Tapering curved and twisted frames

graham_lock

Hi all,

I have what is probably a pretty unusual use case for draft.

I'm designed an RC plane and I'm using frames for the wing spars.

The root rib dimension of the spar in this case is 9.5mm x 6.5mm.

I want the spar to taper to 9.5mm x 3mm at the tip rib.

Draft works fine if the frame is straight and the ends are parallel to each other.

In practice the spar bends along the wing span and twists due to washout along the wing chord.

I thought I may be able write some FeatureScript to iteratively use draft, tweaking the draft angle until the end profile is at the required height within some tolerance.

However, experimenting with draft, manually changing the draft angle, shows that the beam profile is changed along its length rather than just tapering as required.

Does anyone have any idea how to go about this?

Test document at:
https://cad.onshape.com/documents/2a4c80a57076ad9d2299d155/w/ee46e2d2a71b13dcdfd3af1d/e/882efb5a1deffdbb5c38b167

Thank you.

GregBrown

Apologies! I was so focused on the keeping the profile orientation locked to a reference face (that's what I added in my Custom feature) that I missed your part about tapering. As mentioned in the other thread, the sweep feature (and Frame) will not accommodate that, so it looks like it may have to be based on loft...

graham_lock

As an additional note I'm hoping to avoid lofting as the frame just tidily follows the wing skin, lofting would require additional sketches on the root and tip ribs. But maybe the only way forward?

GregBrown

I've done this as a simple extension of the Frame feature, incidentally for the exact same use case (amongst other things)

If you look at the Frame feature in the standard library, you'll see it uses opSweep as the main body creating feature. Since we extended opSweep to support orientation in a number of different ways, it follows that you can create you own version of Frame,

graham_lock

That’s good news thank you!

Is your extension of the Frame feature available??

GregBrown

Here's my old version of it - I'll have another look at it shortly:

https://cad.onshape.com/documents/5bbce0264f6cfc58d7996941/w/b2d51b5da7d429b383af559e/e/89aa9d532129090b2a0cf47b

graham_lock

Thanks Greg.

I've had a quick look, I can see the end trims but I can't see how then to taper the frame to a given tip depth?

https://cad.onshape.com/documents/a5a54c0e90845bff32f56a3e/w/eced314340e75599af22a067/e/0db3101601650059f92e9eb3

Part Studio 'Test 2'

GregBrown

Apologies! I was so focused on the keeping the profile orientation locked to a reference face (that's what I added in my Custom feature) that I missed your part about tapering. As mentioned in the other thread, the sweep feature (and Frame) will not accommodate that, so it looks like it may have to be based on loft...

graham_lock

Thank you.