| Foamflyer's Best Practices |
Washout, the downward twist in wingtips that improves low-speed flight, is sometimes used in airplanes with flat-bottom wings. A good way to make sure each wingtip has the same amount of washout (or any at all) is to get two straight wood dowels or carbon rods. Tape each to the bottom of the wing near the tips. Set the wing on something so you can see both rods, and sight down the wing so you can see see each rod in relation to the other. The rods magnify any angle that might be present in the wing. Correct the wing twist until you have the angle you want. This doesn't work too well with wings that are rounded on the bottom, but is an excellent way of making sure flat-bottom wings are true.
1. Wax Paper: Take a sheet of wax paper, and mix your epoxy on half of the sheet. Then when done, fold the wax paper in half, trapping the epoxy residue inside. This way you can fold it up with no mess and throw it away, and it won't stick to the inside of the trash can.
2. Foam: When epoxying to styrofoam, such as attaching leading or trailing edges to a foam-core wing, once the parts are coated well with epoxy and put together, wiggle them around some to work the epoxy into the pores of the foam. Then let it dry normally. This results in a stronger bond.
3. Bed-Buddy: Ever been caught with cold epoxy? It's much more workable and mixes better when its just above room temperature (about 80-85 F). I use a "Bed-Buddy" to warm it and keep it warm. A Bed-Buddy is like a long sock with some kind of granular chemical in it that stays warm for hours after you microwave it for two minutes. They're designed to keep your feet warm at night, and you can wrap it around your epoxy bottles too between each use. You can also put the epoxy bottles directly in the microwave oven for a short time, but be careful doing it.
4. Inverter: When your epoxy bottles start getting low, it can take a while to get it out, especially when cold. Build a simple wooden "inverter" to hold both bottles upside down, and keep them in it between each use. This way your epoxy will always be ready for use.
Here's an easy way to make sure your servos will fit in your plane properly, especially helpful with scratch-built designs: Take the measurements of your servos, and make a few from wood, identical to the real ones. This may be easy if the manufacturer supplies full-size drawings of the servos. I made my servo blanks from pine blocks, a little plywood for the mounting hole piece, and a dowel for the motor shaft. These servo blanks will not only help in drilling the holes to mount servos, but will assure adequate clearance on all sides. In addition, the dowel is the correct size to press on an actual servo arm, which will help in aligning pushrods or cables. Using this method will help keep your real servos safe and clean during the building process.
To get a fin in correct alignment with a fuselage, try using thread. Make sure you have an accurate center mark near the top-front of the fuselage, and tack-glue a long piece of thread to the top near the nose, a distance from the centerline equal to half the thickness of the fin. Run the thread back to the tail, and hold it against the side of the fin. The thread should touch the side of the fin evenly overall. If it doesn't, then rotate the fin until it does, then tack glue the fin into place, reinforcing it later. Last, remove the thread you tack-glued.
Get a small block of styrofoam and stick your hobby knife in it. This way the blade won't be exposed, and you won't cut your hand if you reach into a drawer or box for it. Always keep new blades in their original container, and throw away used blades into a closed can with a slot cut in the top, don't just throw them into the trash can by themselves.
Most propellers have very sharp edges when new, especially at the trailing edge, which can cut your fingers. Always sand the edges smooth with fine sandpaper as soon as you buy them. Be extra careful when turning over someone else's motors by hand, because they might not have sanded the edges of their props.
If you need an extra-long screw or bolt for something, such as a wing tank or mid-mounted wing, make one by cutting the correct size threaded rod you need, then solder a wheel collar on one end. Next, using a cut-off wheel, cut a slot in the wheel collar for a screwdriver.
If you have a small plane with a very tight engine installation (usually resulting from a very streamlined cowl), often there's no room for a nose gear assembly. Try drilling holes through the engine mount to accept the nose gear wire, and hold it in place with wheel collars. The steering arm can be placed below the engine, even on the outside of the plane. This will work with most engine mounts, even the two-piece ones as long as the engine is rotated 90 degrees.
