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#131
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Setting altimeters with no radio
Newps writes:
It's integral to the system. It's completely separate. You receive WAAS from a satellite. Not a GPS satellite. -- Transpose mxsmanic and gmail to reach me by e-mail. |
#132
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Setting altimeters with no radio
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#133
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Setting altimeters with no radio
I recently experimented with flying a GPS approach using the GPS
reported altitude as the "altimeter"... First, I flew the GPS approach track making notes as to the altimeter reading versus the GPS reported altitude on two GPS units in the cockpit... Now, knowing the average local offset between the GPS datum circle and the local ground altitude as reported by the local barometric pressure altimeter the official pair of altimeters in the pilots lounge... I wound up with 79 feet as my averaged offset between the GPS datum plane and the local altimeter... Notice I am emphasizing the word 'local' here... Your findings will differ with your area and with what they are doing down inside that Colorado mountain at any given instant...... A local WAAS transmitter and a WAAS receiver in my plane would, of course, narrow that altitude difference... Also note the altitude delta I found is almost within allowable altimeter error... Anyway, the second trip around I concentrated on flying the altimeter and IVSI on the Garmins instead of the altimeter - jeez, are they twitchy; according to them I never did establish level flight, they always showed either climb or descent, albeit usually at a rate of ~10 or 20 fpm... Trying to fly for real with an altitude instrument this twitchy would be exhausting.. The descent phase on the various legs of the approach was interesting but doable... So, my little experiment shows that one can do a GPS approach - after a fashion - using the GPS altitude reporting... Knowing in advance what the local differential between the GPS and the cold hard ground would be nice... I intend to next fool around with using the GPS IVSI for flying an ILS in place of the glide slope... I have done this with the barometric IVSI and had the radar guys watch me... Two times out of three they said they could not see any divergence... The one time they did see it I was definitely off the glide slope as I got sloppy on speed control and wound up too fast... Fun stuff to do as opposed to droning around in circles... denny Newps wrote: "Mxsmanic" wrote in message ... No, it is not. It's especially dangerous for RVSM flight, but it's so inaccurate that it should never be used for anything, Your complete misunderstanding of the GPS system is showing. I have two GPS's in the plane, one panel mount and one portable. It is rare that either one is ever off by more than 100 feet in altitude. Using GPS for your altitude for VFR flight would be perfectly fine. |
#134
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Setting altimeters with no radio
Mxsmanic wrote: Newps writes: Exactly, a system. WAAS is part of that system. No, WAAS is a separate system. Wrong, as usual. It's all part of the same system. |
#135
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Setting altimeters with no radio
Mxsmanic wrote: Newps writes: It's integral to the system. It's completely separate. You receive WAAS from a satellite. Not a GPS satellite. A satellite is a satellite. The information that spews forth from that satellite is just information that my receiver makes use of. |
#136
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Setting altimeters with no radio
It's not something you need to know, in order to use the box.
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#137
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Setting altimeters with no radio
"Barney Rubble" wrote in message ... But it would be kind of weird to be above 10K where a Mode-C transponder is required, but not have a radio or altimeter... I've been above 10K without a transponder or radio, it didn't seem weird to me at all. |
#138
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Setting altimeters with no radio
Thanks.
mike "peter" wrote in message You're thinking of height above the ellipsoid, which can be hundreds of feet different from height above the geoid. But the geoid does represent the mean sea level height - including in places that are far from the sea. Internally GPS receivers generally initially calculate height relative to the ellipsoid model of the earth's shape (using the WGS-84 model parameters). However, recent models with which I'm familiar then apply a correction term based on an internal lookup table to convert the ellipsoid height to the geoid height (equivalent to height above MSL) at that particular location. See: http://www.esri.com/news/arcuser/0703/geoid1of3.html The altitudes that end up being displayed by the GPS after its internal correction are therefore based on elevation above MSL with some measurement uncertainty that's dependent on the current satellite geometry. |
#139
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Setting altimeters with no radio
Wow. That's news. What the hell are all these GPS companies trying to sell
us? mike "Mxsmanic" wrote in message ... Neil Gould writes: Ever hear of WAAS? Yes. And it's not part of GPS. -- Transpose mxsmanic and gmail to reach me by e-mail. |
#140
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Setting altimeters with no radio
No. Famous last words are usually "Oh ****."
mike "Mxsmanic" wrote in message ... Travis Marlatte writes: The only ATC clearances for a pressure altitude would be in the flight levels. Since the question was about setting a pressure altimeter, I would say that the flight levels are irrelevant. Below the flight levels, ATC clearances are for pressure compensated altitude above MSL, so yes it is based on pressure and not true altitude but close enough. My GPS gives me a calculated altitude above a theoretical sea level that's also close enough. "Close enough": famous last words. -- Transpose mxsmanic and gmail to reach me by e-mail. |
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