Rudder Trim

[Skippydiesel]

I need to apply a small trim force to achieve a little bit of right rudder.

I would like your advice on the following;

Dimensions of trim tab (including wedge style that might have worked). I hope to keep my trim tab as small/discreet as is effectively possible.
Most effective location on rudder.

I intend to temporarily stick my trim tab in place using double sided tap. Once the most effective size/bend/location has been found it will be riveted in place.

I am sure many of you have been down this track before me, so please be generous with your experience/advice.

[sonex892.]

Hi Skip.
My Sonex with a Jab 3300 needs a lot of right pedal on climb out and cruise. I have tried 3 things.
Firstly an adjustable spring to add forward force to the right rudder pedal. Worked good at speed but if it wasnt released before landing things got interesting. I removed this on a weight reduction campaign a while back.
Secondly tried numerous lengths and widths of a balsa wedge. Could not get enough rudder force at speed with the wedge. For aesthetics the wedge would have been my first choice but it just wasnt good enough. If you only need a small amount force a wedge might be enough.
Third was an aluminium trim tab. This gave the best result. I still need heaps of right rudder during full power at climbout but at cruise its good. I think the tab is about 200mm long. I'll be flying in the morning so will try to remember to measure it. For figuring out the length location and bend I used double sided tape and duct tape for testing flights with both the wedge and tab. I have had the tab rivetted on for about 5 years now.
Steve

[sonex1566]

Hi Skip,
I used to think that it was just me, however I have seen a few others with exactly the same issue. I experimented starting with tiny and gradually growing bigger and bigger. I reckon that mine is around 7" long x 1 1/2" bent out into the airflow. If it was a model plane I'd stick a couple of washers behind the engine mount to give it some right thrust....I tried it with the Jab, but the prop drive looked stupid about an inch off centre in the cowling. If I was really motivated I would have a go making another engine mount with a few degrees right thrust but the prop still in the middle. However the cost of 4130 especially the square tube is bloody high in Australia and my motivation is rather low....The option for the time being is to stand in front of the trim tab if someone takes a picture.

[Skippydiesel]

Hi Skip.
My Sonex with a Jab 3300 needs a lot of right pedal on climb out and cruise. I have tried 3 things.
Firstly an adjustable spring to add forward force to the right rudder pedal. Worked good at speed but if it wasnt released before landing things got interesting. I removed this on a weight reduction campaign a while back.
Secondly tried numerous lengths and widths of a balsa wedge. Could not get enough rudder force at speed with the wedge. For aesthetics the wedge would have been my first choice but it just wasnt good enough. If you only need a small amount force a wedge might be enough.
Third was an aluminium trim tab. This gave the best result. I still need heaps of right rudder during full power at climbout but at cruise its good. I think the tab is about 200mm long. I'll be flying in the morning so will try to remember to measure it. For figuring out the length location and bend I used double sided tape and duct tape for testing flights with both the wedge and tab. I have had the tab rivetted on for about 5 years now.
Steve

Hi Steve,

I like the idea of a balsa wedge - did you have it for the full length(high) of the rudder trailing edge? What was the x sectional dimensions?

With your tab;

Dimensions - 200mm x ??mm. Please include mounting dimensions as well as slip stream.
Location - Where on the rudder did you end up placing your tab?

[Skippydiesel]

Hi Skip,
I used to think that it was just me, however I have seen a few others with exactly the same issue. I experimented starting with tiny and gradually growing bigger and bigger. I reckon that mine is around 7" long x 1 1/2" bent out into the airflow. If it was a model plane I'd stick a couple of washers behind the engine mount to give it some right thrust....I tried it with the Jab, but the prop drive looked stupid about an inch off centre in the cowling. If I was really motivated I would have a go making another engine mount with a few degrees right thrust but the prop still in the middle. However the cost of 4130 especially the square tube is bloody high in Australia and my motivation is rather low....The option for the time being is to stand in front of the trim tab if someone takes a picture.

Hi 1566,

Your tab may be slightly smaller than Steve's at 200mm x ??mm. What are the dimensions of the bit securing the airflow bit to the rudder?

[GraemeSmith]

Sonex have a part:

https://www.sonexaircraft.com/eshop/car ... ing=rudder

Comes with a suggested dimension/placement on the trailing edge of the rudder.

--

Mine is adjusted for neutral rudder in level trimmed flight.

So with an Aerovee - it is still left rudder on climb and right rudder on dive - but in level flight - I can take my feet off.

[DCASonex]

Flying behind a Jabiru, then a CAMit 3300 for last ten years. Just adjust rudder tab for level cruise. Holding left rudder during rotation and climb becomes second nature after a few takeoffs.

David A.

[builderflyer]

I followed Dave Anders' fastest RV-4 example of using a Gurney flap for rudder trim. It's 6" (152mm) tall and 5/8" (16mm) wide which provides enough rudder deflection at cruise speed for no feet required to keep the ball centered. It's located mid span for greater effectiveness and is permanently held on with double sided tape (no need for rivets).

Works for me,

Art,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,Jabiru 3300 #261

[gammaxy]

Dave Anders' fastest RV-4 example of using a Gurney flap for rudder trim

Art,

That's a very interesting trim tab design. Thanks for sharing, I need to learn more about this Gurney flap trim tab technology.

[Skippydiesel]

builderflyer wrote:
Dave Anders' fastest RV-4 example of using a Gurney flap for rudder trim

I hate making additionals holes in my Sonex so the fact that I can get the tab to stay on temperamentally with double sided tape is great news.

Your tab closely resembles a short length of aluminium angle, that I can get from my hardware store. How thick is it?