TLP Nike-Ajax 2-stage build thread

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dedleytedley

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This kit is intended to be built as a 3 D cluster single stage. I'd like to share the fun I had building this bird. As a relative novice at rocketry modifying this bird to a 2-stage offered some interesting challenges. To fire the sustainer motor without electronics I decided to use a low voltage 2 position NC/NO micro switch from a local electronics supplier(see pic attached).
I mounted the switch to the side of one of the three booster motor tubes using a wraparound piece of sheet aluminum with the switch lever protruding into the motor tube. I then plugged the tube with a piece of a spent D motor. I filled the nozzle with some clay and epoxied it in place as a motor stop. I then soldered a length of duplex wire from an estes launcher to the switch. Soldering was a mistake, when I tested the circuit I found that the heat from soldering ruined the switch. I replaced the switch and epoxied the wires in place. The switch when depressed by the inserted motor breaks the circuit and when the motor is spent it ejects(D12-0) alowwing the switch to open and current to flow to the sustainer igniter.
The motor mount was solidly glued together with 5 minute epoxy and I plugged the gap between the motor tubes with the same. Ted

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motor mount side.jpg

MM top.jpg

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The next design challenge was the interstage. The maker supplies three fiberboard bt-80 24mm centering rings to mount the extended inner tube from the top portion into the lower portion. I junked this mounting system and ended the inner sustainer tube at the tailcone. The sustainer motor was set to protrude by 5/8 inch. I selected a 4 inch coupler to serve as the body of the interstage. Then I made two centering rings from 1/8 aircraft plywood with 24mm centers, one was the size to fit inside the coupler and the other was 1/8 inch wider in diameter to top the interstage. I cut a 5 inch length of bt-50 for the core and overlapped it with sections from a paper roll core(I.D. 25mm). I made a bulkhead from plywood and cut notches in it to pass tabs glued into the base of the interstage. Two screw eyes were glued into the bulkhead, one for shockcord and chute, the other for the wires.

interstage parts.jpg

interstage bottom.jpg

interstage top.jpg

interstage with bulkhead.jpg
 
The supporting struts on the interstage are to be made from balsa when built to spec. I made them from aircraft plywood and popsicle sticks so they would be solid enough to help stabilize the sustainer when under g's from the three 24mm cluster.
To place the struts accurately for support it was necessary to build the sustainer, put a 24mm motor in it and place it in the interstage. The 5/8 of motor protruding from the sustainer fits into the core of the interstage to be flush with the cap ring. The tailcone was painted with epoxy glue inside and another wrap of cardstock was epoxied over it minus the overlap. After drying I "painted" the tailcone with thin CA. When spreading CA to stiffen parts use a plastic grocery bag over your hand to smear it around. The glue doesn't harden on the bag as long as you move quickly. The glue will dissolve ink so turn the bag inside out.
With the sustainer in place I flushed the supports to the tailcone and glued them to the cap ring and interstage core tube. After the assembly dried I wasn't satisfied with the rigidity of the interstage/sustainer joint.
I considered a number of options to deal with the flex of the struts and settled on using a scavenged aluminum number dial from an old thermostat. It is about a mm thick 46mm outer diameter and I widened the inner diameter to 26mm. Using a very thin cutting wheel on my dremel Slits were cut into the struts parallel to the cap ring and the stiffening ring was glued in place.
That was much better! Holding the whole rocket flat by the booster and moving it up and down it felt like one continuous body tube. Unfortunately it's a deviation from scale but it's a compromise that was necessary to make it a stable flyer. Ted

interstage with supports.jpg

interstage final assembly.jpg

mount assembled.jpg

sustainer MM parts.jpg
 
A further modification from the kit was the booster fins. A template is supplied with the kit to cut these fins from 1/8 balsa. I chose to make them built up from paper so I cut the template with the root chord extended by 3 mm. I then used the template to mark some file folder stock for the fin covers as one piece. Templates were made for the balsa internal frame for the fins. These were glued, then the covers were painted inside with epoxy and glued onto the frames. After the glue dried CA was painted on the surface of the fins. Later the fins were glued on the B.T. and filleted with epoxy.

