I started this project last April. I originally wanted to build the stock Cosmodrome kit for a local competition, but decided to bump up to at least a dummy second stage for mission points, then I decided to make the sustainer capable of airstarting an 18 mm motor.... then a 24 mm motor... then dual deploy... then quad deploy.... it was all downhill from there.
Fundamentally, what I have is this:
So on to the details, starting first with the Nike booster airframe. Looking at the parts: the stock body tube is 2.6 inches OD and is a tad on the flimsy side, so that was given a single layer of fiberglass. The motor mount was unacceptable at 29 mm, so that went into the parts bin and was replaced with a much longer 38 mm tube. The centering rings are made from the same aircraft-grade ply the fins are crafted from, so they were formed for the 38 mm tube. The fin tangs were shortened slightly to accommodate the larger motor tube. The tubular nylon harness was replaced with braided kevlar, and the mounting point beefed up to a stainless steel U-bolt from the smallish eye bolt.
Here is a shot of me test fitting the fins before hacking down the tangs and after the internals were attached:
By this point in the build, I had a good Rocksim file for at least the boost portion, and I became concerned about fin flutter. I decided to add a second layer of tip-to-tip fiberglass to the fins.
Moving up to the next most complex part, we have the APACHE sustainer. The most complex part of this is the "fin can": coupling pins, space for an igniter, fins, motor retention... it took me a while to settle on the right retention methodology as well. I visited the LHS and picked up a length of steel control rod wire and a length of brass tube that slid tightly but easily over the wire. The plan was to mount these inside the root of the four fins. If you have seen this kit before, you know the rear end is actually a 29 mm body tube centered over the main 24 mm body tube, with a conically shaped (by hand) centering ring at the forward position, just where the fins hit the airframe. The 29 mm outer tube gets cut to accept the fin tangs. Burly construction. I removed a notch from each fin tang after sanding them into the proper beveled shape and epoxied each into place. When all four were done, I carefully epoxied all four coupling pins into place under the fins.
The main 24 mm Apache body tube was hacked into two pieces at the planned break, and a coupling tube was glued into place on the lower (fin can) section. The paper outer-wrap (simulated payload) was added to the top half, but I skipped the simulated antennae (for now at least).
The balsa Apache nosecone was given several coats of epoxy, with constant sanding, to strengthen it and improve its shape. The nosecone is very delicate! I then hacked off most of its length, hollowed out a small cavity inside it, jammed in two lengths of the thinnest OD allthread the LHS had, and epoxied the whole mess together with a 24 mm couping tube to serve as the shoulder. The rear bulkhead of the electronics compartment was made from aircraft plywood, and given a shoulder tube to give a good seal. I am still fleshing out the details on this part, but I have a general plan on where everything is going to sit, where the tracker antenna will run, etc.
Here is a test fit view with a sketch of the recovery harness layout:
The hardest and third component is the interstage connector, AKA the transition section. Stock, this is a massive chunk of balsa, reinforced with a dowel at the top. Weighing all my design options, I chose to replace the lower balsa shoulder with a 2.6 inch paper coupling tube, run a 24 mm central "fire tube" through the middle of the balsa, center the fire tube inside the balsa shell and coupling tube with two plywood centering rings, and use the space between the fire tube, 2.6 inch coupling tube, and two rings as an e-bay for the second Raven.
I call it the "fire tube" because it will house apogee recovery inside it (shot forward) and serve to decouple forcibly the sustainer in case it becomes too bound (for whatever reason) to drag-separate. It will also be the receptacle of ignition gasses in the event that sustainer ignition happens without separation.
First, I tacked on brass coupling tubes at one end of the fire tube with CA:
Note that I have to number my pins: they are aligned well but not perfectly 90 degrees apart, so there is only one way they line up. I was not convinced the CA would hold, so this was fiberglassed over. Then, this was epoxied into the now-hollow and much shorter balsa transition, paying close attention to alignment. Then two centering rings were epoxied into place over the fire tube, one laying against the remaining balsa transition and the second one 9 V battery length back with wiggle room. A quick test fit showed everything was lined up perfectly:
The 2.6 inch coupling tube was given e-bay access cutouts, and epoxied into place over the two centering rings. The Raven is mounted to a plate, and power will be from one or two LiPo cells. I am finishing the e-bay now, but the epoxy is set and man, does she look sweet!
The part I am looking forward to is all my flying options. I have a fiberglass NC for the NIKE stage that gives me a pretty hot "smoke" configuration (~2500 ft on I impulse, out of sight on J). The APACHE stage has launch lugs for testing, which gives me the option of launching it standalone for fun 800 ft dual-deploy launches with an Estes E9, or ~ 2000 ft with an AT F35W.
Full-up though (Rocksim):
Booster: J-410
Sustainer: F-35
Separation: ~2000 ft (just after burnout)
Sustainer Apogee: ~ 6500 ft
Maximum Mach: 1.1 (on booster)
Maximum Acceleration: ~300 m/s2 (30 g's)
I don't know if I have the balls to go all the way to a J booster though! If she folded up on boost I would cry.
I should be able to finish, and be ready for at least a drag separation test, by Saturday the 6th at Plaster Blaster. Friday the 5th I want to finish testing each separately. We'll see though... at the very least the Smoke config will be in the skidmark drag race that evening
Thanks to the following:
Mike at Cosmodrome Rocketry
Adrian at Featherweight Altimeters
Greg at BigRedBee
Wildman and Performance Rocketry (for the Smoke NC)
View attachment Nike Apache Two Stage.rkt
View attachment Apache.rkt
View attachment Nike.rkt
Fundamentally, what I have is this:
- NIKE stage: 38 mm motor mount (36 cm long to hold plenty of motor). Interstage coupler massively modified to hold 1 Raven altimeter, batteries, apogee recovery/failsafe decoupler, main recovery systems, and four coupling tubes.
