GAP
Active Member
- Joined
- Jul 13, 2021
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Well it has been a little over a month since I launched this thing and getting all the data with all the difficulties I have had has taken forever. But now that I finally have analyzed the data I thought I'd write up a little post detailing the flight:
On July 29th 2023 at approximately 3pm Reno time I flew a partial Sub-min 3" rocket named Leave No Doubt to 34,190 ft and Mach 2.84. Some specs of the rocket below:
Diameter: 3"
Motor: CTI M2020 Imax
Wet Weight: 19.2 lbs (if you include the weight of the casing that means the rocket was 80% motor at liftoff)
Predicted Apogee: 45,400 ft
Predicted Speed: Mach 3.1
Primary Altimeter: Entacore AIM Xtra 4.1
Backup Altimeter: Featherweight Blue Raven
Two different video angles are attached here:
1.
View attachment Trimmed Vertical - Trim.mp4
2.
View attachment Horizontal Trim.mp4
The flight appeared nominal and was recovered successfully. Unfortunately, I did pop a fin on lading.
Now to the juicy part, the data!
I was pretty disappointed to see the meager altitude report of 34,000 ft and only Mach 2.8.
However, some explanation for that was given immediately by the condition of the paint post flight...
Quite a lot of paint got stripped off! Running your hand along it feels like sandpaper! This paint is designed to char at 500 deg F. However, I don't think it got that hot since there is no evidence of charring or expansion. Instead I actually think there was an adhesion issue between the paint and the primer causing the paint to get ripped off simply from the aero forces. This is further supported by the fact that the primer underneath is totally fine.
So with the data I have I wanted to calculate the Cd of the vehicle to validate my sims and make sure there wasn't something else going on. Assuming a nominal burn and that the flight is vertical the Cd can be calculated for the entire ascent:
The Cd data during motor burn is definitely not usable. However, there is a time period of around 5 seconds directly after motor burnout which has reasonable data. This shows a paint finish closest to rough camo paint in RasAero II. However, when I changed this in my simulation I still should have got almost 40k ft! This caused me to turn my attention to the motor. If I instead assume a Cd in my calculations I can calculate thrust. I also used the feature in the AIM software to calculate the motor performance. These matched up well and show a motor under performance of around 9%.
I took this back calculated thrust data and made a new .eng file along with setting my finish to rough paint and behold that RasAero II predicts almost the same altitude and speed that I achieved (35,000 ft predicted)! Therefore, I'm pretty confident in saying the motor under performed which is disheartening, but I'm glad the vehicle survived and overall I'm pretty happy with the flight given that it proved what I wanted it to prove.
Additionally, I did some dispersion analysis before the flight with RocketPy. That graph along with the actual measured apogee and landing points is shown. This proved to me at least that RocketPy is relatively reasonable especially for dispersion analysis.
Now it's time to reattach the fin and fly the vehicle again next year. Just need to decide on the motor, CTI or Loki?
On July 29th 2023 at approximately 3pm Reno time I flew a partial Sub-min 3" rocket named Leave No Doubt to 34,190 ft and Mach 2.84. Some specs of the rocket below:
Diameter: 3"
Motor: CTI M2020 Imax
Wet Weight: 19.2 lbs (if you include the weight of the casing that means the rocket was 80% motor at liftoff)
Predicted Apogee: 45,400 ft
Predicted Speed: Mach 3.1
Primary Altimeter: Entacore AIM Xtra 4.1
Backup Altimeter: Featherweight Blue Raven
Two different video angles are attached here:
1.
View attachment Trimmed Vertical - Trim.mp4
2.
View attachment Horizontal Trim.mp4
The flight appeared nominal and was recovered successfully. Unfortunately, I did pop a fin on lading.
Now to the juicy part, the data!
I was pretty disappointed to see the meager altitude report of 34,000 ft and only Mach 2.8.
However, some explanation for that was given immediately by the condition of the paint post flight...
Quite a lot of paint got stripped off! Running your hand along it feels like sandpaper! This paint is designed to char at 500 deg F. However, I don't think it got that hot since there is no evidence of charring or expansion. Instead I actually think there was an adhesion issue between the paint and the primer causing the paint to get ripped off simply from the aero forces. This is further supported by the fact that the primer underneath is totally fine.
So with the data I have I wanted to calculate the Cd of the vehicle to validate my sims and make sure there wasn't something else going on. Assuming a nominal burn and that the flight is vertical the Cd can be calculated for the entire ascent:
The Cd data during motor burn is definitely not usable. However, there is a time period of around 5 seconds directly after motor burnout which has reasonable data. This shows a paint finish closest to rough camo paint in RasAero II. However, when I changed this in my simulation I still should have got almost 40k ft! This caused me to turn my attention to the motor. If I instead assume a Cd in my calculations I can calculate thrust. I also used the feature in the AIM software to calculate the motor performance. These matched up well and show a motor under performance of around 9%.
I took this back calculated thrust data and made a new .eng file along with setting my finish to rough paint and behold that RasAero II predicts almost the same altitude and speed that I achieved (35,000 ft predicted)! Therefore, I'm pretty confident in saying the motor under performed which is disheartening, but I'm glad the vehicle survived and overall I'm pretty happy with the flight given that it proved what I wanted it to prove.
Additionally, I did some dispersion analysis before the flight with RocketPy. That graph along with the actual measured apogee and landing points is shown. This proved to me at least that RocketPy is relatively reasonable especially for dispersion analysis.
Now it's time to reattach the fin and fly the vehicle again next year. Just need to decide on the motor, CTI or Loki?
