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notaxonrotax
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777 empennage question. What is it, please?

Fri Jan 26, 2018 5:12 pm

Hi,

I feel silly for asking this question, but what is this "thing" sticking out of this 777 tail?
Parked rather close to me at Libreville, I couldn`t help noticing this little detail for the very first time.

Image


Thanks!


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113312
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Re: 777 empennage question. What is it, please?

Fri Jan 26, 2018 5:19 pm

APU air intake scoop
 
Flow2706
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Re: 777 empennage question. What is it, please?

Fri Jan 26, 2018 5:24 pm

Not rated on 777, but I think this is the APU Flap (where the APU gets the air from)
 
mmo
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Re: 777 empennage question. What is it, please?

Fri Jan 26, 2018 5:29 pm

Correct. It is the air inlet for the APU.
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LU9092
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Re: 777 empennage question. What is it, please?

Fri Jan 26, 2018 6:15 pm

Are there situations where the 777 flies with APU running? If so, is there any range penalty for extra drag from that intake, or is it negligible?
 
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77west
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Re: 777 empennage question. What is it, please?

Fri Jan 26, 2018 7:33 pm

LU9092 wrote:
Are there situations where the 777 flies with APU running? If so, is there any range penalty for extra drag from that intake, or is it negligible?


Yes, if one of the electrical generators and/or hydraulic pumps is INOP I believe they need to fly with the APU running. I think the fuel it uses would have more impact on range than the inlet flap itself
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PhilBy
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Re: 777 empennage question. What is it, please?

Fri Jan 26, 2018 8:17 pm

LU9092 wrote:
Are there situations where the 777 flies with APU running? If so, is there any range penalty for extra drag from that intake, or is it negligible?


I expect that the drag on the intake is slightly reduced if the APU is running!
 
LU9092
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Re: 777 empennage question. What is it, please?

Fri Jan 26, 2018 8:24 pm

PhilBy wrote:
LU9092 wrote:
Are there situations where the 777 flies with APU running? If so, is there any range penalty for extra drag from that intake, or is it negligible?


I expect that the drag on the intake is slightly reduced if the APU is running!



I don't think it's open when the APU isn't running.
 
BravoOne
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Re: 777 empennage question. What is it, please?

Fri Jan 26, 2018 9:11 pm

In flight you can feel a slight rumble when this door is open.
 
LH707330
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Re: 777 empennage question. What is it, please?

Sat Jan 27, 2018 12:46 am

I'd assume that the door doesn't open all the way when in flight, otherwise the ram pressure would be pretty high.
 
Redbellyguppy
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Re: 777 empennage question. What is it, please?

Sat Jan 27, 2018 1:46 am

The 737 max has a similar door as opposed to the previous vent style on the NG and classic. It does not have a speed limit even if it is inop and deferred open, however, there is a 1% burn penalty and a few hundred pounds performance penalty.
 
BravoOne
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Re: 777 empennage question. What is it, please?

Sat Jan 27, 2018 2:56 pm

[threeid][/threeid]
LH707330 wrote:
I'd assume that the door doesn't open all the way when in flight, otherwise the ram pressure would be pretty high.



I'm pretty sure if goes full open. I get what your saying, so I assume they modulate the ram effect.
 
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notaxonrotax
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Re: 777 empennage question. What is it, please?

Sat Jan 27, 2018 10:47 pm

Thanks, folks!
Is it that visible on other airliners?

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Florianopolis
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Re: 777 empennage question. What is it, please?

Sun Jan 28, 2018 6:46 pm

notaxonrotax wrote:
Is it that visible on other airliners?


747, 757, 767, CRJ, etc




 
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DL_Mech
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Re: 777 empennage question. What is it, please?

Sun Jan 28, 2018 10:14 pm

Florianopolis wrote:
notaxonrotax wrote:
Is it that visible on other airliners?


747, 757, 767, CRJ, etc


But not on the DC-9, MD-80/90. Unless you are underneath the airstair.

Image
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7673mech
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Re: 777 empennage question. What is it, please?

Mon Jan 29, 2018 3:14 am

LH707330 wrote:
I'd assume that the door doesn't open all the way when in flight, otherwise the ram pressure would be pretty high.


On the majority of flights, when APU is not needed it is fully closed in flight.
It is only open when APU is needed in flight and running. Full open. It does not modulate.
 
BravoOne
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Re: 777 empennage question. What is it, please?

Mon Jan 29, 2018 1:14 pm

77west wrote:
LU9092 wrote:
Are there situations where the 777 flies with APU running? If so, is there any range penalty for extra drag from that intake, or is it negligible?


Yes, if one of the electrical generators and/or hydraulic pumps is INOP I believe they need to fly with the APU running. I think the fuel it uses would have more impact on range than the inlet flap itself


ETOPS operators are required to make a cold soak start every so many flights/hours/cycles. Usually done near the end of the homeward bound flight after being aloft for at least six+ hours, or at the specific request of Maintenance. The results are recorded in the log book. Usually the starts are limited to 3 attempts.

Specific operators may have different procedures or requirements and results may vary.

The fuel penalty for an APU door stuck open is rather large at 2.5% for the 777.
 
LU9092
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Re: 777 empennage question. What is it, please?

Mon Jan 29, 2018 3:27 pm

BravoOne wrote:
77west wrote:
LU9092 wrote:
Are there situations where the 777 flies with APU running? If so, is there any range penalty for extra drag from that intake, or is it negligible?


Yes, if one of the electrical generators and/or hydraulic pumps is INOP I believe they need to fly with the APU running. I think the fuel it uses would have more impact on range than the inlet flap itself


ETOPS operators are required to make a cold soak start every so many flights/hours/cycles. Usually done near the end of the homeward bound flight after being aloft for at least six+ hours, or at the specific request of Maintenance. The results are recorded in the log book. Usually the starts are limited to 3 attempts.

Specific operators may have different procedures or requirements and results may vary.

The fuel penalty for an APU door stuck open is rather large at 2.5% for the 777.


Wow, that's pretty significant! Thanks for the info.

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