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Elevator Trim Tab Animation

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Elevator Trim Tab Animation

Postby Rich47 » Thu Jul 20, 2017 5:12 pm

I'm new, here, and hope this is the appropriate place to ask this question.

I'm modeling a Piper Colt with Blender. The Colt uses vertical movement of the horizontal stabilizer leading edge as elevator trim. The stabilizer is hinged on the Y-axis, near the elevator hinge and the leading edge moves up or down depending on the position of the trim crank.

My problem is that when I adjust the trim, in flight, the Elevator moves and not the Horizontal Stabilizer. I've defined the animation for the elevator trim in the airplane model .xml file as shown below:

<!-- Elevator Trim Animation -->
<animation>
<type>rotate</type>
<object-name>Horizontal Stabilizer</object-name>
<property>controls/flight/elevator-trim</property>
<factor>-1.50</factor>
<center>
<x-m> 5.43984 </x-m> <!-- Horizontal Stabilizer/ Hinge Point -->
<y-m> 0.00000 </y-m>
<z-m> 0.30375 </z-m>
</center>
<axis>
<x> 0 </x>
<y> 1 </y>
<z> 0 </z>
</axis>
</animation>

Here, you can see that I've explicitly named the Horizontal Stabilizer as the object to move, when the elevator-trim property is changed, but in the sim, the Elevator moves, instead. Could anyone help with this problem?

I realize this is a small thing. The stabilizer only rotates a few degrees, but like most of us, I'm trying for as realistic a model as possible.

Thanks.

Rich
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Re: Elevator Trim Tab Animation

Postby Thorsten » Thu Jul 20, 2017 5:25 pm

Here, you can see that I've explicitly named the Horizontal Stabilizer as the object to move, when the elevator-trim property is changed, but in the sim, the Elevator moves, instead.


Usually in my experience you're either not editing the file you think you are, or you have some double name assigned. Or a name with a space in it can't be parsed properly...

What you're trying to do should work fine, so there's some mistake elsewhere.
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Re: Elevator Trim Tab Animation

Postby Rich47 » Thu Jul 20, 2017 6:26 pm

Okay, Thorsten, thank you. I'll try removing spaces from my object names, then search for duplicates.

I appreciate your help,

Rich
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Re: Elevator Trim Tab Animation

Postby Thorsten » Fri Jul 21, 2017 6:18 am

Actually, could it be that

controls/flight/elevator-trim

is one of these properties in FG which automatically do something (in this case change elevator position) assuming elevator trim is implemented in a certain way?

If that's the case, you would need to check the FDM and re-do the logic using a different property for the elevator trim surface.

(It would still not explain why the trim surface doesn't move in addition to the elevator surface... but worth checking)

(I've been largely working around everything in /controls/ for the very reason that there's too much hard-coded assumptions involved).
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Re: Elevator Trim Tab Animation

Postby Rich47 » Fri Jul 21, 2017 3:15 pm

Okay, that's interesting.
As a test, I did change the <object-name>Horizontal Stabilizer</object-name> to <object-name>HorizontalStabilizer</object-name> without the space between words in airplanename.xml. I also changed it in the airplanename.ac file. There was no change in behavior. The elevator still moves with activation of the trim control, which seems to verify that this action is hard coded.

BTW, I'm using Yasim for a FDM.

Here is my original <vstab> configuration in airplanename-yasim.xml:

<vstab x="-5.45" y="0" z="0.3"
chord="1.55"
length="1.35"
taper="0.80"
sweep="30">
<stall aoa="16" width="4" peak="1.5"/>
<flap0 start="0" end="1" lift="1.4" drag="1.3"/>
<control-input control="FLAP0" axis="/controls/flight/rudder" invert="true"/>
<control-input control="FLAP0" axis="/controls/flight/rudder-trim" invert="true"/>
<control-output control="FLAP0" prop="/surface-positions/rudder-pos-norm" min="1" max="-1"/><!-- -->
</vstab>

If I change this to:

<hstab x="-5.400" y="0.0" z="0.3"
chord="1.35"
length="1.45"
sweep="10"
taper="1">
<stall aoa="16" width="4" peak="1.5"/>
<flap0 start="0" end="1" lift="1.65" drag="1.4"/> <!-- lift="1.5" drag="1.4" -->
<flap1 start="0" end="1" lift="1.65" drag="1.4"/>
<control-input control="FLAP0" axis="/controls/flight/elevator"/>
<control-input control="FLAP1" axis="/controls/flight/elevator-trim" value="-1.5" invert="true"/><!-- -->
<control-output control="FLAP0" prop="/surface-positions/elevator-pos-norm"/><!-- min="1" max="-1" -->
<control-output control="FLAP1" prop="/surface-positions/elevator-trim-tab-pos-norm"/>
</hstab>

I do get proper movement of the HorizontalStabilizer in sim, as a trim device. So, that problem is solved. Now I have to adjust the “flap0” and “flap1” parameters to get appropriate flight characteristics. I assume I have to change the "start, end, lift, and drag" values.

Thanks, so much for your help.

Rich
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Re: Elevator Trim Tab Animation

Postby wlbragg » Fri Jul 21, 2017 6:35 pm

I can hardy wait to see your Colt. After reading about its history, sounds like a really fun project.
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Re: Elevator Trim Tab Animation

Postby Rich47 » Sat Jul 22, 2017 12:57 pm

Well, I started on this project back in October of last year. I've spent a lot of that time learning Blender and trying to figure out xml and how it relates to the model. I'm retired now, but I was a draftsman for 47 years. I finished up as an AutoCAD draftsman and Blender is not intuitive to a CAD guy like me, so it's been a struggle.

So far, I've got all of the components, inside and out, modeled and textured. Now, I'm trying to tweak the flight characteristics, get the various surfaces and controls to move as they should, and bring it up to as photo realistic as I can. Oh, I'm using someone else sounds and smoke effects, so I have to figure those out and model them, too. It'll be a while before it's ready to publish.

Speaking of history, I'm modeling 27Zulu. I learned to fly in this airplane back in the early 1960s, when I was a high school kid. It was one of the flying school's cross country airplanes, as it had two fuel tanks.

And, yes, it's been fun for me.

Rich
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Re: Elevator Trim Tab Animation

Postby wkitty42 » Fri Jul 28, 2017 11:27 pm

Rich47 wrote in Sat Jul 22, 2017 12:57 pm:Blender is not intuitive to a CAD guy like me

FWIW: blender is not intuitive to anybody... i've messed with it for over six months and it is still nasty... i don't think i've drawn a plain sphere without dragging through the muck with a video or something... it would be so much better and easier to learn if there were actual written instructions that one could read and hilite important parts... AutoCAD, on the other hand, i learned in a few weeks but this was back in the '80s and i was able to earn an A+ score in our drawing class where everything was done on paper with pencil, T-square and french curves...
Last edited by wkitty42 on Wed Aug 02, 2017 9:40 pm, edited 1 time in total.
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Re: Elevator Trim Tab Animation

Postby Rich47 » Wed Aug 02, 2017 12:16 pm

I've been working with Blender since last October, almost a year. I feel comfortable using it with the limited number of commands I've mastered. My main objection is that there is not an intuitive way to create objects accurately, as in AutoCAD. I've tried a few addons, mesh_tinyCAD, for example, and they help.

I also learned AutoCAD in the 80s. However, it was on the job training, after working on the drafting board for 20 years. I was glad to move on to CAD from the board.

I find the online documentation helpful. I did get the book “Blender for Dimmies”, by Jason Gumster. It has helped a lot to get familiar with Blender.

Rich
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