Ever have wheel collars not hold on axles? Or maybe that nosegear keeps twisting because the steering arm won't tighten? Try grinding or filing a flat spot on the wire where the setscrew will go. This provides a better surface for the screw to tighten against. Better yet, grind a flat spot with a small diameter (worn out) cut-off wheel. The small diameter causes the flat spot to actually be concave, which helps the setscrew grip even more.
Several things for RC airplanes can be made from 1, 2, or 3-liter soda bottles.
Get some ammonia, found in the household section of the supermarket. Put some in a spray bottle, and spray both sides of balsa sheet liberally. Carefully bend the sheet to the right shape. You can even tape it to a form, such as aluminum soda cans, and let it dry. Once dry, it may be used as turtle-decks, etc.
Get an old (but straight) telescopic antenna, the same type as on transmitters. Use it as an adjustable-length measuring rod to compare critical measurements on planes during construction. I use this idea to compare the distance from one wingtip to the stabilizer, and to make sure this distance is equal on both sides of the plane. This ensures that the stabilizer is parallel to the wing.
Something to pay attention to when learning to fly is control reversal. Control reversal is when the inputs on the transmitter sticks must be reversed when your plane is flying toward you, rather than away from you.
When flying away from you, there is no problem, just move the stick in the direction you want to turn.
Many new pilots become disoriented when their plane is approaching them. To help with this, move the stick in towards the low wingtip. This will level the wing when your plane is coming toward you, avoiding a sharp bank, and possibly a crash.
Example: Say your plane is coming toward you, and the right wingtip is low, as if banked to the right. Move the stick to your left, toward the low wingtip. This will bring the plane's right wingtip up, and level the wing.
For me, triangle reinforcements have always been difficult to handle due to their shape, especially if they're coated with epoxy.
Try sticking your Xacto knife loosely into one end of the triangle. Then lay it on the bench so that the wide part of the triangle (the hypotenuse) is against the benchtop. Now apply the epoxy or other adhesive to the sides that will contact the airframe.
Next, by using the knife handle, insert the triangle into position in the airframe. Press down with your finger onto the wide side that has no glue, and carefully slide the knife out of the piece.
This way you can cleanly install triangle stock, and not get any glue on your fingers.
Here's what Ralph did to make all those wing ribs for the Joker's Wild planes:
Cut two ribs from 1/16-inch steel. Drill two holes along the center line, one near the leading edge, one near the trailing edge, for 1/4-inch bolts to pass through. Make sure both steel ribs are identical.
Use a steel rib as a template to draw ribs onto balsa sheet. Leave room around each rib. Cut each rib "block" out of the sheeting, and drill the holes in each.
Assemble all ribs on the correct length bolts, and sandwich all between the steel ribs. Using nuts, tighten the assembly down, making sure it's straight.
Now, using a belt sander (a disk sander will work too), remove the extra wood around the ribs down to when the steel begins touching the sander. Cut out the spar notches with a hand saw, and clean them out with a file.
This will make all the ribs for a wing at once, and they'll all be identical, resulting in a straight, uniform wing. It can also be used for a tapered wing (with all the ribs of different size), and bulkheads and formers can be made using this method too.
Fill plastic zip-lock bags of various sizes about 3/4 full of fine sand, and seal each well.
Use these to hold down large parts while building, such as wings. The sand will conform to the shape of parts well. They also work good when gluing sheeting to foam.
When adjusting air-bleed carburetors (the ones with the little hole in the front), a good rule to remember is the word "richen". Split this word in half (rich-en), and when you want the carburetor rich, turn the screw in. Of course leaning the carburetor would be turning the screw out.
