What could be the cause of an uncommanded roll at high speed?What was the first aircraft that could fly inverted?How could a failed left wing cause a roll to the right?What is the difference between a forward, aft, high and low center of gravity?What is the direction convention for Roll angle?Why do aircraft have a crossover airspeed, and why does it increase at higher vertical load factors?Why was the 737 main rudder servo valve’s vulnerability to causing uncommanded reversals never discovered in testing?Why does the A320’s maximum allowable aileron deflection decrease, rather than increase, when the flaps are extended?Why not use the yoke to control yaw, as well as pitch and roll?What is the THS deflection speed?
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What could be the cause of an uncommanded roll at high speed?
What was the first aircraft that could fly inverted?How could a failed left wing cause a roll to the right?What is the difference between a forward, aft, high and low center of gravity?What is the direction convention for Roll angle?Why do aircraft have a crossover airspeed, and why does it increase at higher vertical load factors?Why was the 737 main rudder servo valve’s vulnerability to causing uncommanded reversals never discovered in testing?Why does the A320’s maximum allowable aileron deflection decrease, rather than increase, when the flaps are extended?Why not use the yoke to control yaw, as well as pitch and roll?What is the THS deflection speed?
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margin-bottom:0;
$begingroup$
I have a problem with a T-38. There is uncommanded roll to the left when the aircraft flies at 250 knots. But as the aircraft speed goes up around 500 knots, the uncommanded roll is now to the right. During 500 knots we could control the plane with 15-20 aileron trims.
What may be the problem?
We have replaced a lot of systems and cylinders. And we changed the travel limits of aileron, flap, rudder, and horizontal stabilizer. But no change has been observed.
flight-controls t-38
edited May 29 at 11:52
Rodrigo de Azevedo
9121 gold badge6 silver badges19 bronze badges
asked May 28 at 11:55
Emrah CeylanEmrah Ceylan
175 bronze badges
$endgroup$
|
show 5 more comments
$begingroup$
I have a problem with a T-38. There is uncommanded roll to the left when the aircraft flies at 250 knots. But as the aircraft speed goes up around 500 knots, the uncommanded roll is now to the right. During 500 knots we could control the plane with 15-20 aileron trims.
What may be the problem?
We have replaced a lot of systems and cylinders. And we changed the travel limits of aileron, flap, rudder, and horizontal stabilizer. But no change has been observed.
flight-controls t-38
edited May 29 at 11:52
Rodrigo de Azevedo
9121 gold badge6 silver badges19 bronze badges
asked May 28 at 11:55
Emrah CeylanEmrah Ceylan
175 bronze badges
$endgroup$
8
$begingroup$
It would probably help a lot if you indicated what aircraft you were referring to. Obviously, at 500 kt IAS, you're probably not talking about a Cessna 150, but there are a lot of aircraft that will hit 500kt.
$endgroup$
– FreeMan
May 28 at 12:08
$begingroup$
Have you inspected the geometry of the wings?
$endgroup$
– ratchet freak
May 28 at 12:19
3
$begingroup$
You may wish to edit to clarify this -- as posted, it reads that you have left at low speed, then left at high speed. If, as I suspect, they're opposite, this is different from the case where they're the same direction.
$endgroup$
– Zeiss Ikon
May 28 at 12:21
$begingroup$
Have you checked the aileron actuating system and associated hydraulic lines?
$endgroup$
– Juan Jimenez
May 28 at 13:06
2
$begingroup$
So both at 250 and at 500 knots the uncommanded roll is to the left?
$endgroup$
– Koyovis
May 28 at 13:24
|
show 5 more comments
$begingroup$
I have a problem with a T-38. There is uncommanded roll to the left when the aircraft flies at 250 knots. But as the aircraft speed goes up around 500 knots, the uncommanded roll is now to the right. During 500 knots we could control the plane with 15-20 aileron trims.
What may be the problem?
We have replaced a lot of systems and cylinders. And we changed the travel limits of aileron, flap, rudder, and horizontal stabilizer. But no change has been observed.
flight-controls t-38
edited May 29 at 11:52
Rodrigo de Azevedo
9121 gold badge6 silver badges19 bronze badges
asked May 28 at 11:55
Emrah CeylanEmrah Ceylan
175 bronze badges
$endgroup$
I have a problem with a T-38. There is uncommanded roll to the left when the aircraft flies at 250 knots. But as the aircraft speed goes up around 500 knots, the uncommanded roll is now to the right. During 500 knots we could control the plane with 15-20 aileron trims.
