Re: Modelling an Aircraft

Gronum wrote

> We at EM Software & Systems (in conjunction with the Univ of
> Stellenbosch) will be looking at modeling a passenger aircraft
> (20 to 500MHz).
> We intend to do measurements in an anechoic chamber, on a scaled
> model and compare them with numerically obtained data.
>
> We would appreciate any reference to articles that you consider to be
> good on this subject.
> If you have published something on this subject would you be so kind
> as to send your name, journal and year published?

We have in the past performed quite a few aircraft studies and I have included
a summary below. We have tried in the past to get response of other people on
the list interested in the simulations of antennas on aircraft. I once again
wish to request anybody working in this field to contact me (or put
a similar summary of work in this area on the list), since we feel it will
benefit everybody if we can share some of the findings, problems etc.

==================================================
SUMMARY OF OUR EXPERIENCE WITH SIMULATION OF ANTENNAS ON AIRCRAFT
==================================================

Some information on our activities with simulation of antennas
on aircraft using the SuperNEC program and the Structure Interpolation
and Gridding (SIG) package:

We have in the past 4 years completed 6 major projects involving the
simulation of HF, VHF and UHF antennas on different aircraft.
These were

a) a Mirage fighter aircraft: We simulated the performance of two
antennas (118MHz - 420MHz) and obtained radiation patterns and
coupling between the antennas. We also performed scale model
measurements on a 10:1 copper scale model of the aircraft in an
anechoic chamber to validate the NEC2 results for three principle
plane pattern cuts (azimuth, pitch and roll patterns). We analyzed
the three dimensional radiation patterns of the aircraft using a
program called ASEP (Antenna Systems Evaluation Package) which
we developed ourselves. ASEP performs statistical propagation
calculations based on the NEC2 radiation patterns and the output is
the Probability of Communications (POC) for a given flight profile,
frequency, antenna position, transmit power and receiver sensitivity.
This gives the most useful indication of the suitability of the
antenna and its position on the aircraft for a specific application
(Air-to-ground communications for instance). NEC models was about
10000 segments using 1 plane of symmetry.

b) A Puma helicopter: Same study as above except for the frequency
range 30MHz-420MHz using models of about 6000 segments with no
symmetry. We used 30:1, 20:1 and 10:1 copper scale models validate
the NEC results by measurement in a anechoic chamber compact range.

c) A Lockheed C-130 Hercules transport aircraft: Same study as a)
except for a frequency range of 2-420MHz. Models was up to 12 000
segments with one plane of symmetry. We used 20:1, 30:1 and 72:1
copper scale models to do measurements on in order to validate
results from NEC2 and obtain detailed coupling between communication
and navigation antennas on the aircraft.

d) The Rooivalk Attack helicopter

Freq range 2-420MHz. Once again used scale model verification of
radiation patterns. Used SuperNEC to predict HF near-fields,
3D radiation patterns, VHF/UHF antenna-to-antenna coupling. We
also used ASEP (mentioned earlier) to obtain predictions of the
expected received signal for the aircraft flying through a specific
profile.

e) The Dakota (DC-3) transport aircraft

Simulated between 30 and 420 MHz. Radiation patterns and predicted
receive signals as above. Some additional validation of simulated
results were performed in this instance, however. We performed actual
measurements of the received signal strength from an aircraft in
flight at a specially equipped aircraft test range in South Africa.
These measured results were compared to the ASEP predicted signal
strengths (which uses the aircraft 3D radiation pattern together
with a propagation model). We achieved mean absolute errors of less
than 3 dB between measured and predicted received powers for flights
ranging over 70 nautical miles and altitudes ranging from 300 ft to
10 0000 ft. Some of these results (together with similar measurements
on the Pilatus trainer) will be presented at the ANTEM-96 conference
in Quebec.

f) The Pilatus trainer aircraft

Frequency range 100-150 MHz. Outputs as above.

We required a more advanced version of the NEC2 program because of
the size of problems we were simulating and we rewrote our own
program called "SuperNEC" in the C++ computer language. We introduced
a new iterative solution method which produces results in the order of
number of segments squared rather than the normal NEC2 where the
computer time grows as number of segments cubed. We also converted
the program to run in parallel on workstations which are linked by an
Ethernet LAN. In this way the program was run on 5 workstations in
parallel (3 SUN10 and 2 IBM RISC 600 workstations) which had a
combined memory of 5x64 MByte = 320 MByte RAM for storing the matrix.

I hope this may be of interest to yourself and other people on the list
and if you require any assistance with your simulations we will be happy
to assist.

Regards
Andre Fourie.

P.S. We have published papers on some of the work described above
and if anybody is interested I can provide references or
send you copies. There are 2 papers on the simulation of aircraft
antennas and 4 papers on the SuperNEC program theory. Two articles
were also published on the SIG package and one paper on
the ASEP approach validated with measured (in flight) data will presented
at the ANTEM-96 conference in Quebec during August.

e-mail: fourie_at_odie.ee.wits.ac.za
Tel: intl + 27 11 716 5386
Fax: intl + 27 11 339 4610
Address: Dr. APC Fourie, Dept Elec Eng, PO WITS, 2050, South Africa
Received on Mon Jul 29 1996 - 22:29:00 EDT