OPTIMIZED DESIGN
3D printed airplanes can be lighter than ever thanks to foamy filaments, nevertheless, if we compare LW-PLA with PLA the density is the half which is great, but is also 3 times more flexible and the tensile strength is 10 times lower! The rules have changed!
As you can see the mechanical properties of LW-PLA are very different from normal PLA this means that design concepts should be also different, at least if you want an optimized airframe where the weight will be the minimum possible while maintaining the desired strength defined by several stress load cases. From our point of view, a good design should be compatible with PLA/PETG and still as light as possible for these material, but at the same time compatible with LW-PLA and still strong enough. Achieving that is a real engineering challenge specially for demanding models (from stress point of view) such as aerobatics, sailplanes or racers. Fortunately... we like challenges!
-Stress level: Very high
-Optimal material: PLA
-Stress level: Very low
-Optimal material: LW-PLA
Area optimized:
Shape and thickness was modified to mantain similar stress level along the fitting
MXS-R. Load case: 4KG thrust
Composite airframe is the optimum solution
It is very comfortable to print the whole plane with only one material, unfortunately this is not optimal, the reason is simple, it doesn´t exist the perfect material, mechanical properties of a given material might be very suitable for one zone but bad for another, therefore the combination of material is the most optimized solution, we have not discovered anything, if you analyse full scale airplanes or even old balsa wood RC planes you will see that they are built with several materials.
In the case of our MXS-R the most optimized version requires the use of 4 different materials for the airframe: PLA, LW-PLA, carbon fiber rods and steel rods, Each material carefully chosen and located according to the results of our stress analysis. 3D printing design freedom plus a composite airframe gives us much more room for optimisation therefore the proper use of stress topology optimization tools are now more important than ever.
-Stress level: Very high and exposed to impacts
-Optimal material: Steel rod
-Stress level: High
-Optimal material: PLA
-Stress level: Very low
-Optimal material:LW- PLA
MXS-R. Load case: Free fall 0,4m
Area optimized:
Many zones of the floor were not loaded in any of the defined load cases so we remove it.
-Stress level: Very low
-Optimal material: LW- PLA
-Stress level: High
-Optimal material: PLA
-Stress level: Very high
-Optimal material: CF tube
MXS-R. Load case: Load factor +15G