Rocketry

I finished the modified Estes Nova Payloader just in the nick of time. It is sitting in the trunk of my car ready to be flown at the launch today. It is kind of slapped together, but it’ll do. Naturally I couldn’t stick with the original color scheme. Hopefully it will be a calm day and I’ll return with some good video.

UPDATE: It wasn’t a calm day. The kids had fun launching their rockets, but it was too windy for this one.

Since I am not going to finish Project Overkill in time for Saturday’s launch I decided to slap together a modified Estes Nova Payloader tonight. That’ll allow me to still fly the Muvi video camera.

The modifications I made were fairly minor, but being me I just can’t seem to build a kit as is. First, I made the payload section a pass through so the parachute will come up through the payload section instead of separating the rocket at the bottom of the payload section.  I did this so that the camera will be ejected and hang roughly right side up after the parachute deploys.  Second, I used a different shock cord.  I used a very long kevlar string and tied it to the engine mount between the centering rings instead of gluing it to the inside of the body tube.  Third, I used two 1/4″ launch lugs instead of the one 1/8″ lug that came with the kit.  That means that I’ll be able to use the longer, four foot launch rods.  Since I used two launch lugs, I could put one down near the bottom of the rocket, just to give those few extra inches of flight time before leaving the rod.  I want this rocket flying as fast as possible when it comes off the end of the launch rod since the camera is going to make it way over stable. Fourth, I used bent picture wire as an engine retaining device instead of the standard engine hook. That will allow me to use the longer Apogee D3 motors if it is a really calm day while still being able to use the shorter Estes C6 motors on a normal day.

Once the glue is dry I’ll paint it. Once that is dry I’ll glue the payload section to the body tube, tie the shock cord to the nose cone and camera, and attach the parachute. Then it’ll be done. I should be able to complete it in two sessions if I don’t worry too much about the paint job. This one is more about flying the new video camera than making a beautiful model.

Today the kids had a painting party with two of Miranda’s friends. They painted the rockets that they had built at their first rocket building party back in June.

We started by taking them to iParty to pick out stickers they’ll put on the rockets the day of the launch. Then we went to the hardware store and they picked out their spray paint. The trips from iParty to the hardware store and then back home were adventurous given that it was pouring out! We all got soaked. That did not bode well for the outdoor paint party, but a tarp on the garage floor solved the issue.

The rockets came out pretty well, especially given the kid’s ages (three of them are eight years old and one is four years old) and the fact that we did not do any sanding or priming.

I’ll provide an update on the dual deployment system after one more test, probably tomorrow, but it looks like it works now!

After working on that today I decided to try out the parachute. I have never been successful with a parachute before so I wanted to make sure that I was folding it in a manner that would work. One time when I was a kid I tried a parachute without enough wadding and it melted. Since then I’ve focused on other types of recovery systems. Now I’m building a huge rocket that is going to rely on not one but two parachutes!

This first video is a super slow motion capture, about 1/16th normal speed (3.75fps versus 60fps), of the parachute unfolding. I folded it exactly the way I’m planning too in the rocket and threw it off my deck with a five pound weight attached to it. You can see that it finishes opening right as the weight hits the ground. It’s only fully open for one frame, but it clearly worked.

Having seen that the folding technique works, I wanted to see what this parachute would look like flying through the air fully open. This time I left it unfolded when I threw it. It looked very good floating quickly to the ground.

Here it is at full speed in case you want to see it. Just don’t blink…

I saw this article about building a dual deployment device without black powder and thought that would be perfect for Project Overkill.

I didn’t build it exactly as explained in that article, but close enough. After building it I put in an igniter and tied it together with fishing line. Then I grabbed the shock cord and shook it like crazy. I wanted to see how it would react. The fishing line broke off all the pyrogen from the igniter. Were this a real flight, the main would not have deployed. I need to think about this design and rework it.

