Re: Actual Flying Rotax Installs
![Post Post](./styles/prosilver/imageset/icon_post_target.gif)
So I figured I’d take a hiatus from the keyboard and spend more time flying, less time typing.
I went ahead and tested out my mount. First thing I noticed when I ran it up on the ground was the difference in start up and isolation of vibration of the engine from the airframe. It was very smooth.
When flying it, it felt great. I did a series of high speed turns, full power climbs at high angles of attack, stall work, slips, and just regular old flying to feel the characteristics of the plane now, compared to before. I tried to impose a good amount of torque load, gyroscopic forces from axis change, and load on the engine in a hard climb. As a test if felt appropriate to impose as many loads as possible to make sure it was safe. There was no issues of wear, fatigue, or stressed components.
However, there is one issue. But let’s start here;
Aerovee’s, Jabiru’s, and Rotax’s are all flat engines. (Horizontally opposed, boxers, pankcakes, whatever you want to call them). Both the Aerovee and Jabiru have a prop flange on the crankshaft end which puts all loads at the center of rotational mass of these engines. But these engines are limited by their pitch, diameter and number of blades.
Rotax however is smaller dimensionally, and in weight, than both the Aerovee and Jabiru but it’s gear driven which places the prop shaft about 6” above the crankshaft end. Which in turn gives it an arm with an incredible amount of leverage because of its power output and ability to spin much larger and much heavier propellers. So as you can imagine, the propeller flange moves quite a bit where on the Aerovee and Jabiru it stays relatively centered. With these two you may see some rubbing on the back of your propeller or slightly on your propeller spacer but that’s fairly common and it’s never a big issue.
With all that being said, my engine still torqued over and touched the edge of my prop flange hole.
One thing about Sonex as opposed to other manufactures that primarily use a Rotax, is that the exit hole is much smaller. On any Rotax powered aircraft with a cowl, you’ll notice the exit hole for the propeller shaft gives at least about 1.5” around the entire flange/spacer to allow for this torquing over. Other manufacturers such as Aerotrek, Rans, Kitfox, Vans, use about an 8” exit hole and sometimes a center-stepped spacer to allow for this to happen. That’s why you see spinners usually ranging from 8” and up on anything using a Rotax.
On Sonex’s, my opinion, is the hole is too small for a Rotax. I am running a larger spacer, not a center stepped spacer so I am running the tightest tolerance available. With both mounts (mine and Sonex’s), the spacer rubbed on the same spot on my cowl. If you’re sitting in the airplane, it’s the 7 o’clock area of the exit hole where it rubbed. So instead of fighting it, I began sculpting out a relief in my cowl. It’s not noticeable unless you’re really looking for it when looking at my propeller directly from the side. My 8” spinner pretty much hides it. I would fly and check this wear, and sand away as needed. Eventually I got to the point I just drew a dark area with a sharpie on the wear point on my spacer, and when it was no longer being rubbed away, I knew I had shaved off enough of my cowl and the two were no longer touching. Then just went back and wiped off the mark with some carb cleaner.
So to no fault of Sonex, this is just a characteristic of a Rotax.
I went ahead and flew another Sonex today with a Jabiru 3300 just to compare the engine to airframe isolation, and my plane felt just as good if not better.
But everything is working great.
I went ahead and tested out my mount. First thing I noticed when I ran it up on the ground was the difference in start up and isolation of vibration of the engine from the airframe. It was very smooth.
When flying it, it felt great. I did a series of high speed turns, full power climbs at high angles of attack, stall work, slips, and just regular old flying to feel the characteristics of the plane now, compared to before. I tried to impose a good amount of torque load, gyroscopic forces from axis change, and load on the engine in a hard climb. As a test if felt appropriate to impose as many loads as possible to make sure it was safe. There was no issues of wear, fatigue, or stressed components.
However, there is one issue. But let’s start here;
Aerovee’s, Jabiru’s, and Rotax’s are all flat engines. (Horizontally opposed, boxers, pankcakes, whatever you want to call them). Both the Aerovee and Jabiru have a prop flange on the crankshaft end which puts all loads at the center of rotational mass of these engines. But these engines are limited by their pitch, diameter and number of blades.
Rotax however is smaller dimensionally, and in weight, than both the Aerovee and Jabiru but it’s gear driven which places the prop shaft about 6” above the crankshaft end. Which in turn gives it an arm with an incredible amount of leverage because of its power output and ability to spin much larger and much heavier propellers. So as you can imagine, the propeller flange moves quite a bit where on the Aerovee and Jabiru it stays relatively centered. With these two you may see some rubbing on the back of your propeller or slightly on your propeller spacer but that’s fairly common and it’s never a big issue.
With all that being said, my engine still torqued over and touched the edge of my prop flange hole.
One thing about Sonex as opposed to other manufactures that primarily use a Rotax, is that the exit hole is much smaller. On any Rotax powered aircraft with a cowl, you’ll notice the exit hole for the propeller shaft gives at least about 1.5” around the entire flange/spacer to allow for this torquing over. Other manufacturers such as Aerotrek, Rans, Kitfox, Vans, use about an 8” exit hole and sometimes a center-stepped spacer to allow for this to happen. That’s why you see spinners usually ranging from 8” and up on anything using a Rotax.
On Sonex’s, my opinion, is the hole is too small for a Rotax. I am running a larger spacer, not a center stepped spacer so I am running the tightest tolerance available. With both mounts (mine and Sonex’s), the spacer rubbed on the same spot on my cowl. If you’re sitting in the airplane, it’s the 7 o’clock area of the exit hole where it rubbed. So instead of fighting it, I began sculpting out a relief in my cowl. It’s not noticeable unless you’re really looking for it when looking at my propeller directly from the side. My 8” spinner pretty much hides it. I would fly and check this wear, and sand away as needed. Eventually I got to the point I just drew a dark area with a sharpie on the wear point on my spacer, and when it was no longer being rubbed away, I knew I had shaved off enough of my cowl and the two were no longer touching. Then just went back and wiped off the mark with some carb cleaner.
So to no fault of Sonex, this is just a characteristic of a Rotax.
I went ahead and flew another Sonex today with a Jabiru 3300 just to compare the engine to airframe isolation, and my plane felt just as good if not better.
But everything is working great.