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User currently offlineRelic From United Kingdom, joined Apr 2005, 114 posts, RR: 0
Posted (7 years 6 months 2 days 9 hours ago) and read 2988 times:

Hi everyone
I feel really embarrased asking this question having loved civil aircraft for many years but here goes.
When V1 is reached and the stick is pulled back,what actually moves on the aircraft to pull nose up.
I have always thought that the wing config creates lift at a certain speed.V1 is when the nose wheel starts to lift and elevators create nose up.
I have mailed pilots to find out but with no reply........mind you would you reply to a probably obvious question like this.lol.
Please put me out of my misery
Thanks
Andy

28 replies: All unread, showing first 25:
 
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 1, posted (7 years 6 months 2 days 9 hours ago) and read 2980 times:

Stick aft -> elevator (the hinged part of the horisontal stabiliser) goes up.

This is done at Vr. V1 is the go-no go speed, before which you will abort the takeoff if there is a serious problem (read: engine failure) and after which you go flying no matter what.

Cheers,
/Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineTheGreatChecko From United States of America, joined Mar 2004, 1130 posts, RR: 2
Reply 2, posted (7 years 6 months 2 days 8 hours ago) and read 2975 times:

Technically, the nose is lifted up at VR not V1. V1 is the takeoff decision speed. Below V1, if an engine were to fail, the aircraft would stop on the runway, after V1, the takeoff is continued and the engine failure is an airborne emergency. VR is rotation speed.

What actually brings the nose up? To keep things on the simple side: The elevators on the horizontal stabilizer.

The horizontal stabilizer is shaped opposite to the wings of the aircraft and actually provide a downforce on the tail. When the pilot pulls back on the yoke, the elevators are deflected upwards, changing the angle of attack (the angle between the relative wind and a line drawn from the leading edge of the surface to the trailing edge, this being the back side of the elevator), which causes the elevator to create more downforce, pushing the tail down and the nose up.

Hope this helps, aerodynamics can be difficult to explain without a good picture, but this explanation should suffice. I'm sure someone will add to it.

Checko

[Edited 2007-04-27 23:51:03]


"A pilot's plane she is. She will love you if you deserve it, and try to kill you if you don't...She is the Mighty Q400"
User currently offlineVikkyvik From United States of America, joined Jul 2003, 10107 posts, RR: 26
Reply 3, posted (7 years 6 months 2 days 8 hours ago) and read 2959 times:
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Quoting Relic (Thread starter):
I have always thought that the wing config creates lift at a certain speed.V1 is when the nose wheel starts to lift and elevators create nose up.

Just to clarify: the amount of lift the wing creates increases as speed increases. Technically, the wing is creating lift at 10 knots - just not anywhere near enough to lift the airplane.



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlineRelic From United Kingdom, joined Apr 2005, 114 posts, RR: 0
Reply 4, posted (7 years 6 months 2 days 8 hours ago) and read 2960 times:

Thanks guys
so i wasnt far off then...lol
Thanks for your help.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17068 posts, RR: 66
Reply 5, posted (7 years 6 months 2 days 4 hours ago) and read 2890 times:

In theory: If the pilots do not pull back on the stick/yoke, the aircraft will probably lift off anyway eventually as the wings produce more and more lift. However, runway length and tire max speed are limitations.


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 6, posted (7 years 6 months 2 days ago) and read 2859 times:

Quoting Starlionblue (Reply 5):
In theory: If the pilots do not pull back on the stick/yoke, the aircraft will probably lift off anyway eventually as the wings produce more and more lift. However, runway length and tire max speed are limitations.

Except for the fact that while on the ground, the wing of an airliner is at or near the zero-lift angle of attack. Thus it will not generate any significant lift until rotation.

If it will eventually raise the nose without pilot interaction depends on the trim setting of the aircraft, but with the MLG reaction force aft of the center of gravity it is no all that likely.

Wasn't this covered in another thread here recently?



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineSpeedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0
Reply 7, posted (7 years 6 months 1 day 22 hours ago) and read 2839 times:

It was covered with quite a few posts in this thread:

Why Does The Nose Go Up? (by Xbraniffone Mar 23 2007 in Tech Ops)



Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
User currently offlineA346Dude From Canada, joined Nov 2004, 1287 posts, RR: 7
Reply 8, posted (7 years 6 months 1 day 19 hours ago) and read 2818 times:

Quoting FredT (Reply 6):
Except for the fact that while on the ground, the wing of an airliner is at or near the zero-lift angle of attack. Thus it will not generate any significant lift until rotation.

