Entacore Electronics

[skyangel]

Hello David,
In my latest rocket launch I have used your flight computer - AimXtra. I downloaded the flight data on an Excel spreadsheet and I used the data to calculate and verify some flight characteristics, including the maximum velocity – however I found the following discrepancy.

1. When I calculated the Maximum velocity, based on the altitude change, the calculations show a max. velocity of 356 m/sec at the 2.5 sec time stamp.
2. When I calculated the Maximum velocity, integrating the acceleration data, the calculations show a max. velocity of 262 m/sec at the 2.45 sec time stamp.
3. The AimXtra software shows a Maximum velocity of 286 m/sec.

The flight was almost vertical and there is no noise in the pressure data.

Considering that the calculated Maximum velocity is at the same time stamp for all three calculation methods, the vertical flight and the noisefree barometric data, could you please advise the reason for the discrepancies and what method are you using to calculate the velocity?

[DaviddeBruyn]

The AIM XTRA uses a combination of sensors to calculate the velocity. Sensor readings are weighted according to how accurate they are perceived to be at the time.

The technical name for the method used is the Kalman filter.

Pressure data is almost always a bit off when it comes to velocity calculations because pressure readings are affected by the movement of the rocket through the air. The accelerometer is the best sensor to use if the flight was vertical which explains why it gives the most similar reading to the AIM XTRA calculated value.