Austrian inventor J. Frech's "screw propellers" (1931)
- Thread starter Stargazer
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If only Leonardo could have seen this ! 
( picture via http://www.daviddarling.info/images/Leonardos_helicopter.jpg )
( picture via http://www.daviddarling.info/images/Leonardos_helicopter.jpg )
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Avimimus
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I wonder if there could be anything to such an idea? What would happen if the coil was ducted, tightened toward the back, had compressor blades in it, and was small enough to keep subsonic? Could you generate high airflow speeds at the upper end of what is viable for a prop? Of course, this project has none of those features...
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Screw turbines are in wide use as water power stations. That means, its use is proven, but only
the other way round, drawing off energy from the flow and with a much denser medium.
The mentioned advantages are a low pressure ratio and the ability to work at low flow rates.
For use in an aircraft, those characteristics probably aren't the best, not to mention the efficiency,
which is given as "around 80 %" in some brochures, but generally said to be not very good.
Perhaps an advantage, that is always mentioned for small power stations, situated at small rivers
and creeks could be translated to aviation use: Screw turbines are said to be "fish friendly", as fishes
in the water can pass the turbine unhurt. So maybe an aviation screw turbine would be safe against
bird strikes ?
the other way round, drawing off energy from the flow and with a much denser medium.
The mentioned advantages are a low pressure ratio and the ability to work at low flow rates.
For use in an aircraft, those characteristics probably aren't the best, not to mention the efficiency,
which is given as "around 80 %" in some brochures, but generally said to be not very good.
Perhaps an advantage, that is always mentioned for small power stations, situated at small rivers
and creeks could be translated to aviation use: Screw turbines are said to be "fish friendly", as fishes
in the water can pass the turbine unhurt. So maybe an aviation screw turbine would be safe against
bird strikes ?
