Wing Frequency for Gliders
Checking the wing frequency on a glider always seems to be fiddly - you need to be able to count beats and seconds at the same time, and depending on who you listen to you should count for a minute, or 30 seconds, or something else. With this app all you need do is rest your phone or tablet on the wingtip, press Start, then rock the wingtip up and down. The app will monitor the resonant frequency and when it is sufficiently stable give you the answer! Typically this takes 15 seconds or so, and it will be accurate to within +/- 1 beat per minute.
For consistent results you should perform the test under the same conditions - i.e. glider in cradle vs. on main wheel. There will be a difference between the two readings so do it the same way at each inspection.
What is the Wing Frequency and why measure it?
The wing frequency is the resonant frequency of the glider wings, and is determined by the mass of the wings and their stiffness. It is a requirement in some countries for a measurement of the wing frequency to be done at each annual inspection, and compared to the previous year's measurement. If there is a significant change, especially a reduction, this can indicate that there has been damage to the wing spar, resulting in a loss of stiffness. In this case further investigation is warranted.
Typical gliders have wing frequencies in the range 100-300 beats/minute. Some manufacturers publish a wing frequency for their gliders, and this published figure can also be compared to measured numbers.