Abstract:
High Altitude Long Endurance (HALE) Unmanned Aerial Vehicles (UAVs) have been
considered for use in both civil and military applications for some years. Their
advantages, such as low cost, high survivability, long endurance, easy maintenance etc.
relative to alternatives, make them useful to scientist and military personnel.
In this thesis, a flexible conceptual design methodology for HALE UAVs has been
developed. This has been implemented as a FORTRAN computer code. However, it is
unlike some commercially available general aircraft design software which appears to
the user as a ‘black box’. In this case, the code is broken-down into several subprograms which deal with the different aspects such as parametric study, drag,
performance etc. Each of these can be either used as it stands, tailored to the user
needs in a particular case or by-passed if more accurate methods or known values are
available in a particular area.
During production of the methodology problems were encountered in a number of
areas due to the unusual operating regime and configurations of HALE UAVs.
Obtaining engine data for the high altitude of interest was a problem. This was
addressed through use of an existing engine modeling code to generate data. The high
altitude also leads to low Reynolds numbers and along with the high aspect ratios
typical of HALE UAV configurations, these place such vehicles beyond the validity
limits of data sheet methods for prediction of a number of important parameters.
Improved methods for the prediction of Oswald efficiency and maximum lift
coefficient, in particular, are recommended to be sought.
Accepting the above difficulties, an analysis of the Tier-II Plus, Global Hawk, was
carried out using published data to provide some validation of the methodology and
program. The results obtained provide confidence in the usefulness of the program in
the analysis and investigation of HALE UAVs.