Knowing the density or weight of balsa pieces can be important. It's especially useful when making ailerons or wingtips, because you want the pieces to be "matched", which will result in a better balanced and better flying airplane. To do this, choose balsa that is similar in weight by weighing them on a gram scale. If you don't have a gram scale, use the deflection method: Take the balsa pieces, and using heavy weights or sandbags, hold down a few inches of one end of each balsa piece onto the edge of a table. Make sure that equal amounts of each piece of balsa overhang the edge. Place a smaller weight onto the other end of each piece, and measure how far each one bends from the floor. The one that bends the most generally is the lighter piece. Using this method, you can choose balsa that is similar in density. Keep in mind that if you build from kits, you don't have to use the supplied wood if you don't like it!
After using a bottle of CA adhesive for a plane or two, the tip usually gets cured glue all over it. Remove the tip from the bottle and soak it in a closed jar of acetone. Nail polish remover also works, as long as it's the kind that contains acetone. After about an hour, the cured CA will gel, and is easily peeled off the tip.
If you use a neck strap on your transmitter, beware of getting it caught in a rotating propeller! Some people leave the strap around their neck and detach the transmitter while starting engines. This is a perfect way for it to get caught in the prop, especially if you start your planes on the ground rather than a stand or table. Also, having the transmitter nearby while starting an engine is potentially a hazard. When you pick up the transmitter make sure the strap doesn't swing into the prop.
3-blade propellers are useful when you have a scale plane that's modeled after a plane that uses them. However, since the engine has more mass to turn, the maximum RPM is lower. The general rule is to use a 3-bladed prop one inch smaller in diameter than the 2-blade you would normally use. This will allow close to the same maximum RPM as you would have with a 2-bladed prop. You may also increase the pitch by one inch, but experiment and see what works best with your engine and plane.
Firewalls of planes are normally coated with epoxy to help prevent fuel and oil damage to the wood. On planes with no cowling, apply a coat of epoxy on the firewall after you cover the plane with film covering. Make sure the film overlaps a little onto the firewall. This way the epoxy seals the edges of the film covering. Besides, most film adheres better to wood than epoxy, so that's another plus.
Goldberg Ultracote film covering has a paper backing that you can print on. Cut a 8.5 X 11 inch sheet, put it in an inkjet printer, and print your design on the paper backing (don't use a laser printer or anything that uses heat - it'll destroy your covering). This works well for large lettering. Make sure your image is reversed, so that when it's printed on the backing you can cut it out and it'll be correct when ironed on your plane. If you want to use a piece of covering that's smaller, print the design onto paper first. Then carefully tape the Ultracote to the paper over the design. Then run the whole thing through your printer, and the design should print in the same place.
When cutting a dowel, it's easy to make the cut crooked. To help ensure a nice 90-degree end, especially on larger diameters, try rolling the dowel into the bandsaw or scrollsaw blade.
After sweeping up broken glass off your shop floor, it's difficult to pick up tiny fragments. Try making a loop of duct tape, adhesive side out. Place the loop over your hand, and pat the fragments carefully so they stick to the tape. Then just throw the tape loop in the trash.
Here's a way to attach a receiver antenna to the back of your plane after it exits the fuselage. Take a short length of fuel tubing and make two cuts into it, dividing it into thirds, but make the cuts go through the tubing only halfway. Then pin the tubing to the top of the plane's fin. Thread the antenna through the tubing, lacing it through the cuts. This will keep the antenna somewhat taught and out of the way of control surfaces.
Sometimes there's a need to convert cubic inches to cubic centimeters (cc) or vice-versa where engine displacement is concerned. One cubic inch is equivelent to 16.39 cubic centimeters. So to convert from in3 to cc's, just multiply the in3 by 16.39 to get cc's. To convert cc's to in3, divide the cc's by 16.39 to get in3. And remember, a 7.5cc engine is the same as a .46 (pretty close).
Have you ever had a dent in a balsa leading edge? Try fixing it with water! Get a small diabetic syringe and put water in it. Inject a little water into the balsa into and around the dent in the leading edge. Heat the area with your covering iron. When the water starts boiling, it will build pressure and push the balsa out to its original shape. (Courtesy Victor A.)
