The Ol' Model Doctor

Model Doctor #1
Rust-O-Leum paint is available at most any hardware store at very reasonable prices in both bulk and spray cans. The paint is fuel proof and makes an excellent finishing material.

Model Doctor #2
Alliance brand rubber bands are the preferred brand for wing hold downs and other model applications. They do not deteriorate as rapidly as American brand (and others). Try them!

Model Doctor #3
Some two liter soda bottles have a black plastic reinforcement on the bottom of the bottle. This reinforcement piece makes an excellent radial engine cowling for your next project.

Model Doctor #4
Any yardage goods store sell a variety of straight pins which serve very well for balsa construction. Check out the extra long ball-head pins as an especially handy item.

Model Doctor #5
Trying to repair oil soaked wood can be very frustrating. Try using the product K2R Spot Remover in spray can, available in any super market in the laundry section, to get the oil out of the balsa wood. It works great. Heavily saturated sections may take several applications.

Model Doctor #6
A box of See's candy goes a long way in repairing damaged feelings as a result of an extra long day at the field.

Model Doctor #7
According to the Model Doctor, oil soaked balsa can be successfully glued with thin CA. It anyone is an expert at gluing oil soaked wood, it would be him.

Model Doctor #8
Sure Stick non-shrink spackling from Orchard Supply at $1.79 a pint makes a great, inexpensive filler putty. It's not gritty and sands easily.

Model Doctor #9
An easy way to secure Ny-rod or Golden-rod type push rods to the sides of the fuselage is to use small pieces of light fabric. Take a strip of the fabric and lay over the outer case of the push rod and press against the surface to which you wish to attach the push rod casing. Flow thin CA on to the fabric to bond the fabric to the surface. Oh yea, unless you also want to be bonded to the airframe, use a piece of Saran Wrap between your fingers and the fabric.

Model Doctor #10
If you are having trouble with your engine back firing and kicking off the propeller or spinner, try cutting a washer out of emery cloth. Put this emery cloth washer behind the propeller or spinner back plate, and tighten the propeller nut normally. This solves the problem even for cantankerous four-cycle engines.

Model Doctor #11
When cutting Monocote type covering material, try a Farber-Castell Uni-Ball pen to mark the covering where you want your cuts. These type of pens will actually write on the covering and the marks will wash off with a damp cloth.

Model Doctor #12
The job of cutting Monocote type covering material with an X-acto knife is made much easier when you lay the covering material on a thick bed of newspaper. The newspaper allows the X-acto blade to completely penetrate the covering material, and you will get straight, smooth, even cuts every time.

Model Doctor #13
When sealing your engine compartments with polyester resin or other similar coating materials, fill the mounting bolt holes and blind nuts with Pic Sticker to prevent your sealing material from fouling the threads or otherwise plugging up these areas. Another way of achieving the same result is to use a small birthday cake candle, and drip the melting wax into the holes. After sealing the compartment, the wax is easily pushed aside when you insert the screws.

Model Doctor #14
Nylon control surface hinges were a boon to R/C models. Unfortunately, none of our adhesives stick to them very well. For safety's sake, you should "pin" all your hinges after you assemble the control surfaces to the airframe. Do this by drilling a small hole through the structure and through the hinge material. Insert a round toothpick in the hole and glue with CA or aliphatic resin glue. Some planning is necessary for covering or finishing to avoid the hinge "pins" looking like an after thought. I usually install the hinges in the main structure first, pin them and sand everything smooth. Next, cover the model as you normally would. Lay a strip of covering material on the leading edge of each of the control surfaces. After ironing on this leading edge strip of material, install the control surface and pin the control surface side of the hinge. Now cover the control surface with your covering material. The result is completely pinned hinges without sacrificing a nice covering job.

Model Doctor #15
Given how expensive engines are now days, some preventative maintenance is a must. The easiest way to avoid buying expensive ball bearings is prevent ruining the ones that came with the engine. At the end of the flying day, run the engine up to operating temperature, then disconnect the fuel line in order to run the engine completely out of fuel. Remove the glo plug and dump after run oil into the carb until turning the engine over (with a starter) sprays the after run out the glo plug hole. This usually takes two or three good streams of oil into the carb. I use Marvel Mystery Oil as an after run oil. It works as well as the Prather After Run Oil and at $2.00 a pint, it's a lot less expensive. Isn't it strange how both oils are identical in appearance?

Model Doctor #16
After cutting threads in wood with a tap (for wing hold down bolts, for example) saturate the hole with thin CA to "case harden" the threads. You will have to run the tap through one more time after the CA sets to clean up the threads. The threads will now last longer than the airframe.

Model Doctor #17
Our erstwhile Senior Instructor says Mode 1 is the only way to fly. In most people's opinion, however, Mode 1 gives a whole new meaning to the term, "Dead Stick".

Model Doctor #18
A easy way to add a different look to your creation is to tint the canopy a color that compliments your airplane's color scheme. Rit Cloth Dye, available in most any supermarket, fabric store, or drug store will tint the clear plastic quite well. Mix up the dye in warm water in a container large enough to immerse the entire canopy. Dip the canopy for period of one minute or so, until you get the feel on how fast the dye is "taking". Rinse in cool water and dry off. If it is not dark enough, dip it again. I've had some that I have had to leave in the dye for an hour to get the effect I wanted. You can even be tricky about the tint by making a fixture to hold only a certain part of the canopy in the dye. How about two tone tinting jobs? Anyway, the effects you get are only limited by your imagination.

Model Doctor #19
The black plastic propellers made by Master Airscrew take a lot of punishment without breaking. That makes 'em great for beginners. While we are on the subject of propellers, it's a good idea to paint the tips of your propellers white. You can see the propeller arc easily this way, and better protect body parts (your body, that is). While you are at it, you can use the white paint as an aid in balancing your propellers (the white paint doesn't have to be on both sides of the propeller).

Model Doctor #20
Most stationary and office supply stores stock adhesive backed, vinyl letters and numbers which can be used to inexpensively decorate your airplane.

Model Doctor #21
Bamboo chopsticks with their ends carved to a thin paddle shape make excellent epoxy stirrers. Wipe off the excess epoxy as you go, and they will last forever.

Model Doctor #22
It is far more convenient to use socket head cap screws for most all model applications for many reasons. First, you can get as much torque as you need on the fastener without breaking the screw slot. You can really torque down on the fastener without fear of the driver slipping and going through the entire structure, or sliding across that perfect finish you just applied. The socket head fastener is also the easiest to get to at remote, confined or long distance locations. For long distances, you can make a long distance tool by soldering an allen wrench into a long piece of brass tubing. Try using 2-56 socket head screws for your control horns on all flying surfaces and you will find that you can tighten them down without fear of punching a hole through the structure.

Model Doctor #23
Common sense and AMA rules dictate that your name and address should be on your model. 

Model Doctor #24
Use a paper punch to cut out little circles of gummed paper. Stick these pieces to the backside of firewall blind nuts. Once you do this, you can fuel proof the tank compartment with resin without fouling the threads of the blind nuts.

Model Doctor #25
Roger Caron likes to save money. He uses Velcro to fasten his pilot figure in one plane and then can transfer it around as he pleases. He hasn't lost one yet. It must work , so the Ol' Model Doctor is going to try it. 

Model Doctor #26
Many of the small parts we buy are attached to cardboard display backings and are covered by a protective plastic covering. Save these protective plastic coverings that come as part of the packaging media. They are, in effect, small "bowls" and make excellent vessels in which to mix epoxy. The poly covers that come with coffee and cans of nuts also make excellent epoxy mixing dishes.

Model Doctor #27
Cut square pieces of old tee shirts and other similar, soft material and store same in a plastic bag in handy reach of your work bench. These make excellent all purpose rags, and best of all they are free.

Model Doctor #28
The old (very old, actually) Model Doctor has heard that women's nylon stockings are a cheap substitute for 1/2 ounce fiberglass and are especially handy in covering a wing. Simply slide the nylon over the wing, pull out the wrinkles and apply the resin.

Model Doctor #29
Fabric and yardage stores sell a material product known as "pellon". This can be used for general reinforcement and is especially good for wing center sections. Be careful when you do apply it, as it does have "grain" and should be applied in the direction that affords maximum strength.

