IAS headwind vs. tailwind

Humty72

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A flight instructor asked me what I thought about the subject. A few of them were arguing. One of them had a student come back from a cross country and said going westbound with a headwind his IAS was higher than when he was eastbound with a tailwind. It has been a while since I though about things like that and I don't have any good ref. materials around...... what do you guys think...?:eek:
 

Andy Neill

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All things being equal (weight, power setting, angle of attack, etc.), the airplane can't sense a head or tailwind but will deliver the same airspeed either way.

The question doesn't seem to match the experience level in your profile.
 

Twotter76

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Andy is correct, IAS (indicated airspeed to clarify) will not vary with a headwind or tailwind. The student may have been confusing IAS with groundspeed, which will vary with headwind or tailwind component. The speed of the aircraft through the air will remain the same regardless of wind direction, assuming similar power settings are used at similiar altitudes etc etc. Perhaps the student was at a lower altitude going into the wind and a higher one coming back with the tailwind.

Cheers

Twotter76
 

bobbysamd

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IAS v. Ground Speed

I second the above posts. Look at it this way. Once you leave the surly bounds of earth you become part of the airmass. IAS is the airspeed at which your airplane is traveling through the airmass. Correct it for calibrated, equivalent, true and wind, and you arrive at groundspeed.
 

Humty72

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thanks

'tis what I told the dudes.. but they had some b.s. answer ..
thanks.
laters..





Andy Neill said:


The question doesn't seem to match the experience level in your profile.

ehhhh ok. :D
 

sydeseet

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Think outside the box folks.

IAS will drop off per a given power setting as altitude increases - fewer air molecules impacting the pitot tube and it's mechanisms. TAS increases as we all know up to a certain point at which it will dercreases again. I'd bet the student observed the differences as they related to his altitude (east vs west cardinal altitudes) and assumed it was caused by the wind. Or, as the above post stated, he meant to say groundspeeed.
 

Bluto

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Yeah, the next time I hear a commercial pilot tell me that the airplane will "weathervane" into a steady, non-gusting, non-windshearing, constant wind, I'm gonna lose it. What is so technically complicated about this subject? The airplane doesn't know what the wind is doing. It doesn't care, unless it changes suddenly. The only thing wind will do is affect how quickly, and in which direction, we move relative to the ground.
 

TurboS7

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Come on guys get real, IAS stays the same as long as the weight of the aircraft, altitude,thrust of the powerplant, and temperature and pressure of the air is constant. When any of the above vary the IAS will change one way or the other, it has nothing to do with which direction the aircraft is flying relative to any given wind. To get the most effeciency you should fly with a "high" power setting into a headwind and lower power setting with a tailwind. Your FMC in the airplane you'll eventually be flying will figure all this stuff all out for you, all you will have to do is push buttons and tell it what to do. Welcome to aviation in the 21st century.
 

pilotyip

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Max Range?

In order to get the max range from your airplane, you have to adjust the ISA to account for the head/tail wind. A general rule of thumb, is subtract 10% of the TAS of the tailwind and add 5% of the TAS into a headwind. Never slow down below L/D max, or holding speed. Old rule of thumb in the P-3 was 205 + 1/2 the gross wt/1000-FL+5% of the head wind-10% of the tailwind=max range
 

TurboS7

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Works great but we are not allowed to use that anymore, got to use FMC.
 

pilotyip

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FMC?

In the old days we did not have ILS or FD's on the P-3 everything was manual. We thought when we got a heading bug slewed to the auto pilot we were really going hi-tech.
 
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