Have you ever wanted to add more film covering (Monokote, Ultracote)to a plane you've already flown? It's difficult to get all the oil exhaust off the plane so the film will stick. Try using Cyanoacrylate (CA or superglue) kicker (catalyst). Just spray it on and wipe it off. I've been told it's a very good degreaser. (Courtesy Vince R.)
Sometimes firewalls and engine areas of older planes get soaked with oil from the fuel. This weakens glue joints to the point where a plane could fall apart in midair. Try using Cyanoacrylate (CA or superglue) kicker (catalyst). Just spray it on and wipe it off. I've been told it pulls the oil right out of the wood. Several treatments may be necessary. This also works if a fuel tank develops a leak and the fuselage gets soaked with fuel. (Courtesy Jevan F.)
Here's a good way to balance airplanes. While building your plane, insert a half-inch square piece of plywood where the balance point should be. For a low wing, this should be on the bottom of the wing, and for a high wing this would be on top of the wing (Note: sometimes something will be in the way, like a canopy, and you can't use this technique). When the plane is finished, put a small hook into the plywood and suspend the plane with wire or string. This way you can check the fore-aft balance AND the lateral balance at the same time (Note: a low wing will be suspended inverted).
Whenever I fiberglass a wing center section, I've found it's difficult to get the fiberglass cloth to lay flat after it's been folded in a bag. Here's two ways to make this easier: (1)Use thin CA to tack it down. You may saturate the whole cloth with thin CA, or apply epoxy. On foam wings, make sure you use CA safe for foam. (2)Give the cloth a light spraying of 3M Spray Adhesive, then apply it to the wing. I've found this method to work extremely well, and it's safe for foam. Then apply the epoxy as usual.
When installing control horns onto control surfaces the screwdriver invariably slips. The result is a hole poked into the covering material or a gouge in the balsa. There is a simple tool you can make that will eliminate this damage. Take a small piece of thin plywood and cut a rectangular opening in it just slightly larger than the base of the control horn. Place this opening around the control horn base before tightening the mounting screws. Now when the screwdriver slips there will be no damage to your new aircraft! (Courtesy Fred H., Derby Radio Control Club, Derby Kansas)
If you use nylon wing bolts on your plane that take a slot screwdriver, and you forget your screwdriver, try using a quarter. A quarter is actually easier to use than a screwdriver, since it won't slip off the bolt and damage your wing. What if you forget your quarter too? Usually you can get a quarter from loose change in your pocket, or your car.
Tail wheels and their associated parts take a lot of punishment, especially on rough fields. Sometimes the "tiller" part of the wire that goes into the rudder breaks out. Here's two ways to strengthen it: 1. Put hardwood or plywood into the part of the rudder that the tiller goes into, a piece about half an inch square by the rudder thickness should do for most planes. 2. Position the tiller so that it goes in-between the rudder control horn.
I use 1/8" brass tubing for fuel lines through firewalls. Silicone fuel tubing is connected to the brass on both sides of the firewall. To provide a better fit and extend the life of the silicone fuel tubing, carefully debur the ends of the brass by running a hobby knife along the inside edge of the brass. Then use fine sandpaper to smooth the outside edges. Since brass is a soft metal, the fine sandpaper (about 220 grit) works very well.
On planes with cowlings, I modify the engine's needle valve so it can be adjusted inside while the engine is running. I grind the outside end of the needle valve flat. Then I cut off the head of a hex bolt (either size 6 or 8), and solder the head onto the end of the needle valve. Then you can stick a hex wrench through a small hole in the cowling to adjust the valve.
When I buy a large (4 x 8 ft.) piece of foam, I like to cut a smaller piece off before using the hot wire. My hot wire isn't big enough to use on a full sheet, so I use a reciprocating electric knife, the kind used for meat and bread. It works pretty well for cutting off a usable piece.
If you have a wheel that's too big for the axle, make bushings from brass or aluminum tubing to make up the space. If you get tubing of the correct size, you can also make multiple bushings that fit inside each other, if that is required. Don't let wheels wobble! They'll wear out quicker, and make ground handling difficult.
