Free Flight Report September 2014

                                      Free Flight activity Labor Day - Horace Hagen

I spent some time observing the Free Flight activity over the Labor Day weekend and since I am not directly involved in indoor free flight I asked a few questions:

Question 1 - Covering Material:

Years ago the most commonly used covering material was micro film.  Micro film was made by filling a rectangular container with water and pouring lacquer on its surface.  A wire frame was then lifted from underneath to pull the floating lacquer film up and securing it onto the air frame.  The thickness of the microfilm is 0.25 Microns.  This was a messy procedure and consequently fell out of favor. Today, the most common covering material is manufactured by just one company in large rolls and costs $10,000.00 per roll.  Fortunately there are entrepreneurs who buy a fraction of a  roll and then resell the material in smaller quantities.  The material is primarily used as a separator in the manufacture of thin film capacitors and has a thickness of 0.5 Microns.  The film is transparent and is used that way by most competitors.  Some competitors crumple the film and this produces in a film that looks cloudy and is more visible.  It is interesting to note that this material is used by modelers in other countries as well.

Question 2 – Propellers

There are over 20 Free Flight categories; some propellers use balsa wood blades and others use built up frame construction covered with the same film used for the flying surfaces.  The balsa wood blades are carved from balsa wood blocks or made from balsa wood sheets shaved/sanded down to .005 to .015 inch in thickness and molded to shape.  The built up blades have frames consisting of very thin balsa wood sticks or carbon fiber rod .009 to .015 inches in diameter.  Each propeller can take several hours to build.  On some models variable pitch propellers are used.  The propeller hub is designed to have maximum pitch on a fully wound motor and slowly decreases as the motor winds down.  On the larger models the propeller speed ranges from 30 to 120 RPM.  On the smaller models the propeller speed ranges from 100 to 300 RPM.

Question 3 – Rubber Motors

The rubber used for these models is manufactured by the Good Year Company and is used by Free Flight competitors throughout the world.  “ArmorAll” or similar liquid is used as a lubricant to keep the rubber strands from sticking to each other.  To test and/or estimate the number of winds needed to get to a certain height fractional motors are used. A portion of the rubber motor is replaced with a balsa wood stick of varying lengths. A half motor would use half rubber and half balsa wood stick.  If the model reaches a height of 90 feet with a half motor then a full motor could reach 180 feet which is the maximum in Hangar 1.

Question 4 – Air Frames

Wings and tail surfaces are primarily constructed using balsa wood frames covered with film.  Every competition category has prescribed dimension and weight limits.  Some fuselages are made from solid balsa wood sticks and others are rolled tubes of balsa wood shaved/sanded down to .010 to .015 inches in thickness.  Some models use a boron filament so thin that it is invisible to the naked eye.  The filament is tied to the top of the fuselage at the nose and rubber motor end and placed over a post in the middle.  The idea is to control the warping of the fuselage due to the tension of the rubber motor which can affect the motor’s thrust line.  The air frames and some propellers are so fragile that if you walk passed them quickly you can damage same.  Words of caution – walk don’t run.

Question 5 – Adhesives

To minimize the addition of weight to the model a very common adhesive is Ambroid cement thinned with lacquer thinner.  The second (but heavier) most used adhesive is cyanoacrylate (CA) instant adhesive.

Question 6 – Model Steering

Indoor Free Flight models are at the mercy of air currents within a building.  To prevent a model from colliding with the walls or ceiling a balloon filled with Helium tied to a thin fishing line is used to steer the model.  The balloons are 2 to 3 feet in diameter and provide enough lift for a thin fishing line.  3/8 inch diameter foam caulking covers the top twenty feet of fishing line.  The caulking is soft and prevents the thin fishing line from damaging the model and is more visible.  To steer the model the line (caulking) is positioned in front of the model’s wing and when the wing touches the line it induces a turn.  If the model gets into a position where damage may result the line is positioned next to the propeller to stop same and the model can be moved or will slowly and safely descend along the line.

Question 7 - Height Measurement

To estimate the height of a model in the hangar a novel device is used. The Ikon Coolshot 40i laser range finder is a product developed for golfers. The device can be aimed at the model at any angle and it calculates the height using simple trigonometry. The accuracy of the device is approximately 18 inches. A very useful tool.

If you have not taken the time to watch the Free Flight activity in Hangar 1 you are missing out on a great experience.  I marvel at the patience these true modelers exhibit.  Most are world class competitors using the latest technologies and have brought back the World Championship FAI F1D class Gold, Silver and Bronze medals many times.