booster fins parts.jpg

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Another modification to the kit was the substitution of 2mm thick acrylic for the nosecone fins. When I flew my TLP Bullpup with the balsa nosecone fins they were too fragile and were replaced with the same acrylic. In the bullpup and this rocket it was necessary to extend the shockcord to prevent body tube damage from nosecone backlash.
Ejection baffles were added to both the booster and sustainer and the shockcords were attached there.
The wiring tunnels differ from the instructions, they say to shape them with the width tapering from the ends to the middle. After viewing several photos I saw that was incorrect and made them in four pieces each with the center section(between the fins) having the same width and thickness. The rest of the tunnel tapers gradually to either end.
I like to tape a sheet of sandpaper to a flat smooth piece of wood and rub the piece I'm beveling back and forth against the paper. This works well for fin edges and other straight parts to give a clean straight bevel.
I also didn't like the antennas design so I extended the paper pieces to wrap into a triangular shape with the point trimmed. Short pieces of 3mm dia. dowel were glued into the antenna housing to simulate the actual receivers.

rockets and kids 081.jpg

TLP nike-ajax.jpg
 
My Nike-Ajax had it's maiden flight in primer and the results were mixed. It came off the launch rod with all motors burning and at about fifty feet began spinning wildly!:y: A gust of wind and my mistake in balancing it made it unstable. With a sense of impending doom I watched the sustainer fire pointing almost straight up! It rose nice and straight to a few hundred feet meanwhile the booster popped the interstage and deployed both parachutes. It landed unscathed and the sustainer filled it's chute and landed undamaged.:jaw:
The interstage took a lot of blast damage, the wires and battery were well toasted. The next time I'll use some kevlar inside it. Other than that minor damage the rocket is intact and ready to fly again.
I used CP data from EMRR and calculated for 1.5 calibers. Where I erred was in the balancing I used One unused engine and two SPENT engines in the booster. The difference in weight of the missing propellant was enough to render it at least marginally unstable. That combined with a wind gust likely caused the unstable flight. At least I confirmed the interstages' rigidity, it held up very well under the stress.
Next flight I'll be weighting it with all full engines.:eek: The rocket gods were smiling on me that day!
Here are some pics of the first coat of paint, there is lots of filling and painting to be done yet. Ted

kids and rockets 096.jpg

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I had a mostly successful flight of my Nike-Ajax today. I loaded the booster with a D-12-0 + 2 D-12-3, the sustainer had a D-12-5. My earlier problems with dynamic stability were caused by the launch rod being too short for such a heavy rocket. The weight was reduced by replacing the 9 volt with a AA and using q2g2 for second stage ignition and I used a six foot launch rod. All the booster motors lit and it rose straight to about 300 feet when the sustainer motor fired. That's when things went awry. The upper stage took off at 45 degrees to the boosters' direction for 100 feet or so then took another 45 degree turn upward and again turned after some distance, climbing all the while. Meanwhile the booster deployed and shed the parachute. I must have not clipped it on correctly:bangpan:. While it tumbled down the sustainer parachute deployed and it drifted down. The booster had one fin mangled and the interstage top came off on impact. It's repairable and might even fly again this season. Ted
 
Blast damage from the second stage lighting was extensive and the interstage came apart at the crash. It didn't fly again last year as it's still awaiting repairs. I've decided to try routing the damaging gases through the wall of the interstage support tube and out the top of the interstage. I'll place a plug cut from the base of a used D just below the vent holes in the support tube. I'll cut holes through the top of the interstage between the supports and cover them with low angled shroud pieces to vent the gases. Only the wire ends and the clips will get toasted rather than the battery holder and other wiring. Also one fin was unsalvageable and I need to make another. I recently bought decals for it and have some filling and painting to do.
I'd like to fly it at my local club launches so I'll have to attach a streamer to the ejecting motor.
Sorry no pics but there's video of it on youtube under dedleytedley. Ted
 
Nice, Complex challenging all the makings of a great rocket.

Hope the rebuild goes good! I'd like to see that one in the air!!
 
I think staging midpower models like this are definitley a challenge. Chuck Brandt, the owner of TLP, staged this model years ago. But he owns the company and has had a practice. His plan pack for the Standard Missile calls for a staging using a micro switch, which is what I think you had at the start of the thread.

Bob
 
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