| Author | Message | ||
     Terry Sack (Terrair) |
I have committed to a Continental engine and was hoping to have FADEC controls. There are still some difficulties with the system in higher horsepower engines. I don't mind being one of the first to use a system but I don't want to be the very first one either. Does anyone in the group know of a field proven ignition system for Continental to replace one or both magnetos? Lightspeed seems oriented to the Lycoming crowd. As is Unison. Don't know anything about others. | ||
| Anonymous |
I have no first hand experience with FADEC, but I have a considerable amount of experience with dynamic propeller balancing and vibration analysis. I have discussed FADEC with the people who taught me how to balance propellers. They have told me that FADEC will fine-tune each cylinder for optimum performance. However, the problem with that is that each cylinder is independent of the other cylinders. Meaning that the power pulse is the maximum for each cylinder. When this happens, you set up a torsional vibration that can break the crankshaft. What you really need is to balance the power pulse to precisely balance the opposing firing cylinder. This is what the GAMI injector people are trying to do. Whenever FADEC addresses this problem, and it is my understanding they are trying, then I wouldn't be afraid to try their system. Until then, I think I would wait. Jim Butler | ||
| Eric Holmberg |
Given that the induction and exhaust systems on the Lyc's and Continentals are not the best in the world for matching all of the power outputs of each cylinder, wouldn't tuning each cylinder for best performance come closer to evening out the torque ripples than a mechanical fuel injection system or carburetor (i.e. open loop system)? Actually, thinking about it, it would probably be better to have a non-deterministic system since you wouldn't be in a resonant point for any length of time. Without the FADEC, the power pulses are each substantially different (say 10%) in power output, so the torsion on the crank is different for each rotation. If you have FADEC, the power pulses are, say within 5%, so you double the chance of running at a harmonic of the crank. | ||
| Anonymous |
Eric, According to GAMI, what you are saying isn't true. Yes, the induction and exhaust systems do have enough difference to unbalance the amount of power from each cylinder. The fuel delivery system does as well. By measuring the exhaust gas temperatures and cylinder head temperatures of each cylinder throughout the "leaning" range of the engine, they size the injectors to obtain the precise stoichiometric fuel/air ratio to obtain the same amount of power from each cylinder. FADEC, to my latest understanding, doesn't do this. FADEC optimizes each cylinder without regards to the other cylinder, making the problem of unbalanced cylinder output worse. This has been proven by the problems they have experienced with broken cranks. I believe they are working on the problem, but it has caused them some delay. I know what GAMI is saying is true because I did a vibration spectrum analysis of my IO-540, paying particular attention to the combustion frequency. I then installed the GAMI injectors in an attempt to balance the power pulses. I again did the vibration spectrum analysis and found the vibration level has dropped 25%. I was actually hoping for a greater drop than that. I have discussed this with GAMI and they suggest I do another iteration of lean testing and they will fine-tune the injectors again. As they say, the proof is in the pudding. If the engine vibration levels are low at the combustion frequency, the power levels are balanced. Vibration levels can be easily measured and documented. By the way, what data did you access to arrive at the 5% difference in power pulses with the FADEC system? Jim | ||
| Eric Holmberg |
Jim, The 5- and 10-percent values were just guesses based upon a "typical" air/fuel ratio variation in the book "Engineering Fundamentals of the IC Engine" by Willard Pulkrabek. The values have to be taken with a grain of salt, because the data doesn't say what type of engine it is for. GAMI probably knows some more aircraft-specific values. I now see what you were explaining about optimizing each of the cylinders. With FADEC, an engine could end up with an uneven power balance between cylinders because each one is optimized individually vs. with GAMI where they tune/detune each cylinder to provide the same power output as the other cylinders. Based upon this fact, I would think that the software guys working on the FADEC systems would be able to quickly solve that issue. Have all of the crank failures been on FADEC-only engines? How did you do the vibration analysis? -Eric | ||
