I decided to do some more in-depth analysis and compute the Cd as a function of velocity for this flight. (Warning, it gets geeky)

Drag force is 1/2 * density * velocity^2 * Cd * Area, and it also equals mass * acceleration

therefore Cd = 2 * mass * acceleration/ (density * velocity^2 * area)

Mass was measured, because I took the time to weigh the unloaded rocket and the mass of the motor after recovery (560 g), bringing the post-boost mass to 907 grams.

Area is easy to compute from the nosecone maximum diameter (1.61")

Air density is trickier. It's a function of pressure, temperature, and humidity. The

University of Wyoming has a website that provides balloon sounding data recorded twice a day by the NWS at dozens of locations around the country. I used this data to get the humidity and temperature as a function of pressure for the closest measurement site, to help calculate the density, and I also used it to more accurately convert measured pressure to altitude, which I used later as a check. There are equations for density that you can look up in Wikipedia, but I didn't want to get too deep into the formula, so I used an online calculator to plug in a few points of temperature, pressure, and humidity to get density from the balloon soundings, and determined that starting with the ground-level density and then multiplying by the pressure ratio and the inverse of the absolute temperature ratio got density answers that were very close to the online calculator.

Velocity is provided by the Blue Raven, but it was corrupted by the circumstances of this particular case. First, the raw acceleration values during the 100G burn were pretty different between the two altimeters, indicating that one or both had bad calibrations, while the measurements made by the +/-32G altimeter had good agreement. Second, the vertical velocity calculated by the Blue Raven depends on gyro values that in this case immediately exceeded the gyro measurement range because of the flutter. Knowing that this was a very vertical flight, I decided to just assume a perfectly vertical flight, which lets me just integrate the accelerometer axis that's aligned with the rocket and subtract off gravity.

I adjusted the measured acceleration data during the high-G portion for both units by a fudge factor until the integrated velocity crossed zero at the actual observed apogee time. A second check is to compare the integrated accel-based altitude to the actual altitude measured from the pressure sensor and the balloon soundings. The accel-based altitude was 18143 vs 17784 for the sounding-adjusted barometric altitude, which is close enough (2%) IMO, considering that the rocket wasn't purely vertical during its flight.

With the the high-G accel values adjusted, here is the resulting velocity plot from the two units:

You can actually see the period of major fin flutter where the velocity takes a steeper turn at about 2-4 seconds. The top speed was just over 3200 feet/second, or Mach 2.85.

Here's the result for the Cd vs Mach number for this flight:

Time is going from right to left, starting with the end of the burn (which looks like negative drag), and going to apogee at the left end, where it gets noisy from having very little measurable drag acceleration. The big noisy triangle in the middle is when the fins were cracked and fluttering. There was a brief time in between motor burnout and when the fins failed that I got a meaningful Cd measurement:

Here's what RASAero has for that area:

At Mach 2.60, RasAero has 0.369 after burnout, compared to my measured 0.347. In other words, the rocket was on the way to exceeding the RASAero simulated altitude (and the Tripoli J single-stage record) before the fins failed.