A520
Topic Author
Posts: 103
Joined: Fri Jun 02, 2006 1:12 am

Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 12:22 am

Is there an issue on the centre of gravity of large aircrafts if passengers all (or a majority of them) move to the front or back of the aircraft (triggered may be by a sudden threat at one end - hijacker with a gun?), or to one side? Could the CG move too fast too far and render the aircraft out of control?

Thanks to all
 
curlyheadboy
Posts: 814
Joined: Tue Feb 08, 2005 6:56 am

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 12:45 am

I remember some soccer fans, high on drugs and alchool, started to do this exact thing on a charter flight, time ago. Pilots made an emergency landing and they were (no surprise) arrested. I'll try to find the article, if it's still on the web...
If God had wanted men to fly he would have given them more money...
 
redcordes
Posts: 244
Joined: Wed Jan 18, 2006 6:28 am

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 12:52 am

I've often wondered whether moving the passengers to the back of the doomed Alaska Air DC-9 with the stabilizer stuck in a somewhat nose-down position would have helped make the aircraft more flyable?
"The only source of knowledge is experience." A. Einstein "Science w/o religion is lame. Religion w/o science is blind."
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 12:56 am

Perhaps.

I can tell you for absolute certain that it can be a problem in a Helio Courier with a 200 pound crate and a 200 pound "kicker" both moving to the aft end of the cabin during takeoff.

Quoting A520 (Thread starter):
or to one side?

Absolutely not. They cannot move far enough laterally to be felt, even when hand-flying.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
curlyheadboy
Posts: 814
Joined: Tue Feb 08, 2005 6:56 am

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 1:06 am

Found the article, they were Serbian fans on a JAT 737, they made a mess of the plane (ripped off furnishings, oxygen masks, life vests), assaulted cabin crew, tried to get into the cockpit, tried to destabilize the aircraft by moving around all at once... it happened on Aug 2004.
Must have been a nightmare flight!

I post the link, only in Italian, sorry.

http://ilmattino.caltanet.it/hermes/20040831/MILANO/SPORT/FEFE.htm
If God had wanted men to fly he would have given them more money...
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 1:11 am

As a followup to the above reply let's put some reasonable numbers to the question.

A change in CG is equal to the weight to be shifted times the distance it is moved, divided by the total gross weight of the airplane.

So let's take an example of a plane that weighs 160 thousand pounds at this moment. Let's say thirty passengers at an average weight of 180 pounds rush forward or aft an average distance of 360 inches (thirty feet)

Then: 360 X 5400 = 1,944,000 inch-pounds.
Divided by the 160,000 lb gross weight means the center of gravity shifts
12.15 inches.

Is that enough to cause a problem?
Perhaps.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

RE: Centre Of Gravity If Passengers Move All At On

Tue Aug 22, 2006 1:41 am




Quoting SlamClick (Reply 3):
Quoting A520 (Thread starter):
or to one side?

Absolutely not. They cannot move far enough laterally to be felt, even when hand-flying.

That surprises me, as helicopters (if I'm not mistaken) are susceptible to their CG being out of lateral limits. I realize I'm comparing helicopters to transport-category jets, but the percentage of weight moved and the distance required for it to have an effect seem to be proportional between the two.

That said, Capt. Slam knows a heck of a lot more about the topic than I do....  Smile

Quoting CURLYHEADBOY (Reply 4):
they made a mess of the plane (ripped off furnishings, oxygen masks, life vests), assaulted cabin crew, tried to get into the cockpit, tried to destabilize the aircraft by moving around all at once...

Right....that's when you don the O2 masks and dial the PAX pressurization waaaaay down....  Wink




2H4


Intentionally Left Blank
 
AirWillie6475
Posts: 2372
Joined: Thu Jan 27, 2005 1:45 pm

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 1:54 am

It depends on the weight of the aircraft and that aircraft's CG numbers so a blanket answer for your scenario is not possible. Find the formula for calculating CG and your aircraft cg limitation numbers and see for yourself.
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 2:27 am

Quoting 2H4 (Reply 6):
That surprises me, as helicopters (if I'm not mistaken) are susceptible to their CG being out of lateral limits.

You are quite correct. The differences between helicopters and airplanes is, in my opinion, most marked when talking about flight control and CG management. Many newer helicopters are able to effect an increase in longitudinal CG range though use of horizontal stabilizers, sync elevators and so forth. To my knowledge no such devices have ever been deployed for lateral stability. In general, helicopters have very small CG envelopes for their gross weight. An exception is the tandem rotor CH-47 for obvious reasons.

The conventional helicopter hangs beneath a rotor disk. The CG must fall somewhere almost directly beneath the rotor mast and limitations on CG placement have to do with such things as main rotor yoke - mast bumping, or range of motion of the swashplate. In other words keeping the airframe hanging in a stable condition beneath the rotor disk.

