We will fly at 280 KIAS at FL330 - what will our KTAS likely be?

Question

How do you find this out? Whats the Formula?

And whats the fourmula to convert KIAS airspeed to KTAS ?

Thanks

Answer 1

Fly boy, you need a lesson on how to use the E6b flight ccomputer.

True airspeed (TAS) is the actual speed of the airplane through the air..

TAS is found by correcting calibrated airspeed (CAS) for density altitude.

consult your airplane's Pilot's Operating Handbook to determine CAS based on indicated airspeed.

  Generally, there is little error at cruise speeds; i.e., CAS equals indicated airspeed (IAS).

Thus, as a practical matter, you may usually use IAS rather than CAS to determine true airspeed.

Air density affects the indications of the airspeed indicator and the performance of the airplane.

   . Density altitude is the theoretical altitude in the standard atmosphere where the density is the same as the actual density you are experiencing in flight.

   Density altitude is found by correcting pressure altitude for nonstandard temperature.

Determining True Airspeed and Density Altitude...

obviously at FL330 you will already have the altimeter set to 29.92 so this step could be omitted..........

for flight below 18,000'....

Pressure altitude can be determined by setting the airplane's altimeter to 29.92 and then reading the altitude.

    If this is done in flight, make a note of the altimeter setting before turning it to 29.92.

     After you determine the pressure altitude, reset the altimeter to the current setting.

         3. The outside air temperature (OAT) can be determined by reading the current temperature on the airplane's OAT gauge.

You will need to use the Celsius scale.

You will need a E6b for this.... available at most FBO's or on line from countless "pilot stores"

To Determine True Airspeed and Density Altitude..

True airspeed and density altitude can be calculated on the calculator side of your flight computer.

Rotate the inner scale until the numbers on the inner and outer scales match.

   1. The window that is between "1:30" and "1:50" on the hour scale is labeled "DENSITY ALTITUDE" and the arrow points to the density altitude.

         1. The numbers that rotate through this window are in thousands of feet and range from -10 (or -10,000 ft.) to 45 (or +45,000 ft.).

   2. The window on the right side below "2:00" and "2:30" on the hour scale is used to set the OAT (above the window) over the pressure altitude (numbers in the window).

         1. The OAT is in 5°C increments from +50°C on the left side to -70°C on the right side.

         2. The numbers in the window are in thousands of feet and range from -2 (or -2,000 ft.) to 50 (or 50,000 ft.).

EXAMPLE: What is the TAS and density altitude if the IAS is 130 kt., OAT is -15°C, and the pressure altitude is 5,000 ft.?

   1. Using the inner window on the right side, locate the OAT of -15°C and rotate the disk so the pressure altitude of 5,000 ft. (which is labeled "5" on the scale) is under -15°C, as shown in the figure.

   2. In the window labeled "DENSITY ALTITUDE," read the density altitude of approximately 2,500 ft.

   3. Locate the IAS of 130 kt., or "13," on the inner scale. Without moving the disk, read the TAS on the outer scale opposite the IAS, which is 135 kt.

or.................if you are just trying to get close, a rule of thumb is,increase your indicated airspeed (IAS) by 2% per thousand feet of altitude to obtain the true airspeed (TAS).

Answer 2

About 480 knots.

Answer 3

Who uses an E6-B anymore??..just kidding...But, seriously..I don't..good answers....Most of us that are flying at those speeds/altitudes have equipment/avionics in our aircraft that tells us our TAS, SAT, and TAT etc...takes the math out of it to reduce the workload...I fly a Hawker with proline 21 avionics and a couple of kick butt fms boxes that tell me everything I need to know...however...if this equipment shall fail...we still know how to get that information by using formulas and referring to the flight manual/tab data....hope this helps a little!

Jonathan S

ATP-LRJET,HS-125

CFI/AGI

Answer 4

TAS increases by roughly 2% per 1000' of altitude gain.

280 x 1.66 = 465 KTAS.

you certainly *CAN* use an E6-B to figure out all that stuff, but man...why bother?  I have been flying professionally for years and I have never once felt a need to whip out a flight computer.  Most airspeed indicators have a conversion scale built right in so that you can simply dial in your density altitude and read the result.  More modern aircraft have a digital display right on the airspeed indicator itself (if that plane has an EFIS...which nearly all of them do nowadays)

In addition...KTAS is not a particularly important number.  Aircraft performance (stall speeds, maneuvering speeds etc) are all predicated on KIAS.  Fuel burn is calculated in gallons per hour.  That seems to have more to do with Groundspeed than it does True Airspeed.

The only real realm of flight where TAS is important is when worrying about mach numbers.  And if mach is a concern, its easier to deal in mach numbers than in knots.

You certainly can do all those calculations and figure out your TAS down to the exact knot.  However, you will find that the result is nearly identical to the "rule-of-thumb" calculation I just gave you.  And its not really important enough to warrant any more exactness than that.