Model Doctor #30
Ever try to epoxy something together only to end up with a glob of hard epoxy that needs to be sanded, and sanded, and sanded, and ...........? Next time you need to epoxy something without creating a "epoxy mountain" (two slabs of wood, broken fuselage sides, lead weights in helicopter blades, etc) try this. After applying the epoxy and joining the pieces, apply tape (masking or electrical work fine) over the fresh epoxy. After the epoxy sets, peel the tape off and presto...a relatively flat joint. Sometimes you will have to do some minor sanding to get the tape remnants off, but the result is much better than dealing with a huge ridge of epoxy.

Model Doctor #31
Do helicopters have a CG?....You bet. At least on a Shuttle the CG is about right when you slowly pick up the heli by the rotor head. As you take on more and more of the heli's weight, the rear of the skid should lift first. When the rear of the skid is about one half inch up, the rest of the heli should come off the surface it is sitting on. My Shuttle actually needed nose weight to achieve this condition.

Model Doctor #32
During the process of building your next masterpiece, it may become apparent that tail weight will be required. Lead weight for fishing lines is available at most sporting goods stores in the form of round (about 1/8" diameter) strips, several inches long. This strip lead is easy to cut up and imbed in the model during construction. For example, strips of lead can be inserted under the triangle stock used to reinforce the fin or stabilizer on many model designs. It can also be inserted into wing tips to provide lateral balance.

Model Doctor #33
Plastic engine cowls always look great on you airplane....until you start the engine. Past experience shows that either due to minor bumping, engine vibration or just pure spite, they will start to crack. You can stop the crack from growing by drilling a hole at the end point of the crack. This "crack stopper" is actually a device to relieve the high stress area at the end of the crack and is a common practice in working with sheet metal. the appearance of these cracks also point out that you should have spent some time reinforcing the cowl in the first place.

Model Doctor #34
How do you reinforce a plastic cowl, let me count the ways. One way is to rough up the inside of the cowl with heavy sandpaper (50-80 grit) or by scratching with the sharp point of a #11 Xacto blade. Mix up a batch of resin (epoxy or polyester) and lay fiberglass cloth inside the cowl. The bigger the cowl, the heavier the cloth should be. Another method simply requires the inside of the cowl be clean. SIG manufacturing sells a product called CELASTIC. It comes in large sheets and is about 1/16" thick and is fairly rigid. Cut a section of this material suitable for the area you want to reinforce and moisten it with acetone until it become limp and mushy. This does not take long, nor does it take much acetone. Now lay this material inside the cowl and form it to the contours of the cowl with your fingers. The acetone will literally melt the cowl plastic and the Celastic together and make a rigid, tough structure. After the Celastic dries out it can be sanded, cut, drilled, etc and it will retain its strength. One sheet will last a lifetime, unless you are like the ol' Model Doctor and have a propensity to bust up a lot of cowls.

Model Doctor #35
Tired of trying to figure out conversion between a logical measuring system called metric, and portions of King George's foot? Since the Ol' Model Doctor knew the good King personally, he provides us with the following table for the common sizes we deal with in modeling. 

                                             Inch....................MM
                                             1/32...................1.0
                                             1/16...................1.5
                                             3/32...................2.5
                                             1/8.....................3.0
                                             3/16...................5.0
                                             1/4.....................6.0
                                             5/16...................8.0
                                             3/8.....................9.5
                                             1/2.....................13.0
                                             1........................25.4

Model Doctor #36
Ever had the prop nut, washer, and propeller fly off while airborne? Ever heard that sickening "crack!" when you touch the starter to the engine and then spend the next hour looking for the prop nut in the tall weeds? Well, try this solution. Put a o-ring on the end of the engine crank shaft after you get everything secured. It may keep the prop nut from spinning all the way off next time your engine decides to be cantankerous. By the way, I hope you have been around long enough to know that propellers, especially wooden propellers, compress after being subjected to tightening down of the prop nut. That's why you see so many coming loose early Saturday morning at the field. What was tight for the last flight on Sunday, ain't tight a week later. Check em!

Model Doctor #37
Easy and cheap (a quality the Ol' Model Doctor has spent a lifetime refining) wheel chocks for you model can be made by cutting holes just large enough to accept the tires in foam pipe insulation available at most any hardware store. Cut the insulation in about six inch lengths. When installed, you plane will roll no mo.

Model Doctor #38
How about a cheap fake instrument panel for your next project? Browse through full scale aviation magazines until you find a cockpit view of about the right proportions. A pair of scissors and some white glue put you in business. Learning from sad experience, the Ol' Model Doctor advises that you should pay for the magazine before you cut a page out.

Model Doctor #39
File teeth shaped notches in one end of a piece of brass tubing and it becomes a very effective hole saw. The correct size will put perfect holes in bulkheads for push rod material. A 1/4" I.D. tube will drill out broken dowels from wing leading edges making a difficult repair easier.

Model Doctor #40
If you ever have had trouble getting nylon bolts started when attaching the wing or other major subassembly, try this. Bevel the threaded end of the bolt so it will tend to be self centering when you're trying to get it started. The easiest way to bevel the bolts is to stick 'em in one of those school kit hand held pencil sharpeners and twist.

Model Doctor #41
Are you concerned that a clevis may open up under the stress of flight conditions? There is usually some plastic tubing provided in the package of clevis when they come from the hobby shop. The plastic tubing is provided so you can slide it over the clevis once you have finished with your adjustments to prevent it from opening up. However, the provided plastic tubing often cuts or otherwise falls off the push rod. An excellent replacement (actually better than the originally provided tubing) is silicon fuel tubing. About a 1/4" length is more than sufficient. While on the subject of clevis, you should always use a 2-56 nut on the threaded rod to lock in the clevis once you get the clevis properly adjusted. Not only does this lock nut prevent the push rod from rotating and thereby changing your control surface deflection, you will be amazed as to how much slop is removed from the control system. Most of the threaded push rod ends have the threads pressed on the wire instead of cut on with a die. Couple this sloppy kind of thread with sloppy thread in the clevis itself, and the 2-56 lock nut becomes almost mandatory.

Model Doctor #42
If you scratch build or are trying to repair a model that landed somewhere other than the wheels, a replacement canopy is sometimes a real problem, especially if you are as cheap as the Ol' Model Doctor. Try studying the shapes of various soft drink or other plastic bottles to find exactly the contour you need. You cut the area of the bottle where it necks down to the cap it a variety of sections to make windshields or entire canopies. Don't forget that heat, in the form of hot or boiling water may change the almost right shape to the perfect fit.

Model Doctor #43
In the never ending battle to find a way to secure the receiver antenna to the tail feathers without breaking either, try this. A dress maker's straight pin is one of those guys with the blob of plastic on the head. Take one of these pins and poke it through a piece of fuel tubing which is about 1/4" long. Poke the pin through from the inside of the tubing such that the plastic blob fills up the I.D. of the tubing (if you can't do this, you shouldn't be building models). Now by pinching, twisting and pulling on the piece of fuel tubing you can get the antenna wire started through the fuel tubing and there will be enough friction to keep the wire from pulling out. Now, simply stick the pin into the top of the fin, or the side of the fuselage and pull the antenna taunt. The antenna will stay where you put it, but will move without breaking in the event of a large bump to the airframe. You'll never have to go on search for a newspaper rubber band again.

Model Doctor #44
I hate doing hinges. True, pinned hinges that is. Whether I use epoxy, slow or fast CA, or even spit, I always end up having to tear it all apart due to the fact that my hinge joint is glued fast. What do you do? Well you can just use small wood screws or toothpicks to hold your hinges in place by "pinning them" or you can use this method told to me by an old wise man (he knows who he is). Take a drinking straw and cut off about 4" in length. Pinch one end so that it is flat. Mix your epoxy in a mixing cup not on a piece of cardboard. And while putting the round end into your mouth gently suck epoxy into the straw through the flattened end. Withdraw the straw and then put the flattened end into your hinge gap and blow lightly. After you have done this to all the hinge gaps, say on the trailing edge of your wing insert your hinges and use rubbing alcohol to clean the hinge point of any excess. Oh yeah, use 15 minute epoxy because 5 minute will set too fast.

Model Doctor #45
If you have the Dremel jigsaw combo that has a sanding wheel and low speed Dremel tool attachment I have a suggestion for you. Have you ever noticed that when you turn the unit on the centrifugal force of the rotating sanding wheel causes the sand paper to "lift away" from the wheel ? If you have and you've tried to sand/grind that way, you will catch an edge from time to time and quite possibly ruin a delicate piece of your model. I purchased a small aerosol can of 3M contact cement. Spray your wheel and the back of the sanding disk with a fine mist, allow to get tacky and install in the usual manner pressing the disk against the wheel firmly. Viola! No more caught edges.

