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Rudder Balance Question

SHORTRV7

SHORTRV7

Well Known Member
So my airplane is now painted and currently balancing Rudder, Elevators needed 8 Ounces on left and 5 ounces on right done independently, all good!
But the Rudder needs 26 ounces, seems like a lot to me. The 30.8 inch pounds Balance Limit in the instruction manual isn't making since to me! Looking for answers or explanations from you all!!
Did you balance your Rudder?
 
Remove the rudder from the airplane. Hang it from two wires through the top and bottom rudder hinges hinges. Adjust the wires such that the hinge line is level with the ground. The rudder will probably rest trailing edge down.

Now, either find some known weights or find yourself a set of fish scales with good resolution in the low weight range.

If you're gonna use weights, you measure from the hinge line to the front of the counterbalance. Say that's 8". Divide the spec'd 30.8 inch pounds by the arm you measured (8"). 30.8 inch*pounds/8" = 3.85 pounds. Now, hold the rudder horizontal and put some sort of protection on the counterbalance. Then stack weights centered on that 8" location on the counterbalance until the rudder is balanced level like a table. If you need less than 3.85 pounds of weight on the 8" station on your counterbalance, you're within spec.

The other way is measure from the hinge line to some point on the trailing edge. Say the measurement is 12". Now, divide the 30.8 inch*pounds by the moment arm (12"), and you get 2.56 pounds. Using the fish scales, lift the trailing edge from that point and write down the required "pull" to bring the rudder to level (like a table). If you needed less than 2.56 pounds of pull to get the rudder to balance around the hinge line, you're within spec.
 
Kyle I have the rudder off and have the top and bottom hinge points horizontal. I can get it to be a table top with 26 ozs of weight which is below the 30.8 at the weight location. Is that what I need to call it balanced?

I think I see what you are saying, so if where I want to put the weight I would divid the 30.8 by 11 inches equal 2.8 Lbs which would be acceptable ?
 
Last edited:
SHORTRV7 said:
Kyle I have the rudder off and have the top and bottom hinge points horizontal. I can get it to be a table top with 26 ozs of weight which is below the 30.8 at the weight location. Is that what I need to call it balanced?
Click to expand...

Where (what distance from the hinge line) are you placing the 26 ounces?
 
I think I see what you are saying, so if where I want to put the weight I would divid the 30.8 by 11 inches equal 2.8 Lbs which would be acceptable ?
 
SHORTRV7 said:
I think I see what you are saying, so if where I want to put the weight I would divid the 30.8 by 11 inches equal 2.8 Lbs which would be acceptable ?
Click to expand...

Yes, if you placed 2.8 pounds 11 inches from the hinge line and the surface balanced, the surface would be within tolerance without attaching any additional weight. Just bolt the rudder on and fly.
 
Balance

Could you point out the manual section and page please?
I can't find that and need to make sure it's noted in my "to do" list.
 
Unless something has changed since I bult my mine, I don't recall the 10's plans don't having you statically balance any of the flying surfaces. IIRC I believe that some other models have you do this, but not the 10.
 
Auburntsts said:
We know what flutter is. The question is where in the RV-10 plans does it detail the requirement and/or process for statically balancing the control surfaces?
Click to expand...

I don't believe it is in there. I thought it odd and called Vans. Answer I got was we did it for you with packaged weights and it has a good margin available for adding paint. They said unless you go nuts with paint thickness it will be fine, as the margin is pretty good. It made sense to me, as the elevators were at least twice the size and weight of the 6, so stands to reason that the margin would also increase.
 
I really wish Van’s would provide definitive guidance on control surface balancing requirements.

On my first build I was paranoid about elevator balance. This lead to shaving the provided weights enough to get static balance. After paint I quickly realized this was a mistake as I then had to cut into my (filled and finished) elevator horns to add lead shot.

Moving to the next build (RV-10) I called Van’s on “why are the kit elevator counter weights too small?”. Even before paint the trailing edge would go low. The answer I got was “balance does not necessarily mean static balance”, as in balance is for flutter. So I left them as is and the plane has ~1800 hours on it, never an issue. On the next project (RV-8) I bolted the weights on per plans - done.

I would extrapolate this to the rudder counter weights. I would also point out that there a many flying RVs with no rudder counter weights.

I suggest you build per the plans. If you are very concerned call the experts at Van’s.

Carl
 
There absolutely is a table for measuring the balance on the surfaces for the -10. I’m not where I can access it at the moment, but it certainly exists.

It is in the same table as the control deflection limits.
 
Kyle Boatright said:
There absolutely is a table for measuring the balance on the surfaces for the -10. I’m not where I can access it at the moment, but it certainly exists.

It is in the same table as the control deflection limits.
Click to expand...

Kyle is 100% correct -- I found said column in the table that has the max and min travel limits for all of the control surfaces. It's in the Flight Test Section of the plans. Here's the Column:

Balance Limit (in-lb)
Trailing Edge Heavy
Elevator - 37.5
Aileron - 6.8
Rudder - 30.8

Unfortunately, there's absolutely no verbiage in the accompanying paragraph about said numbers, there meaning, or any process as performing a check or applying any corrective actions for an out of tolerance condition.
 
Auburntsts said:
Kyle is 100% correct -- I found said column in the table that has the max and min travel limits for all of the control surfaces. It's in the Flight Test Section of the plans. Here's the Column:

Balance Limit (in-lb)
Trailing Edge Heavy
Elevator - 37.5
Aileron - 6.8
Rudder - 30.8

Unfortunately, there's absolutely no verbiage in the accompanying paragraph about said numbers, there meaning, or any process as performing a check or applying any corrective actions for an out of tolerance condition.
Click to expand...

Going back to post #11, it appears that a normal build will have adequate margins, by design.
 
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