Build thread: NCR SA-14 Archer

Dane Ronnow

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We're still in the thick of the summer heat here in the desert Southwest. To pass the time, I'm taking on another kit, this time the SA-14 Archer from North Coast Rocketry. I was actually looking at two other NCR kits—the Bounty Hunter and the Lance Delta—and was trying to make up my mind between those two when I took a look at the Archer. I liked the fin shape, and man, check out those strakes. Sign me up.

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The kit has nice body tubes (LOC tubes maybe?)—a 24" lower and 10" upper—with clean, straight fin slots. The coupler and motor tube are thick-wall. Wood parts are decent—a little warping on the fins and strakes, and some splintering on one leading edge, but nothing serious.

The kit has a shock cord system NCR is famous for—an .063" steel cable 18" long that anchors to the aft CR, then 12' of braided Aramid cord (looks like 2mm), and, at the top end, 4' of 1/2" black elastic, which would stretch to around 12'.

Full-color stickers and instructions compliment the kit.

I weighed and measured all components, then entered that data into the OpenRocket design file I had already started. Then I plugged in two motors—the AT G-74-6 and AT G80-7—to check stability. It's overstable on both—2.82 on the G80, and 3.03 on the G74. And it pitches quite a bit in the sims.

I had been thinking about narrowing the fin semispan from the first time I saw a picture of the rocket. I liked the shape, but it stuck out too far for me. Now, with an accurate OR file to run comparisons, I cut the semispan from 5.35" down to 3.45", then ran the sims again. Stability with the G74 dropped to under 2.00, and pitch rate was cut in half.

So, I'm running with that. Once I had the fin shape where I wanted it, I printed out a template and marked the fins. I planned on using a razor saw to do the cutting, so I set up a guide with a straight edge and a clamp. Then I made a couple of passes with a heavy hobby knife, making it easier for the razor saw to settle in without jumping out of the cut.

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These turned out nice, with smooth, straight cuts.

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Then I clamped the fins and block sanded the edges to even everything up.

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Dane Ronnow

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Next up, assembly of the motor tube. NCR kits have an 8.5" MT with three CRs. The CRs are slotted on the outer edge for the fin tabs, and on the inner edge for two struts that keep the CRs in alignment with each other.

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The tab-and-slot idea is a neat system, but the parts in my kit are very loose fitting. Twelve slots and tabs with this much gap is going to make fin alignment difficult.

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I think I'll pass on this method, and just move the mid and aft CRs farther apart.

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I moved on to marking the tube for CR placement, and found the forward CR had a ton of gap. And the hole was off center by nearly 0.1".

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Fortunately, I found one the same size in a spare parts box. It's not drilled for cable attachment, but I'm using a different setup for the shock cord attachment.

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Dane Ronnow

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Since the new plan calls for moving the aft CR from 1" inside the bottom of the BT, to .25" inside, I decided to cover the fin slots with a BT-80 x 24mm cardboard CR for a cleaner look.

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With a new forward CR in hand, I epoxied it and the mid CR in place with J-B Weld, and set it aside to cure.

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Time to paper the fins. But first, I want to round the leading edge. I marked the edges on both sides with a reference line, then block sanded the angles first, then rounded them. Last step before papering, repairing the splintering on the leading edge of one fin.

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Dane Ronnow

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I'm papering the fins with Avery full-sheet labels (#5265). But I want to leave the tabs and root bare for gluing the fins in the body tube, and for fillets. I mark the area, then mask with blue tape.

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With the backing removed from the label sheet, I carefully placed the fin with the leading edge centered from left to right, and at a right angle to the bottom of the sheet. Then I cut the paper from the edge of the fin to the top of the sheet and folded it slowly, rolling the leading edge over. Once the sheet was folded flat, I rolled it with a brayer, from the leading edge to the trailing edge.