A number of helicopters (Bell 212 if I'm not mistaken) require lateral CG as part of the weight & balance. Earlier, simpler aircraft had the requirement but achieved it with seating rules: Solo from left (or center) seat only, and so on.

When thinking about CG shifts as well as control authority "inch-pounds" is the unit of reference. 130 pounds held out 7 inches equals 910 inch-pounds for example. So on a typical jet airliner who knows how many pounds of UP or DOWN force can be generated by the ailerons multiplied by the five or six hundred inches they are from the CG and you can see why fixed wing have so much control authority.

The Airline Transport Pilot license for helicopters (ATH) has sample problems relating to lateral CG.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
curlyheadboy
Posts: 814
Joined: Tue Feb 08, 2005 6:56 am

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 3:30 am

Quoting 2H4 (Reply 6):
Right....that's when you don the O2 masks and dial the PAX pressurization waaaaay down....

LOL! That would have done the trick, you raise cabin altitude and put the bad guys to sleep! Big grin , good one 2H4, i had a good laugh out of it!
If God had wanted men to fly he would have given them more money...
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 3:43 am

Quoting 2H4 (Reply 6):
Right....that's when you don the O2 masks and dial the PAX pressurization waaaaay down....

I kind of favor just running cabin altitude up around ten to eleven thousand, not enough to cause any real injury, then crank the cabin temperature up to the "stuffy" setting. It puts everyone to sleep but not so dramatically that you get letters.

Actually I had a friend who did something like this once. He was flying for a military VIP flight detachment and through a schedule conflict wound up with two parties competing for his seats. One was a well-known entertainer and her other 'talent' and the other was Vice President of an Asian nation and his entourage. He could not transport all of either party and both thought it beneath them to ride with the other and all were in a nasty mood. So he took the steps as above and everyone went to sleep. Happy flight.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
MD-90
Posts: 7835
Joined: Mon Jan 17, 2000 12:45 pm

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 8:37 am

I remember a pilot on the forum authoritatively stating that it was impossible for the passengers on a 747 to move around enough to get it out of c.g.
 
ilikeyyc
Posts: 1326
Joined: Tue Dec 09, 2003 8:09 am

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 8:50 am

Quoting SlamClick (Reply 5):

Good math, Slam. Care to try it with 10,000 pidgeons in the equation?  Silly  Big grin  Wink
Fighting Absurdity with Absurdity!
 
User avatar
Starlionblue
Posts: 17212
Joined: Fri Feb 27, 2004 9:54 pm

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 10:30 am

Quoting MD-90 (Reply 11):
I remember a pilot on the forum authoritatively stating that it was impossible for the passengers on a 747 to move around enough to get it out of c.g.

Using Captain Click's math:

400 pax x 75 kg = 30 000 kg.
All pax more 35 metres = 1 050 000 meter kilos.
747 with some fuel burned off = 350 000 - 30 000 of pax = 320 000 kg.

1 050 000 / 320 000 = 3.28 meters CG shift. I don't know exactly, but I would guess that's well within the CG limits, never mind the control authority of the aircraft.


A more interesting question is how fast you would have to move a hypothetical 30 ton weight back and forth in the fuse 35 metres to overcome the stabilizer trim system and make the aircraft pogo.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

RE: Centre Of Gravity If Passengers Move All At On

Tue Aug 22, 2006 11:20 am




Quoting Starlionblue (Reply 13):
A more interesting question is how fast you would have to move a hypothetical 30 ton weight back and forth in the fuse 35 metres to overcome the stabilizer trim system and make the aircraft pogo.



I can see the headlines now.....






ONLINE AVIATION INTEREST GROUP STEALS AIRLINER, WREAKS HAVOC IN SKIES. CONTROL BARELY REGAINED, FEW INJURED. ALCOHOL A POSSIBLE FACTOR.





Lulea, Sweden (AP) - Investigators are working around the clock to determine the series of events that caused a stolen Boeing 747 to depart controlled flight and nearly crash into the Baltic Sea on Thursday evening.

Witnesses reported seeing an unruly crowd of "airplane nerds" gain access to Arlanda airport in Stockholm, and proceed to steal a parked Boeing 747 airliner.

"The crowd consisted of about two dozen individuals, each wearing pocket protectors and carrying elaborate calculators", reported taxi driver Fredrik Gustafsson. "They were whooping and hollering, and appeared to be involved in a heated discussion. At least one man was injured before even reaching the aircraft, when a fight broke out and large slide rules were used", Gustafsson reported.

The unruly mob appeared to be led by a very calm and wise man, known only as "Captain Slam". It is believed he started the aircraft and initiated the takeoff before things got out of control.

Details are scarce, but reports indicate unauthorized experiments took place in flight, leading to structural damage and a departure from controlled flight.

Control was finally regained when an unnamed quick-thinking maintenance technician leapt into the flight deck, quickly re-rigged the flight controls, and re-trimmed the aircraft.

