on with no vibes at all Very Happy Very Happy Thinking of trying a set of ceramic bearings in the Hyper50. Anyone tried them Question

DaveS

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Post by PDQ on 2009-10-03, 20:40

Dave
I understand ceramic brg parts are vulnerable to shock loads. So be careful with the fitting ! Put the hammer away. Use a press.
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Post by Guest on 2009-10-03, 22:05

On the other hand when i was younger they were all the rage in skateboards and ive never seen one fail even under the harshest of abuse,

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Post by PDQ on 2009-10-03, 23:05

I did find this
Abstract
Ceramic bearings made of silicon nitride were implemented for the purpose of producing bearings capable of operating under severe conditions where traditional rolling bearings made of steel could not operate. However, when all-ceramic bearings in which inner and outer rings and rolling elements are made of silicon nitride are attached to a steel shaft, a difference in the coefficient of linear expansion of steel and silicon nitride results in the expansion of a steel shaft due to a temperature rise during the operation and, in the worst cases, the development of excessive stress and damage of the inner ring made of silicon nitride
so do check the fits
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Post by Andy Sayle on 2009-10-04, 10:06

The bearings in my turbines are Ceramic, primarily because they are required to operate at stupid temperatures (what do you expect when you are stuffed up against a combustion chamber operating at over 1000°C!). I'm not sure of the exact grade of material, although when I built my engine, the balls had the look of Silicon Nitride to them. There are other ceramics used in bearing manufacture, such as Alumina oxide (even higher temp rating than Silicon Nitride, but not as resistiant to chemicals) and Zirconia (a slightly cheaper and lower performing grade, although harder to get hold of).

The construction of the sort of ceramic bearings that would be used in an engine is basically the same as a normal bearing, with the exception of the balls being made from ceramic. That means that although the balls themselves are corrosion proof, all the other bits are not. You can get completey ceramic bearings, the races and everything. These are perhaps a bit pricey though Wink

The Silicon Nitride (comonly available) bearings are indeed slightly less resistant to shock loadings, but they can be used in high load situations too. The material has the benefit of being extremely strong, but a little bit brittle. As Paul said, double check the fits, and try to press them in/on smoothly, rather than belting it with a hammer if you can Smile

Cheers
Andy

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