Elevator/Rudder Balance

[mccarlie]

I'm trying to figure out how to check my balance on each elevator (left hand & right hand). I have painted my airplane with the wings, V & H stabilizers, and control surfaces off. I have checked my ailerons and found them to be right in the middle of 0.0 to 11.31 in lbs. I need to do my rudder and elevators next. I believe I understand how I'm going to do my rudder at the two Hinge/bearing points, but the elevators with only one Hinge point (no bearing) on the outer part of each elevator is a little confusing to me. Do I set one mandrel under the Torque Tube of each elevator, and the other mandrel under the bolt in the only Hinge, even though the Torque Tube is set back from the line of the Hinge line when the two elevators are connected? (I hope that makes sense)

I have a copy of SNL86-44. Thanks, Doug.

[GAHorn]

Install the elevator torque-tube "pylon" assy (Fig 16, item 5) on the inboard-end of the elevator to be balanced, and use the hinge-point of the pylon for the inner balance-point.

click to ENLARGE

[mccarlie]

George, Thank you for helping me understand the proper way to check the balance on my elevators.

Do you or anyone know the actual weight and size of the lead weight they installed in our rudders at the factory?

[GAHorn]

I started to smart-off and respond with the size as $235.75....

But that would have been only a guess!

If your rudder has no wt, simply lay lead wts on the horn until the balance is correct, then melt them down to the proper shape, and install with Cherry Rivets.

[marathonrunner]

I have painted a number of Cessna aircraft from the 170 through the 206. I have never had a balance or weight problem with the rudder and elevator with the orginal weight installed. I have had to add weight to the ailerons on several though. Also if you have a STOL kit you may need to determine if they had any balance weights added. I do know Robertson did. It is not always cut and dry out of the Cessna manuals.

I suppose it also depends on how heavy a paint job was applied. More is not better. Speaking of balance wieghts on ailerons, when preflighting run your hand over the weights to make sure the buck tails are there. I have found them missing and needing reinstallation on a lot of aircraft.

[Indopilot]

Might need to stress cherry rivets and not Cherry Max rivets. Difference being the steel stem of the Max can make things difficult if the weight needs to be removed and replaced. Brian

[GAHorn]

The rivets to hold the weights are NAS-445 (CR163C-4-2 and -8) (Modern designations are CR9163 and can be found in corrosion-resistant grades also.)

Interesting thing about counterweight attachments, I've seen everything from cherry rivets to PK screws. (I've also seen common industrial "pop" rivets.) The important thing to remember is:
1- Inspect for looseness of the rivet and weight on EACH PREFLIGHT.
2- Inspect that rivet/screw does not back out and interfere with the stabilizer outer-rib. (If it does, it may prevent a deflected control surface from being capable of full movment and MAY actually LOCK the controls in flight.)

As marathonrunner mentioned...the aileron counterweights should be inspected EACH PREFLIGHT not only for being "present" but also for security of attachment. VISUALLY and TACTILE-LY check for complete rivet attachment.
(The location and design of these ailerons allows moisture and ice to slide off the wing trailing edge and drop down onto/into the lower skin of the aileron exactly where the weights are. If the water seeps between the weight and the skin, then freezes...it can loosen the weights from their attachment. Flying the airplane with loose weights OR ice in that area can cause LOSS OF the AILERON/CONTROL.)

[n2582d]

Cessna's Service Letter SE 71-27:

It's surprising to me that Cessna did not include the 170 in the list of aircraft this Service Letter applied to. I've found this to be the case on other Service Letters as well; many list the 172 but not the 170 when in fact the problem being addressed is common to both models.

[GAHorn]

Excellent post, Gary!
All: Those MS20470 series rivets are univeral-head AN470 types...used on aileron counterweights....NOT self-expanding rivets such as used on elevator and rudder counterweights.

[mccarlie]

I was hoping someone might know the actual weight or size of the lead weight they installed in our rudders at the factory. Because, unless I'm making a mistake in my balancing procedure, (my wife will remind me from time to time, to take the blinders off) I'm confused about my rudder being way out of balance.