"There are still so many questions", the technician explained. "How do you damage an aircraft in such a way." "What did they do to send the aircraft so violently out of control." "Were they not belted in down there." "I still do not know how they did it."

After control was regained, the aircraft was escorted back to Stockholm, where the rowdy group was detained and held for questioning. Sentencing is expected to take place next month.





2H4


Intentionally Left Blank
 
User avatar
Starlionblue
Posts: 17212
Joined: Fri Feb 27, 2004 9:54 pm

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 11:31 am

 rotfl   rotfl   rotfl   rotfl 
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 11:45 am

Quoting Starlionblue (Reply 13):
Using Captain Click's math:

Never do math in front of an audience!

Quoting Starlionblue (Reply 13):
400 pax

I hope I never have a plane with that many terrorists OR heroes onboard!

Quoting Starlionblue (Reply 13):
x 75 kg

Must be Europeans - Americans weigh a lot more than that!

Quoting Starlionblue (Reply 13):
All pax more 35 metres

Okay now just a minute. I'm pretty sure that is more than half the aisle length on a 747. The running they do TOWARD the CG does not count. Also each person that runs forward offsets one who runs aft - unless the person running aft is me. (You'll recognize me by the parachute. I'm going for help.)

Quoting Starlionblue (Reply 13):
3.28 meters CG shift

It is okay because some ran forward, some ran aft, some ran in little circles. "When in danger, safety in doubt, run in circles, scream and shout!" So adding them algebraically, the net movement was less than the Slammer sliding his seat aft to take a nap - I mean scan the overhead panel.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 1:02 pm

Mathematically, and movement of a mass in the cabin changes the location of the cg as has been stated. The most significant changes would be in terms of pitch. If many people ran forward or aft, and packed themselves tightly, a critical exceedance of the cg limts could occur.
 
turkee
Posts: 65
Joined: Sat Nov 19, 2005 7:21 pm

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 4:52 pm

I've done a lot of weight and balance documentation for B717-200s, and while it isn't a "large" aircraft, it's certainly not small either.

The COG of the aircraft can actually move longitudinally quite a margin in flight, while still remaining in the area allowed for safe operations. For instance, the fuel burning up during flight will shift the COG of an aircraft, and is what the pilots will base their trim tab adjustments on prior to landing. As somebody else has mentioned, lateral movement of the COG isn't really an issue.

The take-off and landing COG limits are a lot smaller than the in-flight limits. Don't ask me why, I'm not a pilot (or a physicist), I just know they are  Wink

Now, when planning a load sheet for pax and dead weight, blocking off three or four rows at the front or rear (or both) of the aircraft really helps to balance out the COG. You can assess it half-way through the check-in stage, and see whether or not you're coming in nose-heavy or tail-heavy, and unblock seats or move baggage loads accordingly. As long as it is within limits at the flight close-out stage, no worries - the passengers can really move around wherever they want during flight and it won't have any effect on the handling of the aircraft - until it comes to landing. I have heard pilots ask passengers to return to their original take-off seats on a light-load aircraft, because that's what their original weight and balance planning was based on.

Probably a bit off-track there, but might be some useful information for readers.

Cheers.
 
User avatar
Starlionblue
Posts: 17212
Joined: Fri Feb 27, 2004 9:54 pm

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 8:46 pm

Quoting SlamClick (Reply 16):
Quoting Starlionblue (Reply 13):
All pax more 35 metres

Okay now just a minute. I'm pretty sure that is more than half the aisle length on a 747. The running they do TOWARD the CG does not count. Also each person that runs forward offsets one who runs aft - unless the person running aft is me. (You'll recognize me by the parachute. I'm going for help.)



Quoting SlamClick (Reply 16):
Quoting Starlionblue (Reply 13):
3.28 meters CG shift

It is okay because some ran forward, some ran aft, some ran in little circles. "When in danger, safety in doubt, run in circles, scream and shout!" So adding them algebraically, the net movement was less than the Slammer sliding his seat aft to take a nap - I mean scan the overhead panel.

I was making certain assumptions.  Wink The most important one is that ALL the 400 pax were moving in the same direction at the same time. Since this is highly unlikely anyway...

Quoting SlamClick (Reply 16):
Quoting Starlionblue (Reply 13):
x 75 kg

Must be Europeans - Americans weigh a lot more than that!

If they're all Baseball batters perhaps. I would hazard that a good mix of Americans would average less than 75kg with clothing. Don't forget that women weigh less on average. But if you were planning to pogo the plane with running pax, you would of course pick big people.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
David L
Posts: 8552
Joined: Tue May 18, 1999 2:26 am

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 10:30 pm

Quoting 2H4 (Reply 14):

It's only a matter of time.  biggrin 
 
vikkyvik
Posts: 11909
Joined: Thu Jul 31, 2003 1:58 pm

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 10:56 pm

Quoting 2H4 (Reply 14):
when a fight broke out and large slide rules were used

Slide rule? What's a slide rule?

