370 hours on the hobbs - Starting on the Left Elevator

SO I installed 4 MK319BS pop rivets in the trailing edges of both sides of the right elevator as shown below:

I may need to order some more of these rivets from Vans before the left elevator is finished. I also need to order an E703 tip rib from Vans as I will be using that for the inboard riblet on the trim tab.

Time to put the right elevator up for a bit and start on the structure for the left elevator. As I look back on it, not a very good track record of working on the plane. I "officially" started on October of 2009, and after enduring about 6 months major home improvement delays and a host of other interruptions, including cold weather, major screw ups requiring major repairs, etc., here I am 2 years later, still trying to finish the tail. Hard for me to swallow, especially when you consider that there are others that have managed to finish the tail kit in about 9 months or less, and at about half the time hour-wise. Oh well, it is what it is. A "one day at a time" approach will net a completed airplane one day, so you just keep at it.

One more pic of the right elevator in all its riveted glory. Had to move it off the tables and benches so I could start working on the left elevator skin. So here it is on the dimpling table. Can't wait to get both of em attached to the HS.

Now on to the left side. This skin is a bit difficult to handle because part of the trailing edge is removed to allow the space for the trim tab. What is a trim tab you may ask? The best way to describe  it is that it is basically a small elevator within an elevator. Thus the use of the word "tab." It's main function is to allow the pilot to make small adjustments to the control surface to lessen the control forces that need to be applied to the elevators to maintain a given pitch attitude for straight and level, climbing, or descending flight.

It does this by changing the amount of force being applied to the horizontal components of the tail. To accomplish this, it moves in the opposite direction of the elevator, which basically makes the elevator move in the opposite direction. For example, if I want to move the elevators up to establish a climb, and I want to hold that attitude for relatively long period of time, your arm may get tired of holding the amount of force it takes to keep the airplane's nose in that attitude. So to fix this you "trim the airplane up," which basically means that the trim tab moves down, which actually adds lift to the elelvator, forcing it to move UP, which raises the nose of the airplane.

The way that I describe this to my flight students is that it is basically a poor man's autpilot, allowing one to fly the airplane essentially hands off of everything is set correctly. So it is a very helpful thing to have on any airplane. In fact, when it is all said and done, I will be able to trim the elevators and the ailerons. Unfortunately Vans does not include a trim tab designed for the rudder, but it looks like this is something that would also be handy, as many pilots report having to hold the rudder just a bit in level flight due to a variety of different factors.  There are other means of addressing any rudder trim issues, and I will cross that bridge when I get to it.

Confused yet? Don't worry, it be more clear as the components are completed. Why am I devoting so much to explaning what a trim tab is? Well, a recent event at the Reno Air Races involving the crash of a modified P-51 resulted in death and severe injuries to many many people. Thus far the pictures and initial investigation as to the cause of this tragic accident appear to be focused on the apparent failure of the trim tab on that airplane. Jimmy Leeward was the pilot, as well as a fellow EAA member, and so this trategy has affected us all. It leaves you wondering how such a small part on the airplane could be responsible for such an accident, but it can.

While I have no aspirations to modify my airplane to go 500 MPH (200MPH is quite enough for me, and is a realistic cruise speed for my airplane), the trim tab system is still a very important one, and so it bears spending the time to ensure that this assembly is done correctly. Failure of any component of an aircraft that directly affects the controllability of that aircraft is one of the continuously sobering thoughts that one has as you embark on a project such as this.

Back to the build.....
This is the left elevator skin with a trim reinforcement plate clecoed to the bottom. This plate serves as the mounting platform for the electric trim servo. The big cavity in the back is where the trim tab will be located.

And another shot of the back side of the left elevator skin clearly showing the cut out for the trim tab. When finished the tab will fit neatly in the space created by the cut out, and when everything is aligned, it will look as though it is just a normal part of the elevator. Here the vinyl has not been trimmed yet.

And a pic after the rivet lines for the stiffeners and spars has been trimmed away with the soldering iron. This is a real crappy job of cutting the vinyl, but the side shown was the last of the 4 that were trimmed, and by that time I was getting tired.

Next is the trim access reinforcement plate after match drilling, deburring, and dimpling, including the skin area to which it is attached. I used my 3 inch yoke to reach all but 2 of the holes that needed to be dimpled. For the remaining 2, I used the flange yoke, which allowed me to insert the yoke inside the hole in the skin in order to reach the last couple holes.

I am using two of my support blocks to hold up the upper skin where the trim tab cavity exists. One problem I found with this skin is that when it is left unsupported in this area, the corner on the end will bend down and it contacts the skin on the opposite side, and this causes scratches and gouges. So you need to be careful when prepping the skin during these times so that you don't damage the skin.

And finally, a pic of the frame parts. I have drilled and deburred the holes for the two rod end bearing support brackets that attach to the forward spar, and I have fluted the two end ribs, exactly the same as was done for the right elevator. The skin for the trim tab is also shown here. Lots of work to do yet.

All for now.