SonexBuilders.net

Hi All,

I have the Sonex dial-a-Trim system on my waiex. I'm still building it... and I installed the system to the plans. (Rear spring just snug full forward, and full up, the tab is about 1/4" from the cable housing) When in this configuration.... it seems like it's holding up elevator at mid travel. It almost seems like too much up trim is available. I know it's all new and tight, but I was wondering is someone could post where there elevator sits when it's on the ground, and if my description sounds right. I'm wiring my panel now... and I still have full access to all of it, if I need to adjust something.

Thanks

On the ground, my stick will pretty much move full range when I crank my trim.

Bryan Cotton wrote:On the ground, my stick will pretty much move full range when I crank my trim.

So.... full down trim is close to full forward stick, and full up trim is close to full back stick? If that's right... then I guess I'm in the right place. So... on a normal take off.... where is your trim?

I usually trim for 80kts on takeoff. The Aerovee doesn't climb well at low speeds, plus it gets hot. So 4-5 turns forward of the aft trim stop for me. Depends on fuel and CG.

I put a little crank knob on mine. Highly recommended!

For a first flight you can either use my recommendation or put it in the middle. Even with trim set wrong forces are light.

I don’t think you need to worry about the trim until you do the weight and balance and find out where the cg is. I originally built my Sonex with the Aerrovee. After 80 hrs I converted to aJab 3300 due to performance issues. With the 3300 my cg is close to the fwd limit, about the base of the instrument panel. My dial a trim is adjusted so the elevator is about 1 in up from neutral at full nose down on the dial. Every thing you put in the a/c along with fuel burn moves the the cg aft. 4 turns up gives 70 on final and any from 3 -4 turns in cruise depending on speed. I suspect you may have the same issue if are using a corvair and don’t add some weight in the tail.
The only issue with the way it is adjusted is on a go around you need to take out 2 turns otherwise the stick force gets very hi holding the nose down.
Keith Rhode
Sonex 214KE

I agree that CG is a big effect on trim. Also here is a picture of the knob I put on my dial-a-trim.

Panther16 wrote:Every thing you put in the a/c along with fuel burn moves the the cg aft. 4 turns up gives 70 on final and any from 3 -4 turns in cruise depending on speed. I suspect you may have the same issue if are using a corvair and don’t add some weight in the tail.

My Odyssey is in the tail of my Corvair powered taildragger for CG reasons. With full fuel and no baggage a single pilot needs to be at least 180 lbs. But there is no loading scenario (within reason) that takes the CG out of the rear limit.

I have the conventional tail on a Model-A with the original trim lever. At approach speeds with 20º flaps setting I can use full up trim and all is well. Using 30º flap on final causes the need for the slightest touch of back-stick pressure. Some have suggested a slightly larger trim tab but I stayed with the plans. Here's what it looks like:

What happens if single pilot below 180? I would have to add 35lbs and I always try to start with full fuel.

Panther16 wrote:I don’t think you need to worry about the trim until you do the weight and balance and find out where the cg is. I originally built my Sonex with the Aerrovee. After 80 hrs I converted to aJab 3300 due to performance issues. With the 3300 my cg is close to the fwd limit, about the base of the instrument panel. My dial a trim is adjusted so the elevator is about 1 in up from neutral at full nose down on the dial. Every thing you put in the a/c along with fuel burn moves the the cg aft. 4 turns up gives 70 on final and any from 3 -4 turns in cruise depending on speed. I suspect you may have the same issue if are using a corvair and don’t add some weight in the tail.
The only issue with the way it is adjusted is on a go around you need to take out 2 turns otherwise the stick force gets very hi holding the nose down.
Keith Rhode
Sonex 214KE

Thanks for the info on that.

I have the forbidden Corvair engine in mine.... but from my research, the 3300 really isn't much lighter once everything is added on. SO... it's a good match info wise.

Bryan Cotton wrote:I agree that CG is a big effect on trim. Also here is a picture of the knob I put on my dial-a-trim.

Cool. I may do that to mine also. Thanks for the pic.