Signed,
Today's crop of engineering students

 Wink

Quoting David L (Reply 20):
It's only a matter of time.

Soooo......who's up for a meet at Arlanda.......
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 11:25 pm

Quoting Turkee (Reply 18):
while it isn't a "large" aircraft, it's certainly not small either.

Kinda comes down to whether or not you'd want one parked on your toes.

Quoting Turkee (Reply 18):
The take-off and landing COG limits are a lot smaller than the in-flight limits. Don't ask me why

The actual limits are given in the shape of the CG envelope. On a typical jetliner it is a graph* where going up is increasing weight, left is forward CG and right is aft CG. The increment across the bottom or top could be inches aft of DATUM or aft of LEMAC, or percent of MAC. The irregularly shaped area within the graph is usually narrower - meaning a shorter allowable CG range - toward the maximum and minimum gross weights.

So at takeoff - the highest weight - it will be probably the narrowest of any point in the flight. As fuel burns off your weight drops down into a broader allowance. Usually the landing weights still fall into a pretty broad zone.

There is another issue. We offset undesired pitch tendencies like 'nose heavy' or 'tail heavy' with stabilizer trim, and we maneuver the plane on this axis with elevator. Both the elevator and the stab trim are more effective at higher speeds, with higher airloads. So these things are least effective at takeoff and landing.

Quoting Turkee (Reply 18):
and is what the pilots will base their trim tab adjustments on prior to landing.

I don't know what your paperwork looks like but it's been my experience that while we do pre-set stab trim for takeoff based on the weight & balance information, on landing we are flying the airplane and trimming according to feel, not paperwork. So on touchdown the trim is wherever the trim is. Lots of pilots as a personal technique may, in some types, begin trimming nose up when the mains touch down. They get a smoother nosewheel touchdown that way.

Quoting Turkee (Reply 18):
but might be some useful information for readers

Indeed, and thanks.

* I'll try to find an illustration and post it.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Centre Of Gravity If Passengers Move All At Once

Tue Aug 22, 2006 11:28 pm

Center of Gravity envelope:



I haven't looked to see what type aircraft yet but this should give you the idea.

edit: Well I still can't see it very well. I'm talking about the graph on the left. The top horizontal line is this plane's max certificated takeoff weight, which looks to be about 210,000 lbs. The line at what looks like 145,500 lbs is the max zero-fuel weight. The greatest allowable CG range seems to be around 135,000 lbs and the range is roughly from 14% to 29% of MAC. Note also the max landing weight at 190,000 pounds. The CG range at that weight is only about 22% to 29% so this plane has some hefty restrictions on forward CG at high gross weights.

[Edited 2006-08-22 16:40:42]
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Centre Of Gravity If Passengers Move All At On

Wed Aug 23, 2006 4:11 am

Quoting SlamClick (Reply 16):
The running they do TOWARD the CG does not count.

In fact they do, just as much as those running away from the CG. A kgm is a kgm, regardless of how it is generated.  Smile

Quoting Turkee (Reply 18):
The take-off and landing COG limits are a lot smaller than the in-flight limits. Don't ask me why, I'm not a pilot (or a physicist), I just know they are Wink

Prominent reasons include manoeuverability margins for rotation and (last but certainly not least!) landing loads on the aircraft structure, upon which CoG has a significant impact.

Quoting SlamClick (Reply 22):
The increment across the bottom or top could be inches aft of DATUM or aft of LEMAC, or percent of MAC.

Or index units... and someone will invariably end up mixing them up, regardless of what chart he is dealing with.  headache 

As for pax moving about, it can definitely make the CoG go out of whack in significant ways, at least in smaller aircraft. Severe constraints are at times put on take-off CoG envelopes when there are potential in-flight movements which can put the aircraft outside of the in-flight CoG limits if they take off at the take-off envelope CoG limits.

If you have a front row passenger standing in line for the aft lav while one flight crew member is in there, and then the F/A takes her trolley and pours a passenger in the last seat row a drink... then you have some weight travelling quite a distance. CoG envelopes are often narrower than you'd think.

If you lot are really interested, I can take a look at some of the heavy iron and see just what it would take to create a problem.

Rgds,
/Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Centre Of Gravity If Passengers Move All At Once

Wed Aug 23, 2006 8:50 am

Quoting FredT (Reply 24):
As for pax moving about, it can definitely make the CoG go out of whack in significant ways

I got ramp checked one night, flying with my boss, the DirOps. The FAA inspector looked at the weight and balance and said: "You are pretty near aft CG limit on this takeoff. How do you know when you take off and retract the gear that won't shift you beyond the aft limit."

Well my boss later said to me that under the certification rules if that were a possibility the FAA would have amended the type certificate to shorten the green band on the stab trim, but it was not his job to train FAA inspectors. What he did say to the Fed was: "Well, the mains retract inboard which doesn't change the CG. The nosegear and the flaps both retract forward, which moves the CG forward. Just how much? Well, I don't know but certainly not as far as when I heave my 250-pound ass out of this seat and walk sixty feet aft to the nearest lav!"

