I got the hard drive hooked up this afternoon, so I have access to some of the pictures taken while building. As time permits they will get posted with some commentary. Wings This is one of those parts you should probably spend a bit of time thinking about. After all, they are what are going to keep you in the air.  I used Styrofoam for a good part of my wings. It is cheap, easy to sand, and takes micro as a attaching agent very well. It also has the ability to spring back when hit or compressed. There is one problem with it that you must be aware of which will be discussed a few pictures down.  In this photo, the trailing edge is getting glued on after the leading edge and center sections have been roughed out. Being a simple guy led me to use what was available to keep the foam in place until the micro had dried. There were very few fancy tools in the garage/hangar so making-do became an art form. I learned the hard way not to work one area to a finished product before other sections were at least roughed out. Hangar rash only happened a couple of times but each time it sure was aggravating! The make-do mindset can be seen in the picture below. If the clamps are not long enough, clamp them together to make them longer! It looks pretty Rube Goldberg, but it worked.   Sanding. You are going to do a lot of sanding. Just when you think you are done, there will be more sanding. Then you will get a break to do glassing, then more sanding. Buy stock in a company that makes wet sandpaper before you get to the glass stage. A piece of angle iron was used as the sanding tool, with 80-grit strips of belt sander paper attached with upholstery glue. There was one problem with this tool, it was very hard to hold after five minutes of pushing and pulling the iron back and forth, so... Did anyone notice how a 3-inch C-clamp makes a great handle? By clamping a bunch of these to the angle iron it was easy control and sand for extended periods of time. If one spot was not getting enough downward pressure and a high spot was forming, just moving a C-clamp over that point and putting more down pressure there solved it. Yep, simple tools for simple minds.   The shot above shows what I alluded to earlier. If one is going to put fuel cells in the wings, DO NOT USE STYROFOAM. MOGAS will melt Styrofoam like it was hot water on a sugar cube. You may not be planning on using MOGAS, but what will you do if 100LL goes away? Are you willing to risk hundreds of hours of rework to replace your wings if 100LL goes away? Use something like urethane foam anywhere fuel has any chance of coming in contact with it. In my case, I chose to put the fuel tanks in the outer wings, requiring urethane foam in that section. This foam can be purchased from Aircraft Spruce. Another place I found it was at a lumber yard. At the yard it was in huge sheets like plywood and had a thin aluminum foil on one side. Each piece was 4 inches thick. Boat yards may also have foam, but it typically is "structural foam" having a much higher density than most people will want to us on a plane (6 lbs/sq ft vice 2 lbs for the foam I used). A final note on foam. To rapidly take off the large sections of foam use a drywall tool. These look like a cheese grater with a handle that allows one to put a good deal of force behind each pass. Just be cautious as you get down to a half inch or so of there the wing surface will be. It really stinks to dig too far and have to plan a patch job early in the game. Wing fuel tanks I chose to put fuel in the outer wings for several reasons: - It would make the plane more stable in roll (higher moment of inertia). As the fuel burns down to the weight I would want to fly anything aerobatic, this effect is diminished meaning the trade-off between reduced roll heavy and better roll lighter was acceptable. - Best fuel to fuel cell weight ratio for the amount of fuel I wanted to carry (25 gallons or 4 hours of flying plus reserve). Inner wings only provide for ~ 15-18 gallons which was not as much as I wanted. Of note, I do not fly around for three or four hours at a time, but because Goliath has the capacity we can fly extended distances more economically if needed. - Fuel in fuselage - bad. If we have a mishap, fuel in my lap just seems dumb. I do not plan on having an accident, but if I do, I do not want to be crisped. - CG. Installed as they are, burning down fuel has a very minimal effect on CG and balance of the plane. This is a bonus for flights near max gross takeoff weight and for flying with a passenger when the tanks are getting close to empty. If I had put fuel further back behind the main spar stability would have suffered.  The decision to make the fuel cells out of aluminum was driven by the desire to be sure MOGAS could be used. I have read the additives in MOGAS have the nasty side effect of eating various types of composite epoxies. Hmm... sounds bad. With the fuel tanks made of aluminum they would not be integral to the wing construction. This was solved by cutting a bed to fit the tank and hold it in place fore and aft and side to side. After the bed was cut the foam was glassed over its surface and to the spars. This means the weight of the tank is being held by fiberglass being pulled perpendicular to it lamination to the spar instead of being pulled directly away from the spar if only the glass of the wing skin were holding it in place. Glassing the inside of the wing did add weight, but the weight is minimal for the strength added. Goliath weighted 698 pounds when she was ready to fly. The hole in the foam is where the tank drain come out the bottom of the cell. These happen to be the lowest points in the fuel system, eliminating the need for a gascolator at the firewall. I still have a gascolator, but it is behind the firewall and even with the top longeron.   Here is what the tank looks like installed. I went with direct read fuel gages because I wanted fewer instruments in the cockpit (and less load on the generator), and even with a total loss of electricity I still know where my fuel was and how much was there. The black probe is a fuel-low warning. It extinguishes a light in the cockpit when the fuel is down to 25 minutes of useful fuel left in the tank. The fuel filler cap is at the end of the wing. I used the full size version. In retrospect, this was overkill and will not be repeated on the next plane. Each tank has two baffle walls in it to prevent sloshing. Each of the four corners where it meets the vertical walls of the tank have a 3/4" cutout to allow for fuel transfer between the divisions in the cell. The inner cell is 6 gallons, the middle cell holds 4 gallons, and the outer cell holds 2.5 gallons. The theoretical capacity of the tanks is 25.64 gallons total, not counting the hardware sticking into each tank and the baffle walls. Actual capacity is exactly 25.5 gallons. I epoxied a block of spruce to the inner side of the tank bed to ensure the tank could not slide inward if Goliath was knife edge. This is probably not needed as the tank is also foamed to the spar and the bed is 1.5" deep. Fuel lines are heavy fuel hose, not the thin-walled clear plastic showing in the picture.   Above is a shot of the foam sealing the gap between the fuel tank and forward spar. This was primarily done so the tank would not be able to shift around.  The "x" on the tank above and the circle in the photo below show where I had leaks in one of the tanks. I was pretty angry with the guy who welded these up for me because part of our contract was that he leak check them. this was not the first time I had a problem with something I thought someone would do the way I specified. It was good that I checked them before putting them in the plane! The solution to the leak problem was to put a can of POR-15 in each tank and slosh it. I have had zero problem since then. There may be other products out there that do the same thing, but I am sold on POR-15. They can be found online.  |
|
David and Goliath >
Building pictures |