Model AviationEducational activity for young people.Educational activity for young people.

Presentation Placed in Public Domain by Bill KuhlPresentation Placed in Public Domain by Bill Kuhl

IntroductionModel aviation has been both an enjoyable and educational activity for much of my life. Two ways it has helped me is demonstrating my thinking was incorrect or inaccurate, and learning the process of refinement. Often I thought small changes in trim, propellers, or rubber motors would not make much of a difference but I was proven wrong. In the process of being proven incorrect I have learned to test individual aspects, record important data, and do the process again after making new changes.

It is my hope that this presentation can be used to promote the virtues of model aviation as a fun and educational activity for young people. Feel free to copy this presentation, I only asked that it is not sold for profit.

Bill Kuhl

History

The first rubber-powered model plane can be credited to the French aviation enthusiast, Alphonse Penaud. Initially he experimented with rubber-powered model helicopters but later turned to building model planes powered by rubber. The Wright brothers were first exposed to flight by the toy helicopter their father gave them based on the helicopter developed by Penaud.

First Rubber-powered Model AirplaneFlew 131 feet in1871.

Modern copy of Penaud’s Planophore

History

The First Aeromodeling Clubs

The first model airplane clubs started in the New York City area as early as 1907. Balsa wood was not used in model planes until around 1911, so models were constructed of materials such as bamboo, pine, and spruce.

Most models were twin pushers, two motor sticks with a prop in the rear of each, coming together in front. Viewed from the top it looked like a capital letter “A”. The propellers turned in opposing directions to cancel the effects of torque. Twin-pusher

History

City Sponsored Model Airplane Clubs

In the 1930’s, even city government promoted model aviationby sponsoring contest and clubs. Detroit Department of Recreation sponsored twenty-two clubs, and even sold modeling supplies. School gyms were open one night a weekfor indoor flying.

History

The Influence of Charles Lindbergh on Aeromodeling

Charles Lindbergh’s historic flight from New York to Paris in 1927 was the driving force to skyrocket the popularity of aeromodeling. Before Lindbergh’s flight only around a dozen model airplane kit manufacturers existed and within a year of the flight there were over two thousand.

Spirit of St. Louis

History

Today, the largest number of young people are exposed tofree flight model airplanes by an event that is part of a competitionheld in many middle and high schools known as “Science Olympiad”. The model airplane event is now known as,“The Wright Stuff”. Planes must be built according to specifications that limit the size and minimum weight of theairplane. Competitions are held at regional and national levels,with the top times equaling what a very skillful indoor modeler might accomplish.

Science Olympiad

Safety

• Relatively safe hobby because the models are light and fly slow.

• Biggest danger is when children do not use good judgment in retrieving a model that is caught in a tree, power line, or on top of a building.

• Students need to be taught safe techniques for working with razor blades. Another option is to pre-cut all pieces.

Safety is of primary importance for any activity for young people. Small rubber powered planes that weigh less than an ounce are relatively safe if used with common sense.

Building

What are the models made of?Balsa Wood

The most popular material for building rubber powered model airplanes is “balsa wood”. It is a very fast- growing tree which reaches a height of 15 feet in the first year, and 60 to 90 feet during the next six to ten years. Most balsa comes from balsa plantations in Ecuador owned and operated by the Baltek Corporation of Northvale, NJ.

Although balsa may appear rather fragile, it is fairly strong for its weight. The weight of balsa can vary considerably, for small models the best performance can be obtained by selecting lighter balsa.

What are the models made of?

Covering

Some models are constructed entirely of balsa wood, but more often a balsa structure is covered with a paper, tissue, or plastic. The covering not only covers the structure for flight, but also adds to the strength of the structure.

Some models use onion skin paper as plan and covering material. This is a strong material but is also rather heavy and can warp the structure as the humidity changes.

