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high alt weird plane position

jayd Guest

im flying right now at 40000 ft in an Airbus a300 american airlines HNAC i think is the maker. but i am noticing that i am traveling at .83 mach, but only like 270kts. and my plane seems to be pointing up about 5 degrees. its kind of weird. is there a reason for this? if i increase throttle i know it will settle back down but i will overspeed. ty.

Pro Member First Officer
antone First Officer

jayd wrote:

im flying right now at 40000 ft in an Airbus a300 american airlines HNAC i think is the maker. but i am noticing that i am traveling at .83 mach, but only like 270kts. and my plane seems to be pointing up about 5 degrees. its kind of weird. is there a reason for this? if i increase throttle i know it will settle back down but i will overspeed. ty.

Your airspeed indicator will underread the higher your altitude. This is because it takes measurements based on the flow of air through the pitot tube. At higher altitudes the atmosphere is thinner - that is, there is less air. If you were at 2000 feet and Mach 0.83 (not at all wise, heh) your indicated airspeed would be a lot higher.

Aircraft do often fly with a slight nose-up attitude at cruise. It's normal, and I think has to do with angle of attack.

jayd Guest

oh ok that helped, thanks a lot =)

Pro Member First Officer
spitfiresrule First Officer

Could.nt have said it better myself. Good post Antone

Pro Member First Officer
to_coolguys First Officer

ya good reply and well done..But i still don;t understand a statement from the poster.How is the plane going to settle back down by increasing the throttle?
Airplan pitch has got nothing to with throttles..If your airplane is trimmed for a particular speed then increasing the throttle will just make the airplane pitch up and climb to maintain that speed...

Pro Member First Officer
antone First Officer

to_coolguys wrote:

ya good reply and well done..But i still don;t understand a statement from the poster.How is the plane going to settle back down by increasing the throttle?
Airplan pitch has got nothing to with throttles..If your airplane is trimmed for a particular speed then increasing the throttle will just make the airplane pitch up and climb to maintain that speed...

I was also puzzled by that. At cruise, I would imagine that an increase in the throttles would tend to cause the aircraft to pitch up (if no trim changes were made) and eventually lose speed.

Pro Member First Officer
antone First Officer

Thanks to all who said nice things about my post. Comments and corrections are welcome too, of course.

An easy mistake is to confuse ground speed and air speed. OP's plane may well be reading 270kts IAS, but if he/she were to look at the GPS, that gives some indication of speed over the ground.

We're left in a strange situation. At cruise, a strong tailwind may well increase our speed over the ground. But it can only decrease KIAS. We need to understand that it's our speed relative to the air around us that's important, not the speed at which we cover ground.

Pro Member Captain
ARD-DC Captain

The nose-up pitch you're experiencing is explained quite simply if you think about it...
I have no experience with the aircraft you mention, but FL400 will be close to it's service ceiling.

As the air is thin up there, the wings are generating less lift than they would at lower altitudes, so the autopilot compensates for the decrease in lift, trimming the aircraft to a nose-up attitude so that it won't lose altitude.

If you were to try maintain the same attitude at FL400 as you would maintain at for example FL330, you willl find that you lose altitude at FL400, simply because there is less air, and therefor less lift at the same airspeed.

This then also explains why the plane would settle back down when you push the throttles; because the aircraft speeds up, meaning the airflow past the wings increases; the aircraft then won't need to pitch-up anymore because there is sufficient lift to keep it level.

Pro Member First Officer
to_coolguys First Officer

wow ARD...This simply did not cross my mind..Something to learn from your post...

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