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I trimmed most of the excess paper, then scored the label along the edge of the blue tape, giving me a reference mark for cutting the paper away. Then I peeled up the tape, and trimmed the tab and trailing edges.

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Next up, installing the bulkhead in the coupler.
 

Dane Ronnow

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I set up the coupler and bulkhead today. And I got most of an ejection baffle built.

First, the coupler. I replaced the 4" one that comes in the kit with a 6". Same diameter, just longer. On a body tube joint that is going to be permanent—epoxied in both tubes—a 4" is fine. But in a separating joint, I like the exposed section to be at least one body tube diameter in length.

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The instructions call for attaching the bulkhead to the aft end of the coupler, but I need more room for the parachute and harness, so I'm recessing the bulkhead 1.75". And to give it a little more resistance to pulling forces, I'm going to epoxy a short sleeve above and below the bulkhead.

I cut the rings from an old coupler tube, then split them and marked the overlap inside the coupler. I trimmed them, then placed them inside the coupler and glued the ends with Elmer's white.

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While the white glue was drying, I set up the bulkhead. I'm installing two eye bolts—one for the lower shock cord, and one for a nose cone tether. (My altimeter rides in the nose cone, so I'm not cementing it to the upper body tube. The tether prevents the loss of the nose cone and altimeter in the event the cone comes loose during the flight.)

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Next, I epoxied the lower ring into the coupler and let that sit for 30 minutes. Then I epoxied the bulkhead in place, followed by the upper ring.

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Dane Ronnow

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The ejection baffle is an Apogee BT-80 kit. It will install in the lower BT, 3" ahead of the forward CR. The kit consists of a 4" thin-wall coupler, the forward and aft plates, and a reinforcing disk for the screw eye.

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I'm adding two short tubes—a 1" piece of BT-55, and a 1.75" piece of BT-60. The idea is to restrict the movement of hot particles from leaving the top of the baffle, and into the parachute area.

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The BT-55 will be epoxied to the lower plate, serving as a choke for the particles, directing them into the mouth of the BT-60, where they are blocked at the upper plate. The flow of gas is completely unrestricted.

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First, I attached an eye bolt to the upper plate. This is the anchor point for the shock cord. Then I epoxied the small tubes in place with J-B Weld.

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I set those parts aside to cure, and cut a .375" sleeve and epoxied it in the end of the main tube for more forward plate support.

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I let everything cure overnight, then epoxied the forward baffle plate.

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More curing, then I'll install the aft plate.
 

NOLA_BAR

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Wow, nice build thread you have here! Using an inner sleeve in a coupler or body tube is a technique I’ve used a few times. I’ll build a cross assembly to mount a screw eye for a Kevlar shock cord, the cross is mounted below and against the ring. Like you said, added strength from pulling force.
 

Dane Ronnow

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Wow, nice build thread you have here! Using an inner sleeve in a coupler or body tube is a technique I’ve used a few times. I’ll build a cross assembly to mount a screw eye for a Kevlar shock cord, the cross is mounted below and against the ring. Like you said, added strength from pulling force.
I've been doing this on my MPR builds whenever a bulkhead or baffle plate with an eye bolt is inside the tube. It's easy, adds very little weight, and makes that joint much stronger.
 

Dane Ronnow

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Time to finish the baffle. I sprayed the inside of the tube and the aft plate with Rustoleum high temp paint, then epoxied the plate in place. After that cured, I attached the lower shock cord tether and coated the surface of the aft plate that faces the motor tube with J-B Weld to give it a little protection from the ejection flame and gas.

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After everything dried, I epoxied the baffle into the lower BT, three inches ahead of where the forward CR will be.

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Next I epoxied the coupler in the bottom of the upper BT.

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Dane Ronnow

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I finished the motor tube assembly with fillets on the CRs, and a coating of J-B Weld on the fire-side of the forward CR, then set it aside to cure.

