Up and Down Only

Two controls

The burner turns propane into a tall flame aimed up into the envelope. Hotter air is thinner, so the envelope full of it weighs less than the same space full of outside air, and the difference is lift. The vent is a panel at the top that the pilot can pull open with a line. It lets hot air out, so the balloon cools and sinks. Most of the time a pilot just stops burning and lets the envelope cool on its own; the vent is for sinking faster and for the end of the flight.

Flying level means giving short burns every so often, enough to make up for the heat lost through the fabric. In the toy, holding level takes the burner about a quarter of the time.

Steering with the layers

The ground slows the wind near it and turns it a little. Higher up the wind is usually faster, and in the Northern Hemisphere it often turns clockwise with height. So the layers stacked above a launch field can each push a balloon a different way. A pilot reads them, then climbs or sinks into the one going closest to where they want to be, and may switch layers several times to zig-zag toward a spot.

Each morning in the toy has five made-up layers. The arrows on the right-hand chart point where each layer pushes, using the same north-up view as the map.

Why it handles like a ship

The envelope in the toy holds about 2,550 cubic metres, which is around two and a half tonnes of air. A burn has to heat all of that before the balloon notices, and then the balloon has to get that mass moving, plus some of the outside air it pushes aside. So a burn shows up as a climb many seconds later, and a climb keeps going after the burner stops. Pilots plan ahead: they stop burning before they reach the height they want, and start before they need it.

Watch the height chart while you fly. The curve keeps bending after you let go of the button.

Reading the wind first

Before launch, pilots look at forecasts and often let go of a small helium balloon and watch which way it drifts as it climbs. The "Release pilot balloon" button does that: it draws the path a small balloon rising at a steady 3 m/s would take from where you are. Untick "Show winds" to fly from that path alone. In the air, pilots also watch smoke, flags, trees, and other balloons.

Hot limits

The fabric has a temperature limit. The flight manuals found for this page give a continuous limit of 120 °C near the fabric and a never-exceed figure a few degrees higher (for example this Sky Balloons manual and this Ultramagic one). The Sky manual also says the parachute vent should not be held open for more than 3 seconds in flight. The toy warns about both. On a hot day, or with more people aboard, the envelope has to run hotter to float, so it gets closer to the limit. The calculator below shows how much.

Landing

A balloon lands wherever the wind takes it, so pilots look ahead for an open field, sink toward it, and use a last burn to soften the touchdown. In the toy, under about 1.5 m/s counts as soft and over 3 m/s as hard. Those are rough lines for a game, not figures from a manual.

• One made-up balloon. Real envelopes come in many sizes, and their weights vary.
• Heat loss is a single rate. Real loss depends on the fabric, sun, wind, and how fast the balloon is moving.
• Winds are five neat layers with short blends between them, and they never change during a flight. Real winds shift, gust, and change with the sun.
• No thermals, no terrain, no trees, no power lines, no airspace. The ground is flat and at sea level.
• The marker drops straight down the moment you press the button.
• On landing the basket stops dead. Real baskets often drag and tip in a breeze.
• The burner is one steady flame with no pilot light, whisper burner, or second burner.

It is a toy for getting a feel for the lag and the layers, not a training aid.

Logbook

Flights you land are logged here, in this browser only.