Rudder Trim

[sonex892.]

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?

The 200mm tab length was a guess. It actually measured 165 x 17 x 30 see placement on photo
The balsa wedge was a long time ago but I think I started long, maybe 18". I did try various locations high and low on the rudder but couldnt get a good enough result. I bought the balsa from bunnings.
Steve

[builderflyer]

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?

My Gurney flap rudder trim was bent up from a scrap of 0.025" thick aluminum. Clean the aluminum well, say with lacquer thinner, before applying the double sided tape and it'll virtually "never" come off in use. The trim will be difficult to remove, but not impossible, should you choose to take it off at a later time.

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

[Skippydiesel]

Sonex 892,

Interesting location - why so low on the rudder?

I have just installed my MK1 tab and have located it exactly 1/2 way - used a peace of 200 x 30 x 1.5 mm curved ) aluminium profile. 15 mm sticks out into the slip stream. Yet to test fly.

[Skippydiesel]

Mk1 over corrected just a "tad". Have removed and cut in 1/2 (now 100mm). Will refit and test again.

[John Monnett]

Over the years and a bunch of aircraft I have used a simple method to determine the size of trim tabs. A length of a common soda straw is taped to the trailing edge of the surface on the side you want to deflect. Make an educated guess as to the length,(say 8 to 6") and test fly. trim the length to adjust. Once you've got it right, then make an aluminum tab to match.

[Skippydiesel]

Mk2 works well BUT as you experienced builder/pilots will know, an adjustment to one control surface will impact on another;

Now have a left wing drop - did have the left flap up as far as it would go, to correct an earlier right wing drop. Have now turned left wing flap down by 1/2 turn of control rod end. Hope to test fly, in the cool of the early morning, tomorrow.

[GraemeSmith]

To my mind you should be rigging the plane to fly straight and level with the pilot sitting in the center of the cockpit. Easy in an Onex. Less so in a Sonex/Waiex. This to represent a pilot/passenger situation. Once that is achieved you can sit on the left. At that point the plane will appear to be "left wing heavy" - but it's not really - just it is out of roll trim because of your weight. At that point you can apply some kind of trimming to the stick to get the plane to roll level. You should not be adjusting control surfaces or they will be "wrong" when a passenger is aboard and also sets you up for unequal yaw characteristics.

In my Sonex - the one thing the builder had not tackled was the rudder trim - professing to just leave his slightly heavy left foot on the rudder. Once I got the rudder trim sorted for level flight - I then DID sit centerline and make sure left and right flaps and ailerons were equally rigged and the plane was flying level. (as well as dimensioning the wingtips to be sure the plane was "square").
With that done - I sat left seat and yes the plane appeared to be left wing heavy. I then used differing weights of bungee on the stick till I found the one to "trim" away the condition. I've arranged it so that if I fly solo - I hook the bungee on. If I have cargo or a passenger - I unhook the bungee.

YMMV

[Bryan Cotton]

Graeme,
I'd like to see your aileron bungee picture. My son and I weigh the same so we are rigging for two-up. But solo I fly from either seat and want to implement something.

[racaldwell]

I also use a bungee but I use it as a supplement to the elevator trim. My spring bias elevator trim does not have the range to trim across 40 to 135 kts. So the bungee is between the seat cushions and I have a cleat on a clip positioned over the seat pan front edge in the center above the spar tunnel. The other end of the bungee is connected to the bellcrank at the rear of the seat pan. This solved my trim range issue.

The cleat came from my old windsurfer junk. The cleat makes it easy to remove or adjust bungee tension.

Rick Caldwell
Xenos 0057 The Air Yacht

[GraemeSmith]

Looking down directly into cockpit of Legacy/A Sonex
Seat Pan removed.
Front of aircraft is at top of picture
Twin Stick

1.jpg (176.88 KiB) Viewed 1249 times

Detail of stick. The Yellow Bungee hooks together two eyes (arrowed) in the stick system applying slight right roll.
Once in the ballpark with a weight of bungee - the "fine tuning" was by adding knots to the bungee to set the length / tension.

2.jpg (73.19 KiB) Viewed 1249 times

To hook or unhook depending on passenger - I remove the stick boot cover (which is held in place with Velcro) and reach in and hook or unhook. VITAL that this is set up that if bungee breaks or is in "unhook" mode there is NO chance that the bungee can jam controls.