Basic Information
Name	Xi-39
Launch date:	24 August 2024
Rocket description	- 3”/ 76.2 aluminum airframe (0.035”/0.89mm) - 4 fins, 2024 aluminum (0.065”/1.65mm) - 3D printed PLA tangent-ogive nosecone - 3D printed PLA boattail fairing/motor retainer - 3D printed PLA aft-mid body coupler - 3D printed PLA aft smoke system support - 3D printed PLA on-board camera bracket & fairing - 3D printed PLA parachute piston - 36 inch ellipsoidal "Fruity Chutes" parachute
Payload	- Blue Raven flight computer (primary role) - Blue Raven flight computer for backup apogee separation – EggTimer Quark altimeter as 2nd apogee backup and backup main deploy - BRB900 GPS transmitter - Liftoff-activated and apogee-activated smoke trackers with Legendary formulation. - SJCAM C100 on-board video camera
Liftoff mass	3.208 kg.
Stability Margin (minimum)	1.85
Flight objectives	- On-board camera bracket modified to point camera at 60° (from vertical) angle to obtain better aft-facing view

Motor details
Motor name	APM-E.14.2 (38mm)
Propellant	AXP-AP4.7 (Ammonium Perchlorate 65.8% /Epoxy (New Classic) 24%/Aluminum 10% /Lampblack 0.2%)
Grain mass	337 grams
Estimated Impulse	657 N-sec. (est.)
Class	J

Additional information

- Rocket was largely re-built following non-recovery of Xi-38 forward section of rocket including AvBay (presumed drowned). The aft/mid body sections were repaired by cutting off dented ends. The AvBay was completely re-built, with 3 new flight computers (2@Blue Raven; 1@Quark). Several pending design improvements were incorporated in the new AvBay. New forward body and newly-printed nosecone with replacement BRB900 GPS transmitter. Parachute for this flight was 36” elliptical (replacement 42” chute ordered but not yet received).

Weather conditions
Temperature	30°C (86°F)
Wind	SSE 20 km/hr (ground level)
Sky	Sunny with cirrus clouds overhead
Other	-
Ceiling	unlimited

Launch Event Description

We were feeling a bit nervous as we were getting ready for this launch, as was to be expected, considering the rocket was largely rebuilt and was outfitted with brand new and flight-unproven recovery electronics. Ground testing indicated everything was fine, however, one can never be sure until it’s time for the real experience to prove this.

All went smoothly during setup of the rocket and launch equipment. Following our checklist as usual, we proceeded to set up the launch rail assembly and the rocket. No glitches were encountered. Once the launcher was set up, the BRB transmitter and receiver were activated and verified that a good GPS signal was obtained. The two Raven units were activated and verified to be functioning nominally. The Quark was activated and, likewise, was verified to be ‘ready for launch’ by its chirping. The lift-off activated smoke charge was powered-up and armed. Finally, the on-board camera was powered-up, set to record mode, and installed in the mid section of the rocket. The final step was to install the aerodynamic fairing that fits over the protruding portion of the on-board camera.

As usual, for filming the flight, I used my Sony HDR-CX240 Handycam fitted with scope tube.

We headed to where the Launch Firing Box was located, 275 feet south of the pad. To be able to follow the flight in a more effective and stable manner, I layed down with my back on the ground, sitting upright initially to follow ascent off the launchpad. After verifying the sky was clear, the countdown proceeded. At the zero mark, the ignition button was pressed. The igniter fired, but the rocket did not move. Some smoke and traces of flame could be seen emanating from the nozzle. After a few seconds, a flash was seen and still the rocket remained stationary. Several seconds later, another flash, then the rocket soared skyward with a loud roar, accelerating at a somewhat slower pace than usual. Shortly after departing the launch rail, the rocket veered significantly to the right, climbing skyward at an angle estimated to be 30 degrees from the vertical. I was able to visually follow the rocket during its powered ascent, thanks to the bright exhaust flame. The motor burned for an estimated two and a half seconds. We lost sight of the rocket after burnout. Shortly after, I spotted the smoke trail and was able to follow the rocket visually until the smoke charge burnt out, approximately a half minute after liftoff. After a short while, the parachute pyro charge was heard firing as a loud ‘pop’ sound, and the fully-inflated parachute was soon spotted, to our right, at a distance estimated to be close to 1000 feet (300m.) away. The rocket gently descended and disappeared over the edge of the nearby berm.

We programmed the GPS coordinates received from the BRB transmitter into the hand-held Garmin GPS unit. Indicated distance was 0.15 miles. We used our printed map of the area with an overlaid grid showing latitude and longitude. We observed that the landing site was in a treed area not too far from an access road. As such, we packed up and headed to our parked car, and drove toward the indicated landing site. When we got close, we walked into the treed area, directed by the Garmin GPS unit. We soon heard a faint “beep-beep…” sound of the Quark, audibly announcing apogee (3-0-2-0 or 3020 feet). We then spotted the parachute, and dangling beneath it, the rocket sections. The chute was snagged on the crown of a tall poplar tree. Realizing we had no way of getting it down at that time, we headed home to better assess the predicament.

