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Why Is It........?  
User currently offlineEnglandair From United Kingdom, joined Oct 2000, 2228 posts, RR: 3
Posted (13 years 10 months 1 week 4 days 13 hours ago) and read 1362 times:

Why is it that even when the aircraft's cruising, the cabin crew seem to pull/push the trollies uphill?

14 replies: All unread, jump to last
 
User currently offlineNicolaki From , joined Dec 1969, posts, RR:
Reply 1, posted (13 years 10 months 1 week 4 days 12 hours ago) and read 1301 times:

Pilots always needs to do minor and sometime major adjustements on the throttles while in flight due due a lot of things, winds, CG always moving ...ect
Once on a flight on an A310 the pilot told me that managing the throtlle is a real "full-time job".

Nicolas - Montreal


User currently offlineFuture_Pilot From , joined Dec 1969, posts, RR:
Reply 2, posted (13 years 10 months 1 week 4 days 12 hours ago) and read 1289 times:

Also if you ever have a chance to visit the flight deck, take a look at the attitude indicator and you will notice that it's showing the aircraft to be cruising with the nose slightly up.

User currently offlineCALPilot From United States of America, joined Oct 1999, 998 posts, RR: 13
Reply 3, posted (13 years 10 months 1 week 4 days 11 hours ago) and read 1289 times:

Sorry Nicolas, that is not correct.

The reason is because large transport aircraft do not have 0 degrees of pitch in level flight. For instance my B757 uses about 4 degrees of nose up pitch for level flight.

I don't know what that A310 pilot was talking about with the throtlles, unless the A/T's were inop. Even then it's not that bad! Even the B727, and DC9, take only small adjustments throughout cruise...


User currently offlineNicolaki From , joined Dec 1969, posts, RR:
Reply 4, posted (13 years 10 months 1 week 4 days 11 hours ago) and read 1279 times:

CALpilot: I was not talking only during cruise, but also all flight mode, climb, cruise, descent.

User currently offlineDL_Mech From United States of America, joined Feb 2000, 1937 posts, RR: 9
Reply 5, posted (13 years 10 months 1 week 4 days 7 hours ago) and read 1262 times:

I was told by a Lockheed engineer that the floor on the L-1011 was designed to be level at cruise. However, when the 70's fuel crunch appeared, airlines started flying the airplane at a lower Mach number to save fuel. The airplane started flying with a slight nose up pitch and f/a's have been pushing carts uphill ever since. You can see that the streaks on the fuselage (cabin door leaks,etc.) all streak at an upward angle.


This plane is built to withstand anything... except a bad pilot.
User currently offlineGreeneyes53787 From United States of America, joined Aug 2000, 844 posts, RR: 0
Reply 6, posted (13 years 10 months 1 week 2 days 13 hours ago) and read 1207 times:

I think the first responder misread the question and thought it pertained to throttles instead of the cart of food inside the passenger cabin.

As to the nose high attitude discussion, I think this idea of moving the crew and passengers around to suit the wings' needs is primitive. With wing boxes fixed (like they are) wings can still be designed to pivot slightly. I don't advocate doing this for take-off or landing. But I think a modifyable wing pitch is a good idea for comfortable flight.

It is an expensive proposition, but probably not as much as people think.

Greeneyes


User currently offlinePrebennorholm From Denmark, joined Mar 2000, 6434 posts, RR: 54
Reply 7, posted (13 years 10 months 1 week 2 days 8 hours ago) and read 1199 times:

What goes up, must come down....
When an airliner cruises at level flight - and we are talking about a heavier-than-air vehicle, not a blimp or such. Then it only does so because its wing accellerates huge amounts of air masses downwards. The energy of accellerating thousands of tonnes of air downwards every minute is simply what keeps the plane in the air.
Most airliners are designed so the fuselage is approximately lined up with the average airflow around it. It means that it must be pointing a little upwards to create minimum drag.
So when the F/Aa are excercising their muscles pulling the buze cart upwards, then they must send a thought to the airline accountant who smiles at the lower fuel bill.
I read somewhere many years ago that the A300 was designed to cruise with a more or less horizontal fuselage attitude in order to maximise comfort mostly for the F/As, but at a small fuel burn disadvantage. Which didn't mean too much since the early A300s were rather short legged. I really don't know if Airbus has discontinued that trend or what. It seems to me that an A320 is more flat at cruise than for instance a 737. But there are so many variables in flight that I as a passenger have no chance to judge that with any accurracy.
In any case I would assume that also Airbus longhoulers - A330/340s - have a fuselage attitude optimised for fuel economy and nothing else.
Best regards, Preben Norholm



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offlineCP744 From Canada, joined Jul 2000, 200 posts, RR: 0
Reply 8, posted (13 years 10 months 1 week 2 days 7 hours ago) and read 1193 times:

I don't want to sound out to lunch.... but...... Am I wrong by thinking the aircraft stays in the air through the pressure difference between the top and bottom of the wing.... I don't think it has anything to do with pushing air downwards?????? Hence Bernoulli’s (sp) principle. Please correct me if I'm wrong.......

