Bell 407 Force Trim only Resets Trim to Center

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Are you using Developer Mode or made changes in it?

No

Have you disabled/removed all your mods and addons?

Yes

Brief description of the issue:

The ā€œForce Trimā€ function was mapped to the ā€œSET ROTOR LONGITUDINAL TRIMā€ axis. When trimming the helicopter forward or backward (via other Rotor Trim assignments) it moves the Rotor Trim as expected. But when the ā€œForce Trimā€ button is pressed, it only resets the trim to neutral. In-flight this causes a sudden jolt because the trim has moved very quickly to the center.

Either the name of the Assignment is wrong/misleading or the function is implemented wrongly. Unless I understand the assignment wrong.

Also if the joystick axis is indeed the ā€œForce Trimā€ We also expect that the cyclic animation should also be frozen while holding in the Force Trim button. So Cyclic in Model freezes while I move my joystick to a different position.

Provide Screenshot(s)/video(s) of the issue encountered:

No image available. The trim is centered when pressing the button assigned.

Detailed steps to reproduce the issue encountered:

Setup joystick as in this post: Bell 407 - #155 by BenderS92

Then trim the helicopter with the Longitudinal Rotor trim (up or down)
Press the button assigned and observe that the Trim merely centers or resets. In-flight it causes an abrupt movement (intensity is dependent on Airspeed and distance from the center)

PC specs and/or peripheral set up if relevant:

Build Version # when you first started experiencing this issue:

1.29.28.0


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Do you have the same issue if you follow the OPā€™s steps to reproduce it?

Provide extra information to complete the original description of the issue:

If relevant, provide additional screenshots/video:

Do you have the same issue if you follow the OPā€™s steps to reproduce it?

Exactly the same issue.

Provide extra information to complete the original description of the issue:

If relevant, provide additional screenshots/video:

Do you have the same issue if you follow the OPā€™s steps to reproduce it?

Same behavior occurs

Provide extra information to complete the original description of the issue:

Perhaps was it build in-sim, with in mind to be RESET ROTOR LONGITUDINAL TRIM rather than SET ROTOR LONGITUDINAL TRIM ?

If relevant, provide additional screenshots/video:

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Hello @BenderS92

Please consider updating your topic title as it does not fully explain what the issue is about.

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Do you have the same issue if you follow the OPā€™s steps to reproduce it?

Yes

Provide extra information to complete the original description of the issue:

Also tested without additional Yoke & Throttle Quads plugged in. Stick/Rudder Pedals only.
Engaging Force Trim using SET ROTOR LONGITUDINAL TRIM results in trim reset to zero.

If relevant, provide additional screenshots/video:

n/a

Do you have the same issue if you follow the OPā€™s steps to reproduce it?

Same issue.

Provide extra information to complete the original description of the issue:

Created a new input profile making sure cyclic axis, trim and ā€˜set rotor longitudinal trimā€™ were assigned correctly and nothing else was conflicting.

If relevant, provide additional screenshots/video:

Manually trimmed fully forward and holding stick full back to maintain attitude.

And after pressing SET ROTOR LONGITUDINAL TRIM this happens.

My understanding of how the force trim release should work is that when the force trim button is depressed and held, the cyclic can be moved without the rotors changing pitch. Thus when flying you can push the nose down to achieve the aircraft attitude you want and then depress the force trim button and centre the cyclic and the aircraft will maintain that attitude. This is how it works in the Dreamfoils 407 and, as I understand, the real aircraft.

Spot on. Sounds about right.

I think one issue is the naming of the bindings mentioned, as it is unclear what they are actually for. Users are assuming (or hoping) that they are intended to function as a ā€œforce trim releaseā€ (technical terminology) in the respective axes but I personally have not seen anything documented to that effect.

To anyone from Asobo who reads this, I will clarify that many users are requesting a binding that does act as a force trim release button. Again for clarity, the word ā€œreleaseā€ means that holding the button releases the force trim mechanism to allow repositioning of the stick. Upon release of the button, the force trim re-engages at the new position.

The B407 add-on for XPlane implements this in a way that is very helpful for users of a desktop joystick: it allows you to position the stick, hold the force trim button as you release the stick, and upon release it implements a virtual center position at the original control position.

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Thatā€™s how it is often simulated for home PC joysticks with centering springs.

That is NOT how it works in real helicopters.