We returned two days later (by then the beeping had ceased, as the battery depleted). With the much appreciated help of a neighbourhood fellow, well-experienced in tree-cutting, the tree was sawn down (thanks Richard!) and the rocket safely recovered (the downed tree will serve as firewood, needed for the long, cold winter). The primary Raven was still active, and immediately started transferring flight data via its Bluetooth connection to my mobile phone. The altitude was reported as 3063 feet (934m.). The rocket appeared to be in pristine condition with the exception of a dent on the lower body, likely a result of being hit by a branch as the tree fell.

Flight Analysis
Event:	Time (sec)	feet	metres
Apogee*	14.0	3231	985
Separation*	15.3	3193	973
Chute deployment	52	699	213
Touchdown	83	-	-
Range	-	981	299
Max. velocity	531 fps	162 m/sec.	-
Descent rates:	ft./sec.	m/sec.
Free-fall	69.4	21.2
Parachute	18.7	5.7

* Corrected for non-standard base temperature.

Post-flight analysis and comments:

Post-flight examination of the flight data indicated that the operation of the two Blue Raven units was fully nominal, with a reported apogee of 3063 feet and 3065 feet. The EggTimer Quark also performed nominally with a reported apogee of 3020 feet (all reported altitudes not corrected for base temperature). The reported apogees for the three units were within 1.5%. All three flight computers fired their pyros nominally.

The Blue Raven unit records many flight parameters using its on-board inertial measurement and gyro chips. One of the more interesting and useful parameter is tilt angle during ascent. The primary Raven and secondary Raven reported a burnout tilt angle of 25.8° and 28.3°, respectively. This is consistent with the estimated 30° ascent tilt angle we’d estimated ‘by eye’. Off the rail, the tilt angle was close to 40°. The fins quickly provided a corrective moment, reducing the tilt angle to 20°. Weathercocking led to further declination until apogee, at which point flight was horizontal.

The reason for the rather severe tilt was discovered during post-flight cleanup of the launcher assembly. A partly-melted launch button was found at the bottom of the rail (the aft button was missing from the rocket). The slow startup of the motor, which spewed licks of flame, was clearly responsible for the partial melting and disbonding. As such, only the upper launch button provided guidance off the rail. In hindsight, we were fortunate that the ascent angle was not worse, as it could have been with only a single launch button whose design provides no control over pitching of the rocket as it moves along the rail. To prevent this serious incident from ever occuring in the future, a third redundant launch button will be added as a failsafe feature. As well, both the lower and upper launch buttons will be attached with screws, in combination with bonding.

The primary Raven and secondary Raven reported a burnout roll rate of 118° and 130° (per second), respectively. This corresponds to a leisurely roll, with time periods of 3.0 and 2.8 seconds.

Operation of the BRB (GPS) unit was fully nominal. GPS-based apogee could not be obtained as the flight data was overwritten due to the long time duration between landing and recovery.

Examination of the Raven axial acceleration data indicated that the APM-E.14.2 motor had a off-nominal burn. The time duration from igniter firing and liftoff was 8 seconds. From the videos, it was apparent that the propellant began to burn immediately after igniter firing (small flames and smoke emanating from nozzle). Forensic analysis of the motor post-flight suggested that the aftmost grain segment was burning. Insufficient chamber pressure prevented stable combustion of all grain segments to occur until several seconds later, when the remainder of the grains ignited with off-nominal performance due to the partial depletion of the aftmost grain. The cause for this anomaly was narrowed down to an oversized nozzle throat. An analysis of E.14 motor firings pointed to the cause as being an initial Kn value that was too low to allow for stable combustion. The Kn for this flight was initially 267. Previously, initial Kn was as high as 360 (static test ST1).

Both smoke systems suffered anomalies. The liftoff-initiated smoke system ignited nominally, however, there was significant smoke leakage into the rocket body interior. This was caused by snap rings that were too loose fitting, resulting in leakage past both nozzles. This resulted in soot coating the lens of the on-board camera. As such, footage was obscurred beginning a few seconds following liftoff. The apogee-activated smoke grain failed to ignite, even though the igniter fired nominally. This was undoubtedly due to the canister being only half-filled with Legendary formulation (stock was depleted without time to prepare a new batch).

Misc photos:

Propellant segments for E.14.2 motor Xi-39\DSCF7611.JPG

Liftoff-activated Smoke Module Xi-39\DSCF7613.JPG

New nosecone and forward body Xi-39\DSCF7609.JPG

Wet sanding nosecone Xi-39\DSCF7549.JPG

Xi-39\DSCF7550.JPG

Styrofoam cradle for BRB GPS-transmitter Xi-39\DSCF7552.JPG

Avionics rack (front, with Ravens) Xi-39\DSCF7616.JPG

Avionics rack (back, with Quark) Xi-39\DSCF7615.JPG

Pyros and Smoke Canister installed Xi-39\DSCF7618.JPG

AvBay ready for flight Xi-39\DSCF7620.JPG

Composite hatch (FRG) for AvBay Xi-39\DSCF7576.JPG