460 hours - finish trimming excess HS skin and check elevator alignment

Every so often during the build, probably more frequently than I am willing to admit, I have an episode of utter stupidity. Such an episode was experienced when I was trying to perform a preliminary alignment check of the elevators the other night as I described in my previous post. Short story is that I think everything is alright now, and my elevators may only be off by about 1/16 of an inch or so. So it is not as bad as I made it out to be in my previous post, and I will explain why as I work through the pics from today's activities.

I may wait to drill the center bearing hole in the control horns  until the tech counselor comes over to inspect my work, to see if I should go ahead and ajust one of the elevators to ensure that the trailing edges are completely aligned with each other.

I have a feeling that this is one of the things that may cause what some people end up describing as a heavy wing on their first flights - misaligned control surfaces or stabilizers, or both. This can result in differential lift between the two surfaces, and the plane will react to that condition accordingly. The question that I must eventually answer for myself is if a 1/16 inch difference is enough to warrant the adjustment, or if I can proceed "as is" with little or no potential impact? I am not after perfection, but I also know that misalignments ultimately result in increased drag as a result of the counter measures that are required to correct them. This, then, will also affect the overall performance of the aircraft.

So with that, here we go with today's exciting adventure....

First pic is of the elevator/HS assembly on the table. I got rid of the foam underneath, replaced that with my drill board, put  a couple of rubber tool box liners on the board, and then set the HS on top of that. I then put another piece of tool box liner over the top of the HS, followed by a long 2x4. Then it just worked out that one of my 4x4 padded blocks, standing on its end, was just about the right size to allow me to clamp it in place to keep the HS from flipping over backward.

Remember that you can click on the pic to make it bigger to see more of the details. So why did I need to do all this special clamping? Well, previously I had the HS turned upside down. The control horns are facing up in this case, making it easier to work with the entire assembly on the table without worrying about everything tipping over. Unfortunately, when everything is turned right side up, the control horns are now facing down. This makes it somewhat difficult to safely position the HS so that both elevators can swing  up and down freely, which is what I needed to do today.

You have to allow the HS trailing edge to hang over the edge of the table or bench, to allow the control horns of the elevators to acheive their entire range of motion. The elevators are then mounted completely off of the table. This raises concern that the weight of the elevators may cause the whole thing to come sliding off of the table, so I wanted to be sure to prevent that from happening.

The above pic also shows the top edge of the HS skin at the tip where the counter balance arm of the elevator is located. So I marked and drilled and cut the same way that I did for the bottom skins, and now the elevators can swing freely through their entire range of motion, limited only by the orientation of my temporary hinge pin placement (top or bottom):

The first pic above shows the completed trimming of the right side top HS skin. The clearance with the counterbalance arm per the plans is a minimum of 1/8 inches. The second pic above shows the 1/4 inch hole drilled on the left side, just prior to using the dremel cutoff wheel to cut the excess aluminum away. This pic is also a bit deceiving, because the elevator is actually in the up position, and therefore the counterbalance in the pic is tipped downward toward the floor.

The elevators are actually overbalanced right now because there is no primer, paint, or clearcoat applied, and the fiberglass tips and hardware to attach them are also not present. This actually made it easier for me to finish the top side trimming of the excess HS skin near each counter balance arm, because it kept the counterbalance arm out of the way without having to remove the elevators, like I hd to do the first time a couple of days ago, because the excess skin was still on both sides of each arm.

And another pic showing the clamping arrangement of the HS. The only other thing I still need to do to make this work perfectly is to clamp some additional blockes to the leading edge tips of each side of the HS to keep it from sliding to one side of the other while mounting the elevators. It takes a small amount of initial force to get the bearings to slide in between the hinge brackets, and this can be just enough to cause the HS to move with my current clamping arrangement.

Next are some pics that show what I needed to do to get the elevators to balance themselves in the almost "in trail" position with the counterbalance arms. I used a screw driver and a punch as counterweights and played around with the location on each elevator until they balanced.

