Sydney Standard Aerodynamic Models (SSAM) Fifth Generation Benchmark Model Aircraft

[Koaib Kaleem]

Hi everyone,

Has anyone developed the vsp cad model of SSAM Fifth generation aircraft model (https://doi.org/10.3390/aerospace10090746).

If i have to start from scratch, then is Fit Model the correct and only approach? Kindly guide if any other steps/ approaches might be available?

Thankyou

[Brandon Litherland]

I'm not seeing anything on the Airshow (https://airshow.openvsp.org/).  Fit Model and lots of matched components will be the way to go.  I also see this is relevant to your other post about planar slices.

[Koaib Kaleem]

Yes, have tried to match the wings and tails exactly with the stl and trying to model fuselage using fit model as well as visualizing it through slices at specific locs (the stl is very noisy).

Will be sharing it shortly so that someone can review it too.

regards

[Koaib Kaleem]

Yes, have tried to match the wings and tails exactly with the stl and trying to model fuselage using fit model as well as visualizing it through slices at specific locs (the stl is very noisy).

Will be sharing it shortly so that someone can review it too.

regards

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[Koaib Kaleem]

Hi,

I have tried modelling the geom, would be very kind if someone inspects it a little bit for accuarcy as well as any tips etc. if geomrtry seems problematic. meshgeom is the stl file i tried to replicate

Thank you 

[Brandon Litherland]

The model looks very nice compared to my higher resolution STL. The resolution might be overkill but should provide clean targets or surfaces for you to match. The file is too large to send here but I have an idea for how to get it to you.

There are the usual skinning recommendations I can see that would improve the surfaces and a few areas where the surfaces don't quite line up but those should be an easy fix.  

I don't immediately have time to document everything for you, although I would like to. This is a really good match, already.
For the moment, have a look at the MQ-28 model from the 2023 VSP Workshop https://openvsp.org/wiki/doku.php?id=workshop2023. It might give you some ideas.

[Brandon Litherland]

I was able to put the mesh in a VSP3 file by itself and upload it to the VSP Airshow here: https://airshow.openvsp.org/vsp/d4YpX7CDokvy9kNNV2cj

Let me know if you have any issues downloading.

[Koaib Kaleem]

Thank you for your feedback.

I was able to download the model and import it as well. 

One thing that is irritating me is in front view i notice the fuselage is too much out of shape (see ss). i think that it can be set via 4-5 cross section skinning but i m not understanding how, can you give me any tip regarding this or i should maybe resort to inserting a crossection.

Also can you rate out of 10, how satisfactory is my skinning in the attached model (i have removed the mesh from the vsp file as file was larger than limit)  (so i may have an idea on how much i should work on it? like will i face may issues if i were to run vlm/pm?) 

My advisor suggested me to check the continuity of geometry by checking if it is water tight or not maybe by running vspaero analyis. The CFD Mesh capabilty came in my mind in this regard. it says that its NOT WATER TIGHT? Can you kindly guide me what could be the reason?

Thank you 

[Koaib Kaleem]

Also i just tried running vspaero analysis, the pattern seems reasonable but not the values. (though i have not yet worked on changing/ analyzing the sim parmeters and tess)

one dominant problem i see is the unsymmetry in load plot, what couold be teh reason behind this.

Thankyou

[Brandon Litherland]

I had a quick look at the latest model.  Part of the issue is that you're trying to loft the "double bubble" engine fairings into the forward section of the body near the cockpit and so you're getting those upward lofting bubbles as VSP tries to interpolate between those.  Trying to keep that aft section near the engines flat on top instead of dipped will help with this.  Another thing I noticed is that you're not using Edit Curve type sections for this and managed to achieve some complex cross-sections just with General Fuse parameters.  Impressive, but there's a better way.  Have a look at the Edit Curve tutorials on the Ground School and Workshop presentations to learn more.  For complex shapes like this, you really need the control and fidelity that Edit gives you.  It could also be that you'll need another component to fully capture the upper surface with combinations of concave to flat or rounded transitions.  
I'll have to take some time later to look at VSPAERO for this.

[Koaib Kaleem]

i tried to replace the the double engine to check if this is the problem but i dont think so its helping or maybe i m misinterprating what you just told. 

i didnt go towrds the edit curve since i read somewhere that we shouldnt go for the edit curve unless cannot achieve via genral fuse.

my aim is to study the low rcs aircraft through shaping so if i use the edit curve will ii be able to change my fuselage shaping parameters? right now i was thinking to maybe play with chines by maybe changing the max width lcation. can u suggest me anything in this regard.

[Brandon Litherland]

We can't know what various fuselage shaping parameters you'll be applying to this aircraft and its variants.  That will fall on you to determine parameters that correspond to points or section location to get what you need.  You may also wish to visit Advanced Links to connect various parameters in the model geometry to your intended variables.  For example, if you want to control the angle of the lower sides, then a new User Parm "Angle" would be connected to your section width at some station to define where the lower point resides.  If you haven't yet, I recommend doing some more Fit Model iteration to get the skinning and sections just right.

Keep going.  You're making great progress.

[Brandon Litherland]

Found it.  On section 4 you have 90 degree side skinning angle. That causes the feature line to stick straight out from the section.  Turn the strength up from 0.05 to 1.0 and you'll see what I mean.

Change your skinning there and I think you'll be happier with the result.

[Brandon Litherland]

You also have zero strength skinning along the cockpit.  This will cause all sorts of problems.  Reskin the cockpit with different angles and strengths and you should be good to go.

[Koaib Kaleem]

Rereplying as I m not sure if my message was posted

Thanks alot, i did what you said, and yes it worked! the crossection is much better.

i wanted to know what can be the minimum strength that can be fesibly kept, is 0.05 ok (asking in genereal)?

regards

[Rob McDonald]

You can pretty much go down to a very small non-zero value.

The zero value is usually used as a way to achieve a sharp corner -- and that can be achieved by allowing the before/after angles to be different.  Also, the spacing of the tessellation before/after the joint is better controlled that way.

So it is usually true that people don't actually want zero strength.  They want to have different angles before/after, so they should use that instead of zero strength.

Rob