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1-26 Association GPS Information

By Bill Vickland


Having satisfactorily tested the concept of GPS scoring at the 2001 Championships at Ionia, the Association has elected to discontinue the use of turn point cameras in favor of inexpensive hand held GPS units for scoring. This concept was first introduce to the Association by Thomas A. Pressley at a meeting during the 2000 Championships at the Texas Soaring Association meet at Midlothian, Texas. To review Tom's excellent presentation, you can read and download his paper, "Using GARMIN Handheld GPS Receivers as Flight Recorders". While I am handing out credits, let me say that Larry Keegan, a technical support representative of Garmin, has graciously provided much of the significant data in this paper regarding the Garmin units.

The 1-26 Association Championships will use Garmin hand held GPS receivers almost exclusively for scoring. However, other hand held GPS brands may be used when coupled with data loggers having the capability to download in International Glider Council (IGC) format. The exclusion of other than Garmin handheld units stems from the requirements of the computer scoring system G7toWIN. The program employs only the Garmin interface protocol. Other hand held units may be used, but must be able to store the track log data and the time marks to a data logger and then must then be downloaded using the IGC interface. I am told that the Lowrance hand held GPS unit, used with a data logger will provide the necessary data, and if your particular GPS hand held can connect to the EW barograph, it too will work for you. There may be other combinations of GPS units and data loggers that will work, but if you intend to use them at the 2002 Championships, you must ensure that they will be acceptable. Tom Pressley will be our scorer this year, and he would have to approve other combinations.

There are approximately 32 Garmin hand held units available, but not all of them are suitable for use for navigating and scoring in our Championships. Later in this article, the various Garmin units are discussed regarding their suitability for 1-26 competition soaring.

The Championship rules are currently being revised to incorporate the GPS scoring system. As conceptualized at this time, the scoring system will operate as follows: The start gate will be a cylinder, radius to be determined by Rules Committee, from ground to an unlimited altitude. Pilots may depart on course without announcing their departure. This will hopefully eliminate gaggles near the gate and greatly improve the safety of our start system. The system will obviously eliminate the photo defense and the relight photo board, to everyone's relief. The pilots start time will be the last departure from the cylinder recorded by the GPS unit before completing the task.

Achieving a turn point will be indicated by evidence of track log data within a circle of mile radius around each turn point. Penalties, to be determined, similar to the turn point photo penalties will be applied if there are no data points, or indication of a line, within the circle. The Rules Committee is hard at work on the revisions needed for our 2002 Champions.

There are 32 different Garmin hand held models in existence, many of which have been discontinued, but which may be effectively used in 1-26 Championship competition scoring. The costs of these units vary from $100 to $1600, but some of them, even the most expensive current models are not useful for Championship scoring. Each of the factors, which influence the utility of the various models, is describe below.