Bill


User currently offlineTimz From United States of America, joined Sep 1999, 6822 posts, RR: 7
Reply 9, posted (13 years 10 months 1 week 2 days 6 hours ago) and read 1200 times:

Presumably the designers could set the wing incidence so the fuselage was level in the cruise, but there may be another reason they don't do that.

I once read that someone (don't recall whether it was Boeing or Douglas or whoever) had found (decades ago) that passengers don't like being pointed down. We don't care how far back the seat tilts during the climb, but we are uncomfortable being tilted forward during the descent.


User currently offlineAirgypsy From United States of America, joined Nov 1999, 130 posts, RR: 2
Reply 10, posted (13 years 10 months 1 week 2 days ago) and read 1179 times:

Critical flight phases require the Angle of Incidence (angle of the wing to the fuselage) to be within a certain range depending on the ammount of lift required.
Not enought AOI and the tail would drag on landing and takeoff.
Too Much AOI and the aircraft fuselage would begin to contribute to "down force"
Perfect AOI is the one that lifts the aircraft without banging the tail and takeoff or landing and keeps the lift of the fuselage neutral to positive at the highest speed.
Angle of Attack (AOA) reduces with speed increase. Ever watch a B-52 depart empty? It appears to be at a nosedown angle because of the huge lift the wing generates. Looks normal when fully loaded.
And this brings in the other factor. The F/A will get a lot more exercise on a fully booked flight.
Airgypsy


User currently offlinePrebennorholm From Denmark, joined Mar 2000, 6434 posts, RR: 54
Reply 11, posted (13 years 10 months 1 week 1 day 12 hours ago) and read 1173 times:

CP744 wrote:
-------------------------------
I don't want to sound out to lunch.... but...... Am I wrong by thinking the aircraft stays in the air through the pressure difference between the top and bottom of the wing.... I don't think it has anything to do with pushing air downwards?????? Hence Bernoulli’s (sp) principle. Please correct me if I'm wrong.......

Bill
-------------------------------
Bill, you are certainly right. But just as the aircraft reacts on that pressure difference - by flying in the air instead of sitting on the ground - then the air masses reacts the same way (or more precisely the opposite way).
There is no way that the air masses can stay unaffected by for instance a 700,000 lbs 747, which tells the air to carry it.
In layman's terms: The air masses are pressed downwards.
To every action there is a corresponding reaction.
It is not so that there is a constant pressure difference which keeps the plane in the air. Instead thousand of tonnes of air per minute is accellerated downwards by the pressure difference. The force needed for that accelleration is the "reaction".
Fortunately air is not weightless - it would make flight impossible.
If you take a cube of air at sea level with sides of the same length as the wing span of a 747-400, then the weight of the air inside that cube is some 300 or 350 tonnes, or roughly the same as a fully loaded 747-400. It takes a lot of power to "push" such air masses downwards in only a fraction of a second. It takes exactly the same power as pushing a 300-350 tonnes boulder the same distance in the same time. That's - again in layman's terms - what makes flight possible.
Best regards, Preben Norholm



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offlineCP744 From Canada, joined Jul 2000, 200 posts, RR: 0
Reply 12, posted (13 years 10 months 1 week 1 day 7 hours ago) and read 1157 times:

Thanks..Preben.....

Bill


User currently offlineFanoftristars From United States of America, joined Jul 2000, 1608 posts, RR: 5
Reply 13, posted (13 years 10 months 1 week 1 day 5 hours ago) and read 1153 times:

My friends mom, who was a flight attendent for United years ago, said she hated working the DC-10 because it had an unusually high angle to push the carts up and down. Is this true or just an incorrect perception?


"FLY DELTA JETS"
User currently offlineFr8tdog From United States of America, joined Feb 2000, 120 posts, RR: 0
Reply 14, posted (13 years 10 months 1 week 13 hours ago) and read 1140 times:

UhOh not the Airpump theory again!.....
It is a combination of Bernoulli's principle and Newtons third law that allows the wing to produce lift.
(in simple terms.)

The airpump theory does not describe, how a rotating drum can develop lift......









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