| Anonymous |
Eric, I agree, FADEC should be able to address this issue. As far as "all the crank failures" there have been other crank failures related to other issues, improper heat treating, etc. The way I do the vibration analyis is to mount an accelerometer on the engine, perpindicular to the axis of the cylinders. If I am looking at the frequency of the propeller only, I also mount a photocell, which picks up a piece of reflective tape on one blade of the propeller. If I am looking at all frequencies present, I don't need the photocell. I then run the engine on the ground, at cruise rpm or higher. The analyzer then gives me the magnitude of all vibrations present, which is shown graphically, and in data form. This vibration signature can be stored and compared to signatures taken at a future date, such as an annual. It is a great tool for predicting oncoming problems. For example, if you see an increase at a certain frequency, all you have to do is figure out what operates at that frequency and do a little investigating. Jim | ||
| Eric Holmberg |
Jim, Any idea where I might be able to get some help doing a vibration analysis once I get my engine installation done? Is this something that you borrowed from work, or did you find someone at a university that was willing to help? Eric | ||
| Anonymous |
Eric, I own this equipment, and do vibration work at my business, among other things. Where do you live? I am willing to do vibration analysis work, and propeller balancing for people who live within a reasonable Express flight from northwest Indiana, or want to bring their aircraft here. I have been doing vibration work for about 6 years now. I use the Dynamic Solutions Systems MicroVib Aircraft Vibration Analyzer. Jim | ||
| LOUIE LACY (Llacy) |
Jim What is your e-mail address. I want to ask you about your rudder trim how big where on the rudder you intalled?? llacy@netease.net | ||
| Anonymous |
Hi Louie, My e-mail address is: butler@ffni.com Great to hear from you. I enjoyed talking with you at Sun-N-Fun. Jim | ||
| Anonymous |
Hi Jim, I am just building my rudder and would also like to hear your opnion about rudder trim tab size. Thanks, Blake | ||
| Eric Holmberg |
Hi Jim, Thanks for the offer. I'm in Colorado, but once I get the plane flying, I will be using it to visit family and friends in Virginia, so I'll be flying over Indiana quite a bit. I'm currently at the engine-installation stage with my Auriga Express. I have a Lycoming 540 core mounted, but am currently designing an automotive conversion that I hope to install. If the design work and static tests prove themselves, I'll go with the auto conversion. If not, I will end up rebuilding the IO-540 core. I'm anticipating a completion date of August, 2003, but that is still dependent upon a lot of things, so it may slip a little. -Eric | ||
| Kevin Dennes (Kdennes) |
Blake. If my memory serves me right (I haven't got the instructions at home with me) I think Larry told me to build the rudder trim tab 4" x 2". I thought that was a bit small and I have built mine at 6" x 3". Of course we still have not flown the aircraft so only time will tell. The disadvantage of building too big is that it is far more difficult to control. Little movement . . . big effect. That is undesireable. Regards. Kevin (from Downunder) | ||
| Anonymous |
Blake, My rudder trim tab is 6" tall and 3" wide. The bottom of the trim tab is located about 10 1/2" up from the bottom tip of the rudder. It is powered by a Mac servo. It works very well. Without using the rudder trim, you really have to stand on the right rudder during takeoff due to the slip stream, and the torque of the engine. (Prior to the Express, I only had experience with C-150, C-172, C-182, Piper Warrior, Arrow etc., none of which had this much power.) With the rudder trim offset about two lines to the right (on the indicator), you only have to put in whatever rudder you need for any crosswind that is present. Also, you can trim to keep the ball centered for any power setting in climb. I would say that for my airplane, the size and sensitivity are perfect. Jim | ||
| Louie Lacy New member Username: Llacy Post Number: 95 Registered: 10-1999 |
It has been several years since I had the Mags off my express and I can't remember which side of the rubber bumpers on the end of the mag shaft go next to the raised area on the shaft. Is it the flat side or the side with the (radiused sp) sides Lou Lacy |