Garmin GPS Characteristics
GPS Model Tracklog Data PointsBattery Life (Hrs)Voltage Track Interval Receiver Channels Cost (MSRP) Used Price * Interface Cable Recommended Reason
GPS 12 1024 24 5 - 8 Set/T 12 $231.00
010-10141-00 No Data
GPS 12CX 2048 36 10 - 32 Set/T 12 $386.00
010-10141-00 Yes
GPS 12MAP 1900 36 10 - 32 Set/T,D 12 $364.00
010-10141-00 Yes
GPS 12XL 1024 24 10 - 32 Set/T 12 $309.00 $142.00 010-10141-00 No Data
GPS II 750 20 10 - 32 Set/T 8 NLA
010-10141-00 No Data
GPS II + 1024 24 10 - 32 Set/T 12 $309.00
010-10141-00 No Data
GPS III 2000 36 10 - 32 Set/T,D 12 $194.00 $175.00 010-10141-00 Yes
GPS III+ 1900 36 10 - 32 Set/T,D 12 $375.00 $200.00 010-10141-00 Yes
GPS V 3000 25 8 - 35 Set/T,D 12 $536.00
010-10141-00 Yes
eTrex 1536 22 2.5 Resolution 12 $145.00
010-10206-00 No Interval
eTrex Summit 3000 22 2.5 Resolution 12 $267.00
010-10206-00 No Interval
eTrex Legend 2048 18 2.5 Set/T,D 12 $268.00
010-10206-00 Yes
eTrex Venture 2048 20 2.5 Set/T,D 12 $194.00
010-10206-00 Yes
eTrex Vista 3000 12 2.5 Set/T,D 12 $375.00
010-10206-00 Yes
eTrex Camo 2000 22 2.5 Resolution 12 $158.00
010-10206-00 No Interval
GPS 38 768 20 5 - 8 Set/T MT8 NLA $200.00 010-10141-00 No Interval
GPS 40 768 20 5 - 8 Set/T MT8 NLA $125.00 010-10141-00 No Interval
GPS 48 1024 24 10 - 32 Set/T 12 $183.00 $100.00 010-10141-00 No Interval
GPS 76 2048 16 10 - 40 Set/T,D 12 $251.00 $195.00 010-10141-00 Yes
GPSMap 76 2048 16 10 - 40 Set/T,D 12 $400.00 $299.00 010-10141-00 Yes
StreetPilot 475 16 10 - 40 Resolution 12 $636.00
010-10141-00 No Interval
StreetPilot Color 950 2.5 10 - 40 Resolution 12 $890.00
010-10141-00 No Interval
StreetPilot III 2000 2 - 20 10 - 40 Resolution 12 $1,272.00
010-10141-00 No Interval
eMap 2000 12 3.15 Resolution 12 $242.00 $175.00 010-10206-00 No Interval
GPS Pilot III 1900 8-10 10 - 32 Set/T 12 $549.00 $475.00 010-10141-00 Yes
GPS 89 2048 20 8 - 40 Set/T MT8 NLA $200.00 010-10141-00 Mixed
GPS 90 2048 20 8 - 40 Set/T MT8 NLA $225.00 010-10141-00 Mixed
GPS 92 2048 24 8 - 40 Set/T 12 $499.00 $300.00 010-10141-00 Yes
GPS 95 XL 768 4 - 6 5 - 40 Set/T,D MT8 $1,000.00 $275.00 320-00017-00 No Data
GPSCOM190 2048 3.5 - 6 9 - 33 Set/T 12 $1,149.00
010-10124-00 Yes
GPS Map 195 1900 8 - 10 6 - 40 Set/T,D 12 $949.00 $775.00 010-10135-02 Yes
GPS Map 295 1000 2.5 6 - 40 Resolution 12 $1,599.00
010-10141-00 No Data
* Interface Cable Description
010-10141-00 four pin round
320-00017-00 six pin flat, 95XL only
010-10135-02 195 only
010-10124-00 190 only
010-10206-00 four pin flat

Number of Track Log Data Points.
The number of track log data points in the various Garmin hand held units varies form 250 to 3000 points, and the interval for recording data points may be set for time, distance, or what Garmin calls resolution. In selecting a GPS, you should ensure that there are sufficient data points available to record a typical contest flight. In selecting a time interval for recording you will need to balance the data-recording interval with the total number of data point. However, you also need to ensure that the recording rate is sufficient to capture your turn point. For example, if you fly through edge of a mile circle at 60 miles per hour, and your GPS unit is logging data every 30 seconds, it is possible to pass through the circle without recording a data point within the circle, so you may have to slow down to spend at least 30 seconds within the circle. However, if your GPS is logging data every 10 seconds, you have to remain within the circle only 10 seconds in order ensure that you have recorded your turn point. Logging every 10 seconds will require more than 1000 data points in a three hour flight, which is calling it very close. Generally, the GPS will wrap around to replace your initial data points when you have used your original data points. Therefore, you will lose your starting data. Logging every 30 seconds will provide three times the flight duration, but you will have to be careful record sufficient data near the turn points. The table below indicates the flying time available using difference recording intervals with available data points.

