Wow, this post is a milestone in this project. What could I possibly be talking about? This post is the 50th actual building post that I've made during the project. Ok, I know, I need to get a life!
Up to this point I have followed the steps in the instruction manual exactly. But now I'm going to start changing the order of things that I do a little bit. I will try to stay with the same general progression of building that is in the manual, but I may have to change that around a bit. The reason I do this is because some things that I like to do while building a plane have to be done a little bit different order. I know this may be a little bit confusing, but here's an example to show what I mean. The instructions call for doing these steps next: Glue in the floor tank in the forward part of the fuselage and then glue in tri-stock to reinforce the firewall. Here is why I need to change the order of how I am doing to do things. I prefer to fuel proof the inside of the fuselage around where the fuel tank goes. If I follow the order of the build according to the manual I will put the fuel tank floor in first, and this will make it almost impossible to fuel proof the area underneath it. So I am changing the order of steps simply because it will make it easier to to what I need to do. From this point on there will probably be more things that will happen like then, and when I change the order of work I will try to remember to let you all know that I am changing it.
As I just said, I prefer to fuel proof the inside of the fuselage in the area around the fuel tank. This is something I learned the hard way. I once had a Ultra Sport 60 that developed a small fuel leak, which proceeded to soak the wood around the fuel tank. Because the wood was soaking up the fuel I didn't notice that it was leaking. I found out the hard way when I was pulling an inside loop and the wing separated from the fuselage. The fuel weakened the glue on the former that was the from hold down for the wing, and the entire former pulled out. The fuselage became a very nice lawn dart and planted itself in the ground. On a side note, the wing very delicately floated down and landed in the top of a small tree. So now I have an extra Ultra Sport wing! But I learned a lesson about fuelproofing the fuselage. Since I have started doing that I usually now notice a fuel leak because the fuel will not soak into the wood and will usually run out of the fuselage where you can notice it. Is this important? IF we all do proper airplane maintenance it probably doesn't matter as much because about once a month you will pull out the fuel tank and check all the fittings to make sure they are tight. You all do that right? Neither do I. I will try and do these checks on all of my planes at least 2 twice a summer. But with the number of planes I have it sometimes doesn't happen and I get fuel leaks. The reality is that parts come loose. Fuel tubes get holes in them. Fuel tank stoppers shift. Screws come undone. Because of this fuel leaks do happen. To fuel proof the fuselage I will do it using one of two different methods. I prefer to put straight epoxy on the wood and and heat it with my heat gun (the one I use for covering) and as the heat thins the epoxy I will spread it with an epoxy brush. One thing you have to be aware of when doing this is that heating the epoxy will shorten the setting time. So start with 30 minute epoxy, and don't try to cover too large of an area. The reason this is my preferred method is because thinning can sometimes ruin the epoxy. If you thin epoxy too much it will never set properly, and remain rubbery. Now with that said, my second method is to actually thin the epoxy with denatured alcohol. If you do thin the epoxy please don't use too much alcohol. Start with putting in a couple of drops (an eyedropper is great for this) and mixing it in and test to see how easy the epoxy is to spread. If you do get too much in it will cause the epoxy to never set properly. It would be a good idea to practice a few times to see how it turns out. Once you have done it a few times you'll get an idea of how much to thin it out.
Since I want to fuelproof the inside of the fuselage I need to do things in a little bit different order so I can the entire area fuelproofed easier. So the general order that I'm going to followed now will be to reinforce the firewall, apply epoxy to the inside area, and then glue in the fuel tank floor. To start out we need to reinforce the firewall with the supplied balsa tri-stock (picture #1). As a side note, using this method will add A LOT of extra strength to your airplane. Like I said in a previous post, the joint here between the firewall and the fuselage is very critical because this is where the power provided by your engine is transferred to the rest of the airframe. The more strength you can add to this joint, the better off you will be. Before you glue in these pieces you will want to make sure that they clear all of the “things” on the back of your firewall. For instance, on the right side of the firewall is the hole for the throttle pushrod, so you don't want to cover that hole up. The easiest thing to do here is simply cut the tri-stock so it's not put on over the hole (picture #2). You will also want to carve away a bit of the tri-stock on the left side so that it doesn't interfere with the blind nuts on the backside of the firewall and the steering pushrod (picture #3). This is one of the few places where I will use 5-minute epoxy (a part that is quick and easy to place), so mix up a little bit of 5-minute epoxy and glue the tri-stock into place. Pictures #4 and #5 show the placement of the tri-stock.
Before we apply the epoxy fuelproofing you will need to mark where the tank floor meets the side of the fuselage. This is important because you don't want to apply epoxy over where those two parts will meet. You want a strong wood to wood bond between the tank floor and the fuselage side, and covering that area with epoxy will make for a weaker joint. Picture #6 shows where I will not apply the fuelproofing. I simply place the fuel tank floor in place and marked with a pencil where it will sit. Since this is a cramped area to work in I choose to thin the epoxy instead of heating it. I started with 30-minute epoxy and thinned it just enough to spread it. Use a disposable epoxy brush to “paint” the entire area, taking care to not cover the area that you marked earlier. You will also want to take care to not get epoxy in the threads of the blind nuts for the motor mount and the front landing gear mount. One other note is to make sure you have good ventilation when you do this. Epoxy stinks, and it usually give me a headache. Once you have the area completely coated set the fuselage aside and let the epoxy dry completely before moving on.
Pictures
1. Balsa tri-stock used to reinforce the firewall.
2. Marking opening that need to be worked around when applying the tri-stock.
3. Carve the tri-stock to go around blind nuts and the hole for the steering pushrod.
4. Right tri-stock applied.
5. Left tri-stock applied.
6. Marking where the fuel tank floor will be glued to the fuselage sides.
7. Using a disposable epoxy brush to apply thinned epoxy to the area around the fuel tank.
8. Using a disposable epoxy brush to apply thinned epoxy to the area around the fuel tank.
Until next time
Ken