Toms Technical Tips
by Tom Wright of Advanced Composite Tech, Somerset PA
About the Author:
Thomas J. Wright is the owner of Advanced Composite Technologies and has been custom building aircraft since 1982. The company employees six fulltime staff members. They are responsible for building over 30 aircraft of various types, currently completing their eighth Velocity.
I find that building anything is a series of assembly and disassembly steps. It seems to proceed like this: make the part, see how it fits, temporarily fasten the part in place, determine how to make it fit better and what to do to it next, unfasten and remove, go modify it and try again until it is acceptable. To be able to assemble and disassemble quickly we sometimes use CECOS but they are not always the best tool, especially if there are nuts, bolts, and nut plates involved. So to that end I have found a very quick and inexpensive device that allows assembly of a nut plated part without using your good aircraft-quality screws and bolts. Go to your local hardware store and find thumb screws one inch long, with fine threads in each size you will be using, i.e. 8-32, 1/4-28, 10-32. Also get knurled thumb nuts in the same threads and hex nuts all in fine thread. For those of you who dont know about threads, there are two types of threads that are used on fasteners: national course (nc) and national fine (nf). Aircraft bolts, nuts, nut plates are fine. The two thread types are not interchangeable with each other. Continuing at the hardware store, purchase a dozen or so thumb screws, thumb nuts and regular hex nuts, and a can of red spray paint. Since these are all temporary fasting devices that we dont want to leave in our completed plane, we will spray everything red so we dont forget to remove. Install the thumb nut onto the thumb screw now when you have to attach something to a nut plate. For example, on an aileron hinge, simply place the screw through the hole and turn into the nut plate until it gets tight, then turn the thumb nut tight against the skin drawing the nut plate tight against the underside and through, holding the part in place. The red nuts can be used anyplace in place of your aircraft nuts; they spin on easily with fingers and are easily removable, for temporary fitting purposes. If you cant find this hardware at a local hardware store, try a really big international company Mc Master Carr, Cleveland, Ohio they have everything man has ever invented.
Again at the hardware store, usually in the paint department, you can find sanding blocks that are made of spongy foam with abrasive surfaces of various roughness/grits. These are excellent to use for sanding and forming various concave edges, etc. For straight surfaces I use 3M adhesive-backed paper for use on air boards: obtain a good straight piece of 1x3x12 and screw another 1x3x12 right down center to form a T. Countersink the screws, then use the adhesive-backed paper on the flat surface (it glues itself). Use whatever grit you want. When finished, remove the paper in one piece with a putty knife. Cut in half to make two pieces 3 x 6. Fold each piece in half with the sticky backs against themselves. Now you have good pieces of really tough sandpaper that will not wrinkle when youre trying to use it. Its rigid enough to get into thin, tight areas like the door gap space and make a good sand line.
To save one complete cure-sand-fill cycle, heres a trick Ive been using for years. After the parts have been laminated and partially cured, apply your micro fill (the glass on the part must be stiff enough that it does not distort from the application of the filler) and squeegee. Another way to fill glassed surfaces is to sprinkle micro powder directly onto the glassed surface while it is still wet. The micro will soak up the excess wet epoxy. It becomes a thin film of filler that chemically bonds to the glass. Spread it very thin, only enough to fill the small valleys in the glass. Let cure then sand as you would ordinarily do finish.
Toms Technical Tips: Part 2
As a builder of many types of aircraft, I have discovered many little tricks that make working and building more enjoyable and less frustrating.
To clean the sticky residue from masking tape of duck tape from parts without scratching the surfaces, try a product called "Opps," available at Wal-Mart. Simply wet the area, let stand a minute or two and wipe off. Using a paper towel wetted and placed over the gooey stuff also helps. It even works on Plexiglas, however the paper towel will make fine scratches, so use a soft cloth towel for Plexiglas.
