RG-2
Robert's second full-custom rocket, with TeleMetrum electronic-deployment.
Motivation
After the success of RG-1, Robert decided it would be fun to build a similar rocket in smaller diameter to try and get more than a mile above ground on a G motor. The timing coincided with the first prototype builds of TeleMetrum v0.2, so naturally he insisted on designing the rocket to fly one.
Bdale and Keith both liked the design and wanted to join in the fun, so the plan is to be ready for a 3-way drag race on Cesaroni Pro29 full-G motors at NCR Mile High Mayhem 2010.
Design Details
- 38mm phenolic air frame
- 29mm phenolic motor mount
- Giant Leap Pinnacle 38mm nose cone
- 1/8 inch birch plywood fins in a custom shape, with rounded edges
- 1/4 inch birch plywood centering rings and bulkheads, CNC milled, the two that hold the fins are notched for perfect fin alignment.
- avionics bay design similar to Bdale's Trick-o-Treat
Build
The build began on 21 March 2010, cutting all the phenolic and fin blanks for 4 "kits" of parts.
The first step was to CNC machine all the rings and bulkheads, then clean them up and fit them by sanding carefully.
Next, we cut out the fins using our radial arm saw, and beveled them by hand using sandpaper flat on a table surface, hand-holding the fins at the desired bevel angle. Bdale cheated a bit on his fins using his Dremel with sanding drum to quickly remove most of the material then finishing up with sandpaper on the table... but that requires a very steady hand with a Dremel! We beveled the leading and trailing edges for looks and to reduce drag, but since these rockets won't break mach on a G the exact profile isn't critical.
Assembly started by sanding the outside of the 29mm phenolic motor mount, and using a piece of angle to mark a reference line along the entire length of the mount. We use this reference line to get the first fin aligned perfectly. Next, we put the two fin-locking rings on the MMT along with the HAMR retainer body, and used the fins to work out from the aft of the MMT exactly where the fin-forward ring needed to be, marking the aft edge of this ring's position on the MMT. The fin forward ring's position is the critical part of building a fin can the way we do, so we take extra time to get this right.
We then smeared 5-minute hobby epoxy around the MMT at this mark, and pushed the fin-forward ring into place from the aft end of the MMT, pushing an epoxy fillet on the ring's leading edge, and leaving the aft side of the ring fairly dry. We align the ring so that one of the locking tabs is positioned with one edge on the line up the MMT, so that when we put the first fin in place we can use that line to ensure it's straight along the MMT. And we're very careful to make sure the ring is "square" to the MMT. While we have some spare epoxy, we also smear the front of the MMT and slide on the zipperless fin can ring from the front. Then we let the epoxy cure. Do not glue the aft ring to the MMT yet! That comes much later.
To be continued...
Flights
All three prototypes were first flown at NCR Mile High Mayhem 2010, on the new Cesaroni 159G54 c-slot long burning red flame "full G" motors.
Bdale's broke a mile, but we somehow failed to pull the TeleMetrum data before re-using the board in another airframe, so we can't prove that. However, the fin can separated and has not been recovered. So much for painting a tiny fin can black!
We learned the hard way with Robert's airframe that silver Krylon paint is metallic enough to hamper GPS reception, but the UHF downlink was strong and we found the rocket easily using RDF techniques. Robert's also separated at apogee, but thanks to the flourescent pink paint job, it was found between the rest of the airframe and the flight line.
Keith's flew nominally.
Robert flew his for the second time at Tripoli Colorado's Spring Fling 2010, again on a 159G54. It dragged a bit on the rail, ended up in a non-vertical trajectory, and again failed to break a mile AGL. Oh well.
Conclusions
This is a fun little rocket, and is indeed capable of breaking a mile AGL from Colorado launch sites using the 159G54 reload from Cesaroni. It was Robert's first introduction to flying drogueless dual-deploy. Building without the Giant Leap rail guides and tower launching would be a good plan for future renditions to get more altitude, though as Robert points out, that would make it harder to sport fly at random launches. The slide-in ebay design worked out very well, and keeps the number of airframe junctions down.