topic Re: How might I model a semi-elliptical airfoil? in Fusion Design, Validate & Document Forum

How might I model a semi-elliptical airfoil?

michaelbuffington — Thu, 04 May 2017 19:13:41 GMT

I thought this would be easy to model using some profiles and the lofting tool, but now I'm stumped.

The following picture shows a section of the airfoil of the left wing and the general shape of the right wing.

While the wing tapers the airfoil remains essentially the same shape though is decreased in scale, as can be seen in this section profile:

Note that even while this section is positioned nearly at the wing tip, the wing tip itself doesn't end in an airfoil profile. It's "rolled" into the wing's edge. Sort of like a fillet, but because this is a wing, it needs to actually be a specific shape for optimal wing effectiveness.

I've made dozens of attempts trying to model this. I've tried using rails while creating a loft but have very little control of the shape when doing so. I've tried variations of sweeps with somewhat better results, but all have then required I do an extrude operation where I cut the final wing shape (like the following) but end up with a problematic trailing edge:

So, how might I do this?

Re: How might I model a semi-elliptical airfoil?

SaeedHamza — Thu, 04 May 2017 20:12:07 GMT

Hi,

Please check this screencast, it may help you

Kind regards, Saeed

Re: How might I model a semi-elliptical airfoil?

michaelbuffington — Thu, 04 May 2017 20:51:55 GMT

Thanks for creating this.

Unfortunately, the geometry I'm trying to create is quite a bit more complicated. Let me show what I mean.

Here's a view of the trailing edge of the wing - note how at the root of the wing (the vertical face on the right) is quite tall compared to the tip of the wing on the left. In fact, the tip is an edge, and not a face at all:

In your example the geometry is the same height from root to tip, making a sweep or a loft of something like an arc very easy.

The shape I'm trying to model requires that the profile taper along the leading edge path as well as sweep along that same path. Here's a top view showing that leading edge path:

To help illustrate the goal here are some sections of the model, starting from near the root and ending near the tip.

Here's a link to the actual model I'm using as an example. It was originally made using SolidWorks.

http://a360.co/2pKWRXe

Re: How might I model a semi-elliptical airfoil?

TrippyLighting — Thu, 04 May 2017 20:58:37 GMT

It might be helpful if you could provide a hand sketch that shows what you imagine for the geometry to look like.

The Wing tips of an airplane look deceptively simple but can be quite a challenge to loft properly.

Here's a link form my collection that goes deep not details and features a number of to lot gurus. That might help to address the problem.

Re: How might I model a semi-elliptical airfoil?

TrippyLighting — Thu, 04 May 2017 21:22:01 GMT

Ahh...post overlap 😉

Here's a quick screencast of things you might have already tried but who knows..

There are also lofting techniques that work better in the patch environment.

Re: How might I model a semi-elliptical airfoil?

SaeedHamza — Thu, 04 May 2017 21:35:56 GMT

Hi Peter,

I made a screencast that you will love 😉

I call it stupid but functional 😛

please check it out

Kind regards, Saeed

Re: How might I model a semi-elliptical airfoil?

TrippyLighting — Thu, 04 May 2017 21:47:13 GMT

I appreciate you helping out, but your screencasts lack a few important details.

An Airfoil shape cannot be created with the technique you are showing. The front of an airfoil is not a simple radius. These are often precisely calculated profile to provide optimum airflow and lift in case of an airplane.

The difficulty as I understand it is to maintain the same shape across the entire wingspan and the idea is that it simply scales towards the end of the wing. I am not even sure the techniques I am showing are 100% accurate.

Re: How might I model a semi-elliptical airfoil?

SaeedHamza — Thu, 04 May 2017 21:54:06 GMT

Thanks for the tip, but I don't really get it, isn't lofting between a profile and a point will give an accurate geometry between them

I mean if you are referring to that radius I used it was just to give the idea, so could you please explain more

Regards

Re: How might I model a semi-elliptical airfoil?

davebYYPCU — Thu, 04 May 2017 22:03:49 GMT

I think that @TrippyLighting has nailed it,

now it depends on that flat face trailing edge, and stepped top view for it,

After the swept/rail operation you can trim that section away, similar to @SaeedHamza extrude cut.

