WORLD ALTITUDE RECORD

The science of high altitude kite flight

While it is possible to fly kites to very high altitude or even record altitude without any knowledge of lift, drag, catenary, air density or metereology, knowledge of these sciences increases the chances of success significantly and I believe it will cut the time it takes to break the record by half.

If I knew nothing of lift, line drag and air density I may try to fly a small kite with a thick line on a hot day to record altitude. Common sense would dictate that a kite needs to be as light as possible consistant with strength and the line needs to be light. We don’t need to be a scientist to understand that. However, it is not clear how much these factors are crutial to the success or failure of the record attempts.  It took me 2 years of trial and error to come to the successful formula for kite design, line choice and wind conditions. It probably would have taken 10 year had I taken a methodical and thorough look at the physics of flight and the materials that have contributed to our achievements so far.It was an unknown area of flight dynamics and physical interactions with natural elements. This is not to say that there wasn’t a wealth of knowledge about the atmosphere and material science but there was little knowlege of these things as applied to high altitude kite flight. It was clear after 12 months of testing small kites on local fields that I need to investigate every aspect of flight science, line properties, kite design, GPS, atmospheric properties. Not only is the technologhy important but other aspects of the record attempts such as CASA regulations and potential flight locations needed investigation. I needed to develop this project properly otherwise I would waste thousands of hours in fruitless activity and 10’s of thousands of dollars in materials and expenditure on services.

The diagrams above show the effect of wind speed and drag on line angle and flying angle.

On the left is a diagram of launch methods depending on the ground wind strength.

Many of the methods used for launching a big kite were deveoped from practice and observation in the field but just as important was the facts obtained from metereology sites.

Wind gradient

This satellite image is important for us to get an overview of weather patterns and systems which may impact on the record attempt. Systems generally come from the west, northwest or south west. Australia is unique in that its entire southern coastline is exposed to antartic and Southern Ocean systems. The southern parts of the Australian mainland are  often like an oven but washed by sudden intrusion of cold air. This makes for a large and frequent variations in temperature and winds, particularly on southern and eastern coastal areas. The southerly buster is a well know wind that brings relief to the Sydney region on hot summer days. 

What would a guitar tuner have to do with kite line tension? Like a guitar string, kite line under tension vibrates. How rapidly the guitar string vibrates when plucked mostly depends on the mass and length of the string. Similarly a kite line under tension sings a tune as the wind blows. As long as the wind is strong enough to vibrate the kite line, the line will vibrate at a higher pitch as the tension increases. The pitch of the sound of the vibrating kite line is proportional to the tension. The tension is measured in Kg or lb. It happens that the relationship between line tension and pitch can be expressed as a formula then a program can be written that converts the sound picked up by a microphone into a Kg tension output. A similar program is MiniTuner but it is used to tune a guitar by comparing pitch of a plucked note to standard pitch.

Below is a prototype of a tensiometer using load cells from a bathroom scale. It needs further development as it is cumbersome and has too many sharp bits that may damage the line.

Another way of measuring tension is a tensiometer (above) this one has 2 fixed guide wheels either end and a central pulley that transfers the line tension to a load cell which outputs a voltage to a processor chip which displays tension values on LCD screen. This instrument is over $2,500. The plucked string method would potentially be mcuh cheaper but it would need to be evaluated for accuracy.

This graph below displays data that is essential to develop line sag estimates for an entire length of line. This determines how big a kite needs to be to counteract drag.

Above - This MS excel program calculates the dimensions of a standard delta. It maintains the relationships of all dimensions in correct proportions.

Just some of the Flight calculator parameters in a excel program I call Big Kite Flight Calculator. It took over six months of work. I didn’t know much about MS excel before I started. It has over 50 formulas behind the cell outputs and over 10 lookup tables. To calculate how high a kite may fly requires 30 input variables and fixed values. Some are dynamic variables, that is require, lookup tables to avoid circular references or data loops that lock the spreadsheet.