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Using
Propellers for Hovercraft
Since the time of
early aviation, propellers have provided thrust for
many vehicles which are not in contact with the ground while in
operation. One such vehicle is the hovercraft. Some of the advantages
and disadvantages of thrust applications for propellers will be
referred to as they relate to operation on a hovercraft.
Advantages
Of
Propellers
An advantage of
propellers for hovercraft is the lower response time to
changes in engine throttle. This makes the hovercraft acceleration and
control more effective as the reaction time for the craft is reduced.
Another propeller
advantage is lower overall weight in comparison to a
comparable centrifugal blower. The resulting hovercraft can have a
higher power to weight ratio for better performance.
Also for
performance reasons, propellers typically develop a higher
average thrust per horse power ratio. This results in a lower
power requirement to achieve the same thrust as a similar centrifugal
blower.
Because a
propeller can produce thrust while operating at a higher
rotational speed, direct coupling to the engine can be used in some
applications, reducing overall craft weight.
Disadvantages
Of
Propellers
However,
propellers have disadvantages as well. The safety of the
enclosure is an issue for craft weight. Some larger propellers will
require additional strength to provide adequate protection. The extra
materials needed for large guards can quickly accumulate, adding
excessive weight to the craft.
Propellers also
have a higher rotational speed for a given air flow
than a centrifugal blower providing similar air flow. This represents
another safety concern for equipment or personnel in the plane of
rotation of the propeller.
For the above
reasons, propeller installation often requires a
certain degree of precision. This precision installation and alignment
is especially important if the propeller will be ducted to improve
thrust.
Thrust from
propellers is not the result of air escaping at high
pressure. The lower pressure air may not be best suited for
applications where high pressure is a necessity.
Conclusion
Carefully
consider the specifications and operating conditions of the
intended hovercraft before assuming that a propeller is needed. If
weight is a primary concern, then a properly fitted propeller may work
best. If higher pressure air flow is required, you may decide to use
different air flow equipment.
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