Basic Information
Name	Xi-36
Launch date:	26 August 2023
Rocket description	- 3”/ 76.2 aluminum airframe (0.035”/0.89mm) - 4 fins, 2024 aluminum (0.065”/1.65mm) - 3D printed tangent-ogive PLA nosecone - 3D printed PLA boattail fairing/motor retainer - 42 inch ellipsoidal "Fruity Chutes" parachute
Payload	- Raven4 altimeter (primary role) - Raven3 altimeter for backup apogee separation and backup main deploy - BREO-N flight computer (2^nd backup, apogee only) - BRB900 GPS transmitter - Liftoff-activated and apogee-activated smoke trackers with Legendary formulation. - SJCAM C100 on-board video camera, aft-facing
Liftoff mass	3.546 kg.
Stability Margin (minimum)	1.98
Flight objectives	-6^th flight of JEM motor. New Raven4 flight computer and new BRB900 unit

Motor details
Motor name	JEM (51mm)
Propellant	KNDX
Grain mass	477 grams
Estimated Impulse	593 N-sec. (est.)
Class	J

Additional information

- Raven4 replaces one of the BREO units to provide better cold-weather reliability. This is the 1^st flight of this unit. A new BRB900 GPS unit is installed to provide greater reliability due to glitches encountered in previous flights.

Weather conditions
Temperature	20°C (68°F)
Wind	SSW 5-10 km/hr (ground level)
Sky	Mixed clouds, bright sun
Other	-
Ceiling	unlimited

Launch Event Description

Once we arrived at the launch site (a 10 minute walk), we followed our checklist to set up the launch system and prep the rocket. Once the launcher was set up, the BRB transmitter and receiver were activated and verified that a good GPS signal was obtained. The BREO unit and backup Raven3 unit were activated and verified to be functioning nominally. The Raven4 unit was then switched on. There was no response. The power was cycled a couple of times, however, to no avail. As the two backup units were both operating nominally, launch rules allow for the launch to procede. The access hatch was then closed. The lift-off activated smoke charge was powered-up then armed. The on-board camera was powered-up and set to record mode.

For filming the flight, I used my Sony HDR-CX240 Handycam fitted with scope tube. Once again, I wore wearable binoculars to help visually follow the rocket in flight.

We headed to where the Launch Controller was located, 275 feet south of the pad. To be able to follow the flight in a more effective and stable manner, I lied down with my back on the ground. After verifying the sky was clear, the countdown proceeded. At the zero mark, the ignition button was pressed. The igniter fired and immediately the rocket soared skyward, accelerating quickly, climbing straight vertical, leaving a dense white smoke trail in its wake. After less than 10 seconds, apogee was reached (estimated at perhaps 1000 feet) and the rocket arced downward, still spewing a dense smoke trail. Clearly, apogee was much lower than the expected 3500 feet peak. The rocket separation charge fired and the rocket tumbled earthward at a good clip. Around 5 seconds later, the chute charge was seen to fire and immediately the parachute blossomed and the rocket began its gentle descent. The rocket drifted with the wind, landing about ½ minute later over the brim of the berm that runs the length of the launch range. Downrange distance was estimated at 800-1000 feet.

We then programmed the transmitted GPS coordinates into the hand-held Garmin unit.

The indicated distance to touchdown site was 0.17 miles. We headed to the touchdown site and when we arrived at the indicated location, the rocket was not seen. Visually it was hard to scan due to the tall grass and thistles present at the site. As the rocket had disappeared over the berm, we knew from experience that the last GPS coordinates received at the landing site would not indicate the exact touchdown location. As such, I took a fresh reading and the coordinates indicated the rocket lay a further 154 feet downwind. We headed in that direction and soon spotted the rocket. All parts of the rocket appeared to be present. Raven beeped out an apogee of 1204 feet (367m.). As I made a preliminary inspection of the rocket components, I noticed that the aft section, which houses the motor, appeared badly burned. Closer inspection revealed two large burn throughs. Clearly the motor suffered a significant anomaly.

