Dudes/Ramblings on speed calculation

[peirof]

Hi, 

 

This doubt isn't unique to the F18, but I didn't know where to put it. If administrators think they should move it.

 

The doubt is about the calculation of the instantaneous speed of the plane, as I read (sponsors by "San Google"). 

 

The speed in modern aircraft is calculated by biting the speed of air passing through a duct longitudinally on the plane. 

 

That's why traveling the same distance as in horizontals, the speed of when you fly at low altitude is considerably higher than when you fly at high altitude. Since the air at low altitude is more than it is, and with the speed measurement system, the system "reads" that more air passes and that the plane goes faster

 

This raises some doubts for me:

 

- The direction in which the wind blows, affects the speed that "reads" the plane? 

 

- The density of the air (whether there is a storm or an anticyclon), affects the speed that "reads" the plane? 

 

Perhaps this system in the 2 GM, or in the '70s, was the only way to know the speed. But at present, there would be no other more reliable ways, GPS for example, to measure speed? (and leave the system traditionally as "backup. 

 

It would not be more useful to know these two speeds: (proposed names) 

 

- Actual speed, distance traveled AT SEA LEVEL/TIME

 

- Speed compensated (by the earth's curvature), the speed in height... If a plane that flies at 30000 feet, and travels 10 miles, it will be really traveling less than 10 miles of terrain, by the effect of the earth's curvature and vice versa. An aircraft flying at 30000 feet and traversing 10 miles of terrain (at elevation 0), at 30000 feet will have to have traveled more distance (I don't know, maybe 12 miles), that would result in a speed compensated (by height) higher

 

A morning rambling.. 

 

What do you think

Edited July 27, 2021 by peirof

[speed-of-heat]

ground speed … is a thing

Edited July 27, 2021 by speed-of-heat

[Dunx]

Some good stuff here...

https://en.wikipedia.org/wiki/Airspeed

 

[Bunny Clark]

Yup, aircraft measure airspeed in a few different ways. Different ones have different uses. 

 

Indicated Airspeed is, as you describe, the direct measurement of ram air pressure from the pitot static system. This is the speed indicated on the analogue standby airspeed gauge. 

 

Calibrated Airspeed is derived from taking the Indicated Airspeed value and correcting it for various known errors imparted by the aircraft's hardware. This is the speed that is displayed in the HUD speed box. This speed is effected by density altitude, so it will be relatively lower at higher altitudes as you noted. This speed is extremely helpful for pilots because it reflects the speed and density of air going over the wings and control surfaces, so it will inform you of the way the aircraft will handle. An aircraft at 300 Knots CAS will handle the same regardless of altitude, air density, or wind. 

 

True Airspeed is the speed at which the aircraft is moving through the air around it, regardless of density and wind. You can come up with an approximation of this number by correcting for aircraft altitude, air density, and air temperature. Or you can measure it more exactly with a GPS system. This speed is displayed to the left of your aircraft symbol on the HSI and marked with a "T".

 

Ground Speed is similar to True Airspeed, but corrected for wind, so it indicates the velocity of your track over the ground. This speed is most useful for navigation. It is displayed to the right of your aircraft symbol on the HSI and marked with a "G".

 

There is also the Mach number, which represents your speed relative to the speed of sound. This is also a very important number as it has implications for the way your aircraft will handle and how efficiently it is moving through the air. It is displayed on the HUD and marked with an "M".

[Brun]

4 hours ago, peirof said:

- Speed compensated (by the earth's curvature), the speed in height... If a plane that flies at 30000 feet, and travels 10 miles, it will be really traveling less than 10 miles of terrain, by the effect of the earth's curvature and vice versa. An aircraft flying at 30000 feet and traversing 10 miles of terrain (at elevation 0), at 30000 feet will have to have traveled more distance (I don't know, maybe 12 miles), that would result in a speed compensated (by height) higher

 

Radius of the Earth is 21 million feet. Think about that for a minute.

[peirof]

Congratulations, a masterful response. It has solved many doubts... Thank you

 

En 27/7/2021 a las 9:05, Bunny Clark dijo:

Yup, aircraft measure airspeed in a few different ways. Different ones have different uses. 

 

Indicated Airspeed is, as you describe, the direct measurement of ram air pressure from the pitot static system. This is the speed indicated on the analogue standby airspeed gauge. 

 

Calibrated Airspeed is derived from taking the Indicated Airspeed value and correcting it for various known errors imparted by the aircraft's hardware. This is the speed that is displayed in the HUD speed box. This speed is effected by density altitude, so it will be relatively lower at higher altitudes as you noted. This speed is extremely helpful for pilots because it reflects the speed and density of air going over the wings and control surfaces, so it will inform you of the way the aircraft will handle. An aircraft at 300 Knots CAS will handle the same regardless of altitude, air density, or wind. 

 

True Airspeed is the speed at which the aircraft is moving through the air around it, regardless of density and wind. You can come up with an approximation of this number by correcting for aircraft altitude, air density, and air temperature. Or you can measure it more exactly with a GPS system. This speed is displayed to the left of your aircraft symbol on the HSI and marked with a "T".

 

Ground Speed is similar to True Airspeed, but corrected for wind, so it indicates the velocity of your track over the ground. This speed is most useful for navigation. It is displayed to the right of your aircraft symbol on the HSI and marked with a "G".

 

There is also the Mach number, which represents your speed relative to the speed of sound. This is also a very important number as it has implications for the way your aircraft will handle and how efficiently it is moving through the air. It is displayed on the HUD and marked with an "M".