Since having my Schenck HT0B balancer with the CAB720 vector display I have learnt so much more about balancing turbines than I knew before and also dispelled a lot of ideas we used to have and what I still see displayed on these forums I am am not specifically talking about this forum. I used to have Thomas Baumguard's ones which I made 2 of for doing balancing for Simjets that we didnt send back to Simjet for balancing. This worked ok but I knew that we still could not achieve the balance of the factory engine and was never really happy. So I bit the bullet and bought a second hand balancer direct from Schenck that had been gone through and serviced and I also commissioned the local Schenck guy in Sydney to come to Brisbane and calibrate and commission the unit and also give us some training on it. We balanced a rotor assembly as a dumb bell on my original home made balancer to get ready when the Schenck arrived, spent about 8 hrs to get the best balance we could on it then put that rotor in the Schenck as a dumb bell so we didnt take the assembly apart to see just how good the home made balancer was and it turned out that the best sensitivity I could get from it was 20gram/mm on the home made balancer, this was done while the Schenck guy was at the workshop and straight after he had done the calibration run on the Schenck. I can tell you with complete confidence if you pull the engine apart to service it or do any work on bearings etc that even though you think it was balanced previously it is now well out of balance when you put the engine back to gether. We have proved this time and time again. You can NEVER get the compressor back in the same spot. Also lets talk about different types of balancing. The two used for model jet turbines is a "dumb bell balance" or a "core balance" 80% of engines either by commercial manufacturers or home builder are done by the dumb bell balance method. This is fine until you take the compressor off to fit it all back into the engine, you will never get that compressor and nut on the exact positions they were in when you balanced it.

We balance all the engines by the core balance method (we can do dumb bell of course like the one you can get access to). The tailcone and front cover only are removed from the engine and the complete engine is then put into the balancer table on special brackets. The registration mark is placed on the turbine wheel and the engine is spun up with compressed air from the compressor end. We balance at between 4000 or 5000 rpm it doesnt really seem to matter on testing this previously. Once the engine rpm has reached the setting we stipulate the machine takes 2 secs to do the measurement and we get a direct readout of imbalance and angle on both the turbine wheel and compressor at the same time. This makes it really easy to do the balancing each run. My website has many more pics and explanation if you want to look at it.

http://www.kyle.com.au/Balancing/bal..._a_turbine.htm

Now to some actual measurements as requested to back up what I am saying. My offsider has a jetjoe 1200 he did some development work on when they first appeared and it was balanced by my balancer to under 1gram/mm and it was working well for about 3 hrs of running in a model when it spat a fuel needle out of the fuel ring while inflight (a common problem from what we have seen with the engines). He marked the compressor and nut where it was then took the engine apart and replaced the fuel needle and put 2 new bearings in the engine. Reassembled the engine taking extreme care to get it back in the right position put it back in the balancer and hey presto... 40gram/mm out of balance on the compressor and about 35 on the turbine wheel. We have checked this over and over again with different engines just to confirm that you can not get the compressor back in the same place once you pull it apart. This is why we only core balance in stead of dumb bell balance. We can prove this because my balancer shows this as the engine is balanced in the exact running assembly. To my knowledge the only companys using this type of core balancer is myself ( Iam sure the only one in the southern hemisphere), Kerry Sterner in the USA the Simjet factory in Denmark. I think Gbooster in Germany also use a core balancer. I have only had the balancer since September last year but having such a fine piece of test equipment is a joy. The customers so far most all have said they can hear the difference as soon as they start the engine as we not only do Simjet but all makes and models of turbines. There has been comments on this thread about commercial engines and jet joe and homebuilts all flame waring each other about whose is better but I can tell you we have seen many other commercial engines from the factory certainly not having perfect balancing done. I can also tell you we just recently did a 1400 and a 1800 engine that we balanced that was balanced in the factory and they were over 90gram/mm out at the turbine end and around 50 gram/mm at the compressor end...of course they are now under 1 gram/mm .

Regards

Mark Kyle
Kyle Communications
Simjet Australia