• Jon

"You've Designed This Wrong!"

Updated: Oct 31

Since starting this project last year it has been a truly exciting learning curve. It feels like 3D printing is starting to become more and more mainstream as people see the exciting possibilities on offer from the technology that is getting better and more affordable everyday.


One of the things I enjoy is the ability to try different approaches to solving the problems associated with model aircraft, namely; strength and weight.


I had an email this morning from someone telling me that I had done it 'wrong'. In this case we were talking about using infill to provide the support structure through the wing. 'Wrong' implies that as a design solution it fails to solve the primary problems, strength and weight. Given that these aeroplanes fly using this method clearly indicates that the problems of strength hand weight are satisfied. (In fairness he was refering to the Avanti, which I haven't flown but was complaining about the design methods themselves.)





I think I understand where this comes from. For many years, if you were going to build model aircraft at home you would use balsa wood, arranging pieces such that you had traditional spars and ribs, this is the model aircraft design dogma. Where does it say that this is the only way to do it? New technologies should free us up to try different things. You would struggle to strengthen your balsa wing by setting wood into a 3 dimensional cubic arrangement.


I am not saying that my way is right, in fact I am trying to argue that there isn't a right way, each method of solving the primary problems of strength and weight has its pros and cons. I have used different solutions throughout my models and, some models I have in development use both defined wing structure with spars AND slicer infill.


I understand the cons associated with the infill method too.


INFILL METHOD


PROS:

- Quick(er) design process.

- Strong. The cubic pattern in particular provides strength in all directions.

- Flexibility of design. In other words you can increase or decrease as necessary. Also buy increasing the infill print speed you can lighten the infill. I usually use double the wall speed.

- Easier to print and with faster print times.


CONS

- Non-specific support. Sometimes support is needed in a particular place, this can be overcome by adding a wall (cut) in especially.

- Weight, not always, but can be heavier.

- Allows an element of variability in printed weight due to the variety or printers, settings, etc. I have printed the same part and found it 30% heavier after changing a single Cura setting.

- Any channels cut out for control runs, etc, actually add to the weight by introducing a new wall. this also increase print time.


The alternative I'll call the defined structure method.


DEFINED STRUCTURE


PROS:

- Targeted support. You can make sure there are supports exactly where they are needed

- Printed weight is more stable from machine to machine.

- In some circunstances it is lighter. I found a 7% saving on a wing part that had many channels required (this increases infill method weights). Simpler wing parts have proven to be heavier!

- Strong.


CONS

- Considerably more design time. Whilst this is not neccessarily of concern to the end user, design time should be considered. I can certainly make models available cheaper if they take less time to design.

- Potentially longer print times, and more complex prints with more retractions etc.

- Not always a weight saving depending on the part in question.


I think there is room for both techniques and also the hybrid technique whereby we define some structure where needed but use infill where we don't. Ultimately I believe the blending of these techniques will be best suited to solving the problems of strength and weight.


The email I received this morning was less than tactful in telling me what they thought, (perhaps he forget that another human who spent a fair amount of time on this work was going to read it?) but I am always willing to receive feedback on these designs. Tell me your ideas for how we design planes for 3D printing going forward.




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