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AFROBINSON808
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Posts: 11
Joined: Wed Apr 29, 2020 10:43 pm

747-400 elevator control system

Wed May 20, 2020 7:09 pm

Hi all,

I've read on a pprune.org forum that the B747-400 had a revised elevator control system compared to earlier 747 variants.

Does anyone have any illustrations/drawings/etc. of the 744's elevator system?

Thanks
 
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DL_Mech
Posts: 2410
Joined: Fri Feb 18, 2000 7:48 am

Re: 747-400 elevator control system

Wed May 20, 2020 11:56 pm

This plane is built to withstand anything... except a bad pilot.
 
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747classic
Posts: 3017
Joined: Sat Aug 15, 2009 9:13 am

Re: 747-400 elevator control system

Sun May 24, 2020 3:19 pm

The elevator control system on 747-100/200/300/SP series is hydraulic powered by :

LH outb elevator , hyd syst 1
LH inb...elevator, hyd syst 3&4
RH inb...elevator, hyd syst 1&2
RH outb elevator, hyd syst 4

From the first 747-400, starting at L/N 696 (and also at several late built 747-200/300 aircraft after L/N 696), the hydraulic system power to the elevators was changed :

LH outb elevator , hyd syst 1
LH inb...elevator, hyd syst 1&2
RH inb...elevator, hyd syst 3&4
RH outb elevator, hyd syst 4

On the 744 Stab Trim is all electric (no manual stab trim levers in the cockpit).
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
Max Q
Posts: 8131
Joined: Wed May 09, 2001 12:40 pm

Re: 747-400 elevator control system

Tue May 26, 2020 6:20 am

747classic wrote:
The elevator control system on 747-100/200/300/SP series is hydraulic powered by :

LH outb elevator , hyd syst 1
LH inb...elevator, hyd syst 3&4
RH inb...elevator, hyd syst 1&2
RH outb elevator, hyd syst 4

From the first 747-400, starting at L/N 696 (and also at several late built 747-200/300 aircraft after L/N 696), the hydraulic system power to the elevators was changed :

LH outb elevator , hyd syst 1
LH inb...elevator, hyd syst 1&2
RH inb...elevator, hyd syst 3&4
RH outb elevator, hyd syst 4

On the 744 Stab Trim is all electric (no manual stab trim levers in the cockpit).



I never noticed manual stab trim levers in the cockpit of the Classic

Where are they located ?
The best contribution to safety is a competent Pilot.


GGg
 
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jetmech
Posts: 2365
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Re: 747-400 elevator control system

Tue May 26, 2020 6:29 am

747classic wrote:
From the first 747-400, starting at L/N 696 (and also at several late built 747-200/300 aircraft after L/N 696), the hydraulic system power to the elevators was changed.

Any information on why this change was made? I remember being told that it was due to the HST, but this is evidently not so if some classics had the new layout.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
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747classic
Posts: 3017
Joined: Sat Aug 15, 2009 9:13 am

Re: 747-400 elevator control system

Tue May 26, 2020 7:48 am

Max Q wrote:

On the 744 Stab Trim is all electric (no manual stab trim levers in the cockpit).



I never noticed manual stab trim levers in the cockpit of the Classic

Where are they located ?[/quote]

The two levers (marked : Stab & Trim) left of the speedbrake/spoiler lever (left of the P/L's)

747-206B


747-451


jetmech wrote:
747classic wrote:
From the first 747-400, starting at L/N 696 (and also at several late built 747-200/300 aircraft after L/N 696), the hydraulic system power to the elevators was changed.


Any information on why this change was made? I remember being told that it was due to the HST, but this is evidently not so if some classics had the new layout.

Regards, JetMech


Standarization of horizontal stabilizer production to -400 standard, with provisions for tail tank installation, requiring re-routing of hydraulic lines.
I operated two 747-200 aircraft, built after L/N 696 with the changed hydraulic system lay-out, requiring minor changes in emergency procedures.
Aircraft involved : L/N 712, 747-21AC, PH-MCF and L/N 878, 747-228F, PH-MCN.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
Max Q
Posts: 8131
Joined: Wed May 09, 2001 12:40 pm

Re: 747-400 elevator control system

Tue May 26, 2020 10:07 am

747classic wrote:
Max Q wrote:

On the 744 Stab Trim is all electric (no manual stab trim levers in the cockpit).



I never noticed manual stab trim levers in the cockpit of the Classic

Where are they located ?


The two levers (marked : Stab & Trim) left of the speedbrake/spoiler lever (left of the P/L's)

747-206B


747-451


jetmech wrote:
747classic wrote:
From the first 747-400, starting at L/N 696 (and also at several late built 747-200/300 aircraft after L/N 696), the hydraulic system power to the elevators was changed.