What may be the problem?
We have replaced a lot of systems and cylinders. And we changed the travel limits of aileron, flap, rudder, and horizontal stabilizer. But no change has been observed.
flight-controls t-38
flight-controls t-38
edited May 29 at 11:52
Rodrigo de Azevedo
9121 gold badge6 silver badges19 bronze badges
asked May 28 at 11:55
Emrah CeylanEmrah Ceylan
175 bronze badges
edited May 29 at 11:52
Rodrigo de Azevedo
9121 gold badge6 silver badges19 bronze badges
asked May 28 at 11:55
Emrah CeylanEmrah Ceylan
175 bronze badges
edited May 29 at 11:52
Rodrigo de Azevedo
9121 gold badge6 silver badges19 bronze badges
edited May 29 at 11:52
Rodrigo de Azevedo
9121 gold badge6 silver badges19 bronze badges
edited May 29 at 11:52
Rodrigo de Azevedo
9121 gold badge6 silver badges19 bronze badges
9121 gold badge6 silver badges19 bronze badges
asked May 28 at 11:55
Emrah CeylanEmrah Ceylan
175 bronze badges
asked May 28 at 11:55
Emrah CeylanEmrah Ceylan
175 bronze badges
asked May 28 at 11:55
Emrah CeylanEmrah Ceylan
175 bronze badges
175 bronze badges
8
$begingroup$
It would probably help a lot if you indicated what aircraft you were referring to. Obviously, at 500 kt IAS, you're probably not talking about a Cessna 150, but there are a lot of aircraft that will hit 500kt.
$endgroup$
– FreeMan
May 28 at 12:08
$begingroup$
Have you inspected the geometry of the wings?
$endgroup$
– ratchet freak
May 28 at 12:19
3
$begingroup$
You may wish to edit to clarify this -- as posted, it reads that you have left at low speed, then left at high speed. If, as I suspect, they're opposite, this is different from the case where they're the same direction.
$endgroup$
– Zeiss Ikon
May 28 at 12:21
$begingroup$
Have you checked the aileron actuating system and associated hydraulic lines?
$endgroup$
– Juan Jimenez
May 28 at 13:06
2
$begingroup$
So both at 250 and at 500 knots the uncommanded roll is to the left?
$endgroup$
– Koyovis
May 28 at 13:24
|
show 5 more comments
8
$begingroup$
It would probably help a lot if you indicated what aircraft you were referring to. Obviously, at 500 kt IAS, you're probably not talking about a Cessna 150, but there are a lot of aircraft that will hit 500kt.
$endgroup$
– FreeMan
May 28 at 12:08
$begingroup$
Have you inspected the geometry of the wings?
$endgroup$
– ratchet freak
May 28 at 12:19
3
$begingroup$
You may wish to edit to clarify this -- as posted, it reads that you have left at low speed, then left at high speed. If, as I suspect, they're opposite, this is different from the case where they're the same direction.
$endgroup$
– Zeiss Ikon
May 28 at 12:21
$begingroup$
Have you checked the aileron actuating system and associated hydraulic lines?
$endgroup$
– Juan Jimenez
May 28 at 13:06
2
$begingroup$
So both at 250 and at 500 knots the uncommanded roll is to the left?
$endgroup$
– Koyovis
May 28 at 13:24
8
8
$begingroup$
It would probably help a lot if you indicated what aircraft you were referring to. Obviously, at 500 kt IAS, you're probably not talking about a Cessna 150, but there are a lot of aircraft that will hit 500kt.
$endgroup$
– FreeMan
May 28 at 12:08
$begingroup$
It would probably help a lot if you indicated what aircraft you were referring to. Obviously, at 500 kt IAS, you're probably not talking about a Cessna 150, but there are a lot of aircraft that will hit 500kt.
$endgroup$
– FreeMan
May 28 at 12:08
$begingroup$
Have you inspected the geometry of the wings?
$endgroup$
– ratchet freak
May 28 at 12:19
$begingroup$
Have you inspected the geometry of the wings?