Next is a shot of my digital smart level I used to check the range of motion on each elevator

Results from the top side were that I have plenty of range both up and down on both elevators. Plans state that the max travel is 30 degrees up and 25 degrees down. I found that the elevators would travel as far as about 35 degrees up, and I have clearance for about 32 degrees of down before the horns hit the edge of the trimmed bottom flange of the rear HS spar. At about 35 degrees up you encounter a bit of rubbing on the inboard LE of the elevator skin against the extended portion of the HS skin edge. This serves as a gap seal and seems to be quite effective, but the tolerances are very close between the HS skin and the elevator LE, so this needs to be carefully checked and adjusted if necessary.

While checking the elevator LEs during the range of motion tests, you can also see how well your elevator LE rolling exercise worked out by checking the gap line between the extended HS skin edges and the LE of each elevator. It's not very appealing seeing all the uneven bend lines in the elevator compared with the straight line of the extended HS skins. But what is important here is the freedom of movement of the control surface and clearance between all the skins, regardless of how ugly or non-linear the lines might be.

If you have achieved that, but the elevator LE roll has left some uneven or unsymetrical lines, I read a post that suggests that you can take a rubber mallet or perhaps a wood dowel and continue to reform the closed LEs enough to correct the uneven appearance. As far as I am concerned, both elevators swing freely with no binding or resistance. So unless someone more knowledgible than me tells me that I should try to "pretty up" the uneven LE rolls in a couple of places, I will probably keep them as is for now.

I was quite pleased with the movement of each elevator - very smooth and quiet and solid, with no play or slop in the hinges at all.

Next are some shots of attempting to place the elevators "in trail" by clamping the now freely moving counterbalance arms flush with the HS top and bottom skins. This was the first step in checking the alignment of the elevators.

The next step was to take something rather long that is truly straight, and lay it across both elevators, and then measure the angle or gap between the elevator skin that the bottom of the straight edge. This is done on both elevators. Then you compare the measurements. If they match, then you are golden. If not, then one elevator is not aligned with the other one, and you have some decisions to make.

Here is the pic of a piece of angle that used that is 36 inches long x 1/8 inch thick x 2 inch sides. I confirmed that this piece of aluminum is absolutely straight and true. I drew a center line on the angle, and lined it up with the cetner bearing on the HS. Note the gaps between the ends of the angle and the elevator skins on both sides.

And from the front:

This is where I got confused the other night. I originally thought that the straight edge was supposed to sit flat across both elevators. So when I saw the gap on one side, and pushed down on that side of the straight edge, I ended up with about a 1/2 inch gap on the other side, and completely freaked out, because for some stupid reason I was expecting the traight edge to lay flat across both elevators.

So, stupid me has since realized that the elevators are tapered, being wider at the root end and narrower at the tip end. So of course a straight edge is not going to lay flat across both elevators. DUH! Once I got that sorted out in my head, I took the correct measurements,and determined that I am only about 1/16 of an inch out of alignment, depending on where you place the straight edge. That may be acceptable or it may not, so we'll see.

Next is a pic of the control horns. One elevator is balanced and the other is not, which is why the horns appear to be out of alignment. I took the bolt that is supposed to be used to attach the horns to the center bearing once the holes are drilled, and laid it across the top of each horn. I am concerned that this bolt may not be quite long enough to cover the distance between the two horns,esecially after all the required washers are added to it. I believe I have also read some posts from other builders about this problem as well, so I may need to do some research to find out how to handle this one.

And lastly is a pic of the elevators in their overbalanced condition. It is really cool to see this assembly in place and moving as expected. So things are not quite as bad as I made them out to be the other night. Just another day on the build......

I will make a few more checks for alignment, and record my findings and specfic measurements. I also need to flip it over and perform the same checks from the bottom side. One note about the Avery tools temprorary hinge pins: I had to take them out and reposition them from the bottom in order to check the range of motion for the UP position. This is because the threads of the hinge pins are still a bit too long for the opening in the elevator at the tip to allow for full range of movement both up and down. The one at the root is almost completely underneath the HS and elevator skins when installed, but the one at the tip still sticks out a bit far to allow movement of the control surface on the side where the threads of the pins are sticking up.

So your choices are to grind or cut off the excess threads, or to take them out and reinstall them on the other side of the elevator to allow free movement of the surface in the opposite direction.

All for now...