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WWII No-Cal Free Flight Plans

A collection of 8 profile scale free-flight designs by Paul Bradley.

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The group of No-Cal plans being presented were originally developed as rubber powered free flight models for competition under rules defined by the Flying Aces Club (FAC). The term No-Cal comes from "no calories" meaning a profile model. The rules governing FAC No-Cal models are very simple; the wing span is limited to 16", the airplane being modeled must be recognizable, and the model can be represented with the landing gear in the up position if the full scale airplane has retractable landing gear. Each model flew well under rubber power. With the availability of some of the small electric motors, such as the Kennway KR1-D, these models were also converted to electric power. They proved to be great electric powered free flights. Some modifications were made to the structure to accommodate the heavier weight of electric power. These notes provide some general construction guidelines for the rubber powered models, as shown on the plans, and for conversion to electric power.

GENERAL CONSTRUCTION

As presented, each of the no-cal models are intended for either indoor flying, or flying in very calm outdoor conditions using rubber power. As a result, the structure has been designed to be very light, and to be lightly loaded. For the most part, each major component is made from strip wood with some sheet balsa parts in strategic areas. Construction simply involves covering the plan with a suitable adhesive layer, such as plastic wrap, and then laying out the outlines and sheet wood parts over the plan. The pieces can be held in place using your favorite method. I like to use straight pins that are placed over strip wood in an `X' pattern where the wood is trapped at the bottom of the `X'. I have also used pins with flat bottom plastic heads that can be placed near the part with the head applying clamping pressure to the part. This latter method works well on material that is fairly small in cross section, and soft. The key thing you want to avoid is having the wood actually pierced by the placement device.

The most significant construction note deals with the method used to form the outlines where the plans call for "wet form". To achieve the lightest weight, and also the best overall structural efficiency, almost all of the major component outlines are formed entirely with strip wood that has been molded to the proper shape. On the surface, this may sound like a lot of work and added assembly requirements to develop forms for molding the parts. The process that was used to build the prototypes of each model was actually very easy, very fast, and required no forms. This process works for gentle curves or very tight curves such as the tail surfaces on the T-28 and Mustang. The technique involves the use of a low wattage soldering iron, 25W, a work surface, and the piece of strip wood to be formed. After the soldering iron is heated, I wet the strip wood in my mouth in the area that will receive all of the immediate bending. Usually one or two strokes through my mouth provides plenty of moisture. I let the wood strip stand for about 30 sec and then begin the forming process. This is done by placing the wood strip on the work surface and then holding the barrel of the soldering iron lightly on the wood at the middle of the area to be formed. Gently pull the wood strip up against the soldering iron, and begin sliding the iron back and forth a small amount while pulling up on the strip. As you do this, you will be able to mold the strip into just about any desired curve. Work the strip for awhile, and then compare the emerging shape to the plan. You do not have to get it exact, just close to the target shape. It may be necessary to re-wet the area being formed several times before the target shape is achieved. Once the shape is close, place the formed strip over the plan and pin in place to the outline. This is where the exact shape is developed. The wood is still wet from the forming process and will conform to the final shape as developed with the pins. When it dries, it will hold the shape very nicely. That is all there is to it. With a little practice, you can zap out an outline in very little time. The results will be very light, and surprisingly durable. Some scorching may occur during the forming process. It can be removed by light sanding, but be careful not to remove too much material.

Covering is done before the components are assembled. The best covering material is tissue. This can be the super light weight variety known as Japanese tissue, or the type typically found in craft stores. The latter type is a bit heavier, but not so much as to seriously affect the finished model's flying ability. It is best to add any markings to the covering before it is applied to the structure. There are probably as many methods for doing this as there are modelers building this type of model. The most common method is to select a tissue paper that is close to the base color of the full scale airplane being modeled. Panel lines and related markings are then drawn on the tissue with a fine tipped marking pen. The plan can be used as a guide for the markings. Place the tissue paper over the plan, and then trace the markings. The tissue is transparent enough to be able to see the lines on the plan. The basic problem with this method is developing light colors, such as white, on a colored tissue paper. Some of the colored tissue paper can be bleached in the white areas. This is done by developing the outline with the marking pen. Then make up a diluted solution of bleach and water. Test the mixture on a scrap piece of the tissue. Using a small brush, cotton swab, etc. lightly stroke on the test tissue piece some of the bleach solution. After a short while, the tissue should lose the color in the affected area and return to a white paper base color. It is important not to get too much bleach in the solution as it will weaken the tissue. Once you are satisfied with the result, you can carefully apply the bleach solution to the inside of the guide lines you have drawn on the tissue to be used as covering. You will get some bleed, so be careful how close you work to the outlines. This process can produce some striking results for white lettering, stars, and related areas. Not all tissue colors work with this trick, but many do, so give them a try. Markings on the prototype models were developed by printing the base color and related markings on white tissue using a color ink jet printer. This worked extremely well, but does require access to a computer and color ink jet printer.

