If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#51
|
|||
|
|||
Questions on high altitude pressures
Frank Barchi wrote:
Just an extra, extra point.....there is no FL 120 You might not be aware of it, but there's actually life (and flying) outside of the USA. |
#52
|
|||
|
|||
Questions on high altitude pressures
Wolfgang Schwanke wrote:
In theory you could use GPS altitudes when flying MSL/QNH setting, No. Even with MSL/QNH setting, as you call it, the barometric altimeter does *not* show the true geometric altitude. More precisely, it only shows it in two cases: 1. When sitting on the ground at the reference altitude for the given altimeter setting (QNH) 2. When the atmosphere happens to be an ICAO standard atmosphere. |
#53
|
|||
|
|||
Questions on high altitude pressures
Just to throw a little more fuel on this fire - GPS altitude is in
widespread use in the soaring world and has proven to be very useful for computing height above ground and final glides to destinations. It can also be used to give vertical motion, although not as accurately as a pressure instrument. The biggest difference (other than the previously discussed pressure altitude vs height above the ellipsoid issue) is that while an altimeter, when set to the correct pressure (mb or in hg) for QFE or QNH, is stable in the short term but will become more innacurate over time due to atmospheric pressure changes (not talking about flight levels here), GPS is less accurate in the short term (altitude varies with geometry, etc) but extremely stable over the long term. I won't waste my time on argueing with Mxsmanic - he is really clueless - but it sometimes amazes me how many "real" pilots have a poor grasp on what altimeters really indicate! Speaking of accuracy, anybody remember what the altitude tolerance of an altimeter is? In military jets it's +- 75 feet or so - I have no idea what it is for the non-TSO'd altimeter in my LS6. Which means that as long as your GPS is tracking 4+ satellites with good geometry and no SA, it's altitude (QNH) is probably better than what is shown on your altimeter (but only if you know the difference between MSL and HAE, which can be over 100' in many places...). So - use your altimeter (set correctly) for IFR, and use your aviation GPS to help avoid hitting the hard stuff! Kirk |
#54
|
|||
|
|||
Questions on high altitude pressures
|
#55
|
|||
|
|||
Questions on high altitude pressures
Given the nature of this thread, some of you will enjoy this video,
http://www.grayeagles.org/video.htm and others will let the lettering on the side of this rebuilt Mustang, named "Feburary", ruin the entire experience. The video is worth watching, especially this close to Veteran's Day. |
#56
|
|||
|
|||
Questions on high altitude pressures
On Nov 28, 9:19*am, John Smith wrote:
wrote: So - use your altimeter (set correctly) for IFR, and use your aviation GPS to help avoid hitting the hard stuff! Actually, I use my eyes for that. Well, if you can see out the window, who cares about altitude anyway! Now, at night, no moon, some haze, maybe over water.... Kirk |
#57
|
|||
|
|||
Questions on high altitude pressures
|
#58
|
|||
|
|||
Questions on high altitude pressures
On Nov 29, 3:30*am, John Smith wrote:
wrote: So - use your altimeter (set correctly) for IFR, and use your aviation GPS to help avoid hitting the hard stuff! Actually, I use my eyes for that. Well, if you can see out the window, who cares about altitude anyway! Now, at night, no moon, some haze, maybe over water.... Wouldn't that be IFR? Or really stupid night VFR...(which I realize is not legal in some countries). Of course, there has never been a case of a misset or misread altimeter resulting in a pilot running a perfectly good airplane into the ground, has there - especially with those horrible triple-pointer altimeters! Much harder to do that with a GPS, especially if it has a terrain database to give AGL height (well, you still have to read the instruments...). Which is why most modern avionics setups have exactly that arrangement. And it can be done cheap - $200 PDA with GPS and some software does the same thing. Kirk |
#59
|
|||
|
|||
Questions on high altitude pressures
|
#60
|
|||
|
|||
Questions on high altitude pressures
Mxsmanic wrote in
: es330td writes: This brings up an interesting wrinkle then as GPS altitude info is not dependent on external pressure so pilots must be careful to ignore that info if available. As stated before, in Class A everyone sets their altimeter to 29.92 so that as long as everyone is wrong together everything is okay. Adding GPS info into the mix splits the groups into two; one that is wrong together at 29.92 and another that is right at actual altitude. GPS is too inaccurate for most purposes in vertical positioning, anyway. It is not designed to determine altitude with a high degree of accuracy, and can easily be hundreds of feet off. You#re aan idiot. Bertie |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
High Altitude Waypoints | Dennis Johnson | Instrument Flight Rules | 7 | May 2nd 08 02:44 AM |
High Altitude Linnies | TTaylor at cc.usu.edu | Soaring | 4 | August 4th 06 10:47 PM |
High altitude & RPM | abripl | Home Built | 1 | September 1st 05 12:12 AM |
High-altitude autorotations? | Bill McClain | Military Aviation | 17 | March 15th 04 05:23 PM |
Low and high altitude airways | David Megginson | Instrument Flight Rules | 7 | September 9th 03 01:18 AM |