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Boeing 747 Pitch Up On Touchdown  
User currently offlineReggaebird From Jamaica, joined Nov 1999, 1176 posts, RR: 0
Posted (4 years 10 months 2 weeks 4 days 3 hours ago) and read 7980 times:

I observed a Virgin Atlantic Boeing 747-400 landing at Boston Logan Airport recently and noticed a pronounced pitch up on touchdown. I reviewed other 747 landing videos and did not see the same thing. Does anyone know what causes it?

See what I am referring to here:
http://www.youtube.com/watch?v=sDVurrpvnPc

15 replies: All unread, jump to last
 
User currently offlineUAL747 From , joined Dec 1969, posts, RR:
Reply 1, posted (4 years 10 months 2 weeks 4 days 2 hours ago) and read 7973 times:

I believe, and I know someone will correct me, but I think when the spoilers are raised to their full position, it causes an upward pitch of the aircraft.

UAL


User currently onlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4200 posts, RR: 37
Reply 2, posted (4 years 10 months 2 weeks 4 days ago) and read 7901 times:

Spoiler deployement on touchdown, when not properly counteracted by the pilot flying, causes a pronounced pitch up.


Chicks dig winglets.
User currently offlineLowrider From United States of America, joined Jun 2004, 3220 posts, RR: 10
Reply 3, posted (4 years 10 months 2 weeks 3 days 9 hours ago) and read 7713 times:

The only times I have noticed it is when:
1. The outboard spoilers deploy significantly earlier than the inboard ones
2. The inboard do not deploy due to some malfunction
3. Landing with a very aft CG.
4. Conducting an autoland where the autopilot attempts to arrest the sink rate just prior to touchdown.

#'s 1 and 2 do not seem to be the case, and cause a very dramatic pitch up to the point where a tail strike is a possibility.



Proud OOTSK member
User currently offlinePJFlysFast From United States of America, joined May 2006, 463 posts, RR: 1
Reply 4, posted (4 years 10 months 2 weeks 3 days 6 hours ago) and read 7615 times:

It appears that the elevator was manipulated to raise the nose at touchdown. Perhaps the pilot flying was trying to minimize the descent rate but just a bit too late.

User currently offlineUAL747 From , joined Dec 1969, posts, RR:
Reply 5, posted (4 years 10 months 2 weeks 3 days 2 hours ago) and read 7558 times:

I'm going with the spoilers, as I believe this was explained by a 747 pilot here back a few years ago. I'm also going to suggest some aerodynamic breaking as well.

UAL


User currently offlineTb727 From United States of America, joined Jun 2005, 1597 posts, RR: 9
Reply 6, posted (4 years 10 months 2 weeks 3 days 1 hour ago) and read 7522 times:



Quoting UAL747 (Reply 5):
I'm also going to suggest some aerodynamic breaking as well.

I hope not!



Too lazy to work, too scared to steal!
User currently offlinePoint8six From United Kingdom, joined Apr 2008, 94 posts, RR: 0
Reply 7, posted (4 years 10 months 2 weeks 2 days 19 hours ago) and read 7446 times:

Have observed the pitch-up after touchdown from pilots (mainly inexperienced on type) who have continued the flare after touchdown. Aerodynamic braking is possible but not recommended due tailstrike threat.

User currently offlineFaro From Egypt, joined Aug 2007, 1548 posts, RR: 0
Reply 8, posted (4 years 10 months 2 weeks 2 days 19 hours ago) and read 7441 times:



Quoting Lowrider (Reply 3):
The only times I have noticed it is when:
1. The outboard spoilers deploy significantly earlier than the inboard ones
2. The inboard do not deploy due to some malfunction
3. Landing with a very aft CG.
4. Conducting an autoland where the autopilot attempts to arrest the sink rate just prior to touchdown.

#'s 1 and 2 do not seem to be the case, and cause a very dramatic pitch up to the point where a tail strike is a possibility.

Do fly-by-wire airliners like the A320 and 777 automatically compensate for pitch-up on ground spoiler deployment in the normal control law during landing?

Faro



The chalice not my son
User currently offlineReggaebird From Jamaica, joined Nov 1999, 1176 posts, RR: 0
Reply 9, posted (4 years 10 months 2 weeks 2 days 15 hours ago) and read 7389 times:



Quoting Lowrider (Reply 3):
The only times I have noticed it is when:
1. The outboard spoilers deploy significantly earlier than the inboard ones
2. The inboard do not deploy due to some malfunction
3. Landing with a very aft CG.
4. Conducting an autoland where the autopilot attempts to arrest the sink rate just prior to touchdown.

