Constraining Airfoils

[Drewpan]

Hi All,

As some of you know, my current Drawing Project is an Aircraft.

The Tutorials I am following leave a lot to be desired in terms of good Workflow practices but I am trying to do

them using what I have learned HERE and applying it to the new things I am learning THERE.

My question this time around is about Constraining Airfoils.

There are several Airfoil Apps available that use standard .csv or .dat files for Data that I have installed and become

comfortable with in terms of importing an Airfoil. These airfoil shapes are either generated on the fly or scaled as

needed. The method I have chosen is the generate on the fly so that I can calculate the size I need for my Model and

get a File that drops straight in and I then position. The critical number to know to do this is the length of the Chord

of the Airfoil. The Chord is the line from the Leading Edge to the Trailing Edge. The actual Airfoil shape is generated

from fairly complex mathematics into a bunch of defined Points that are then joined based on the length of the Chord

from the shape Template for the Airfoil you are using.

The resulting Airfoil is then generated as an Un-constrained Sketch onto the Plane which you told Fusion to project

it on to. Like this:

The Airfoil that is generated is unconstrained and what I would like to know is - is there an easy way to Constrain it,

or do I just have to live with the Sketch being like that?

Initially I thought that the problem was that the new Sketch was just hanging in Space and I tried to Constrain it by

locating the centre of the Leading Edge, which should be the front of the Chord, and defining distances from the

Origin. This doesn't seem to work, in fact if you are not careful in the way you do it it will change the whole shape

of the Airfoil.

If I select the Blue Line Curve I can Move it and such. This says to me that it is all linked together in some way and

possibly regenerates on the fly as you move it. If this is the case then why isn't it, or why cannot it be Constrained.

If I lock down one of the points, shouldn't the rest of the automagicly generated points now also be locked down?

Even if I had to lock down two of the Points, say either end of the Chord, to prevent it from rotating about a Point,

it still should Constrain somehow?

I agree that some of this problem may have to be in how the App generates the shape. That being said, if I am

basically importing a defined shape, I don't see why it then can't be constrained by locking down the position of one

or two Points. All of the points in the Shape are relative to each other in a strictly defined way.

Also, another really annoying thing if anyone knows how to fix this:

When I created the Planes to place the Airfoils, I created them in my Top Level. I thought at the time that they are just

Planes, not realising that the Airfoil Shapes are generated as Sketches WHERE the planes are located in the design.

After I had positioned the Airfoils in the correct place on the Canvases I realised where the new Sketches ended up.

This occurred even though the Active Component was the Wing Assembly I had created and NOT the Top Level. So

what I have now is three orphan Sketches in my Top Level that I really want in the Wing Assembly. I can live with

this but it annoys me.

Can someone confirm how to fix this? I tried selecting and moving the Sketches but it doesn't work. I am about to

try rolling back the Timeline and setting the Active Component to the Wing Assembly THEN creating the Planes,

but before I do that I want to check if that is the correct way to fix it.

I realise that there may be no answer to if there is an easy way to Constrain imported shapes. It may be something

that the Devs might have to think about because surely this is not the ONLY time this sort of thing happens.

Cheers

Andrew

[davebYYPCU · Accepted solution]

Easy one first.

Timeline to end of file.

Expand the browser arrows, to see everything.

Select Top construction plane in the list, and click drag to the wing Component. 

When I did this, Fusion was good enough to know I was going to do that again, but decided to do them all, along with the sketches.

Next, what did the tutorial say about the spline to be constrained - crickets?

Next fully constrain splines with Fix command.  Otherwise you have 4 constraints required on every spline point, good luck.

So what is the big picture, 1:1 Replica, scaled model, flying r/c model, Learning Fusion, all these things determine how to do each stage.

For example, if you can't see inside the windows, why would you detail the fuselage bulkhead, instead of a solid tube?

So for the finer points, (I make rc aircraft) your airfoil does not match much of the canvass.

Nice wing panels are done with a top and bottom spline curve with 4 points each.  Airfoil data is overrated, and Fusion will choke on your spline point count.

Some things to think about.

[wersy]

To understand how to work with fit point splines, you need to study it more intensively.
To fully constrain such a spline, each point must be dimensioned in its position and the handles in their length and angular position.

This spline is fully constrained

Now you can imagine what it means to constrain an airfoil with "some more" points.

[Drewpan]

Hi,

The Tutorial I am watching is for a Lockheed L-1011. This is supposed to be a real large scale flying model when complete. It is supposed to use either ducted fans or real turbines. Wingspan and length are a little over 2m. The

guy who is  doing the Tutorial also sells a Kit for his version of the aircraft.

I am so far only up to setting up the wings, the next video is creating them and the structure inside like Ribs. I

personally have an interest in aeroplanes but don't fly them anymore. I just thought this would make a change from

the usual Steam Engines and Machines I usually use for practice and learning Fusion. I am most interested in how he

is going to change his internal structure into Laser Cutable pieces.

You can find the Tutorial here: RC CAD-2-VR - YouTube I am about to start Video 3 in the Series.

I find this guy interesting, but as previously mentioned, most people here would eat him alive. He knows how to

use Fusion but is obviously self taught and definitely NOT an engineer. I am trying to ignore the bad workflow stuff

and use what I have learned here instead, but learn his techniques for some things. My version is a bit different

to his - it is far from perfect but a little more calculated. Much of his stuff is by eyeball and about right. He doesn't

even use the Timeline. When he made a mistake he deleted and started again - I just rolled back the Timeline and

fixed mine.

I would agree that most Airfoil stuff probably is overkill for a smaller Model as there would probably be so much

power available it would overcome any deficiencies. I think that this is a combination of trying to get the Model at

least close to the original in general Shape while still having a useful RC Model.

I would have to say also that while a 2m wingspan is much smaller than a REAL aircraft (OK, a UAV is Real), it isn't

too small by a lot. Actual Aerodynamics would play a part in this design to a point. For my purposes I have Scaled it

to 1/24. He doesn't say what Scale he uses but my numbers I calculated are pretty close to his - within 3% for

measurements he states he uses and ones I worked out.

In terms of internal Structure, it is supposed to be a buildable and flyable Model. That Structure may be unseen

in the finished build but would be critical in a real Model to actually fly.

So.

Fusion was a bit stubborn but I got the Planes and Sketches where I wanted them. It also copied all of them.

How to construct the actual Wings is in the Tutorial I am about to do, so I don't know the answer about Splines yet.

Model is a Lockheed L-1011 Airliner. He doesn't state what Scale he uses but since the base .jpgs I am using for

a Canvas came from WikiPedia and happen to have measurements on them I am scaling mine to as close to 1/24

as I can.

The Model could be set up to actually install Servos, Radios and either Ducted Fans or Turbines. I don't know any

Large Scale RC enthusiasts anymore so IF I build this it will be for display only. That being said, the capability to

actually get it into the air would make it interesting. The Fuselage Frames I only guessed at 3mm because he didn't

say what size his were. I have used 3mm for Laser Cuts before and can get 5mm. It is easy to change. I suppose

he is trying to sell his Model Kit so he doesn't give away too many of his Secrets. If I was ACTUALLY going to build

it or something similar, to sell my own version of a Kit I would try to calculate what strength I needed and

incorporate it into the Model.

In terms of the Airfoil not matching the Canvas - I agree. The Airfoil is based on the one he uses and was created

using the actual measurement of the Chord from the Canvas. I noticed this when I created it. The other two are

pretty close. Since I haven't yet watched the next Tutorial I was going to wait and see what he does about it. So far

I am just following what he does and tidying things up as I go - like trying to keep everything Constrained (hence the

original question). I am guessing but it maybe sorts itself out when he Blends the Wing Box to the Wing. The position

at present is ok Top and Side but too high for Front view. Maybe I will reposition it in line with the Slats and see what

happens with Blending.

As I said, this Project is more for personal interest, practice and learning so I am happy to see what he does and try

to replicate his end result. I read Daniel Raymer's excellent book on Aircraft Conceptual Design many years ago and

how aeroplanes are designed and built always interested me. I Pushed them around the Sky for 17 years and never

really lost the Bug.

Right now this Project is just really Modelling practice. Why Model something you are not interested in?

Thanks for you reply. I will send you a copy of the final File if it get finished.

Cheers

Andrew

[TrippyLighting]

It is not advisable to use fit-point splines with that many points to approximate airfoils. the result is almost always (99.9%) broken or very uneven curvature. The geometry might look fine when looked at with the bare eye, but the curvature problems can cause modeling problems.

The point data used as input uses math and algorithms to arrive at the specific point distribution.

A fir-point spline also uses math and algorithms to create a curve. However, the math and algorithms are different and as such the point data from one set of math is not directly compatible with point data required by another set of math.   

[davebYYPCU]

Interesting.  You are right that guy didn’t grab me either, a couple of years back.  No timeline and building inside out, is the hard way.

Canvass has the outline, building outside in, keeps me motivated as a lot of the model is done quickly.  Adding construction inside is a lot easier.

Export to laser is as easy as dxf from the face of each part, after all is said and done, ribs are the shape of the construction “cavity”, same for bulkheads.

Models don’t have anywhere near the power to weight problems of full size.

Might help....