Questions about control systems for Boeings
Thread Starter
Join Date: Nov 2007
Location: Canada
Age: 56
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
Questions about control systems for Boeings
Hi all, first time poster here.
I am making an independent documentary and a small part of it concerns aviation and more specifically the Boeing 757 and 767 control systems.
It is my understanding that European aircraft manufacturers such as Airbus use fly-by-wire technology in their airliners. I understand that the flight systems computers set limits on the pilot's input so that if the pilot attempts, by accident or otherwise, to make a dangerous maneuver, the system sets limits on the control inputs. For example I was told that the pilot of an Airbus would not be able to put the airplane in a nose high angle above 30 degrees high.
That's the Europeans - Is this correct?
But the Americans such as Boeing claim that they prefer to leave the full control of the aircraft at the hands of the pilot. The flight computer doesn't set those same limits, rather it just lets the pilot know with an alarm or a warning that the situation is getting potentially dangerous.
That's the Americans - Is this correct?
Furthermore, I am building a small homebuilt Sonex two seater aircraft at home in my garage. My controls are directly connected to the control surfaces, for example my rudder is activated via a cable linked to the center stick. And likewise the flaps and ailerons are connected to the cockpit via push/pull rods directly linked to the flap handle and the center stick. No fly-by-wire here, no electric motors to do the work for me, no hydraulics, no auto-pilots either..... unless you count my knees around the stick as a form of auto-pilot.
But what about the Boeing 757s and 767s? Do they use direct mechanical links to the control surface motors/pumps or do they use electric signals to activate the motors/pumps of the control surfaces?
I know that on my car, the cruise button can be somewhat similar to an aircraft auto-pilot in that I set the limit for the speed and let the systems do the rest. But as soon as I touch the brake or gas or shift the gear, the cruise control de-activates itself and surrenders the controls back to me.
Is this the same thing with a 757 or a 767? If you turn on the auto-pilot will it deactivate itself as soon as the pilot touches the controls or will it require that the pilot first deactivates the auto-pilot? And if the pilot attempts to make some control inputs while the auto-pilot is activated, will the airplane react to the pilot or to the auto-pilot?
Thanx all for your help in advance. I hope I am not bothering anyone with my noob questions.
Cheers
I am making an independent documentary and a small part of it concerns aviation and more specifically the Boeing 757 and 767 control systems.
It is my understanding that European aircraft manufacturers such as Airbus use fly-by-wire technology in their airliners. I understand that the flight systems computers set limits on the pilot's input so that if the pilot attempts, by accident or otherwise, to make a dangerous maneuver, the system sets limits on the control inputs. For example I was told that the pilot of an Airbus would not be able to put the airplane in a nose high angle above 30 degrees high.
That's the Europeans - Is this correct?
But the Americans such as Boeing claim that they prefer to leave the full control of the aircraft at the hands of the pilot. The flight computer doesn't set those same limits, rather it just lets the pilot know with an alarm or a warning that the situation is getting potentially dangerous.
That's the Americans - Is this correct?
Furthermore, I am building a small homebuilt Sonex two seater aircraft at home in my garage. My controls are directly connected to the control surfaces, for example my rudder is activated via a cable linked to the center stick. And likewise the flaps and ailerons are connected to the cockpit via push/pull rods directly linked to the flap handle and the center stick. No fly-by-wire here, no electric motors to do the work for me, no hydraulics, no auto-pilots either..... unless you count my knees around the stick as a form of auto-pilot.
But what about the Boeing 757s and 767s? Do they use direct mechanical links to the control surface motors/pumps or do they use electric signals to activate the motors/pumps of the control surfaces?
I know that on my car, the cruise button can be somewhat similar to an aircraft auto-pilot in that I set the limit for the speed and let the systems do the rest. But as soon as I touch the brake or gas or shift the gear, the cruise control de-activates itself and surrenders the controls back to me.
Is this the same thing with a 757 or a 767? If you turn on the auto-pilot will it deactivate itself as soon as the pilot touches the controls or will it require that the pilot first deactivates the auto-pilot? And if the pilot attempts to make some control inputs while the auto-pilot is activated, will the airplane react to the pilot or to the auto-pilot?
Thanx all for your help in advance. I hope I am not bothering anyone with my noob questions.
Cheers
Last edited by Pepe Lapiu; 11th Nov 2007 at 12:37.
Thread Starter
Join Date: Nov 2007
Location: Canada
Age: 56
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
I have tried asking these questions above on several different forums and yet no one has come forward to answer any of them. I don't know why. I called Boeing directly and they told me that since 9/1 they don't release technical data about their aircrafts.
