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32 votes
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Would building a large asphalt square or painted dark black area create a "thermal generator" for glider use?

Yes, if it was large enough you could expect decent thermals from it, but not all the time. I've flown over mall parking lots where there is maybe 20 acres of asphalt, expecting a boomer, but no joy. ...
John K's user avatar
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29 votes
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What is Density Altitude?

The concept of 'density altitude' is kind of like the concept of 'wind chill'. Stick with me here, I'm going somewhere with this. Cold weather is dangerous for the human body, and wind (because of ...
Steve V.'s user avatar
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25 votes

Why are pressure levels raised on warm days?

Remember, altimeters sense pressure rather than density. Pressure is essentially a measure of the weight of the atmosphere above a specific point. You can imagine the pressure being measured as the ...
PilotDan's user avatar
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13 votes
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What is wind "CALM"?

Wind "CALM" means a wind speed less than 0.5m/s (1 kt) according to ICAO Annex 3, Appendix 3: 4.1.5.2 In local routine and special reports and in METAR and SPECI: ... d) when a wind ...
DeltaLima's user avatar
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13 votes

What is Density Altitude?

Try this article https://www.aopa.org/training-and-safety/active-pilots/safety-and-technique/weather/density-altitude As a pilot, we like higher Pressure and Cold Temperatures - it makes the air ...
CrossRoads's user avatar
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12 votes

Would building a large asphalt square or painted dark black area create a "thermal generator" for glider use?

I made a short LES simulation The color is thhe potential temperature and the scale span is 1.8 K between blue and red. There is a hot patch 100 m x 100 m in the middle. There is 0.1 K.m/s (~110 W/m^...
Vladimir F Героям слава's user avatar
12 votes
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How can I check before my flight that the cloud separation requirements in VFR flight rules are met?

Make it simple: OVC: It's a ceiling. The only thing you're concerned about is the altitude of the base. BKN: It's also considered a ceiling. The only thing you're concerned about is the altitude of ...
John K's user avatar
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12 votes
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With existing tech and knowledge of meteorology, can aircraft be designed to reliably improve their range or loiter using updrafts to gain altitude?

Thermals are finite. This means they have a useful diameter which is smaller than the diameter of the smallest circle most airplanes can fly. The wing loading of a heavy (= full ballast tanks) glider ...
Peter Kämpf's user avatar
11 votes
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How do pilots clear an aircraft to fly through a hurricane?

The aircraft they're flying is an Lockheed WP-3D Orion, not a jet- the NOAA doesn't fly its Gulfstream IVs into the storm, as I've noted elsewhere. There is always a risk associated with piloting an ...
aeroalias's user avatar
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11 votes
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What is the difference between QNH and QFF?

Both QNH and QFF are pressure measurements at a meteorological station (e.g. airport), with the pressure height-corrected back to sea level. The difference is in the assumptions that are used for the ...
DeltaLima's user avatar
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9 votes
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What’s the setting range altimeters can handle?

There are actually multiple different answers depending on the specific type of altimeter system and what standard applies. The stand-alone altimeters in older aircraft and small GA aircraft (panel ...
Gerry's user avatar
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9 votes
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Can the "G" and "VRB" wind conditions be combined in METARs?

Yes, it is possible for a METAR to contain both VRB and G. VRB10G25KT is valid. The reason it rarely happens is because, as wind speed increases, major variations in wind directions tend to disappear....
60levelchange's user avatar
8 votes

How does latitude affect the air temperature at 8 km altitude where planes fly?

In the troposphere, air at altitude is colder than air at ground level. But surprisingly, air at altitude at the poles can be warmer than air at altitude at the equator. From the wiki article on ...
Koyovis's user avatar
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8 votes

Can the "G" and "VRB" wind conditions be combined in METARs?

As other answers say, yes, this is valid. It appears approximately 150K times in our database of 85 million METARs[1]. This database is built from data provided by NOAA and covers roughly 16 months.[2]...
Tim M.'s user avatar
  • 181
7 votes

Would building a large asphalt square or painted dark black area create a "thermal generator" for glider use?

