In August 1998 Aerosonde "Laima" flew into the record books by making the first crossing of the North Atlantic by a robotic aircraft and becoming the smallest aircraft to make the crossing.

"Laima", named after the Latvian Goddess of good fortune, was one of three Phase I Aerosondes built in Melbourne, Australia by Environmental Systems and Services (ES&S) for the University of Washington under a contract from the US Office of Naval Research. The Phase I Aerosonde, first defined by Holland, McGeer and Youngren (1992), has been developed to operational status by a consortium consisting of ES&S, The Insitu Group from Washington State, and The Australian Bureau of Meteorology.

The basic characteristics are described in Table 1

"Laima"'s flight commenced at Bell Island Airport using manual control and launch from a car roof rack.

Autonomous flight was commanded soon after takeoff. After system checkout, the Aerosonde was sent on its way at 09:59 UTC August 20 1998. Because of the limitations of UHF communications, "Laima" proceeded to completely robotic mode at 10:37 UTC.

at right, sister ship Trumper at launch
[photo: Keith Gosse]

The specified flight plan consisted of a series of way points for a route that went flight slightly south of a great circle (shortest distance) to the landing site at DERA Benbecula Range in the Outer Hebrides Fig. 1. Altitude was specified at 1680 m dropping to around 150 m on approach to Benbecula. Before launch, complete flight simulations had been made using winds provided by the U.S. NOAA/NCEP model to provide approximate times at each way point.

Figure 1 : Flight track of Aerosonde "Laima"

The first robotic aircraft to cross the North Atlantic.

*Approximate only: Potential variation 3.7-4.3 kg fuel used, 540-610 km/litre

The flight track took "Laima" across a weak cold front and along an occluded frontal zone Fig. 2. Satellite imagery for the period Fig. 3 indicated that "Laima" was in moderate to heavy rain for 14-18 hours, or well over half the entire flight. This was the longest sustained period of flight in continuous rain yet experienced by an Aerosonde, and some accumulation of water inside the fuselage was experienced.

Figure 2 : Surface isobaric and frontal analysis

Figure 3 : Infrared satellite imagery

"Laima" stored information on GPS location and altitude, and winds for the entire flight. Unfortunately, temperature and humidity observations were not taken. The time-variation of altitude along the track in Fig. 4 indicates that "Laima" closely followed its specified flight plan.

Figure 4 : Altitude variations

Enroute winds Fig. 5 were always a tailwind and varied from south westerly early in the flight to to northwesterly off Scotland. The maximum winds encountered were over 20 ms-1 (40 kt or 70 km/h) and the wind speed changes associated with passage through the weak frontal zones can be seen near 10 and 20 hours into the flight.

Winds predicted by the flight simulation within the NCEP Aviation Model analysis and forecast field conducted at the final update time are indicated by the heavy lines. These were obtained by linear time interpolation between NCEP analyses at 00 and 12 UTC on August 20 and the 00 UTC analysis and 12 UTC forecast on August 21.

The remarkably good agreement between the NCEP winds and those experienced during the flight resulted in the accurate estimation of "Laima"'s arrival time at Benbecula.

Figure 5 : Wind direction and speed

"Laima" was one of four aircraft launched from Bell Island during the week of 17 August. "Piper" was lost to what turned out to be a fairly obvious software problem in the transition from manual to automatic control, while "Trumper" and "Millionaire" were lost over the North Atlantic.

Since we had no enroute communication we do not know why "Trumper" and "Millionaire" failed to arrive, but the fault is presumed to lie with one or another of several low-reliability parts in the current design. These are being redesigned as the development program proceeds.

The North Atlantic crossing by "Laima" capped a good year for the Aerosonde project. We have just completed a 3-year development program that has provided the Phase I aircraft that completed the transatlantic crossing. Further developments will lead us to a more robust and flexible aircraft for routine operations, with the first aircraft going into operations in 1999.

In preparation for this, we have undertaken 360 h of operations in field exercises off the Australian West Coast (Operational trial for the Bureau of Meteorology), from Vancouver Island (for the Canadian AES), and from Dongsha Island with scientists from Taiwan for the South China Sea Monsoon Experiment. Some general milestones that have been achieved are provided in Table 3.

There is a lot left to do, but there is no longer any doubt that the concept works.

Acknowledgements

The Atlantic demonstration was possible only because of the efforts of many people and organisations. We would like in particular to thank the staff of Transport Canada, Nav. Canada, the UK Meteorological Office, and the UK Civil Aviation Authority.

We are also very grateful indeed to our very gracious and enthusiastic hosts on Bell Island and at the Benbecula Range.

The celebration is tempered with sadness. Sir James Lighthill was a great friend of the project during a difficult early period. He died in July whilst attempting his fifth swim around Sark Island in the English Channel. James would have been delighted to see this success.

The Aerosonde project has received its major funding by an Australian Tax-Syndication Program at Environmental Systems and Services (ES&S), together with grants from the US Office of Naval Research and Department of Energy, and the Australian Bureau of Meteorology.

The major sponsors for the North Atlantic Flight were the US Office of Naval Research and ES&S, with additional support provided by the University of Washington, The Insitu Group, the Boeing Co. and L-3 Communications, Conic Division.

As a footnote, "Laima" now hangs proudly in the Seattle Museum of Flight, Washington, USA