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Why is an aircraft aisle not level when cruising?
I searched online for an answer to this but just saw arguing. I am not an expert and am sorry if I am asking this question incorrectly or using the wrong terminology.
An aisle in an aircraft during cruise is almost imperceptibly sloped down from front to back (if a can is dropped it rolls back). Why not just make the aisle level? What I see online is that the wings have to have a certain angle of attack. It seems to me, though, that aircraft designers could tweak the wing incidence angle so the wings have the right angle of attack with zero pitch. Thank you for considering my question. |
Originally Posted by Eboy
(Post 10313769)
I searched online for an answer to this but just saw arguing. I am not an expert and am sorry if I am asking this question incorrectly or using the wrong terminology.
An aisle in an aircraft during cruise is almost imperceptibly sloped down from front to back (if a can is dropped it rolls back). Why not just make the aisle level? What I see online is that the wings have to have a certain angle of attack. It seems to me, though, that aircraft designers could tweak the wing incidence angle so the wings have the right angle of attack with zero pitch. Thank you for considering my question. |
Briefly touched on in a recent discussion elsewhere: https://www.pprune.org/rumours-news/...l#post10310305
As has been mentioned, transport aircraft that are optimized to maximize L/D are designed to fly with a small, positive pitch attitude. To design an airplane to fly with deck angle of exactly zero in cruise would be to leave unrealized performance on the table! Separately, optimization of takeoff, landing, and ground operations usually results in a slightly negative deck angle when taxiing. I strongly doubt that any commercial transport airplane has ever been designed to have exactly zero deck angle either during ground taxi or cruise. |
You are correct. The wing does have an incidence angle. However, the c of g and aircraft mass will change throughout the flight as fuel is used (swept wing aircraft) the 'deck angle' will therefore change as the angle of attack alters to compensate for altitude, airspeed, and lift requirement. There is also the fact that the fuselage adds to the total lift of the aircraft and there will be a sweet spot angle for the entire aircraft to meet the airflow.
Someone clever will be along in a bit with some maths to explain. |
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RevMan2. I was going to do that but just did t want to show off! |
See I told you so.
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Thank You RevMan2 just please don't ask us any questions ...
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On the DC3, the Pilots could tell when the flight attendant walked to the rear of the aircraft because the autopilot applied forward trim. This is an adjustment the pilot makes to enable the aircraft to fly level without having to apply forward or backward pressure on the controls. At the beginning of a flight when the aircraft is heavy with fuel it will fly slow and nose up, as fuel burns off it gets lighter and flys faster, the nose then needs to be moved down or it will climb. |
Originally Posted by krismiler
(Post 10313945)
On the DC3, the Pilots could tell when the flight attendant walked to the rear of the aircraft because the autopilot applied forward trim. |
No smart arse, it's to illustrate how changing weight distribution affects an aircraft and how it is dealt with, either by the pilots if being flown manually or by the automatics if engaged. The person asking the question is obviously not a pilot so I've kept the explanation as simple as possible. I've avoided using complicated technical terms such as centre of pressure, angle of attack,formulae for lift and why a rearward CofG is beneficial in certain situations but detrimental in others.
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Clearly in the big jets, if the floor is sloping front to back, it's because all the FA's are in the back gossiping. |
Originally Posted by RevMan2
(Post 10314004)
And if the floor’s sloping back to front, it’s because the cockpit just got paid and haven’t had time to get the cash to the bank.... |
Originally Posted by krismiler
(Post 10313976)
No smart arse,.
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Originally Posted by TURIN
(Post 10313784)
There is also the fact that the fuselage adds to the total lift of the aircraft and there will be a sweet spot angle for the entire aircraft to meet the airflow.
I suspect I have read somewhere that for best efficiency the fuselage is operated at positive angle of attack and it generates some lift. The floor of course could be arranged to be horizontal even with a +ve pitch on the hull, however that is apparently not done:-) |
Gosh, explaining all of this has been a bit of an uphill struggle.
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Ouch DRUK. After that observation - it's downhill all the way ...
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RevMan2 - you don't happen to be a mapmaker, do you? ;)
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Hokulea - Sshhhhh!
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The floor of course could be arranged to be horizontal even with a +ve pitch on the hull, however that is apparently not done:-) The crew bunks on the 747-400 were slightly inclined, down towards the nose, which made them flat. Very comfy they were, too! |
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