The day of a droptest is always a stressful one, as even small mistakes can lead to failure. If the parachute does not deploy, the system will shatter on ground impact. One software bug, and all data could be lost. Changing weather, the helicopter is grounded, and other factors. But for PERIPHAS’ second droptest, all seemed well, at first…

We gathered early in the morning to pack everything into our cars and drive up to the farthest valley of Canton Glarus, where Wichlen was waiting for us again. The structures subteam started assembling the system, the ground station was put together and weather checks were conducted. With the sun shining brightly in the cloudless sky, we waited for the arrival of our helicopter. And, like Swiss clockwork, it did.

A helicopter creates a strong downwash, which is a strong wind created by the helicopter blades. The blades push the air downwards, and the air lifts the helicopter upwards. Heavy helicopters create more downwash, and a Super Puma is very big. The pilots flew over our position at a very low altitude, and the downwash was incredibly strong! So strong it threw the groundstation monitor to the ground, destroying it. This spelled doom to our mission, as we are unable to operate our system without a monitor. But with some quick thinking and reaction of our teammembers, we were able source another monitor down in Glarus, and our drop test could continue with only a short delay.

On that day, we were testing the implementation of our first controller. And on that day we learned that successful simulations do not guarantee success on the real system. After detaching from the helicopter, the system performed a few nominal turns. It then dove into a horizontal position while spiraling extremely aggressively , which threatened to crash our system into the ground at high speeds. Luckily, we had an ace up our sleeve! We triggered our safety spiral, which is a hard-coded steering input that successfully stabilized the system, and brought it down slowly. See if you can spot the moment we triggered the spiral in the video:parachute:

We are working hard on finding the source that caused the instability of the system and mitigate it. We are looking forward to our next droptest on the 19. of May, where we will implement our lessons learned.:rocket: