feat(fw_performance_model): scale vehicle weight by remaining fuel by mahima-yoga · Pull Request #27901 · PX4/PX4-Autopilot

mahima-yoga · 2026-07-14T17:01:54Z

Thought I would push something to get the discussion going:

Solved Problem

The FW performance model scales trim throttle, min/stall airspeed, and climb/sink rates from the static WEIGHT_GROSS parameter. For combustion vehicles a large share of the takeoff weight is fuel, so these limits become increasingly wrong
as fuel burns off during flight - which leads to inefficient flight.

Solution

Add an optional WEIGHT_FUEL parameter (mass of a full fuel load). When set, the weight used by the performance model is reduced by the burned fuel mass derived from fuel_tank_status (remaining fuel preferred, then percentage, then consumed fuel), low-pass filtered to reject sloshing.

Also adds weight_ratio to TecsStatus (appended field, uLog-compatible) for log analysis.

Test coverage

Needs to be tested.
Unit tests for the weight-ratio math and the fuel-fraction fallback chain
(make tests TESTFILTER=PerformanceModel)

Some points / limitations:

Currently only supports a single fuel tank.
Filter parameters haven't been tested / verified.

Add a WEIGHT_FUEL parameter for the mass of a full fuel load. When set, the weight used for trim throttle, min/stall airspeed, and climb/sink rate scaling is reduced by the burned fuel mass derived from fuel_tank_status (filtered to reject sloshing). Disabled by default.

github-actions · 2026-07-14T17:09:37Z

🔎 FLASH Analysis

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 --------------  -------------- 
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 --------------  -------------- 
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Updated: 2026-07-15T12:18:04

mbjd

Cool stuff! Looks nice and correct, some minor points below 👇

mbjd · 2026-07-15T09:13:14Z

+		// only a single fuel tank is supported: use the first reported tank id and ignore all others
+		if (_fuel_tank_id < 0) {
+			_fuel_tank_id = fuel_tank_status.fuel_tank_id;
+		}


could we not support multiple instances very easily too?

Change weight param to fuel density or total fuel mass when all tanks are full (assume the same fuel is in all tanks)

Just below, loop over all tanks, accumulate the consumed fuel weight, and convert that back to the fraction of total tank volume

or just always use weight

maybe multiple tanks are outlandish enough to not worry as well though

I shall give this a think

github-actions · 2026-07-15T12:12:06Z

💡 Commit messages could be improved

Not blocking, but these commit messages could use some cleanup.

Commit	Message	Suggestion
`1063b60e6f`	fix: don't set max climb/sink rates based on fuel fraction	Missing conventional commit format (e.g. "feat(ekf2): add something")
`1c24ac533a`	chore: shorten param description	Missing conventional commit format (e.g. "feat(ekf2): add something")
`c49a08d329`	chore: move _fuel_fraction_remaining constraint	Missing conventional commit format (e.g. "feat(ekf2): add something")

See the commit message convention for details.

This comment will be automatically removed once the issues are resolved.

hamishwillee

@mahima-yoga When you're done, this may well require an update to https://docs.px4.io/main/en/config_fw/weight_and_altitude_tuning#vehicle-weight-compensation

mahima-yoga requested review from mbjd and sfuhrer July 14, 2026 17:03

mbjd reviewed Jul 15, 2026

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mahima-yoga added 3 commits July 15, 2026 14:09

fix: don't set max climb/sink rates based on fuel fraction

1063b60

chore: shorten param description

1c24ac5

chore: move _fuel_fraction_remaining constraint

c49a08d

hamishwillee reviewed Jul 16, 2026

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feat(fw_performance_model): scale vehicle weight by remaining fuel#27901

feat(fw_performance_model): scale vehicle weight by remaining fuel#27901
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mahima-yoga commented Jul 14, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Solved Problem

Solution

Test coverage

Some points / limitations:

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github-actions Bot commented Jul 15, 2026

💡 Commit messages could be improved

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mahima-yoga commented Jul 14, 2026 •

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