Rudder Trim - Sneak Preview

As some of you know, I have been slaving away in the shop working on rudder trim for my -10. This was my first deviation from VANS plans and as I learned, when you're working off a blank canvas, things go MUCH slower.

I thought rudder trim would take 3-4 days and I'd be on to the next thing. The truth is, it took me 3 weeks. Not so much beause it was difficult, but because I would come to a road block and have to take a break for the night. Usually, by the time I woke up, I'd have a soluton. Then it was back to the shop until I hit the next road block. When you're off the beaten path and your doing your own design, there seems to be many obstacles.

Let me start by saying thank you to Vic Syracuse for helping me through some of my builder rookie questions. I took his Rudder Trim design and refined it a bit. Vic was a great help!

With all the respect of those who have gone before me, I had a couple of goals.

A) I didn't like the screw forest on one side of the rudder. I don't like having the door screws mixed in with the servo screws. To my eye, having them all grouped together looks unorganized. I started this project trying to avoid the "Honey I shot the rudder with a shotgun" appearance. Painted or unpainted screws, that was simply a look I wanted to avoid.

B) The servo isn't mounted parallel to the rudder stiffiner holes. So you end up with holes that just don't look straight. One screw is higher than the other. It just didn't appear real organized.

C) I wanted the exit fairing to be level and I wanted the push rod to exit the rudder level too. I don't like having the fairing angled upward (perpendicular to the Trailing Edge).

In general it needs to look clean and the lines need to be consistent with the airflow across the plane. Your eyes sweep the countours of the plane from front to back and the rudder trim needed to blend in with those lines - not stand out.

So off the to shop........

First I made some test fittings of the trim tab and the servo. I found that the traditional "L" brackets just didn't work too well. The clevis kept bottoming out on the bracket when it was fully extended. So I came up with this design. It allows the clevis to rotate around the "L" brackets with clearance beyond the .7" that the Ray Allen T2-7A servo travels.





Next I found that if I wanted the push rod to run parallel to the ground, it would still bind on the sides of the brackets because it was pushing them at an angle and not in-line. I came up with bending the ears on the L-brackets to match the angle created by the trailing edge of the rudder and the stiffener lines.

If you look closely at this photo, you will see two lines. The red one is perfectly perpendicular to the trailing edge. The black one is drawn parallel to the stiffiner holes. This is the line I want the push rod to operate on. I clamped the brackets together and laid them against the trailing edge. Then I used a hand seamer and put a bend in the ears so they matched the black line. (Look closely, you'll see they are angled a hair to the right.) - After I completed the bend, I drilled the 1/8" hole for the clevis pin to ride in.



You can see how the clevis rides on the brackets in this photo.



So that took care of the problem of getting the servo mounted squarely, having the push rod run parallel to the stiffiner holes, and have the fairing be mounted perfectly in-line with the lines of the aircraft.


(Continued in the next message)

... continued

Now, what to do about all those screws!!

I came up with a different idea and decided to mount the servo inside the left rudder skin and put an access door on the right rudder skin. This would put four (organized & parallel) screws on the left side of the rudder. It would also put eight (organized & parallel) screws on the right side of the rudder to hold the access door in place.

In order to mount the servo on the inside of the left skin, I had to create a doubler to keep from bending the skins. I created a doubler made from 5" x 5" x .032". I cut a lightening hole in the middle of it. Dimpled it and put it into position. All the rivets holding the doubler in place will be flush 3/32" rivets and ultimately painted over. All that will stand out are the four screws holding the servo in place.

Now the access door. I created a doubler for the access door out of 6" x 6" x .032". Cut a hole in the middle, file it down, deburr, and dimple. (Sounds simple, but it's a pain).

Anyway, this photo will give you some idea. You're looking at the right side of the rudder and through the access door. You can see the servo doubler on the other side.



Here's a little closer look.



Here it is with the servo mounted in place.



Once you put the door on it, it looks like this. The door is parallel to the stiffiner lines. You can see the eight scews that will hold the door in place. On the right side of the rudder, you'll only see these screws evenly spaced and organized.



Here's a photo of the other side. You can see the four scews that will be holding the servo into position. They're inline with the stiffener lines.



I just cleco'd it all together and I had to take some photos! I wanted to wait until it was all riveted before I let the cat out of the bag, but I couldn't wait.

