Tuesday, October 3, 2017

Why I Like Free Flight Part II

I have been overwhelmed by the number of views to my last post so I have decided to expand on that and share a little more about myself.  One thing that bothers me, is wasting anything and I am really impressed by things that are efficient.  I know I could do a better job of not wasting and I realize that other people have different needs; you are not going to pull a horse trailer with a Prius. What impresses me most of about my hybrid car is that the engineering that has been done in so many aspects to improve the gas mileage. The factors that contribute to the total result working together are many but the end result is I drive car that averages 60 mpg in the warmer months. Just some of the areas where improvements were made were recapturing energy from coasting and braking, drag reduction, increased thermal efficiency in the internal combustion engine, constantly variable transmission, and using battery power to help power the car some of the time.  It is a total system working together.

Typical Large Glow Engine Powered Free Flight - Dave Edmondson
Hybrid Car System of Engineering Ideas Work Together

Now how does this relate to free flight?  I see the competition free flight airplane as a total system that is optimized in many ways to give the longest duration given the constraints such as size, power, and minimum weight.  There are so many factors that can be optimized such as; the aspects of the construction materials such as balsa density and grain, building structure types, covering material, and warps built in to give the proper flight path for a free flying model airplane. With power system if it is a motor it should have a high power to weight ratio given constraints to the competition classification. Aspects of the propeller such as diameter, pitch, and pitch ratio can make a difference in power models including rubber powered models.

This Balsa Structure Made for Very Stiff Balsa Wing

Bob Hanford has Flown Free Flight Contests from a Young Age 
Beyond keeping your competition free flight model aloft consistently above a specified length of time, you want it to come down reliably after that specified time. This is where the dethermalizer system (DT) comes in to bring the model down quickly without damage while lifting air (thermals) can be trying to carry it higher still. There are many systems that are used but it is often a tradeoff between weight, cost, and what the builder prefers to use. The DT system can often take a fair amount of tweaking to work as reliable as possible.

Pressurized Fuel System and DT Timer on Dan Berry's Plane
Now after the model is built, you need to test fly it. With no control from the ground to save it should it fly in a path that results in a crash, you develop procedures to slowly lengthen the time of the motor run and length of glide before DT. If this model is rubber powered you use less turns of the rubber motor but you must be aware that the model might fly radically different with more turns of the rubber and increased power. For any type of model test glides are done first but this might only give a very rough idea how it will fly under power.  To me this is the most interesting and sometimes frustrating aspect of free flight models, the adjustment process. In getting your model to fly properly it calls on your knowledge of aerodynamic theory and putting it to practical use. Like any good experiment you want to change only a single variable at a time.

Rubber Powered Model Needs Propeller and Rubber Strands Matched - Skeeter Surgine

If you are flying indoor free flight it is a rather controlled environment but flying outdoor free flight which I have greater interest in now, has many additional aspects you must consider. There is the thermal air currents that you want to launch into but there is also sinking air, turbulence, and wind that will drift your model to parts unknown.  This year I purchased a used radio telemetry system which am I learning to use. A small radio transmitter is attached to the airplane that sends out a signal that you locate with a directional antenna.

Tiny RF Location Transmitter

Directional Antenna and Receiver 

My Indoor Rubber Powered Model
As the investment guru Jim Cramer likes to point out, here is the bottom line. Outdoor free flight model aviation gives one endless opportunities to learn engineering skills and practice real world experiments. By just timing the flight duration over a series of many flights you can see the results of many factors working together in a system operating in a changing environment. As a bonus for those of us passionate with the hobby, the thrill of seeing the model airplane flying with no external control is a major high.

Note: I did not mention gliders, topic for another post.

Hank Sperzel a Big Inspiration to Me

Bill Kuhl

Related Blog Articles 

Related Links to My Short Videos
https://youtu.be/8efeH5pGhe8 - My Background in Free Flight Model Airplanes
https://youtu.be/pQnNaRu4ah8 - Learning to use Walston Tracking System
https://youtu.be/2hifn3N3OZY - Guillow's Lancer with fuse DT
https://youtu.be/abp5nQBiHnU - Texas Timers Micro DT
https://youtu.be/LFCQFKum2QU - High Speed of Glow Powered Free Flight Ruth Bane

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