I had a little trouble keeping a straight face.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
lowrider
Posts: 2542
Joined: Wed Jun 30, 2004 3:09 am

RE: Centre Of Gravity If Passengers Move All At Once

Wed Aug 23, 2006 9:40 am

When flying jumpers, having significant numbers leave the aircraft at the same time can make for interesting times as well.
Proud OOTSK member
 
User avatar
Starlionblue
Posts: 17212
Joined: Fri Feb 27, 2004 9:54 pm

RE: Centre Of Gravity If Passengers Move All At Once

Wed Aug 23, 2006 10:19 am

Quoting Lowrider (Reply 26):
When flying jumpers, having significant numbers leave the aircraft at the same time can make for interesting times as well.

I always wondered why one of our jump plane pilot would go into a spinning dive as soon as he dropped the last jumper. Personally, I think he missed his Lansen. Big grin
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
zeke
Posts: 10103
Joined: Thu Dec 14, 2006 1:42 pm

RE: Centre Of Gravity If Passengers Move All At Once

Wed Aug 23, 2006 10:57 am

On the Airbus its a QRH item to move pax to about to help with CG location in the event of abnormal gear extension.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
greasespot
Posts: 2955
Joined: Sat Apr 24, 2004 10:48 am

RE: Centre Of Gravity If Passengers Move All At Once

Wed Aug 23, 2006 11:08 am

Funny story.....When I was 16 flying home frome Germany the captain said "If you look out the left window you can see Glasgow...As people crossed over to look i yelled OMG it is going to tip over........People scrambled back over and fell....I the proceeded to spend the flight sitting next to the F/A's and had a meeting with the Toronto AC Station manager on arrival.

GS
Sometimes all you can do is look them in the eye and ask " how much did your mom drink when she was pregnant with you?"
 
turkee
Posts: 65
Joined: Sat Nov 19, 2005 7:21 pm

RE: Centre Of Gravity If Passengers Move All At Once

Wed Aug 23, 2006 12:45 pm

I didn't find that funny.

Thanks SlamClick and FredT for your comments  Smile
 
User avatar
HAWK21M
Posts: 29929
Joined: Fri Jan 05, 2001 10:05 pm

RE: Centre Of Gravity If Passengers Move All At Once

Wed Aug 23, 2006 1:41 pm

Quoting Greasespot (Reply 29):
When I was 16 flying home frome Germany the captain said "If you look out the left window you can see Glasgow...As people crossed over to look i yelled OMG it is going to tip over

Amazing people actually reacted.

Quoting Zeke (Reply 28):
On the Airbus its a QRH item to move pax to about to help with CG location in the event of abnormal gear extension.

Pls elaborate.

regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
ImperialEagle
Posts: 2238
Joined: Sat Jan 14, 2006 10:53 am

RE: Centre Of Gravity If Passengers Move All At Once

Thu Aug 24, 2006 12:10 pm

Back in the summer of '64 UA lost a 700 series Viscount near Newport, Tennessee. The aircraft had been observed flying in an erratic manner at a very low altitude--and trailing smoke just before it suddenly nosed up and stalled ---"falling" to the ground.

There were about 45 souls on board so that was a pretty good load for that series Viscount in the configuration of the day---if not a full load---with the crew included.

I don't know if I ever saw whether or not they finally figured out what happened, but there were some interesting theories.

One of the most interesting theories went something like: a fire of unknown origin started inside the fuselage in the forward part of the cabin (flush motor on a lav or something on the radio rack?).

A distress call went out to Knoxville Center to report a fire on board. Crew was trying to make Knoxville but was well east of the city in a mountainous area. Smoke in the flight deck. Crew member opened side window to try to see but actually pulled even more smoke forward. Nonetheless, someone evidently did fly the airplane a good ways with his head outside the window to see---hence the "erratic" flight path.

One of the "witnesses" who saw smoke coming from the side of the aircraft also reported seeing a body fall. Sure enough, the remains of one male pax was found some distance from the main wreckage. They also found the emergency over-wing window exit near the remains. The general theory was that this guy decided it was better to take a chance jumping, rather than burning!

But with that overwing exit opened up the fire really had some fuel to work with (oxygen) so the pax all rushed to the rear of the cabin (where they were all found) causing an extreme cg change that caused the flight crew to loose control of the aircraft.

Somewhere---- around here---- I have my Viscount 700 series cockpit ops manual--- so I guess I could try to find it and figure out this theory.
Does anyone else remember this accident and/or whether it was ever "officially" solved?
"If everything seems under control, you're just not going fast enough!"
 
