Why is it that?

[tcco94]

Well I finally took the posky 777 for a spin. I love it but ive noticed this with multiple airplanes. There cruise speeds say like 400-500 knots or something im just guessing I cant exactly remember but in that range. When I go above 330 knots it says over speed. Im even at cruising altitude of 32,000 feet?

Any help?
Thanks

[Brett_Henderson]

You answered your own question  ;)

Your homework assignment is to explain the difference between 'indicated airpseed' , and 'true airspeed'


(hint: altitude is the biggest factor)

[tcco94]

Ohhhh,
Okay I think I get what you mean.

When im gaining altitude im gaining my true airspeed but my indicated airspeed is staying the same?

I looked at my GPS while im in the flight right now and it says 510 which I believe is my true airspeed?

[Brett_Henderson]

That's "close".. but you'll enjoy this all so much more if you you do some research and are able to explain it to someone else..

After all.. a 777 pilot should know (and understand) these things  :)

[tcco94]

Doing the research as we speak, if i get it tonight ill try again.

This is why I dont fly these huge 777's but im finding it alot funner than a 747  :o

[tcco94]

Google is useful  8-)
Lets try again here,

So the indicated airspeed is the airspeed that the airplane things its speed is by the molecules going through the pitot tube.

True airspeed is how fast the airplane is really going but at higher altitudes the air is less dense so less molecules in the pitot tube and a less indicated airspeed.

So if I was going 300 knots at sea-level it would be the same as going 100 knots at 30,000 feet.

Is this right

[Brett_Henderson]

Your interpretation is a little askew,, but YES.. you are understanding it.

Every little piece of aeronautic data adds up in your brain.. pilots need to understand this stuff.. not just have it explained to them..

VERY good !

[FlightHound]

[quote]

Every little piece of aeronautic data adds up in your brain.. pilots need to understand this stuff.. not just have it explained to them..
quote]

That's why when you get older, you need an occasional brain fart!  ;D

[tcco94]

Okay thanks!
It makes alot more since when I did the research why its diffrent at higher altitudes.

I use to always think I was going 300 kts.  ::)

[Brett_Henderson]

Ok.. now here's where it get's interesting..

Your wings "see" the same thing that the pitot tube sees. They "think" they're moving through air at the indicated (lower) airspeed.

To your advantage at higher altitudes, drag is relatively low (considering your TRUE airspeed).. but you get nearer the "Coffin Corner"..

[expat]

One thing not yet pointed out is that at the sort of altitudes you are talking about, knots are not used, you should be working in Mach, and as a lose rule be flying at about .8. Mach takes into account altitude and air density the two things that you fighting against to remain flying in knots......or so is my understanding :-?

Matt