387 hours on the hobbs - pics for previous posts and working on the trim tab

So yesterday, aside from eating the annual feast, I spent time working on the plane as much as I could, while waiting for my parts to arrive from Van's, which did not show up on Wednesday as I had hoped. Mail always gets bumped on the biggest travel days of the the year. How do I know that? Three seperate stints in my earlier days busting bags for three different airlines, that's how. Stupid Holidays. Anyway, I digress. Plenty of work to do regardless.

To catch up a bit, lots of text and and no pics for the past few posts, so here are some pics....
First is my smelting pot  - the olive can bent into shape foe melting/pouring the lead:

The lead counterweight, dog dish, and dirt, after the pouring had been done. Note that there are no holes in the lead any longer, after spending over an hour drilling them out the other night. I love progress! Not shown is the aluminum foil that I had wrapped around the entire part and cut the holes out so that lead would only end up going down the holes and not globbed all over the rest of it.

This is the inboard side of the trim tab, marked 1/8 inch inboard of the true cut line. I ended up cutting the tabs off right to the cut line and deburring them on the scotch brite wheel. Two hands on the dremel tool adn careful cutting here.... Really trying hard to make this a one-trim-tab effort.

Next is the line to cut the tabs off of the elevator. There is some detail about this in the plans worth mentioning here. Question is where do you decide to draw the line, and based on what reference? Answer is that the plans say to place a square angle up against the trailing edge of the elevator where it is cut out for the trim tab, and draw a line perpendicular  to that line for the "bend" line (in my case it is a "Cut" line). All fine and good, but you still don't know exactly where to draw the line - without carefully revewing the plans that is.

What I did is measured the length the trim tab skin at the leading edge - came out to about 17 and 22/32 inches. I then transferred that measurement from the inboard trailing edge of the elevator, outward that same distance, and made a mark. I then took the square, aligned it with the TE of the elevator, and drew the line across the tab on that mark.
This should allow the skins from the elevator and the trim tab to just butt up against each other, but you don't know for sure until you get the trim tab clamped into place.

Only problem with this is, when I look at other sites where people have bent the tabs over, the gap in the strain relief cutout at the bottom and top of the two above pics is MUCH smaller than what my mark indicates. IOW, the bend line is at a point that is actually a bit longer than the line that I drew.

Back to the plans to sort this out - Van's calls for a MINIMUM gap between the trim tab and the elevator of at least 3/32 inches to prevent the possibility of the two components from binding while under normal flight loads. So when I add that distance to my original measurement, it then looks much closer to the bend line I see in other builders logs. My approach was to go ahead and cut the tabs off the trim tab skin flush to the outside edges, since this is the final bend line that is called out in the plans for the trim tab. I then left a healthy amount of excess material on the elevator so that I can trim it up only as necessary once I start fitting the trim tab in place to achieve the optimal 3/32 inch clearance. Don't want to cut too much off and end up with too wide of a gap, which will add drag and not look very professional either. This is actually another plus for choosing to install the riblets instead of bending the dreaded tabs, because you can cheat a bit by moving the webs of the riblets on both the elevator and trim tab in or out to create the correct gap. Just have to be sure to maintain proper edge distance for the rivets that will insert into the flanges of each riblet.

How did I cut the tabs? I used the dremel tool and the reinforced cutoff wheel just as before:

First cut finished, next step is final cut and debure the edge so it is flush with the edges on both ends of the tab.

Pieces after the initial cut was performed

The last pic above shows the dremel tool and flex cable/cutoff wheel setup. What is not easily seen is that I have a 2x4 block of wood between the elevator skin where the clamp is located. I did this to provide some rigidity to the elevator skin where the tabs are located. You do NOT want the skin flapping around while you try to cut these tabs off. The tabs on the trim tab skin are relatively easy to do, because they are on the ends, but the elevator tabs are surrounded by vital areas of the elevator skin that cannot be compromised, or you will be purchasing a new elevator skin. So utmost care must be taken when trimming the tabs from the elevator. Both hands on the dremel tool, moving slowly as you get closer to the TE of the elevator. If you are worried about this, you can cut it up to a certain point, adn take a pair of snips or cutters to remove that last portion nearest the elevator skin.

Next you can see the inboard bottom trim tab edge, all cut and deburred, with the trim tab servo push rod control horn clecoed into place. This is the attach point of the clevis from the trim tab servo to the trim tab that will make it go up and down.

I read a post on someone's builders log that has me pondering this a bit. He pointed out that the two halves of the control horn are not riveted together for some reason - instead, each half of the horn is riveted separately to the skin. Yes, they do butt up against each other fairly well, but he pointed out that this is a potential collection point for moisture, and is therefore susceptible to corrosion over time. For reasons  I have stated in previous posts, this is not an area where you want to take chances or do a poor job of completing the trim tab. It can cost you your life someday, so it warrants careful consideration for preventing moisture from getting in between the two halves of the control horn. Suggestions are to use proseal, which I have none of yet, prime it, seal it, RTV, etc. I will put primer on these parts but I am not sure that this will be enough. Even more curious is why Van's does not to rivet the horn halves to each other. I find this quite strange for such a highly concentrated load point where the pushrod attaches to the horn.

Note the top of the pic where the clevis and the attachment pin have been inserted into the hole at the front of the horn. I also deburred this hole but did NOT run a drill bit through it. The last thing you want to do here is to enlargen the hole where the clevis pin is inserted. You do NOT want excessive play here or it may lead to problems trimming the airplane later on. Some folks choose to insert a cleco in here as well. I chose not to do that either. The clevis pin needs to just fit inside the hole adn be somewhat snug, but not binding

Lastly, here is a pic of the flop tube I received in a previous parts order from Van's:

I spent a considerable amount of time studying the plans for the wing tanks so I could understand how the flop tube assembly differs from the standard fuel pick up line assembly. the flop tube does exactly what it implies - it will "flop" from top to bottom and from side to side of the fuel tank so that when I am upside down and making cork screws in the sky, the engine will still be able to draw fuel from the tank. My system will contain one flop tube in the left tank, while the other tank will have a standard fuel pickup line, so all aerobatics will be done with fuel selected from the left tank.

I then studied the plan diagrams that show the plumbing of the fuel system into the fuselage. I now think I have a fairly clear understanding of how the fuel pickup lines and vent lines are routed through the fuselage from the wings. Amazes me how many 90 degree bends there are in the lines and fittings. If I did that in a 2 cycle RC airplane engine it would not stand a chance without some type of pump system in place. I guess the RV is the same way, in that I think it will have three fuel pumps installed - 1 auxiliary pump for each tank, and the engine driven fuel pump.

Hoping that my parts arrive today - Black Friday. Next steps are to drill and coutersink the trim tab front spar, elevator rear spar, prime the inside of the trim tab skin, bend the trim tab skin TE, align and drill the holes in the piano wire hinge, and fabricate the three riblets. Lots of stuff to do, but none of it overtly time consuming. Also read up on the hinge placement. Turns out to be another area where Van's is severely lacking in detailed info about this. A lot of confusion about how to mark the holes in the hinge, and the sequence of drilling, dimpling, and countersinking that must be done in the correct order to get it right. Study every detail in the plans, think it through, and it should come together just fine.....