Not true. Unless the lift vector is parallel to the ground (and it's not even close), there will be at least some vertical component of lift.



You know the gear is up and locked when it takes full throttle to taxi to the terminal.
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 9, posted (7 years 6 months 1 day 12 hours ago) and read 2764 times:

A346Dude,
the definition of the zero-lift angle of attack is the angle of attack where the lift coefficient is zero, thus there is no lift, the lift vector has a magnitude of zero and thus no direction at all. Not parallell to the ground, not perpendicular to it.

If the lift vector has a non-zero magnitude on the ground roll it is by definition perpendicular to the ground in the aircraft xz plane, as it is perpendicular to the freestream velocity vector.

In real life, there will be positive lift along some parts of the wing and negative lift along some parts, due to washout, but on the whole no significant lift is generated. Lift generates induced drag, and if you have the option to design away the induced drag while accelerating on the take-off roll it'd be pretty daft not to do it.

Cheers,
/Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineVikkyvik From United States of America, joined Jul 2003, 10107 posts, RR: 26
Reply 10, posted (7 years 6 months 1 day 11 hours ago) and read 2747 times:
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Quoting FredT (Reply 9):

In real life, there will be positive lift along some parts of the wing and negative lift along some parts, due to washout, but on the whole no significant lift is generated. Lift generates induced drag, and if you have the option to design away the induced drag while accelerating on the take-off roll it'd be pretty daft not to do it.

Is this specifically due to some effect of the ground on the airflow? I'd think that if the aircraft were flying in level flight (at a deck angle of zero), it would be nowhere near zero-lift angle of attack.

Thanks.

~Vik



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 11, posted (7 years 6 months 1 day 10 hours ago) and read 2721 times:

No, in flight at zero deck angle the AoA will be that of the angle of incidence, which is above the zero-lift AoA. In real life, most airliners tend to cruise with a degree or two of positive pitch attitude.

On the ground, most airliners are slightly nose down to keep the aircraft from generating lift until you want it - at rotation.

Rgds,
/Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineA346Dude From Canada, joined Nov 2004, 1287 posts, RR: 7
Reply 12, posted (7 years 6 months 1 day 8 hours ago) and read 2702 times:

Quoting FredT (Reply 9):
the definition of the zero-lift angle of attack is the angle of attack where the lift coefficient is zero, thus there is no lift, the lift vector has a magnitude of zero and thus no direction at all. Not parallell to the ground, not perpendicular to it.



Quoting FredT (Reply 9):
In real life, there will be positive lift along some parts of the wing and negative lift along some parts, due to washout, but on the whole no significant lift is generated.

 Confused

I don't get it? How could a wing that is roughly parallel to the ground create no net lift? After all, the cruise attitude is only slightly more nose-up than the attitude on the ground.

Furthermore, if the wing is not creating lift, how does the tail alone generate enough force to rotate the airplane?



You know the gear is up and locked when it takes full throttle to taxi to the terminal.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17068 posts, RR: 66
Reply 13, posted (7 years 6 months 1 day 6 hours ago) and read 2683 times:

Quoting A346Dude (Reply 12):
Furthermore, if the wing is not creating lift, how does the tail alone generate enough force to rotate the airplane?

This thread did a nice turn. Anyway the stabilizer generates enough downforce to rotate the plane, increasing the angle of attack of the wing from "little or no lift" to "lots of lift". The wing does the "heavy lifting".



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 14, posted (7 years 6 months 1 day ago) and read 2648 times:

Quoting A346Dude (Reply 12):
Furthermore, if the wing is not creating lift, how does the tail alone generate enough force to rotate the airplane?

The weight of the aircraft is still carried by the landing gear.



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineQFA380 From Australia, joined Jul 2005, 2081 posts, RR: 1
Reply 15, posted (7 years 6 months 23 hours ago) and read 2639 times:

Quoting Vikkyvik (Reply 3):
Just to clarify: the amount of lift the wing creates increases as speed increases. Technically, the wing is creating lift at 10 knots - just not anywhere near enough to lift the airplane.