$endgroup$
– ratchet freak
May 28 at 12:19
3
3
$begingroup$
You may wish to edit to clarify this -- as posted, it reads that you have left at low speed, then left at high speed. If, as I suspect, they're opposite, this is different from the case where they're the same direction.
$endgroup$
– Zeiss Ikon
May 28 at 12:21
$begingroup$
You may wish to edit to clarify this -- as posted, it reads that you have left at low speed, then left at high speed. If, as I suspect, they're opposite, this is different from the case where they're the same direction.
$endgroup$
– Zeiss Ikon
May 28 at 12:21
$begingroup$
Have you checked the aileron actuating system and associated hydraulic lines?
$endgroup$
– Juan Jimenez
May 28 at 13:06
$begingroup$
Have you checked the aileron actuating system and associated hydraulic lines?
$endgroup$
– Juan Jimenez
May 28 at 13:06
2
2
$begingroup$
So both at 250 and at 500 knots the uncommanded roll is to the left?
$endgroup$
– Koyovis
May 28 at 13:24
$begingroup$
So both at 250 and at 500 knots the uncommanded roll is to the left?
$endgroup$
– Koyovis
May 28 at 13:24
|
show 5 more comments
4 Answers
4
active
oldest
votes
$begingroup$
I once went on-site to troubleshoot an airliner with an uncommanded roll problem. The operator had rigged this and rigged that and were in the process of ordering new aileron power control units, pretty much out of desperation. I asked about the trim actuator, which they had replaced with a known good unit off another aircraft, making them think that couldn't be the problem. I centered the trim and went to look at the position of the rig pin holes in the aileron control circuit. They were mis-aligned.
The trim actuator on this airplane was an electric linear type with an internal Linear Variable Displacement Transducer (LVDT), that supplied the position signal to the cockpit trim indicator (or EICAS in this case), that was "dithering", that is, the signal was drifting around. When you thought the trim was centered, it was actually offset, and this error would randomly change as the actuator was moved. On the original airplane the actuator was installed on, the dithering wasn't enough to cause a snag to be raised by the flight crew so its internal problem went undetected.
The variations in roll you saw at speed may be some other phenomenon, or it just could have been coincidental variations in the trim indication on that flight.
So, if it was me, the trim system itself would be an item to cross off the list before proceeding to more desperate measures. Do a thorough functional test of the trim system and its indication, and also look for things like backlash within the actuator itself or in the linkage.
answered May 28 at 12:51
John KJohn K
44.5k1 gold badge83 silver badges154 bronze badges
$endgroup$
$begingroup$
It sounds like roll trim is a function of speed, not a random dither.
$endgroup$
– Koyovis
May 28 at 13:26
6
$begingroup$
Maybe, maybe not. You would have to go out and do a carefully documented series of tests to establish what is going on precisely. Was the shift with speed a direct, repeatable condition or just a one time coincidence. We don't have all the information and are just spitballing here. Golden rule of troubleshooting: eliminate the easy/cheap things first.
$endgroup$
– John K
May 28 at 13:38
add a comment
|
$begingroup$
If this were a model aircraft with a wide speed range (like, say, a hand launch glider), I'd expect this to be a cross-trim problem. Generally, the rudder will have more authority at lower speeds, while aileron will gain authority as speed increases.
Based on that, I'd suggest verifying the rigging of the airframe; look for a fin, rudder, or rudder trim that's generating yaw in the direction of your lower speed uncommanded roll (yaw will produce roll due to whatever mechanism provides roll stability). The aileron trim that offsets that uncommanded yaw will overpower it as speed increases, producing your uncommanded roll in the opposite direction.
answered May 28 at 12:18
Zeiss IkonZeiss Ikon
5,1149 silver badges23 bronze badges
$endgroup$
$begingroup$
Good answer but if it were a model, I'd suspect that something was broken or loose and moving under the increased aerodynamic load of high speed. Or an incorrect thrust line.
$endgroup$
– Robin Bennett
May 29 at 8:40
$begingroup$
@RobinBennett A thrust line problem is tied to power setting; it'll happen during takeoff/launch even more than at high speed (because less aero forces on the surfaces at low speed and high power). Broken or loose will be erratic.
