Dominator Rudder Trim Tab

[Penguin]

I notice that I have to use a small amount of left rudder pedal to keep yaw in check at cruise.
My rudder centering device is in good shape - nice and flat, square with the rudder.
I suppose the centering device could be used in lieu of a rudder trim tab, but really doesn't strike me as appropriate for that task. It would be difficult to bend, I think.
Your thoughts?

 

[helipaddy]

I've found that the dominator flies best when you put no pressure on the pedals, both in the climb and the cruise, just accept where the pedals go and the climb rate increases.
Are you using a slip ball or some string?

 

[Penguin]

I've found that the dominator flies best when you put no pressure on the pedals, both in the climb and the cruise, just accept where the pedals go and the climb rate increases.
Are you using a slip ball or some string?

Slip indicator.
The ASI backs up what my butt is telling me.
When I use left rudder to center the slip indicator, I gain airspeed.
My conclusion is that, left to its own devices, I tend to fly in a slight crab (yawed).

 

[helipaddy]

I mounted a slip indicator too and thought it was level, when I tried to use it I lost a good bit of climb rate, I've figured that by leaving the rudder to its own devices during a climb makes a noticeable difference. I put string up on my compass and there was a big difference between the yaw string and ball.

47mph indicated gives me best rate of climb. With no pedal input, the trim string is just a bit off centre, if I centre the string, my climb rate is less.

 

[Passin' Thru]

I notice that I have to use a small amount of left rudder pedal to keep yaw in check at cruise.
My rudder centering device is in good shape - nice and flat, square with the rudder.
I suppose the centering device could be used in lieu of a rudder trim tab, but really doesn't strike me as appropriate for that task. It would be difficult to bend, I think.
Your thoughts?

Larry, I'm not sure how yours is made, but my home made one had the slotted alignment finger attached to the tab with 2 #8 machine screws with elastic stop nuts and washers.
To trim the rudder, I adjusted the relation of the tab to the slotted alignment finger. In your instance, to apply a bit of left rudder pressure you would angle the tab a bit to the right relative to the slotted alignment finger. Mine would fly perfectly true with feet off the pedals.
If yours is riveted, you may need to drill out the rearmost rivet and replace with a machine screw, nut and washers. Elongate hole to side as required.
BTW: I think that gizmo is called an "anti-servo tab".

 

[jcarleto]

I've seem more than a couple of crucifix tails with the anti-servo device and a small additional fixed trim tab with a couple of degrees of offset.

 

[Penguin]

Thanks, Pete and Jon.
Pete - The anti-servo tab (better terminology) is not easily bent as it is made rigid vertically by the piano hinge at the front and horizontally by a 90deg bend at the bottom.
Which pretty much limits 'tweaking' to the upper rear quadrant and it is very reluctant to give.
Jon - how small is small? maybe 4"x2"?

 

[jcarleto]

Here's a picture of one I see frequently. I think it is about 3" x 6" more or less.

 

[Penguin]

Very clear.
Thanks!

 

[Penguin]

Larry, I'm not sure how yours is made, but my home made one had the slotted alignment finger attached to the tab with 2 #8 machine screws with elastic stop nuts and washers.
To trim the rudder, I adjusted the relation of the tab to the slotted alignment finger. In your instance, to apply a bit of left rudder pressure you would angle the tab a bit to the right relative to the slotted alignment finger. Mine would fly perfectly true with feet off the pedals.

Pete - I took your advice rather than adding a separate trim tab.
Pic is of a temporary test solution. It tracks very nicely now with a noteworthy increase in speed and likely fuel efficiency.
Yet I was surprised how much trim it took. As you may see, I put a couple of adjustment holes. I'd say it is 1" offset at the trailing edge.

 

[cburg]

On Weight Shift Control (WSC) trikes and Powered Paragliders (PPG) we angle the engine thrust line…just slightly. Otherwise they have a turn under power.

I think my Monarch would do better with a couple of degrees. I currently needs trim tab on it.

This assumes the turn/yaw only occur under power (flies straight dead stick). Otherwise, a trim tab seems unavoidable.

However, I am considering varying my rudder pedal return spring tension as an alternative.

Your thoughts?

Chuck

 

[Penguin]

Chuck - I don't know a damn thing.
But I do know that I want the rudder to return to a dead straight flight attitude if a cable breaks or something in the linkage malfunctions - e.g., a pulley falls off.
Using pedal springs wouldn't address that root problem.
I think some sort of trim tab would be better.
You raise a good question about dead stick. Next time I fly I'll chop power and observe yaw.

 

[bmoore2156]

I removed the anti servo tab on my RAF /sh
My rudder pedals were VERY hard to push. If someone set there toes on the pedals in the other seat, it would almost be impossible For me to use them. I have lubed my cables, greased my steering. They are easy to press on the ground but under power they were hard. I remove the anti servo tab and it improved it 100%. I have since flown in winds gusting to 30 and have used full L and R rudder with no I'll effects. I think the large h stab on mine stops the rudder from fludder. I notice in cross wind, I have to hold slight rudder to correct the yaw string whereas before the anti servo tab would do it.
I am not sure I would omit it for the Dom tail tho. It may flutter with the smaller h stab.

 

[MikeBoyette]

The Anti-Servo tab is designed to do just that. The rudder is quarter cord wise balanced and without the tab if you push the rudder it would stay there. The tab is designed to make the rudder return to center. It has some adjustment to account for some flaws like maybe one cable a tiny bit longer than the other. It is not designed to be a trim tab. If rigged properly the tab should be centered behind the tail when pedals are even. It also provides some aerodynamic feedback to the pedals.

Mike, I have never seen anyone have to deflect theirs as much as you have had to deflect yours..You might want to ensure everything is rigged correctly. I would checked for a steretched cable as well.

 

[Penguin]

Mike - it surprised me, too. The cables and pulleys are all as new. Pedals are level and rudder square to keel at rest.
Note in the pic that the slotted tab is well centered and square.

 

[GyroRon]

I wonder if your upper tail brace is true... if the tail is canted on top to one side this could cause problems

 

[Penguin]

Ron - Good thought. I'll take a look at it this morning.
I preflight it every time since I've seen the bolt in the cheekplate fail on another machine.
But I'll take a look from a different perspective.

 

[NoWingsAttached]

I wonder if the engine is pushing straight ahead or if it is pushing to one side. Sounds a bit like the engine isn't lined up with the birdie.

 

[phantom]

it could be something up front creating a sideways pressure, at one time I put the body on a gyro and did not need the rudder offset any more, without the body it needed the rudder offset, turned out that the body was not lined up with the keel.

Norm

 

[GyroRon]

So Larold.... did you fix it?