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Spartan_GR
03-13-2005, 03:18 PM
This is a question about basic technical stuff for airplanes... just a thing that i really wonder how it works.

The speedometer on a plane, how does it work? I mean, how can a airplane know what its speed is? Since it does not have wheels turning on a road, how does it counting its speed in the air?

I know that It may sound as a silly question http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Spartan_GR
03-13-2005, 03:18 PM
This is a question about basic technical stuff for airplanes... just a thing that i really wonder how it works.

The speedometer on a plane, how does it work? I mean, how can a airplane know what its speed is? Since it does not have wheels turning on a road, how does it counting its speed in the air?

I know that It may sound as a silly question http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

civildog
03-13-2005, 03:22 PM
Go here, it'll show how the pitot tube is used on planes to measure airspeed.

www.grc.nasa.gov/WWW/K-12/airplane/pitot.html (http://www.grc.nasa.gov/WWW/K-12/airplane/pitot.html)

RAF92_Mustang
03-13-2005, 03:26 PM
The airspeed is gauged between ram air from the pitot tube, and static ports. The ram air gauges the speed the airplane is passing through the air.

http://nasaui.ited.uidaho.edu/nasaspark/safety/instruments/pitotstatic.jpg

Spartan_GR
03-13-2005, 03:43 PM
thanks http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Taylortony
03-13-2005, 06:25 PM
To be precise you have a metal diaphram that is corrugated to allow it to expand and contract, to this is attached an arm mechanism and a ratchet , the air pressure (PITOT) is felt inside the bellows and expands the bellows outward that moves the arm and the moves the toothed ratchet along, a little cog sitting on the ratchet will then turn and that is connected to the pointer and turns to show your speed... Static is on the outside of the bellows and allows the instrument to compensate for altitude and thinner air ie higher u go less airpressure outside bellows so less resistance to expansion.... similar the pitot head will also have static in it so a small orifice is drilled into the pitot to let that escape and allow only true moving air to effect the reading ( PITOT )
Thats it in a basic form

An altimeter on the other hand is just a sealed diaphram similar to above as you go higher it expands due to a reduction in external presore sure outside the bellows ( Static )and indicates your height ... setting the local air pressure before take off etc simply applies a force to the chamber to resist expansion etc and as such alters the reading........

there are various springs and temp compensation in both but you should be able to get the idea....

You could make a simple one yourself if you taped a ridged ruler or similar to a balloon and blew it up, the ruler would move out, a cog sitting at a fixed point on the rule would then turn as the rule moved... see simple http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif