faz777
Topic Author
Posts: 14
Joined: Tue Aug 30, 2011 7:17 am

Indentation On B747 Horizontal Stabilizers

Mon Jul 02, 2012 11:48 pm

Hi,

Interested at the reason there is an indentation around the insertion point for the horizontal stabilizer into the main aircraft body.

best demonstrated in this picture
http://www.airliners.net/photo/573755/M/

could it be improved airflow? i imagine the air towards the back of the aircraft would be more turbulent?

noticed similarities on other aircraft but the 747 looks to have the largest.

thanks all.
 
PapaChuck
Posts: 111
Joined: Mon Aug 16, 2010 2:51 pm

RE: Indentation On B747 Horizontal Stabilizers

Mon Jul 02, 2012 11:59 pm

The horizontal stabilizer moves as one complete unit to provide pitch trim. In order to remain flush with the fuselage throughout the full range of motion, the fuselage is flattened in that area. It appears to be concave in comparison to the curved fuselage around it, but I believe it is indeed flat.

PC
In-trail spacing is a team effort.
 
roseflyer
Posts: 9606
Joined: Fri Feb 13, 2004 9:34 am

RE: Indentation On B747 Horizontal Stabilizers

Tue Jul 03, 2012 12:06 am

Quoting faz777 (Thread starter):


could it be improved airflow? i imagine the air towards the back of the aircraft would be more turbulent?

As mentioned, this is where the stabilizer rotates for trim control. It is mostly flat. The fuselage tapers behind this area, so there is no need for it to be flat. There is 1-2 inches of clearance between the stabilizer and fuselage skin.

Quoting faz777 (Thread starter):

noticed similarities on other aircraft but the 747 looks to have the largest.

The 747 stabilizer is the biggest and moves the most.
If you have never designed an airplane part before, let the real designers do the work!
 
faz777
Topic Author
Posts: 14
Joined: Tue Aug 30, 2011 7:17 am

RE: Indentation On B747 Horizontal Stabilizers

Tue Jul 03, 2012 12:12 am

Thanks alot!

makes perfect sense, didn't realise the stabilizer was indeed a moving part by itself.
 
LH707330
Posts: 1498
Joined: Fri Jun 15, 2012 11:27 pm

RE: Indentation On B747 Horizontal Stabilizers

Tue Jul 03, 2012 12:30 am

Area ruling. Almost all aircraft have that pinch there. Take one of those snap-fit models and remove the tail feathers, that will make it more obvious.

Quoting PapaChuck (Reply 1):
It appears to be concave in comparison to the curved fuselage around it, but I believe it is indeed flat.

I think it is concave down to the mount, and the stabilizer swings through a swept-shape indent for +/-15 degrees for trim.
 
PapaChuck
Posts: 111
Joined: Mon Aug 16, 2010 2:51 pm

RE: Indentation On B747 Horizontal Stabilizers

Tue Jul 03, 2012 1:13 am

I must correct myself. Seems to be that area ruling is quite a common theme:


View Large View Medium
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Photo © Benjamin Freer


View Large View Medium
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Photo © Derek Morrison



Even with a slight concavity, it's still a fairly easy shape to make the horizontal stab fit flush with.

PC
In-trail spacing is a team effort.

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