Rocketry

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.

I’ve decided that I’d like to get my high power rocketry level 1 certification. I do have a LOC IV kit down in the cellar I could slap together and fire off with a small H motor for that purpose. Of course, being me, I just can’t do something that simple. Why follow the KISS principle when you can get overly complex?

With this in mind I’ve decided to start Project Overkill. This rocket with be much stronger than it needs to be. It will be much larger than it needs to be. It will be much heavier than it needs to be. It will be more complex than it needs to be. It will be daunting and intimidating to build, but it will be fun.

The basic idea is simple, three fins and a nose cone. However, the body tube will be four inches in diameter and the rocket will be about six and a half feet tall. It will fly on an H, a small I, or a big I. The H will drive it about 900 feet and the small I will push it up to 1,500 feet. I won’t use the big I for now since I don’t have access to a field big enough.

Since I’m concerned about recovering the rocket within the field I’m going to use a dual deployment system, even though that isn’t strictly needed. I decided I didn’t want to have to go through the hassle of dealing with black powder so I’m using one based on an igniter melting through fishing line similar to this one.

I also plan to fly a video camera in the rocket. I picked up a Muvi video camera similar to this one on sale with that in mind. I haven’t figured out how I’m going to mount it, but I guess I will.

I’ve simulated this rocket in RockSim. It looks like it will fly just fine. When I first simulated it RockSim predicted that it would be heavy enough that the best engine would be an I212, so I ordered one. However, as the parts started to arrive it became clear that the sample parts I had picked from the RockSim database were heavier than the actual parts. For example, I had picked a 60″ parachute and it was listed as 14 ounces. The actual 72″ parachute that I purchased only weighs 6 1/2 ounces. I decided that I should use a smaller engine for the first flight and ordered an H125. Of course, that means that if it survives the first flight, I have a second, larger motor to fly it a second time on the same day.

The current plan is to launch Project Overkill on July 17th at Woodsom Farm Park in Amesbury, MA if it is finished in time. If I don’t finish it in time then I’ll launch it in September (the next HPR launch in Amesbury). I’m not going to stress out and push to finish by July 17th. If I finish by then, great. If not, so be it.

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.

On May 22nd my two kids (3 and 8 years old) launched their first rockets.

Matthew built an Estes Amazon and Miranda built an Estes Crossfire ISX.  I let them each pick out one spray paint color at the local hardware store.  Matthew picked a horrible florescent green, but once that was sprayed onto the black rocket, it turned into a decent green.  Miranda picked a super glossy dark blue.

I originally planned to let them draw on the rockets with markers, but the marker didn’t stick to the glossy blue.  Even a Sharpie marker couldn’t touch it.  So we tried model paint.  That didn’t work out well either.  The glossy blue was just too slippery.  In the end I bought a bunch of stickers.  The kids had a blast covering their rockets with stickers.  Miranda just used a ton of smiley faces and named her rocket “Giggle Powered”.  Matthew used various stickers plus the original Amazon sticker that came with the kit.  He stuck with the name “Amazon”.

[Clicking the image will display a slideshow of photos from the day.]

Matthew’s Amazon flew six times on Estes C6-5s without incident.  Each flight was perfect with a nice slow lift-off and safe recovery.  On one flight it landed in some tall grass and took a few minutes to find, but we found it easily.

Miranda’s Giggle Powered on the other hand had a much more adventurous day.  The shock cord broke on the first flight.  The body landed without any recovery system attached, but it bounced on the grass and survived without damage.  I tied the shock cord together and it broke again on the second launch and the third.  Before the next one I added a long section to the shock cord. That did the trick.  This time it landed safely under the streamer.

The fifth launch went without incident as well.  On the sixth launch it hit a wind gust and flew off course.  It went well into the trees and I thought it was gone forever.  I spent a while beating my way through the overgrowth and finally saw it hanging high in a tree.  However, the guys running the launch had a 30 foot pole with a hook at the top.  Using that I was able to bring the rocket back.  Despite all the broken shock cords and a crash into the trees Giggle Powered survived the day.

Despite launching on Estes B4-4s instead of the C6-5s Giggle Powered was still very fast and flew very high. Following it with the camera was next to impossible.

Each kid now has their rocket hanging on their bedroom wall.  They both enjoyed building and flying them.  It was a great experience for all of us.