Saw something strange yesterday: Flying out of Malpensa, there was an Alitalia MD-80 on the tarmac with one part of the horizontal tail fully deflected, and the other part level! What’s thaaat? Didn’t know the old DC-9 ++ family has an asymmetric tail! Too bad I didn’t have a camera with me.
By: Helican - 15th April 2005 at 01:20
ok..guess I stand corrected. Only repeated what was said on a tech log thread at pprune.
By: Helican - 15th April 2005 at 01:20
ok..guess I stand corrected. Only repeated what was said on a tech log thread at pprune.
By: Whiskey Delta - 15th April 2005 at 01:00
whiskey Delta,
Your right, I’m not a DC-9 driver, but I assure all of you, when the jet is on the ground one of the hydraulic systems are shut off so the corresponding elevator droops until the system is pressurized.
TTP
Thanks TTP, that sounds about right. I could have sworn that I watched a drooping elevator align itself soon before takeoff and I assumed that a before takeoff procedure had activated a system that caused that. I’ve only spent 1 flight on a MD-80 jumpseat and never thought to ask the question at the time.
By: Whiskey Delta - 15th April 2005 at 01:00
whiskey Delta,
Your right, I’m not a DC-9 driver, but I assure all of you, when the jet is on the ground one of the hydraulic systems are shut off so the corresponding elevator droops until the system is pressurized.
TTP
Thanks TTP, that sounds about right. I could have sworn that I watched a drooping elevator align itself soon before takeoff and I assumed that a before takeoff procedure had activated a system that caused that. I’ve only spent 1 flight on a MD-80 jumpseat and never thought to ask the question at the time.
By: TTP - 15th April 2005 at 00:44
whiskey Delta,
Your right, I’m not a DC-9 driver, but I assure all of you, when the jet is on the ground one of the hydraulic systems are shut off so the corresponding elevator droops until the system is pressurized.
Helican, Your statements are way off the mark! Passenger Jets are not toys that streamline their flight controls as they gain speed, they are all hydraulically actuated.
On the 727 only one of 3 hydraulic systems are activated on the ground while onloading or boarding pax, so you will notice the leading edge slats are drooped down, much like the DC-9 elevator, as soon as the other Hydraulic systems are activated everything goes back into a normal state.
TTP
By: TTP - 15th April 2005 at 00:44
whiskey Delta,
Your right, I’m not a DC-9 driver, but I assure all of you, when the jet is on the ground one of the hydraulic systems are shut off so the corresponding elevator droops until the system is pressurized.
Helican, Your statements are way off the mark! Passenger Jets are not toys that streamline their flight controls as they gain speed, they are all hydraulically actuated.
On the 727 only one of 3 hydraulic systems are activated on the ground while onloading or boarding pax, so you will notice the leading edge slats are drooped down, much like the DC-9 elevator, as soon as the other Hydraulic systems are activated everything goes back into a normal state.
TTP
By: wysiwyg - 14th April 2005 at 22:17
The elevators on the MD-80 series are not powered, but rather of the servo tab variety. This means that they are free to flap with the wind on the ground, and are moved in flight by the servo tab increasing or decreasing the lift on that surface..moving the elevator up or down and again controlling the aircraft.
http://www.airliners.net/open.file/382601/M/
The control checks on the MD-80 series elevators apparently needs to be done at a minimun taxi speed of 10-15kts.
Was that the same as the 707?
By: wysiwyg - 14th April 2005 at 22:17
The elevators on the MD-80 series are not powered, but rather of the servo tab variety. This means that they are free to flap with the wind on the ground, and are moved in flight by the servo tab increasing or decreasing the lift on that surface..moving the elevator up or down and again controlling the aircraft.
http://www.airliners.net/open.file/382601/M/
The control checks on the MD-80 series elevators apparently needs to be done at a minimun taxi speed of 10-15kts.
Was that the same as the 707?
By: Whiskey Delta - 14th April 2005 at 05:55
The elevators on the MD-80 series are not powered, but rather of the servo tab variety. This means that they are free to flap with the wind on the ground, and are moved in flight by the servo tab increasing or decreasing the lift on that surface..moving the elevator up or down and again controlling the aircraft.
http://www.airliners.net/open.file/382601/M/
The control checks on the MD-80 series elevators apparently needs to be done at a minimun taxi speed of 10-15kts.