Is this why nobody answers on the forums as well?
Can anyone tell me where to to who I can go to get answers for the questions above?
Thanx
Is this why nobody answers on the forums as well?
Can anyone tell me where to to who I can go to get answers for the questions above?
Thanx
You initial post was only three hours ago, Pepe. I think if you wait for a while, you'll get a response. I don't work on wide-body aircraft so I can't comment except for the autopilot question. They can be overidden if forces exceeding a predetermined amount are applied to the controls. Around 8lbs if I remember correctly.
Join Date: Feb 2007
Location: Back at base
Posts: 16
Likes: 0
Received 0 Likes
on
0 Posts
Pepe
Any control input from the pilot will disengage the autopilot and give control back to him/her.
Inputs to the PCA's are via cables, pushrods or bellcranks etc.
Regards
Gascan
Any control input from the pilot will disengage the autopilot and give control back to him/her.
Inputs to the PCA's are via cables, pushrods or bellcranks etc.
Regards
Gascan
Thread Starter
Join Date: Nov 2007
Location: Canada
Age: 56
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
What's PCA stand for? I assume the C is for controls.
And the controls to the tail/rudder and V-stab ..... all controlled with a cable running from the stick all the way back to the tail?
And the controls to the tail/rudder and V-stab ..... all controlled with a cable running from the stick all the way back to the tail?
Join Date: Feb 2005
Location: Merseyside
Posts: 40
Likes: 0
Received 0 Likes
on
0 Posts
If you browse www.smartcockpit.com I am sure you will find answers to all your questions
Join Date: Jul 2007
Location: UK
Posts: 83
Likes: 0
Received 0 Likes
on
0 Posts
hope i can help a little, although will keep it very brief as the complexities of a modern airliners control system cannot be fully explained here.
firstly as you have already been told, any input by either pilot will disconnect the autopilot (that is to say a force applied in excess of a predetermined figure).
next, the three primary control surfaces, (rudder, elevators and ailerons) are controlled by a cable system linked to the control column ( or rudder peddals) which utilise cable quadrants,bellcranks and push rods to operate a servo valve on the assossiated power control actuator. movement of the servo valve allows hydraulic pressure to drive the body of the actuator, which is connected to the control surface, to a position proportionate to the control column displacement. The cable runs are duplicated and the control surface pca's are triplicated. (757).
This is a very very basic overveiw, as the system although now old technology is far more complicated than can be fully explained here. once you start adding autopilots, temp compensation, airspeed factors etc, it cannot be explained to its full outside of a classroom on a full type coarse.
hope that helps.
firstly as you have already been told, any input by either pilot will disconnect the autopilot (that is to say a force applied in excess of a predetermined figure).
next, the three primary control surfaces, (rudder, elevators and ailerons) are controlled by a cable system linked to the control column ( or rudder peddals) which utilise cable quadrants,bellcranks and push rods to operate a servo valve on the assossiated power control actuator. movement of the servo valve allows hydraulic pressure to drive the body of the actuator, which is connected to the control surface, to a position proportionate to the control column displacement. The cable runs are duplicated and the control surface pca's are triplicated. (757).
This is a very very basic overveiw, as the system although now old technology is far more complicated than can be fully explained here. once you start adding autopilots, temp compensation, airspeed factors etc, it cannot be explained to its full outside of a classroom on a full type coarse.
hope that helps.
Thread Starter
Join Date: Nov 2007
Location: Canada
Age: 56
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
Thank you all for your replies.
I have asked these questions on SEVERAL forums and this is the only place anyone has even attempted to answer them.
So thank you all very much once again, you were all very helpful.
Cheers,
Pepe Lapiu
I have asked these questions on SEVERAL forums and this is the only place anyone has even attempted to answer them.
So thank you all very much once again, you were all very helpful.
Cheers,
Pepe Lapiu
Thread Starter
Join Date: Nov 2007
Location: Canada
Age: 56
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
Thread Starter
Join Date: Nov 2007
Location: Canada
Age: 56
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
As you surely know with small aircrafts everything is a compromise. With a useful weight of only 550 pounds if some features are selected some other features have to be thrown out. So for the sake of keeping the weight down I basically had to choose between a coffee machine and a Browning .50 chaingun under each wing.
So let's just say that if we ever meet up there you'll be looking pretty darn foolish trying to throw your coffee pot at me.
So let's just say that if we ever meet up there you'll be looking pretty darn foolish trying to throw your coffee pot at me.
