Lofting a wing

[carlweitman50]

Hello,
I am trying to create a wingskin for my RC model of the Airbus A320 NEO. In the first component, the sketches named root airfoil and mid section airfoil are the profiles I want to loft. The rails are in sketch 8. When I select everything, the loft shape looks a bit strange from the front view, and I’m not sure how to fix it.
This is important because I am making a flying model, and I need the shape to be as smooth and consistent as possible. If anyone knows how to solve this, I would really appreciate any suggestions.
Thank you!

[kacper.suchomski]

Hi

Sketch „root airfoil” seems to be corrupted; it probably has an open loop.

I can't point it to the Loft command, unlike other sketches.

[TheCADWhisperer]

@carlweitman50 

Examine the Attached file (I wasn't sure whether you wanted a Solid or a Surface Loft.

Either way, should work.

[carlweitman50]

@TheCADWhisperer 

There is still a problem tho:

If you look at your loft from the front then it still looks kind of weird, as I have observed when I tried to loft it. This will create problems when I try and fly this model.

[davebYYPCU]

You will need more Rails.

Usually positioned where spars and aileron / flaps hinges are positioned.

Might help.

[carlweitman50]

Yeah that probably will help but I am still worried that the other parts will have a weird connection. I think that maybe I can split up the airfoil into 40 points on each and then draw lines between, and those will be my rails.

[Drewpan]

Hi,

Many people who model aircraft, and boats and other things, seem to get hooked

on designing them from the inside out. A much better way is to do so from the

outside in. It is much harder to make these models when you make the frames

inside and then try to skin the frames.

There are a number of aircraft modellers on the forum like @wersy and @davebYYPCU .

They taught me to model outside in. This involves creating the outer surface of the model

and creating the inside parts like skinning an onion. When modelling larger flying RC

models, as you mentioned, it is very important to get the airfoils correct so that the

aerodynamics work. There are a number of websites out there that do airfoils and you

can create, scale and download the airfoils from. I use www.airfoiltools.com 

I also use the Fusion Plugins for airfoils available on the AutoDesk website.

The basic method of creating from the outside in works like this. Take an airfoil like the

NASA SC2-0614. This airfoil is available from airfoiltools and is used for modelling the

Lockheed 1011. I downloaded it and a Curtis C-72 to model the wing of the L-1011, including

the required 2 degree twist. I used one of the airfoil plugins to create a solid wing to begin.

To build the skin was easy after that. I Lofted a surface of the outside skin and then used the

Thicken tool to make a 3mm skin body. This is about right for a model with a 4m wingspan. I then

used my thickened skin as a tool to cut the outside surface of my original lofted wing. Now I

have the Skin and the Core. I made the skin a new component. Now I need the ribs of the wings

internal structure. I created a rectangular pattern of rectangles 5mm wide and spaced along

the wing core. I began with 12 but you can make as many as you want with the pattern tool.

Using the rectangles and the Combine Tool, you do a Combine Intersect on the wing core. This

will create the Ribs you need. Keep the Core as you still need it to create the Spars. Once you

have the Ribs you can do simple Lofts and Cut out the the Rib internals.

This whole process took me about 15 minutes to do. It took me quite

a lot longer to LEARN but once I got the hang of it it is very quick and

easy and I have never modeled a boat or aircraft the old way since.

Lofting the wing was easy with the airfoils and plugins and needed the

three airfoils and the Leading and Trailing edges were the Rails for the

Loft. The Fuselage was done a similar way. Model the OUTSIDE as a Solid

and carve off the parts I needed - Skin, Bulkheads then add Stringers.

While I am not saying you should discard what you have done already,

although sometimes this is a better solution, you may want to consider it.

The L-1011 I modeled was from a series of Tutorial Videos that were very

polished and professional videos. Unfortunately the guy who created the

videos wanted you to buy his Plans for his model and the Content of the

videos made it very clear that he was a really good modeller but had no

real idea on how to use fusion properly. I came to the forum looking for

help and was taught the Outside in method.

Cheers

Andrew

[wersy]

As @davebYYPCU alraedy said, You need more rails.

Furthermore it is better to split the profile in upper end lower spline to avoid distortion of the trailin edges.

Root

Middle

[davebYYPCU]

All your drama is associated with the airfoils, loft without rails had some alignment curves instead of straight they were tending to be tangency curves.  Those airfoils with more than 4 or five points are causing Fusion to work too hard.

I didn’t see what span size you are using,  Replace the airfoils with 2x 4 point Splines, (top and bottom curves) by projecting those points from the given data.  Then use alignment handles to match the curves required.  If you do, you won’t need rails, but I do use them for as said, spars and hinging.

Your chord line did not align to a spline point in the airfoil, so Fusion is not being controlled by the LE Rail at a spline point, etc.

Might help….

[carlweitman50]

Yes, I understand, but I don’t think trying to copy the airfoil by creating my own spline is a good idea, since it can distort the aerodynamics. I will try to add more rails instead.

[davebYYPCU]

One swipe with sand paper will distort the result.  Who said your imported data is accurate?

You are presumably modelling at reduced scale not full size, you need model airfoils not scale ones.

How will you model the thin TE of those airfoils?

Might help….

[carlweitman50]

I downloaded the airfoils from airfoiltools.com, and I believe the data is accurate. I am already using model aircraft airfoils. The root airfoil is the MH32, which is optimal for Reynolds numbers around 300,000 – 1,500,000; this airfoil is a scale model. The midsection airfoil is the SD7037, which is optimal for Reynolds numbers of 200,000 – 700,000. Both airfoils are designed for model aircraft and are perfect for my model.

[davebYYPCU]

So you have compared the curve combs, especially at the LE.  The mid airfoil is as expected.  The root airfoil is not nice, and not sure if you noticed the comment about the LE chord line not aligned to a spline point, things like this will limit Fusions ability to make clean results.

Might help….

[carlweitman50]

I see what you mean now. It must be my airfoil app importer in Fusion that is malfunctioning. They removed the other one, Airfoil Dat to spline, so I am using another one now. If anybody here knows another way to import airfoils in Fusion then please let me know.

[wersy]

The fundamental problem is that fit point splines are not ideal for airfoils from dat files.

[davebYYPCU]

What washout angle do you prefer?  From mid rib out, or full wingspan?

Why are the airfoils vertical?  You are immediately distorting the shape with a 6 degree LE dihedral.

You can use my method if you wish, this one is 2 degrees full span washout, 

Loft without Rails.

Might help...

[carlweitman50 · Accepted solution]

Thanks!

However, I found another solution. Instead of using Loft, I can use Sweep, which fixes the problem. Adding washout or dihedral no longer distorts the shape. The drawback is that you cannot use multiple airfoils, but that is fine by me. I ran a CFD simulation of this wing in SimScale, and with 0 degrees of washout and 5 degrees of incidence, the total lifting force was 38.1 kg and the drag I think was 1.8 kg (at a speed of 200 km/h).

[mrm1018]

My friend, you're over nerdulating this.  The accuracy of the airfoil within the means that you are able to model it and fabricate it will have no appreciable impact on how the model flies.  You could create gross imperfections to the airfoil shape, plus minus 1 ~ 2mm and likely more, and you will not see a difference in the model's performance.

A larger determination of how the model flies will be the result of a low wing loading, power loading, proper center of gravity location, proper angles of incidence between wing and horizontal stabilizer - and thrust angles.  And probably beyond that, it will depend more on how skillful you are at determining the appropriate structures and constructing them.

This is coming from someone that used to design, manufacture, and sell RC airplanes.