Parametric spline modification (rotation/translation)

[giulianoj.zennaro]

Hello,

After multiple searches on the forum, it appears to me that there is no way to parametrically edit a spline. The scale tool is the only one that is usable, whereas there is no way to move the spline in a rigid manner. Constraining one of the points of the spline to something which is parametrically defined in space also does not work as the spline is not updated properly when the parameter is changed. 

This issue seems to affect few people, however it has been the case for years with already several people mentioning it and no viable workaround. Here is an example of a post clearly describing the issue with images : https://forums.autodesk.com/t5/fusion-design-validate-document/how-to-fix-the-relative-shape-of-a-sp...

In my specific case, I need to design a wing parametrically since I want to export multiple step files with slight geometric variations for CFD simulations. One of the parameters I need to modify is twist and so the profile (spline) at one end of the wing has to be rotated parametrically. Another parameter I have involves the translation of a profile. Obviously, being an airfoil, the splines are made from far too many points to manually constrain them all (I use airfoil DAT to spline).

Have there been any updates on this necessary feature, new viable workarounds or a separate possible workflow for my specific use case ? 

Thank you in advance for your time and suggestions !

PS : for the twist variation, I have a possible workflow which I still haven’t tested. I could draw one profile at each end of the wing and multiple construction lines representing the chord along the wingspan. The construction lines can easily have their angle changed from parameters and I can connect them all in 3D with lines or splines which then can be used as rails for a loft. For the second profile, I can then manually rotate it each time, export the model and then rotate back to zero before choosing the new desired twist. My issue here however is I’m not sure I can select a curve which is composed of multiple splines or other curves, even if they’re coincident and tangent (another major issue I have run into), as a rail.

[giulianoj.zennaro]

Indeed lofting rib to rib is not ideal. Actually, it technically may resemble more what the real wing sail is like since it is made of ribs that are covered by a film similar to rc planes, but for my purpose which is an exercise and proof of concept, I doubt this difference matters too much. For a smoother sail, like previously mentioned I could have only the two ends that are modeled and then use rails that pass trough construction lines that represent the chord along the span.

What exactly surprises you in loft 13 ? As far as I'm concerned the current winglet geometry seems fine except for the fact that the junction with the rest of the sail is not smooth. But that is the same as what i described in the previous paragraph. I indeed intended the transition from 12 to 6 in that bend unless there is a reason to avoid that ?

The parameters I want to change are :

- winglet height

- winglet chord ratio (the ratio of the base to the tip)

- winglet semi span

- additionally (and more importantly), I want to change the twist of the sail (not done yet). That would be equivalent to rotating the ribs of the sail. If you lookup sail twist on internet, you'll see what I mean.

Those parameters then impose the root chord, tip chord and their location. All the parameters and functions are already defined in the file ready to be used. The idea is so that when viewed from above, the leading edge of the winglet should be straight.

[giulianoj.zennaro]

I am not quite sure what you have changed there other than extend the rail all the way to the tip of the winglet ? Actually, how did you make the whole curve select-able in one go ? Since it is an arc+line, when I had previously tried to select them one rail, it did not work.

[davebYYPCU]

For body 2. I have created a Rail 3d sketch.

i used a Sweep for the top portion.  (Will do the same for main panel with washout as time permits)

I then lofted the body faces (allows for tangency) with rails, for the transitioning curved portion, joined to the sweep.

See if the parameter changes for semi span break my model, ( not tested but think is stable for that one)

Wing Twist is known as washout here.

Concern for terrible shrinkage inside outline of my first picture a while ago.

Might help….

[TrippyLighting]

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@davebYYPCU wrote:

Fusion can make this model, using the right tools for the job.

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I wonder how you can make that assessment, given that in a previous post you mentioned:

" I am yet to understand the description of the parameter changes you mention,

but I will work that out, eventually." Have you?

If this were a pure modeling exercise I might agree with you. However, reading @wersy's and @MichaelT_123's posts I am convinced it isn't.

[wersy]

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@giulianoj.zennaro  schrieb:

Indeed lofting rib to rib is not ideal.

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It's just not ideal, it's out of the question if the root profile and end profile are not the same.
This is more the rule, especially when twisting. In most cases, you then have a lift generating profile on the inside and a more symmetrical profile on the outside.
However, there are many more problems when it comes then to twisting around the aileron axis 🙂

[davebYYPCU]

Thank you for the answers as we go on.

My intent is to produce the model as a smoothed functioning model before attempting to add parametric changing into the mix.   

Trippy - not yet. 

Need a nice model of the thing before changing it's parameters in a stable manner.

Which brings me to here, 

Current model has the winglet TE parallel to the LE, it would be my contention that the top view curve continues out to produce the nicer model.  Could be @giulianoj.zennaro didn't know how to get that done.  It's up to the OP, on this part of the feedback.

Expected and Tested - Semispan changes did not break my Body 2.

Winglet height - equals length of main panel, but you have no parameter for that. Just an offset from an unused rib, odd.

Changing chord length of any rib is my current task.

Later...

[davebYYPCU]

Working so far, some obvious short cuts in outlines but you can go there if you wish.

Twisted main panel tested between (+)1 and 5 degrees   Negative values breaks the Loft so far.

Currently the Winglet tip rib is 25% of Main Tip Rib. 

