How is a helicopter or aeroplane speed measured?

Question

How is a helicopter or aeroplane speed measured?

Answer 1

While modern aircraft may have radio or satelite navigation aids that can measure groundspeed indirectly the classic airspeed indicator uses a pito tube - this has two holes, one measures the staric air pressure (an opening at right angles to the direction of flight) and a second hole measures the dynamic air pressure (an opening at the front, measuring the pressure of air flowing towards the aircraft.



The difference is pressure is then converted into airspeed.



You cannot directly measure the groundspeed, that isto say the speed the aircraft is moving in relation to the ground.



To convert airspeed to groundspeed you need to either know the windspeed and direction (and airspeed as measured by the airspeed indicator) , or measure groundspeed indirectly by other navigational means and do some trigonometry to work out the factor due to windspeed and direction

Answer 2

Hi: Aircraft speed is measured using a pitot tube.

This is a small tube protruding from the wing or on the side of the aircraft.

It measures the pressure of the air impacting on it and transposes that pressure to an airspeed.

This does not account for the speed of the headwind or tailwind.

Once you calculate the headwind or tailwind you add or subtract that from the airspeed to get ground speed. The airspeed indicator does not account for the wind. You have to calculate that or let your GPS figure it out...LOL

You also need to account for air pressure or density altitude to get the true-airspeed, but for your purposes i think that's as deep as i need to go on the subject without confusing you.

Hope this all helps.



regards



russ

Answer 3

Aircraft uses pitot pressure (AKA ram air pressure or air impack pressure cuase by the aircraft moving througth the air) to measure airspeed. This pressure goes trough a tube called pitot tube. The pitot tube collects all this pressure and send it to the airspeed indicator via pito-static system pluming-which runs from the pitot tube to the indicator. When this pressure reach the indictor, it will go inside a pressure sensitive diaphram. The diaphram will expand due to the pressure--kind of like blowing into a ballon and inflate it, the harder you blow, the bigger it gets. So the faster the aircraft move through the air, the bigger the diaphram gets. The diaphram is mechanicaly conected to a calibrated dial pionter, so when the diaphram change size, the pointer will move therefore, giving the pilot an indication of the airspeed in proportion to the ram pressure. Static pressure (AKA atmopheric or ambient pressure) is also send to the airspeed indicator via the pluming from the aircraft static ports--this ports are little holes on the aircraft fusalage. This pressure is used to compensate for the change in aircraft altittude which will cause an inaccuarate reading of the airspeed since pressure in higher alttitude is less than on the ground. Its kind of like a vent for the airspeed diaphram so that it will change it size with the pressure (static pressure) around it. This will also correct "some" errors result by the actaual wind blowing on the aircraft since pressure will be higher where the wind hits and it will be sense by the static ports. If the pilot wants a more accurate reading of his airspeed, then he have to utilized a subsystem of the pitot static system called SCADC stands for Standar Air Data Cumputer or a TASC stands for True Air Speed Computer. Them things are badass coz it actually give the pilot the true airspeed regardless of the actual wind speed. It still uses pitot and static pressure input, but air density and temp are also added. this cumputer will calculate all this factor that affect airspeed and send it to the indicator electricaly. The actual workings of the system is far beyond what I can put in this yahoo Q/A. I dont wanna right an intire book here. Pilot can also utilize INS stands for Inertial Navigation Sytem. This things use accelerometers to calculate aircraft velocities. I just wanna add that spaccrafts uses INS since there aint no wheels or air to measure in space. Pilot can also use GPS, I assume you already know what it means. Or the pilot can call ATIS stands for Automatic Terminal Information Service to give them the speed of the wind he/she flying at. There are plenty of ways to do it, brother. And for them dudes who said only GPS is the only way to find True airspeed, well, its up to you to believe them, but the know what they're talking about tho. Like everybody said, "there are a million ways to kill a cat". ;)

Answer 4

GPS and radar can determine speed relative to the ground.



