F27500
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Such a Long Tail Cone You Have!

Fri Dec 28, 2018 6:01 pm

it seems like this is the case on so many models nowadays (the latest being the A220).; designing planes with an awfully long tailcone.

The A220 tailcone practically looks like a long handle. I notice it also on 777, A320 , MRJ, and 787; some more pronounced than others.

I'm curious, is there an advantage to having the fin so far forward and so much sticking out behind it? To me. it just looks a bit odd.
 
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shamrock350
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Re: Such a Long Tail Cone You Have!

Fri Dec 28, 2018 6:31 pm

The tail cone is probably one of the most difficult parts of an aircraft to judge airflow, I believe an extended tail cone is better aerodynamically but the shape also has a large part to play. The 777 and A380 both feature a similar flat, screwdriver like design while all other Airbus models plus the 787 and 737MAX have a cone shape.

I've read the flat screwdriver style is more aerodynamic but the cone design is simpler and outweighs any aerodynamic advantage.
 
LH707330
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Re: Such a Long Tail Cone You Have!

Fri Dec 28, 2018 8:37 pm

It seems there's three main designs:

Boat tail: 707, 737, 747, MD-11 (debatable), DC-10
Screwdriver/beaver: MD80 (later), 777, A380, A350 (kinda), A220, MD-11 (debatable)
Cone: 757, 767, 787, A300/10/20/30/40

The 777 design posed a problem with the APU exhaust, which had two kinks in it and became an expensive implementation, so B went back to the cone for the 787. What's interesting is the hybrid screwdriver designs (380, 220), where the APU tube goes through the screwdriver. Maybe that's the best compromise.
 
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seabosdca
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Re: Such a Long Tail Cone You Have!

Fri Dec 28, 2018 9:09 pm

Interesting that Boeing saw enough benefit to bother totally redesigning the 737 tailcone for the MAX. It went from a 747-style boat tail design, as used on all previous 737s, to the closest Boeing could get to a 787-style cone given the shape of the rest of the empennage.
 
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LAX772LR
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Re: Such a Long Tail Cone You Have!

Sat Dec 29, 2018 3:08 am

LH707330 wrote:
which had two kinks in it

Can you explain this a little bit more (or perhaps a diagram)?

Not familiar with how it poses a problem.
I myself, suspect a more prosaic motive... ~Thranduil
 
Opaque
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Re: Such a Long Tail Cone You Have!

Sat Dec 29, 2018 9:03 am

seabosdca wrote:
Interesting that Boeing saw enough benefit to bother totally redesigning the 737 tailcone for the MAX. It went from a 747-style boat tail design, as used on all previous 737s, to the closest Boeing could get to a 787-style cone given the shape of the rest of the empennage.


The entire aft section from the horizontal stabiliser back was reprofiled for better aerodynamics, so they might as well change the cone shape while at it.
 
WIederling
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Re: Such a Long Tail Cone You Have!

Sat Dec 29, 2018 11:32 am

seabosdca wrote:
Interesting that Boeing saw enough benefit to bother totally redesigning the 737 tailcone for the MAX. It went from a 747-style boat tail design, as used on all previous 737s, to the closest Boeing could get to a 787-style cone given the shape of the rest of the empennage.


Back when the MAX details were made public I had wondered about the
reason for changing the tail.

My fresh guess after the Lion Air crash:
The MAX has ( look at MCAS ) strong ruder (H,V) authority issues.
If you can avoid having turbulent airflow around the base of the tails V- and H- aero surfaces.
you get improved authority in problematic situations. small bits help.
Murphy is an optimist
 
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Horstroad
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Re: Such a Long Tail Cone You Have!

Sat Dec 29, 2018 2:21 pm

LAX772LR wrote:
LH707330 wrote:
which had two kinks in it

Can you explain this a little bit more (or perhaps a diagram)?


Image
Image
I don't know why the photo is on its side... it should be rotated 90° to the right


I find the MD11 APU ducting way more complex... with the inlet aft of the APU, wrapping around the APU compartment to connect to the APU from the front.
The tail cone on the MD11 is empty except for a ladder. This allows it to be lowered under the fuselage for an engine change. They changed the design from the DC10 to the MD11 which made it longer, so now it's split into to sections to allow clearance to the ground during lowering of the tail cone. The APU had to be moved forward under the horizontal stabilizer, which makes the APU compartment very cramped
 
TSS
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Re: Such a Long Tail Cone You Have!

