Basic Information
Name	Xi-41
Launch date:	28 December 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 NFB - 42 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	3.329 kg.
Stability Margin (minimum)	1.83
Flight objectives	- Higher altitude flight using APM-J.1 motor.

Motor details
Motor name	APM-J.1 (44.5mm)
Propellant	AXP-AP7.2 (Ammonium Perchlorate 68% /Epoxy (West System) 23.7%/Aluminum 8% /Lampblack 0.3%)
Grain mass	379 grams
Estimated Impulse	776 N-sec.
Class	J

Additional information

- The rocket is the same as that for Xi-40, except for motor.

- Third launch clip added for redundancy..

Weather conditions
Temperature	-2°C (28°F)
Wind	SW 15-20 km/hr (ground level)
Sky	Bright sun with clear blue sky
Other	-8° wind chill
Ceiling	unlimited

Launch Event Description

Although it was not as cold as the previous flight, as a precaution, the AvBay was wrapped with a pair of chemical hand-warmers and insulation blanket, which was removed just prior to loading the rocket onto the launch rail.

Initially things went smoothly during setup of the rocket and launch equipment. The BRB transmitter and receiver were activated and verified that a good GPS signal was obtained. Both Blue Raven units were powered up nominally. To confirm the status of the Ravens, in particular to verify the status of the pyros, the Featherweight app on my smartphone was started. Raven s/n1181 was checked first and verified that it was “go”. I then proceded to check Raven s/n1182. A message appeared on the screen “firmware updated needed”. I was taken aback by this, and not desiring to do an update in the field (no WiFi), hit the “cancel” option. Another message came up warning that cancelling may result in firmware incompatability.

Nevertheless, I tried cancelling but the first message once again appeared. I was caught in a loop. So I tried saying “OK” to update the firmware, hoping this would lead to an escape. No such luck, and the firmware update started, or appeared to start. It was getting late, as the sun sets early this time of the year, and it was getting colder, so I exited the app. I then noticed that the affected Raven was not in the “set for launch” mode, undoubtedly due to my (rash, in hindsight) decision to initiate the update. We made the decision to fire up the Quark flight computer, and if it started up nominally, we would fly with the two active flight computers, rather than three. The only signficant drawback was that the apogee-activated smoke charge was connected to the now-inactive Raven.

Fortunately, the Quark activated nominally. We then completed the pre-launch setup. 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. It was kept in an insulated box until just prior to launch.

We headed to where the Launch Firing Box was located, 275 feet south of the pad. After verifying the sky was clear, the countdown proceeded. At the zero mark, the ignition button was pressed. After a second or so, the rocket soared skyward with a loud roar and bright flame, accelerating at a quick pace thanks to the powerful APM-J.1 motor. The motor burned for an estimated two seconds. We lost sight of the rocket after burnout, but were able to follow the smoke trail from the lift-off actuated smoke grain until it faded as the rocket climbed ever higher. We searched for sign of the apogee pyro smoke cloud and after nearly 20 seconds, we spotted it. Shortly after we could see the smoke cloud from the backup apogee pyro and noticed the faint smoke trail from the lift-off activated smoke charge. We were able to follow the rocket’s free-fall descent, as the smoke grain burned for a longer time than expected. As well, the “twinking” of the sun glinting off the rocket’s two chrome bands helped us to maintain visual contact. This twinkling continued to provide a visual cue of the rocket’s location even after the smoke grain burned out. After descending for around a minute, the main pyro was seen to fire and the chute blossomed. At this point, the rocket had drifted quite far downwind and as such, the chute could barely be seen. The rocket soon disappeared behind the berm that runs along the length of the launch range.

We programmed the GPS coordinates received from the BRB transmitter into the hand-held Garmin GPS unit. Indicated distance was 1/2 mile (800 m.). Our two guests (Richard S. and his buddy Mark) volunteered to head to the landing site, using their ATV, to fetch the rocket. To help them find the rocket, we pinpointed the touchdown site on my printed map with gridlines indicating latitude and longitude. While they headed out, my brother Blair and I packed up and headed to our parked car. When we arrived, Richard and Mark had the rocket with them, and mentioned that it was found exactly where expected. The Quark was beeping out the recorded apogee of 5152 feet. I then opened the Featherweight app, and the active Raven unit gave an indicated apogee of 5201 feet. All the rocket components were present and appeared to be in pristine condition.

Flight Analysis
Event:	Time (sec)	feet	metres
Apogee*	16.8	4898	1493
Separation*	16.9	4891	1491
Chute deployment	78.5	590	180
Touchdown	117	-	-
Range	-	2546	776
Max. velocity	720 fps	219 m/sec.	mach 0.665
Descent rates:	ft./sec.	m/sec.
Free-fall	85	26
Parachute	20.4	6.2

* Corrected for non-standard base temperature.

Post-flight analysis and comments:

Post-flight examination of the flight data indicated that the operation of the Blue Raven s/n 1181 unit was fully nominal, with a reported barometric apogee of 5202 feet. The Raven “inertial navigation max altitude” was 5158 feet.

A comparison was done of altitude versus time for the Raven and BRB GPS data. The corrected Raven altitude closely followed that of the GPS altitude, except near apogee, where GPS altitude was slightly higher.

In regard to the “update firmware issue”, Adrian of Featherweight Altimeters stated that WiFi access is not needed to perform the update in the field, as the firmware is present with the phone app (seems kind of odd to me as I never loaded that latest update on my phone). I asked Adrian how to avoid this in the future, and his suggestion was to power up the Ravens and apps prior to heading out to the launch site in case there is a pending update. To be honest, I would prefer not to use the app in the field, at least not prior to the flight. However, the pyro status is not easy to confirm using the onboard LEDs and beeper. The LEDs blink way too quickly and the beeper is nearly inaudible, especially s/n1182.

The Eggtimer Quark performed nominally with a reported apogee of 5152 feet (reported altitude not corrected for base temperature). Operation of the BRB (GPS) unit was fully nominal. GPS-based apogee was 5043 feet (1537m.), which is within 3% of the corrected Raven apogee. Maximum reported acceleration of the rocket during motor burn was 18G’s.

Examination of the Raven axial acceleration data indicated that the APM-J.1 motor had a fully nominal burn that matched static test results. Burn time was 1.75 seconds.

Fortuitously, the liftoff-actuated smoke grain burned for a lot longer than expected. The 68 second burn time was about double the expected burn time. This is likely due to the grain igniting at one end only, even though both end igniters has fired. The long burn, in absence of the apogee-activated smoke charge, was certainly beneficial in tracking the rocket during descent.

The on-board video camera worked nominally, providing good footage of the entire flight.

Examination of the rocket components verified all were in pristine condition.

Misc photos:

Propellant grain, as cast Xi-41\DSCF7740.JPG

Grain segments Xi-41\DSCF7741.JPG

APM-J.1 nozzle Xi-41\DSCF7742.JPG

Xi-41\DSCF7743.JPG

AvBay ready for flight Xi-41\DSCF7757.JPG

3D printed motor thrust bulkhead and boattail Xi-41\DSCF7747.JPG

Lift-off actuated smoke charge, installed Xi-41\DSCF7753.JPG

Apogee smoke charge, mounted on AvBay bulkhead Xi-41\DSCF7755.JPG

Nosecone, with BRB transmitter inside Xi-41\DSCF7759.JPG