The model you attached has a curved TE, and that works ok, in Fusion, if you want it, but doesn't have the Trailing edge face.

What is the end game for your project, taking the model to Render, Animation, or more likely CAM.

If you are going to CAM, then you will need to go to 2 or 3 Lofts, and do the wingtip separately, as outlined in the thread, Trippy linked to.

You will need the airfoil scaled and placed near the tip, a top and bottom "spar" as rails, placed very close to the Trailing edge to maintain the shape from the solidworks version.

At least you have a few more ideas how to get it done.

Re: How might I model a semi-elliptical airfoil?

michaelbuffington — Thu, 04 May 2017 22:06:56 GMT

I should mention that it's not critical that the same airfoil shape be maintained from root to tip. Afterall, it simply can't maintain that shape as the profile follows the taper of the wing. Given infinite slices, every slice must be slightly different as the slices stack from root to tip, otherwise you get a simple straight, zero taper wing.

The only really critical part is that the shape honor the shape as seen from above, and the shape as seen from the front (or back), while maintaining some form of functional airfoil. If a loft could work within those constraints it'd probably get as "accurate" as is possible, but the lofting often bulges things out on one side, or creates weird dips on other sides. I haven't found a way to actual enforce the constraints consistently.

A note on accuracy - it's hard to say what that word even means here. Even if we did know what that meant, we couldn't achieve it. No humans or machines could, really. You could place each molecule one by one and it'd still be too bumpy to call it "perfect". We're just aiming for good enough.

Re: How might I model a semi-elliptical airfoil?

michaelbuffington — Thu, 04 May 2017 22:13:27 GMT

Thanks.

The model would be used to make molds for a composite wing. I'm fine with multiple lofts if that's the only way because it won't have a measurable impact on the final object.

But I'm also vexed by the challenge. Clearly it can be done - the design I linked to above is evidence of that.

I'm going to try a few other approaches next because I want to know it can be done.

An approach I have thought of came up as I considered what the constraints should be. If the final shape complied to the top down silhouette and the back/front silhouette, while maintaining a consistent airfoil from root to tip, that'd be a success. So I should try that. I should see if I can have the loft use rails that enforce those constraints. Wish me luck!

Re: How might I model a semi-elliptical airfoil?

michaelbuffington — Thu, 04 May 2017 22:18:13 GMT

Both of these methods should do exactly what I want.

I'll need to give them both a try again (as I'd done almost exactly the same steps earlier without success). Maybe I need to mirror your steps identically, then see where I'm missing something.

Re: How might I model a semi-elliptical airfoil?

davebYYPCU — Thu, 04 May 2017 22:26:20 GMT

Gooday Michael,

I thought you would be making the mold, and thanks for the feedback,

Follow the sweep with rail to 99.8% as Trippy showed, and then loft the rest, will be as good as the router can do.

Re: How might I model a semi-elliptical airfoil?

TrippyLighting — Thu, 04 May 2017 22:30:57 GMT

@davebYYPCU wrote:

... and then loft the rest...

Ha, I had not even thought of that!

That's a good tip for the tip 😉

Re: How might I model a semi-elliptical airfoil?

Anonymous — Sun, 25 Jun 2017 03:28:09 GMT

nice job!

Re: How might I model a semi-elliptical airfoil?

cekuhnen — Sun, 25 Jun 2017 06:12:35 GMT

@michaelbuffington

If you can share the model I can take a look at it.

Betreff: How might I model a semi-elliptical airfoil?

WHolzwarth — Sun, 25 Jun 2017 13:00:16 GMT

Here's my attempt. Unfortunately I've been switching on history too late.

A first attempt used a surface Loft with rails without the tip point, but it wasn't smooth enough.

Next attempt used Sweep with path and guide rail, similar to Peter's video. This was looking better, but didn't really match the existing sections.

Tip region used a loft to a extruded guiding surface for better tangency.

It's not really straightforward, I'm still learning ..

Re: How might I model a semi-elliptical airfoil?

Anonymous — Tue, 02 Oct 2018 00:10:50 GMT

this doesn't have a the correct aerofoil profile