If you have an airplane that you really want to take care of and look good for a long time, you have to occaisionally clean it really well. Do this by disassembling what you can (remove the wing and landing gear) and wipe it down with alcohol from the drug store. This will remove fuel oil residue well. This is also a good cleaning for film covering when you have to apply new film over old.
If you purchase fuel in plastic bottles, when they're empty, put it in an out of the way place with the cap off for about a day. This will allow the residual fuel to evaporate. If you place the cap on without airing it out, you have a potential bomb if an ignition source should ever penetrate the bottle. After the bottle is aired out, crush it, then replace the cap. Then recycle the plastic if you can at a recycling center. Many places don't take plastic, so if it does end up in a landfill, at least it will take up less space by being crushed. You should air out and crush metal fuel cans too.
If you use wheel collars with the tiny hex setscrews (I think most of us do), sometimes while tightening them the hex wrench rounds off a little, causing it to stick in the setscrew. So you end up turning the hex wrench to loosen the wheel collar just to get the wrench out. But now the setscrew may not be tight anymore. To check it, just turn it with your fingers. If it doesn't turn, it's tight enough. If you can turn it, try to tighten it more.
Sometimes I carve foam with a drill bit in my rotary tool, but I need a certain depth. I measure the depth I need on the bit, and wrap a piece of masking tape around the bit above the mark. Then when the bit is spinning, I know not to go past the edge of the tape. This will work if you need a not-all-the-way-through hole in almost any material.
Need an antenna tube inside that long fuselage? Next time you go to your favorite restaurant, grab five or six extra straws. At home, cut each with scissors lengthwise, colapse it in on itself and add a little tape. This colapse make the straw a smaller diameter, which works best for receiver antennas. Then make a small cut in one end, colapse it a little, and stick it into the next straw, and apply tape. You can chain several of these together, then put into the fuselage for holding the antenna.
There's no smoking signs at gas stations, as it could be dangerous to smoke while filling your gas tank. So why smoke while you fuel your airplane?
In your field box, keep the fuel storage, and starting battery, at opposite ends. If they're next to each other, and the battery or power panel shorts, it could ignite fuel vapors. I have two separate boxes, one has the fuel and pump, the other has the battery and tools. When I want to fuel, I just plug the fuel pump into the power panel on the other box. And even though there's two field boxes, they're easier for me to carry instead of one big heavy box.
Need a long straight hole through solid foam or several pieces of balsa, either in a fuselage or wing? Take an aluminum arrow shaft, and cut small notches on one end, as if to make it a saw. Put the shaft in a drill, and it will cut long straight holes for cables, pushrods, antennas, etc.
Have you ever tried soldering clevises or other small parts and didn't have anything to hold it with? Try a plain old wood clothespin. They work great for holding small hot parts while soldering, and they have many other modeling uses too.
After holding parts together attached with epoxy, you notice some epoxy got on your fingers. Before it's fully cured, just remove the epoxy with isopropyl alcohol (rubbing alcohol) and a rag. It does a good job of removing epoxy.
Here is a great model cleaner formula. It works better than Windex or similar cleaners and is inexpensive. 1/2 Gallon Model Cleaner: 1/4 cup ammonia, 1/2 pint denatured alcohol (not isopropyl alcohol), 1/2 teaspoon liquid detergent, and water as required to make 1/2 gallon total. (Courtesy Paul)
Sometimes it's necessary to cut off a bolt that is too long, especially on a firewall where the excess bolt might puncture the fuel tank. Wrap a piece of tape around the bolt with the edge of the tape even with the end of the bolt, making a "flag". Use a pen to mark on the tape where to cut the bolt. Using your Dremel or other rotary tool, cut the bolt at the mark. Since you don't cut through all of the tape, the excess bolt is captured, and will not fly away. This prevents it from hitting you, and keeps your workshop cleaner.
