Wednesday, March 23, 2016

Calibration and the Free Flight Model Airplane

In recent months I have been experimenting with the Lego NXT robotics that I had purchased a few years ago. My focus lately has been to learn the different methods in algorithms for following a black line on a white background. Simpler methods work but result in a somewhat jerky path around the black line track.  Then I tried a program that starts with a “self-calibration” before going around the track and the performance was amazing, it followed the path really smooth and much faster.

Lego NXT Following Black Line Around a Track
Quadcopter Must Calibrate to Ground Below

This had me thinking about the definition of “calibration” and all the different places this idea is used. Calibration is adjusting to known or unvarying measure. Quadcopters do this to figure out what is level in relation to the ground below but what about some areas that are not so high tech? How about when you tune your musical instruments by comparing to a few notes on another instrument that is in tune? My mind then started thinking about free flight model airplanes and selecting the launch position and adjusting the power phase of the flight. During this process you are adjusting to the flying conditions at the time, would this be like a calibration process.

Rubber Powered Free Flight Should Drift Away from the Trees

For a free flight model airplane instead of using electronic instruments to record data such as light levels or distance from the ground you most likely will just feel the wind on your face to determine where to launch although contest flyers might use electronic devices for thermal detection. As the model plane normally will drift with the wind you will want to position yourself far upwind in the field boundaries. The velocity is what is important; in the physics definition, velocity is a combination of speed and direction.  Where the free flight airplane lands downwind normally results from the direction the airplane drifts and the speed the wind is blowing. In strong wind the airplane will normally drift farther.

Electric Free Flight Should Land Before Trees in the Background

If it is windy you will position upwind as far as possible but further adjustments might be possible to shorten the length of the flight. For rubber powered models reducing the number of winds should shorten the length of the flight. If it is a glow engine or electric powered model the timer that shuts off the length of the power at a time period is what you adjust.

Until the flight has ended you really do not know what to expect although experience in similar conditions will give you a better idea. I start out adjusting the length of power run to be really short and gradually lengthened as I observe how far down the field the airplane lands.

AMA Maxi Jr Launch

AMA Maxi Jr Path Changed and Landed on this Roof

The real life scenario of flying a free flight model airplanes outdoors is so much more complicated than this in that the air movement can quickly change, velocity (direction and speed) and the airplane can change course and fly a different direction. Thermal air currents cannot only take your airplane much higher but also change the velocity of the wind on the field. For this reason I normally fly my sport free flight model without dethermalizers early morning or evening when thermal activity is less prevalent. 

Indoor Free Flight Launched Close to Wall

Flying a rubber powered free flight indoors hopefully the amount of moving air will be very minimal but still there will be adjustments needed to best utilize the flying space. Based on the minimum width and height of the flying area you will need to adjust the diameter of circle that the airplane flies and have the airplane circle to the inside of that edge.  The maximum height the airplane can obtain will be limited by the ceiling height. If it is a smooth ceiling some bouncing from the ceiling might be alright but if there are rafters that the airplane could be caught in it is preferable to avoid letting the airplane climb over a certain height. Fewer winds can be used in the rubber motor but more common is to use a smaller width rubber strip or a different propeller.  

Sky Bunny Almost Landed in the Lake

Calling the launching of free flight model airplanes calibration might really be a stretch in that values are not normally measured and the values can vary a great deal. Yet I think my general point of the article is valid in that before launching a model airplane that flies completely with no control from the ground it is important to think about the factors that could influence the flight and adjust accordingly. With practice hopefully your human algorithms will be refined.

Bill Kuhl

Related Links

Basic Quadcopters   - my webpage

AMA Maxa Jr Perfect from the Start

Pushing the Edge with Small Field Free Flight

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