First, some fun stuff. Last Sunday, after flying some contest rockets, I flew the Mars Lander as a Quadcopter, as Ray King used my camera to take photos and video. And he got this great shot:
And some video. Ray followed it, so there is some better video of the model flying at far distances than my other video have shown. Also a good idea of what it is like when I pitch the nose over to do a high-speed horizontal pass.
And now the not so good news. Thursday, the Mars Lander had a Cato. Catastrophic failure. But, no, it did not get burned, or blowed up. It did not even have a rocket motor in it. Jamie Claye brought up the possibility of using some 3D printed props that rotated CW and CCW. He took an existing folding prop design and modified it, for a mirror-image. Ray King (who lives about an hour from me) brought to that Sunday launch, some sets of folding props he made on his 3D printer, using Jamie's file. But there were some issues, the tips did not print well enough. A complication of the process. But I got an idea of how they worked out physically, particularly when mounted to a motor.
Thursday, I got a set of props that Jamie Claye made. The tips did print better. So I decided to try to do a Quadcopter flight to test them out.
Throttled up, building up RPM and thrust for takeoff, and a very brief weird noise occurred….. and I realized it had lost a prop blade, or more (and never left the ground). Stopped it, and saw no blades, it broke all 8 of them.
Pretty much at the 45 degree pivot part of the blade root, the airfoil cross-section is visible on what’s left. I did not find any of the broken blades, they went out into the grass.
But two of them hit the Descent Stage and added more damage. But that’s OK, it’s the version-2 stage that crashed a few weeks ago, I wasn’t going to risk any new parts.
I had a GoPro going but it quit on me, no video.
Even before flying, I had wondered a couple of things. The blade area is not as wide overall as the props I have used, less prop area.
Even with a bit more span, the reduced area would mean the props would have to spin faster to try to produce equal thrust to the fixed props. Also, the irregularities in the surface would cause various aerodynamic issues, partly drag, and also loss of lift, so needing even more RPM to equal the fixed props (therefore even more stress on the props).
I’m not sure where to go from here. Using stronger material itself, won’t solve enough of the problems. Needs a totally revised prop with more area, like the ones I have used, or “Bull-nosed” props. Ironically, that whole 45 degree thing, is not needed for this model. That 45 degree angle portion allows the folded prop to be “wider” when folded, to allow for the width of a plane’s fuselage up front. And that is the weakest link, that angled section. If it was straight across, that would help. But the bullet nut for the prop won't let it fold back 90 degrees. However, making the hub a bit wider (spacing the holes out farther) to account for the bullet nut could do it.
But given everything, I do not know if 3D folding props can end up being something viable that I can trust.
So, it may be back to using rubber bands to hold the props till a servo releases them, the original set-up, not the different set-up with that bigger digital servo.