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How Does An Aircraft Rotate?  
User currently offlineGoinv From United Kingdom, joined Jan 2005, 264 posts, RR: 2
Posted (7 years 9 months 1 week 5 days 14 hours ago) and read 11578 times:

You're in an aircraft sitting at the end of the runway. Forward thrust is applied. At a predetermined speed Vr is reached (rotate) followed by V2 (which I understand is the speed at which the aircraft can become airborne)

How does the aeroplane lift it's nose wheel up in the air to start the climb ?

I would assume that there are no mechanical or hydraulic systems on the plane (like a road digger which phsysically lifts the nose).

Is it as simple as "at Vr there is sufficient wind passing over the control surfaces so that when the pilot flying pulls back on the stick the ailerons (?) move causing a change in wind direction over the control surfaces which forces the noise of the plane up ?

Sorry if some of my terminology is wrong and if this is a question with an obvious answer.

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16 replies: All unread, jump to last
 
User currently offlineRichardPrice From , joined Dec 1969, posts, RR:
Reply 1, posted (7 years 9 months 1 week 5 days 14 hours ago) and read 11575 times:

Quoting Goinv (Thread starter):
Is it as simple as "at Vr there is sufficient wind passing over the control surfaces so that when the pilot flying pulls back on the stick the ailerons (?) move causing a change in wind direction over the control surfaces which forces the noise of the plane up ?

Thats it, in a nutshell, terminology not-with-standing.


User currently offlineBoeing Nut From , joined Dec 1969, posts, RR:
Reply 2, posted (7 years 9 months 1 week 5 days 14 hours ago) and read 11575 times:

The horizontal stabilizors, or rear wings if you will, apply a downward force to the tail which occurs when the pilot pulls back on the stick or yoke. The in turn increases the angle of attack of the wing which creates lift and presto! Airborne.

User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 3, posted (7 years 9 months 1 week 5 days 14 hours ago) and read 11575 times:

Quoting Goinv (Thread starter):
Is it as simple as "at Vr there is sufficient wind passing over the control surfaces so that when the pilot flying pulls back on the stick the ailerons (?) move causing a change in wind direction over the control surfaces which forces the noise of the plane up ?

Yes, it is that simple, but the control surfaces that control pitch are the elevators, not ailerons.


User currently offlineBoeing Nut From , joined Dec 1969, posts, RR:
Reply 4, posted (7 years 9 months 1 week 5 days 14 hours ago) and read 11571 times:

Quoting Goinv (Thread starter):
Sorry if some of my terminology is wrong and if this is a question with an obvious answer.

Don't worry, the only dumb question is the one that isn't asked.

Regards


User currently offlineCdfmxtech From United States of America, joined Jul 2000, 1338 posts, RR: 27
Reply 5, posted (7 years 9 months 1 week 5 days 14 hours ago) and read 11552 times:

http://selair.selkirk.bc.ca/aerodynamics1/Stability/Page2.html
Pretty helpful

How does the aeroplane lift it's nose wheel up in the air to start the climb ?
The small little wings on the aft end of the airplane called Horizontal stabilziers have panels on them called elevators. These elevators are go up and down and control whats called the PITCH of the aircraft. If the pilot pulls back on the control column, he wants the plane to go NOSE UP. The elevators will move up and the air acting on the surface will make the aircraft pitch up. Since the elevators are in the back, the nose of the aircraft starts to ROTATE upwards. This is as basic as I can make it.

I would assume that there are no mechanical or hydraulic systems on the plane (like a road digger which phsysically lifts the nose).
You assume correctly.

Is it as simple as "at Vr there is sufficient wind passing over the control surfaces so that when the pilot flying pulls back on the stick the ailerons (?) move causing a change in wind direction over the control surfaces which forces the noise of the plane up ?
Yeah, you could say that. Just substitute "airflow" for wind and "elevators: for ailerons.

Sorry if some of my terminology is wrong and if this is a question with an obvious answer.
The only stupid question is the one not asked.


User currently offlineSLCPilot From United States of America, joined Aug 2003, 581 posts, RR: 3
Reply 6, posted (7 years 9 months 1 week 5 days 14 hours ago) and read 11547 times:

As a very young child I was very disturbed. It was very difficult for me to see how the power from the engines was transmitted to rotational power in the wheels for taxi and T/O.

I also had a hard time understanding why, when "sitting" on a board, I was unable to lift with sufficient strength to hold my self in the air. It was easy enough to dismiss it as weak arms.

Thankfully, two weeks ago, both questions were answered.

Cheers!

SLCPilot



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User currently offlineBrownBat From , joined Dec 1969, posts, RR:
Reply 7, posted (7 years 9 months 1 week 5 days 13 hours ago) and read 11522 times:

Quoting Goinv (Thread starter):
How does the aeroplane lift it's nose wheel up in the air to start the climb ?

