Must say that I am absolutely delighted with my recent investment in MOI !!!

I have - however - run into a little trouble trying to model the engine cowl in the attached aircraft.

I can create a surface from the propeller spinner opening to the rear surface - but not from both the prop spinner opening plus the air intake opening.

The TK4 aircraft was designed in 1937 when all complex surfaces would have been created by hand, by pattern makers - and may not be mathematically accurate.

I know MOI is not really meant for "reverse engineering" - but any suggestions from experienced users would be greatly appreciated.


John

Hi John,
Here is a surface added to the front



And a link to the file:

https://skydrive.live.com/?cid=641344b395278ed0&sc=documents&uc=1&id=641344B395278ED0%21175#

I put the netwrok result on blue then showed where I deleted some surfaces and recreated them with a sweep.

I wont be able to help too much with this model, if you want to start to look at the tangent results of the surfaces.. You are modeling this by "patchwork" and although it can be done, it will be a more advanced/complex way to do it.. Basically, redoing many of your curves and an endless redo/fix scenario....

Hi John, so if you have a kind of irregular outline that you want to surface, like one that seems to be kind of suddenly interrupted like at this spot here:



That can be an indication that you should try to build a broader more extended shape and then trim that shape by some side profile curves to arrive at that final outline rather than trying to build a surface directly to it initially.

So in your case here that might be something like build 3 curves like this:



Then Loft those to make a surface:




Then get some profile curves from the front side:




And use those to make holes in the extended full surface:




This general concept of building an extended piece and trimming it back can help in quite a few difficult surface construction situations. It can take a little while before it becomes natural to think about it, because it is easy to fall into a tendency of trying to surface everything directly right in the first construction. But surface creation works best with a more regular and kind of non-interrupted curve layout.

3DM model file also attached.

Hope this helps! If that's not the right kind of result that you need could you post an image reference of how it is supposed to be shaped?

- Michael

Ahh, Burr beat me this time!

You can see Burr used a slightly different technique which is more like divide up the outline so that you've got 4-sided regions to surface instead of trying to do too large of an area all in one single surface pass.

- Michael

Hahahahaaa. Gotcha!

But not really. That was more what I was eluding too. It really needs to be approached differently, unless the poor surface structure is not an issue.

Bit like the problem I had with the front of a Hawker Typhoon which I found vitually impossible to create using MoI. I had already done it using Sub-D poly modelling but I could not get the surfaces in MoI. The front of a Typhoon is similar to the example but with a much bigger air intake and much more reversal of surface curvature.

Hi Steve, yeah when you've got shapes that are sort of flowing and blending in multiple directions at the same time sub-d smoothing often tends to be better suited for creating stuff like that.

That's when you're getting to areas where the parts that you are creating are less structured, they're less defined just by profile curve and then the profile-curve driven paradigm that MoI is focused on doesn't match with them as well as it does with other kinds of shapes.

Sometimes though the underlying profile curves are there but are really coming from a larger extended surface that is cut off at a certain point.

A lot of times vehicles are in a kind of gray zone having some aspects that are good for NURBS like cut out areas but then other things like melty blendy areas that are good for sub-d.

- Michael

Many thanks to all !!! I am in awe at the expertise brought into play on my behalf.

It's now 11:30pm here ( in the model aircraft design office ) and my brain hurts - so I will sleep on it and follow your suggestions tomorrow.

My normal method when faced with such problems, is to keep trying different approaches until something clicks - I don't have to work to any deadlines - but sometimes this leads to brain-fade.


Thanks again


John

Hi Michael - I like the approach !

Sadly, from the side elevation the circular openings are not in a plane.

But it is always useful to learn new techniques.


John

Hi BurrMan ,

Many thanks for your feedback - it looks pretty good. I just would never have thought of doing it that way.

There is one very slight issue, the surfaces of the cowl itself does not quite flow smoothly into the surfaces of the front fuselage. If you look at the "Top View" you can see it

Following your example, I shall try to create a smoother blend

John

Hello StevMacc !

Any chance of seeing a picture of your Sub-D Typhoon ? What modeling software did you use ?

The only experience I have of this type of modelling, (if I have understood) is a trial use of "Sculptris"

It may be me - but I couldn't seem to control the surfaces created with any precision.


John

At last - the near-perfect surface model of the TK4 front engine cowl !!!!!

With thanks to Michael and BurrMan - who both pointed the way for me.

My mistake. It's actually a Tempest. I haven't actually finished it but here is a screen shot of the fuselage. This is in Modo. The part I had difficulty with in MoI is the fuselage forward of the wing where the air intake is blended to the engine cover. If you have the chance to see a real one, it is made of fairly small pieces of aluminium bashed with a hammer and riveted together. There are a fair few gaps.

Nice model Steve !

I have no experience of Modo.

How does the user interface compare with MOI ?

What do you plan to do with the model when finished ?

John

PS: UK aircraft of that era were all made by skilled sheet metal workers doing things by eye and touch.

It was quite common to see notes like "Blend smoothly between ribs" on manufacturing drawings.

I only model aircraft as a hobby, so I am not going to do anything with it other than render, print and maybe hang it on my wall!

Modo is a very different type of modeller to MoI so the UI requirements are very different as well. There have been many threads on here where Michael discusses the difference between a Nurbs modeller like MoI and sub-d polygon modellers like Modo.

For ease of use, MoI stands out amongst Nurbs modellers. I also use Alias Design, which is far more powerful than MoI in the Nurbs surfacing field, but is probably the hardest UI I have ever had the misfortune to learn.

Modo is designed to have a very fast workflow when modelling in sub-d but because of that, it is not as easy to learn as Cinema 4D.

Good point. When the real ones were made. the metalworkers were essentially sculpting in sheet aluminium. That, I think, is why it is difficult to do in a Nurbs modeller. Sculpting type operations are better done in Sub-D.

Here's one attempt



I think I'll try one with a thicker area for the blend...

Tightened it up a bit.. Working on blending it into the body towards the back.