In this final level-2 EZI-65 lesson, we will finish and assemble the rocket.

• Finishing
• Final Assembly
• Ejection Testing
• 38mm Motor Adapter

Finishing

Everyone has their favorite way of finishing rockets, but there are some things that are always good advice. You must prime the rocket before painting. Make sure to use a primer compatible with the paint you're planning to use. Take your time in the priming, this is where your determine the ultimate quality of the finish.

Sand your rocket exterior smooth. It should be smooth to sight and touch all over. Fill any open fiberglass weave with automotive spot putty. Once you think the exterior is perfect, put on the first coat of primer. Let this dry thoroughly. Now you can see the spots you missed. Fill any remaining imperfections and prime again. Repeat this process until you're happy with your result. The paint will never cover imperfections you leave at this stage. However, minor imperfections will also not be noticeable in the finished product.

Blow molded nose cones have always been a problem for me. The sanding you do to remove the mold marks and parting line raises "fuzzies" which you can't sand out. Alternating applications of primer and sanding are the only way to conquer the fuzz. Also, the paint never sticks as well to the nose cone as it does to any other parts. If possible, design your paint scheme so that the nose is a solid color. If you try to mask the nose cone, the tape will pull the paint and primer right off the nose.

I did manage to mask and paint on the nose cone of my V2, but it required using low-tack tape and touching up by hand. For the EZI, which isn't a model of anything, using a solid-color nose should be no problem.

Primer is very forgiving, but paint is less so. When priming, and especially when painting, apply light coats and paint a section of your rocket in 2-4 passes. With Krylon, these coats can be very close together, but too heavy a coat will cause the paint to sag and even run. Your first coat shouldn't even fully color the rocket. If you're painting white over gray primer, as I was, the gray should still show through a little after the first coat. It will be completely gone by the third coat. On this rocket, I even did a fourth coat just to make sure the white was solid and even. I built a little lazy susan which sits in my paint booth, which makes it easy to turn the rocket, paint about a quarter of it, turn, paint again, etc.

For most of my rockets, I've used Krylon brand spray paint cans. A superior system is the automotive paints, but these require an expensive setup and a paint booth. Automotive paints are definitely the way to go if you have the facilities. People have recommended Kilz brand primer for use under Krylon paint, .but I haven't tried this myself. If you do use spray can paint, make sure you get high-quality paint which allows you to "recoat any time." Krylon can be found in automotive stores and some national department stores such as Sears and K-mart. You usually can't find it in hardware stores, though. You will use almost two cans of primer on this rocket. If you paint the entire rocket the same color, you might be able to do it with one can of paint, but more likely two.

Forget masking tape, model masking film, drafting tape, etc. The tape for masking is ordinary clear tape (such as "Scotch tape"), although the partially opaque kind is easier to see than the truly transparent kind. Clear tape leaves razor-sharp lines and is easy to use. However, it is very high-tack and will pull up paint if you didn't prime or the paint isn't fully dry. Be careful not to handle the tape too much before applying and make a fold in one end so you have a handle to pull it up with. Once the tape is positioned correctly, run a finger along the edge to make sure it's fully down against the body.

Design your paint scheme so that your lightest colors are painted first. In my case, most of the body was white so I painted the entire airframe white before anything else. My nose cone and fin can were done in Krylon Brass so I painted the nose cone separately and the fin can next. This is where the "recoat anytime" paint is important since you'll generally be painting several different colors in stages. By painting the darker colors later, you can use less paint (1 or 2 coats), which will make the "steps" between the paint less noticeable. Also, try to make the color changes at joints in the airframe. An abrupt change of color will hide the seam nicely, which was easy to do with my Mondrian paint design.

Final Assembly

Once all the paint is dry, it's time to put your rocket together! Install the altimeter into the electronics bay. I decided to leave the forward eyebolt attached and unscrew the aft end since it's easier to get to. Install the switches into the electronics bay tube with small bolts and nuts (I used brass #2 bolts). Remember that the down position of the switches will be "on" so for the power switch, the two terminals that you used should be on the bottom and for the charge shorting switches the four you used should be on top. If you used another switch configuration, just make sure that the power switch is "closed" when down and the shorting switch is "open."

Attach the longer tubular nylon strap to the eyebolt on the forward centering ring and to the eyebolt at the aft end of the altimeter bay with quick links. If you decided to use a drogue parachute or streamer, attach it to the altimeter bay quick link too. (If you are using a Nomex shield, put in over the quicklink at the altimeter bay.)

Attach the other tubular nylon strap to the nosecone and parachute at one end with a quick link and the other to the eyebolt inside the payload section. (If you are using a Nomex shield, put in over the quicklink in the payload section.) Make sure you attach the nose cone, parachute and strap to the quick link. Don't attach the parachute or strap to the nose cone attachment directly as it will break.

One thing I noticed is that the rocket seemed heavier to me once I assembled it. I weighed it again and it's now 5.15# all-told. That's a big increase over 3.9# (more than a pound) for the altimeter, recovery system and paint! Oh, well this rocket certainly won't need any nose weight to fly on a K550 now. Also I'm going to go up to a 44" parachute just to be safe.

And, there it is! Time to take your pictures before it gets scraped up or otherwise damaged.

Ejection Testing

It's a good idea to test your recovery system to make sure the parts separate properly with your ejection charges. You can calculate the amount of ejection charge needed with the help of the calculator in the INFOcentral article on Black Powder Use. For the main parachute I get 0.9g (13" payload section minus the 3" nose cone shoulder) and for the apogee separate I get 1.1g (15" to the top centering ring, minus the 2 1/2" altimeter bay shounder) for a 15psi pressurization. 0.9 and 1.1 grams are pretty hard to measure. Most of the payload section will be filled up with parachute anyway. 1g is probably too much, so I decided to start with about a 3/4 scoop of powder for the main ejection charge. For the apogee ejection charge, I decided to use a full 1 scoop charge since there's essentially nothing in the main airframe.

For the test, load an empty plugged motor casing into the rocket to block the motor mount tube. Build an ejection charge. I used a Robbie's Rockets flashbulb-based charge since I had it. You can also build your charges as described by Pete Kerckhoff of Programmin' by Pete. Put your charge into the aft ejection charge holder in the altimeter bay and pass the wire out through the other end. Touch a 9v battery to the leads. The two pieces should shoot apart satisfactorily. Repeat the test with the main parachute bay. Note that you will need to pack the parachute and install the nose cone for this test.

If you want to protect the rocket from grass stains or scratches, you can put the parts in two sleeping bags. Whatever you do, be sure to do it outside because burnt black powder is stinky. Once you get the right charge, make up some ejection charges for use in the field and you're ready to fly!

38mm Motor Adapter

If you want to use this rocket for level-1 certification, you will need to build an adapter for 38mm motors into the EZI's 54mm motor tube. LOC/Precision makes a motor mount adapter, which I used as the basis for mine. I ordered an extra centering ring to act as the thrust right an mounted a 38mm Aero-Pack motor retainer. So my motor adapter also has motor retention and is retained in the EZI motor mount tube with the larger Aero-Pack retainer.

Of course, after all this work to beef up the rocket, do you really want to fly it on a wimpy little I motor? If you do, make sure you use a powerful enough motor. For my 5.15# final weight, I would want at least an I161 (5.15# × 4.45N/# × 5x = 115Ns, absolute minimum).