One thing I’ve done since that test that may help is build a guide for the fishing line that extends right up to and across the break between the two halves of the container. I’ve also added a tab near the bottom of one of the halves to try to keep them aligned a little better. Finally, I added some screws to hold the fishing line instead of just tying it on the back side. I’ll give it a go tomorrow night and see how it works out. I can’t try it right now because the epoxy is still wet.

I read somewhere that if you are going to use an eye bolt for a shock cord mount in a high powered rocket you should use one that is welded shut. The person who wrote that article was claiming that the strain on the bolt can open the eye if it isn’t welded shut.

That seemed like a bit of overkill to me, but then again this is Project Overkill so… I definitely considered it. All of the sources I know about don’t have the type that is welded shut, but I came up with another idea. Take a look at these rope clamps.

If you take them apart they look like this.

If you take one of those U shaped bolts, four of the nuts, and add a couple of washers, I bet that’s pretty strong and probably over kill. So, that’s what I did.

You can’t see the washers, but I did put a couple on the bottom of the centering ring. I figure that’s where they are needed.

I’ve worked on the fins on and off over the last few days. I started out making 1/8 inch birch plywood fins with tabs long enough to pass through the body tube all the way to the motor mount. I figure that’ll add much more strength than the fins that came with the LOC IV kit I started with. The tabs on the LOC fins were just 1/8 of an inch deep or so. They were enough to pass through the body tube and get a glue fillet on the inside, but no where near long enough to attach to the motor tube and centering rings.

Once I had three of those plywood fins cut, I cut six 1/8 inch balsa fins slightly larger but without the through the tube tabs. I then attached one balsa fin to each side of each of the three plywood fins. This gave me the ability to shape the fins without sacrificing much of the plywood.

[In this photo only the leftmost fin is seen straight on. The others are seen at a bit of an angle. When viewed straight on they appear more uniform.]

I decided this time around to try to shape the fins into an airfoil. I’ve never done that before and I know it is fairly exacting, so I was pretty nervous about getting it right. I started by laying down a piece of tape one inch from the rear edge of the fin to use as a guide while sanding the initial bevel. The tip is only two inches long so this is half the length of the tip. I then beveled the rear end of the fin. I did that on both sides. At this point the fin was 3/8 inch thick one inch from the rear edge, but only 1/16 inch along the rear edge. This was just a plain, straight bevel. I did not put any curve into that bevel yet. Once I had done both sides of the rear edge, I moved to the forward edge. Here I started by adding a bevel, but quickly turned it into a blunt rounded curve. Once both sides of the forward edge were rounded I added a curve from the rear bevel to the front rounded edge. That gave me a nice airfoil shape. I don’t know if they are good enough, but they look decent to my untrained eye.

I know that I should have tapered the fins so that the chord to thickness ratio remained constant for the entire span, but I just couldn’t bring myself to attempt that type of complexity yet. Maybe on the next big rocket.

I also added a coat of cyanoacrylate (CA or super glue). I wanted to make the balsa a little more resistant to dings and dents. The CA seemed to wick into the fibers and add some strength. Once it was dry I gave them a good sanding.

We had a little rocket building party at our place.  Miranda invited two of her friends over and the three of them and Matthew built rockets.  The three girls each built a FlisKits skill level 1 Whatchamacallit.  Matthew built the larger, but still skill level 1, Thing-a-ma-Jig.

[Rockets built by Matthew, Miranda, and Miranda’s friends]

The fins on these kits were interesting. Because of the way they interlock with each other it was very easy to align them properly and we didn’t need any sort of jig to hold them while they dried, though we did use a little tape to hold them together.

Overall the party went well.  Three eight year olds and a three year old are a little bit much for me to handle on my own for a build like this, but my wonderful wife helped out and it was a good afternoon.

We will have the girls over another day to paint the rockets. We’ll bring all the kids to the local hardware store and let them each pick a color. We’ll also take them to a store where they can buy stickers (I’m thinking iParty). When we get back to our home they’ll spray paint the rockets one color each. The morning of the launch they can put on the stickers.