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

Log rotation on config change¶

A log file is internally consistent: the columns advertised in its header match every row in the file, and the row cadence (50 vs 208 Hz) stays constant from first row to last. To preserve that invariant, the firmware closes the active log and opens a new one if any of these settings change while logging is on:

Setting changed	Why rotation happens
`Log Rate` (50 ↔ 208 Hz)	Row cadence changes; mixed cadence in one file confuses replay tools
`Read Boom` toggle	Boom columns appear/disappear in the row
`Read EFIS Data` toggle	EFIS columns appear/disappear in the row
EFIS type (e.g. Dynon ↔ VN-300)	EFIS column set differs (VN-300 has its own column block)

When rotation fires, the success page shows: "The active log file was rotated because the change affects column set or sample cadence; subsequent rows go into a fresh log_NNN.csv." The closed file gets its sidecar .meta written and (if a VN-300 UTC date is available) is renamed to YYYY-MM-DD_NNN.csv. The new file gets the next sequence number and a fresh header.

For post-flight analysis: one flight that included a mid-flight config change produces multiple log_NNN.csv files. Each is a coherent segment with its own header. Stitch them together by timestamp (the timeStamp column is millis() since power-on, so it's continuous across files until reboot).

Changes that do NOT trigger rotation (the column set and cadence stay the same):

Flap calibration adjustments (alpha_0, AOA setpoints, polynomial coefficients)
AHRS algorithm choice (Madgwick ↔ EKF6)
Audio settings, volume curves
Aircraft Vno / Vfe / G-limit values

Column values (e.g. DerivedAOA) may shift subtly mid-file in those cases — downstream analysis tooling typically handles that gracefully.

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.