$endgroup$
– Zeiss Ikon
May 29 at 10:55
add a comment
|
$begingroup$
If the flight control is a hydraulic system, have you changed the fluid recently, if yes you need to purge the system for air bubbles, otherwise you need to check the fluid quality for impurity.
answered May 28 at 12:49
user40476user40476
1,2935 silver badges24 bronze badges
$endgroup$
add a comment
|
$begingroup$
http://www.aiaahouston.org/Horizons/ATS2019-Presentation-SS-Tang.pdf
This presentation was given in AIAA Houston Section Annual Technical Symposium (ATS) at NASA Johnson Space Center, Gilruth Center. A new discovered root cause for uncommanded roll, pitch and yaw was given.
A technical paper was presented and a live demonstration was shown in the 2019 AIAA AVIATION FORUM and EXPOSITION. A Youtube video shows this phenomenon.
Hope this may help you to understand the uncommanded roll. Actually, it was not "uncommanded". It was indirectly commanded.
answered Jun 21 at 16:30
Steve S. TangSteve S. Tang
1
$endgroup$
add a comment
|
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4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
I once went on-site to troubleshoot an airliner with an uncommanded roll problem. The operator had rigged this and rigged that and were in the process of ordering new aileron power control units, pretty much out of desperation. I asked about the trim actuator, which they had replaced with a known good unit off another aircraft, making them think that couldn't be the problem. I centered the trim and went to look at the position of the rig pin holes in the aileron control circuit. They were mis-aligned.
The trim actuator on this airplane was an electric linear type with an internal Linear Variable Displacement Transducer (LVDT), that supplied the position signal to the cockpit trim indicator (or EICAS in this case), that was "dithering", that is, the signal was drifting around. When you thought the trim was centered, it was actually offset, and this error would randomly change as the actuator was moved. On the original airplane the actuator was installed on, the dithering wasn't enough to cause a snag to be raised by the flight crew so its internal problem went undetected.
The variations in roll you saw at speed may be some other phenomenon, or it just could have been coincidental variations in the trim indication on that flight.
So, if it was me, the trim system itself would be an item to cross off the list before proceeding to more desperate measures. Do a thorough functional test of the trim system and its indication, and also look for things like backlash within the actuator itself or in the linkage.
answered May 28 at 12:51
John KJohn K
44.5k1 gold badge83 silver badges154 bronze badges
$endgroup$
$begingroup$
It sounds like roll trim is a function of speed, not a random dither.
$endgroup$
– Koyovis
May 28 at 13:26
6
$begingroup$
Maybe, maybe not. You would have to go out and do a carefully documented series of tests to establish what is going on precisely. Was the shift with speed a direct, repeatable condition or just a one time coincidence. We don't have all the information and are just spitballing here. Golden rule of troubleshooting: eliminate the easy/cheap things first.
$endgroup$
– John K
May 28 at 13:38
add a comment
|
$begingroup$
I once went on-site to troubleshoot an airliner with an uncommanded roll problem. The operator had rigged this and rigged that and were in the process of ordering new aileron power control units, pretty much out of desperation. I asked about the trim actuator, which they had replaced with a known good unit off another aircraft, making them think that couldn't be the problem. I centered the trim and went to look at the position of the rig pin holes in the aileron control circuit. They were mis-aligned.
The trim actuator on this airplane was an electric linear type with an internal Linear Variable Displacement Transducer (LVDT), that supplied the position signal to the cockpit trim indicator (or EICAS in this case), that was "dithering", that is, the signal was drifting around. When you thought the trim was centered, it was actually offset, and this error would randomly change as the actuator was moved. On the original airplane the actuator was installed on, the dithering wasn't enough to cause a snag to be raised by the flight crew so its internal problem went undetected.
The variations in roll you saw at speed may be some other phenomenon, or it just could have been coincidental variations in the trim indication on that flight.
So, if it was me, the trim system itself would be an item to cross off the list before proceeding to more desperate measures. Do a thorough functional test of the trim system and its indication, and also look for things like backlash within the actuator itself or in the linkage.
answered May 28 at 12:51
John KJohn K
44.5k1 gold badge83 silver badges154 bronze badges
$endgroup$
$begingroup$
It sounds like roll trim is a function of speed, not a random dither.