Model Doctor #46
The construction phase of a built up balsa model has been known to take several weeks, and sometimes more time! During this period it happens occasionally that a finished sanded piece, all ready for covering or painting gets bumped and dented. There is a way to get these dents out of balsa without additional filler material.

First, wet the dented area with plain ol' water. Make sure the dented section is well saturated and the water has soaked into the wood. Then take a Monokote iron, set to its hottest position and gently iron over the dented area. The steam being generated in the wood forces open the compressed section (i.e. the dent). I have seen this method take out some pretty big dents. In fact, it is not uncommon that a little additional sanding is required because the "dent" ends up higher then the surrounding area.

Model Doctor #47
Didya ever go through all the trouble to make up your control surface push rods only to find at installation time they were a 1/4" too short? Try this as an easy way to get the lengths exactly right. Tie a string to the control horn on the control surface. Drop the free end of the string through the fuselage. With the control surface in the neutral position, tie the other end of the string to the servo arm. Cut off the excess string at both tie points. Now, cut the string at both tie points and what you end up with is a piece of string which is the exact length of the push rod you will need to fabricate.

Model Doctor #48
If you have been flying R/C for more than two years, you will have started to collect transmitter and receiver battery packs that don't quite measure up any longer to cycle testing (you do routinely cycle test your battery packs, don't you?). Don't throw them away because there are some useful applications for these "unsafe for flight" battery packs. First, snip off the connector pigtail for use in making up your new battery packs. You will find homemade packs to be just as good, and substantially cheaper, as those supplied by your radio manufacturer. Disassemble and separate the cells in the old pack. If you have discharged the pack down to a low voltage, you can use a VOM (volt - ohm meter) to determine which of the cells are really no good. They will be the one(s) that are still significantly less that 1.2 volts, measured after you have let the discharged battery pack sit for about an hour. Deposit those low voltage cells in you favorite round container. The remaining cells can be wired up in series to make a self contained electric fuel pump, or wired in parallel with a glo connector added to make a engine starting pack, or can be wired in parallel and used as nose weight (in lieu of lead) with the added benefit of being an on board ignition system; you can even get fancy with a micro switch on the throttle servo so the current only comes on at low speeds. These are just a few uses of old, tired nicads.

Model Doctor #49
When you are through flying for the day, you should always prepare your engine for lay up, even if you intend to fly again the very next day. The hard bearing surfaces inside your engine can easily rust within a matter of hours. The quick and simple solution is to first run the engine completely out of fuel. Make sure the engine is up to normal operating temperature before you pull the fuel line off the carburetor. Then remove the glo plug and pour after run oil down the carburetor and into the cylinder (into the crank case vent fitting for four stroke engines). Turn the engine over with your starter until you are satisfied that the oil has been thoroughly distributed throughout the engine. Be careful because oil will come blasting out the glo plug hole during this operation. Reinstall the glo plug and you'll be ready to go next time with an engine that is in A-1 shape. There are some after run oils sold at the hobby shops that do a fine job. For cheap people like me, Marvel Mystery Oil or any Automatic Transmission Fluid also work just fine. Both are even the same color as the expensive spread....strange, isn't it?

Model Doctor #50
Hanger rash is the bane of every modeler. A cheap and easy way to afford some protection to your pride and joy is as follows. For a wing cover try taking a beach towel and fold it in half, lengthwise. Ask the wife to sew the towel together down its length and across one end. Note that your wife must do the sewing part, because you are obviously not qualified to operate a sewing machine. Presto, a wing cover. For the tail surfaces, find three Styrofoam blocks of appropriate size. Hog out slots in the blocks such that you can slide a block over each end of the horizontal stab and over the top of the fin. You can even get fancy and glue some dowel stock into the Styrofoam block so you can rubber band it in place. Presto - chango, tail feather protection.

Model Doctor #51
A big advantage with gliders is that there is almost no clean up involved. Power planes, on the other hand, can be a huge pain especially if you drip oil on to the front room carpet while you are carrying them back into the house after a day's flying. I have seem a variety of fluids used for cleaning up the gooey mess of exhaust residue. My personal favorite, being the el-cheapo that I am, is a 50-50 mixture of suds less ammonia and water. It cuts through the grease in short order, and leaves no scummy film on the airplane. However, as with Windex and other commercial cleaning solutions there are some drawbacks. Most important of these is that many cleaning solutions are highly corrosive. Therefore, you should avoid spraying them on engines and exposed radio switches. I have had switch failure directly because I continuously sprayed my cleaning solution on the switch. The switch internals were a rotted mess when I took it apart to see what went wrong. One answer to this problem is to use rubbing alcohol as a cleaning solution in engine compartments and around electronics. I routinely douse down my entire helicopter (engine, radio and all) with the stuff to clean it up. If used with a spray bottle, the alcohol can be blasted on to engines, engine compartments, etc. without necessity to rub the grease off with a rag. Give it a try.

Model Doctor #52
Do you have trouble getting you airplane to come to a complete stop when the engine is idling on the taxiway? Do you glace away and then look back only to find the airplane sitting in the drainage culvert? Try this bunkey....

Take the wheel collars holding the nose wheel on the landing gear wire and readjust them so they are sandwiching the nose wheel tightly, causing it to bind slightly on the axle. The amount of "bind" can be set such that a brisk engine idle will not cause the airplane to move. If done correctly, this braking action will not cause any problems in taxi or takeoff. You can also do a the same thing with the main gear wheels, but getting them so the "bind" is equal on both sides is difficult. Differential in binding on the mains will effect taxi and takeoff.

Model Doctor #53
I have found my purse strings tight from time to time, and that has driven me to search for alternate painting mediums to use on my planes. I think I have found a great, inexpensive alternative. OSH sells a wide color range of enamels in aerosol spray cans for $1.99 each. However, they are not nitro proof. The solution to fuel proofing is a coat or two of clear "Diamond Finish" Flecto Varathane. This is also available in aerosol spray cans and comes in satin, semi-gloss and high gloss. Another advantage of using the Varathane as a fuel proofer is that it can be cleaned up with water, if caught in time. It sprays on as a milky white, but dries crystal clear without tinting the base color. It costs $7.49 per can.

Model Doctor #54
How 'bout a quick and dirty wind velocity meter? Take your propeller balancer and attach a Top Flite 11 x 8 prop. Hold the balancer in the wind to achieve the maximum propeller RPM. Measure the RPM with your tachometer. Divide that RPM reading by 100 and the resulting number will be within 2 MPH of the actual wind velocity.

Model Doctor #55
Hanger rash is the bane of every modeler. A cheap and easy way to afford some protection to your pride and joy is as follows. For a wing cover try taking a beach towel and fold it in half, lengthwise. Ask the wife to sew the towel together down its length and across one end. Note that your wife must do the sewing part, because you are obviously not qualified to operate a sewing machine. Presto, a wing cover. For the tail surfaces, find three Styrofoam blocks of appropriate size. Hog out slots in the blocks such that you can slide a block over each end of the horizontal stab and over the top of the fin. You can even get fancy and glue some dowel stock into the Styrofoam block so you can rubber band it in place. Presto - chango, tail feather protection.

Model Doctor #56
The construction phase of a built up balsa model has been known to take several weeks, and sometimes more time! During this period it happens occasionally that a finished sanded piece, all ready for covering or painting gets bumped and dented. There is a way to get these dents out of balsa without additional filler material.

First, wet the dented area with plain ol' water. Make sure the dented section is well saturated and the water has soaked into the wood. Then take a Monokote iron, set to its hottest position and gently iron over the dented area. The steam being generated in the wood forces open the compressed section (i.e. the dent). I have seen this method take out some pretty big dents. In fact, it is not uncommon that a little additional sanding is required because the "dent" ends up higher then the surrounding area.

Model Doctor #57
Do you have trouble getting you airplane to come to a complete stop when the engine is idling on the taxiway? Do you glace away and then look back only to find the airplane sitting in the drainage culvert? Try this bunkey....

Take the wheel collars holding the nose wheel on the landing gear wire and readjust them so they are sandwiching the nose wheel tightly, causing it to bind slightly on the axle. The amount of "bind" can be set such that a brisk engine idle will not cause the airplane to move. If done correctly, this braking action will not cause any problems in taxi or takeoff. You can also do a the same thing with the main gear wheels, but getting them so the "bind" is equal on both sides is difficult. Differential in binding on the mains will effect taxi and takeoff.

