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How Things Fly - A Basic Principle of Propeller Aerodynamics


How do airplane propellers work in varied weather conditions ?  Are they better in some weather conditions, and worse in others ?

Begin for example, with a small block of wood in the shape of a cube standing by itself, isolated within the surrounding air.  It is displacing space
with its volume and therefore nothing else can occupy this same space, including air.  This is simply based on the principle that no two defined
entities of matter – solid, liquid, or gas - can occupy the same space.1  Where the block of wood is occupying space nothing else can be in its place – including air.  Quite simple.  Enough to insult a two-year-old’s intelligence.

Now take a droplet of water.  It too is occupying a place in space and therefore nothing else can occupy this same space, including air.  Where there is a droplet of water, there cannot be air occupying this same space.  This is quite simple too, just like the above example. 

Now take many droplets of water such that in a given volume of space, half is occupied by the water droplets and half by the air.  This could
simulate a heavy downpour of rain, or a torrential rainstorm.  In a downpour of rain, at any instant of time, water droplets are occupying a
percentage of the space - say 50% - and the air the other 50%.

Airplane propellers are designed to push air to generate thrust.  They are not designed to push water.  Referring to our rain model, in a volumetric space in front of the propeller, the space that was once occupied by air is now only half occupied by air and the other half by water droplets.  Only half the air is available to generate thrust.

During a rainfall, the air is essentially perforated by rain droplets and may cause a propeller to be ineffective for delivering thrust it needs to keep an airplane aloft.  It may stall, and fall out of the sky. 

Jet aircraft do not have this problem.  Jet aircraft are thought to have replaced the older-style-propeller airplane for transportation.  Propeller aircraft are still thought to be okay in good weather, but may not succeed beyond near-ideal conditions.  In this respect, a jet airliner
is considered a safer transport.  Also, the term “turbo-prop” gives an impression of an advanced design or an up-to-date technology, but a turbo-prop is still a propeller airplane.


A turboprop versus a jet aircraft


1.  This principle provides that the original defined entity of matter remains unaltered.