I like putting receiver antennas through tubes in fuselages or wings. The more flexible antennas (such as JR) are very difficult to stuff through the tubes. Put a cable in the tube, and tack-glue the end of the antenna to the cable, then carefully pull the cable out, which pulls the antenna through.
In warm summer months, keep in mind several RC items that deserve a temperature-controlled environment. Batteries left in airplanes that are hung in the garage can get too hot. Fuel can evaporate quicker. Monokote and other film coverings can separate from their backing. CA glues can age quicker. Try to keep these things cool so they�ll be ready to use in good condition when you need them.
Make an inexpensive tack cloth by lightly misting a paper towel with water, then wipe your balsa plane before covering. This will remove balsa dust, even dust that vacuuming doesn't get. This should result in a better covering finish.
If you're building a plane from a plan, and you need to trace unusual shapes like formers, try this: Make a photocopy of the parts on the plan you need. Place the photocopy upside down onto balsa sheet, then iron it on high heat. Some of the toner from the copy will transfer onto the balsa sheet, so you can cut the part out. Be careful though, because this process reverses the image, so it's good for symmetrical shapes only.
For control surface hinges I usually use the Sig or Dubro mylar hinge material, so I can economically cut hinges to the size I want. Before installation, I sand each with about 220-grit sandpaper, so thin CA will adhere better. I also cut the corners off, making them "dog-eared". This makes it easier to put them into the slot in the balsa.
Next time you mix epoxy on something and use it on your plane, you can check the cure rate by checking the residual leftover from mixing. This way you don't have to mess with the parts you epoxied, possibly bumping them out of position. And if you're impatient like me, ALWAYS use 5-minute epoxy!
1. Use a "hole pencil" or other device to accurately mark where to drill holes for the engine mount.
2. Check blind nuts before you install them in a firewall. Sometimes the threads aren't quite right and it's better to know before you use them.
3. When possible, it's easier to install blind nuts to the firewall before the firewall is attached to the fuselage.
4. Always use traiangle stock in the corners near a firewall, these add a lot of strength to the corners.
5. After the blind nuts are in the firewall, use a little thick CA or epoxy around the outside flange to secure them, but make sure you don't get glue on any threads.
6. Use hex bolts for engine mounts, and use the little hex wrenches. The 90-degree bend in the tool allows better leverage when tightening engine bolts.
When breaking in a new engine, always follow the manufacturer's instructions, and use the correct propeller. Never break-in an engine as a pusher! Pushers don't have as much airflow over them as tractors and can overheat when breaking-in. If you have your new engine going onto a pusher plane, break-in the engine on a test stand first.
You can extend the shelf life of cyanoacrylate adhesive (CA) by keeping it cool in the refrigerator. What this is really doing is keeping it dry, as CA reacts with moisture to cure.
Balsa, plywood, and a film covering is not the only stuff available! Try using EPS foam, EPP foam, BluCor foam, Coroplast, paint, and hot glue. Of course these less-expensive and more versatile materials are more appropriate for electric-powered planes (hint...hint)
Forget CA and epoxy! I've been using nothing but hot glue exclusively, even in places where you'd think epoxy is the only answer. Hot glue is much less expensive than other adhesives (especially CA). Of course hot glue is used on electric-powered foam planes (hint...hint).
Here's a quick way to check center of gravity location - mark where the CG should be on the bottom of each wing half. Then put a small bead of hot glue over the mark. Now you can hold up the plane by your fingertips, feeling for the bead, and check the balance point quicker.
When constructing slope soaring gliders made of EPP foam, Household Goop is excellent for attaching tail surfaces and wing to fuselage. It adheres really well to Coroplast, strapping tape, and the EPP foam itself. Don't worry about the disclaimer on the Goop packaging, it says do not use on foam, but it DOES work on EPP (however it will melt EPS foam).
Right after using Household Goop on your slope soarer, ensure that the parts (such as the wing) are in the proper alignment, and apply a bead of hot glue at the intersection of the parts. Since the hot glue will dry quickly, it works well to hold the parts in the proper alignment while the much stronger Household Goop cures.