Building Questions

How long does it take to build a model airplane? This can vary a lot but the simplest planes such as the AMA Cub or Delta Dart can be completed in about an hour. Planes with ribs in wing and tail could take considerably longer.

Can you repair the plane if it breaks? Unless a really large truck runs over your plane, any breaks to the balsa wood should be easily glued. A bigger problem is when the plane becomes severally warped, if the warp is bad enough, better to build a new plane.

What Tools & Materials are Needed

The Essentials - razor blade or modeling knife, pins, and glue.

Building Surface that pins can be pushedinto ceiling tile sections or cardboard.

Normally plans are covered with wax paper, but some planes use the plan as the covering material.

Helpful to have a sanding block.

Gluestick is used to attach covering material to balsa framework.

What Tools & Materials are Needed

Winders

Essential to get flying times of more than a few seconds, is a mechanical winder. The rubber motor is stretched and lubricated, and turns are wound in as the winder is brought closer to the other end of the rubber loop. Common ratios for winders are; 15:1 and 5:1.

5:1 Winder 15:1 WinderArmorall can be

used as a lubricant

Flying

Free Flight

The cost of simple rubber-powered airplanes is low, but that is not why they are known as “free flight”, it is because they do not have any external control. The flight path is controlled by the trim adjustments in the model, the stability built into the model, and how the wind blows.

Where can these models be flown?

Flying indoors in a gym is a year-round activity.

Models can be flown outdoors when the breeze is very light.

Indoor Flying Gallery

Outdoor Flying Gallery

Educational AspectsI owe as much, if not more, to my uncle who introduced me to model airplanes when I was a kid 30+ years ago than I do to any of my university professors in helping me to become the knowledgeable structural engineer that I am today.

Thanks Uncle Tom.

Cliff

I know what you mean Cliff. I had an uncle who gave me a model airplane kit at Christmas time when I was maybe 9 years old. I thought it was a very big deal. This same uncle later gave me his old Boy Scout Manual. That uncle probably had a bigger influence on my life and the way I turned out than anyone else, even my parents.

Ed

Educational Aspects

Accuracy

Building and adjusting the model accurately can make a huge difference in the performance. As you build additional models, you will want to improve the accuracy of your work for aesthetic reasons. Hopefully this desire to do more accurate work will transfer into all areas of your life.

Educational AspectsCreativity

Designing and building your model airplane is rather easy to do. With some understanding of aerodynamics and using “rule of thumb” proportions, anyone can design a successful model.

There are many more unusual types of aircraft that can provide additional challenges such as flying wings or “canards” (tail first).

Flying Flying WingWing

aircraft in aircraft in

flight flight indoors.indoors.

Educational Aspects

Test Theories

Even the simplest model plane, flies according to the principles of aerodynamics and physics. Often the “common sense” ideas we have on the factors that affect flight performance are proven inaccurate. Small changes can make a huge difference; hopefully model aviation will open your mind to new ways of thinking.

Educational Aspects

Mathematics - Example calculation of winder turns.

Maximum turns per inch for 3/32" rubber is 129, for our rubber motor 10" long, maximum turns would be 1290. For sport flying 80% would result in 1032 turns.

129 x 10 = 1290 1290 x .8 = 1032

Once we know the total turns, it is easy to calculate the total cranks of the winder needed. Simply divide the total turns by the ratio of the winder.

For example using the 5:1: 1032 / 5 = 206.4, truncating to a whole number would be 206 winder turns.

Educational Aspects

Physics

How Does the Rubber Motor Work (in terms of energy transfer)?

When you crank the winder, mechanical energy is converted to potential energy stored in the rubber. To be more precise, this is elastic potential energy. Harcourts Dictionary defines elastic potential energy as "the energy made available for use by the return of an elastic body to its original configuration."

Potential energy of the wound rubber is converted to kinetic energy of the spinning propeller. Harcourts Dictionary defines kinetic energy as "the energy inherent in the motion of a body"

The EndThe End

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