$endgroup$
– Koyovis
May 28 at 13:26
6
$begingroup$
Maybe, maybe not. You would have to go out and do a carefully documented series of tests to establish what is going on precisely. Was the shift with speed a direct, repeatable condition or just a one time coincidence. We don't have all the information and are just spitballing here. Golden rule of troubleshooting: eliminate the easy/cheap things first.
$endgroup$
– John K
May 28 at 13:38
add a comment
|
$begingroup$
I once went on-site to troubleshoot an airliner with an uncommanded roll problem. The operator had rigged this and rigged that and were in the process of ordering new aileron power control units, pretty much out of desperation. I asked about the trim actuator, which they had replaced with a known good unit off another aircraft, making them think that couldn't be the problem. I centered the trim and went to look at the position of the rig pin holes in the aileron control circuit. They were mis-aligned.
The trim actuator on this airplane was an electric linear type with an internal Linear Variable Displacement Transducer (LVDT), that supplied the position signal to the cockpit trim indicator (or EICAS in this case), that was "dithering", that is, the signal was drifting around. When you thought the trim was centered, it was actually offset, and this error would randomly change as the actuator was moved. On the original airplane the actuator was installed on, the dithering wasn't enough to cause a snag to be raised by the flight crew so its internal problem went undetected.
The variations in roll you saw at speed may be some other phenomenon, or it just could have been coincidental variations in the trim indication on that flight.
So, if it was me, the trim system itself would be an item to cross off the list before proceeding to more desperate measures. Do a thorough functional test of the trim system and its indication, and also look for things like backlash within the actuator itself or in the linkage.
answered May 28 at 12:51
John KJohn K
44.5k1 gold badge83 silver badges154 bronze badges
$endgroup$
I once went on-site to troubleshoot an airliner with an uncommanded roll problem. The operator had rigged this and rigged that and were in the process of ordering new aileron power control units, pretty much out of desperation. I asked about the trim actuator, which they had replaced with a known good unit off another aircraft, making them think that couldn't be the problem. I centered the trim and went to look at the position of the rig pin holes in the aileron control circuit. They were mis-aligned.
The trim actuator on this airplane was an electric linear type with an internal Linear Variable Displacement Transducer (LVDT), that supplied the position signal to the cockpit trim indicator (or EICAS in this case), that was "dithering", that is, the signal was drifting around. When you thought the trim was centered, it was actually offset, and this error would randomly change as the actuator was moved. On the original airplane the actuator was installed on, the dithering wasn't enough to cause a snag to be raised by the flight crew so its internal problem went undetected.
The variations in roll you saw at speed may be some other phenomenon, or it just could have been coincidental variations in the trim indication on that flight.
So, if it was me, the trim system itself would be an item to cross off the list before proceeding to more desperate measures. Do a thorough functional test of the trim system and its indication, and also look for things like backlash within the actuator itself or in the linkage.
answered May 28 at 12:51
John KJohn K
44.5k1 gold badge83 silver badges154 bronze badges
answered May 28 at 12:51
John KJohn K
44.5k1 gold badge83 silver badges154 bronze badges
answered May 28 at 12:51
John KJohn K
44.5k1 gold badge83 silver badges154 bronze badges
answered May 28 at 12:51
John KJohn K
44.5k1 gold badge83 silver badges154 bronze badges
44.5k1 gold badge83 silver badges154 bronze badges
$begingroup$
It sounds like roll trim is a function of speed, not a random dither.
$endgroup$
– Koyovis
May 28 at 13:26
6
$begingroup$
Maybe, maybe not. You would have to go out and do a carefully documented series of tests to establish what is going on precisely. Was the shift with speed a direct, repeatable condition or just a one time coincidence. We don't have all the information and are just spitballing here. Golden rule of troubleshooting: eliminate the easy/cheap things first.
$endgroup$
– John K
May 28 at 13:38
add a comment
|
$begingroup$
It sounds like roll trim is a function of speed, not a random dither.
$endgroup$
– Koyovis
May 28 at 13:26
6
$begingroup$
Maybe, maybe not. You would have to go out and do a carefully documented series of tests to establish what is going on precisely. Was the shift with speed a direct, repeatable condition or just a one time coincidence. We don't have all the information and are just spitballing here. Golden rule of troubleshooting: eliminate the easy/cheap things first.
