Overview
Flight Data Files
CAD
Video
Simulator Files:
12-17-2017
I've spent a few hours digging through RASAero, Open Rocket, BurnSim, the Mass Budget, and hitting all of the above with healthy doses of common sense. Andrew gave me a few good ideas on where to start sanity checking our numbers. I know these values still sound on the high side, but I'm inclined to believe them pending flaws in the sim files. I would be very happy to hit 80% of these values though, knowing how these kinds of flights go.
In case anyone was curious, the rocksim file the previous rasaero numbers were based off of still was using an off axis piston and was almost 2 feet longer than the current design. This has led to some stability problems with the current design. At Burnout we hit a stability margin of 1.11. As this happens at Mach 3.35 I think we should increase the fin size to compensate.
These files are now correct to the design, as I understand it.
Motor file: 70kNs Rev 6
Composite Fin Can, OD of fin collar 6.25 in, 1/4 thick fins. .75 in edge chamfer .05 in rounding on edges.
Surface Finish: Rough Camouflage Pain
Rocket Length 11 feet 8 inches
GLOW is 158 lbs according to Mass Budget
Aft Closure include Boat Tail to 5.6 in aft diameter
Here are the relevant quantities.
GLOW: 158 lbs, +/- 14 lbs
Burnout Altitude: 12,200 ft AGL
Burnout Velocity 3,700 ft/s (Mach 3.35)
Maximum Altitude: 125,600 ft +/- 23,100 ft (from mass deltas)
These values came from some hand runs of RasAero
The next set of values came from OpenRocket on a dataset of 500 runs through Cassandra (Thanks Josh!). The raw values are quite different than the Open Rocket values, but with a healthy fudge factor (screwing with finishes and fin thicknesses) to get supersonic cd's to match those of RasAero, the numbers were similar. Second semester we should improve Cassandra's aerodynamics. Anyways, Cassandra gives the following
GLOW = 158 lbs
Apogee 131,529 +/- 6,443 ft
Median Apogee = 133,142 (An average flight is pretty close to the average of the flights, which is good)
3-Sigma Altitude = 138,870 ft
Landing Zone = 4.3 miles east of base camp +/- 1.4 miles
1-28-2018
Take a look at the fin profiles on the manual page of the RAS Aero website. I think the only styles that are reasonable to assume that we could manufacture are hexagonal, hexagonal blunt-base, and rounded (not including square, because... yeah). With a realistic, if not generous, tip radius of 0.05 inches and a hexagonal profile, I'm getting 83kft out of a 65,000 Ns motor in a 156 lb rocket. This assumes an ISP of ~212 s, which I think is achievable. Playing around with rounded or hexagonal blunt-base yields lower altitudes, mostly in the 65kft range. I think we should keep the target altitude of 80 kft, and be thankful that things have essentially randomly aligned with that goal. I have attached my motor file and simulation file for your consideration. Other happy news: the rocket will reach a max velocity of ~3100 fps at 13kft, which is only around mach 2.9 at that altitude. Not saying that it is trivial to keep the fins on any supersonic rocket, but < mach 3 makes Matthew's life easier.