I personally painted my aircraft and painted all my control surfaces, with care not to be paint heavy, with the trailing edges pointed up. I lean towards my balancing procedure being correct, because my ailerons balanced in the middle of the limits and both my elevators balanced at the farthest limits allowed, which doesn't surprise me. I also primed the inside of all my control surfaces, but they balanced within limits.

My caluations show my rudder to be very, very light in the trailing edge, and I need to remove 4.83 lbs of weight from where my lead weight is located to balance. I'll be surprised if there is that much lead weight in there; besides, I could see being a few oz. off +/-, but not a few lbs.

If you notice in the picture above, at the rudder leading edge tip you can see that there is a weight installed and exposed at the tip. I know that from that exposed weight tip back to the second small oblong hole where my weight installed ends is 5.5 in. From that hole straight across (or up if installed on the aircraft) to the leading edge touching that weight (using a 90 degree scribe) measures 3.5 in. If no one knows the actual weight and size of this lead weight, can anyone confirm the size for me in their rudders using a scribe like I did? It would help me to know if I have the original weight or not. This is a process of elimination to find where the mistake is. Do I have the wrong lead weight installed, which means myself and previous owners have been fortunate while flying this way, or could it be possible the SNL 86-44 limits (4.00 lbs at +23 in. to +27 in) have a typo for our rudders? My rudder is balancing right now with 4.00 lbs at +8.5 in.

[marathonrunner]

4 pounds is correct. I have a hard time believing that you have too much paint. I also reskinned my rudder with primer inside and out. I painted it and it fell well within lmits. Without actually looking at the way you are checking the balance I would think maybe a problem in that area. It looks correct in the photo though. If you want to call me my number is 907-947-4017 and I would be happy to talk to you about it. As a wise old mechanic once told me..."You can do the same thing wrong for years and call it experience" I always like a mystery like this one. Keep us informed. This is just my initial gut shot but I will think it through and see if I can come up with an answer. I do not have my plane here to confirm your dimensions on the lead.

[c170b53]

Where is your weight located when the surface is parallel? And I could be all wrong but 24 "inches /per pound. The factory balance weight being 4 pounds. If you're using a 4 pound balance weight on your balance beam and you're arriving at 8.5" to parallel, then you are underweight

[mccarlie]

Where is your weight located when the surface is parallel? And I could be all wrong but 24 "inches /per pound. The factory balance weight being 4 pounds. If you're using a 4 pound balance weight on your balance beam and you're arriving at 8.5" to parallel, then you are underweight

I,m not exactly sure I understand your question or where the 24 in./per pound is coming from. I'm using 4 lbs on my balance beam and that balances my rudder at +8.5 in. in front of my hinge line. If I put the same 4 pounds on the balance beam at a minimum of +23 in. (according to Cessna's limits) in front of the hinge line it takes 2.5 lbs at my trailing edge (if I reminder correctly is about -26 in. behind the hinge line) of the rudder to balance. So, I agree my trailing edge is underweight. That's why I need to know the original size and/or weight was installed in our rudders. And if anyone using a scribe, safety wire, or anything similar and next time they are at their 170 could swing their rudder to one side or other and go up through that second hole and confirm or close guess to size of their weight would help me. Thanks, Doug.

[sfarringer]

You mention that you believe that you want to balance with 4 lbs at 23 inches. This would be a moment of 92 inch-lbs.
The balance table attached to Cessna SNL 86-44 tells me that the balance moment should be +23 to +27 inch-lbs.
If you are using a 4 pound weight on your fixture, then you want to achieve balance with your fixture weight at 5.75 to 6.75 inches in front of the hinge line.
Cessna SNL 86-44 also says that the weight installed in the rudder by the factory was 4 to 4.12 lbs.

[c170b53]

Sorry I was going to follow-up on this but got busy elsewhere. From the service letter the balance moment is in distance and magnitude of inch / for one pound. Therefore one pound at 24" fwd of the hinge line should balance your flight control. Since you reported it balancing at 8" plus with 4 lbs that means you're under weight with reference to the weight. You need more lead not less. Use a one pound weight to reduce errors and you'll probably find yourself in the correct ball park. It stands to reason that the factory applied minimal paint and therefore your adding of weight to the surface will result in an underweight condition but again unless someone has added internal repairs you'll be close.