Model Doctor #58
I have found my purse strings tight from time to time, and that has driven me to search for alternate painting mediums to use on my planes. I think I have found a great, inexpensive alternative. OSH sells a wide color range of enamels in aerosol spray cans for $1.99 each. However, they are not nitro proof. The solution to fuel proofing is a coat or two of clear "Diamond Finish" Flecto Varathane. This is also available in aerosol spray cans and comes in satin, semi-gloss and high gloss. Another advantage of using the Varathane as a fuel proofer is that it can be cleaned up with water, if caught in time. It sprays on as a milky white, but dries crystal clear without tinting the base color. It costs $7.49 per can.

Model Doctor #59

The ol' Model Doctor has addressed ways to secure your receiver antenna in past articles. Here's a few more.

Of course you know that you are never supposed to tie a knot in the antenna wire. However, you can get heat shrink tubing at most any electronics store of a size that just fits over the antenna wire (usually 22 ga wire). Heat the heat shrink tubing on to about the last inch or so of the antenna wire, leaving about three inches of the heat shrink extending beyond the antenna wire itself. You can then tie as many knots as you want in the heat shrink (i.e. tie the heat shrink to a rubber band) without effecting the antenna in any way.

The inner tubing of most flexible control rod (i.e NYROD, Goldenrod, etc.) makes a great fastening point for the receiver antenna. Glue a short piece (1/2" or so) to an appropriate place on the aft section of the fuselage (vertical or horizontal stab, fuselage side, etc). Run your antenna wire through the piece of tubing. Then wrap the antenna wire on the downstream side of the tube with just enough masking tape to prevent it from easily pulling back though the tube.

Speaking of antennas, never exit the receiver antenna wire to the exterior of the fuselage by running it out via the wing saddle, or anywhere near the wing-fuselage joint. The vibration and relative movement between the two during flight will eventually sever the antenna wire. The proper method is to punch an exit hole in the fuselage, near the receiver location and away from exhaust residue. Obtain from any electronic store heavy sleeving material of the size that will allow the antenna to slide through. CA about a three inch piece of this sleeving in the antenna hole such that about a 1/2" or so is inside the fuselage. Pass the antenna wire through the sleeving and attach to the rear of the fuselage by one of the Doctor's suggested methods. However, before you pass the wire through the fuselage, put a strain relief on the wire inside the fuselage to prevent it from being pulled out of the receiver. The best and cheapest strain relief is either a button or a broken off portion of a servo output arm. Simply weave the wire through the holes in the button or servo arm about three times and its done. Make sure you position the strain relief on the antenna wire such that there is some slack antenna inside the fuselage when all is done.

Model Doctor #60
The Model Doctor occasionally puts his brain in neutral by simply stealing ideas from others. The following was inspired by the PCC newsletter.

When you car corners poorly, you start looking at suspension or tire/wheel adjustments. When your airplane turns poorly, you may need to look at control adjustments. Many aircraft designs require a setup called, "aileron differential" to help the airplane turn better. The basic idea here is that the aileron moving in the up direction travels further that the opposite side aileron moving in the down direction. For example, the Goldberg Cub specifies 3/8" upward deflection and only 1/4" downward deflection.

The effect of the Goldberg Cub specification is that the downward moving aileron adds lift to one side of the plane (along with a small amount of drag), causing the airplane to roll toward the side with less lift, but it will also yaw away from the roll direction because of the drag induced by the aileron deflection. On the other side of the wing, the upward moving aileron reduces lift on that side for added roll effect, and also creates drag. The notion of having increased upward movement is to create more drag on that side of the airplane to offset the drag on the downward deflecting side, which creates an overall effect of the airplane yawing into the direction of the roll. This helps the airplane turn into the direction of the roll. This combination of roll and yaw will result in very smooth turns, once you get the amount of differential figured out. Of course, the differential can be applied in the other direction, depending on the result you are trying to achieve. You may want to use differential to eliminate any yaw when rolling the airplane.

Unless you use a servo for each aileron along with a computer radio to achieve differential electronically, you will have to build in aileron differential mechanically. There are at least two ways to get the job done. The first method is to offset the push rod attachments to the servo output arm or wheel. Typically, you mount the servo in the airplane and attach the push rods to the servo output wheel such that the push rods are at the midpoint of the wheel. That is to say if you drew a line from the attachment point of one of the push rods over to the other push rod, that line would pass directly over the output wheel attachment screw. That arrangement will result in exactly equal push rod movement in both directions; i.e. the same amount of up and down. To get differential, move, equally, both push rod attachment points around the wheel toward one another such that a line drawn between the two attachment points would fall either above or below the wheel attachment screw. The direction and amount you offset the push rod attachment points depends on the effect you are trying to get and the configuration of your airplane. Keep in mind the above example with the Cub when thinking about whether or not you want more up than down aileron.

The second method the achieve differential is by offsetting the control horn or torque rod attached to the aileron itself. If you looked straight on to the end of the aileron with the horn or torque rod attached, and that control horn or torque rod is exactly perpendicular to the aileron cross section, then equal fore and aft movements of the push rod attached to the control horn will cause equal up and down movement of the aileron. However, if you were to cant the control horn either forward or aft as opposed to a perpendicular installation, then equal fore and aft movement of the attached push rod will not result in equal up and down movement of the aileron. Again the direction and amount of the cant is dependent on the effect you are trying to achieve.

Try messing around with this effect, you may turn a dog into a pretty good flyer. By the way, this identical approach works with elevator set up. Ever had an airplane that requires more down than up elevator to respond the same whether upright or inverted?? Differential elevator will fix this such that your transmitter sticks won't know there is a difference.

Model Doctor #61
I don't want to be accused of labeling the Ol' Model Doctor as really sneaky, but......

Doc keeps the remains of one of his most monumental crashes out in the back forty and out of sight. When he is angling for a new kit in the household budget, he carts the remains off to the flying field for the day (loading up the car when no one is looking). When he returns home that afternoon, he ceremoniously drags these same remains through the house; acting real sad and heartbroken. After several days of moping around, Mrs. Doc can't stand it anymore and tells him to order up another!

I am told it works every time, as long as you remember to brush off the cobwebs and dust first. The one time the Doc forgot.....well, you know that limp he has?

Model Doctor #62
A broken metal engine mount or similar member can often be repaired and returned to original strength with a product called J.B. WELD. This is a type of epoxy that is very strong and will withstand high temperatures. Use in accordance with the directions and you won't be disappointed. It is available at most hardware and auto parts stores.

Model Doctor #63
Scott Morasci has found an easy way to cut complicated designs and numbers from both trim Monokote as well as regular Monokote. He draws out the design on paper and cuts out the paper to create a full sized pattern for the design. Then, using spray adhesive, he sprays the Monokote backing with adhesive. The adhesive will grab the full size paper pattern (make sure you lay down the pattern in such a way that the cut out Monokote comes out correctly). Cut out the monokote with a new #11 Xacto blade. Setting the Monokote on a glass surface also helps with clean cuts. When the design is cut out and you peel the Monokote backing off, you get a piece of Monokote faithfully duplicates your design and, you also end up with a reusable pattern.

Model Doctor #64
Here's something you might want to watch out for the next time you're walking around a flea market. Latch on to a child's wagon, similar to the old Radio Flyer wagons sold at most toy stores.

At a recent contest, I saw a fellow who had taken a child's wagon (aka Radio Flyer) and designed a nicely finished, plywood field box to fit within the confines of the wagon's cargo area. This included provisions for starting battery, fuel, parts, paper towels, etc; i.e. all that stuff you normally take to the field with you. Since there was substantial surface area inside the wagon, the box did not have to be very deep to accommodate all the "stuff" you need in a field box. In addition to this nicely compartmented field box inside the wagon, the field box was made such that at each corner of the wagon there was a receptacle that would firmly grip a 3/4" PVC pipe. He would then "plug in" a cradle fabricated from PVC pipe that was designed to hold whatever airplane he brought with him, at what ever height above the wagon he wanted it to be.

Obviously, a universal type cradle design would accommodate many types of aircraft, while a specific design might be required for some kind of trick scale aircraft. In addition, there is no need to glue the entire cradle assembly together with the PVC glue. Depending on how collapsible the cradle needs to be; you can drill, then pin (screws with wing nuts) many of the joints together so you can easily store the cradle inside the car. Remember to mark (color code) the parts in such a way that you can quickly assemble it at the field.

