This page documents Bill Robinson's helicopter rocket. It was last successfully launched at the Poway Powow in 1998. There has been periodic interest in helicopter recovery on the Water Rocket list, so I talked Bill into dusting it off for some photographs the other day.
This rocket has the best hang time of any rocket I've ever seen, bar none. The 1998 launch was truly remarkable: on the way down it spun VERY fast, floating slowly toward the earth, guy wires singing.
I shot a bunch of photos of it at the time, and later discovered that the film in my camera wasn't loaded correctly. D'oh! So finally, here in February of 2005, I got some nice photos.
We were hoping to launch it, but alas, it sprung some major leaks. We did, though, drop it from Bill's tall balcony, and I shot some video, to at least get a feel for how well it works (see below).
It's worth noting that Bill worked very hard to get this rocket working as well as it does: it was not a slam-dunk, by any means. There were many test launches, and much fiddling, to get it working right. All the effort was well worth it, though.
OK, here are a few photos, with comments, and some short video. Click on any photo for a much larger version. I hope this will help aspiring Helicopter Recovery practitioners.
Here's a shot of the entire rocket, folded and ready to launch. Note the green ring of plastic, cut from a bottle, holding the blades closed. A standard airspeed flap is used to trigger deployment: when the flap springs open, monofilament lines attached to the green ring lift it up, allowing the blades to fall free.
Here's a closer view of the blades. Note that the base of each blade has an extra "fin" attached to it, so that the folded rocket has decent stability. Note also that the hinges have no stops: Bill used guy wires to set the angle of the blades when they are open. Blade angle (aka "cone angle") turned out to be a critical factor in the success of this rocket.
This is hard to see, but it's a closeup of the airspeed flap. It's a little easier to see in the larger version. Note the small launch flap, and the monofilament crossed over the flap, that runs down to the retaining ring.
Here's a shot of the blades unfolded. Note the monofilament guy wires that set the blade angle, and also the monofilament that connects the tips of the blades to each other, keeping them evenly spaced with respect to each other.
Finally, I wanted a shot of the end of a blade. Note the carefully carved airfoil shape: this is important! As the blades are slicing through the air, they are generating significant lift. That's a major reason for the remarkable hang time of this rocket. You can't see it from the photos, but with the rocket in helicopter position (nose down), the blades are also tilted slightly down. This keeps the helicopter spinning. If the blades were flat, or tilted up, the rotation would eventually slow and stop.
Lastly, here's some video of the rocket being dropped from Bill's tall balcony (there are some really steep hills here in San Francisco, and luckily Bill lives on one of them). There are 2 versions, both are about 1MB in size: the first is a standard QuickTime movie, fairly small. The second is a Divx-compressed AVI, which is recommended, if you have the software you need to view it, because it's a lot easier to see what's going on. (Note: I am not a "video on the web" expert. Please let me know if you have trouble viewing the video, and I'll fix it if I can.)