4 ms·

How would you accurately simulate the force needed to turn the trim wheel under aerodynamic loads that vary with elevator position? It sounds like a very tricky

by tlb 7y ago

How would you accurately simulate the force needed to turn the trim wheel under aerodynamic loads that vary with elevator position? It sounds like a very tricky mechanical setup.

krallja 7y ago
Brakes, or a strong motor.
- jayalpha 7y ago
  crank handle with a translation?
- dbcurtis 7y ago
  The way I would approach it (based on mechantronics I have done for robots) is to back up the control wheel with an encoded motor. (Position/rotation encoder on the tail shaft.) The encoder will give you wheel position, the motor allows you to apply arbitrary torque to the wheel to simulate the feedback forces felt by the pilot. Typically, that would be done by measuring motor current and writing a control loop that controlled for target wheel position (based on encoder) and target maximum motor current (as a proxy for torque). Then the simulator would give out the simulated results of wheel position and torque, which the control loop would attempt to follow with its control law. Alternatively, you could put an actual torque sensor between the motor and the control wheel, which might buy you some accuracy at considerably more expense. For a flight simulator, expense is unlikely to be an issue -- I tend not to have that luxury, and typically don't need that much accuracy anyway. These kind of control systems are all over modern aircraft, much less simulators. Any new grad control systems engineer should be able to knock something like this out.
  - blattimwind 7y ago
    > The way I would approach it (based on mechantronics I have done for robots) is to back up the control wheel with an encoded motor. (Position/rotation encoder on the tail shaft.) The encoder will give you wheel position, the motor allows you to apply arbitrary torque to the wheel to simulate the feedback forces felt by the pilot. Typically, that would be done by measuring motor current and writing a control loop that controlled for target wheel position (based on encoder) and target maximum motor current (as a proxy for torque). Then the simulator would give out the simulated results of wheel position and torque, which the control loop would attempt to follow with its control law. Or you just buy a COTS servo that does all that for you. Just saying, hardly a need to reinvent these particular wheels...
    - dbcurtis 7y ago
      Yeah, good point. I'm sure there are servos that have the required specs. I'm just not in the habit of looking at catalogs where the prices are that high :) Maybe I should switch to building flight simulators so that I can order the good stuff :)
      - rasz 7y ago
        racing sim guys already figured it out http://opensimwheel.wikidot.com/ http://opensimwheel.wikidot.com/
mikeash 7y ago
The mechanical part seems easy enough. Tricky to calculate the appropriate force, but I’m sure the aerodynamics people are more than up to the task.
ackfoo 7y ago
No need to do so. The aerodynamic forces on the manual trim wheel on Ethiopia 302 were excessive because they were flying about 50kts overspeed. The simulator is not supposed to teach what it feels like to fly the plane when it is so far outside of its certified flight envelope that even test pilots have not been there. Instead, the simulator is supposed to teach you how to fly the plane and respond to emergencies so that the aircraft does not depart from the flight envelope to the point where a single failure or control input will cause a crash. Simulating the sensations of flying the 737 Max upside-down would also require a tricky mechanical setup, but no one feels that such a thing is necessary or appropriate. Natalie Kitroeff is the chief anti-Boeing cheerleader at NYT. She has a bachelor in International Affairs from Princeton. I can see no evidence that she has a technical degree, or enough understanding of aerodynamics or any other technical matter to comment on whether someone fixed the drip in her kitchen sink properly. She is the poster child for post-facts non-technical journalism. The facts of Ethiopian 302 are abundantly clear from the preliminary report: a single component, the AOA sensor, failed causing a common and easily-remedied runaway electric trim condition for which there was a clear and comprehensive memory checklist that, had it been followed, would have resolved this problem without even the slightest inconvenience to passengers. The fact is, the pilots did not know how to fly the plane manually. The CVR indicates that they had poor cockpit resource management. Their training was hopelessly inadequate. The right seat pilot arrived in the 737 Max type with 98 hours total flight time. They turned the inevitable failure of a single component into a disaster. Natalie Kitroeff is either a clickbait journalist with no understanding or regard for the simple facts of the matter, or else she is part of a purposeful effort to undermine Boeing, create chaos, and destabilize America and the West. The facts are clear and unequivocal. All the trolls on here should read the preliminary report. Take a few minutes to look at the data from the FDR. Then put away the torches and pitchforks and stop supporting the fact-free idiots attacking what is almost the last company that actually makes stuff in the USA.
deleted 7y ago
[deleted]
matthewdgreen 7y ago
This previous story (https://news.ycombinator.com/item?id=19902068 https://news.ycombinator.com/item?id=19902068) implies that the simulators try to simulate the forces, and in a particular simulation even the simulator crew wasn't able to move the wheel: "What the U.S. crew found was eye-opening. Keeping the aircraft level required significant aft-column pressure by the captain, and aerodynamic forces prevented the first officer from moving the trim wheel a full turn. They resorted to a little-known procedure to regain control."
- A2017U1 7y ago
  So how accurate is it?
RockyMcNuts 7y ago
If pilots are trained in how to recognize the emergency and what to do, and they are instructed that in an actual emergency the forces on the trim wheel (presumably what they are referring to) will vary, they will respond appropriately. Simulators can't exactly replicate extreme conditions, upsets and whatnot. If you're training for trim runaway it would be helpful to simulate the full forces but I'm not sure if it reflects a worrying lack of preparedness. The most important fix is that the MCAS should not be able to put the trim in an extreme position, the fact that it did is quite worrying. This particular article seems much ado about very little.
- karmelapple 7y ago
  Did you see this previous article? https://news.ycombinator.com/item?id=19902068 https://news.ycombinator.com/item?id=19902068 There seems to be massive issues with the force required.
  - RockyMcNuts 7y ago
    That seems like a different issue. Root problem seems to be: Software puts trim in an extreme position. It should never do that. Aviation Week article: if you are in an electric trim runaway, you need to turn off electric trim, then in order to turn the trim wheel manually, you need to nose down to reduce aerodynamic forces. Seems necessary to train for which it suggests was not the case. NYT article: Simulator doesn't simulate the forces on the trim wheel correctly (although Aviation Week suggests they were able to simulate something useful) The NYT article really seems like the least of the problems.
ctchocula 7y ago
Mentour Pilot has a video where he does that exact simulation for a 737NG flight simulator in order to show how difficult it is to trim manually [1]. [1] https://www.youtube.com/watch?v=aoNOVlxJmow https://www.youtube.com/watch?v=aoNOVlxJmow

