Flight time and LiPo sizing — capacity, discharge, hover time

“How long will it fly?” is the most common question — and the most often wrong. Bench peaks, marketing mAh and a neighbour’s “12 minutes” do not replace a calc with AUW, hover current, usable capacity and mission mix.

What eCalc means by flight time

In xcopterCalc, times depend on Battery max. discharge (usable fraction of nominal capacity). You get, among others:

• Hover Flight Time — hover only at AUW
• Mixed Flight Time — geometric mean between hover and max current (cruise approximation)
• min. Flight Time — full throttle, independent of weight

From the help: never deep-discharge LiPos — plan for at least ~10 % remaining after flight. Designing to 100 % empty plans cell abuse.

Also watch Load/C-rate (green continuous, yellow to peak, red over limit). A pack can have enough mAh and still be C-starved — Setup too marginal.

Mechanism

Pack energy ≈ capacity × average voltage. In hover the drive draws a relatively steady total current. Rough check:

usable mAh ÷ hover current (A) × 60 ≈ minutes in pure hover

eCalc does this consistently with sag, efficiencies and your discharge fraction — better than the hand formula, which remains useful for sanity checks.

Below ~20 °C cell chemistry, internal resistance rises; eCalc does not currently model that — pre-warm cells (20–30 °C) in cold weather.

Rules of thumb

1. Define the mission: photo hover, cruise, race heats.
2. Include the chosen pack in AUW (heavier ≠ automatically longer).
3. Set max discharge to e.g. 70–80 %, keep a reserve.
4. Read hover and mixed times together.
5. Keep C-rate in green/yellow; peaks only briefly.
6. Make the drive efficient first (Sizing) — fewer amps beat buying endless mAh.

Worked example: camera platform, ~12 min hover target

Assumptions:

• Flat quad, 450 mm frame, 15” props
• AUW 2300 g including gimbal
• Total hover current ≈ 18 A after iterations
• Goal: ~12 min hover at 80 % discharge

Usable capacity for 12 min at 18 A:

18 A × (12/60) h = 3.6 Ah → at 80 % discharge, nominal ≈ 3.6 / 0.8 = 4.5 Ah

So aim near 6S ~4500–5000 mAh, then re-run with the new pack weight. Check C-rate and temperature (Motor overheating).

Steps in xcopterCalc

1. Open xcopterCalc with your planned drive.
2. Battery: cells, capacity, type (list or custom per cell).
3. Set max. discharge to 70–80 %.
4. Charge state normal for averages (full when comparing fresh-pack peaks).
5. Calculate → read Hover / Mixed / min times and Load.
6. Change capacity or cell count, update AUW, recalculate.
7. If accessories draw from the flight pack, enter accessory current (0 A if separately powered).

No invented prefill parameters.

FAQ

Why is real time shorter?
Wind, climbs, VTX, cold cells, stick time, deeper discharge than planned. Mixed time is an estimate, not a warranty.

Does 2P help?
More capacity and often better C headroom, but more weight. Always recalc AUW.

Solar / negative accessory?
Help allows negative accessory current for panel feed-in — stay realistic.