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My plan was to cut the angles on the strakes next. But as I was laying them out to measure for the cuts, I noticed one of them was a completely different grade of balsa than the other three, a much heavier, harder wood. Where the other three weighed in at about .4 oz. each, this odd strake weighed more than twice that, at .95 oz.

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These strakes were warped when I first unpacked them. One had a pretty serious twist. I tried flattening them by wetting them and pressing them between two pieces of plate glass with books stacked on top, then letting them dry for a week. Two attempts at that with no success.

Now with this difference in grade and weight, I decided to throw in the towel on these, and ordered a sheet of 1/4" hard balsa from BMS. I'll cut new strakes when that arrives.
 
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Dane Ronnow

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I changed my mind on replacing the strakes with new balsa. I found a piece of scrap 1/4" long enough to cut one strake, so I'm keeping the other three light ones. The warp in them isn't so bad that I can't pin them when I epoxy them to the body tube.

The average difference in weight with the new strake is less than .2 oz. Much better.

These are the strakes with ends trimmed:

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For the strake that was twisted, I wanted to take one more stab at straightening it, but rather than press it between glass with books stacked on top, I wanted to try applying torque. I soaked the strake for 30 mins in water. At the 15 min mark, I twisted it in the opposite direction several times to free up the grain. I did the same after 30 mins. Soaking wet, the straked gave little resistance, and maintained a straight profile after twisting.

Then I clamped the ends, supporting the clamps to keep the strake ends parallel.

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I have no idea if this will work, but I figured it was worth a shot. Stay tuned.
 

Dane Ronnow

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Clamping wet balsa to remove a twist was a complete bust. I had to laugh at myself when I pulled the clamp, thinking, "What did you expect? You were clamping a wet sponge."

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The twist was still there, so I went ahead and cut a new strake, then sanded the edges and rounded the leading and trailing ends. Then I marked the tube for placement.

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Next, I attached a 2.125" sleeve to the top of the body tube with CA to reinforce it against zippering. Then I notched the strakes to fit.

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After the CA dried, I installed the motor rube assembly using J-B Weld.

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After the J-B was fully cured, I did a test fit on the fins and discovered the tab roots were short by 1/16". So I cut a stirring stick into narrow strips and glued them to the tab roots with Elmer's yellow.

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As soon as the Elmer's is dry, I'll install the fins.
 

Dane Ronnow

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Looks great with nice detail. 👍 Waiting to fly mine next month.

That's a great looking rocket. I'm taking a few liberties with the paint and decals on mine; more red, and custom vinyl from Stickershock. The nose cone will be red, because I'm sharing it with my HV Arcas build that's waiting for primer and paint. But aren't these cool rockets to look at?

Anyway, thanks for the feedback. Post a pic here when yours flies.
 

Dane Ronnow

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I attached the fins to the body tube using 30 min. BSI epoxy for the fin/BT joints, and J-B Weld for the fin tab/MT joints.

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Before doing the internal fillets, I used a dab of J-B Weld to form a small dam at the end of each tab to keep the 30 min. epoxy from running over the edge and ending up where the aft CR will fit.

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I used J-B Weld for the tab/MT fillets, and 30 min. BSI for the tab/BT fillets.

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After the fillets cured, I attached a small piece of coupler between two fin tabs to reinforce the body tube where the aft rail button will be located.

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Dane Ronnow

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Holes for the rail buttons and pressure relief vents were cut next. I'm using well nuts for the buttons, so the holes are 5/16" diameter.

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Then I test fitted the aft well nut and button to make sure the nut would compress fully.

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Then I cut the forward rail button hole just ahead of the aft baffle plate to take advantage of the thickness of the body tube and coupler.

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Then I drilled four 3/32" holes for the vents. These are located 1/2" below the bottom edge of the inserted upper BT coupler.

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Strakes are next.
 

Dane Ronnow

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Before I attached the strakes, I buttoned up the back end with the aft CR and motor retainer.

