A method for estimating the thrust and lift performance of an
integrated hovercraft
1.0 Summary and Introduction
An integrated hovercraft uses a single engine and fan to provide thrust and lift. A portion of the
airflow from the thrust fan is diverted by a splitter plate and ducts to supply air to the cushion.
The parameters governing the performance of the thrust and lift system, such as the position of
the splitter and size of the thrust duct, are often fixed early in the design process, and it can be
difficult to correct errors which come to light once the craft has been completed. Other factors,
such as the selection of the fan and drive ratios, can be costly to change.
Critical to the success of an integrated hovercraft design is the relationship of lift and thrust. It is
quite possible to set up a craft such that there is not adequate lift until thrust is close to
maximum, and whilst this is not too much of a problem for racing craft, it may lead to some
difficulties in the case of cruising craft. A better design would generate adequate lift whilst the
thrust is still a smaller fraction of the maximum.
There are established methods for analysing the performance of thrust fans (Reference 7 &
Reference 1), and tabular data is widely used to successfully predict thrust performance. In
addition, Reference 6 deals with the selection of lift fans. Reference 7 introduces the means to
evaluate the lift performances of integrated fans but does not integrate the lift and thrust
calculations.
A goal in this work was to develop a method of predicting the performance of an integrated fan
system in such a way as to understand the relationship between lift and thrust for the full range
of engine speeds, and in particular to identify the key data relating to the system, such as the
engine speed at which the craft will first lift, maximum thrust, etc. A subsidiary goal was to
provide the means for convenient calculation of the key parameters to allow the evaluation of
the relative performance of proposed designs.
The means