Turning an area into a distance
A survey grid is a set of parallel lines, so the total distance flown is the number of lines times the length of each. The number of lines is the width of the block across the flight direction divided by the line spacing, rounded up, and the length of each line is the area divided by that width. For a block of 80 acres treated as square, that is 323,749 square metres, about 569 m on a side. At 45 m spacing you get 13 lines of 569 m, which is 7.4 km of flying. At 8 m/s that is a little over 15 minutes on the lines alone.
Line orientation is the one free choice in the layout and it is worth using. Running lines along the long axis of the block gives fewer, longer lines and fewer turns, which is faster. Running them across the wind is usually smoother and gives more consistent ground speed than fighting a headwind on half the passes and being pushed on the other half. When the two arguments conflict, the wind usually wins on a windy day and the geometry wins on a calm one.
What turns actually cost
A turn is not a pivot. The aircraft decelerates out of the line, turns, translates across to the next line and accelerates back to survey speed, and on many missions it also stops taking pictures and starts again. Ten seconds a turn is a reasonable starting figure for a small multirotor at moderate speed and it can be double that at higher speeds or wider spacing. Thirteen lines gives twelve turns; at ten seconds each that is two minutes, which is about 12 percent on top of the line time.
The overhead scales badly on small blocks. A five acre site at the same spacing has short lines and almost the same number of turns per unit area, so the fraction of the flight spent turning goes up sharply. That is one reason small sites feel disproportionately slow, and it is a reason to fly them at wider spacing and finer altitude rather than the reverse.
The transit comes out of every pack, not the job
This is the mistake that makes plans optimistic. If the block is 150 m from where you launch, that is not 150 m taken off the day once. It is 300 m out and back on every single pack, because the aircraft returns to you to be swapped. Four packs, 300 m each way at 8 m/s, is about two and a half minutes of transit that produced no survey data. The calculator subtracts the round trip from each pack before working out how much survey each pack can do, which is why the pack count is sometimes one higher than a naive division suggests.
| Where the time goes on a typical block | Share |
|---|---|
| Flying survey lines | The majority, and the only part producing data |
| Turning at the ends of lines | 10 to 20% of air time, more on small blocks |
| Transit out and back, every pack | Grows with distance and with pack count together |
| Pack swaps on the ground | Often the largest single block of the day |
| Setup, site walk, checks, pack-down | Fixed, and rarely as short as planned |
How many packs to bring
More than the calculator says. The pack count here is the arithmetic minimum on the assumptions you gave it, and the assumptions are the optimistic version: a steady wind, no reflown lines, no pack that turns out to be tired, and the block exactly the shape you told it. A reflight of two lines because a cloud shadow ruined them costs a pack. Charging on site is possible but it is slower than people plan for, and putting a pack straight on charge while it is still warm from the flight is not good for it, so the queue is longer than the charger rating suggests.
To build the inputs this page needs: get the line spacing from the drone mapping and GSD calculator, get the usable minutes per pack from the drone flight time calculator, and check the charge current and time for the swap plan with the LiPo pack and charging calculator. If part of the site is a structure rather than open ground, the drone inspection shot planner handles that separately, because a grid over a building is not the same problem.
The two things that actually hurt people
Lithium polymer packs are a real fire hazard, not a theoretical one. A pack that has been punctured, crushed in a crash, swollen into a pillow shape, or run flat below its cutoff can ignite without warning and burns hot enough that smothering it is not a plan. Almost every pack fire that gets written about happened while the pack was charging with nobody in the room. Charge where you can see it, on a surface that does not care, and stop the charge if a pack gets hot or gains thickness. A damaged pack should be moved away from anything that will burn and kept there; for getting rid of it, follow whatever your local hazardous waste program says, because that is a local question and not one a website should answer.
Propellers cut. They are stiff, they turn fast, and a multirotor that has armed on the ground is a running machine. A drone that loses a motor in flight does not glide anywhere; it comes down more or less where it was. Keep people out from under the aircraft and keep your hands away from the arms while the battery is connected.
What this page does not tell you
Nothing on this page is a statement of law and no number it produces is evidence of compliance. Drone flight in the United States is regulated federally, the rules for recreational flying and for flying as part of a business are not the same set of rules, and they are revised. There are requirements around who may operate, what has to be registered, what has to broadcast identification, and where you may fly at all; controlled airspace requires authorization before you enter it, obtained through the official channels. None of those are described here on purpose, because a stale summary on a calculator page is worse than no summary. Check the current requirements at the FAA and use the official airspace tools before every flight, not once when you bought the aircraft.
State, county and city rules sit on top of the federal ones and cover things federal rules do not: where you may take off and land, what happens over a park or a beach, and privacy. They vary between neighbouring towns. Find out who owns the ground you launch from and what they allow.
A planned altitude, a planned standoff or a planned flight line from this calculator is an engineering figure for a camera and a battery. Whether you may actually fly it is a separate question with a separate answer.
Questions people ask
How many acres can one battery cover?
It depends entirely on line spacing and speed, which is why this page asks for both rather than quoting a figure. Coverage rate in square metres per second is simply spacing times ground speed: 45 m spacing at 8 m/s covers 360 square metres per second, which is about 5.3 acres per minute of line flying, before turns and transit. Halve the altitude to get finer imagery and you roughly halve the spacing, which halves the rate. Any headline figure of acres per battery is quietly assuming a particular spacing and speed, so ask what they were before comparing.
Should the flight lines run along the long axis or across it?
Along the long axis if you want the fewest turns, which is usually the faster flight. Across the wind if the wind is a factor, because consistent ground speed matters for consistent shot spacing and a following wind on alternate passes makes the interval requirement uneven. On a long narrow corridor there is not much of a choice, and on a square block the difference is small. Where it matters most is a block that is three or four times longer than it is wide, where the wrong orientation can add a third to the turn count.
The calculator assumes a square block. My site is an odd shape.
Use the long or corridor option and give the width across the flight lines, which handles most real shapes better than a square assumption. For a genuinely irregular boundary, take the bounding rectangle rather than the true area, because the aircraft flies full lines across the block and only the ends get trimmed. Planning to the true area of a ragged polygon underestimates the flying by whatever the boundary wastes, and on a very irregular site that can be a quarter of the job.
Can I charge packs on site to avoid carrying so many?
You can, and people do, but plan the time honestly. A pack should cool before it goes on charge, a fast charge is harder on the pack than a slower one, and a field charger running from a vehicle or a generator is usually slower than a bench setup. The result is that a charging cycle is often longer than a flight cycle, so charging keeps a job going rather than keeping it fast. Charging must also be attended, which means somebody is watching the charger instead of the aircraft. Treat on-site charging as the plan for a long day, not as a substitute for enough packs.