ALexeu
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Droppings After Take-off

Fri Nov 16, 2007 5:57 pm

I've seen several a.netters mentioning droppings after take-off. I feel it aswell, but only on 737s or A320s. I never felt it in A340 or an turboprop/piston aircraft. My question is: what are the kind droppings after-take-off?

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n710ps
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RE: Droppings After Take-off

Fri Nov 16, 2007 6:01 pm

Droppings? You mean as in birds tend to like the narrow body medium range jetliners more so than others?  Wink
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pilotboi
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RE: Droppings After Take-off

Fri Nov 16, 2007 6:03 pm

Are you talking about the feeling of going down? Could this be when flaps are retracted? Flaps increase lift on takeoff and when they are retracted, lift is slightly decreased, reducing in a lower VSI then before retraction, which can create a negative G feeling. This is very obviously if you've ever flown the Piper Arrow (or any Piper) and do a go-around or touch-and-go. When the flaps are brought up, you can definatly feel a drop. Scary sometimes, especially if you have trees right below you. You start screaming "climb, baby, climb".
 
ALexeu
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RE: Droppings After Take-off

Fri Nov 16, 2007 6:07 pm



Quoting Pilotboi (Reply 2):
Could this be when flaps are retracted? Flaps increase lift on takeoff and when they are retracted, lift is slightly decreased, reducing in a lower VSI then before retraction, which can create a negative G feeling.

I tought this aswell, but it doesn' t make sence, because they happen before flap retraction, and i felt it as soon as wee took-off (maybe 5 seconds). It also happens in first minute of flight, several times.
 
Soku39
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RE: Droppings After Take-off

Fri Nov 16, 2007 7:06 pm



Quoting AlexEU (Reply 3):
i felt it as soon as wee took-off (maybe 5 seconds). It also happens in first minute of flight, several times.

Well I only fly Cessna's, so I have no idea how a turbojet's takeoff profile workds however, I know at that point (5-60 seconds after take off) I would only be 100-500 feet above the ground at that point, which is plenty low enough to catch windshear on a really windy day. What happens is sometimes you will have a large headwind, say 10-20 kts and that wind may stop and start back up. This will cause the airplane's wings to lose lift, as less air flows over the wings. Due to the phase of the flight you have to pitch down some to keep your airpspeed up (avoiding departure stalls), and this can result in a "sinking feeling" in the seat of the pants. Jets are also affected by windshear though not as dramaticaly at lower wind velocities, due to the fact they have so much more thrust compared to their weight. For a jet to experience this you will need to be dealing with higher wind velocities. All that being said, when you got the sinking feeling did those take offs occur on gusty days, maybe days where the wind was gusting as much as 30, or 40 knots?, because you will catch heavy windshear on up to the boundary layer.
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YWG
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RE: Droppings After Take-off

Fri Nov 16, 2007 8:42 pm



Quoting Pilotboi (Reply 2):
Could this be when flaps are retracted? Flaps increase lift on takeoff and when they are retracted, lift is slightly decreased, reducing in a lower VSI then before retraction, which can create a negative G feeling.

This is correct. In addition, this negative G feeling is coupled with the reduction of thrust as the crew powers back a bit as the plane picks up speed through the air makes for a mixed bag of feelings in your stomach. It happens in everything from general to commercial aviation.
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dragon6172
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RE: Droppings After Take-off

Fri Nov 16, 2007 11:38 pm

My hypothesis is that this is caused by the opposite of the ground effect air cushion that causes the plane to float on decent to the runway. Shorly after lift off, leaving that "cushion", the plane settles just a bit, percieved as a drop.
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BoeingOnFinal
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RE: Droppings After Take-off

Sat Nov 17, 2007 12:30 am

I was thinking the same thing, ground effect. Although I can't say I have experienced it myself, and it is of course less likely to be felt in a high winged C-172, it is plausible that you can feel the small decrease of lift as you gradually leave the ground effect (at a height of about half the wing span in general).

If it was a one time thing, you can get slightly less than 1G when your trim is not set correctly, causing over rotation. You push the stick forward to correct it, and a loss of lift can be experienced.
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Starlionblue
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RE: Droppings After Take-off

Sat Nov 17, 2007 1:25 pm



Quoting N710PS (Reply 1):
Droppings? You mean as in birds tend to like the narrow body medium range jetliners more so than others?

I just thought the plane was pooping. This preoccupation with poop comes from having small kids.
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iwok
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RE: Droppings After Take-off

Mon Nov 19, 2007 5:44 am



Quoting AlexEU (Thread starter):
I've seen several a.netters mentioning droppings after take-off. I feel it aswell, but only on 737s or A320s. I never felt it in A340 or an turboprop/piston aircraft. My question is: what are the kind droppings after-take-off?

No wonder people run to the loo as soon as the aircraft hits 10,000ft.  Smile

Serisouly, I think this just is a feeling that indicates that the G force level has reduced maybe from flaps coming in, LG coming in, AOA being reduced or anything else that we tend to reduce the rate of climb. The body senses a reduced g level and thinks it is dropping down. This is why flying by the seat of the pants is not recommended.

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jush
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RE: Droppings After Take-off

Mon Nov 19, 2007 7:39 am

I noticed this too and in my case it was not a drop but the pilot starting to increase climb. Sounds strange but that sometimes creates a feeling of a drop.
That and the flap case.

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jush
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ALexeu
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RE: Droppings After Take-off

Mon Nov 19, 2007 2:27 pm



Quoting Jush (Reply 10):
I noticed this too and in my case it was not a drop but the pilot starting to increase climb. Sounds strange but that sometimes creates a feeling of a drop.

Yes, but as soon as he increases, he decreases and so on, like some sort of frequency. The higher we climb it becomes less and less noticeable.

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