Is speed-lift linear? So at the wing is creating 10 times as much life at 100knots than it is at 10 knots? With flaps and what not at the same settings.


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 16, posted (7 years 6 months 22 hours ago) and read 2632 times:

No, both lift and drag are proportional to the dynamic pressure, which is proportional to the (true) air speed squared. At 100 knots you will have 100 times more lift than you would at ten knots, all things else being equal.

Regds,
/Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineRwy04LGA From United States of America, joined Jul 2005, 3176 posts, RR: 8
Reply 17, posted (7 years 5 months 3 weeks 4 days 1 hour ago) and read 2396 times:

If you've ever seen cockpit videos of takeoffs, notice that the pilot's (PF) hand is on the throttles up until 'V1' is called by the copilot (PNF). After V1, the airplane is committed to flight and cannot be stopped on the remaining length of runway. Therefore, the PF removes his hand from the throttles and grasps the control wheel. When the PNF calls 'Rotate' (VR), the PF will pull back on the stick until the aircraft has attained the proper attitude for unsticking from the runway.

PF pilot flying
PNF pilot not flying.

The two pilots sometimes switch roles for the purpose of letting the junior pilot gain practical experience. The Captain might not be the PF and the copilot might not be the PNF. Hence these specific terms.



Just accept that some days, you're the pigeon, and other days the statue
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 18, posted (7 years 5 months 3 weeks 4 days ago) and read 2374 times:

Quote:

British Airways Operations Manual
*** British Airways Flight Operations Department Notice ***

There appears to be some confusion over the new pilot role titles. This notice will hopefully clear up any misunderstandings. The titles P1, P2 and Co-Pilot will now cease to have any meaning, within the BA operations manuals. They are to be replaced by Handling Pilot, Non-handling Pilot, Handling Landing Pilot, Non-Handling Landing Pilot, Handling Non-Landing
Pilot, and Non Handling Non-Landing Pilot.
The Landing Pilot, is initially the Handling Pilot and will handle the take-off and landing except in role reversal when he is the Non-Handling Pilot for taxi until the Handling Non-Landing Pilot, hands the Handling to the Landing Pilot at eighty knots.
The Non-Landing (Non-Handling, since the Landing Pilot is Handling) Pilot reads the checklist to the Handling Pilot until after Before Descent Checklist completion, when the Handling Landing Pilot hands the handling to the Non-Handling Non-Landing Pilot who then becomes the Handling Non-Landing Pilot.
The Landing Pilot is the Non-Handling Pilot until the "decision altitude" call, when the Handling Non-Landing Pilot hands the handling to the Non-Handling Landing Pilot, unless the latter calls "go-around", in which case the Handling Non-Landing Pilot, continues handling and the Non-Handling Landing Pilot continues non-handling until the next call of "land" or "go-around", as appropriate.
In view of the recent confusion over these rules, it was deemed necessary to restate them clearly.

So if anyone has any questions please keep them to themselves.

Rather likely to be a spoof of course... but you never know! Big grin



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineChrisMUC From Germany, joined Jul 2006, 66 posts, RR: 0
Reply 19, posted (7 years 5 months 3 weeks 3 days 18 hours ago) and read 2341 times:

Quoting Rwy04LGA (Reply 17):
The two pilots sometimes switch roles for the purpose of letting the junior pilot gain practical experience. The Captain might not be the PF and the copilot might not be the PNF.

I think (at least I hope so) that at most companies it's a fifty-fifty share between Cpt and F/O being PF.
At my company always CM1 (Cpt) has his hand on the thrust levers, either if he's PF or PNF. Call outs are done by the PNF.
This is because RTOs are very time and safety critical, so if the PIC (CM1) thinks that an aborted T/O is necessary, he/she can do it without consulting the F/O.


User currently offlineMidEx216 From United States of America, joined Jun 2005, 651 posts, RR: 4
Reply 20, posted (7 years 5 months 3 weeks 3 days 1 hour ago) and read 2240 times:

In reality, when you pull the stick back, the elevators go up, creating an inverted airfoil shape. Rather than creating nose up, it creates tail down. Given the main gear as a pivoting point, the tail does in fact go down, but then the nose comes up (like a see-saw), and the forward momentum of the engines, along with lessened back-pressure on the stick (which allows the wings to have superior lift over the elevators again) lifts the wheels off the ground.