Track Log Flight Times as a Function of Interval and Available Data Points
Available Data 10 Second Interval 15 Second Interval 30 Second Interval
1000 2.8 hrs 4.2 hrs 8.3 hrs
2000 5.6 hrs 8.3 hrs 16.7 hrs
3000 8.3 hrs 12.5 hrs 25.0 hrs

The trade-offs are obvious. You can use a unit with only 1000 data points effectively with an interval of 15 seconds. However, if you choose to make a second attempt at the task on the same day, you will have to either erase your first flight, or download it to the scorers computer before starting your second attempt. Pilots who want to spend as little time possible in the turn point circle will use an interval of only 10 seconds. You can erase the existing track log just before going through the start gate, providing you a full complement of data points for the task. For those who live on the edge, it is even feasible to shut off the GPS unit between turn points, thus saving data points, and then turning the unit on before arriving at the turn point. The rules will permit it. But if you have experienced the frustration of forgetting to take your photo defense, a mistake in this mode will be at least as frustrating.

Data Recording Rates
The Garmin hand held units record data by three different means, time sampling, distance sampling and what Garmin calls resolution. In some units you can select any one of these means and in some, only one. The attached spreadsheet shows which units offer which means. You should avoid units that provide only the Resolution means. This method monitors both distance and direction of motion, and while thermaling, will almost continuously record data. This of course, will exhaust your track log data very quickly. The time means provides the greatest control as you can set the recording rate from 1 second to 60 seconds, with of course, the consequences described above. I am not aware of anyone who has used the Distance means, but it may be an efficient way to record the flight.

Number of Channels
Since 1996 or 1997, Garmin has provided 12 receiver channels in its hand held units. Previous models may employ a multi-track receiver that may lose satellite connection in tight thermals, depending on the location of your antenna. If the unit is using satellites primarily on one side of the glider, a tight bank to the other side may result in the loss of signal. The unit would then have to initialize again in order to continue recording data. Having said that, pilots using the Garmin 90, which is included in this category, report satisfactory results.

Battery Life
Battery life is an important consideration if you intend to use only the internal (AA) batteries of the Garmin units, rather than wiring the unit into your glider battery. Battery life varies from 2.5 hours to 36 hours. My experience suggests that where a battery life range is given, it is dependent upon the use of the moving map. If intend to use the moving map, you should definitely use the lower number in your planning. If you wire your system into your glider battery system, you should also retain good batteries in the unit itself. This provides for backup if your primary battery should go dead.

Database, Mapbase, and Moving Maps
Garmin classifies their hand held units in three categories. Outdoor, Marine and Aviation. The Aviation units generally include the Jepperson database, which may or may not be useful to a contest pilot. It is not a benefit for scoring purposes. Some units have a Mapbase including major highways, and some can download detailed local county maps from Garmin's Mapsource CD including almost every dirt road in the county. The MapSource downloads require about 8 MB of memory per county. Only a few of the units can accept the detailed road maps. I don't find the moving map to be an essential feature, but it is nice to have. I find that 99% of my navigation uses only bearing, track and distance data.

Altitude and Compass Data
Both of these sound as though they would be effective tools for use in competition. Some units like the Garmin III Pilot measure both altitude and glide ratio, which sound like keen features to have. I use the glide ratio feature only occasionally, and I could fly as effectively without it.

Voltage
Voltage is significant only if you intend to connect your GPS unit to your glider battery system. Units cannot be used that list a single voltage requirement of less that your battery system. If your battery provides a voltage within the operating range listed you can connect it to your system.

Cost
The spreadsheet includes both Manufactures Recommended Retail Price (MSRP), and where I have data, the approximate cost of used units. My primary source of data for used units is eBay. I have received excellent recommendations regarding the Garmin III plus and the Garmin 89 and 90 which include the Jepperson database. These units are regularly sold on eBay for prices ranging from $150 to $225. The Garmin III Pilot, which includes the Jepperson database, has sold for $450 on eBay.

Additional Information
You can obtain additional information regarding each unit by accessing the Garmin website at www.Garmin.com. Go to the Outdoor, Marine or Aviation section for information concerning the unit you are searching additional information. You should download, and read Tom Pressley's paper on the SSA web page.

I hope this information assists you in choosing an inexpensive unit that you can use at the Championships. If you have additional questions regarding any units, contact me at BillVickland@comcast.com or call me at 703-527-5302. We will attempt to find someone in the Association who has used the unit and can recommend it, or we can call Larry Keegan for additional information.