User avatar
Jetlagged
Posts: 2562
Joined: Sun Jan 23, 2005 3:00 pm

RE: Centre Of Gravity If Passengers Move All At Once

Sat Sep 02, 2006 9:21 am

Of course, if you replaced the cabin floor with a conveyor belt ..... Big grin

I remember a TAA 727 pilot joking that flying into Sydney over Bondi Beach they always had to compensate for the change in roll trim as all the passengers moved over to the side of the plane with a view of the topless sunbathers.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Centre Of Gravity If Passengers Move All At Once

Sat Sep 02, 2006 9:24 am

Quoting Jetlagged (Reply 33):

Which is why in Saint Maarten there is a rule at Maho beach that the scenery must distribute themselves equally on both sides of the extended centerline.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
Tom12
Posts: 1050
Joined: Tue Dec 27, 2005 7:29 am

RE: Centre Of Gravity If Passengers Move All At Once

Sun Sep 03, 2006 7:15 am

You would think that this would be possible. Maybe not in the likes of a 777 bu somehing little like a Fokker 50? .... would be pretty scary if it was possible and you were on the jet!

Thanks, Tom
"Per noctem volamus" - Royal Air Force Bomber Squadron IX
 
jamesbuk
Posts: 3712
Joined: Mon May 02, 2005 11:52 pm

RE: Centre Of Gravity If Passengers Move All At Once

Mon Sep 04, 2006 8:13 am

Quoting Jetlagged (Reply 33):

Thats slightly true, our flying club took a flight over to LE torquet (?) and on the way there i was in a piper seneca, as we were landing the owner of the school said oh look topless women, we all looked to the left and the pilot flying said he could feel that he had to put a bit of left roll in to compensate lol.


Rgds --James--
You cant have your cake and eat it... What the hells the point in having it then!!!
 
zotan
Posts: 582
Joined: Thu Jan 13, 2005 7:42 am

RE: Centre Of Gravity If Passengers Move All At Once

Mon Sep 04, 2006 8:21 am

The smaller the plane, the more effect it would have.

I was departing MYF once, and my seat slid back right after rotation because it wasn't locked in place. (This was in a C-152). The plane nosed up, and I had to apply a lot of down pressure on the yoke to correct.
 
jamesbuk
Posts: 3712
Joined: Mon May 02, 2005 11:52 pm

RE: Centre Of Gravity If Passengers Move All At Once

Mon Sep 04, 2006 8:27 am

Quoting ZOTAN (Reply 37):
ZOTAN

Hence in the Checklist "Make sure your seat is fully secure and locked before takeoff" kind of like if you normally have a skinny flight inst then have a rather large one you feel the difference! ive had a similar case, i flew a C152 back from france, as i took off the aircraft pitched back to 20' rather strongly and the airspeed was bleeding off quickly, so i pushed forward, and for the life of me i couldnt work out why it was doing this, the trim was in neutral!, really strange.

rgds --James--
You cant have your cake and eat it... What the hells the point in having it then!!!
 
TimePilot
Posts: 290
Joined: Sat Sep 03, 2005 10:40 pm

RE: Centre Of Gravity If Passengers Move All At On

Mon Sep 04, 2006 3:34 pm

To the original poster, A520. Funny that you should be from Swizerland, as this reminds me of something that happened in Zurich many years back. There are boats that go up and down the Limat with a spoken tour. On one side of the Limat is a mens-only swim spot, and on the other is the women-only, top-less swim spot. I remember the when going past boat captain saying:

"DON'T EVERYONE GET UP AT ONCE AND RUSH TO THAT SIDE OF THE BOAT!!!!!!!!"
 
DernierVirage
Posts: 222
Joined: Wed Aug 02, 2006 3:55 am

RE: Centre Of Gravity If Passengers Move All At Once

Sat Sep 23, 2006 2:24 am

My comment below is a little bit away from the original post, but it may be useful as part of the various discussions above...

A few years ago I was on a flight in a A320 (Dragonair, from Hong Kong to Qingdao), I was the only passenger in business class, in row 1. There were either 2 or 4 rows in business class (sorry that I forget how the cabin was configured at that time). The economy cabin was very full. Before departure, the chief purser told me that they had to move some passengers into the business cabin to balance the weight. Does this make sense ?
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Centre Of Gravity If Passengers Move All At Once

Sat Sep 23, 2006 3:24 am

Quoting DernierVirage (Reply 40):
The economy cabin was very full. Before departure, the chief purser told me that they had to move some passengers into the business cabin to balance the weight. Does this make sense ?

Yes - if the cabin is configured as I would expect First, Business, Coach from front to rear.

Sometimes, with very light loads in the 1st and/or business, and coach being very full we wind up being a little bit tail-heavy. There are two solutions: Re-load the bags toward the forward pit, which often makes for short delays, or simply upgrade a few passengers to the front end.