Anyway, with his set up all he had to do was lift the wagon out of the car, plug in the cradle, set the airplane on the cradle, and roll the whole kit and caboodle out to the pits. Similarly, when it was his turn to fly, the whole thing, airplane and all, rolled easily out to the flight line.

Model Doctor #65
Have you had to bend any brass tubing lately? Oh, I know about the various size spring sets you can buy that assist you in making a smooth bend, but what if you don't have a spring, or can't find it, or whatever? Here's what I found. Closely wrap the section to be bent with soft wire, like bailing wire. You'll be able to make a nice, almost kink free bend. Just unwrap the wire when you're done. Don't have any soft wire you say? Try stout twine like a mason's twine.

Model Doctor #66
Here's how Elmer Hanes Jr. attached a clever water rudder to his Eagle 63 for float flying. Elmer simply drilled a hole completely through the fuselage just forward of the vertical fin. Into this hole he glued a piece of inner Nyrod tubing which was long enough to stick out both the top and bottom of the fuselage about an eight of an inch. A piece of music wire with a brass rudder soldered on, a nose wheel steering arm, and some wheel collars attach the rudder assembly to the fuselage through this plastic tube. A linkage wire with adjustable clevis connecting the steering arm to the airplane's rudder control horn are all that is needed to put you in business. All very neat and simple, and the neatest thing is how easily it is removed for going back to land flying.

Model Doctor #67
From the Northeast Sailplane Products catalog comes this hint. To remove epoxy from yourself safely, use white vinegar. It's safe, cheap, and, of course, smelly. However, for approximately two thirds of the modelers that the Doc knows, the vinegar odor would be an improvement.

Model Doctor #68
Tired of stripping servo gears when something bumps the control surfaces on your plane? The answer is a inexpensive, effective restraining device from John DuGrosse. Take spring loaded, wooden clothespins and epoxy two pieces of 3/4" X 2" X 1/8" thick lite ply (one to each side) to the clothespin jaws to form a clamp. To use, simply clamp over the control surface and it's mating fixed surface to immobilize the whole system.

Model Doctor #69
Quit guessing at the setup of you airplanes. John DuGrosse has designed an accurate deflection degree indicator that can be fabricated from scrap found around your shop, and maybe a quick trip down to the drug store. All you need is a clothespin, a plastic school type protractor, some brass tubing, screws and a fishing weight.

Start by drilling a hole in the protractor exactly at the zero by ninety degree center axis. The hole should be sized such that you can just slip in one of those brass eyelets that come with your servo mounting grommets. Peen the small side of the eyelet over the protractor plastic to keep it in place in the protractor. Take a three inch long piece of 1/8" brass tubing and flatten the center section over a length of about 1/2". Drill a #44 hole (i.e. the right size for a 2-56 screw) through this flattened section. Take a small size of music wire and solder it into one end of the brass tube. This music wire will be the pointer to read against the protractor, so you may want to file a point on to the end if the wire. The distance between the hole drilled into the brass tube and the end of the pointer wire should be slightly less that the distance between the hole drilled into the protractor and the outside edge of the protractor. Solder the other end of the brass tube to a lead weight. John used a one ounce fishing weight, but the less weight you can get away with, the better. The amount of weight required will depend on the freedom of movement when the pointer assembly is attached to the protractor. Attach the pointer assembly to the protractor using a 2-56 screw, flat washers and either Locktite or a jam nut to keep everything in place. Set the protractor on a known level surface, such that the pointer can move freely, and bend adjust until the pointer is at the ninety degree mark on the protractor. Take a standard wooden clothes pin and cut about a half an inch off of one leg. Cut a groove on the outside of the long leg about one to two inches long. Epoxy one side of the protractor into this groove.

To use, simply clamp the device on to the horizontal surface to be adjusted. For example, after a trim flight, set the airplane on a suitable surface and clip the indicator onto the control surface. Read the degrees deflection on the protractor. Reset the transmitter trim to its center position, and then adjust the clevis until your previous deflection reading is obtained.

Model Doctor #70
A very non-messy way to keep epoxy out of hinges, is to cut small rectangles of discarded backing from those iron-on coverings. Cut a small slit in the plastic so it will slip over the hinge, pushing it right up against the hinge knuckle. Apply the epoxy to the hinge with a toothpick, then slip the hinge in place. After the epoxy has set, tear the plastic strip out, then cut a new piece to be used when attaching the control surface.

Model Doctor #71
The ol' Model Doctor has a helicopter rule of thumb, in spite of having two left thumbs. If the tail boom shakes, the imbalance is likely in the rotor head assembly. If it is the landing skids that shake, the imbalance is likely in the engine fan or clutch assembly.

Model Doctor #72
If you turn a beer can upside down, the concave end of the can makes a nifty epoxy mixing bowl. If you are worried about shaking up the can contents, the Ol' Model Doctor runs a free beer can emptying service just to make life a little easier for all Gold Country Flyers members.

Model Doctor #73
Try drilling a hole in the handle end of your small Xacto knife holder. Thread a key ring into this hole. Now you have a knife that won't roll off the work bench and has a built in hanger, as well.

Model Doctor #74
Are you getting tired of your CA glue nozzle always plugging up? Try this as an easy solution. Tie a piece of string about 12" long solidly around the neck of the glue bottle. Tie a loop about one inch in diameter in the free end of the string. Now, when you are through applying glue, twirl the bottle around with your finger in the loop of the string. Centrifugal force will push the glue out of the nozzle and back into the bottle.

George Reverman

Model Doctor #75
From Charles E. Snyder of Brandywine, MA comes an idea that should be of great help to all model builders. To keep fiberglass cloth or tape from unraveling and making all those nasty, loose threads, try spraying the part to be cut with spray hair set. It dries in seconds, does not get too stiff to work with and makes a nice clean edge. In addition, he has found it to be compatible with all adhesives and coatings.

Model Doctor #76
I have recommended using "Goop" or "PFM" in the past and I still do. However, I have found it is often a little too thick to use. Here is the proper way to thin these miracle adhesives. It can be thinned by using Toulene or Xylene available at your local hardware store. Be frugal, it only takes a little.

Model Doctor #77
Bob Barnett came across a nifty way to reinforce ABS plastic parts (cowlings, wheel pants, etc) that are supplied with most kits now days. The Ol' Model Doctor has previously talked about using fiberglass and resin, and SIG Celastic as ABS reinforcements. Bob's method uses fiberglass cloth and the blue ABS cement found at most any hardware store. The blue cement is the same stuff that you use to glue your lawn sprinkler pipe together. Simply lay the cloth inside the ABS part then paint on the blue goo. Let the glue set up and you're ready to go.

Model Doctor #78
Need something to act as a wheel chock when you are transporting your model around in the back of the pickup truck? Try taking a toilet paper or paper towel cardboard tube and cutting in a hole large enough to accommodate the model's wheel about mid point of its length. Makes an excellent (and cheap) wheel chock.

Model Doctor #79
For those of you who still use rubber bands to hold down the wing (ugh!!), try this. When you get the wing mounted and all the rubber bands you need over the wing, put one more rubber band on the rear dowel going across the fuselage (not back over the wing). Now, when you are done flying for the day, slide your hold down rubber bands off the front dowel. This rear rubber band will keep the others from flying all over the place.

Model Doctor #80
Getting a foam rubber wrapped fuel tank slid into a narrow fuselage is sometimes cause for using less than polite language. To make this seemingly impossible task an easy job try this. Save the clear plastic backing that comes with Monokote (and almost all other shrink coatings). Wrap your fuel tank with foam rubber as you want it to end up in the fuselage. Now tightly wrap the clear plastic around the tank/foam rubber; so tight as to compress the foam rubber as much as possible. Now slide the tank/foam rubber/clear plastic into the fuselage. Once in place, pull the clear plastic out and the foam will expand to tightly fit the tank in place.

Model Doctor #81
Did you ever have a problem where your wire landing gear seems to get weaker and weaker. A possible solution is to remove the gear from the airframe and remove all the hardware from the gear wire (i.e. - the wheels, collars, pants, etc). Preheat your kitchen oven to 450 F degrees. Place the wire on a cookie sheet in the oven for one hour. Turn off the oven and let the gear and the oven cool down together. Don't try to speed up the cooling process! What you have just done is to re-temper the music wire and you should have put new life into that old gear. Note that soldered joints should not be harmed as solder doesn't melt until about 700 F degrees.

Model Doctor #82
Installing cable pushrods for the throttle linkage has its advantages. One of them is that it doesn't have to be an exact length. It can be cut long and still serve well. The cable will flex when pushed forward and not cause a bind at the servo.

Model Doctor #83
If you have trouble cutting a cable without fraying it try melting some solder into the area you wish to cut. When hardened, use a Dremel cut off wheel to get a perfect cut.

Model Doctor #84
Want a cleaner running and looking engine? The ol' Model Doctor sez to put about three ounces of automotive fuel injection cleaner into a gallon of fuel. It is said to remove varnish and carbon from the engine. Will it harm your engine? We don't know; however, the Ol' Doc has been drinking it over ice cubes for years now. He shows signs of just a minimal amount of varnish and carbon.

Model Doctor #85
Looking for an inexpensive alternate to dope thinner? The manufacturer of paints used on most race cars, PPG, has a product labeled as PPG 876 that works well.

Model Doctor #86
People who have tried it claim that Formula 560 is an excellent canopy glue from the makers of ZAP. It is supposedly better than the old standby RC 56, which has been the standard up to now.

Model Doctor #87
Proving once again that Ol' Doc can actually read (I know he says he gets Playboy Magazine for the articles), he passes on that he read somewhere that it take two #64 rubber bands for each pound of total aircraft weight. Therefore, a six pound airplane would require at least six rubber bands on each side of the airplane to properly secure the wing, if you follow this theory. Be sure to account for the weight of a full fuel tank and the weight of the extra electrons of a fully charged battery.

Novices will often tend to orient their aircraft perpendicular to the ground with the hope that their instructor will save the day. The pull out from such an attitude will stress the wing hold down rubber bands to the limit.

Another way to determine if there are enough rubber bands (aside from the test procedure mentioned above) is to install six or eight bands on each side. The holding the fuselage directly in front of the wing (usually just above the fuel tank bay) attempt to lift the wing up from the saddle. Use a fair amount of force in this test. If you have enough rubber bands, the wing should not move at all. In most cases using new rubber bands, you should not need more than eight to a side.

Model Doctor #88
Have you lusted over one of those really spiffy transmitter cases advertised by Tower Hobbies and others? Well, you can achieve the same utility at about one forth the cost by using a plastic or composite brief case. I have seen these at flea markets for just a few dollars and they will easily hold two transmitters. You can get them new at a large office supply store for less than $20. The next problem is to get the foam rubber cut out to the shapes you need to fit the brief case and the transmitters. The foam can be obtained at any furniture upholster's shop or craft store. Cutting the foam so it looks like a professionally cut piece is easy...if you have an electric carving knife. Yep, the same thing that carves up Tom Turkey does a first rate job on the big slabs of foam. Anyway, I ended up with a two transmitter case that can take being bounced around in the trunk of your car without breaking off those tiny transmitter rate switches.

Model Doctor #89
Dubro makes a fitting set for the purpose of setting up a one gallon fuel can for easy attachment of fill and vent tubing. This same fitting set can be installed in that red plastic inner seal that comes with most plastic bottles of fuel. Punch two holes in this plastic seal, just as you would in setting up the cap of a metal fuel can. Install the pick up fuel line and filter, and vent fitting in the same way you would with a metal can. Now, use a very short piece of fuel tubing to hook up the filler piece that come with the DuBro fitting set. That way you can plug the filler piece into the vent hole of the fitting set AND still screw the plastic bottle cap onto the bottle, thereby sealing in the entire filler system and the fuel. The whole thing ends up more air tight than the metal fuel can version for the same amount of work, and can be easily transferred from one bottle to the next.

Model Doctor #90
For those who read my misfortunes while painting the Bucker Jungmann, here's a tip that might have help. You can remove masking tape with a lessened chance of pulling up the paint if you heat the tape with a heat gun as you pull the tape. Just a little heat is all that is needed; don't overdo it. Also, pull the tape back over itself when you are removing it to further reduce the risk of pulling paint up.

Model Doctor #91
If you have a "favorite" or otherwise standard fuel can you use in your flight box, then you routinely transfer fuel from one can to another. While you are doing this transfer, it is the perfect opportunity to make sure you are using only the cleanest of fuels. Put a "Mr. Coffee" or similar coffee filter in the funnel you use for the transfer for super fine filtration of the go juice.
Howard Smith

Model Doctor #92
It has become very popular to use multiple servos for single control functions. For example, splitting the elevators using a separate servo for each side for control redundancy, or utilizing one servo for each aileron to eliminate complex linkages are now commonplace. For those of you that follow this practice keep in mind that your receiver expects a certain power draw for each channel. When you utilize a "Y" connector to connect two or more servos to a single channel, you increase the power draw at that channel substantially. Further, if you start doubling up servos and those servos are the big quarter scale variety, and then use long servo leads, then put the whole mess under flight loads, you can overload the power output section of your receiver and cause component failure. Such a failure is usually immediately followed by the crash.

How do you know when you've put too much power output load on any one channel? I don't know. The power draw can be measured easily enough with a ammeter, but the receiver specs with respect to max power output from each channel are generally not available. I do know that I have had a mysterious servo drift problem with two large servos on a single channel go away when I pared the channel down to one servo. Modern computer radios ease this problem by allowing you to use two separate channels for the same control by mixing them together on the transmitter.

Keep this in mind as a possible cause if you are getting inconsistent performance for you radio system.

Model Doctor #93
There are a variety of methods to prevent airborne battery pack connectors and servo extension connectors from coming apart. The neatness of you radio installation has a lot to do with the susceptibility of your system for such a catastrophe. There are commercially available plastic clips, and the old stand by - plastic tape. Here is a new twist: Slide a piece of 3/8" or 1/2" heat shrink over one of the pig tails, then push the connector together. When satisfied, slide the heat shrink over the connection and shrink it down with your heat gun. The connector will never come apart and the installation looks very neat. The heat shrink can be easily removed with an Xacto knife.

Model Doctor #94
Neatness counts in your radio installations beyond just the appearance of your handiwork. Neat installations make maintenance and trouble shooting much easier, and they are far less prone to accidental damage (i.e. squeezing wires between the fuselage and wing, nicking a wire with a screw, etc.).

A standard for radio installations has been the use of the nylon pull ties used in the electronics industry for bundling wire runs to keep servo pig tails out of the way. These are especially prevalent in R/C helicopters. However, these pull ties are rigid and tend to have sharp edges. Coupled with the vibration of the plane (worse yet in a helicopter), the pull ties have been know to cut right through a servo lead.

A better alternative is available from some motorcycle shops in the form of one foot long, 1/2" wide Velcro strips. These strips are double sided in that the fuzzy stuff is on one side of the strip and the velcroie stuff in on the other side (I's proud of my ability to use technical terms). These strips can be used in the same manner as the pull ties, but are much softer around the wires.

Model Doctor #95
Do you wear glasses? Do you spray paint your models? The next time you do both at the same time, try this. Stretch a piece of Saran Wrap over the glasses using some Scotch tape to hold it in place. Now, when you are done painting simply peel off the Saran Wrap and you'll have glasses that you can actually see through.
Lowcountry R/C Flyer

Model Doctor #96
by Brooks Goodnow
Drill a small hole in the ferrule of your new paint brush and drop some CA in it. Now you won't lose nearly as many bristles on your work.

Model Doctor #97
by Brooks Goodnow
After doping, rinse the paint brush with thinner until clean, then wash the brush with warm, soapy water. Squeeze dry with a paper towel. Place the brush(s) in a jar, handle down. I use an old mayonnaise jar. You'll find that when the brush dries, it will be soft and with no paint or thinner to harden the bristles.

Model Doctor #98
by Bob Hatschek

(a greatly condensed version of his article in the FLYOFF)

Everybody seems to have a secret on keeping CA adhesives usable for long periods of time. One of the most popular is to store the CA in the refrigerator. However, the answer may really be simply keeping moisture away from the opened container. Bob does this by storing the opened CA bottles in a plastic baggie that has silica gel desiccant bags included. The silica gel keeps the moisture out and the CA flowing..... Oh yea, the silica gel can be revitalized by baking in you oven.