"Cue the Circus Music!"
User currently offlineRwessel From United States of America, joined Jan 2007, 2368 posts, RR: 2
Reply 21, posted (7 years 5 months 3 weeks 2 days ago) and read 2166 times:
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Quoting MidEx216 (Reply 20):
In reality, when you pull the stick back, the elevators go up, creating an inverted airfoil shape. Rather than creating nose up, it creates tail down. Given the main gear as a pivoting point, the tail does in fact go down, but then the nose comes up (like a see-saw),

This is more or less correct.

Quoting MidEx216 (Reply 20):
and the forward momentum of the engines, along with lessened back-pressure on the stick (which allows the wings to have superior lift over the elevators again) lifts the wheels off the ground.

This unfortunately is completely incorrect. First, just tilting the aircraft up does not change the momentum of the engines, which is still straight forward. Second, it's quite aircraft dependent on whether or not you need to reduce back pressure on the stick after rotation, but on almost all, you will have to maintain at least *some* back pressure, unless you want the nose to drop. You *might* have to reduce back pressure a bit *after* the wheel leave the ground, since the CG will be ahead of the main gear (assuming a trike), and after takeoff the aircraft will want to rotate around the more forward CG, increasing the lever arm of the tail, thus increasing the rotation. On the flip side, as you start climbing you need to increase your deck angle to keep the same pitch (since the relative wind will now be coming from somewhat above the aircraft), so you might not have to release back pressure.

Finally, what causes the aircraft to lift off the ground is in increase in lift by the main wing, since it's angle of attack in increased by the rotation. The horizontal stabilizer, under normal conditions (and assuming a conventional configuration), always produces "down" lift, since you always load the airplane such that it's a bit nose heavy (CG ahead of the center of lift). The main wing overcomes the tails downward force by the simple expedient of being vastly bigger.


User currently offlineSilverComet From Mauritius, joined Apr 2007, 85 posts, RR: 0
Reply 22, posted (7 years 5 months 3 weeks 1 day 23 hours ago) and read 2158 times:

Quoting Rwessel (Reply 21):
increase your deck angle to keep the same pitch

What's the difference between deck angle and pitch?

Quoting Rwessel (Reply 21):
since the relative wind will now be coming from somewhat above the aircraft

If the relative wind is coming from above the aircraft, chances are the AoA is negative. Not a good place to be at when you're low and slow. I do, however, agree that as you gain speed, AoA decreases for a constant pitch attitude and your flight path angle increases.

Pitch = AoA + FPA.


User currently offlineRwessel From United States of America, joined Jan 2007, 2368 posts, RR: 2
Reply 23, posted (7 years 5 months 3 weeks 1 day 22 hours ago) and read 2154 times:
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Quoting SilverComet (Reply 22):
What's the difference between deck angle and pitch?

Indeed I meant Angle of Attack and not pitch.

Quoting SilverComet (Reply 22):
If the relative wind is coming from above the aircraft, chances are the AoA is negative. Not a good place to be at when you're low and slow. I do, however, agree that as you gain speed, AoA decreases for a constant pitch attitude and your flight path angle increases.

I should have been clearer about the frame of reference. I was referring to the path of the relative wind as seen by an outside observer, which in climbing flight appears to be coming from above.

All in all, not very clear.  Sad


User currently offlineRelic From United Kingdom, joined Apr 2005, 114 posts, RR: 0
Reply 24, posted (7 years 5 months 3 weeks 1 day 19 hours ago) and read 2127 times:

Well....I didnt expect this much info.Many thanks to everyone who has left comments.
I thought i had the basics of "Nose up",but the info and calculations on this topic have really put me straight.
Many thanks
Andy


25 Vikkyvik : Actually, it will change the momentum of the engines. Momentum is a vector, with a magnitude and a direction. Tilt the engines, and you've changed th
26 Rwessel : Are you saying that if I have a moving object, and I rotate it, it's going to change direction? Sorry, no.
27 Vikkyvik : Ah, I see what you were saying. I thought you were talking about the force it was applying to the aircraft (changing the aircraft's momentum). Just m
28 Post contains images FredT : And to be really strict about the semantics and physics, you have a moment applied to a rigid body* (i e not about any specific point of the rigid bo
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