We’ve been elaborating with Andrew (and others) on how to get some evidence that “it’s going to fly” for a while. Mainly after reading through the “Airship Design” book by Charles P. Burgess some ideas came in. I really liked the one inspired by the book – let’s dive our model in a water!
As nicely summed by Chris “It should be possible to make baby-scale blimps and test them under water to observe accurate performance characteristics (at least of the envelope etc – doesn’t scale so well for the thrusters)”. Quite surprisingly this is exactly what they did 100 years ago.
Anyway, venturing this way would be enormous distraction for our project. So we’ve been thinking about some more modern approach like putting our model in some sort of Game-engine which would test its physics.
Looking around, I found OpenVSP.
OpenVSP, also known as Open Vehicle Sketch Pad, is an open source parametric aircraft geometry tool originally developed by NASA. It can be used to create 3D models of aircraft and to support engineering analysis of those models.Wikipedia
Apparently this tool should have all we need to be able to design and test our airship. I couldn’t wait and refreshed our OpenSCAD airship design and exported it into STL (it took 4 hrs of rendering). OpenVSP was clever enough to import it instantly.
While watching tutoring videos on OpenVSP, I realised that this goes far beyond my 9pm brain capacities (I never thought that propellers are such a science!) so I condescended to sort of randomly applying whatever methods while testing if I’ll get any sensible output.
Comp Geom – Mesh, Intersect, Trim
This above actually seems to be giving all surface areas. As STL model comes in unit-less, output area is the same.
This method actually starts giving some interesting values – yet again without any units – looks like it is possible to get cross-section areas through our whole airship. These values are absolutely essential to be able to predict airship’s performance through its surface area coefficients and also the slenderness ratio.
Well, here I am sort of lost. I actually think that OpenVSP assumes here that our airship is filled with some sort of material, while it is practically hollow. Still it gave interesting graphical output.
Browsing through all analysis available – I reached the most interesting one – a Parasitic drag. Getting a help from Wikipedia:
Parasitic drag, also known as profile drag, is a type of aerodynamic drag that acts on any object when the object is moving through a fluid. Parasitic drag is a combination of form drag and skin friction drag. It affects all objects regardless of whether they are capable of generating lift.
Total drag on an aircraft is made up of parasitic drag and lift-induced drag. Parasitic drag comprises all types of drag except lift-induced drag.Wikipedia
Unfortunately I haven’t been able to convince OpenVSP to give me any reasonable output on this as it somehow needs to work with a “reference wing” model.
OpenVSP link on the tool description here.
Thinking about OpenVSP now, it’s been an interesting trip. This is clearly a complex and powerful application which can help a lot. Question here is, if it is worth time-investment at this stage, or we can utilise our time better (building a physical model). Whatever it’s going to be, we are not seeing this application for the last time!