by tlb 7y ago

How would you accurately simulate the force needed to turn the trim wheel under aerodynamic loads that vary with elevator position? It sounds like a very tricky mechanical setup.

krallja 7y ago

Brakes, or a strong motor.

jayalpha 7y ago
crank handle with a translation?
dbcurtis 7y ago
The way I would approach it (based on mechantronics I have done for robots) is to back up the control wheel with an encoded motor. (Position/rotation encoder on the tail shaft.) The encoder will give you wheel position, the motor allows you to apply arbitrary torque to the wheel to simulate the feedback forces felt by the pilot. Typically, that would be done by measuring motor current and writing a control loop that controlled for target wheel position (based on encoder) and target maximum motor current (as a proxy for torque). Then the simulator would give out the simulated results of wheel position and torque, which the control loop would attempt to follow with its control law. Alternatively, you could put an actual torque sensor between the motor and the control wheel, which might buy you some accuracy at considerably more expense. For a flight simulator, expense is unlikely to be an issue -- I tend not to have that luxury, and typically don't need that much accuracy anyway. These kind of control systems are all over modern aircraft, much less simulators. Any new grad control systems engineer should be able to knock something like this out.
- blattimwind 7y ago
  > The way I would approach it (based on mechantronics I have done for robots) is to back up the control wheel with an encoded motor. (Position/rotation encoder on the tail shaft.) The encoder will give you wheel position, the motor allows you to apply arbitrary torque to the wheel to simulate the feedback forces felt by the pilot. Typically, that would be done by measuring motor current and writing a control loop that controlled for target wheel position (based on encoder) and target maximum motor current (as a proxy for torque). Then the simulator would give out the simulated results of wheel position and torque, which the control loop would attempt to follow with its control law. Or you just buy a COTS servo that does all that for you. Just saying, hardly a need to reinvent these particular wheels...
  - dbcurtis 7y ago
    Yeah, good point. I'm sure there are servos that have the required specs. I'm just not in the habit of looking at catalogs where the prices are that high :) Maybe I should switch to building flight simulators so that I can order the good stuff :)
    - rasz 7y ago
      racing sim guys already figured it out http://opensimwheel.wikidot.com/ http://opensimwheel.wikidot.com/

mikeash 7y ago

The mechanical part seems easy enough. Tricky to calculate the appropriate force, but I’m sure the aerodynamics people are more than up to the task.