Sat Dec 29, 2018 4:14 pm

Horstroad wrote:
Image


Possibly off-topic, but what is the purpose of the spring-loaded hatch near the bottom of the photo? That seems like an awful lot of resistance to overcome just to inspect something, but on the other hand you'd never have to wonder if it closed tight after you were done.
Able to kill active threads stone dead with a single post!
 
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Horstroad
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Re: Such a Long Tail Cone You Have!

Sat Dec 29, 2018 5:41 pm

TSS wrote:
Possibly off-topic, but what is the purpose of the spring-loaded hatch near the bottom of the photo? That seems like an awful lot of resistance to overcome just to inspect something, but on the other hand you'd never have to wonder if it closed tight after you were done.

Those are overpressure vents in case a duct fails inside the compartment. The compartment is otherwise more or less sealed. If you would blow high pressure pneumatic air or exhaust gases in the compartment, the structure might fail if the pressure is not vented.
 
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LAX772LR
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Re: Such a Long Tail Cone You Have!

Sat Dec 29, 2018 6:09 pm

Horstroad wrote:
LAX772LR wrote:
LH707330 wrote:
which had two kinks in it

Can you explain this a little bit more (or perhaps a diagram)?

I don't know why the photo is on its side... it should be rotated 90° to the right

Thank you for that.

I guess I was thrown off by the word "kink," as I knew that it canted to one side.

Still wondering how that presents a deterring engineering issue though, such that it'd make them want to avoid it in future models?
I myself, suspect a more prosaic motive... ~Thranduil
 
FlyHossD
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Re: Such a Long Tail Cone You Have!

Sat Dec 29, 2018 7:33 pm

WIederling wrote:
seabosdca wrote:
Interesting that Boeing saw enough benefit to bother totally redesigning the 737 tailcone for the MAX. It went from a 747-style boat tail design, as used on all previous 737s, to the closest Boeing could get to a 787-style cone given the shape of the rest of the empennage.


Back when the MAX details were made public I had wondered about the
reason for changing the tail.

My fresh guess after the Lion Air crash:
The MAX has ( look at MCAS ) strong ruder (H,V) authority issues.
If you can avoid having turbulent airflow around the base of the tails V- and H- aero surfaces.
you get improved authority in problematic situations. small bits help.


I don't see the need to conflate the Lion Air tragedy - relating to the MCAS and pitch trim - with rudder authority. Rather it appears that Boeing saw an opportunity to improve the aerodynamics of the tail cone to further improve the fuel efficiency of the 737 Max aircraft.
My statements do not represent my former employer or my current employer and are my opinions only.
 
aeropix
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Re: Such a Long Tail Cone You Have!

Sat Dec 29, 2018 8:41 pm

TSS wrote:
Possibly off-topic, but what is the purpose of the spring-loaded hatch near the bottom of the photo? That seems like an awful lot of resistance to overcome just to inspect something, but on the other hand you'd never have to wonder if it closed tight after you were done.


It seems to be a pair of pressure relief vents in case the APU exploded, to prevent blowing the whole tailcone off. One on each side of the APU muffler shroud. Edited to add - answered upstream before I refreshed the browser window.
 
LH707330
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Re: Such a Long Tail Cone You Have!

Sat Dec 29, 2018 8:50 pm

LAX772LR wrote:
Horstroad wrote:
LAX772LR wrote:
Can you explain this a little bit more (or perhaps a diagram)?

I don't know why the photo is on its side... it should be rotated 90° to the right

Thank you for that.

I guess I was thrown off by the word "kink," as I knew that it canted to one side.

Still wondering how that presents a deterring engineering issue though, such that it'd make them want to avoid it in future models?

Thanks for the pictures. I had thought it had an S-turn in it, instead of just a curve, my bad. Looks like production cost and noise were the killers:

viewtopic.php?t=756265
 
stratclub
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Re: Such a Long Tail Cone You Have!

Sun Dec 30, 2018 12:29 am

MCAS has nothing to do with this thread. There is no problem with pitch up authority on the 737 MAX.

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