That still doesn’t explain why they move independantly of each other on the ground. In the picture you linked to you can see that the right side of the elevator doesn’t match with the left. You can see the deflection of the servo tab don’t match either. The deflection should always be the same right since both tabs are directly connected by cable to the pilot yoke? Even if the wind should push one elevator and it’s tab upward the resulting movement would move the yoke and in turn move the other servo tab.
Our stabilator is similar but doesn’t have the split. The wind can bounce the control surface around but it also moves the yoke since movement of the elevator moves the servo tab and then moves the yoke.
By: Whiskey Delta - 14th April 2005 at 05:55
The elevators on the MD-80 series are not powered, but rather of the servo tab variety. This means that they are free to flap with the wind on the ground, and are moved in flight by the servo tab increasing or decreasing the lift on that surface..moving the elevator up or down and again controlling the aircraft.
http://www.airliners.net/open.file/382601/M/
The control checks on the MD-80 series elevators apparently needs to be done at a minimun taxi speed of 10-15kts.
That still doesn’t explain why they move independantly of each other on the ground. In the picture you linked to you can see that the right side of the elevator doesn’t match with the left. You can see the deflection of the servo tab don’t match either. The deflection should always be the same right since both tabs are directly connected by cable to the pilot yoke? Even if the wind should push one elevator and it’s tab upward the resulting movement would move the yoke and in turn move the other servo tab.
Our stabilator is similar but doesn’t have the split. The wind can bounce the control surface around but it also moves the yoke since movement of the elevator moves the servo tab and then moves the yoke.
By: Helican - 13th April 2005 at 23:45
The elevators on the MD-80 series are not powered, but rather of the servo tab variety. This means that they are free to flap with the wind on the ground, and are moved in flight by the servo tab increasing or decreasing the lift on that surface..moving the elevator up or down and again controlling the aircraft.
http://www.airliners.net/open.file/382601/M/
The control checks on the MD-80 series elevators apparently needs to be done at a minimun taxi speed of 10-15kts.
By: Helican - 13th April 2005 at 23:45
The elevators on the MD-80 series are not powered, but rather of the servo tab variety. This means that they are free to flap with the wind on the ground, and are moved in flight by the servo tab increasing or decreasing the lift on that surface..moving the elevator up or down and again controlling the aircraft.
http://www.airliners.net/open.file/382601/M/
The control checks on the MD-80 series elevators apparently needs to be done at a minimun taxi speed of 10-15kts.
By: concordesst - 13th April 2005 at 23:26
I envy you (and your knowledge), its an absolute pleasure to read this, i think its fascinating.
By: concordesst - 13th April 2005 at 23:26
I envy you (and your knowledge), its an absolute pleasure to read this, i think its fascinating.
By: Flex 35 - 13th April 2005 at 23:18
I’m sure on the BAe 146/Avro RJ’s when they apply takeoff thrust the elevator gets brought back to its normal position. They very often taxi on to the active with the elevator fully up, and taxi off after landing fully up as well.
Interesting thread. 🙂
Flex 35
By: Flex 35 - 13th April 2005 at 23:18
I’m sure on the BAe 146/Avro RJ’s when they apply takeoff thrust the elevator gets brought back to its normal position. They very often taxi on to the active with the elevator fully up, and taxi off after landing fully up as well.
Interesting thread. 🙂
Flex 35
By: wysiwyg - 13th April 2005 at 22:39
It could be that the hydraulics push the surface against the airflow while the airflow is useds to return it.
By: wysiwyg - 13th April 2005 at 22:39
It could be that the hydraulics push the surface against the airflow while the airflow is useds to return it.
By: Whiskey Delta - 13th April 2005 at 20:47
I wonder what the hydraulic system has to do with it. This diagram shows the #1 system providing pressure for the elevator (I’d assume some sort of boost pump). Perhaps the hydraulics aren’t activated on the ground leaving the 2 halves to flap in the wind.
I’ve pondered this a few times as we taxi behind a MD-80. 🙂
By: Whiskey Delta - 13th April 2005 at 20:47
I wonder what the hydraulic system has to do with it. This diagram shows the #1 system providing pressure for the elevator (I’d assume some sort of boost pump). Perhaps the hydraulics aren’t activated on the ground leaving the 2 halves to flap in the wind.
I’ve pondered this a few times as we taxi behind a MD-80. 🙂
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April 13, 2005 at 12:04 pm