Yes. Sunlight is about 1000 W/m2. Absorbing it is a good way to get some heat. We can improve on your design a bit. A good portion of sunlight is visible to the eye, but some of it is not. Not all ...
Anonymous Physicist's user avatar
6 votes
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How do barometric altimetry systems compensate for nonstandard pressure lapse rates?

They don't. Since all aircraft in an area are (or at least should be) having roughly the same error, the errors cancel out and there is no practical effect on vertical separation. Falsely low ...
StephenS's user avatar
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6 votes

What is Density Altitude?

Suppose you are at a given place, with a given temperature, and the barometer shows –for example– 25.84 inches of air pressure. That's precisely the pressure at 4000 ft of altitude within the '...
xxavier's user avatar
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6 votes

Why on weather surface charts high pressure is blue and low pressure is red?

The red color is universally associated with evil, suffering, blood, fire... Low pressures are associated with rain, storms, even with hurricanes and tornados... High pressures are associated with ...
xxavier's user avatar
  • 11.1k
6 votes

With existing tech and knowledge of meteorology, can aircraft be designed to reliably improve their range or loiter using updrafts to gain altitude?

You should not forget the infrared mongolfiers. This system was invented by French Centre National d'Etudes Spatiales (national spatial studies center) in 1977. It can fly between 18000 and 28000 ...
Serge Ballesta's user avatar
6 votes
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How can I determine the level of clouds of operational significance in METAR?

Codes used: NSC: Nil significant cloud CAVOK: Ceiling and visibility ok BRK: Broken (5 to 7 ...
mins's user avatar
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5 votes

What is the physical definition of turbulence?

Image source Turbulence is merely the measure of Reynolds number of a fluid at rest or motion ( (turbulence occurs when fluid is in motion) let's say you light up a cigarette and when the smoke is at ...
Harsha Arya's user avatar
5 votes

Is the size of hail on the ground any indication of the winds and updrafts of a thunderstorm?

The October 2018 issue of AOPA's "Flight Training" magazine provided the following illustration and comments. A 24mph updraft will form ~1/4" hail, while a 98mph updraft will form 4" hail. Down ...
jwzumwalt's user avatar
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5 votes
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Is the "PROB" in a TAF only applying to the next group or all following ones?

PROB40 is targeted only on the immediate TEMPO group. If there are several PROB/TEMPOs both keywords must be repeated every time. Also, PROB is never associated with BECMG or FM groups, which indicate ...
busdriver's user avatar
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5 votes
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How does latitude affect the air temperature at 8 km altitude where planes fly?

The temperature decreases at approximately 3.57 degree Fahrenheit per 1000', the adiabatic lapse rate, until hitting the tropopause, the boundary between the troposphere (lower altitudes) and the ...
MikeY's user avatar
  • 1,973
5 votes

How does latitude affect the air temperature at 8 km altitude where planes fly?

The airplanes do not cruise at a certain altitude, but at a certain pressure level. That could be an irrelevant nitpick if the temperature did not directly affect the pressure as a function of ...
Vladimir F Героям слава's user avatar
5 votes
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How to interpret BECMG and TEMPO in TAF?

The BECMG group in a TAF describes a gradual change which will take place over a prolonged period of time, but will be the prevailing weather once that change is complete. The time period described in ...
J W's user avatar
  • 16.6k
5 votes

What is the difference between Cloud Ceiling and Cloud Base?

They are not the same thing. Cloud base is simply the bottom "surface" level of the a cloud regardless of the sky coverage. Where cloud coverage constitutes a ceiling, then the cloud base ...
John K's user avatar
  • 132k
5 votes

What is the difference between Cloud Ceiling and Cloud Base?

Simply put, a cloud base is the bottom of a cloud layer of any size. A cloud ceiling is the height of the first cloud layer that constitutes at least a broken layer.
Dean F.'s user avatar
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