Topic Author
Posts: 132
Joined: Thu Mar 18, 2004 3:28 pm

Horizontal Stabilizer Travel Area

Sun Aug 22, 2004 3:18 pm

I have noticed that most airliners have a flat area on the fuselage to allow the horizontal stabilizer to move up and down.
My question is:
Why is that area flat so much in front of the actual travel area of the stabilizer?
Travel? Why would i travel if I can watch it on TV?
Posts: 64
Joined: Wed Aug 11, 2004 12:03 am

RE: Horizontal Stabilizer Travel Area

Sun Aug 22, 2004 6:30 pm

HUH? What are you talking about dude?  Confused
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RE: Horizontal Stabilizer Travel Area

Sun Aug 22, 2004 9:23 pm

View the thing from above. The fuselage is a cone at this point - the diameter is greater forward of the horizontal stab and smaller aft of it. Of course the recess is going to be greater where the cone is larger. The horizontal stab rotates but any point of it stays in a plane parallel to the aicraft centerline.

This came up here recently because a passenger made a big fuss and refused to board one of our planes because it had this big "dent" and no one would do anything about it. She was referring to this recess to allow the stab to pivot.
Happiness is not seeing another trite Ste. Maarten photo all week long.
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RE: Horizontal Stabilizer Travel Area

Mon Aug 23, 2004 6:08 am

Hey Videns

Unfortunately you have not made any reference to a picture. That would have been a help.

But take a look here:

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Photo © Normando Carvalho Jr.

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Photo © Dale Coleman
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Photo © Enio Beal Jr.

I guess part of the mechanism for adjusting the horizontal stabilizer is located in front of the stabilizer (inside the fuselage).
If you take a closer look at the 777 and the 747 then this area seems smaller than on the A320 and the 737. Since the big planes have a bigger fuselage then there is (almost) enough room inside the tail cone for the mechanism.
On the smaller planes the tail cone has a bigger dent above and below the stabilizer to create enough space inside the cone for the mechanism. The reflection above the stabilizer (starting at the windows) on the A320 clearly illustrates this dent.
Part of the reason for this big surface could be the need for smoothness to reduce aerodynamical resistance from the tail.

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Look at me, I´m riding high, I´m the airbornmaster of the sky...
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RE: Horizontal Stabilizer Travel Area

Mon Aug 23, 2004 6:25 am

The 'dented' surface around the horizontal stabilizer's trim path has nothing to do with fitting the mechanisms that move the stabilizer. Rather, the depression simply forms a smooth and continuous plane for the control surface to move on - if it weren't there, the front and back of the stabilizer would sort-of stick out, due to the tapering of the tail.

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Joined: Mon May 17, 2004 11:38 am

RE: Horizontal Stabilizer Travel Area

Mon Aug 23, 2004 1:13 pm

QuantasA332 is correct (of course). On the A320, the mechanism for operating the stab is called the THS (Trimmable Horizontal Stabilizer) Actuator. The THS Actuator is mounted on the front spar of the stab. It's quite compact, and does not require any change to the fuselage profile.
The primary function of the design engineer is to make things difficult for the manufacturer and impossible for the AME.

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