I came up with a better wing design. I also have more design details.
Alpha Quality Wing Design
I should have included this in part 2. This is a rough diagram that I drew for the wing. This is the first one I drew for the Kilo3D design, just to help me visualize what it was going to look like. I quickly rejected some ideas and added many new ones.
Iterative Design Process
I wanted to post that early diagram to emphasize the iterative nature of the design process. When working on a new model airplane design, a solid understanding of the theory involved helps. Experience helps, too. But there is no substitute for trying things out and learning from your mistakes. Sometimes all you need to do is draw it on a sheet of paper (like I did) to see the error of your ways.
Bag of Tricks
With experience, you start to develop a list of design ideas that you have tried before and worked well. They tend to be a “given” for any new design. Not sacred must-haves, but handy stepping stones that get you to a completed design quicker.
I’m always experimenting with new ideas, but if you look at all of my foam designs, it would not be hard to spot my special signature in all of them.
More Design Constraints
My RC designs are easy to build and inexpensive. That is both a personal preference and an important goal for a design I am going to publish.
I only like to use easy to source materials. If the local Walmart has it in stock, then I can count on most folks being able to find it.
I care about design elegance. Call it professional pride. I do not want there to be any nasty surprises to the building or flying of any of my designs. If it is not going to be fun to fly, then why bother?
Wing Revision 2
A couple of days after I posted the Kilo3D wing design I got an idea for a better wing shape. The main problem that I saw with that design was that the main spar went from 20% of the chord at the wing root to 33% of the chord at the tips. Not terrible, but not great either. I wanted to use a single uncut dowel for leading edge protection, so the leading edge could not be swept.
Or could it? Thin wooden dowels are pretty flexible. I grabbed a 1/8 inch dowel (3 mm) and tried bending it. It was very flexible! Even if I decide to use a thicker dowel, like 3/16 inch (5 mm), it is still pretty flexible. The leading edge only needs to be swept back a small amount. Two inches of sweep (5 cm) got the main spar to go from 27% of the chord at the root to 22% of the chord at the tips. Perfect!
(Hmm. With 1.5 inches of sweep, it would go from 27% to 27%. Revision 3?)
I like this design a lot better. To account for the fuselage, there are two unswept inches around the root (one inch for each wing half). The wing now has a more traingular shape, which is better looking and should help with strength.
The fuselage in an airplane helps guide the air around the wing, specially if the wing is mounted through the middle of the fuselage, like in our case here. This effect is good through up to about a third of the wingspan. The good news is that thickening the wing around the root is a great way to add strength to it.
If you look at the Kilo3D wing design, that is exactly what I did. The relatively thick blue section reinforces the wing root and the main spar. In fact, the main spar is buried throughout the entire wing span. This is both for strength reasons and for aesthetics.
The plan is to make the flaperon out of 3/16 inch thick foam (5 mm). They are 18 inches wide and taper from 3 to 2 inches (46 cm by 8 cm to 5 cm). I have tried to build ailerons like these in the past out of foam and it did not work out. Foam is a bit too weak for the task. I tried various methods to reinforce the foam, but they added more weight and complication than I wanted.
The best solution I found was a thin sheet of balsa. I will probably do the same here. In fact, I’m tempted to make all the moving control surfaces out of balsa. As a bonus, that would give the airplane design a unique look.
Videos and Forum
I plan to shoot and post videos of the construction process and even the airplane flying. To me, it is a given that I have to do that.
In a few more days I’ll be launching a discussion forum for Kilo3D. They seem like the best solution for keeping all of the information for a given model airplane design in one place.
The bad news is that I ordered the power system for this airplane about a month ago and I’m still waiting for it to arrive. I get the feeling we are in the middle of the “hurry up and build before the good weather gets here” season. Because of that, it might be a couple of weeks before I actually build and test fly one of these.
The good news is that I have started working on another design using a power system that I do have on hand. Look for an article about that design very soon.