#'s 1 and 2 do not seem to be the case, and cause a very dramatic pitch up to the point where a tail strike is a possibility.

What a great amount of information. Thank you so much!!!


User currently offlineAaron747 From Japan, joined Aug 2003, 8153 posts, RR: 26
Reply 10, posted (4 years 10 months 2 weeks 2 days 11 hours ago) and read 7319 times:



Quoting UAL747 (Reply 5):
I'm also going to suggest some aerodynamic breaking as well.

There was hardly any elevator input visible in the video to suggest aerodynamic braking - which isn't needed on the 747 anyway with all twelve spoiler panels deployed. Still, this video was nothing compared to the crap I've seen JAL 747 drivers pulling - massive rudder inputs before nosegear touchdown, narrowly avoided tailstrikes due to landing with all kinds of extra trim, see-saw x/wind landing touchdowns (pretty hard to do given the 74's low body gear trucks) - you name it.



If you need someone to blame / throw a rock in the air / you'll hit someone guilty
User currently offlineLowrider From United States of America, joined Jun 2004, 3220 posts, RR: 10
Reply 11, posted (4 years 10 months 2 weeks 2 days 7 hours ago) and read 7259 times:



Quoting Point8six (Reply 7):
Aerodynamic braking is possible but not recommended due tailstrike threat.

Agreed. Boeing has published data to show that aerodynamic braking is largely ineffective at pitch angles less than approx 20 degrees. Tailstikes will occur on the 74 at about 12.5 degrees, depending on conditions. It is better to get the nose down and let the brakes, reversers, and spoilers do thier job.

Quoting Faro (Reply 8):
Do fly-by-wire airliners like the A320 and 777 automatically compensate for pitch-up on ground spoiler deployment in the normal control law during landing?

I am sorry, but I don't know the answer to that, but I suspect that they do. I do not have any experience or formal training on fly by wire types, but I have been told that, in the normal mode, fly by wire systems attempt to squelch any uncommanded pitch or roll excusions.



Proud OOTSK member
User currently offlineRampkontroler From United States of America, joined Sep 2001, 859 posts, RR: 6
Reply 12, posted (4 years 10 months 2 weeks 2 days 6 hours ago) and read 7240 times:



Quoting Tb727 (Reply 6):

Quoting UAL747 (Reply 5):
I'm also going to suggest some aerodynamic breaking as well.

I hope not!

Ha ha! Good one...I caught that too!


User currently offlineFlybaurLAX From United States of America, joined Oct 2008, 638 posts, RR: 0
Reply 13, posted (4 years 10 months 2 weeks 2 days 4 hours ago) and read 7213 times:



Quoting PJFlysFast (Reply 4):
It appears that the elevator was manipulated to raise the nose at touchdown.

I see it too. I don't know why he'd do that, perhaps just accidentally pulled back a little too much? Maybe he sneezed  Wink



Boilerup! Go Purdue!
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 14, posted (4 years 10 months 2 weeks 1 day 22 hours ago) and read 7154 times:



Quoting Faro (Reply 8):
Do fly-by-wire airliners like the A320 and 777 automatically compensate for pitch-up on ground spoiler deployment in the normal control law during landing?

The web suggests that both the A320 and the 777 use C* type pitch control laws, which work on pitch rate at low speed. So, if you don't move the stick/yoke during landing, the control law will automatically reject disturbances caused by spoiler deployment.

Good info here:
http://www.skybrary.aero/index.php/Fly-By-Wire

Tom.


User currently offlineFrancoflier From France, joined Oct 2001, 3766 posts, RR: 11
Reply 15, posted (4 years 10 months 2 weeks 1 day 13 hours ago) and read 7093 times:



Quoting FlybaurLAX (Reply 13):
I don't know why he'd do that, perhaps just accidentally pulled back a little too much?

Probably just a false impression of being about to hit the runway a bit too firmly. Even though some of the wheels had already contacted the ground, it was probably not felt in the cockpit, and the pilot thought he was still in the flare.

While the spoiler deployment normally does not generate any pitch up tendency (unless the inboards are inop), it will compound any additional back pressure applied on the yoke during touchdown.

Touching down with the thrust set above idle can also result in an undesired pitch up motion.



Looks like I picked the wrong week to quit posting...
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