Posted for "Angier M. Ames" <N2811a@comcast.net>:

Hi Marv,

Several weeks ago and before beginning the balancing process, I did eliminate a significant source of friction. The left elevator inboard hinge bolt holes did not line up perfectly with those on the other hinge half attached to the HS. The elevator hinge half was determined to be .034 low. This was corrected by slotting the hinge attach holes downward .034 with a 3/16 endmill in my Bridgeport...a really useful tool to have kicking around.

Now, with the elevators attached and bolted together at the center weldment, but without the 4 hinge bolts being tightened, there is very smooth motion.

All five hinges on the HS are well alligned as evidenced by slippery smooth motion of a 1/4" stainless shaft riding in the bearings. Each elevator half must be balanced separately and this is much more easily accomplished on the bench rather than the plane.

"I think what you are experiencing is a result of the friction between 1) the bushings and their axles, 2) the bushings and the hinges, or 3) a combination of both."

Actually, I don't think this is the case. Before machining the bushings, I simply substituted the .063 stainless pins for the 1/4" bolts on the bench and observed the same result.

Now, if the elevator is 100% mass balanced and the hinge is located on the spar centerline, my twisted logic would lead me to think that one could place the elevator in any position from in trail to 90deg up or down and it would stay in that position. Doesn't seem to work that way though. What do you think?

Angier


[Angier, you've got me there.  But, when I think about "100% mass balanced" I have a hard time accepting that that one can achieve that condition when dealing with 50%+/- of the assembly at a time when perform the balancing. While you might be able to perfectly balance the elvator halves separately, the act of joining them together is going to create a new assembly with different dynamics than the parts of the whole disply on their own.  While your 1/4" stainless shaft might float easily through the bearings, remember that the ball part of the bearing is going to be locked to the hinge brackets with the attach bolts, and that the bearings balls' motion in their races are what govern the rotation of the elevator.  After you've roughly balanced the 2 halves of the elevator I would suggest that you assemble it to the stab with the proper sized bolts and nuts tightened to the proper torque, and check the balance again.  Treating the assembly as a unit is going to give you a truer picture of what you're going to be dealing with on the finished product, and that's where the balancing is going to have to work.

I know that it's close to heresy to suggest that you might not need to strive for perfection here, but getting as close as reasonable prior to painting is probably what you should be shooting for.  Once you've achieved a level of balance that logic says is right, I'd go ahead and overbalance the counterweights by an ounce or so.  The final result is going to be determined by the amount of filler, primer and paint that will ultimately be applied and you're probably going to have to adjust the end result slightly after all the finishing is completed.  If you really want to be anal about it, I suspect the proper way to balance the elevators is to actually balance the entire "pitch control system", as the addition of the pushrods, bobweight, control sticks, trim system, and all their associated hardware are actually going to enter into the picture when all is said and done.  IF that is actually the case (you aero guys out there need to correct me if I'm way off base, please!), then getting the elevators to within an ounce or two of perfection at this stage should allow you to get on with the building process.  You gotta draw the line somewhere.  At least that is my humble opinion.

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