Where to begin?
I started with designing a few model airplane glider wing sections. Nice exercise but quite obvious with FDM plastic, weight is going to be a serious issue.
I decided to step back from traditional flying model aircraft design and work on something much more basic. Like the hand tossed folded paper airplane.
I took a full sized sheet of printer paper and folded it in to a dart shape. Like I have done all my 70+ years of life.
It flew as expected in the house, harmlessly impacting the couch on the other side of the room.
OK, now I have the shape. Can I print one on the FDM printer? Fusion 360 and 20 minutes or so, I had the shape.
Version #1 was printed. About a third shorter in length to save material and to fit the printer. Checked the weight of the paper version. 4.7 grams. Then the weight of the smaller 3D printed version. 11.7 grams. uh-oh…
Took it outside to test. It flew like a rock. Or a falling leaf. Maybe needs more weight in the nose (more weight?) Duhh!
Version #2. Added more material to the nose. Version #2 weights 16.69 grams. Another rock toss. No glide here.
Version #3. Widen the wing area and more weight in the nose. Total weight is now. 18.5 grams. Is it just a bigger rock? NO! it’s very fast but does fly like a lawn dart. Finally some stability.
Version #4 is exactly the same CAD file but using lightweight PLA (Overture AIR) which is supposed to be 20% lighter than standard PLA. Total weight now 13.1 grams
13.1 / 18.5 = 0.708. About 29% lighter! Now heading in the right direction.
New version now flying like a very fast paper version. But it does fly and for a good distance. More a trajectory than a glide. Weight is the reason, and still the big issue.
Conclusion is very high attention needs to be paid to material weight and design strength in designing flying model aircraft.
--------------
One subject are not presented. Model airplanes often set in full sunshine and certainly fly in full sunshine. A 100 degree (Texas) flying day in full sunshine is certain to cause distortion in the FDM printed model airplane parts. Especially PLA.
ASA, ABS, PA and PC need to be considered and tested for hot weather flying. Carbon fiber is not going to make a big difference IMHO.
I have had PLA parts fail due to heat involving some accessory mounting brackets I designed for a bicycle rider friend. ASA used to replace failed parts. No more issues so far. Many months of outdoor sun exposure.
Here we go…
 |
 |
| Version #3 on build plate | Prototype and two failures |