Once I get the parts primed and riveted, I'll come back with some cleco free images.

I hope this gives some of you your own ideas too.

Phil

I just learned another lesson. I was putting the fairing on and when I did a test run of the servo, I discovered the cleco in the very front of the fairing (the one missing in the photo) will rub on the push rod.

It's close enough to the pushrod that when I dimple and rivet, the rivet will probably touch it too.

Another lesson learned.

I'll get an order placed with Spruce tonight and get some new fairings sent in. On the next one, I'll put a rivet on each side of the front, instead of only one directly over the push rod.

Now you all know, I'll have a little rider hole hiding underneath that fairing.

Phil

There are lots of ways to skin the cat.

If I was building one of the smaller yank and bank RV's that just had a basic VFR package, minimal interior layout, and just a simple plane; I definately would have considered something barebones, simple, and easy.

But my plans for the -10 are higher. I'm looking for a much more integrated airplane when it's all said and done. So a couple of weeks extra work isn't much to ask and worth all the trouble.

A little more info please

RV7-N263JK said:

Why go to all this trouble including having to flutter test the rudder, when a simple cable clamp on the rudder cable going to a vernier control works great and is very simple. Piper had this on all the Comanche aircraft and never had a problem

Click to expand...

I'm having a tough time envisioning this, could you provide a little more information? It seems to me that a vernier control clamped to the rudder cable would impede free movement of the rudders. I'm obviously missing something.

Thanks

Quote from Phil.

"In general it needs to look clean and the lines need to be consistent with the airflow across the plane. Your eyes sweep the contours of the plane from front to back and the rudder trim needed to blend in with those lines - not stand out".

I agree totally.

Which is why I am looking at cutting a tab out of the rudder, instead of scabbing a piece of hinge on to the back of the rudder.

This will also allow internally driving the tab, no rod/clevis/fairing sticking out.

As to the spring on the cable setup, a buddy and I have tried it on his 10, so far with three attempts, we still havent gotten it to work correctly. The spring tension is quite a balancing act------you need enough tension to actually pull the cable, but not so much that you make the rudder pedal "feel" go screwy. At this time, we have a teeter totter like arrangement, driven by the servo, with a spring to each cable. I am now thinking if this type of setup is going to work, it is going to take a fixed spring to bias in right rudder, and a second spring working in opposition to the first, to relax the preset tension.

There are a couple of benefits to this kind of trim----if we can get it working, that is. One, it installs into the tunnel, no need to cut into the rudder, and two, easier to retrofit into a flying plane.

As the rudder sees almost no aerodynamic balance from the counterweight side area, the trim load is virtually totally carried by the spring.

Spring bias works well on the ailerons, I suspect because they are aerodynamically balanced, one up, one down, forces opposing, so only a small load needs to be carried by the trim spring.

Hey Mike,

I've been kicking around that same idea, but I haven't quite nailed down a design for it yet. I've got some ideas, but nothing I feel real good about.

Before the project is done and if I happen to stumble on an idea, I will build a a second rudder and see how it works.

In the mean time, I'm going to continue on......

Phil

PS: I've heard the same thing about the spring bias. I know a few who have tried it and none of them have been happy.

Phil, well I suspect you will get there before me, as I am just about to get the panel installed, still a long way from actually doing any work on the rudder trim. I did however, install a rudder trim indicator, and the stick has a two axis coolie hat wired for rudder.

But the mental/planning stage is in full swing.

I really was hoping for the spring bias/rudder cable thing to work, even had thoughts of kitting it---------install with two clamps, and four screws, in the tunnel, wiring a cinch.

Oh, well.

Hi Phil,

Well...I had 2 replies for you....the first was just to say to bag the hinge idea but, I'd thought it best to at least offer a suggestion ....so:

I can tell from your posts and the pics that you've supplied (nose ribs) in the past that you're striving to build the best that you can.

That said.....IMHO a mini tab such as the elevator trim would blend in with the rudder better....or even a glued on wedge or riveted metal tab as has been used countless times in the past (and can be added later if required). The hinge will probably function OK....but......let me try to be as tactful as I can here..........it's more of what I'd expect to see on a quicksilver ultralight than on an expensive RV10 like you're building. IMHO....the piano hinge doesn't compliment the beautiful work you did on the access panel and the fairing.

