Material needed :
- polythene flexible sheet (the one used to cover the salad in the vegetable garden will do)
- 60 gr/m2 glass cloth
- 120 gr/m2 glass cloth
- packing paper light
- a small piece of nylon cloth
- epoxy resin
- pure alcohol (the one used for liquors 95%)
- off course the wings with the shells
- an old fridge or freezer compressor (must be working) to be used as vacuum pump
- plastic to make a sealed bag and tape to seal it

Cut a piece of polythene big enough to envelope the wing (top and bottom) and make an invitation bent on the line of the leading edge (photo 1).
Cut a piece of packing paper like the polythene size.
Cut a piece of 60 gr glass cloth like the polythene size.
Cut 2 triangular pieces of 120gr glass cloth with base half the wing central cord and high 3/4 of the wing span (photo 2)
Cut 3 squares 1"x1" of nylon cloth

Now take the polythene sheet, place on it the paper and the 60gr cloth on the paper (no wax or detatching agent is needed as the epoxy will not stick on the polythene).
Mix the resin and the catalyst and dilute with the alcohol (40% about). For each wing in the photos I did use 12 gr resin, 5 gr catalyst and 6/7 gr alcohol. In my opinion it is better to dilute the resin beause it will be more fluid and you will need less resin to soak the glass cloth; remember that all the weight you place in this operation will increase the wing weight, whilst the alcohol will go away.
Now soak the whole surface using as less resin as...Continue Reading

First you need a sound file of your flight. Remember that the closer the pass to the microphone the more precise will the estimation be. If the passes are too far from the microphone the frequency analysis (and therefore the speed result) will not be real.
Second you need a spectrogram progam, which can be downloaded from internet, but you can also find as app for android in the playstore. With this program you will see graphically (and read) the incoming (higher) and outgoing (lower) frequencies (remember that the more preccise the reads will be the more real the result will be).
Third you need to calculate the sound speed, which depends on local temperature (°C) and humidity (%) of the moment (this latter is not much effective and could be ignored, but temperature is important as it could change results significantly), but this is included in the datasheet supplied herebelow. I suggest to separate the single passes audio and produce multiple frequency readings in order to have more speed computing which can give an idea of your model speed (input data are to be placed in the orange columns).
Hope this will be helpful for all those that do not want to put a gps data logger on the plane.
Finally remember that all the apps using Doppler effect to compute the speed of your model ignore the humidity datum and get the local temperature datum from the meteo system, that is why they require the gps to be on, therefore they can not be used on a second moment. If they do not ask the gps to be on do not trust their results.