Stock ELSA RV-12, 173 hours, current on all SB's, firewall mod accomplished.
Over the past couple of flying hours I have noticed a slight change in the spinner "picture" (edge of spinner/ edge of cowl) as viewed from the left side of the cockpit in different flying regimes. F'rinstance: at idle, some movement is seen, at run-up the spinner appears motionless. It stays "frozen" all during climbout at 5,000 RPM, no vibration felt.
Upon level-off, somewhere around 5,000 RPM, a very slight "wobble" is seen on the spinner and it remains at all RPMs down to about 3500 whereupon the spinner "freezes" in appearance. During the wobble, a very slight vibration is felt in the cabin and through the stick. Were it not for the visible change in the spinner picture, I would probably have written this off to "auto-rough."
I wish I could be more specific about the RPMs but we have had very little smooth weather/VFR ceilings and the plane is usually getting kicked around a good bit.
I have carefully inspected the engine mount/torque, motor mounts and cowl security. No fluid leaks observed. I inspected and checked torque on all prop bolts. The blades are dead-even on the SmartLevel. Prop was professionally balanced about a year ago.
Here's where it gets interesting... I can stop the "wobble" by climbing or pulling positive G's in a turn. When I release the load, the wobble and the vibration slowly return. There is clearly a relationship here but I'm going to need somebody smarter than me to figure it out.
I know on some cars there is a thrust bearing on the crank that will sometimes let the crank move longitudinally a little bit but I don't know about the Rotax 912ULS. In any event, I can't see how this movement would cause these symptoms.
I have carefully examined the airframe for anything which might cause the plane to vibrate and make the spinner appear to wobble vis-a-vis the cowl front edge.
I downloaded the data from the Dynon but cannot see any anything out of line there. All the gauges are solidly in the green at all times. No alarms. Due to the fixed-pitch prop, the RPMs are constantly changing somewhat in rough air.
I welcome any and all ideas. I will be phoning Sensenich and Rotax on Monday to see if there are any precedents.
Jim
#120264
Over the past couple of flying hours I have noticed a slight change in the spinner "picture" (edge of spinner/ edge of cowl) as viewed from the left side of the cockpit in different flying regimes. F'rinstance: at idle, some movement is seen, at run-up the spinner appears motionless. It stays "frozen" all during climbout at 5,000 RPM, no vibration felt.
Upon level-off, somewhere around 5,000 RPM, a very slight "wobble" is seen on the spinner and it remains at all RPMs down to about 3500 whereupon the spinner "freezes" in appearance. During the wobble, a very slight vibration is felt in the cabin and through the stick. Were it not for the visible change in the spinner picture, I would probably have written this off to "auto-rough."
I wish I could be more specific about the RPMs but we have had very little smooth weather/VFR ceilings and the plane is usually getting kicked around a good bit.
I have carefully inspected the engine mount/torque, motor mounts and cowl security. No fluid leaks observed. I inspected and checked torque on all prop bolts. The blades are dead-even on the SmartLevel. Prop was professionally balanced about a year ago.
Here's where it gets interesting... I can stop the "wobble" by climbing or pulling positive G's in a turn. When I release the load, the wobble and the vibration slowly return. There is clearly a relationship here but I'm going to need somebody smarter than me to figure it out.
I know on some cars there is a thrust bearing on the crank that will sometimes let the crank move longitudinally a little bit but I don't know about the Rotax 912ULS. In any event, I can't see how this movement would cause these symptoms.
I have carefully examined the airframe for anything which might cause the plane to vibrate and make the spinner appear to wobble vis-a-vis the cowl front edge.
I downloaded the data from the Dynon but cannot see any anything out of line there. All the gauges are solidly in the green at all times. No alarms. Due to the fixed-pitch prop, the RPMs are constantly changing somewhat in rough air.
I welcome any and all ideas. I will be phoning Sensenich and Rotax on Monday to see if there are any precedents.
Jim
#120264