2005 PTAR – Logger analysis

2005 Imperial Bank President’s Trophy Air Race

Held at Tempe, Bloemfontein – 26 to 28 May 2005

Analysis of Logger Tracks

By Chris Booysen

Air Observer GPS loggers were used both for the test flying of aircraft with inadequate history as well as being fitted to aircraft in the race on both race days. SAPFA has approximately 20 loggers and so 20 aircraft were logged each day. 13 aircraft were logged on both days.

The loggers record the longitude and latitude and altitude every second, in other words the three dimensional position of the aircraft every second. Using these plotted positions the software can calculate the heading, climb/decent and ground speed of the aircraft. In addition the actual distance flown each day is calculated by the software

What is important to note is that there are a number of factors that affect the speed achieved by an aircraft. There is the inherent speed of the aircraft and the crew ability. The crew can increase the overall speed by flying in a straight line, using the winds, climbing and descending at the correct speeds and flying the aircraft in the most aerodynamic configuration (ie as “smoothly” as possible). Handicaps are set to remove the differences in the inherent speed of the aircraft and not the crew ability. GPS logging of aircraft can give an indication as to the accuracy of the flight. It can also give some indication of the usage of winds but it cannot give any indication of how well the aircraft was flown by the pilot. For example, it is impossible to detect a pilot that provides constant control input on the horizontal and vertical plain by means od a logger download. Constant input increase drag and reduces speed.

It is still the intention of SAPFA to purchase additional GPS loggers out of any surplus made at the Air Race until we are in the position to fit a logger in each aircraft.

On both days of the race there was a strong North Westerly wind. An analysis of the logger tracks shows that it was essential to climb as early as possible and as high as possible on the leg from Tierpoort Dam to Barkley East. Aircraft that climbed quickly to 10 000 ft gained approximately 40 knots when compared with the average speed they achieved in the next two legs back to Tempe into the headwind. Those aircraft that climbed slowly only gained about 36 knots while those that stayed low gained far less.
A table of the information gathered from the aircraft logged for both days is set out below.

The tracks flown on Day 1 by logged aircraft were fairly accurate with the exception of two aircraft that got lost. One flew past Tierpoort Dam, almost to Edenburg and the took approximately 35 minutes to find the dam. Another aircraft flew to the right of the mast at Springfontein and missed it. That aircraft flew approximately 120 NM until they eventually found the station (see top map).

The tracks flown on Day 2 were also flown fairly accurately. The leg from Koffiefontein back to Tempe seemed to catch most participants as that leg showed the largest deviation by most aircraft.

On an overall basis the shortest distance (of aircraft logged) was flown by Race 56 – ZU-APZ flown by Dieter Bock and Mark Steyn and the second shortest distance by Race 5- ZS-KSZ flown by Wally and George Brink. These competitors were placed 52nd and 53rd respectively. As mentioned above there are other factors that affect the speed of an aircraft but both these teams are experienced and their positions must be (at least partly) due to a harsh handicap. The Day 2 track of Dieter Bock shows that it is possible to go off course and still remain competitive. The correction when off track must be done to intercept the track at the next turning point.

It is interesting to note that the additional distances flown this year were greater than last year. Last year the winner was logged and only flew 2.4 miles over the two days racing. As the 2005 winner was not logged on Day 1 we do not have a comparison. The aircraft in 3rd (Race 104 Chris Briers and Jack Onderstall) and 5th position (Dave Mandel and Rod Crichton) in 2005 were logged and flew additional distances of 5.99 NM and 7.27 NM respectively.

A number of GPS loggers had problems. There were instances of loggers that were turned on late which meant that the software could not calculate the accurate distance flown. There was one instance where the logger lost satellite reception, one instance where the logger was turned off by the crew (after getting lost) and one instance where the logger failed to download any information.

Logger data – aircraft fitted with loggers for both days