Looking at the pics I don't think it's too late for you to convert over to a basic tab like on the elevator. Would be relatively easy to build and would blend right in with the rest of the rudder. I might have some wedge material left over from another project if you need some??

Keep in mind that I'm real picky....for me it has to not only function properly.....but it has to look like it came 'from the factory'. FWIW.....I put NO rudder trim on my RV10 and have never felt that it 'needed' one.

Good Luck with whatever you decide.

No harm no foul, Rick!

I am in complete agreement with both of you.

Since I couldn't come up with a piano-hinge-free idea, I went ahead and plagiarized a couple of other designs and then added a few more touches of personal taste.

It's really far from perfect, but it's a few steps closer to something easier on the eyes. (At least in my feeble mind.)

I'm really hoping that working on the elevators will give me a chance to explore some other ideas and come up with something even cleaner and more integrated. If I do come up with an idea, I'm not too proud to start over again and build another rudder. (Heck I already have 2.25 Vertical Stabs in the garage.)

It's definitely not the the last time I'll visit rudder trim. But it is enough to get me going with a little cleaner design...

Phil

Ha......it's kind of like having a friend who gets a 'not so good toupee'.....you could look the other way....but if you are REALLY his friend you tell him . (Hope nobody reading this has a 'bad toupee' ).

I think I'll enjoy watching you build your airplane from the sidelines as much as I would enjoy it doing it myself .

Alrighty, I finally took some photos of it tonight.

Here you go...

If you're willing to cut the trailing edge of the rudder, you could use the same method that we use for the elevator trim. I've seen it done on ailerons and it looks factory made. I think the push rod was even hidden on the inside of the tab, but that could be my imagination.

Looking Good!

I think taking the extra time was worth it.

Your servo installation looks better than Pro.

My thoughts:

Your tab may be of more length than necessary.

The hinge you are using looks like the rolled hinge and not the extruded. This may not be good especially with the length. The softer material hinges can be bent easily even with the fingers.

If this gets bent you could end up with some strange harmonics and possibly flutter.

On Vans Aileron trim tab that they provide as an option is only about 6" as best I can remember.

Do you need to balance this assembly? (I don't know)

Your actuator tab is thin aluminum and subject to high levels of stress especially when not in the straight trailing condition.

I suggest you make the same config for the actuator tab out of two pieces of .025 or .032 4130 sheet, and then plate or prime it right away.

I know I am going on and on, but flying brothers that are reading this, a fluttering trim tab means a fluttering control surface, and besides Ice or Cumulo Granite there would not be much worse.

Consider a comparable speed aircraft in the certified realm, you will see what seems to be overkill on the "trim tab" design itself.

This is what I did, for my left aileron, caveat, it has NOT been flight tested either.

http://www.vansairforce.com/community/showthread.php?t=14993

Tom,

I really really like that trim-tab and it's similar to what I want to do on my second rudder! I just couldn't quite visualize it.

Hmmmm. I might try building the second one sooner than I thought.

Send me a PM

Phil said:

Tom,

I really really like that trim-tab and it's similar to what I want to do on my second rudder! I just couldn't quite visualize it.

Hmmmm. I might try building the second one sooner than I thought.

Click to expand...

Send me a PM

I think I have a lil chunk of structural (Extruded) hinge in my garage.

When you make an effort to do the super custom tab be patient with yourself, it took me at least three tries to get the tab to actually match the trailing edge of my control surface and still have that non hinge side radius work properly.

Make sure it cant over travel and jam either.

You also will want a false spar (like the elevator where the hing attaches) and a rib above and below the tab cut out.

Disclaimer, I ain't no engineer, heck I don't even know how to drive a train!

RV-10 Electric Rudder Trim

I have finally finished my Electric Rudder Trim on my RV-10 this past weekend. The airplane is now back together, but the weather in the mid-west was freezing rain all weekend and I didn?t get a chance to flight test. But initial testing with a fixed trim tab would indicate that this should meet my design requirements.



Pictures are suppose to be worth a thousand words, so I will save myself the typing and post lots of pictures instead.





http://picasaweb.google.com/rdoerr10/RV10ElectricRudderTrim





Thank You
Ray Doerr
40250 (N519RV ? 341 Hrs)

Ray, I like it!!

Waiting for the PIREP.