In real helicopters, force trim applies pressure to the control stick to hold it where it is. (real helicopter controls donā€™t have centering springsā€¦) Pressing the force trim button ā€œinterruptsā€ this mechanism and allows the stick to be moved freely to a new position.

When the force trim button is released, the mechanism re-engages and the stick is essentially locked into this new position. (The forces are weak enough that the pilot can overpower them, but theyā€™re strong enough to hold the stick in that position so that the pilot doesnā€™t have to exert much force to maintain a desired attitude)

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I just use the rotor long and rotor lang trim function mapped to a hat switch.

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That functionality is called Beep Trim. It is the slower brother of Force Trim. It works great in the Sim and is for small adjustments.

Very nice explanation thanks.

For any joystick to work as a real helicopter does, the manufacturers will have to build this force-release mechanism into the joystick. That will probably make it unaffordable. Would be cool though.

IS THAT WHAT THAT IS?! I was having the worst time trying to figure that out. :laughing: I have heli Assists off but that strange ā€˜joltā€™ was grinding my gears, no pun intended.

I thought it was something with the anti-stall (that I leave on).

Iā€™ll have to leave Force Trim off then.

Still doesnā€™t excuse the fact that the 407 needs a lot of work.

My question is: do you need an automatic trim system in the aircraft (like SAS) in order to have Force Trim Release? I.e. does the force trim release button disconnect the auto trim system or does it disconnect the cyclic from the swashplate entirely?

See this for exampleā€¦
Helicopter Control Forces.

No, many unaugmented helis, including the 407 (or at least the one modeledā€¦it is a factory option IRL) have force trim but not SAS.

EDIT: I just read the article you linked. That is an excellent write-up and he explains everything better than I could. I guess your question was more about what SAS has to do with any of this, and the answer is nothing. Stability augmentation has different goals than force trim alone. Helicopters with SAS/AP will have a lot of things integrated, but I believe the goal of auto trim is mostly to prevent the SAS/AP servos from overloading.

EDIT^2: This article from the same site will help too This would be a pretty good site for some technical-minded simmers to read about helicopters!

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Think of SAS as part of an Automatic Flight Control System (AFCS) and Force Trim as part of the Flight Control System (FCS).

SAS is automatic and Force Trim is manual.

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No, you donĀ“t need. They are different things: force trim just locks the cyclic in the current position. BellĀ“s solution (existing not only in the 407 but also in the older 204 and 205) applies a magenetic force to the control to lock it in position. If you try to move cyclic that force is increasing. That therefore feels like a spring centering, but as explained before, cyclics donĀ“t have any centering spring. ItĀ“s intended to relax piloting and to avoid that you donĀ“t need to hold cyclic with your legs for instance if you need your hands to check map, tune radio, etc.

SAS helps to improve stability. ItĀ“s like the yaw damper in airplanes. But SAS is an active system while force trim is just a control lock. Original Huey for instance has force trim but no SAS. It just has a prehistoric gyroscopic ā€œstabilization barā€ on top of the main rotor. However some UH-1N variants were modified to include a SAS system, that actually operates servos on the rotor.

Cheers

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Thanks for the explanation. Which makes sense. I am not a pilot but have flown a lot of helos in various sims and there seem to be different flavours of force trim. In the 407 pressing the force trim release button allows one to essentially ā€œdisconnectā€ the cyclic and move it to another (presumably more comfortable) position and then releasing the button re-engages the cyclic. In the H145 the trim release button works quite differently. I think that the H145 is usually or normally flown with AFCS on and pressing the force trim release button actually overrides the AFCS and allows the pilot to make control inputs with the cyclic. Releasing the force trim button allows the AFCS to resume. Similarly, in the H145 the beep trim buttons actually adjust the AFCS trim. Anyway, I find helicopter systems quite fascinating.
I wonder if they are contemplating adding SAS to the 407. Would be a nice enhancement.
John.

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Basically they are similar things with different names and features. But at the end either you have a manual trim or an assisted trim. The classical 4-way hat switch is still very handy alone but in some cases you need a computer which helps you to keep a given attitude or even the hover state because there are some operational limitations and risks you can mitigate. Imagine a hoist operation at night with strong wind and fully manual. That can be a real pain. But on the other hand there are cases where no computer could do what a skilled pilot does: predict the movements of a ship deck on rough seas.

I always liked those videos where they bring things to their limits :laughing:

Cheers

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