CMercieca

Hi,
These questions have been on my mind for a long time.I tried searching but I found nothing.

1) Why does increasing the speed increase TAT?

2) What is the diffrence between the INS and IRS ,except the diffrence in the gyros( the INS uses eletric and the IRS laser. Correct?) And can you update them while in flight or is it just a single time at the gate?

Thanks in Advance

vagabond

When I saw "INS and IRS" I got pretty excited and thought "finally, a question I can answer!" But that was before I read the entire question.

In my world, INS stands for Immigration and Naturalization Service (or we used to call it the Interrogation and Nazification Service). Congress has since split it up to two different entities. IRS, of course, stands for Internal Revenue Service.

Sorry, I guess you can't take the law out of the girl.

Cubdriver

TAT total air temperature, is obtained by adding the heat due to friction of traveling at speed to your air temperature. For example, the temperature probe sticks out into 25 F air, but the airspeed is 225 kts., it will add a few degrees due to friction which is enough to throw off true airspeed calculations.

INS inertial navigation system, uses 3 actual rotating mechanical gyros to determine position, one each for pitch, roll and yaw, and definitely needs to be corrected from time to time when actual lat-long are known. Transoceanic aircraft originally used them before gps to get nav data on the open seas, away from radio navaids, but gps is taking its place since it is far more accurate and simple. Aircraft crossed the oceans and in the last 100 miles or so got a reference location from ATC before navigating to local destinations. Concorde and the MD11 used it, to name a few.

IRS inertial reference system, uses 3 ring lasers but does not require reference to known locations or calibration other than the initial fix. It uses the difference in the time it takes light to make its way around a triangular "ring" which indicates which path was shorter due to aircraft movement. Talk about sensitivity... plus they now are made the same size as a dime. I cannot name an aircraft that uses it, but there must be plenty. Rickair or one of the other aerospace people will have something hopefully to add.

I took a course at aerospace school called aircraft stability and spaceflight dynamics. They covered gyros among other things. It was an intense course, very good for understanding the math behind aircraft and satellite movements.

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Rama

We use ins's updated by gps now in the 74 classics at my company. Also a stand alone gps for back up/cross reference and mel relief.

Slice

The F-16 has laser ring gyros although GPS is the primary means of navigation these days.

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CMercieca

Thanks guys. I appreciate it.

Ewfflyer

Sweet, never heard of the IRS system. Dead on descriptions!

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EDC757

We use 3 IRS units on the 757 at United to fly to the Hawaiian islands. The 767 have the same and can be updated by the GPS unit and the 757 cannot. But you can see how accurate they are when another 757 1000’ below shows up on the radar altimeter when your half way there. They automatically update with the VORTACs when we come in-range of the islands.

soon2bfo

Our ERJ fleet has a mix of IRS and INS units. The INS unit finds its starting position by referencing the magnetic flux lines, and the force of the rotation of the earth on the gyros (faster at the equator = more force -altitude correction). The IRS uses the last known position, or the GPS if it doesn't agree with the IRS. We also have the exact position of each gate that we can input to the IRS if the GPS isn't happy (never happens). Its pure freaking magic for sure, makes navigation simple.

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CessnaCitationX

I know NW 757-300s have them. I also know AS 737-400s had them at least in the early 90s. (I have the Systems Handbook for the -400.)