Turbine engines

Even though the main campus have their graduation this week and everyone there are done with their finals, there is yet a lot of work to be done for us at the aviation campus. While others are leaving for the summer to visit friends and family we are still going at it hard in school. However, we are getting close to our summer break also.

This semester we are focusing on maintenance of aircraft engines. For the last few weeks we have been learning more specifically about turbine engines which are used in modern airliner aircraft as well as some smaller aircraft also. Since these engines are finding more and more applications in the aviation world these are probably the type of engines that I will be working with in the future. So, in other words, it is important to pay attention to what we do on the mechanics floor and to retain as much as possible from books and lectures.

For a couple of weeks now our class have been divided into smaller groups of five so that we can work together in uninstalling, reinstalling and rigging an actual turbo-prop engine on one of our aircraft. We started by making a checklist based on the aircraft maintenance manual that will function as our guide through the process. Then we use the maintenance manual to see exact details of instruction concerning the different steps we work through. The real test of our workmanship will be tested when we pull the aircraft out on the airport ramp to run up the engines. If we have connected everything adequately the engines should run fine.

There was one little catch to our task at hand. The engine that was assigned to my group had not been running at all for a couple years. Time generally destroys engines, but the engine itself was supposedly intact. Something was wrong with the igniter plug circuit and the starter-generator unit would not start in the start-only mode. Thanks to our previous training in troubleshooting throughout our training we were able to isolate the problems ourselves. We replaced a circuit breaker for the igniter circuit and nothing was wrong with the starter-generator other than it appeared that is was connected incorrectly.

After we had discovered and fixed the discrepancies we found, we could mount the engine back onto to aircraft. Precision and team work is necessary for safety and not to damage anything. After the engine was secured on its mount everything else had to get back together. Nuts and fluid fittings have to be torqued to specific values, electrical connections and bolts need to be safetied with pins and wire. For the engine to operate properly, rigging of the various controls on the engine is critical. It was difficult to comprehend all the different relationships between the arms, control cables and mechanical stops the engine was designed for in order not to burn itself up.

We did not manage to get the engine back together on schedule, so the group decided to get up early the next day we finished to see if it would run. I must admit that it was a bit suspenseful to see whether we had managed to do our job correctly and if this powerful machine would run after such a long time. I took some footage of the first start-up where we can see how it went.

So as you could see the start-up was a great success! For you flight enthusiasts out there, this aircraft is a Kingair Beechcraft. The US military used it during many years and called it the U-21 but no longer in military service. The civilian model is Beechcraft 65-A90. You may have noted the pilot sticking his hand out the window showing two fingers just before he engages the starter signaling the start-up of number two engine (the right hand one from pilot’s perspective). It is to signal to the ground crew what he is intending to do in case you were wondering what kind of hippie-school I am doing to. It is not the peace-sign he is signaling and neither is it any for of insulting gesture. For the very observant person you may notice some minor flame coming out of the exhaust. This happened as gas was introduced into the combustion chamber and ignition taking place. Normally this should not happen, but it was probably some carbon or dirt that has accumulated in the engine during its inoperative years that was now burnt off.

After debriefing our instructor informed us that the engine did not produce quite enough torque when running at idle. This is most likely a rigging issue that needs to be fine tuned. It is normal for an engine like this to be rigged according to the manual and then tweaked a little bit to make it run exactly as desired.

Hope you guys enjoyed!


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