$endgroup$
– John K
May 28 at 13:38
$begingroup$
It sounds like roll trim is a function of speed, not a random dither.
$endgroup$
– Koyovis
May 28 at 13:26
$begingroup$
It sounds like roll trim is a function of speed, not a random dither.
$endgroup$
– Koyovis
May 28 at 13:26
6
6
$begingroup$
Maybe, maybe not. You would have to go out and do a carefully documented series of tests to establish what is going on precisely. Was the shift with speed a direct, repeatable condition or just a one time coincidence. We don't have all the information and are just spitballing here. Golden rule of troubleshooting: eliminate the easy/cheap things first.
$endgroup$
– John K
May 28 at 13:38
$begingroup$
Maybe, maybe not. You would have to go out and do a carefully documented series of tests to establish what is going on precisely. Was the shift with speed a direct, repeatable condition or just a one time coincidence. We don't have all the information and are just spitballing here. Golden rule of troubleshooting: eliminate the easy/cheap things first.
$endgroup$
– John K
May 28 at 13:38
add a comment
|
$begingroup$
If this were a model aircraft with a wide speed range (like, say, a hand launch glider), I'd expect this to be a cross-trim problem. Generally, the rudder will have more authority at lower speeds, while aileron will gain authority as speed increases.
Based on that, I'd suggest verifying the rigging of the airframe; look for a fin, rudder, or rudder trim that's generating yaw in the direction of your lower speed uncommanded roll (yaw will produce roll due to whatever mechanism provides roll stability). The aileron trim that offsets that uncommanded yaw will overpower it as speed increases, producing your uncommanded roll in the opposite direction.
answered May 28 at 12:18
Zeiss IkonZeiss Ikon
5,1149 silver badges23 bronze badges
$endgroup$
$begingroup$
Good answer but if it were a model, I'd suspect that something was broken or loose and moving under the increased aerodynamic load of high speed. Or an incorrect thrust line.
$endgroup$
– Robin Bennett
May 29 at 8:40
$begingroup$
@RobinBennett A thrust line problem is tied to power setting; it'll happen during takeoff/launch even more than at high speed (because less aero forces on the surfaces at low speed and high power). Broken or loose will be erratic.
$endgroup$
– Zeiss Ikon
May 29 at 10:55
add a comment
|
$begingroup$
If this were a model aircraft with a wide speed range (like, say, a hand launch glider), I'd expect this to be a cross-trim problem. Generally, the rudder will have more authority at lower speeds, while aileron will gain authority as speed increases.
Based on that, I'd suggest verifying the rigging of the airframe; look for a fin, rudder, or rudder trim that's generating yaw in the direction of your lower speed uncommanded roll (yaw will produce roll due to whatever mechanism provides roll stability). The aileron trim that offsets that uncommanded yaw will overpower it as speed increases, producing your uncommanded roll in the opposite direction.
answered May 28 at 12:18
Zeiss IkonZeiss Ikon
5,1149 silver badges23 bronze badges
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Good answer but if it were a model, I'd suspect that something was broken or loose and moving under the increased aerodynamic load of high speed. Or an incorrect thrust line.
$endgroup$
– Robin Bennett
May 29 at 8:40
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@RobinBennett A thrust line problem is tied to power setting; it'll happen during takeoff/launch even more than at high speed (because less aero forces on the surfaces at low speed and high power). Broken or loose will be erratic.
$endgroup$
– Zeiss Ikon
May 29 at 10:55
add a comment
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If this were a model aircraft with a wide speed range (like, say, a hand launch glider), I'd expect this to be a cross-trim problem. Generally, the rudder will have more authority at lower speeds, while aileron will gain authority as speed increases.
Based on that, I'd suggest verifying the rigging of the airframe; look for a fin, rudder, or rudder trim that's generating yaw in the direction of your lower speed uncommanded roll (yaw will produce roll due to whatever mechanism provides roll stability). The aileron trim that offsets that uncommanded yaw will overpower it as speed increases, producing your uncommanded roll in the opposite direction.
answered May 28 at 12:18
Zeiss IkonZeiss Ikon
5,1149 silver badges23 bronze badges
$endgroup$
If this were a model aircraft with a wide speed range (like, say, a hand launch glider), I'd expect this to be a cross-trim problem. Generally, the rudder will have more authority at lower speeds, while aileron will gain authority as speed increases.