However the pilot needs to be aware of airspeed to keep his aircraft operating within it's performance envelope so aircraft have a 'true airspeed' indicator on board. Air is picked up through a probe that is mounted on the nose or wing (in a clean airflow) of the aircraft and transferred to an airspeed indicator on the instrument panel.

Answer 5

The pitot tube, which faces forward, measures stagnation pressure- the pressure generated by stopping the flow over the airplane.



The static ports are on the side of the airplane and measure ambient pressure without a factor of speed.



The difference gives the dynamic pressure, which is .5*air density*speed squared. The airspeed indicator is calibrated to give an airspeed reading at sea level pressure (the indicated air speed or IAS). You have to calculate the true air speed or TAS by knowing your altitude (gives the air density correction). With TAS you can estimate groundspeed if you know the winds aloft speeds.



Phew!



The IAS is important in itself for stall and maneuvering speeds; the TAS for navigation.

Answer 6

Its called a pitot, pronounced (pee-toe). It measures wind on the inlet of the tube pressing in against a rubber diaphragm to give you true airspeed.

Answer 7

you fly past a ''speed man'' usually employed by the civil aviation authority he uses a special tape measure

then he yells your speed to you

Answer 8

It is measured using a PITOT TUBE~~This is measured in Knots. Airspeed is the speed in which air is passing over the wings and for a small airplane you have to have at least 55 knots of airspeed (average) to become airborn. To help you reach and maintain this you always take off and land INTO the wind. Groundspeed is the speed that you are traveling if you were on the ground. So, you could be flying at 75 knots airspeed into a strong headwind and only be flying at 15-20 MPH in groundspeed.

Answer 9

An aircraft's speed is measured in either ground speed or airspeed. Ground speed takes any winds into account. Air speed does not. A thumbs down already? You must be bored.

Answer 10

The most basic method to measure airspeed is through a device called a Pitot tube. The tube has a small hole in the front where incoming air applies pressure in a dynamic way. This pressure is compared with one coming from a static port, which is not in the plane of motion, so as to not measure any (or as little as possible) dynamic component of the pressure.

The measurement is called "indicated airspeed", which is quire different from the real speed of travel, as we will see.

The first thing that makes indicated airspeed to be off is called position error. The Pitot tube is supposed to be perpendicular to the direction of motion, but being fixed on the airframe, is not always perpendicular, since an aircraft will vary is angle of attack as a function of its speed and weight, and flap deflection. Flight tests with supplementary external equipment establishes the correction error. Airspeed corrected for position error is called calibrated airspeed.

But this is still not exactly the real speed, as air density and pressure changes with altitude and temperature. If one carries the correction due to air pressure (as well as compression effect when flying at speed close to the speed of sound), then we have the true airspeed.

Which is not the ground speed, as airspeed is relative to the air, which moves if there is wind.

Complicated? You betcha.

The airspeed is what concerns the pilot for a safety point of view. How fast to go to takeoff, how fast to go when landing, and so on, is regulated by airspeed, since this is the only speed that matters for the wing. But an airplane has to go from point A to point B, and those are not affected by wind speed, or varying air pressure.

Modern aircraft are equipped with gyroscopes that sense acceleration and therefore motions, and are able to derive a speed that is correlated with actual ground speed. These are futher agumented by radio emitters, which are located at known points along the way, and which allow triangulation to determine the true position. With any drift in the position relative to what was computed now being known, a better assessment of the actual ground speed is established.

And recently, let's not forget GPS based equipements that can give you position and speed quite accurately.



As for the wind speed, it is known from the various weather and meteorological stations. Doppler radar can measure wind speed, and recent weather forecasts are available to pilots prior to departure, and updated through radio during flight. All the available information is fed into navigation computers by the flight crew, allowing a accurate estimation of the ground speed, and thus allowing a good prediction of the time of arrival at destination.

Answer 11

im not sure exactly but thinking about it....there mist be some sort of ''hole'' in the plane that funnels air past some sort of ''vain'' type spinning thing,sensors on it will show its speed......

then again its very easy to tell the speed using GPS.