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Allan1-Visitor
1-Visitor
July 20, 2010
Question

Airfoil splines

  • July 20, 2010
  • 10 replies
  • 7801 views

Hi,

I'm just getting to grips with WF4 student/personal ed. To learn pro e I have started a project to model a vintage sailplane, top down, which I intend to scale down to create flying models in two different scales. Having now spent some time getting started there are three problems I need to get sorted up front

1) I can load airfoil shapes easy enough by using pts files/splines but I would like the shape to be parameterised. ie the airfoil changes with span and due to Reynolds number effects changes with scale. I am also likely to change the airfoil profile a number of times while prototyping and testing. Is there a way to have the airfoil profile parameterised in a family table or something similar?.

2) In sketcher the airfoil needs to be constrained so that the top surface is tangent to a plane normal to the sketch plane.

i.e the chord and angle of attack dimensioned, the tangent constrain would then determine vertical height so the top surface just touches the plane.

This works with circular geometry but proe does not allow a spline curve to be constrained this way, probably because it does not know that the intent is that the spline points are fixed relative to each other and scale only with chord, any suggestions?

3) I have not studied this yet but will ask anyway. What is the best way to create different versions of my model to different scales. I am modeling the surface shape of the sailplane in full size than want to create two different versions (and sets of drawings) to 1:4 and 1:6 scale. I can not just scale the whole model because things like material thickness will be standard thickness plywood in the scale models.

Many Thanks

Allan


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10 replies

DavidButz1-Visitor
1-Visitor
July 20, 2010

Allan,

In general, you can probably do everything you want to one way or another, although I'm not completely clear on all your requirements. Comments on your 3 questions:

1. You can certainly "parameterize" your model in many ways. I'm guessing that Relations might be even better than Family Tables, depending on how you are controlling your geometry. If you can generate straightforward logical and mathematical control outside of Pro, you should be able to incorporate your driving logic into Relations. What are you controlling, exactly? If you have to change the coordinates of every single point on your splines individually, things could be cumbersone, but if a change to a chord length and an angle, for example, update everything appropriately, you should have no problems.

2. By "plane normal to the sketch plane" do you mean horizontal? I'm not sure I understand what you are doing here. If you have an angle of attack defined, your angle is set, and location is probably fixed as well. Are you just trying to locate the highest point on the airfoil?

3. Probably you can do what you need with a combination of Parameters, Relations, and a bit of conditional logic if necessary. Family Tables are also a possibility.

If you give us a little more detail, we can probably help you more specifically.


Good luck to you; you're ambitious to start out with airfoil geometry. I would recommend researching the ptc knowledge base on the subject. In the past they have included airfoils in course exercises, illustrating scaling the section along the span and twisting the foil using angles in a General Blend.

David

Allan1-VisitorAuthor
1-Visitor
July 21, 2010

David,

In regard to constraining the airfoil spline I am indeed trying to locate the highest point on the airfoil. I set the angle of attack and want the high point of the airfoil to set the vertical location, therefore as I change angle of attack the high point will stay on the same horizontal line. It is fine with circular geometry but I can not make it work with a spline. I could post a sample but I only have the student version.

Many Thanks

Allan

DavidButz1-Visitor
1-Visitor
July 21, 2010

Allan,

OK, two separate issues, as I see it: (1) Design approach, & (2) Sketcher problem.

1. Are you sure this is the way you want to control the airfoil? If you have more than one section along the span (of varying size and attack angle), and you constrain them all with highest-point-in-the-same-plane, aren't you in danger of creating a "wavy" wing where the leading edge moves around in an uncontrolled way? In other words, don't you want to control the straightness or gentle curve of the leading edge or its center, then let the developing foil twist around that control?

2. You have come across a Sketcher limitation for sure. I have tried a few ways to trick it, unsuccessful so far. However, depending on your data, there still may be a way. Do you have any way of calculating the high point outside of Sketcher? If you do, you may be able to solve the Sketcher problem as follows. You can control tangency of a spline at its endpoint through dimensioning. Pick the spline, pick its endpoint, pick a coincident horizontol centerline, and place the dimension. Change the dimension value to 90, and you have tangency. If you can split your spline into two parts at the high point and dimension the ends of each where they meet in this manner, you may be able to force the issue. It depends on what you have for input. Meanwhile, I'll try another "trick" or two in Sketcher. BTW, is your input a curve for the entire foil section or just the top section? How many points define it?

David

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