- APACHE stage: Basically a 24 mm minimum diameter airframe. Fin roots were used to firmly attach steel coupling pins. Balsa nosecone was modified to provide additional space for a second Raven altimeter and a BigRedBee Tx. Two runs of (thin) allthread connect the nosecone to a baseplate that holds the main recovery charge and serves as an attachment point for the harness. Airstart wires run outside the airframe.
So on to the details, starting first with the Nike booster airframe. Looking at the parts: the stock body tube is 2.6 inches OD and is a tad on the flimsy side, so that was given a single layer of fiberglass. The motor mount was unacceptable at 29 mm, so that went into the parts bin and was replaced with a much longer 38 mm tube. The centering rings are made from the same aircraft-grade ply the fins are crafted from, so they were formed for the 38 mm tube. The fin tangs were shortened slightly to accommodate the larger motor tube. The tubular nylon harness was replaced with braided kevlar, and the mounting point beefed up to a stainless steel U-bolt from the smallish eye bolt.
Here is a shot of me test fitting the fins before hacking down the tangs and after the internals were attached:
By this point in the build, I had a good Rocksim file for at least the boost portion, and I became concerned about fin flutter. I decided to add a second layer of tip-to-tip fiberglass to the fins.
Moving up to the next most complex part, we have the APACHE sustainer. The most complex part of this is the "fin can": coupling pins, space for an igniter, fins, motor retention... it took me a while to settle on the right retention methodology as well. I visited the LHS and picked up a length of steel control rod wire and a length of brass tube that slid tightly but easily over the wire. The plan was to mount these inside the root of the four fins. If you have seen this kit before, you know the rear end is actually a 29 mm body tube centered over the main 24 mm body tube, with a conically shaped (by hand) centering ring at the forward position, just where the fins hit the airframe. The 29 mm outer tube gets cut to accept the fin tangs. Burly construction. I removed a notch from each fin tang after sanding them into the proper beveled shape and epoxied each into place. When all four were done, I carefully epoxied all four coupling pins into place under the fins.
The main 24 mm Apache body tube was hacked into two pieces at the planned break, and a coupling tube was glued into place on the lower (fin can) section. The paper outer-wrap (simulated payload) was added to the top half, but I skipped the simulated antennae (for now at least).
The balsa Apache nosecone was given several coats of epoxy, with constant sanding, to strengthen it and improve its shape. The nosecone is very delicate! I then hacked off most of its length, hollowed out a small cavity inside it, jammed in two lengths of the thinnest OD allthread the LHS had, and epoxied the whole mess together with a 24 mm couping tube to serve as the shoulder. The rear bulkhead of the electronics compartment was made from aircraft plywood, and given a shoulder tube to give a good seal. I am still fleshing out the details on this part, but I have a general plan on where everything is going to sit, where the tracker antenna will run, etc.
Here is a test fit view with a sketch of the recovery harness layout:
The hardest and third component is the interstage connector, AKA the transition section. Stock, this is a massive chunk of balsa, reinforced with a dowel at the top. Weighing all my design options, I chose to replace the lower balsa shoulder with a 2.6 inch paper coupling tube, run a 24 mm central "fire tube" through the middle of the balsa, center the fire tube inside the balsa shell and coupling tube with two plywood centering rings, and use the space between the fire tube, 2.6 inch coupling tube, and two rings as an e-bay for the second Raven.
I call it the "fire tube" because it will house apogee recovery inside it (shot forward) and serve to decouple forcibly the sustainer in case it becomes too bound (for whatever reason) to drag-separate. It will also be the receptacle of ignition gasses in the event that sustainer ignition happens without separation.
First, I tacked on brass coupling tubes at one end of the fire tube with CA:
Note that I have to number my pins: they are aligned well but not perfectly 90 degrees apart, so there is only one way they line up. I was not convinced the CA would hold, so this was fiberglassed over. Then, this was epoxied into the now-hollow and much shorter balsa transition, paying close attention to alignment. Then two centering rings were epoxied into place over the fire tube, one laying against the remaining balsa transition and the second one 9 V battery length back with wiggle room. A quick test fit showed everything was lined up perfectly:
The 2.6 inch coupling tube was given e-bay access cutouts, and epoxied into place over the two centering rings. The Raven is mounted to a plate, and power will be from one or two LiPo cells. I am finishing the e-bay now, but the epoxy is set and man, does she look sweet!
The part I am looking forward to is all my flying options. I have a fiberglass NC for the NIKE stage that gives me a pretty hot "smoke" configuration (~2500 ft on I impulse, out of sight on J). The APACHE stage has launch lugs for testing, which gives me the option of launching it standalone for fun 800 ft dual-deploy launches with an Estes E9, or ~ 2000 ft with an AT F35W.
Full-up though (Rocksim):
Booster: J-410
Sustainer: F-35
Separation: ~2000 ft (just after burnout)
Sustainer Apogee: ~ 6500 ft
Maximum Mach: 1.1 (on booster)
Maximum Acceleration: ~300 m/s2 (30 g's)
I don't know if I have the balls to go all the way to a J booster though! If she folded up on boost I would cry.
I should be able to finish, and be ready for at least a drag separation test, by Saturday the 6th at Plaster Blaster. Friday the 5th I want to finish testing each separately. We'll see though... at the very least the Smoke config will be in the skidmark drag race that evening
Thanks to the following:
Mike at Cosmodrome Rocketry
Adrian at Featherweight Altimeters
Greg at BigRedBee
Wildman and Performance Rocketry (for the Smoke NC)
View attachment Nike Apache Two Stage.rkt
View attachment Apache.rkt
View attachment Nike.rkt
