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Wooden propellers are tolerant against vibrations. Therefore wooden propellers without any limit of life time last longer than metal or carbon propellers, for these only have a limited service life. For four-stroke engines with direct drive mainly wooden propellers are recommended, especially due to the self-generated engine vibrations and possible resonances in connection with a fibre composite construction. For example virtually all aircrafts of the Red-Bull-Race series fly with tuned and specially adjusted wooden propeller blades, because only this material meets the requirements.
The greenhouse effect which will in the long run lead to a global warming of the earth and to disastrous climate changes is for the most part referred to the increase of the CO2 concentration in the earths atmosphere. According to that the worldwide carbon emission is among the most urging problems of environmental protection.
During its growth period a tree extracts CO2 from the air, uses the carbon for the building of its own organic substance (see above) and then releases the oxygen. A 25-meter-high beech for example every day releases that amount of O2 which 3 human beings need for breathing.
