On transponders and TAS...

[Anxyous]

I was just wondering what the actual usage of these are? :-?

[Brett_Henderson]

A transponder is a device thast makes an airplane more than just radar reflection to ATC. It "squawks" the 4-digit code dialed into it by the pilot, so that the radar "blip" can be identified and kept track of during instrument flights, or VFR-flight-following. All, non radar assited, VFR flights just squawk '1200'.

More advanced (and the most common) types will also relay altitude information to ATC.

If by "TAS"

[Anxyous]

I know that about the transponder... I'm more interested in what it's exactly used for though, and if some radars only pick up certain transponder codes or something.

And sorry, by TAS I mean True Air-Speed.


Thanks!  :)

[SkyDreamer]

A transponder is a really neat peace of equipment if I lose my ablity to transmit but can receive I can IDENT and the controller knows I can receive his transmitions

CODES
VFR             1200
Emergency  7700
Lost Communications 7600
Hi Jacked      7500
Oceanc        2000    I am pretty sure

The transponder is used to identify the aircraft on radar basically it tells the controller who you are without it you are just a blimp out of hundred usually certain airspaces require like BRAVO to have a mode C which bascially sends them your altitude on the screen so they dont keep saying Cessna 478RC say altitude they can look at it on the scope

Another feature of the transponder is the Iden which basically send the data block on radar which is used to idenify the controller is looking at the correct aircraft

True Airspeed is kinda hard to explain but it can be fiquired on a E6B flight computer but really when flying theres not much point I go by Indicated airspeed and Ground speed cause its just easer for me

Hope this helps

[RitterKreuz]

Think of true airspeed like this.

You know that indicated airspeed is the speed you read from the airspeed indicator. for example 120 knots.

The airspeed indicator works by detecting the speed of air as it "blows" into the pitot tube.

You also know that as you increase altitude, air density decreases. That its... the air molecules spread out further apart from one another.

because of the reduction in air density, fewer tiny air molecules enter the "pitot tube" and therefore fewer air molecules "feed" the airspeed indicator.

This causes the airspeed indicator to show a speed which is slightly slower than how fast you are actually moving through the air.

The higher you climb, the more pronounced this error is.

"True airspeed" defined as "the aircraft's actual speed through an air mass" is what you come up with when you use various methods which correct for this "error" of fewer molecules entering the pitot tube.

Modern airliners and business jets use "Air Data Computers" which take inputs like altitude and airspeed and groundspeed etc and they are able to calculate corrections ofr you instantly. Even some small single engine aircraft have a calibrator on the airspeed indicator which can be turned manually to correct for this error given certain known variables like temperature and altitude.

However, the DC-3 or B-17 for example, use air driven gauges all the way up, and therefore the indicated airspeed will be slower and slower as you climb higher and higher.

for example. assume on a day with absolutely no wind... a B-17 at 10,000 feet might indicate 140 knots, while a B-17 at 23,000 feet might indicate 114 knots. the issue is, that neither B-17 is necessarily "outrunning" the other... because through the air mass, both planes are going the same "true airspeed" of say 143 knots.

"True airspeed" defined as "the aircraft's actual speed through an air mass" is what you come up with when you use various methods which correct for this "error" of fewer molecules entering the pitot tube.

in terms of time speed distance and fuel consumption problems, true airspeed is used as a "base number" for calculating ground speed, our ultimately important speed number.

[C]

[quote]

Oceanic      

[SkyDreamer]

Sweets