Model Doctor #99
A good surface to use for mixing epoxy is a notepad. After each use, the top sheet can be torn off, and the surface is ready for the next use. These notepads usually can be obtained for free as advertising from local businesses. For mixing sticks, there are a myriad of sizes and shapes available from craft and hobby stores for building "toothpick" models. They come in a large bag for a reasonable price. (Most common toothpicks are too small for most R/C use, and Popsicle sticks are kind of large.) I have found these two tips to be the most convenient and mess free way to deal with epoxy.
Mark Kallio

Model Doctor #100
The easiest way I have found to epoxy hinges in control surfaces and be sure to get the glue to fill the hinge slot is to use a plastic drinking straw as a disposable "hypodermic". Flatten the end of the straw between your fingers and test fit into the hinge slot so you will get the hang of inserting it. Then mix your epoxy, scoop some up in the end of the flattened straw, insert it into the slot, and "milk" the epoxy into the slot. You can then wipe the outside of the hinge slots off before inserting the hinges. This assures that each slot is filled with epoxy. I then like to take a small drill and drill though the control surface and pin the hinges with a toothpick. The toothpick should then be cut off flush, and a small piece of covering placed over the pin. These are only noticeable upon close inspection, and the benefit to the control surface is substantial.
Mark Kallio

Model Doctor #101
I came across a great way to cut hinge slots in wings and control surfaces. In the Bottom of my toolbox I found a circular saw blade with a hole for a 1/4 inch mandrel. I am sure there are many sources for such a blade at your local hardware store. Using a 1/4-20 bolt as a mandrel, I chucked this into my drill press. You should then "square" the blade to the table of the drill press (the markings on the drill press are usually not accurate enough for this) by setting the blade flush on the table and tightening it down. Then set the depth you want for the hinge slot. This cuts perfectly aligned hinge slots of the right size for pinned hinges. I have tried a lot of methods for cutting hinge slots, different jigs, etc., but I haven't found anything that works as well as this.
Mark Kallio

Model Doctor #102
Ever had trouble peeling the backing from mylar covering material? I certainly have, especially with the lower temp coverings. The easiest way to prevent a nervous breakdown trying to peel this stuff is to use two pieces of masking tape. At a corner of the mylar, stick a piece of masking tape on the front and back of the covering , with about half hanging over the edge so that the pieces of tape stick together past the edge of the covering material. Then peel the two pieces of tape apart, and presto! the backing peels right off. Happy covering!
Mark Kallio

Model Doctor #103
This month's tip shows you one of the most useful and inexpensive tools in my workshop. They are simply pieces of scrap aluminum angle iron cut to various links and of various sizes. I find that a selection of 1", 2", and 3" pieces varying in length from 1" to 6" to be quite helpful, and these can be obtained at a metal supply shop. If you have a metal fabricator near you, you might try asking him to sell you some scraps of angle about these sizes. Since these lengths are considered trash to these fellows, you may get lucky and get them for free. Even if you don't, the cost should be minimal, and as useful as these are I would have purchased new stock and cut it up into pieces to obtain these tools.

What good are they, you ask? Well, here are a few of the things I use them for, and I 'm sure you can come up with more once you start using them. First off, this is a great way to align the table on disk/belt sanders, drill presses, band saws, etc. You can use them to hold items to be glued or drilled exactly perpendicular to the work surface, such as drilling into the edge of sheeting, or holding ribs at 90 degrees to the table while your adhesive dries.
Mark Kallio

Model Doctor #104
An easy and cheap way to obtain an instrument panel for that sport model is to look through a full-size plane magazine for an advertisement showing instruments. I found one I liked and used my scanner to scan the image into the computer, and then pasted It into my word processor, scaling it to different sizes. This could also be done using a copy machine that will reduce. If using the computer, any size can be easily scaled, and I printed out several different sizes to have on hand. The ones I did were all in black and white, but if you have access to a color scanner and color printer, some really nice instrument panels can be made this way. One could also add color to black and white copied instruments using markers or colored pencils for even more realism. Shown is one of the planes that I have installed these instruments in. An instrument panel really adds a finishing touch to any model. Happy Modeling!
Mark Kallio

Model Doctor #105
Curving Balsa
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.
From Jeff's R/C Aviation Web Page

Model Doctor #106
Wing - Tail Alignment
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.
From Jeff's R/C Aviation Web Page

Model Doctor #107
Here's a flying tip for new pilots:
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. In other words, when landing just tell yourself "push it up" as you always move the stick in the direction of the low wing.
From Jeff's R/C Aviation Web Page

Model Doctor #108
Installing Triangle Stock
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 bench top. 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.
From Jeff's R/C Aviation Web Page

Model Doctor #109
Sandbag Weights
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.
From Jeff's R/C Aviation Web Page

Model Doctor #110
Cutting Balsa

When cutting a piece of wood with an Exacto knife, draw the knife so that if gets "caught" by the grain, it will go towards the scrap piece of material. This should always be done even with the use of a straightedge as the knife could be drawn towards it and possibly push the straightedge out of alignment.
From Jeff's R/C Aviation Web Page

Model Doctor #111
Servo Holes

When trying to install a servo in a plane, try this clever idea. Often, the cramped quarters inside your pride and joy doesn't leave enough room for a standard size drill. Use a standard Exacto handle with a 1/16" drill bit installed (yea, it will fit). The pilot hole can now be drilled by turning the handle and will make an acceptable hole for the servo mounting screw.
From Jeff's R/C Aviation Web Page

Model Doctor #112
Installing Easy Hinges

When installing CyA hinges, mark and slot balsa as you normally would. First, cut approx. 1/8 inch off the out side corners at 45 degrees so that the hinges go in easier. Then take a T-pin and insert through the hinge at the center so that the hinge can be pushed in only half way into the surface you are hinging. This keeps the hinge from being pushed too far into only one surface. once the control surface is in place, then remove the T-pin. Take your thin CyA with a small applicator tube and place 2 to 3 drops onto each hinge while keeping the surface pushed tightly against the trailing edge. It's best to do the two end hinges prior to gluing in the interior ones. Flex the control surface slightly and the CyA will soak right in. While you have it flexed, add 2 or 3 more drops on each hinge. As long as the CyA is being wicked in, you're OK. Do not put on any more than this or you will have it all over the MonoKote and your fingers. If this does happen, better have a real bottle of debonder handy.
From Jeff's R/C Aviation Web Page

Model Doctor #113
Installing Radio Gear

As a general rule while installing radios and servos, keep all weight forward. Most all airplanes have a short nose moment. For example, to balance a nose heavy aircraft, 1 oz. at the tail could be all it needs. While the same aircraft, being tail heavy, could take as much as 10 oz. or more to balance. It's a lot easier to add a little weight to the tail than a ton of weight to the nose. The best thing to do when you're unsure, is to temporarily place the battery, receiver and servos in place and check the C. G. without adding dead weight. But don't forget to check that lateral balance as well. It's best to check this prior to covering and after all radio gear and the engine are installed. In this way you can add small amounts of weight to the extreme tips of the wing, reducing the overall "balancing" weight greatly.
From Jeff's R/C Aviation Web Page

Model Doctor #114
Fiberglass Hint

How do you get the creases or lumps out of the fiberglass cloth we use to reinforce the center section of the wing? This method will completely eliminate them. Prior to applying the fiberglass cloth to the center section of the wing, take the time to iron it flat with your clothes iron. This will make it soooooo much easier to achieve a FLAT surface. Next, place the glass cloth or the center of the wing and tack it down to the surface with one drop of CyA (each corner, top and bottom). This may require that you may have to pull the cloth taught, but don't overdo it! Now you should have the cloth resting smoothly on the top of the wing. Now apply the resins (or CyA) over the cloth. You may find that after 3/4 of the cloth is attached that you now have puckers along one edge or the other, but this is easy to fix. Lift the material where you tacked it to the wing (remember I said to tack it down, not permanently attach it), pull taught, and tack it down again. There you have it!
From Jeff's R/C Aviation Web Page

Model Doctor #115
Polish that Gear
Have you ever found that the aluminum landing gear that came with your new pride and joy looked so ragged that you either want to paint or replace it? Here's a way that will not only make it look better than new, but will take less than 30 minutes! First you'll need the following materials:

400 to 600 grit Wet-or-Dry Sand Paper
Emery Cloth
Twinkler Silver Polish
Aluminum "Mag Wheel" Polish

If your landing gear looks really crappy and has allot of scratches, the first thing you'll need to do is to wet sand the aluminum (sound a little strange, but this goes pretty quickly). Keep your sanding strokes long and lengthwise along the gear. After most of the scratches are gone, the next step is to go over the landing gear with the Emery Cloth (don't wet sand with Emery Cloth, use it dry!). Just as you did earlier, keep your sanding strokes long and lengthwise along the gear. Now wipe down the gear to remove all the dust and crud. After that, apply the Twinkle silver polish and buff. Don't try to get the gear to shine at this point, that will come after the next step. Now go over the gear with the Emery Cloth lightly, this will bring the aluminum to it's optimum sheen this is the real/ trick, and I must admit was discovered by pure dumb luck). As a final step, go over the gear with the Mag Wheel Polish to protect the luster of the aluminum.

