I have been doing a bit of research on many different builder sites to gain a consensus of what to do to avoid the problems experienced by hundreds of folks when completing the left elevator and trim tab assemblies. There is so much useful info out there that I am starting to become overwhelmed. So this post is dedicated to listing several pointers and things to be done to ensure that the remainder of this part of the build is as error and headache - free as possible. If nothing else, this list will show just how involved this process really is, and why it takes so long to do it all correctly.
1. Use riblets instead of bending the tabs on the elevator and trim tab- ABSOLUTELY! I need to make 3, two of them from the ribs used in the airfoil practice kit from the RV Sport Air workshop, and one from the end of an E703 elevator tip rib. I need to order the additional tip rib from Vans, and will most likely do that tomorrow. I checked the dimensions of the angles of all the ribs, and there is a bit of a difference between the E703 and the practice kit ribs, but apparently this works out correctly of they are used on the right places, or maybe it is a moot point and you just need to cut them on the right place to get the correct dimension for the riblet. If I have it understood correctly, I will use the two practice kit ribs for the elevator and the outboard end (small end) of the trim tab, and the E703 tip riblet for the inboard section of the trim tab (closest to the Rudder).
2. NO, I will NOT bend the existing tabs, but will cut them off instead, using a reinforced dremel cutoff wheel and my flex shaft extension that I got for Xmas last year. Even though I have found several sites that explain and show pics of the correct way to bend the tabs on the left elevator and the trim tab skin, it's just too much work, with a very high percentage of screwing it up, and I think it is also a really bad decision on Vans part to continue with this poor and troublesome design implementation.
3. I WILL NOT bend the trailing edges of the trim tab OR the elevator skins until AFTER cutting off the tabs on each end. (not talking a bout the tabs on the skins, but the normal being of the trailing edge). This is actually more important if I was going to bend the tabs instead of removing them, but to be consistent, I will delay bending the TEs until after the tabs are removed.
4. I WILL leave at least 1/8 of an inch EXTRA material on the skins where the bend tabs are located to ensure that I have sufficient depth to retain a 3/32 inch clearance between the edges of the elevator and the trim tab. You can use the webs of the riblets to close up the gap and form the crisp edge between the elevator and the trim tab by waiting to rivet them to the skins until after the hinges have been final positioned and drilled. Then you can position the riblets to provide just right clearance, drill the rivet holes, and attach.
5. There is some mention on some sites about leaving the stiffeners off of the area where the rear elevator spar is attached to the elevator skin, and this has to do with hving enough clearance to get a no hole yoke inside there to use hard rivets instead of pop rivets. Apparently if you back rivet all the stiffeners in this area, and perhaps this is even another area where not bending the TE of the skin comes into play, then it makes it hard to rivet this spar into place with solid rivets. I may need to think about riveting the bottom of the spar first, followed by the top, or perhaps this has more to do with leaving the riblets unattached so you can get into the space with the no hole yoke - just not quite sure yet.
6. I WILL NOT attach the riblets or drill the rivet holes for them until I know where they need to be positioned to provide the correct 3/32 inches of clearance between the trim tab and the elevator.
7. I WILL remember to check for any interferance of the riblet flanges with the holes for the trim tab control horn to ensure that I will be able to attach these correctly. Apparently this bcomes an area of concern depending on your decision to place the riblets with the web facing in or out.
8. I WILL place my riblets (Pending the answer to concern number 7 of course) as follows: Elevator and outboard riblet will be web-out, and the inboard trim tab riblet will be web in. Why? Simple. Web out is the same end result that you would get if you were to bend the tabs on the end of each skin. This reduces drag as well as eliminates areas where ice, snow, mud, dirt, or any other foreign substance can accumulate and cause other serious problems. The inboard riblet will match the contour of the root rib of the elevator (web in), and will allow solid rivets in this area. This area is always checked on every preflight, and is easily accessible to check for foreign debris and remove it. Having the web in also allows the use of solid rivets instead of pop rivets.
9. Where blind or pop rivets are necessary, I will use MK319BS rivets, with holes drilled to 7/64 of an inch for a good tight fit.
10. I WILL NOT make riblets that have an additional set of tabs on the top and bottom that will overlap the flangs of the rear elevator spar. They would not have existed had I chosen to bend the tabs, and there is NO REASON to add them to the riblets, which are providing a SIGNIFICANT AMOUNT of additional structural support anyway, moreso than you would have by just bending the ends of the tab skins. The other reason I will not do this is that it would require a great deal more fabrication effort to include these extra tabs, and I am just not willing to go there. I include this step because some builders have gone the extra mile by forming a riblet with additional tabs that overlap the rear elevator spar or the forward spar of the trim tab.
11. For the next Lead counter weight mounting hole drilling exercise for the left elevator, I WILL do that differently than before. Found a great post on a builders web site where he described how he did it, and it just so happens to be the same method that I was mulling over in my brain as I started to free-hand drill the mounting holes for the right elevator. In fact, I used a similar process to mark and drill the holes for the HS404 and HS405 ribs on the HS a long while back, and it worked great.
The process is:
- Cleco the ribs, counterweight, and counterweight skin in place per the plans.
- Transfer the pre-punched hole location from the counterweight skin to the front of the lead counterweight using a sharpee. These holes are pre-punched to #41 size so they are small, adn provide a precise starting point for each hole.
- Take apart the counterweight assembly, and take the newly marked lead counterweight to the drill press, and drill the holes in the counterweight using the drill press. Now you have two straight holes in the counterweight that can be used as drill guide for drilling out the forward flanges of the tip rib and the counter balance rib.
- Re-assemble the counterweight parts, drill out the holes in the front of the counterbalance skin to final size, then drill the holes in the front flanges of the tip rib and counterbalance rib by running the drill bit through the previously drilled holes in the lead counterweight.
This process ensures that the holes in the rib flanges should be smack dead center without any risk of screwing them up as some have done by free handing the drilling of the counterweight. Should have done it this way for the right side but it came out OK I think.
So my brain is tired after all that. I am sure I missed some things, such as ordering the tip rib, some more MK319BS pop rivets, and some AN3 or AN4 nut plates for adding additional weight to balance the elevator, should that become necessary after painting.
As you can see, there is a lot going on during this assembly..........
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