151–160 of 191 posts
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Or just fly with the jetstream in all cases, all the way around the earth if necessary. Some trips would be quite long, but think how much fuel they'd be saving!
A 200 MPH tailwind doesn't compensate for a 20,000-mile-longer flight.
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The radius of the earth + 30,000 ft is about 0.14% more than just the radius of the earth. Basically ignore it, unless you are programming guidance control systems.
This reminds me of a math puzzle I read many years ago. It went something like this: "Assume the Earth is a perfect sphere, and its circumference is 25,000 miles. You have a 25,000 mile long rope looped all the way around the Equator, so it is tight against the surface. Now you want to raise the rope one foot in the air, all the way around. How much more rope do you need?" I thought about this and said, "You need a l…
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https://www.grc.nasa.gov/www/k-12/airplane/move.html ground speed is the speed of the plane, relative to an observer on the ground, air speed is how fast the people on the plane are going relative to themselves. Airspeed = Ground Speed - Wind Speed (wind blowing towards front of plan is positive, tailwind is negative)
For a given altitude, trim, and power, the airspeed is always the same no matter the wind. Wind only affects groundspeed. Ground speed = true airspeed + wind component (where you're computing a vector based on wind direction to determine what amount of it is either tail wind (+) or headwind (-).
If acceleration is zero.
(Internet, therefore pedantry).
Earlier quoted context omitted.
This reminds me of a math puzzle I read many years ago. It went something like this: "Assume the Earth is a perfect sphere, and its circumference is 25,000 miles. You have a 25,000 mile long rope looped all the way around the Equator, so it is tight against the surface. Now you want to raise the rope one foot in the air, all the way around. How much more rope do you need?" I thought about this and said, "You need a l…
circumference = 2 pi r, so increasing the radius by 1 foot will increase the circumference by 2 pi feet, not pi feet.
I'd better buy an extra 3-4 feet of rope before I try this experiment.
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Private pilot here. As others have pointed out, the difference is mostly negligible, but ground speed is the speed of the vertical projection of the aircraft's location on the earth's surface.
So essentially the speed at which the plane's shadow on earth travels while projecting on level ground.
Note to readers, land speed not equal to air speed. As the article discusses it doesn't break the sound barrier. That said, the news here is that the jet stream is carrying more energy than it has in the past (air mass is moving faster, kinetic energy content is 1/2mv^2). I read a paper a long time ago which talked about the impact of thermal 'tubes' where denser cold air travelling at speed would "punch holes" in hi…
Do you know if the rides in higher energy jet streams are less comfortable, or is it undetectable by the passengers?
This is probably a stupid question, but how is "ground speed" measured? Is it how quickly the airplane moves past a fixed point at it's altitude, or along the earth's surface? I.e. the plane is effectively moving along the surface of a sphere, but if the plane is 30,000 ft up, then the radius of the plane's sphere is 30,000 ft greater than the radius of the "ground" so traveling at the same angular velocity will requ…
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GPS measurements are comprised of a 2D surface coordinate system (e.g. lat/long) and an altitude above mean sea level. So, "speed" as measured by GPS is speed along the Earth's surface. EDIT: assuming a constant altitude flight
No, GPS measurements are taken as receiver distance from orbiting satellites whose orbits are calculated in a 3-D+t inertial reference frame (ECI), which is then converted to an earth-centered-earth-fixed (ECEF) coordinate. From there an end user devices can transform to desired Datum reference (a model of the Earth's surface) depending on the application. Everything about GPS is inherently 3D+t.
If you fly from point A to point B in one hour at 10,000 feet, and then fly from point A to point B in one hour at 30,000 feet, GPS will report the same speed for both flights. It does not bother to correct for the slightly longer path at 30,000 feet because that level of precision is simply not needed for commercial aviation.
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Yes, for those readers who may not be familiar - the speed of sound changes with altitude. At sea level, it is around 750mph but at 40,000 feet it is around 620mph IIRC. It is affected by the density of the air (which is a combination of the air pressure and temperature) - hence why they use Mach numbers to denote airspeed above certain altitudes as that takes into consideration the air density to give you a speed re…
> [The speed of sound] is affected by the density of the air (which is a combination of the air pressure and temperature)... This is incorrect. The speed of sound in an ideal gas is a function of temperature only, and not its density. Namely, it is sqrt(gamma x R x T), where R and gamma are unchanging properties of the gas.
Note to readers, land speed not equal to air speed. As the article discusses it doesn't break the sound barrier. That said, the news here is that the jet stream is carrying more energy than it has in the past (air mass is moving faster, kinetic energy content is 1/2mv^2). I read a paper a long time ago which talked about the impact of thermal 'tubes' where denser cold air travelling at speed would "punch holes" in hi…
Do you know if the rides in higher energy jet streams are less comfortable, or is it undetectable by the passengers?