Return-to-home energy budget
Whether the battery can bring the drone home against the wind: return groundspeed, time, energy, the margin left, and the farthest round trip that keeps the reserve.
Planning and education aid. Not for primary navigation. Full disclaimer
Experimental: not yet fully verified. How results are checked
Coming home at 5 m/s takes 5 min and 15 Wh, leaving 15 Wh of margin.
- Return time
- Energy to return
- Margin
- Farthest out-and-back
Provenance
- Computed by
- drone.power.rth-budget 1.0.0, core 0.1.0
- Model
- Steady wind along the track: return GS = V − w, outbound GS = V + w; energy = power × time; round trip d = E / (P·(1/(V+w) + 1/(V−w)))
- Accuracy
- Exact for a steady along-track wind and constant power. Gusts, climbs, and cold packs need more margin.
- Notes
- 1 shown with the answer
- Cites
- Leishman, J. G., Cambridge University Press, Principles of Helicopter Aerodynamics
Something look off?
How we got thisFormula, worked example, sources, and proof
Model: Steady wind along the track: return GS = V − w, outbound GS = V + w; energy = power × time; round trip d = E / (P·(1/(V+w) + 1/(V−w)))
Accuracy: Exact for a steady along-track wind and constant power. Gusts, climbs, and cold packs need more margin.
Worked example: 1.5 km out, 15 m/s airspeed, 10 m/s headwind home. Source: add-drone-suite return scenario: return groundspeed 5 m/s. It is golden test vector v001, and every build checks the tool still gives its answer within its tolerance.
You enter
- Airspeed
- 15 m/s
- Distance home
- 1.5 km
- Headwind on the way home
- 10 m/s
- Cruise power
- 180 W
- Remaining energy
- 40 Wh
- Reserve to keep
- 10 Wh
You get
- Return groundspeed
- 5 m/s
- Return time
- 5 min
- Energy to return
- 15 Wh
- Margin
- 15 Wh
- Farthest out-and-back
- 2.5 km
Review: Not yet independently reviewed by a Part 107 remote pilot.
Last verified: 2026-09-18, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.
Status: version 1.0.0, core 0.1.0. See this tool in the verification report.
Checked against: 5 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.
Sources
- Principles of Helicopter Aerodynamics, Leishman, J. G., Cambridge University Press, 2nd edition. Chapter 2 (momentum theory: ideal hover power T^1.5/√(2ρA), figure of merit).
Experimental means this tool has not yet met the stable bar: at least 20 golden vectors, differential tests, and an independent worked example.