thanks guys,

you may be right steve. i have never tried this before so i don't know how to actually do it. it seemed to me that a blend with higher continuity would make sense. however the sweep is doing what i want. i'm not sure how it figures it all out but it is doing it.

i do get a lot of graphics issues with the surfaces. so its good to know that it is just graphics and not a real problem. it may be nice to be able to see the actual surface mesh in moi though based on what you are saying. at least to be able to check the real thing without having to go to another program. however, i've got what i need at this point. again my only purpose was to kick the tires on moi to see if its a good downstream program for PROP_DESIGN. i believe that it is. just a little tricky in areas.

Hi anthony,

> it may be nice to be able to see the actual surface mesh
> in moi though based on what you are saying.

You mean the surface control points? You can do that in MoI by separating out the surface so that it's not joined to anything else and then you can turn on the control point cage with Edit > Show pts.

But that shows you the control polygon hull of the surface - the surface itself is a smooth spline that is influenced by those hull points.

Your video card does not know how to show a mathematically continuous spline directly - any program that you load the surface into is going to need to break it down into triangles in order to display it just like MoI does, and most of the time they do it actually quite a bit rougher than MoI does. That kind of slightly jagged angular type silhouette is a pervasive type of display artifact that's common to pretty much all CAD programs.

It's just not something to really worry about so much - as long as the only thing that looks weird is a slight angularity but things are not leaking grossly outside of boundaries or look like pieces are sticking through each other then it's pretty safe to assume that you're just seeing a slightly coarse display mesh in that particular area.


> at least to be able to check the real thing without having to
> go to another program

Normally the best way to check it in MoI is to export to a polygon mesh format like OBJ for example and then crank the export mesh density way up. The export mesher does not take shortcuts with how it analyzes the mesh and decides to subdivide it, so you can use it to generate a more accurate polygon representation and examine that. But you won't be able to use that method with the "no save" version though, since it relies on going through the process of saving to a poly format.

- Michael

thanks michael,

i posted the final example pics on my website:

http://propdesign.weebly.com/screenshots.html

i mention MoI on my website as well at various places. All good words of course. This does it for me. Fantastic program. Thanks for all the help. I couldn't have done it without you. I couldn't even import the points at first. So the forum support was definitely important.

No problem anthony, I'm glad that you are liking MoI!

- Michael

hi michael,

hard not to love moi. here are some pics of the surface definitions from moi using the instructions you gave. awesome feature. this really explains the piecewise linear thing to me now.

Hi Michael,

I played around with MoI today and got an even better result. Sweep, fillet, revolve, and boolean ops were used to create what you see. It was very easy and fast to create, once you know what to do. Basically (as you stated earlier) the fix for this thread topic was instead of thinking of this as a blend op, think of it as a sweep op. Then everything is great.

Thanks for the help. Awesome program.

Anthony

Anthony,
Your program is really going to turn out NICE!!!! I always like seeing your threads come by.

Thanks burrman,

Your help has been very useful. PROP_DESIGN is essentially complete. I am only doing minor maintenance to it these days. Recently I recompiled it to get a little more speed.

I have been learning MoI some more and am able to make better models. I'm still learning though. I tried things a slightly different way and got even better results. The only problem I'm having right now is figuring out what causes bad surfaces or bad visualizations to occur. It seems rather random. Some of the graphics problems I reported earlier in this thread I can make go away depending how the model is made. But I don't have a handle on it yet. Some times rebuild helps and some times it makes things worse. The way that you go about the sweep changes things a lot too.

I'm going to mess with it more until I get something repeatable. Here are some pics of a more accurate model. The trailing edge fillet blends into the shank much more realistically now. Out at the tip of the blade the model is all distorted, when you zoom in. So I have to figure it out more. I didn't show that in the pics.

I have all the latest screenshots on my website.

Hi anthony,

> The only problem I'm having right now is figuring out what
> causes bad surfaces or bad visualizations to occur.

But keep in mind that the problem of a little bit of polygonal looking silhouette in the visualization is a normal part of the realtime viewport display mechanism and is not something that you should actively work on avoiding.

- Michael

Hi Michael,

I believe my problem is stemming from the following, based on my recent tests. It seems I have to increase the trailing edge radius (ter) by a factor of 3 and break the circle up into four pieces. Doing these two things allows the sweep op to create the desired geometry. If I don't scale the ter at all then I get very random results. If I scale the ter by 2.5, MoI will create geometry in a repeatable fashion. However, not the geometry it does when the ter is scaled up by 3.

Once I got a handle on everything, all that you have to do is select the circle, select the airfoil and do a two rail sweep. If the ter is big enough and the circle is broke up into four pieces (presumably to match the four airfoil curve segments) then everything is accurate, repeatable, and displays properly. Rebuild and mesh size had some affect, but not really anything related to my problems.

On a different note:

I realized that having the variable pitch blade shank on the swept blade does not make sense in reality. I was doing it just to kick the tires on MoI. But for the sake of reducing confusion I put my novel fixed pitch blade attachment on the swept blade and the traditional variable pitch attachment on the straight blades. The swept design is for the Airbus A400M military transport and the straight blades are for the Piaggio Avanti II business turboprop. Both very cool planes.

Thanks to everyone for your help, I believe I have everything under control now. I'm going to remove all the old pics I attached to save server space. As always these pics are also on the PROP_DESIGN website.

And just to summarize this thread; basically the answer was not to use blend, use sweep instead.

I created a screencast showing how I made the Airbus A400M model. I plan on adding one for the Piaggio Avanti II as well. The screencast can be found here:

http://www.youtube.com/user/propdesignsupport

It's about 15 minute long and there is no sound. In this case I scaled the ter by 2.5 and rebuilt the ter and the rails. This prevented downstream errors that would occur. Scaling the ter alone did not fix the problem. The rebuild was necessary.

Cool video !

Thanks Pilou,

I was rushing to finish within 15 minutes. Having been modelling these all day long I was a little bleary eyed as well, lol. The more I work with these the more it looks like rebuilding the ter may be the key. I will have to try it with the actual ter, no scaling, but rebuild it. It looks like breaking the circle in four pieces and rebuilding it with 25 points is the trick. It doesn't seem like rebuilding the rails does anything. The sweep seems to have some of its own logic that we don't have access too. But that doesn't seem to be much of an issue.

I know that rebuilding the whole airfoil is a disaster. Basically I just keep ruling things out. I'm getting very close to the culprit of my repeatability woes.

I played around with things some more and found that the variability is coming from the ter rebuild and the ter size. One model I don't have to scale the ter up to get the desired results, however, I have to rebuild it with more points. In another model I have to scale it up and rebuild it. To complicate things more how many points you add in the rebuild affects things. Given all the different combinations of possible things going on, there is going to be a lot of variability, no way around it.

Found the problem. I tried rebuilding the suction and pressure side curves as well as the trailing edge radius (ter). I added roughly double the points to each and everything worked. I will update the screencasts on my youtube page in the coming days.

Update; Unfortunately, the above did not entirely fix the problems. Later on operations failed to create good geo. So I'm still going to have to play around and see what exactly causes so much variability.

I found the problem. If I rebuild most of the lines, arcs, and circles used throughout the entire modelling process everything works fine. I did not need to scale the ter up at all.

Latest pictures are available at; http://propdesign.weebly.com/screenshots.html

Latest screencasts are available at; http://www.youtube.com/user/propdesignsupport/