When they do the upgrades there are a couple of considerations. 1. Some cabin crew like to give the non-revs a break. If the non-revs are dressed properly and know how to behave in first class they might get the shot. 2. People who paid a lot of money for a first class ticket would resent having a bunch of loud-mouthed employees get the same privilege and had the bad manners to force the paying passenger to listen to their bitching about the company. Believe it or not, it does happen. 3. Sometimes the cabin crew know some of the 'regulars' back in coach, the passengers who fly coach every week. These folks are the bread-and-butter of the airlines and it would be smart to upgrade them when you have a chance. 4. Sometimes the bean counters are aware of this potential source of extra revenue and will insist that people PAY for the privilege of being upgraded even when it MUST be done for weight & balance reasons.

On a related note: Thank you from the bottom of my heart to every flight attendant who ever upgraded me! Thank you! Thank you to the handful of flight attendants who, over the years, found a way for me to stay on the plane when I might well have been bumped. A special thanks for the wonderful cabin staff of that now-departed airline who let me ride on a flight attendant jumpseat knowing full well that I could not reciprocate. Big hugs to you. And finally, to that one cattlecar captain who found an excuse to bump me for no reason I can figure out - go to hell! The rest of you were great.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
DernierVirage
Posts: 222
Joined: Wed Aug 02, 2006 3:55 am

RE: Centre Of Gravity If Passengers Move All At Once

Sat Sep 23, 2006 3:36 am

Quoting SlamClick (Reply 41):
Sometimes, with very light loads in the 1st and/or business, and coach being very full we wind up being a little bit tail-heavy. There are two solutions: Re-load the bags toward the forward pit, which often makes for short delays, or simply upgrade a few passengers to the front end.

Thank you for this information; in fact, the incident I mentioned is the only time this has ever happened to me in a similar situation

Quoting SlamClick (Reply 41):
Yes - if the cabin is configured as I would expect First, Business, Coach from front to rear.

It in fact was just business, then coach

Quoting SlamClick (Reply 41):
When they do the upgrades

On this occasion, the chief purser selected 2 middle aged Hong Kong couples, who seemed very surprised at what was happening !! (In fact, Dragonair are in my experience very careful about upgrades, which only seem to be given in cases of over-booking.

Again, thanks for your reply !
 
bhmbaglock
Posts: 2489
Joined: Thu Jul 14, 2005 7:51 am

RE: Centre Of Gravity If Passengers Move All At Once

Sat Sep 23, 2006 12:08 pm

Quoting SlamClick (Reply 3):
Absolutely not. They cannot move far enough laterally to be felt, even when hand-flying.

I was on a DC-3 one time where about 40 jumpers all moved to one side(left as I recall) together as an experiment. It did cause a slight(very) change in attitude but nothing major; really pissed off the pilot though but he's the type who'd get pissed(US pissed, not UK pissed) if you gave him a million dollars in cash too.

Quoting Lowrider (Reply 26):
When flying jumpers, having significant numbers leave the aircraft at the same time can make for interesting times as well.

Certain aircraft like the Shorts Skyvan can be very scary if the CG gets too far aft, i.e. too many jumpers on the ramp.

With some older jump planes, i.e. D-18, Queen Air, Twin Bo, etc. it used to be common practice for the jumpers seated in the very rear of the aircraft to move forward as much as possible for takeoff and simply stand to move the CG forward. Once the a/c had good airspeed and was trimmed out nicely they would return to the rear and sit down. This was typically used only for shorter runways and could also be influenced by the qty of fuel on board, ambient temp, etc.

After a number of fatalities in the late 80's, early 90's in crashes that could have been prevented if occupants had been wearing seat belts, DZs and the FAA began to enforce the already existing rules requiring everybody to wear a seatbelt for takeoff.
Where are all of my respected members going?
 
User avatar
Starlionblue
Posts: 17212
Joined: Fri Feb 27, 2004 9:54 pm

RE: Centre Of Gravity If Passengers Move All At Once

Sat Sep 23, 2006 12:35 pm

Quoting BHMBAGLOCK (Reply 43):

After a number of fatalities in the late 80's, early 90's in crashes that could have been prevented if occupants had been wearing seat belts, DZs and the FAA began to enforce the already existing rules requiring everybody to wear a seatbelt for takeoff.

All the planes I jumped out of didn't have more than two seats. I sat on the floor of Islanders and one engine Cessnas, often with a leg dangling out of the hatch when we had reached 1000ft. Then again, we were crammed in tighter than sardines so any small bumps would have had no effect.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
bhmbaglock
Posts: 2489
Joined: Thu Jul 14, 2005 7:51 am

RE: Centre Of Gravity If Passengers Move All At Once

Sat Sep 23, 2006 10:15 pm

Quoting Starlionblue (Reply 44):
Then again, we were crammed in tighter than sardines so any small bumps would have had no effect.

Trust me on this, even if packed in tight, it's more than a bump if you crash and you would be better off with seatbelts. I say this as somebody who has been in a airplane crash without benefit of the seatbelt. Luckily I was all the way forward and facing rear and ended up with nothing more than a bruised butt and a few cuts and scrapes. Others on the a/c were much more seriously injured but amazingly nobody was killed.
Where are all of my respected members going?
 