Flight Analysis
Event:	Time (sec)	feet	metres
Apogee*	8.9	1233	376
Separation*	11.7	1192	363
Chute deployment	16	798	243
Touchdown	59	-	-
Range	-	816	249
Max. velocity	367 ft/sec.	119 m/sec.	mach 0.33
Descent rates:	ft./sec.	m/sec.
Free-fall	87.7	26.7
Parachute	17.9	5.5

* Corrected for non-standard base temperature.

Post-flight analysis and comments:

“Flight of the gremlins”

Post-flight examination of the flight data indicated that the operation of both the Raven3 and BREO were fully nominal. Reported apogee of the BREO was 367 m. (1204 ft), essentially the same as the Raven3. The reason for the new Raven4 unit not initiating during the pre-flight procedure was determined to low voltage of the 9V battery. The voltage was found to be 4.91V. This was a brand-new battery installed for this flight, a standard 9V lithium cell (Amazon Basics). When installed, some days prior to the flight, the voltage had been measured at 9.61 volts. A thorough inspection of the wiring (which was newly installed) turned up nothing amiss. Testing with a new battery installed could not replicate this anomaly. As such, no explanation could be found for the low battery condition. For the next flight, the battery voltage will be monitored closely after installation and leading up to the subsequent launch.

The new BRB (GPS) transmitter suffered an anomaly. Downloaded GPS data stream began at the landing site and terminated when I powered down the unit after recovery at the pad. The flight data had apparently been overwritten as a result of a brief power glitch, presumably upon touchdown. Careful examination of the wiring suggested that one of the terminal block screws may have not been tightened fully (which is odd, as I always double-check such). This could have resulted in a brief power loss when the nosecone contacted the ground upon landing.

A major anomaly occurred during motor burn. The motor bulkhead was found to be severly burnt through. This occurred at the 0.60 second mark of the motor firing, based on the acceleration data from Raven3. Following the breach of the bulkhead, the hot gases from the combustion of the remaining propellant burned two large gashes in the aft airframe. It was this anomaly that resulted in the low apogee achieved, as the expected apogee was around 3500 feet. The Raven3 acceleration data also indicated an anomalous burn of the JEM motor, most likely a partial inhibitor failure. Dissection of the motor revealed that the forward grain segment had abnormal amount of inhibitor/casting tube burnt away (the aft two segments displayed normal burning, leaving most of the inhibitor/casting tube intact). This sort of anomaly has been seen before in static and flights of the JEM motor, although this time the degree of inhibitor breach was greater. Using the rocket acceleration data, it was possible to obtain a fairly accurate estimation of chamber pressure at the time of the failure. A pressure of 1200 psi was calculated, which compares to a MEOP of 985 psi. At a pressure of 1200 psi, the bulkhead is subjected to a high bending stress, but its structural limit should not have been exceeded. Such burn-though of a motor bulkhead has never been experienced before in any motor that I have fired, so it is something of a mystery as to the exact cause. The bulkhead was protected with a layer of thermal insulation that has served well in the past.

The lift-off activated smoke grain burned nominally. The post-apogee smoke charge was not initiated, as it was to be activated by the Raven4.

Once again, the SJCAM C100 on-board video camera worked well, providing good quality footage of the entire flight. The footage helped with forensics. At the moment of the motor anomaly, the rocket trajectory could be seen to momentarily waver from its vertical attitude, as a result of the lateral thrust component as the combustion gases exited through the gouges burned in the sidewall of the rocket airframe . Two fins could be seen departing the rocket shortly after, possibly as a result of this disturbance. Despite the loss of the two (adjacent) fins, the rocket recovered and maintained its stable, nose-forward trajectory.

JEM Motor and propellant:

JEM motor Xi-36\DSCF7253.JPG

KNDX propellang segments Xi-36\DSCF7259.JPG

Raven data:

Barometric and axial acceleration curves Xi-36\Xi-36-Raven-basicl.jpg

Axial acceleration curve Xi-36\Xi-36-Raven-accel.jpg

BREO data:

BREO altitude vs time Xi-36\Xi-36_BREO.gif

Big Red Bee :

Landing site and walk back to pad Xi-36\Xi-36_BRB_plotted all.jpg

Launch photos:

Rocket set up for launch, with my brother Blair Xi-36\IMG_20230826_162916.jpg