The next sub assembly to do is the elevator. This is the trailing edge of the tail and it's primary function is to control pitch movement for the aircraft in flight. The initial assembly of this structure is somewhat less complex than the horizontal stab, but as always just as critical to get straight and square.
The nose, tip and rear ribs I formed fit almost perfectly and with a bit of trimming squared up the spar really nicely.
Being able to interpret the plans is becoming more apparent as I progress through this build. One item missing on the plans is the distance from the elevator spar to the elevator rear support channel seen below. The builder is left to decide where this fits. From what I can determine, the placement is designed to be back far enough so the flanges on the support channel are equal in height to the inner rear ribs. This would make sense as the skin and elevator hinge assemblies attach here. Front to back spacing is held temporarily in place with tape, squaring the whole thing up proved to be a bit tricky but I got it done without too much issue.
I had some discussion with Ron at this point, as I wasn't happy with the rigidity of the elevator assembly. I know that things will square up and get stiffer once the skin is on, but the assembly seems a bit lacking in structure at the middle where all the force and weight is acting on the elevator in flight.
Ron suggested I make a small modification that he is doing on his 701 builds by adding a 016 gusset plate across the top and bottom of the elevator centre section, extended out to the spar.
I liked the idea and set out to make the suggested gusset plates. Even at 016 thickness this will strengthen the centre spar of the elevator without causing undue problems adding the elevator skins.
I've drilled them out to A3 and will wait for A4 holes once the skins are on. One on the lower side....
...... and one on the upper side:
The last pieces to be fit on the elevator spar skeleton are the tip ribs. It's a bit of a juggle to get them in the exact right position, but they fit perfectly. Figuring out the order to drill them and the attachment angles to the spar was fun, but I got it done. A pair of wide neck welder's vicegrips are excellent for holding things together for drilling (note the protective masking tape on the pads to avoid scratching the aluminum):
Here is a picture of the elevator tip rib clecoed into place. The final rivets here are four A5 rivets which also hold on the outboard elevator pivot pins. Ron and I are going to weld up enough sets for each airplane being built and the holes will be matched with the A3 pilot holes I've drilled here.
As mentioned in my previous blog post, I'm considering options for a system to control the elevator trim tab. The plans call for a Ray Allen trim actuator and digital trim position indicator for the cockpit. But at $400+ I'm exploring alternatives, including substituting in a giant scale RC servo.
The Ray Allen system is spec'd to provide 40 pounds of linear push/pull force. Current metal gear RC servos are more than capable of meeting or beating that spec and with a bit of microprocessor power and programming are an attractive alternative. The whole replacement system from front to back including servo, a cockpit indicator and voltage regulators will likely be less than $100. The question is how?
Welcome to the world of Arduino, a programmable microprocessor board based on the AT328 chipset. With a bit of time, I believe I can use the Arduino to not only control the trim servo but provide failover support and control correlation. In addition, I have many options for how I want it to display in the cockpit, from a simple bar graph LED to a more intuitive graphic display. Only imagination limits me here. I',m also considering an Arduino board for controlling LED navigation lights and LED strobes.
So what does an Arduino processor look like? There are several models of boards all with different strengths and weaknesses, but most of either are related to what the board is capable of providing. I want the board to be simple to use but small for space considerations behind the control panel. For my prototype and likely final design, I've settled on the smaller sized Arduino Nano for the trim system:
I went on Amazon and ordered the Arduino Nano board and the associated mounting pins. I was able to find a 3 pack that included the unsoldered breakout pins. My plan is to use one board to prototype the trim system, one board to make for the airplane (wire soldered to the board) and one spare (in case one decides to poof into blue smoke if I screw up). I also ordered a voltage step-down board (top of picture) - the trim servo operates on 6 volts, so i needed a way to power it from the 12 volt system:
The easiest way to prototype and learn how to use the Arduino board, is to mount the pins on the breadboard, then place the Arduino on the pins. From there careful soldering each pin of the Arduino:
The Arduino is supported by a large online community of programmers, experimenters, robotic designers, musicians and others. It's simple but powerful programming language is easy to learn and because it is "open source code" based, there are literally thousands of example projects to build from and modify. I won't get much more into it here, but if this interests you, check out https://www.arduino.cc/
After getting everything together, I powered up the Aruduino from the USB port of my laptop ..... IT'S ALIVE! (I guess it's a stretch to consider that this might count as the first "power" my aircraft has had - I'm such a geek!)
After a bit of fussing around with loading up the correct USB drivers so that the Arduino programming application on the laptop can talk to the board, I uploaded my first "sketch", (the Arduino name of a coded program that instructs the board what to do). In this case, I added an LED and used the basic "Blink" sketch which tells the board to blink it's on board LED light
Again, I know this sounds geeky, but it's really cool! I messed around with the sketch and changed the blink rate and patterns and uploaded it again to see the result. I've got a bunch of learning to do, but a work colleague sent me some links to YouTube instructional videos which I'll work through and learn what this board can do.
Well, that's it for tonight. Back to the shop Thursday night to work more on the elevator. Got to finish the centre section, the elevator upper/lower control horns and start looking at how the elevator trim gets mounted. Got some disassembly, deburring and priming to do as well.
Thanks for reading, more to come :)
Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.