The models are covered on one side only. Since the motor stick is placed on the right side (as you look down on the model with the nose up), the fuselage/fin is covered on the left side. The wing and stab are covered on the top. The suggested adhesive for attaching the covering to the structure is either glue stick, or a spray adhesive such as 3M77. The spray adhesive is probably the easiest. Just spray the component being covered lightly with the adhesive, and then place the covering material over the component. The one drawback to the spray adhesive is the difficulty in adjusting the position of the tissue once it comes in contact with the structure. Basically, once in place, that is it. Some repositioning can be done when first applying the tissue, but you have to work quickly. Glue stick, on the other hand, does offer an ability to "work' the tissue after being applied. Alcohol can be applied to the area where the tissue has been applied with glue stick, and the tissue can then be lifted and repositioned. It is also possible to apply glue stick to the entire framework, let it dry, place the tissue in the desired position, and then wet the contact areas with alcohol to create a secure bond. Wrinkles and puckers should be worked out as much as possible, but do not shrink the tissue after it is applied. The structure cannot handle the forces of shrunk tissue. It will warp and distort.

After covering all components, they can be assembled into the final airframe. First the motor stick assembly should be attached to the fuselage. Be sure it is glued wherever it comes into contact with the fuselage structure. Next I like to glue the wing in position. Once dry, I then add the stab. This makes it easier to make sure the wing and stab are aligned without any built in twist (as you look from the rear of the model). Insert the prop assembly into the prop hanger, and the model is ready for the initial flights.

In their rubber power configuration, flight trimming begins with low power flights. Hand gliding does not really give much information. Start with 1/16" rubber that is made into a loop that is about twice the motor stick length. It will be necessary to use a mechanical winder to wind the motor. Start with a motor that is wound to about 30% of the number of turns for a fully wound motor. The actual number of turn will vary depending on the rubber you have. Make up a test motor and wind it until it breaks. Note the number of turns and subtract about 10%. This will give you a good baseline for the maximum turns figure. With the motor wound to 30% of the maximum value, launch the model. It should fly in a left circle and not show any tendency to stall or dive. Adjustments can be made by warping the surfaces. If there is a noticeable stall, it may be necessary to add some ballast to the nose. The easiest way to do this is simply stick a small dab of clay on the nose in a sheet area. Continue the low power flights until you have a stable left circle pattern. Once this is achieved increase the number of winds to 50%, then 70% and finally 100%. During each successive increase in power, it may be necessary to compensate for the increased torque causing the left turn to become too tight. Some right thrust can be added to the prop hanger to help compensate. It is also possible to bend the prop hanger to give some down thrust to help control any tendency to "balloon" during higher power portions of the flight.

ELECTRIC CONVERSION

Each of the No-Cal plans make nice electric powered free flights. In this configuration, they are best suited to outdoor flying in relatively calm conditions. Conversions have been done using the Kennway KR1-D motor using either two 50mh batteries, or a 3.3f capacitor. Both conversions produced very satisfying results. The capacitor based models if kept light can provide flights in the 30 sec duration range. This is really nice for limited area flying such as front yards and school yards. The battery based models are good for 1 to 2 minutes if you are careful not to fly in lift. If lift is encountered, then anything is possible.

Some modifications are necessary to allow the structure to handle the higher weight of electric power. The most notable change is to the fuselage/fin. For my conversions, is simply cut the fuselage/fin from a sheet of light 1/20" sheet balsa. By light I mean a sheet that is not more than 6lb/ft3 density. In this configuration, no motor stick is needed. The sheet wood based fuselage/fin was then covered with marked tissue just as the open frame rubber powered model. The wing and stab structure were retained as shown on the plans. For the wing, gussets were added to the center rib joint area to provide a bit more bending strength near the root. Like any electric model, weight is everything, so careful wood selection will make a big difference in the overall flight duration that can be achieved. Lighter also means more survivable if the model should encounter the ground in an attitude that was not intended.

The motor was simply glued to the fuselage with thick CA. After the entire model is assembled and the motor is in place, the battery pack or capacitor is added. This is done by taping the battery pack or capacitor to the fuselage in a position that brings the center of gravity to the desired location (connecting wires in place). Remove the prop from the motor, and add a dab of modeling clay to the nose that is equal in weight to the prop. Test glide the model to confirm that the CG is right. The model should provide a flat glide to the touch down point. An abrupt dive or stall would suggest a possible incidence problem between the wing and the stab. If that is the case, warp the stab to compensate. For a glide that is just a bit too steep or slightly stall prone, move the power source accordingly. When satisfied with the glide, the power pack can be permanently fixed to the fuselage with a drop of thick CA. Remove the clay, install the prop, and you are ready for your first flights.

The flight pattern should be a gentle left turn with a very gradual climb. With no drift, I have had flights in excess of two minutes (using batteries) where the model flew in a circle around me like it was a control line ship. The left circle lets you see the finished side of the model which looks great as it flies in a circle over your head. A lot of fun with very little time invested.

One final note. I have found for these models when using the Kennway KR1-D motor that a 2" Superior prop to be the very best. I tried many different props that are commonly used for these small electrics including a few of my own carved wonders. The 2" Superior prop consistently provided the best duration and thrust performance.

If you decide to build one of these models, I would love to hear about your results. You can shoot me an e-mail at BradleyP(at)ix.netcom.com.

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