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KingGhidorah

What is proper way to use trim in helicopter?

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Maybe the self-explanatory question should also include "when" as well. In the sim (dcs or fsx) I've typically only used the force trim functions during a cruise phase, when I don't feel like holding the stick in position.

 

So many changes to the flight dynamics take place as you are transitioning through the speeds either into, or out of a hover, through translation lift speed. If I'm on a landing approach, should I use the force trim, and then transition down through the speeds using that particular trim setting, and then try to establish my hover with the force trim established in the descent? When I take off originally, should I trim the helicopter into a stable hover initially, and then keep that trim setting as I climb, and acclerate away? Other than standard cruise, I find it hard to know exactly when is the proper time to use that force trim button to zero out the forces, or rather I should just hold the helicopter in balance without it.

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I'd say it should be used like with any aircraft... with the necessary adaptation to the fact that, overall, cyclic and anti-torque controls are a lot less "heavy" than in fixed wing aircraft.

 

We should trim to reduce forces in the cyclic. In DCS we can use additional anti-torque trimming in "cheat" / "non-pro" mode, but as far as I know trim IRL is available for cyclic only on most helicopters.

 

My experience and the way I use trim in DCS is always in order to minimize control forces, but to be honest, and since IRL helicopter controls are light, and in particular in a PC-based sim without proper hardware, these forces can be unplausible, is that, during approach / transition to IGE / landing / transition to OGE / takeoff, I set trim to neutral, to better "feel" the forces... only re-trimming again as I set cruise power / collective.

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This is an example of a topic that I probably could have answered my own question if I had searched the DCS forums first. A real Huey pilot said that during training they were forbidden to use the Force Trim, and that in practice it was only used for long cruise, but not for hovering or landing approach. If so, I don't want to "cheat" by making it a part of my normal practice.

 

Without trim though, I find it hard as hell to get the proper level of precision while holding the joystick in a deflected position, even with a Hall Effect stick like the Warthog.

 

During the same discussion somebody suggested achieving finer control using the Joystick Saturation feature instead of Curves. Like a curve it flattens out the input, but the control remains linear throughout the range. The tradeoff is that you lop off some control at the edge: Hard over on the joystick doesn't correspond to what is possible.

 

That seems a bit much to me: I don't want to lose that much joystick range. However, I did find that with the Saturation set to 85%, it gives me a much finer control than a slight Curve would over the hover and approach, in the area that I hold the joystick, so that I no longer need to use trim. Only a slight amount of control authority is lost at extreme deflections which you would never use anyway. I have a Warthog joystick, with a stiff spring, so maybe this is a Y.M.M.V.

 

I tested the 85% saturation value including deflections required for autorotations on the Huey (still have more than enough range) and that seems like a good value for me for now, which allows me to have a good precision control while not develop an overreliance on trim. Briefly did a flight on the Mi-8 too, which I don't really know how to fly yet, and this value really helped me out there also.

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FSX implemented a force trim feature. Hit CTRL+SHFT+U and it's activated, again to deactivate. I only use it, though, in birds without a force trim "gauge" of some sort.

When using HTR, it really works great. Then again, I am a huge fan of that software, given how well FS9/X didn't model in helicopter forces.

You might to take a glance through the forum on Hovercontrol.com. If it's info for flight sim helicopters, they know it, as well as RW stuff. They have some excellent for-real Aeronautical Engineers, as well as a number of real world helicopter pilots. Pretty darn good site. They have a couple of info articles on how to make the sim model helicopters as best it can too, by Jordan Moore (who is also a darn good helicopter developer!). Check them out, and his Personal Edition Bell-412. One of the best around, as far as I know.

Just my 2 cents worth, if it's even worth that :D

Pat☺

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