User avatar
Devilfish
Posts: 5377
Joined: Tue Jan 24, 2006 7:52 am

RE: Centre Of Gravity If Passengers Move All At Once

Sat Sep 23, 2006 11:16 pm

Quoting Starlionblue (Reply 13):
400 pax x 75 kg = 30 000 kg.
All pax more 35 metres = 1 050 000 meter kilos.



Quoting SlamClick (Reply 16):
I'm pretty sure that is more than half the aisle length on a 747.

Looking at the 744's seatmap, how difficult would it be to tightly pack all 400 passengers aft, or forward and up the upper deck to attain the 35 meter moment arm, with all the seats in the way?  scratchchin  On second thought, does that parachute take two?  Smile

Quoting FredT (Reply 24):
If you lot are really interested, I can take a look at some of the heavy iron and see just what it would take to create a problem.

Sir, you need not ask, this is A.nuts.  yes 
"Everyone is entitled to my opinion." - Garfield
 
User avatar
Starlionblue
Posts: 17212
Joined: Fri Feb 27, 2004 9:54 pm

RE: Centre Of Gravity If Passengers Move All At Once

Sun Sep 24, 2006 1:29 am

Quoting BHMBAGLOCK (Reply 45):
Quoting Starlionblue (Reply 44):
Then again, we were crammed in tighter than sardines so any small bumps would have had no effect.

Trust me on this, even if packed in tight, it's more than a bump if you crash and you would be better off with seatbelts. I say this as somebody who has been in a airplane crash without benefit of the seatbelt. Luckily I was all the way forward and facing rear and ended up with nothing more than a bruised butt and a few cuts and scrapes. Others on the a/c were much more seriously injured but amazingly nobody was killed.

You make a compelling argument.

Quoting DEVILFISH (Reply 46):

Looking at the 744's seatmap, how difficult would it be to tightly pack all 400 passengers aft, or forward and up the upper deck to attain the 35 meter moment arm, with all the seats in the way? scratchchin On second thought, does that parachute take two?

It would not really be that hard. AS I recall, El Al flew almost 1000 people on a 747 evacuation flight. Running up and down all at once would be tricky though.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
Devilfish
Posts: 5377
Joined: Tue Jan 24, 2006 7:52 am

RE: Centre Of Gravity If Passengers Move All At On

Sun Sep 24, 2006 4:23 am

Quoting Starlionblue (Reply 47):
It would not really be that hard. AS I recall, El Al flew almost 1000 people on a 747 evacuation flight.

We're only talking about 400 pax. Assuming the a/c is perfectly balanced and the CG is exactly at midpoint of the 744's 70.7 meter length from nosetip to tailend, that would mean half of the pax will be outside the plane (or standing one on top of the other) to simulate the concentrated load acting 35m from the CG. Spreading the 400 someway forward because all can't be contained at the cramped tail section distributes the load and reduces the moment - although I wouldn't join such an experiment to find out the critical displacement.

Quoting Starlionblue (Reply 47):
Running up and down all at once would be tricky though.

Not interested in moving loads or the pogo effect.

Cheers.

[Edited 2006-09-23 21:24:18]
"Everyone is entitled to my opinion." - Garfield
 
User avatar
jetmech
Posts: 2316
Joined: Wed Mar 29, 2006 2:14 am

RE: Centre Of Gravity If Passengers Move All At Once

Sun Sep 24, 2006 9:05 am

Within certain limits, the longitudinal trim of an aircraft is self correcting. Imagine a 747 trimmed to be longitudinally neutral at some set of constant conditions ( i.e. a given combination of altitude, airspeed etc.) If all the passengers moved aft, the C of G would also move aft. This would decrease the moment formed with the C of L, which would serve to reduce the incidence of the tailplane with respect to producing down-force. This reduction in tailplane down-force would tend to drop the nose of the aircraft and compensate for the aft movement of passengers.

If all the passengers moved forward, the C of G would also move forward. This would increase the moment formed with the C of L, which would serve to increase the incidence of the tailplane with respect to producing down-force. This increase in tailplane down-force would tend to lift the nose of the aircraft and compensate for the forward movement of passengers.

Obviously, this self correcting mechanism would only work over a relatively narrow range of C of G position. IIRC, it is always desirable for the C of G to be forward of the C of L at all times in commercial aircraft. With Airbus aircraft, the fuel in the horizontal stabiliser is used to actively trim the aircraft. The pilots can over-ride this automatic system, but they can only manually transfer fuel forward (i.e. move the C of G further forward of the C of L) which makes the aircraft more stable, never backwards which de-stabilises the aircraft.
JetMech split the back of his pants. He can feel the wind in his hair :shock: .

Who is online

Users browsing this forum: No registered users and 9 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos