370A Gyro causing aileron oscilation ??
03-26-2015, 06:13 AM
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370A Gyro causing aileron oscilation ??
Went to fly my turbine powered F-86 yesterday for the first time in 4 or 5 months. After starting the engine as soon as the throttle was advanced both ailerons were oscilating half throw (1/4" or so) in both direction a little like the old galloping ghost radios used to do. While I have not proven it yet I am assuming it was caused by my JR 370A gyro. The airplane was totally static. Being turbine powered I am quite sure that vibration is not the issue. I am on my out to the driveway to start up and make sure it is still doing it. After that if it is still acting up I will eliminate the gyro and restart the engine.
In the mean time if anybody has seen this before or has an idea whats going on please let me know. I am reasonably sure it wasnt doing this the last time I flew it.
In the mean time if anybody has seen this before or has an idea whats going on please let me know. I am reasonably sure it wasnt doing this the last time I flew it.
03-26-2015, 07:28 AM
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MEMS gyros are prone to acoustic interference, I have had it (by coincidence also in an F-86) and I am aware of others who have had it. Usually the gyro makers know how to overcome it so that it isn't a problem. With mine it occurred only at certain rpm, I got big aileron glitches or fluttering. If that is the problem but you have not had it before then perhaps something has gone faulty with the gyro or firmware to suddenly make it susceptible again, or less likely something in the turbine has changed ever so slightly and it is now making the frequencies that upset the gyro.
Or it could just have gone plain faulty!
Or it could just have gone plain faulty!
03-26-2015, 08:17 AM
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Using a Y. First thing I found upon closer inspection is that my 14 plus year old aileron servos have quite a bit of slop in the gear train. I am going to go get some up to date metal gear servos and replace these old ones. Then I will see where I am at.
03-27-2015, 06:18 AM
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Problem solved. First of all in my initial post I over estimated the amount of aileron movement it was more like 3/32 " to1/8" up and down which is quite a bit less than 1/4 ". As I stated above upon inspection I found a lot of slop in my overall alieron control setup. It was caused by a number of things. Primarily 15 plus year old nylon geared servos that were just old and worn and probably not that great to begin with when new 15 plus years ago. A tiny bit of slop in the hole in the servo arm was another factor. And a tiny bit of slop in the clevis to aileron horn connection. I have installed modern day metal gear top notch servos with new servo arms and new clevis"s and just about all slop and play is gone. I just now ran the engine and still have a tiny bit of aileron bounce up and down but not much. Now I am ready to try taking the gyro out of the loop and see if that is where the small remaining movement is coming from. Unfortunatly getting to the receiver to unplug and swap around connectors is near impossible with out a mayor tear down. Not sure I am going to do that or not. The very small remaining amount of aileron movement is probably acceptable and something I can live with.
Vincent........would you mind explaining why a "y" harness setup is unacceptable on this gyro . It has been a while since I installed this but I am pretty sure I recall how it is set up. I am running the two ailerons on a "Y" that then goes to the gyro and from the gyro a single cable to the aileron channel of the rx. Whats wrong with that ?
Vincent........would you mind explaining why a "y" harness setup is unacceptable on this gyro . It has been a while since I installed this but I am pretty sure I recall how it is set up. I am running the two ailerons on a "Y" that then goes to the gyro and from the gyro a single cable to the aileron channel of the rx. Whats wrong with that ?
03-27-2015, 07:09 AM
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I was responding to the gentleman with the screen name Vincent. He made several posts regarding "y" connectors and match box but he gives NO explanation or reason for his statements. He may very well be correct but I need more than just a statement telling me to do something. I need to know the reasons behind the statement.
Barracuda ....... I take it your name is also Vincent ?? Sorry for the confusion.
Now on to my issue. I was able to get the gyro out of the loop and now have the ailerons going directly into the receiver with a "y" harness. I re ran the engine and now my ailerons are rock solid without even a hint of a twich. Rock solid !!!
As mentioned before this a 60" BVM F-86 with RAM 500 for power. Been flying it since the spring of 2001 with an estimated 300-400 flights. I only installed the gyro about 18 months ago and havent flown it much since then. I did feel like it helped a little with regard to wing rock but not tremendously. I have it programmed for very low sensitivity and not a lot of aileron movement. This airplane has huge ailerons and my total aileron throw is only up or down maybe 1/8 to 3/16 ".
Since this aileron twitch or bouncing was only happening with engine running at 1/3 throttle or above and since I have the gyro rigidly mounted directly on top of the inlet duct which is directly connected to the engine bypass which the engine is directly mounted to there must be a very small amount of gyro movement or vibration that is upsetting the gyro ever so slightly. I guess my next step is to find a different mounting location for the gyro.
Barracuda ....... I take it your name is also Vincent ?? Sorry for the confusion.
Now on to my issue. I was able to get the gyro out of the loop and now have the ailerons going directly into the receiver with a "y" harness. I re ran the engine and now my ailerons are rock solid without even a hint of a twich. Rock solid !!!
As mentioned before this a 60" BVM F-86 with RAM 500 for power. Been flying it since the spring of 2001 with an estimated 300-400 flights. I only installed the gyro about 18 months ago and havent flown it much since then. I did feel like it helped a little with regard to wing rock but not tremendously. I have it programmed for very low sensitivity and not a lot of aileron movement. This airplane has huge ailerons and my total aileron throw is only up or down maybe 1/8 to 3/16 ".
Since this aileron twitch or bouncing was only happening with engine running at 1/3 throttle or above and since I have the gyro rigidly mounted directly on top of the inlet duct which is directly connected to the engine bypass which the engine is directly mounted to there must be a very small amount of gyro movement or vibration that is upsetting the gyro ever so slightly. I guess my next step is to find a different mounting location for the gyro.
03-27-2015, 07:14 AM
#12
Andy Griffith actually.
The gyro needs to be flat and in the area of least vibration.
Start with low gain and increase it until you get some oscillation in flight then back it off slightly. Best to have it on a slider or knob. Always be able to turn it off if there's an issue.
Again, with a model that old I would undo and redo every connection that you can reach and check for any loose connections.
Could you define "rigidly mounted"? Best gyro tape around is 3M VHB tape, you can pick the model up by the gyro in most cases but it can be broke loose by twisting, also it provides a measure of vibration isolation.
The gyro needs to be flat and in the area of least vibration.
Start with low gain and increase it until you get some oscillation in flight then back it off slightly. Best to have it on a slider or knob. Always be able to turn it off if there's an issue.
Again, with a model that old I would undo and redo every connection that you can reach and check for any loose connections.
Could you define "rigidly mounted"? Best gyro tape around is 3M VHB tape, you can pick the model up by the gyro in most cases but it can be broke loose by twisting, also it provides a measure of vibration isolation.
