Understanding OnSpeed Logs¶

OnSpeed records flight data to CSV files on the microSD card at 50 Hz by default (configurable to 208 Hz via the web interface).

File Format¶

Format: CSV with headers (comma-separated values)
Rate: 50 Hz default (one row every 20 ms); optionally 208 Hz (IMU rate)
Naming: log_NNN.csv (sequential numbering). When a VN-300 EFIS provides a UTC timestamp, the file is renamed to YYYY-MM-DD_NNN.csv at close so the date travels with the file. Dynon, Garmin, and no-EFIS logs keep log_NNN.csv.
Size: A 1-hour flight produces approximately 50–100 MB of data

Metadata sidecar¶

Each log_NNN.csv is written alongside a log_NNN.meta plain-text sidecar. The firmware refreshes the sidecar every 30 seconds while the log is open and rewrites it once at close, so a flight that ends with a power yank still leaves a usable sidecar (worst case: the last 30 s of metadata is missing). The first 30 seconds of any flight are an exception — a power yank in that window leaves no sidecar at all, and the /logs page renders em-dashes for that flight rather than a misleading zero-valued line. One key=value per line:

duration_ms=1842113
row_count=92106
max_ias_kt=148
max_alt_ft=8420
firmware=4.20+1825dff
efis_type=dynon_skyview
time_of_day_start=14:32:08
gps_fix_seen=1

time_of_day_start is captured from any EFIS that publishes a clock (Dynon SkyView, VN-300, Garmin G3X, MGL). utc_start is VN-300-only. The /logs page reads the sidecar to populate the start-time, duration, max IAS, and max pressure altitude columns. The max_alt_ft value comes from the Palt column — every altitude OnSpeed records is pressure altitude (ISA 1013.25 hPa reference); there is no Kollsman/QNH correction.

Key Columns¶

Core Flight Data¶

Column	Units	Description
`timeStamp`	ms	Milliseconds since power-on
`IAS`	knots	Indicated airspeed
`Palt`	ft	Pressure altitude
`AngleofAttack`	degrees	Computed AOA (from pressure polynomial)
`DerivedAOA`	degrees	SmoothedPitch - FlightPath (AHRS-derived)
`flapsPos`	degrees	Detected flap position (snapped to the nearest configured detent)
`OAT`	°C	Outside air temperature
`TAS`	knots	True airspeed

Pressure Sensors¶

Column	Units	Description
`Pfwd`	counts	Raw pitot pressure (14-bit ADC: 0–16383)
`PfwdSmoothed`	PSI	Pitot pressure (EMA smoothed)
`P45`	counts	Raw AOA pressure (14-bit ADC)
`P45Smoothed`	PSI	AOA pressure (EMA smoothed)
`PStatic`	PSI	Static pressure
`CoeffP`	—	Pressure coefficient (P45 / Pfwd)

IMU Data¶

Column	Units	Description
`VerticalG`	G	Vertical acceleration (body frame)
`LateralG`	G	Lateral acceleration (body frame)
`ForwardG`	G	Forward acceleration (body frame)
`RollRate`	deg/s	Roll angular rate
`PitchRate`	deg/s	Pitch angular rate
`YawRate`	deg/s	Yaw angular rate
`Pitch`	degrees	Pitch angle (AHRS output)
`Roll`	degrees	Roll angle (AHRS output)
`imuTemp`	°C	IMU sensor temperature

Computed Values¶

Column	Units	Description
`EarthVerticalG`	G	Vertical G in earth frame
`FlightPath`	degrees	Flight path angle = arcsin(VSI/TAS)
`VSI`	fpm	Vertical speed (Kalman filtered)
`Altitude`	ft	Pressure altitude, Kalman-filtered. Same quantity as `Palt` (column 7), smoothed with vertical accel.

EFIS Data (when connected)¶

For Dynon, Garmin, or MGL EFIS:

Column	Units	Description
`efisIAS`	knots	IAS from EFIS
`efisPitch`	degrees	Pitch from EFIS
`efisRoll`	degrees	Roll from EFIS
`efisLateralG`	G	Lateral G from EFIS
`efisVerticalG`	G	Vertical G from EFIS
`efisPercentLift`	%	Percent lift / AOA from EFIS (0–99%)
`efisPalt`	ft	Pressure altitude from EFIS
`efisVSI`	fpm	Vertical speed from EFIS
`efisTAS`	knots	True airspeed from EFIS
`efisOAT`	°C	OAT from EFIS
`efisFuelRemaining`	gal	Fuel remaining
`efisFuelFlow`	gph	Fuel flow
`efisMAP`	inHg	Manifold pressure
`efisRPM`	rpm	Engine RPM
`efisPercentPower`	%	Percent power
`efisMagHeading`	degrees	Magnetic heading
`efisAge`	ms	Time since last EFIS packet

For VectorNav VN-300, the columns use vn prefix instead (e.g., vnPitch, vnRoll, vnGnssLat, etc.) — see CSV Log Columns Reference for the complete list.

Boom Data (when connected)¶

Column	Units	Description
`boomAlpha`	degrees	Reference AOA from boom
`boomBeta`	degrees	Sideslip from boom
`boomIAS`	knots	IAS from boom
`boomAge`	ms	Time since last boom packet

Other¶

Column	Units	Description
`DataMark`	0–99	Pilot annotation mark (wraps at 100)

Tail-Optional (Format Version 2)¶

Appended at the very end of every row, after CoeffP. Older firmware (format version 1) omits these columns entirely.

Column	Units	Description
`flapsRawADC`	counts	Raw flap-lever pot ADC reading. Replay tools interpolate the L/Dmax pip across detent transitions using this value and the configured `<FLAPPOTPOSITIONS>` boundaries.

Loading Logs in Python¶

import pandas as pd

df = pd.read_csv("log_001.csv")

# Plot IAS vs DerivedAOA
import matplotlib.pyplot as plt
plt.scatter(df["IAS"], df["DerivedAOA"], s=1, alpha=0.3)
plt.xlabel("IAS (knots)")
plt.ylabel("DerivedAOA (degrees)")
plt.show()

SD Card Management¶

Capacity: depends on your card size. A 32GB card holds hundreds of hours of flight data.
Format: FAT32. Use the FORMAT console command or format on a computer.
When full: the system stops logging. Download and delete old logs periodically.