How do you measure airspeed

Recover password. Remembered your password? Back to login. Ask a racecar driver what their top speed is, and it is an easy answer. No calculations required. The same applies to a sprinter or marathon runner. Airspeed in the world of aviation, however, is a more complex topic. We have not just one type of airspeed, but many, and each has a different purpose. Today we will focus on true airspeed including a review of what true airspeed is, how to calculate true airspeed, and the purpose of true airspeed.

True airspeed is used for navigational and aircraft performance purposes. The rule of thumb method is the least precise, but fastest and easiest way to estimate true airspeed. The easiest way to accurately calculate TAS is to have a digital device app do it for you. All you need to do is gather the data and input it so your app can handle all the behind-the-scenes computations.

Follow the below steps to calculate true airspeed using a flight app:. Once all the information is entered into the app, it will generate a true airspeed value for you with no math involved on your part. At high altitude, the compressibility of air changes, so even CAS becomes more and more unreliable.

For the SR Blackbird with a ceiling of For more conventional aircraft, EAS is not used. Thus, EAS is what a perfect dynamic pressure sensor would show when properly calibrated for the air compressibility at the current altitude.

The aircraft's behavior at Mach 1 at sea level is about the same as the behavior of the aircraft at an altitude of feet. A Mach number below 1 means that the plane moves subsonic. A Mach number above 1 indicates supersonic flight. The Mach number is critical because a number of phenomena take place just around Mach 1 transonic speed , for example a sudden increase in drag induced by shock-wave generation sonic-boom. Aircraft that are not designed to fly supersonic will break up at Mach 1.

The shape of the aircraft can cause parts of the aircraft being at or above Mach 1 while the fuselage is subsonic. Flying near Mach 1 can be quite dangerous, for most fast but subsonic aircraft Mach 0. High flying aircraft, like passenger aircraft, can reach that limit easy while descending. The speed of sound changes with the compressibility and hence temperature of air, the Mach number is dependent on altitude as the air temperature drops at higher altitudes.

The precise relation between TAS, Mach number and altitude is a complicated formulae and depends in essence on the local weather pattern determining the pressure and temperature gradients in the atmosphere. For the complete V speed "definitions" list please visit Wikipedia. Here a small abstract. Note that V speed definitions can depend of local Flight rules. Most V speeds depend on the aircraft configuration how much it weights etc.

V speeds are used to compare aircraft performance and will be mentioned in the aircraft flight manual AFM. This air compression increases the air density and the pressure in the pitot tube. To account for compressibility, the pilot refers to an air speed compressibility chart. The greater the CAS and the higher the altitude, the more the pilot must subtract to attain the equivalent air speed EAS. The air will be more compressed the faster the aircraft is traveling and the higher the pressure altitude.

Equivalency charts are used to make this correction. The pilot enters the CAS and pressure altitude into the chart and determines how much to subtract.

I can attest that it works well in practice. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Is it possible to accurately measure airspeed without pitot tube?

Ask Question. Asked 4 years ago. Active 1 year, 1 month ago. Viewed 7k times. Improve this question. While your answer is correct, it is quite different from what I asked, as your answer was about discerning the airspeed of an airliner from the inside with a hand-held GPS. I'm looking into other ways an avionics system could be designed, without a pitot tube - so this assumes that I have all access to the instruments.

But I don't even have any instrument to measure the airspeed without a pitot tube. And the reasons why one cannot calculate airspeed with the remaining instruments it the same. Yes they would measure the airspeed but I think it goes without saying that there are probably good reasons pitot tubes are used instead. Show 1 more comment. Active Oldest Votes.

Some other technology being investigated there's also ongoing research and trials about using LIDAR to directly measure airspeed. Improve this answer. KorvinStarmast 4, 26 26 silver badges 38 38 bronze badges. Using the sun makes sense somewhat but your heading would be too important probably, which is already not the best data you have with an IMU device.

Either an AoA vane on the fuselage or a simple flapper switch on the wing leading edge or often an actual horn or whistle whose opening is placed on the wing at such an angle that it makes a noise at a certain AoA. Show 4 more comments. It mentions at the end that the method was not always accurate: An inherent source of error in the system is noise generated by ambient or background illumination.

Community Bot 1. Koyovis Koyovis It does so with a low update rate and with a phase shift time delay since it computes the velocity from previous position signals. I've tried to not exceed max speed using my handphone GPS when I drove in a car without a speedometer, it is very hard to do since it always tells you how fast you were going 5 seconds ago. Least of all those onboard Northwest , Aeroperu , or Air France Pitot failures are among the least survivable accidents in aviation.