The pilot pulls up on the yoke. Without the pilot the plane will still be at the gate.


User currently offlineVikkyvik From United States of America, joined Jul 2003, 9805 posts, RR: 26
Reply 8, posted (7 years 9 months 1 week 5 days 12 hours ago) and read 11494 times:
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Quoting Goinv (Thread starter):
You're in an aircraft sitting at the end of the runway. Forward thrust is applied. At a predetermined speed Vr is reached (rotate) followed by V2 (which I understand is the speed at which the aircraft can become airborne)

Also note that V2 is not the speed at which an aircraft can become airborne. Technically, an aircraft will likely be able to become airborne even below Vr.

V2, I believe, is the takeoff safety speed. It is the speed that the aircraft must be able to achieve, with an engine failure after V1, in order to meet climb gradient and obstacle clearance requirements.

Quoting Boeing Nut (Reply 2):
The in turn increases the angle of attack of the wing which creates lift and presto! Airborne.

Indeed, though a better way to phrase it would be to say that increasing the angle of attack increases the lift. The wings are already generating a significant amount of lift before rotation. Rotation increases the lift past the point where lift is greater than the weight of the airplane (hence, the airplane climbs).

~Vik



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User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 9, posted (7 years 9 months 1 week 5 days 12 hours ago) and read 11490 times:

Quoting Vikkyvik (Reply 8):
Technically, an aircraft will likely be able to become airborne even below Vr.

True, but not safely. A Cessna 172R, for example, can rotate in as little as 40kts, however, one will be flying on "ground effect." If one goes one-wingspan length above the runway, the ground effect diminishes, and if the aircraft is not at or above the normal Vr (Cessna 172R: 57kts), then one will stall.

Actually, that is how soft field takeoffs are conducted.


User currently offlineVikkyvik From United States of America, joined Jul 2003, 9805 posts, RR: 26
Reply 10, posted (7 years 9 months 1 week 5 days 12 hours ago) and read 11457 times:
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Quoting N231YE (Reply 9):
True, but not safely.

Yep. Hence "technically..."  Smile

Quoting N231YE (Reply 9):
and if the aircraft is not at or above the normal Vr (Cessna 172R: 57kts), then one will stall.

I would say that that depends on the circumstances (mostly, on the aircraft, and on what the pilot is trying to do with said aircraft). Obviously, I don't know for sure, but I'd say that it's not a hard and fast rule that once above ground effect, if not at or above Vr, stall will result. Anyway, I'm pretty sure we're in agreement  Smile

Quoting SLCPilot (Reply 6):
Thankfully, two weeks ago, both questions were answered.

Now I'd like to know what happened two weeks ago.  Confused  Wink



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlineBoeing Nut From , joined Dec 1969, posts, RR:
Reply 11, posted (7 years 9 months 1 week 5 days 12 hours ago) and read 11452 times:

Quoting BrownBat (Reply 7):
Without the pilot the plane will still be at the gate.

Incorrect.


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User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 12, posted (7 years 9 months 1 week 5 days 9 hours ago) and read 11376 times:

Quoting Vikkyvik (Reply 10):
Yep. Hence "technically..."

Yeah, I subconsciously read over the "technically" part-my bad, but I guess I explained it a little more in depth.  smile 


User currently offlinePilotpip From United States of America, joined Sep 2003, 3149 posts, RR: 11
Reply 13, posted (7 years 9 months 1 week 5 days 4 hours ago) and read 11300 times:

Quoting Boeing Nut (Reply 11):
Incorrect

The only difference with that one is that the pilot is sitting in a La-Z-Boy in front of a computer monitor.  Smile



DMI
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 14, posted (7 years 9 months 1 week 5 days 4 hours ago) and read 11287 times:

Quoting Boeing Nut (Reply 2):
The in turn increases the angle of attack of the wing which creates lift and presto! Airborne.

More lift you mean. It is not like the wing creates no lift prior to the point when an aircraft rotates. Since the wing is lifting some of the weight off the ground, it puts less stress on main undercarriage when the tailplan pushes the aft of the plane down.

It would be nice if that tailplane force is the only downforce the wheels feel with the wing completely lifting the plane.

A wing lifting doesn't mean going up, it means held up, that more lift will allow the plane to go up and less lift will make it go down.



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User currently offlineLfutia From Netherlands, joined Dec 2002, 3335 posts, RR: 27
Reply 15, posted (7 years 9 months 1 week 5 days 4 hours ago) and read 11277 times:
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Quoting XJRamper,

RUN to the back...... NOW!!!!

[Edited 2006-10-25 05:00:43]


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User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 16, posted (7 years 9 months 1 week 4 days 16 hours ago) and read 11150 times:

Pulling back on the Control column operates Elevator PCAs on the control surface to deflect the Tail down,raising the nose.
regds
MEL



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