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The hardest part about attaching the strakes was the flat bottom on a round tube, with just enough epoxy between them to make everything slippery. An adjustment at the bottom end moved the top end out of position. Readjust the top, and the bottom moved. And, of course, tipping off vertical with any other adjustment.

I got smart on strakes 2, 3 and 4, and pinned them into position first, top and bottom, then lifted them out, epoxied them, and slipped them back in between the pins. Then it was a simple matter of aligning it with the fin.

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Now I've got to work up the nerve to do the fillets—fins and strakes. I'm using RocketPoxy G5000 for the first time. My previous one (and only) fillet was with Titebond Quick & Thick. That was alright, just not as strong as epoxy. This is a heavier rocket, with a little faster descent rate under the parachute. So, a little harder landing on an unforgiving lakebed. Anyway, yeah, G5000.

Stay tuned.
 

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One thing you could do next time for the strakes is to sand the bottom before gluing them to the tube. Take some sandpaper, wrap it around the body tube, sand each strake's bottom edge on the sandpaper. You should end up with a slightly rounded bottom edge, which will conform to the tube more easily.
 

Dane Ronnow

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One thing you could do next time for the strakes is to sand the bottom before gluing them to the tube. Take some sandpaper, wrap it around the body tube, sand each strake's bottom edge on the sandpaper. You should end up with a slightly rounded bottom edge, which will conform to the tube more easily.

I thought about doing that, but I was worried I wouldn't get an even curve and possibly make matters worse. Knowing what I know now, though, I'd give it a shot. Still, the pins worked pretty good, although it did take a little effort to pierce the tube without bending the pin.
 

Dane Ronnow

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I completed the first set of fillets today using the RocketPoxy G5000. And I have to say that those who say the consistency of this stuff is like peanut butter, must keep their peanut butter in the fridge. Mine was pretty stiff.

Anyway, standard method for marking lines—scoring the tube and fin with carbon paper—then laying the masking tape.

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I used a very small container (1 oz. measuring cup), so mixing parts A and B was a little difficult to do with the supplied tongue depressors. I ended up doing all the stirring with a wooden coffee stirring stick.

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After mixing, I applied the RocketPoxy, then let it sit for about 20 minutes.

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Then I pulled the fillets, using a 5/8" ball for the fins (5/16" radius), and a 3/8" ball for the strakes (3/16" radius).

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I let those sit for 5 minutes, then pulled the tape. All in all, I think they turned out pretty good.

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I'll let this cure overnight, then do the other three sets.
 

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I use pop-sickle stick to mix RocketPoxy.

Another thing I now do is after pulling off the tape, run a gloved finger wetted with alcohol along the edges. The tape causes the epoxy to be slightly raised (tape thickness) and easier to smooth this edge before epoxy cures rather than sanding after cure.
 

Dane Ronnow

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I use pop-sickle stick to mix RocketPoxy.

The first thing I did after finishing up the this set of fillets was to pick up popsicle sticks from Hobby Lobby. They're half the width of the tongue depressor, but thicker than a coffee stirring stick.

Good advice on removing the edge with a gloved finger. I used the edge of a coffee stirring stick, being careful not to disturb the formed fillet. It worked pretty good, but I think a gloved finger would work better. I'll find out later today.
 

Dane Ronnow

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I found that using a metal paint stirring stick from Tamiya, that it works very well on epoxy.

Fifteen seconds into the mixing process, I thought about grabbing a flat-head screwdriver, then changed my mind. If I don't have the tools I'm going to use laid out in front of me before I start working with epoxy, I hate stopping to find something else.
 

Dane Ronnow

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I finished the fillets. As I mentioned above, this was my first time using RocketPoxy, or any other kind of epoxy, for external fillets. Much smoother and easier to pull than Titebond Q&T. More work to mix, of course, and those 17.5" strakes added a lot of time to each application. But absolutely, my go-to adhesive for fillets from now on.

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This completes construction of the SA-14 Archer. Next up, primer and paint.

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