ackfoo 7y ago

No need to do so. The aerodynamic forces on the manual trim wheel on Ethiopia 302 were excessive because they were flying about 50kts overspeed. The simulator is not supposed to teach what it feels like to fly the plane when it is so far outside of its certified flight envelope that even test pilots have not been there. Instead, the simulator is supposed to teach you how to fly the plane and respond to emergencies so that the aircraft does not depart from the flight envelope to the point where a single failure or control input will cause a crash. Simulating the sensations of flying the 737 Max upside-down would also require a tricky mechanical setup, but no one feels that such a thing is necessary or appropriate. Natalie Kitroeff is the chief anti-Boeing cheerleader at NYT. She has a bachelor in International Affairs from Princeton. I can see no evidence that she has a technical degree, or enough understanding of aerodynamics or any other technical matter to comment on whether someone fixed the drip in her kitchen sink properly. She is the poster child for post-facts non-technical journalism. The facts of Ethiopian 302 are abundantly clear from the preliminary report: a single component, the AOA sensor, failed causing a common and easily-remedied runaway electric trim condition for which there was a clear and comprehensive memory checklist that, had it been followed, would have resolved this problem without even the slightest inconvenience to passengers. The fact is, the pilots did not know how to fly the plane manually. The CVR indicates that they had poor cockpit resource management. Their training was hopelessly inadequate. The right seat pilot arrived in the 737 Max type with 98 hours total flight time. They turned the inevitable failure of a single component into a disaster. Natalie Kitroeff is either a clickbait journalist with no understanding or regard for the simple facts of the matter, or else she is part of a purposeful effort to undermine Boeing, create chaos, and destabilize America and the West. The facts are clear and unequivocal. All the trolls on here should read the preliminary report. Take a few minutes to look at the data from the FDR. Then put away the torches and pitchforks and stop supporting the fact-free idiots attacking what is almost the last company that actually makes stuff in the USA.

deleted 7y ago

[deleted]

matthewdgreen 7y ago

This previous story (https://news.ycombinator.com/item?id=19902068 https://news.ycombinator.com/item?id=19902068) implies that the simulators try to simulate the forces, and in a particular simulation even the simulator crew wasn't able to move the wheel: "What the U.S. crew found was eye-opening. Keeping the aircraft level required significant aft-column pressure by the captain, and aerodynamic forces prevented the first officer from moving the trim wheel a full turn. They resorted to a little-known procedure to regain control."

A2017U1 7y ago
So how accurate is it?

RockyMcNuts 7y ago

If pilots are trained in how to recognize the emergency and what to do, and they are instructed that in an actual emergency the forces on the trim wheel (presumably what they are referring to) will vary, they will respond appropriately. Simulators can't exactly replicate extreme conditions, upsets and whatnot. If you're training for trim runaway it would be helpful to simulate the full forces but I'm not sure if it reflects a worrying lack of preparedness. The most important fix is that the MCAS should not be able to put the trim in an extreme position, the fact that it did is quite worrying. This particular article seems much ado about very little.

karmelapple 7y ago
Did you see this previous article? https://news.ycombinator.com/item?id=19902068 https://news.ycombinator.com/item?id=19902068 There seems to be massive issues with the force required.
- RockyMcNuts 7y ago
  That seems like a different issue. Root problem seems to be: Software puts trim in an extreme position. It should never do that. Aviation Week article: if you are in an electric trim runaway, you need to turn off electric trim, then in order to turn the trim wheel manually, you need to nose down to reduce aerodynamic forces. Seems necessary to train for which it suggests was not the case. NYT article: Simulator doesn't simulate the forces on the trim wheel correctly (although Aviation Week suggests they were able to simulate something useful) The NYT article really seems like the least of the problems.

ctchocula 7y ago

Mentour Pilot has a video where he does that exact simulation for a 737NG flight simulator in order to show how difficult it is to trim manually [1]. [1] https://www.youtube.com/watch?v=aoNOVlxJmow https://www.youtube.com/watch?v=aoNOVlxJmow