Based on that, I'd suggest verifying the rigging of the airframe; look for a fin, rudder, or rudder trim that's generating yaw in the direction of your lower speed uncommanded roll (yaw will produce roll due to whatever mechanism provides roll stability). The aileron trim that offsets that uncommanded yaw will overpower it as speed increases, producing your uncommanded roll in the opposite direction.
answered May 28 at 12:18
Zeiss IkonZeiss Ikon
5,1149 silver badges23 bronze badges
answered May 28 at 12:18
Zeiss IkonZeiss Ikon
5,1149 silver badges23 bronze badges
answered May 28 at 12:18
Zeiss IkonZeiss Ikon
5,1149 silver badges23 bronze badges
answered May 28 at 12:18
Zeiss IkonZeiss Ikon
5,1149 silver badges23 bronze badges
5,1149 silver badges23 bronze badges
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Good answer but if it were a model, I'd suspect that something was broken or loose and moving under the increased aerodynamic load of high speed. Or an incorrect thrust line.
$endgroup$
– Robin Bennett
May 29 at 8:40
$begingroup$
@RobinBennett A thrust line problem is tied to power setting; it'll happen during takeoff/launch even more than at high speed (because less aero forces on the surfaces at low speed and high power). Broken or loose will be erratic.
$endgroup$
– Zeiss Ikon
May 29 at 10:55
add a comment
|
$begingroup$
Good answer but if it were a model, I'd suspect that something was broken or loose and moving under the increased aerodynamic load of high speed. Or an incorrect thrust line.
$endgroup$
– Robin Bennett
May 29 at 8:40
$begingroup$
@RobinBennett A thrust line problem is tied to power setting; it'll happen during takeoff/launch even more than at high speed (because less aero forces on the surfaces at low speed and high power). Broken or loose will be erratic.
$endgroup$
– Zeiss Ikon
May 29 at 10:55
$begingroup$
Good answer but if it were a model, I'd suspect that something was broken or loose and moving under the increased aerodynamic load of high speed. Or an incorrect thrust line.
$endgroup$
– Robin Bennett
May 29 at 8:40
$begingroup$
Good answer but if it were a model, I'd suspect that something was broken or loose and moving under the increased aerodynamic load of high speed. Or an incorrect thrust line.
$endgroup$
– Robin Bennett
May 29 at 8:40
$begingroup$
@RobinBennett A thrust line problem is tied to power setting; it'll happen during takeoff/launch even more than at high speed (because less aero forces on the surfaces at low speed and high power). Broken or loose will be erratic.
$endgroup$
– Zeiss Ikon
May 29 at 10:55
$begingroup$
@RobinBennett A thrust line problem is tied to power setting; it'll happen during takeoff/launch even more than at high speed (because less aero forces on the surfaces at low speed and high power). Broken or loose will be erratic.
$endgroup$
– Zeiss Ikon
May 29 at 10:55
add a comment
|
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If the flight control is a hydraulic system, have you changed the fluid recently, if yes you need to purge the system for air bubbles, otherwise you need to check the fluid quality for impurity.
answered May 28 at 12:49
user40476user40476
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If the flight control is a hydraulic system, have you changed the fluid recently, if yes you need to purge the system for air bubbles, otherwise you need to check the fluid quality for impurity.
answered May 28 at 12:49
user40476user40476
1,2935 silver badges24 bronze badges
$endgroup$
add a comment
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$begingroup$
If the flight control is a hydraulic system, have you changed the fluid recently, if yes you need to purge the system for air bubbles, otherwise you need to check the fluid quality for impurity.
answered May 28 at 12:49
user40476user40476
1,2935 silver badges24 bronze badges
$endgroup$
If the flight control is a hydraulic system, have you changed the fluid recently, if yes you need to purge the system for air bubbles, otherwise you need to check the fluid quality for impurity.
answered May 28 at 12:49
user40476user40476
1,2935 silver badges24 bronze badges
answered May 28 at 12:49
user40476user40476
1,2935 silver badges24 bronze badges
answered May 28 at 12:49
user40476user40476
1,2935 silver badges24 bronze badges
answered May 28 at 12:49
user40476user40476
1,2935 silver badges24 bronze badges
1,2935 silver badges24 bronze badges
add a comment
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add a comment
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http://www.aiaahouston.org/Horizons/ATS2019-Presentation-SS-Tang.pdf
This presentation was given in AIAA Houston Section Annual Technical Symposium (ATS) at NASA Johnson Space Center, Gilruth Center. A new discovered root cause for uncommanded roll, pitch and yaw was given.