Any information on why this change was made? I remember being told that it was due to the HST, but this is evidently not so if some classics had the new layout.

Regards, JetMech


Standarization of horizontal stabilizer production to -400 standard, with provisions for tail tank installation, requiring re-routing of hydraulic lines.
I operated two 747-200 aircraft, built after L/N 696 with the changed hydraulic system lay-out, requiring minor changes in emergency procedures.
Aircraft involved : L/N 712, 747-21AC, PH-MCF and L/N 878, 747-228F, PH-MCN.[/quote]


Got it,

Early production 757s also had these, just noticed the stabtrim ‘wheel’ on the left side of the console with the white cross on it and the trim indicator next to it

707/ 727 and 737 aircraft had fold out handles on this wheel for manual trimming.
I know there’s no such thing on a 747 but does that ‘trim wheel’ rotate?
The best contribution to safety is a competent Pilot.


GGg
 
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747classic
Posts: 3017
Joined: Sat Aug 15, 2009 9:13 am

Re: 747-400 elevator control system

Tue May 26, 2020 10:32 am

Max Q wrote:


Got it,

Early production 757s also had these, just noticed the stabtrim ‘wheel’ on the left side of the console with the white cross on it and the trim indicator next to it

707/ 727 and 737 aircraft had fold out handles on this wheel for manual trimming.
I know there’s no such thing on a 747 but does that ‘trim wheel’ rotate?


Yes, with sound, to alert the crew that the aircraft was (auto)trimming.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
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Horstroad
Posts: 504
Joined: Thu Apr 08, 2010 8:19 pm

Re: 747-400 elevator control system

Tue May 26, 2020 1:43 pm

747classic wrote:
On the 744 Stab Trim is all electric (no manual stab trim levers in the cockpit).

Why did they drop the manual trim levers on the B747-400 but keep/reintroduce them on the newly designed B777 6 years later?
 
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747classic
Posts: 3017
Joined: Sat Aug 15, 2009 9:13 am

Re: 747-400 elevator control system

Tue May 26, 2020 2:11 pm

Horstroad wrote:
747classic wrote:
On the 744 Stab Trim is all electric (no manual stab trim levers in the cockpit).

Why did they drop the manual trim levers on the B747-400 but keep/reintroduce them on the newly designed B777 6 years later?


The mechanical manual trim levers are replaced by alternate electric stabilizer trim switches on the 744 (see the 747-451 picture above - right of both red quarded stab hyd shut off switches, just below the P/L's.)
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
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DL_Mech
Posts: 2410
Joined: Fri Feb 18, 2000 7:48 am

Re: 747-400 elevator control system

Tue May 26, 2020 2:17 pm

Horstroad wrote:
747classic wrote:
On the 744 Stab Trim is all electric (no manual stab trim levers in the cockpit).

Why did they drop the manual trim levers on the B747-400 but keep/reintroduce them on the newly designed B777 6 years later?


The Stab Trim levers in the 777 are for alternate Stab Trim control. There are actual control cables running from the levers below the cockpit to the Stab Trim Control Modules in the tail. This is one of the ways you can control the airplane without fly by wire. You can also control roll on the airplane by using one spoiler on each wing connected by control cable from control wheel to spoiler PCU.
This plane is built to withstand anything... except a bad pilot.
 
AFROBINSON808
Topic Author
Posts: 11
Joined: Wed Apr 29, 2020 10:43 pm

Re: 747-400 elevator control system

Tue May 26, 2020 3:02 pm

747classic wrote:
Standarization of horizontal stabilizer production to -400 standard, with provisions for tail tank installation, requiring re-routing of hydraulic lines.


Do you mean to say there that some 747 classics had the horizontal stabilizer tank?
 
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747classic
Posts: 3017
Joined: Sat Aug 15, 2009 9:13 am

Re: 747-400 elevator control system

Tue May 26, 2020 3:30 pm

AFROBINSON808 wrote:
747classic wrote:
Standarization of horizontal stabilizer production to -400 standard, with provisions for tail tank installation, requiring re-routing of hydraulic lines.


Do you mean to say there that some 747 classics had the horizontal stabilizer tank?


No, only the 400 horizontal stabilizer structure was used at late built 747-200/300's. These structure was prepared for a horizontal stabilizer tank, however the combination horizontal stabilizer tank and 747classic was never certified.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
Max Q
Posts: 8131
Joined: Wed May 09, 2001 12:40 pm

Re: 747-400 elevator control system

Wed May 27, 2020 5:41 am

Thanks 74C for the information
The best contribution to safety is a competent Pilot.


GGg

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