Performance Rocketry 4-inch Nike Smoke (Part 1 - Introduction, Parts Orginization and Engine Mount Construction)

Nike Smoke on launcher

 

The Nike Smoke program was developed to study high altitude wind patterns to aid in the design of larger rockets.  After boost, when the rocket begins to decelerate, it would begin to vent a smoke producing chemical into the atmosphere from a tank located in the oversized nose of the rocket.

Smoke Trail Measurement

 

Data plot of smoke trail from analyzing the camera footage

 

The chemical would react with the air and produce a persistent "smoke trail" that would be visible to cameras and measuring equipment on the ground.  By tracking the speed and direction of the smoke trail as it drifted in the various atmospheric winds, engineers could generate wind models and gain better understanding the crosswind forces acting on high altitude rockets.

If your interested in learning more about the Nike Smoke program, take a look at the following video:

NASA: Smoke Trail Wind Shear Measurements

G. Harry Stein Nike Smoke scale drawing

My Performance Rocketry 4-inch, all fiberglass Nike Smoke was originally supposed to be my Level-1  NAR High Power Certification rocket.  However, at some point during construction, I determined that the finished launch weight of the rocket was going to be in the neighborhood of 8lbs!  While I could probably eek a pretty anemic flight out of an I motor, this rocket really wants a nice easy lifting J, and so I decided to use it as my Level-2 rocket instead.

Getting an idea of the size of the kit

This was a loooooong build for me.  It was my first all fiberglass rocket and my first high power build in over a decade.  I also made a major modification to the design as I will detail below.  I added a small avionics bay in the shoulder of the nosecone to allow for electronic deployment.  This added significantly to the time and complexity of the build.

Figure 1 - Kit contents plus a few things not included in the kit

These kits are "bare bones".  They only include the main structural components: Body Tube, Nosecone, Nosecone bulkhead, Fins, Motor Tube and Centering Rings.  Everything else (recovery hardware, shock cord, rail buttons, etc...) must be purchased separately.  Still the kit was a pretty good value and being constructed entirely of fiberglass, if built right, it should last for many, many flights.

 

 

Figure 2 - Centering ring reinforcement

The kit came with 2 fiberglass centering rings which I augmented by laminating them together with 2 1/2" plywood centering rings.  This was done for both rigidity and also to allow for the tapping into the rings for the rail button launch guides.

 

Figure 3 - Centering ring sizing with sanding drum

The fiberglass (and also the plywood) centering rings required a bit of sanding on both the outside and the inside of the rings to get an ideal fit.  I used my sanding disc for the outside sanding and for the inside sanding, I purchased a set of sanding drums.  These made sanding the now 1/2" thick centering rings much easier. 

 

Figure 4 - Marking the motor retainer flange holes

I decided to go with Aeropack flanged motor retention, so the holes for the flange piece had to be marked and drilled.




Figure 5 - drilling the motor retention flange

holes

The flange bolts were 1/8" so I was able to use my Dremel to drill the flange holes.  There are six holes in all, so I went pretty slow and checked the alignment between each hole to make sure everything was lining up.

Figure 6 - Motor retention flange attached.

Another thing to watch out for here besides the flange holes not lining up is that the flange has to be perfectly centered on the inside hole of the centering ring.  If it's not, you will end up with a small "lip" of the motor tube interfering with the motor case when you try insert it into the rocket.  All-in-all, this step went very smooth considering all the things that could have gone wrong.

 

Figure 7 - Fillets using JB Weld

After the motor retention flange is attached, the centering rings can be epoxied to the motor tube.  Because of the possibility of high heat transferring from the outside of the engine case to the motor tube, I elected to use JB Weld steel reinforced, high temperature epoxy for both attaching the rings and for the reinforcing fillets.  This epoxy is slightly heavier than standard epoxy, but I think the extra temperature margin it provides is worth the weight trade off.

 

 

Figure 8 - Hole for shock cord retention hardware

Once the epoxy for the centering rings had dried, it was time to drill a hole for the 1/4" stainless steel shock cord retention eyelet.  My first attempt (shown in Figure 8 above) was too close the motor tube for the nut to fit, so I had to plug that hole (with JB Weld) and drill a new hole a bit more centered in the ring.

 

 

With the hole corrected, the eyelet was attached and the nut permanently glued onto the threads.  I used JB Weld here too, not because this area will see a lot of heat, but because JB Weld adheres very well to metal surfaces.

Well that about wraps it up for the motor mount assembly.  The next step is installing the motor mount into the main body tube and attaching the fins which will be "through the wall" and anchor to the outside of the motor mount tube.