Yesterday, 12:39 PM
After 40 years of building and working on Rotorway helicopters, this week I discovered something that I had never experienced before. I have a client who had a shop rebuild his engine and I told him that I required at least 5 hours of trouble free hovering before we would take the helicopter to altitude. This precaution is to prove that the newly rebuilt engine and all re-installed components were working properly before risking our lives in the air.
My client was getting bored with just hovering and so began doing quick stops from one end of my grass strip to the other. At the 3 hour mark he noticed what seemed like a slight miss in the engine and he set it down for me to take a look at it. I advised that we change the fuel filter and check the fuel screen to insure sufficient fuel flow as a first check. We installed a new fuel filter and the screen was clean. On start-up the engine ran well but in hover there was an occasional miss.
We checked every connection, wire, and hose to try to find something that would cause the miss to no avail. The next time we started the engine it was running very roughly and would die after a few seconds of running. At that point I thought that perhaps we had some bad fuel so we drained the fuel system and added fresh 91 octane. With fresh fuel in the tanks we now could not even get the engine to fire or even backfire. What could be the problem?
We were both thankful for my 5 hours of testing near the ground before altitude flight rule. After 19 real autorotations due to engine or system failures in my career I am not wanting to make it 20.
We spent several days trouble shooting every system and could not find a reason why we now had no spark or fuel injection. The Fadec computers seemed fine but the engine would not fire on either fadec. Tuesday evening ended with both of us frustrated and brain fried so I called a buddy who has just retired from his auto service and engine shop and he agreed to come out yesterday morning to give the engine his expert opinion.
Before Jeff arrived we removed the main drive belts from the engine pulley so that the engine start could be attempted inside of our air conditioned workshop instead of out in the 110 heat index humid air outside. Jeff verified no spark and no fuel injection signals and yet the computer fired up and checked out ready to provide those signals. The computer was not getting the crank position signals from either of the crank sensors. I have heard of a crank sensor going bad but have not had one happen on any of the helicopters that I have flown or worked on.
How could both crank sensors go bad at the same time? Jeff told us that was nearly impossible so there was another reason why they were not sending the required signal to the computers. He had us remove the drive pulley and flywheel so that we could inspect the trigger wheel that activates the crank sensors. Jeff checked the gap between the trigger wheel teeth and the crank sensor and one gap was too wide and one was too tight. He next used an large screw driver to pry the crank hub to the side and it shifted .080" in either direction.
Problem discovered. The top crank bearing is allowing the crankshaft and attached trigger wheel to wobble back and forth preventing the crank sensors from receiving the 360 degrees of data that the computer needs to fire the spark plugs and fuel injectors. It was as if the crank sensors had failed but it was actually the top engine crank bearing that failed after only 3 hours, that is if the engine builder had even installed a new bearing and now I am doubtful of that.
My client is not going to have the same engine builder even touch his engine. We removed it and called Joe Huff who agreed to do a full tear down and blueprint of the engine with installation of any needed components. It is on its way to Texas to Joe's shop as I write this.
My client was getting bored with just hovering and so began doing quick stops from one end of my grass strip to the other. At the 3 hour mark he noticed what seemed like a slight miss in the engine and he set it down for me to take a look at it. I advised that we change the fuel filter and check the fuel screen to insure sufficient fuel flow as a first check. We installed a new fuel filter and the screen was clean. On start-up the engine ran well but in hover there was an occasional miss.
We checked every connection, wire, and hose to try to find something that would cause the miss to no avail. The next time we started the engine it was running very roughly and would die after a few seconds of running. At that point I thought that perhaps we had some bad fuel so we drained the fuel system and added fresh 91 octane. With fresh fuel in the tanks we now could not even get the engine to fire or even backfire. What could be the problem?
We were both thankful for my 5 hours of testing near the ground before altitude flight rule. After 19 real autorotations due to engine or system failures in my career I am not wanting to make it 20.
We spent several days trouble shooting every system and could not find a reason why we now had no spark or fuel injection. The Fadec computers seemed fine but the engine would not fire on either fadec. Tuesday evening ended with both of us frustrated and brain fried so I called a buddy who has just retired from his auto service and engine shop and he agreed to come out yesterday morning to give the engine his expert opinion.
Before Jeff arrived we removed the main drive belts from the engine pulley so that the engine start could be attempted inside of our air conditioned workshop instead of out in the 110 heat index humid air outside. Jeff verified no spark and no fuel injection signals and yet the computer fired up and checked out ready to provide those signals. The computer was not getting the crank position signals from either of the crank sensors. I have heard of a crank sensor going bad but have not had one happen on any of the helicopters that I have flown or worked on.
How could both crank sensors go bad at the same time? Jeff told us that was nearly impossible so there was another reason why they were not sending the required signal to the computers. He had us remove the drive pulley and flywheel so that we could inspect the trigger wheel that activates the crank sensors. Jeff checked the gap between the trigger wheel teeth and the crank sensor and one gap was too wide and one was too tight. He next used an large screw driver to pry the crank hub to the side and it shifted .080" in either direction.
Problem discovered. The top crank bearing is allowing the crankshaft and attached trigger wheel to wobble back and forth preventing the crank sensors from receiving the 360 degrees of data that the computer needs to fire the spark plugs and fuel injectors. It was as if the crank sensors had failed but it was actually the top engine crank bearing that failed after only 3 hours, that is if the engine builder had even installed a new bearing and now I am doubtful of that.
My client is not going to have the same engine builder even touch his engine. We removed it and called Joe Huff who agreed to do a full tear down and blueprint of the engine with installation of any needed components. It is on its way to Texas to Joe's shop as I write this.