Changing Winglet tip rib chord length has worked up to 500mm.

Changing Semispan still works

Changing the Main Panel length will work within reason - not tested

Add more parameters as you see fit.

Changing parameter values is taking a little while to update.

Might help...

[wersy]

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@davebYYPCU  schrieb:

Changing chord length of any rib is my current task.

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- Number or rib spacing must be variable.
The ribs result from the wing by intersection (design from outside to inside)

- The wing can have different profiles (root/wingend)
- The wing can be curved.
- Twist must be variable.

- The profiles must be variable

But not everything has to be solved at once.

[giulianoj.zennaro]

Thank you very much !

I just had a chance to have a quick look as I am busy today. The workflow is completely different, I would never have thought of that. Really neat ! I'll try to re-make it myself following your steps like that I'll learn and also see if anything is missing.

Quick question, would there be a way to have the twist angle be a function of height. Right now the twist is linear with height with the parameter being the magnitude at the top. Ideally, it would be nice to make it as a function of height (twist_deg = f(height)). I guess otherwise I could make it in discrete steps, but that's not as smooth then. Also, the rotation point for the twist should not be the nose (or the origin in this case), but a point at a fixed distance in front of the flap. I guess that should be easy to change.

On a side note, there is a slight issue with the mirroring plane. The line used to create the plane is the line corresponding to the top of the sail with no winglet, not the base of the winglet and so the twist is not the same. Just a minor correction I'll have to remember.

Again, thank you really much for your time. The change of workflow definitely opens up new options !

[giulianoj.zennaro]

In general, yes, those are definitely necessary options. In my case, the geometry of the sail is known and all I need to change is the twist angle. Then again, for the winglet, if I really get involved in optimizing it, those parameters would be needed. But I don't think I need that yet as this is mainly an exercise to learn some CFD.

[wersy]

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@giulianoj.zennaro  schrieb:
 But I don't think I need that yet as this is mainly an exercise to learn some CFD.

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Which program do you use for CFD?

[giulianoj.zennaro]

I will be using Fluent.

[wersy]

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@giulianoj.zennaro  schrieb:

Also, the rotation point for the twist should not be the nose (or the origin in this case), but a point at a fixed distance in front of the flap. I guess that should be easy to change.

For FDC, it is irrelevant on which axis is twisted. This makes no difference to the lift distribution.
At least that's what I was told by a former flight captain who does the aerodynamic calculations for me.

[giulianoj.zennaro]

I think it will make a difference as the actual sail to simulate is made of two parts : the leading edge and the flap which we are working on. If you lookup AC72, you'll see the geometry (or refer to post number 7). Changing the axis of rotation affects the gap between the two parts.

[wersy]

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@giulianoj.zennaro  schrieb:

If you lookup AC72, you'll see the geometry (or refer to post number 7).

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Sorry, I overlooked the fact that it was about a sailing boat.

[davebYYPCU]

Appreciate the feedback, pleased to be of assistance.

Mirror error, - did not see it, but should be easy fix, I think Fusion would not take my original selection, (cut end edge of the first sweep), and was under some time pressure at the time.

Function of twist angle you asked about, can you describe how that works, I am afraid that would require a Loft, now that would introduce complexity errors, when using scaled bodies as the profiles, that are easier to avoid with Sweep.

Changing pivot is not a big drama.  (is not in your model).  Watching them on TV I had not thought of that.

Might help….

[giulianoj.zennaro]

In the case of a sailboat, the wind profile is twisted because of the wind gradient that is generated from the terrain (less wind closer to the ground). The wind gradient is logarithmic and so is the twist needed in the sail. Additionally, if there is too much power in the sail, the sailors may decide to specifically twist the top portion of the sail which is the part that contributes the most to heeling.

So rather than having the angle change linearly with height, it would be nice for it to be logarithmic. Maybe if each line in the initial sketch representing the chord of the sail was rotated by the required amount, by connecting the ends of each one, a guide rail could be made and then used in a loft. What kind of error would that lead to ? And I assume there is no way to use 3d rails in a sweep?

[davebYYPCU]

That makes sense, and is accommodated by shortening the higher rib chord lines.  No?

Correct me if I am wrong, the varying chord length combining with the zero to x washout, does your function?  Or are you saying the washout would be zero > 5 > 2, or f(height) as you go higher?

This is the current TE curve in a side view.

3d Rails are acceptable - utilised in my first Sweep.  (Loft - limit is segmented rails require tangent connections, Sweep not so much, preferable)

Fixed the Mirror with 3 point plane.

Might help…

[wersy]

I would be interested in how a controlled twist (of a symmetrical profil) is technically realized in a sailboat, which must be both - negative and positive.

By the way, I have sailed in regattas and know the special features of the sails.

[giulianoj.zennaro]

In the case of a normal sail, twist control is pretty limited and is done via the kicker/vang. Here is a more detailed explanation on why we need to control it and when : https://www.northsails.com/en-dach/blogs/north-sails-blog/north-u-understanding-twist-by-bill-gladst...

In the case of a wing sail, the flap is made up of several segments which are each each controlled by hydraulic actuators at the top and bottom of them. For more details : https://www.ansys.com/advantage-magazine/volume-xiv-issue-2-2020/faster-than-the-wind