N1BZRich(at)aol.com
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 Posted: Wed Feb 20, 2008 4:33 pm Post subject: Just for Grins |
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Hello List,
I guess I was a little bored this afternoon being that the winds and rainy weather had kept me on the ground since last Friday, so obviously I needed to get some flying time. Even though the winds were almost a direct cross at 11 gusting to 19 when I departed, I knew that 31BZ could handle that. I had been wondering for some time how my automotive GPS would work in the airplane. It is a Garmin Street Pilot (don't remember the model number) and I use it in both vehicles even though the truck has On Star. I specifically ordered the 'Vette without On Star as I don't particularly want Big Brother to know how fast and how often I am tempted to put the "pedal to the metal" so to speak.
Anyway, the auto GPS basically has two modes - a map mode that gives speed and basic "letters" headings plus a map that you can determine the scale of; and the second mode is where you tell it a specific address that you want directions to and it will give turn by turn directions, both spoken and written across the top of the map for the next turn. It also gives the "letters" driving direction and instead of speed, an arrival time. I knew this would be basically useless in the air, but figured it would be fun to see some really high mph numbers in the map mode - that is if it would actually show aircraft type speeds (it does).
Well, as I said in the subject line, just for grins, today was the day to try it. First thing I noticed taxiing out was that it has a great diagram of the airport; as the ramp, taxiways, and runway show up in great detail at JGG. It showed my position as right on the narrow taxiway as I taxied out for takeoff. Once on the runway it showed me right on the centerline, so it's accuracy must be pretty good. Of course my taxi speeds was shown on the unit while taxiing out.
Maybe now is a good time to go over how 31BZ is equipped so we can make some comparisons as to speed while in the air. 31BZ has a dual Grand Rapids EFIS with a built in GR GPS in one of the units. I also have a back up Garmin 296 that is mounted on the center consol under the fuel selector. My GR EFIS is the model that has the Synthetic Approach (SAP) mode that gives highway in the sky steering to what ever runway you tell it to use at the airport you are going to. Really a neat set up and now having flown numerous SAPs to various airports, I am convinced it is much easier and accurate than any GCA or ILS that I ever flew for real in fighters or in one of my previous Bonanzas. All you really have to do is put the flight path vector inside of the steering boxes that come at you from the approach end of the runway as shown on the GR screen and if you do that it will take you right down to the flare. Amazing thing. And a great way to impress someone when you take them for a flight as most pilots have only heard of "highway in the sky" steering.
Well, this is getting long, but the auto Garmin works just fine in the air in the map mode. It is kind of neat to be flying around the area with speeds showing as high as 170 mph on the auto unit. I wonder what the little munchkins (the little guys inside a GPS that make it work) inside the auto Garmin thought when they saw they were "driving" that fast. The ceiling was relatively low and it was slightly bumpy so I didn't want to go much faster. Next time I try it, I want to see if it will go over 200, again, just for grins. I did try it in the "go to an address mode" telling it to take me home, but the thing kept having to re-calculate as I was not on or near a specific road long enough at the speeds I was using. I am sure the munchkins inside were really confused.
Bottom line: The auto GPS speed was always within 1 mph of the ground speed shown on my Grand Rapid EFIS which I had set in the mph mode. Now that we know that, I do see one use for an auto GPS in an airplane (particularly if you don't yet have an aviation unit) and that would be when doing that part of your flight testing to see how accurate your airspeed system is. You could fly the standard calibration wind triangles marking down what the auto GPS unit gives you for ground speeds as you hold a set indicated airspeed for all three legs of the wind triangles. Of course the easy way is to fly formation with someone that has a really accurate airspeed system, but until you do check your system, you really have no idea just how accurate your airspeed system (or systems) is (are). Everyone has calibrated their airspeed during your phase one testing - haven't you? 
Blue Skies,
Buz
Delicious ideas to please the pickiest eaters. Watch the video on AOL Living.
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