A technical paper was presented and a live demonstration was shown in the 2019 AIAA AVIATION FORUM and EXPOSITION. A Youtube video shows this phenomenon.
Hope this may help you to understand the uncommanded roll. Actually, it was not "uncommanded". It was indirectly commanded.
answered Jun 21 at 16:30
Steve S. TangSteve S. Tang
1
$endgroup$
add a comment
|
$begingroup$
http://www.aiaahouston.org/Horizons/ATS2019-Presentation-SS-Tang.pdf
This presentation was given in AIAA Houston Section Annual Technical Symposium (ATS) at NASA Johnson Space Center, Gilruth Center. A new discovered root cause for uncommanded roll, pitch and yaw was given.
A technical paper was presented and a live demonstration was shown in the 2019 AIAA AVIATION FORUM and EXPOSITION. A Youtube video shows this phenomenon.
Hope this may help you to understand the uncommanded roll. Actually, it was not "uncommanded". It was indirectly commanded.
answered Jun 21 at 16:30
Steve S. TangSteve S. Tang
1
$endgroup$
add a comment
|
$begingroup$
http://www.aiaahouston.org/Horizons/ATS2019-Presentation-SS-Tang.pdf
This presentation was given in AIAA Houston Section Annual Technical Symposium (ATS) at NASA Johnson Space Center, Gilruth Center. A new discovered root cause for uncommanded roll, pitch and yaw was given.
A technical paper was presented and a live demonstration was shown in the 2019 AIAA AVIATION FORUM and EXPOSITION. A Youtube video shows this phenomenon.
Hope this may help you to understand the uncommanded roll. Actually, it was not "uncommanded". It was indirectly commanded.
answered Jun 21 at 16:30
Steve S. TangSteve S. Tang
1
$endgroup$
http://www.aiaahouston.org/Horizons/ATS2019-Presentation-SS-Tang.pdf
This presentation was given in AIAA Houston Section Annual Technical Symposium (ATS) at NASA Johnson Space Center, Gilruth Center. A new discovered root cause for uncommanded roll, pitch and yaw was given.
A technical paper was presented and a live demonstration was shown in the 2019 AIAA AVIATION FORUM and EXPOSITION. A Youtube video shows this phenomenon.
Hope this may help you to understand the uncommanded roll. Actually, it was not "uncommanded". It was indirectly commanded.
answered Jun 21 at 16:30
Steve S. TangSteve S. Tang
1
answered Jun 21 at 16:30
Steve S. TangSteve S. Tang
1
answered Jun 21 at 16:30
Steve S. TangSteve S. Tang
1
answered Jun 21 at 16:30
Steve S. TangSteve S. Tang
1
1
add a comment
|
add a comment
|
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It would probably help a lot if you indicated what aircraft you were referring to. Obviously, at 500 kt IAS, you're probably not talking about a Cessna 150, but there are a lot of aircraft that will hit 500kt.
$endgroup$
– FreeMan
May 28 at 12:08
$begingroup$
Have you inspected the geometry of the wings?
$endgroup$
– ratchet freak
May 28 at 12:19
3
$begingroup$
You may wish to edit to clarify this -- as posted, it reads that you have left at low speed, then left at high speed. If, as I suspect, they're opposite, this is different from the case where they're the same direction.
$endgroup$
– Zeiss Ikon
May 28 at 12:21
$begingroup$
Have you checked the aileron actuating system and associated hydraulic lines?
$endgroup$
– Juan Jimenez
May 28 at 13:06
2
$begingroup$
So both at 250 and at 500 knots the uncommanded roll is to the left?
$endgroup$
– Koyovis
May 28 at 13:24