Streamer testing, or…

… driving fast on small country roads.

The testing this weekend went pretty well! As always though, there were some obstacles along the way.

The testing was done on Visingsö, where my family has a country house. There are many straight and open roads there, with little traffic, so testing like this could be done safely.

It was very windy on Saturday, with gusts of wind in excess of 5 m/s, the tip of the waves breaking on the lake Vättern. As I didn’t have a wind speed meter (d’oh!), I had no idea of the exact wind speed. Since I didn’t know yet whether I would have time for more tests, I decided to have a go anyway. I had a number of streamers, and we decided to drive both with and against the wind with some of them. I had streamers 4, 6, and 10 inches in width, 8, 10, 12.5, 15, and 20 times as long, and in a number of different materials from airbag cloth to nylon and even super light mylar plastic film.

The test were carried out by attaching the streamers directly to a dynamometer (which measures force in Newtons) stuck to the end of a pole, then sticking it out of the window of a car. Our little high-def camera was mounted on the pole to film the readout and streamer. I was lucky enough to have access to a convertible (a Saab 900 Aero nonetheless! What else to do aerospace research in?), which I thought would make measuring easier, but it was way too windy to work with the roof down so it didn’t matter in the end.

I ran though the tests on Saturday with all the streamers, but I wasn’t very happy with the windy conditions. Luckily, Sunday was nearly completely calm so we ran some tests at different speeds that day too.

Our tough and rugged GoPro HD Hero serving as extra data recorder in the foreground. That camera capturies 60 frames per second in HD, in wide-angle to boot!

I’m really happy that I got all that data out of the testing, but I haven’t had time to draw any hard conclusions yet. However, the weight of the material makes a huge difference. A heavy streamer provides a LOT more drag than a light one! I’m sure we can now make one that can help deploy our parachute just right

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The art of making streamers

Jacob writes

After two presentations at Bergtorpsskolan in Täby and two more at Naturvetargymnasiet in Södertälje the school visit part of our outreach plan is done for the time being. All work is now focused on the tasks that need to be finished for the Critical Design Review in the beginning of June!

One such task is choosing the proper streamer for the landing system.

In order to minimize the risk of the parachute getting entangled with the free-flying-unit (the ejected part of the experiment), it needs to be pulled out and away from it. We hope to be able to do this with a simple streamer, which is kind of like a long ribbon of cloth or plastic.

Streamers are commonly used on model rockets in place of parachutes, but we haven’t found any good info on them being used for anything bigger. This means we have to do some testing! What we’re mostly interested in is how the drag from the streamers varies with speed, the weight of the material, and the dimensions of the streamer itself.

This weekend I have a great opportunity to test just this my holding them out on a stick from a car, but first I need something to test! During lunch today I headed to a hobby store which just happened to have some streamers for model rockets at hand… including some big 7*70 inch ones!

The model rocket streamers are very light while the info we’ve found on the subject says that a heavier streamer might provide a lot more drag. However, thanks to the LAPLander team we have a lot of thick, heat- and tear-proof airbag cloth lying around at the lab, so I immediately got to work cutting out more streamers of various dimensions from that.

It’s going to be fun sitting in the back seat of a convertable testing all these during the weekend, I’ll write up a post about how it went next week!

Oh, and here’s a pic from one of the presentations we held at Bergtorpsskolan. It’s been great fun and the students have been really interested, and haven’t been afraid of asking us tricky questions! Hopefully we can go out and do this again after summer.

David and a group of students at Bergtorpsskolan