Latest report which includes 7 alleged drone/model incidents. Not all were in fact drones, one being a balloon and one being a model glider. The detailed report for the Airprox with the glider makes interesting reading and shows that it is not all down to pilots and unsubstantiated sightings.
Report Summary page : http://www.airproxboard.org.uk/Reports-and-analysis/Monthly-summaries/2016/Monthly-meeting-January-2016/ (http://www.airproxboard.org.uk/Reports-and-analysis/Monthly-summaries/2016/Monthly-meeting-January-2016/)
Model glider Report : http://www.airproxboard.org.uk/uploadedFiles/Content/Standard_content/Airprox_report_files/2015/Recent_Assessed_Reports/Airprox%20Report%202015191.pdf (http://www.airproxboard.org.uk/uploadedFiles/Content/Standard_content/Airprox_report_files/2015/Recent_Assessed_Reports/Airprox%20Report%202015191.pdf)
In that glider report, it says in the table that the separation reported by the pilot was 25ft, but it also records that the altitudes of the aircraft were 2150ft and 1540ft respectively.
So how can they be 25ft apart?
Edit read the summary, they used AGL for the height of the glider (which seems odd, since the GPS would give ASL, right? This would mean they were a fair distance apart?)
I think they concluded that the pilot was probably wrong, that he thought it was nearer because it was such a large model and that they were 350ft apart.
I am surprised they can be so accurate with a GPS height, from my experience they can vary quite a bit.
If I remember correctly from my full size flight, you set the barometer pressure on take off, and before landing, to the settings given to you by ATC to determine your height.
Yup, with altitude above sea level always being the reference. 'Height' is used to describe an elevation above something, wheras altitude is always above sea level.
And if you think a GPS altitude varies, you should see what an altimeter can do. It's just a pressure capsule with a scale on it, so any time the sea level temperature isn't at 15 Celsius, it's in error.
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Quote from: elmattbo on March 02, 2016, 08:37:46 PM
Yup, with altitude above sea level always being the reference. 'Height' is used to describe an elevation above something, wheras altitude is always above sea level.
And if you think a GPS altitude varies, you should see what an altimeter can do. It's just a pressure capsule with a scale on it, so any time the sea level temperature isn't at 15 Celsius, it's in error.
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Need to be a bit more specific. You are referring to barometric altimeters. Radio or radar altimeters are much more precise and good enough for autolanding.
The baro variant is why you set yours according to what ATC tell you before take off and landing right?
I think I remember we were given a figure, which we used to "calibrate" our barometer too on the day.
This is a bit off topic, so apologies, but here we go....
You set an altimeter to a local pressure setting before departure which is given from ATC. It's called the QNH and is essentially the pressure setting that makes your altimeter read the altitude above sea level at the airfield. It's airfield and time dependent though; as you move to another airfield or as weather systems gradually pass through the QNH will change and you will have to reset it - 1mb = 30' of altitude. The error I mentioned is because an altimeter doesn't actually measure altitude, it measures pressure and the scale on it is calibrated for a standard day - when it's 15 degrees at sea level and the temperature drops by 2 degrees per thousand feet as you climb. If it's anything different to that then there will be an error. Low temperatures make it over read (dangerous!) and high temperatures make it under read. As electrorotor said a radio altimeter doesn't have this error, but it only works below 2500' and will only tell you the height of the terrain immediately below you, so not much use for navigating or avoiding air traffic.
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While I'm thinking about it and as another aside (even more off topic here!) but of more relevance to model aircraft is density altitude. Hot temperatures and high altitudes kill aircraft performance. An airspeed indicator is (like an altimeter) a pressure measuring device calibrated for speed on a standard day at sea level. As you climb, it under reads your true airspeed and as the temperature increases it under reads as well - both reduce the density of the air. However for a given indicated airspeed a wing will perform identically which is why we use it. What this means for you is that on a cold winters day your model will perform way better than a hot day in the summer. The props will produce more thrust, the wings will produce more lift and it will be easier to launch as you won't have to throw it so hard to get above the stall speed. Your batteries will be crap, but hey, you can't have it all.
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That's how I remember it, but with less detail. Thanks for the clarification. ;D
A calm winters day is always the best flying. Nice still thick air is the best. Does have a fair few down sides like you say though. ;D