Speaking of acrylic, why not protect it from the start. As soon as you unpack your new parts, protect the Plexiglas by wrapping it in your best bath towels.
Buy a product called "Spray Lat," from A/C Spruce - sign shops also have it. Paint at least four dry coats on all surfaces of your windows and windshield. Put at least six coats on the inside of the windshield, the thicker, the better. Allow to dry between coats. If you apply this product too thinly and try to peel it off, it will tear away in small pieces and you will have an almost impossible job to remove the film on your windows. Painted thick (four to five coats), it is strong enough to prevent itself from tearing, and stays in one big film which is easy to tear off in one piece, especially on the inside of the windshield after the panel is in.
To trim your windows to size, follow the instructions in the plans. After they are to size, peel some of the Spray Lat from the edges all the way around, approximately 2". Apply two layers of duck tape over the Spray Lat surface with the duck tape to within about 1" of the edges. This becomes the bonding surface. Sand with 80 grit and install per plans. You can even clecoe these in if you are very careful when you drill the holes. Use nothing bigger than 3/32 diameter for the initial drilling, then absolutely no holes bigger than 1/8", and use a Plexiglas bit. To keep the clecoes from sticking in the epoxy, dip the ends in vaseline prior to installing in the holes. It makes for easy removal after cure. Install clecoes from the outside so you don't pull the Plexiglas away upon removal.
Do not use WD 40 or any silicone based product any place on the surface of your airplane. The fiberglass, even though cured, still absorbs the silicone. Nothing will ever stick to the surface, including your epoxy and glass laminations or fillers.
Use duck tape on surfaces to prevent laminations from sticking to the surfaces. You can even make you own fiberglass angles and various shapes. Simply buy angle the size you want, apply duck tape, glass over it with four ply and after cure, remove. Now you have fiberglass angles to use for you needs. Another way is to nail some 1x3 wood furring strips together and duck tape them to use as a mold to make fiberglass parts, angles, flats, etc. You can use your scrap pieces of bid for this.
Use Permatex Antiseize to install together any aluminum parts that must fit tight, especially elevator tube plugs which fit tight. They never seize. This prevents the aluminum from galling into each other and allows you to rotate the plugs freely for drilling.
Use containers from grocery items for parts bins to sort and store items. Cut the top off of any gallon jug, clean it out, and you have a container to mix large quantities of epoxy or filler, especially big laminations, wing skins, etc.
You can use a hole saw to drill a washer shaped piece out of a plastic jug. Use as a wear washer between the aluminum seat hinges. This prevents the aluminum pieces from wearing against each other as you move the seat back.
Need to find a big wrench for the nose gear nut? It's a 1 13/16 hex nut and that size open end wrench is very difficult to find. Buying a complete set in that size is big bucks. McMaster Carr has a vast assortment of inexpensive wrenches for less that $20. each. I purchased a 30 degree angle thin-head short handle P. N. 5414A52 and it works great. Just make a pipe extension to use for tightening the elastic stop nut. It's really tight, but has to be to keep the nose gear fork at he proper tightness and prevent shimmy.
When designing panels that are somewhat complicated or difficult to visualize, instead of using the actual foam to cut up and maybe get it incorrect, try using cardboard pieces first as a temporary pattern before cutting the actual parts to size.
To determine the correct length to make those hoses: Most of us don't want inexpensive fuel and oil lines in our expensive airplane, so we tend to go way over the actual requirement for hoses and they can get expensive. In order to prevent having a line made too short or too long at the hydraulic shop, obtain some inexpensive vynal tubing from a hardware store. Slip over the the fittings you need to connect. Route the vynal tubing over and around to obtain the best routing, even slipping over the fittings. This is to simulate the actual hose in place. Mark the hose for length and application. Now take this hose to the hydraulic shop where you get your hoses made up, and have the more expensive hose made exactly like your vynal hose. They will fit every time. The hydraulic shop can help you select the correct type for the application.