Ye Olde Rocket Forum - View Single Post

This one wasn't on The List, but I thought it might be an interesting design to think about:

The Argo D-4 Javelin, 1/10th scale (of course!)

Similar to the SLS Brighton, I designed this to have interchangeable motor mounts based on an ST-20 parent tube. The 3 arrangements I've tried out so far are 4x 18mm, 2x 24mm, and 1x 29mm. In the case of the 2x 24mm, the gap between the tubes and the wall is so small (~0.004") that it would not be possible to have this particular mount be "Hollow Tube Coupler"-based as the others can be; it'll probably just need a bit of added reinforcement/cross beams/heavier centering rings to make sure it's durable enough. Interchangeability would most likely be accomplished with an engine hook retention system like in the Brighton (the way it is currently set up presents a bit of a problem for 29mm motor retention (anything that can't use a hook), because it currently needs the aft centering ring flush with the end of the body tube; this could be solved by just putting up with a 29mm mount that extends out the back a bit). The rocket itself is based on BT-70H for the Honest John booster, ST-16 for the 2 Nike stages, and then a bit of an interesting piece of work on the upper stage container/payload. The payload, to be true 1/10th scale, would need to be 1.9" in diameter, which is fairly far off from any current tube size (ST-18 is closest at -0.06", ST-20 would be next at +0.14"). To solve this, I had the payload based on ST-18, then the modeler could apply a few sheets of ~6"x6" paper to build up the diameter to the proper (20 lb. copy paper is ~0.0038" per sheet, which would probably end up being around 6 or 7 wraps, depending on the gluing method used). Another method might be to use self-adhesive label sheets, but that would probably be tricky to apply/expensive. Anyway... once the diameter has been built up to 1.9" to match the corresponding nose and transition pieces, the rocket can be otherwise based on off-the-shelf parts. Stability doesn't seem to be a problem, despite all the fins (the ~1/2 oz "paper weight" at the top probably helps a little bit). Fins could be accomplished in a similar manner to the Saturn 1B, with a set of 3/32" or 1/8" cheater fins that could probably take more abuse from the more powerful 24mm and 29mm motors, or a set of scale fins that could be built up. The built up fins, due to their size (4.5"x4" for the booster) might need something a bit more rigid than paper for sheeting, perhaps even a skin of 1/32" balsa or 1/64" plywood, depending on how the structure can be laid out. The thicknesses of the fins are reasonable, ranging from 3/16" at the center of the root of the booster fins, to a bit more than 1/32" (0.039") at the tips of the 2nd stage fins (3rd stage fins are actually thicker at the tip at 0.046"). The booster fins are also TTW, since the bottom 3.25" is actually a subtle paper shroud, making slotting quite simple. The shroud is supported at its forward end by a double centering ring that is glued together on its own; due to the thickness of the BT-70H, having a 'halfway' centering ring to support the shroud would leave much too large of a gap, so instead, I designed the rocket to use a standard 2.175" diameter ring flush with the end of the tube, glued to a 2.238" (just large enough to account for the slope and thickness of the shroud) diameter ring that butts against the aft end of the tube. The only other issue I can recall is the difficult looking Honest John to Nike transition, which has a few sharp steps that might present an issue to the nose cone machine. If this is the case, the cone could be modified so that a paper shroud would fit over the top (like in the Apollo capsule kit) to provide the sharp separation within the transition.

Well, that went on a bit longer than I though.

Flights:
Many of the most popular motor configurations turned out to have some nice Dv's. B6's appear to be a nice motor for demo flights (and are still able to fly from a 36" rod), though even 2 E9's doesn't go too high (it even gets up to speed within 36" as well). With the new ValueRockets site making a lot of the smaller composites affordable again, I also included D10's, D13's, and E15's in the list, all of which give great deployment velocities, though I fear some of the maximum velocities (over 350 MPH, in the case of the D10) might be a bit quick for such a skinny, balsa-finned rocket.

4x18mm

4x B6-4 ... 314' ... 97 MPH ... 8.49 ft/s Dv ... 3/16" x 36" rod
4x C6-5 ... 823' ... 171 MPH ... 12.07 ft/s Dv ... 3/16" x 36" rod
4x D10-5 ... 1732' ... 361 MPH ... 9.12 ft/s Dv ... 3/16" x 36" rod
4x D13W-7 ... 1746' ... 337 MPH ... 5.59 ft/s Dv ... 3/16" x 36" rod

2x24mm

2x E9-6 ... 1331' ... 220 MPH ... 7.62 ft/s Dv ... 3/16" x 36" rod
2x D12-5 ... 802' ... 172 MPH ... 11.86 ft/s Dv ... 3/16" x 36" rod
2x E15W-7 ... 1914' ... 317 MPH ... 4.87 ft/s Dv ... 3/16" x 36" rod

1x29mm

1x F25W-6 ... 1721' ... 296 MPH ... 10.68 ft/s Dv ... 3/16" x 36" rod
1x F40W-7 ... 1807' ... 329 MPH ... 4.24 ft/s Dv ... 3/16" x 36" rod
1x G33J-7 ... 2197' ... 341 MPH ... 4.04 ft/s Dv ... 3/16" x 36" rod

Enjoy.