You'll be quite amazed at the looks of your "NEW" gear, as I was when I did this last week. The only draw-back to this process is your fingers will get a little dirty (OK, really filthy!) because of the aluminum dust, BUT I'm here to tell you, the finish looks stupendous!
From Jeff's R/C Aviation Web Page

Model Doctor #116
CyA Tip Clogs Unstuck

One of the real hassles of using the gap filling CyA's is, as always, the clogged tip on the bottle. As everyone who uses it knows. even with the best of techniques, the nozzle gets clogged long before the CyA is gone. There are several ways to solve this problem.

1. Cut off the tip. Now you are rid of the clog and with that 1/4" hole in the end of the nozzle the CyA is really easy to get out.
2. Drill out the tip. Same as above but now you also have a drill that is full of glue.
3. Throw the bottle across the shop and go get a new one. of course, if it's 11:30 on a Friday night you can kiss off wowing them with your new Belchfire 60 at the field Saturday.

Here is a solution that will work. Buy a package of extra tips and don't mutilate the tip when clogged. Instead, put it in a tightly capped jar (baby food or olive oil), filled with acetone. Acetone will dissolve the CyA and will not affect the nozzle. The next day it will be as good as new. Make sure the tip is dry and free of acetone before installing on the bottle. Remember, acetone is a fire hazard so treat it as such.
From Jeff's R/C Aviation Web Page

Model doctor #117
In our hobby we need lots of knickknacks with which to build our models, and some things are not often found in model shops. For example, do not throw away broken Tx aerials, or any other extendible antenna which comes with portable radios. This contraption offers an excellent variety of thin brass tubes which are very useful for bushes, small pushrods, tubing, guides, etc.

Model Doctor #118
If any of you build models from scratch or from a plan, you will know how tedious it is to copy ribs, formers, etc on to wood. I found an excellent way of doing this. You make a photocopy of the part you want to copy, dampen the paper with some cellulose thinner, place the paper on the wood facing down and iron it with an electric iron and hey presto, the ink from the photocopy is transferred to the wood.

Model Doctor #119
Nowadays it is common practice to seal our balsa covered models with laminating epoxy only (without any cloth) before painting. A lot of elbow grease is needed, however, to smooth down the resultant surface, and most of the time a second coat would also be necessary. For flat surfaces or straight curves (not compound curves) I have solved this problem and eased the process. After applying the epoxy place a smooth piece of plastic large enough to cover the whole area and without any creases over the surface, and smooth it out so that no creases appear. This may be a bit tedious, but you will get used to do it quickly. Remove any surplus epoxy that oozes out from the ends and leave overnight. When cured, remove the plastic sheet and you have a very smooth surface which needs a minimum of sanding. Needless to say, you can only do, for example, one surface of a wing at a time. While acknowledging the fact that there are other more sophisticated ways of achieving a smooth finish without too much sweat, I think this method is cheap and easy. What is actually happening is that the surface tension of the epoxy keeps it on the surface of the wood and as a result does not seep into the grain, leaving a glassy cover over the wood - just what you need! Again, attention must previously be given to producing a very smooth surface, otherwise the -results weal! -not -be-good.

Model Doctor #120
A lot has been said in the magazines on how to produce miniature rivets on scale models. One method which I have never seen is the use of those subminiature circular pieces of paper that fall out from a Telex machine!! I am aware that Telex machines are rapidly going out of existence, but if you ever saw one, you will note that it has a yellow and narrow strip of paper in the form of a roll which is punched with miniature holes (two sizes) while the machine is working - the tiny pieces of paper are perfect as scale rivets on normal sized scale models. Putting them on the model is another matter, as it needs quite a bit of patience - I use a small modeling pin to get hold of each of them, and dip each one of them in diluted PVA glue - thirty rivets is the maximum I could manage in one session!!!!

Model Doctor #121
When you rig up your fuel tank in your model, the usual practice is to use three outlets, one for the feed, one for filling and emptying (which end must be at the bottom of the tank) and another to act as a vent (which end must be at the top of the tank). Although when using two outlets only this idea is not so useful, it can also be used. Instead of bending the brass tubes so that their end is at the top or bottom (making it very awkward to insert the rubber plug) just bend them slightly up and down and use a short piece of silicone tubing to carry on to the top or bottom - it makes life easier!!!

Model Doctor #122
Broken or old and unwanted mains plugs and sockets, connectors, etc can come in quite handy in our hobby. The British type of three pin 13 amp plugs and sockets are particularly useful when you need any sort of collet for holding wheels in place or spacing your engine out from the firewall. The smaller two pin ones, even those sockets for bayonet type bulbs have small brass fittings which can be utilized for many things in our hobby. I have also come across large broken mains switches which have large diameter collets and large screws - I have used a couple of these to restrict air flow in my pneumatic retracts - a small piece of sheet brass or alum between the screw and the pipe will minimize the risk of puncturing the air pipe.

Model Doctor #123
When aligning wings with fuselage, all kit instructions emphasize accurate measurements generally from the wing tips to the end of the fuselage, but fail to suggest how. I found a very handy tool to do this job - your transmitter aerial!! Just extend it to the required length on one sic and see if the measurement of the other side tallies without varying the length, of course.

Model Doctor #124
Mike's Painting Tip
I am building a Midwest Cap 232. I am covering it with Ultracote deep blue, turquoise, and white, just like the ad. Now it was time to paint the cowl and wheel pants. Where do I get the paint that matches Ultracote? So I came up with Chevron Perfect paint, and let me tell you the perfect part is only a name. The blue was about four shades off and the white didn't even match, not to mention they don't have the turquoise. Oh well, every thing I've been doing on this plane has come out rotten, that's why it hasn't been to Show & Tell. Anyway, I went to Car Color in Salinas on Abott St. and brought a piece of my covering. The guy scanned it in a photo-type of computer of some sort, got the paint code, mixed the paint, and guess what? Matches perfect; and to make things better they put it in a spray can, a regular aerosol type, for nine bucks and it sprays like a paint gun. Now I've got six inches of one color that matches. Oh well, good luck and good painting.
Submitted by Mike Aliorri Salinas Area Modelers

Model Doctor #125

Here's a tip my buddy Jay and I just discovered. Please excuse if you already have it.

I was unsatisfied with my World Models T-34 performance with a OS-46LA, and wanted to upgrade to a OS 46FX. The footprint of the FX is slightly larger than the LA, so I needed to adjust the engine mount. While wrenching on it, I sheared the screw head off, and conventional methods would not remove it. This was a typical screw to blind nut through the firewall type installation, with Loctite. After contemplation and consternation I knew that my last resort short of a difficult removal and reinstallation of the blind nut in a very inaccessible place would be to heat the screw shank. But how? A torch or any other flame in the engine compartment is just asking for trouble. Charred wood, burning epoxy, and other visions danced through my head. Then Jay said, "how about a soldering iron applied to the screw shank and heated to melt the loctite? No flame, and it still gets plenty hot. " I heated it, applied a good vice grips and unscrewed it with ease. I tried it, it worked, and it saved me a whole lot of time and aggravation.

I hope this saves some other people time and aggravation. 

Share as you see fit.
Chris Larson

Model Doctor #126

After a day of flying....take the oil/fuel covered rubber bands and place them in a container containing "corn starch". Shake em up good so that they are covered well. The corn starch soaks up the oil and you'll have almost new rubber bands for that next flying session.  Snap them before securing that wing and you'll find that most of the corn starch just flys off.....leaving a fresh rubber band.
 

Cheers,   Bill Varney    Fredericksburg Aeromasters

Model Doctor #127

Actually, this is a link to someone else's web site. Lyman Slack (of the Florida Slacks) has created quite a web site. This link is to his version of a Model Doctor section and has a wealth of information. I admit I've stooped to the depths of laziness when I don't even copy someone's work; I just connect it with a link. Here ya go.......