DeltaRomeo

DeltaRomeo

doug reeves: unfluencer
Staff member
I'm curious if anyone has a cockpit-adjustable rudder trim on their RV-4/6/7/8/9. My old trim tab fell off (taped on) and the ball in the T/B was never really 'right in the middle' when it was on. Before I stick on another one I was entertaining the idea of building another rudder with a movable tab. Sometimes I'm full throttle (traveling) and other times I'm quite a bit slower (formation practice). Calls for different trims...if you wanted to be a stickler.

Anybody have a picture online or some text?

Best,
Doug
 
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Idea only

Dougie

I've often thought of the same project. In my mind (no comment), I think it would be easy to fabricate either a manual or electric trim for the rudder. All you would need would be to attach a servo coupled with a spring to the (right) rudder cable. This would allow increased "pull" on the rudder in one direction to account for the torque. To take it a little farther, you could even attach a Ray Allen LED guage to indicate amount of trim.

I may attempt this, but am more anxious to just finish.......maybe during the conditional?

Hwood
 
I should have clarified in the first post that I was thinking of a simple manual trim setup with no visual indicator (check before flight). A small verneir knob under my left knee - that sort of thing.

b,d
 
Another idea

Well.......then here is an idea I have seen that works quite well.

Carry a little spring clamp and when at cruise, while holding the proper amount of trim, put the clamp on the rudder cable as it comes out of the spar box, thus holding the proper amount of trim. (Really, I have seen this, but you must be from Alabama to appreciate it!)
It actually works quite well.
 
On my -6, I installed springs to keep the rudder pedals from falling slack when parked. I extended the metal straps that connected the pedal to the cable so that I could put an additional hole forward of the pedal. Attached a spring to that hole and to the gusset on the firewall. One spring for each pedal. Then, I shortened the spring on the right pedal, which put a little more pull on that pedal, effectively providing rudder trim. After a couple of experimental tries I got the spring tension to where the ball was centered in cruise. Worked great.
If you want it adjustable, you can attach a vernier cable to the firewall end of the spring to change the spring tension and adjust rudder trim to your liking. You should never have to apply any pressure to the left side so attaching to the right side only should work just fine.
 
I like SF's idea of doing it with a spring bias (although the Alabama method does have it's appeal for simplicity!) rather than makign a new rudder - unless I was making a new rudder for some other reason. Thinking about doing the mod to a flying airplane, it seems a whole lot easier to work in one place than to have to run cables or even wiring all the way from front to back....Of course, on an -8, you can take the forward baggage floor out, and it's easy to get at the place between the pedals and the firewall - that might be uglier on a 6/7.

My thought on doing it aerodynamically Doug is that the tab required is so small, it seems a waste to do a lot of metalworking and mechanicing to get what you need.

Paul
 
Good points SF and Paul! SF, could you take a picture of your setup sometime when you're out at the hanger? Your idea seems very interesting (and much less complex than a new rudder).

B,
D
 
I like the idea of a spring bias as well because it would work similar to the manual spring biased aileron trim which most people seem to like for it's simplicity and effectiveness.
The trick now is to decide the best place to install the springs themselves, and to set it up where the lever to control it is in a practical location.

I like where this is going.
 
Unfortunately, I can't take a picture, since the plane now resides in merry old England!
However, I can say that it was very easy to install, since I did it after it had been flying. The springs I used came from Home Depot and were really inexpensive.
My method was to place a piece of wood between the gusset and fuselage skin at the firewall. (The vertical gusset at the bottom outer corner on each side.The wood makes sure you don't drill into the skin.) Then I just drilled a number 40 hole to capture one end of the spring.
At the rudder pedal, there are two parallel pieces of steel that bolt to the rudder cable clevis and to the rudder pedal itself. I just made a longer version for the outside/fuselage skin side of the pedal attach point with the extra length to the forward side of the pedal, drilled another hole and hooked in the spring. Oui La!
On my -8, I plan to do something similar by hooking the spring at the arm where the rear seat rudder pedal option hooks on and extend the spring forward to the landing gear column. This will take the adjustable pedals out of the equation.
Aren't experimental aircraft wonderful!!!
 
Adjustable rudder trim on a -6

A friend of mine ,Pat Hatch ,built one on his -6. Look at Van's website under -6 builders for Pats link. He has built 3 very nice RV's,and knows his stuff..I believe its electric, but can't remember for sure.

Bill E.
 
rudder trim

Doug,

I saw exactly what you are asking about on Danny Parker's RV-6. If memory serves me correctly he had the early thinner skins on his rudder and the prop pulses from the big Harzell/0-360 formed a couple of cracks on the trailing edge. His remedy was to cut out that section and he installed a small adjustable trim tab that he fabricated himself. The work was truly beautiful and he ended up with a better airplane.

You should be able to find him through the Livermore, CA chapter. If your going to do this Danny's design is a great way to go.

FWIW, Danny was the person responable for getting me into the RV hobby. For 5 years he answered my questions, let me read his RVator's, and listened politely to how one day I would pull the trigger and build one of these too.

Best,
 
Rudder Trim in VAF Newsletter

I've held onto a reprint of a rudder trim system devised by Jim Cone, and featured in an older VAF Newsletter. You can see it, complete with a hand drawing and photos at http://bmnellis.com/BuilderIdeas.htm. Click on Jim Cone Rudder Trim.

Haven't made one yet but I might although my EPM Av wedge is doing a good job. www.epm-avcorp.com/trimtab.html. I used the best 3M double stick tape I could find, then did a fillet around the edges with JB Weld for Epoxy.
 
Bob, that is perfect! Thanks for finding that URL!!!

When my first EPM trim tab fell off awhile back (on with bad tape) I immediately felt a strange vibration in my feet. My first thought was flutter so I quickly powered back and cautiously flew back to the field and landed (with an elevated heart rate). What it was was about ten inches of tape still stuck to the rudder fluttering in the breeze (so I guess it technically was flutter <g>).

Scared the bageebees out of me for a second, though.

b,
d
 
A builder in Little Rock designed a rudder trim system (but never installed it) that worked a little different. It was an airfoil of sorts that would attach under the fuselage and be deflect-able from the cockpit. The airflow would be disrupted enough to induce yaw. Forgive the poor artwork - I think it gets the idea across. Of course the only thing below the skin is the airfoil - the pulley, arm, and cables are all in the fuselage.

ruddertrim1be.gif



ruddertrim28xf.jpg


ruddertrim7wv.gif
 
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Two options

Doug,
You might try contacting Mike Seager. Mike has more time in RV's than anyone and has built two different types of rudder trim systems for his own aircarft. He can give you commentary on both, as well as things he's tried that have not worked out so well. In a nutshell, he much prefers the system built into the rudder ala the electric MAC trim system as opposed to the spring bias type, although they both will work. He has installed them as retrofits to an existing rudder and has also built them during the construction of new rudders. You can probably guess which was easier...Good luck!

Bob
 
Rudder Trim

I built an electric rudder trim into my RV-4 rudder from the outset. It is about 3x6" in size, it should have been a bit larger. With the speed range of the RV-4 I thought it was desirable. I followed the elevator trim tab construction method, and utilized a MAC trim servo to move. This was before Van came out with electric trim, and I didn't want to put the servo mass in the rudder without any counterbalance, so I mounted it in the aft fuse and ran a short bowden cable to the tab, again in similar fashion to manual elevator tab. I flutter tested to Vne with no problems. I run out of right trim in a full power climb, so a larger (higher aspect ratio) tab would be an improvement.
 
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