Napa Valley air balloon: how it stays up and who chooses where it goes

Take the parts one at a time and the whole thing stops being mysterious.

The envelope. The fabric bag above your head holds a large volume of air, and its only job is to keep that air together. It is open at the bottom, which is why the heat stays in: hot air rises inside the bag and cannot spill downwards past the cooler air below it. At the top there is a vent panel on a line, and pulling that line lets hot air out of the crown.

The burner. Above the basket, aimed up into the mouth of the envelope, sits the burner, fed from cylinders in the basket. The pilot opens the blast valve, a column of flame goes into the bag for a few seconds, and the air inside gets hotter. That is the only source of lift a Napa Valley air balloon has, and it is also the only loud thing on the whole flight.

The physics in one line. Warm air is thinner than cool air, so a bag of warm air inside a body of cool air weighs less than the air it displaces and it rises — exactly like a cork under water. Heat it more and it climbs; let heat out of the crown, or simply let it cool, and it sinks.

The lag is the skill. Nothing happens the instant the pilot acts. A burn now shows up as a climb in a few seconds and keeps working after the valve closes, and a descent has the same inertia in reverse. Flying a Napa Valley air balloon well is therefore mostly about anticipation: acting for where you want to be half a minute from now rather than where you are. Watch the pilot rather than the view for a couple of minutes and you can see them reading the lag.

This is the part that changes how people watch the flight. Ask a pilot where you are going and the honest answer is a shrug and a direction.

You travel with the air, not through it. Once the basket leaves the grass, the balloon is a piece of the air mass. That is why there is no draught in the basket even when the balloon is moving over the ground quickly, and why the flags below you are the only way to tell you have any speed at all. A Napa Valley air balloon has no way to turn across the wind, and no brake.

But the air is not one thing. Wind direction and strength change with height, sometimes sharply within a few hundred metres. A pilot who knows the valley knows roughly which layer goes which way on a given morning, and can move between them by climbing or descending. That is the whole of the steering, and it is why you will feel the burner go on and the balloon settle at a new height more than once. Watching a pilot hunt for a layer is watching a Napa Valley air balloon being steered.

Which is why the landing field is a surprise. Nobody can file a route. The pilot picks a field as the flight develops, weighing where the air is taking the balloon, what is below, and how much fuel is left. That decision is taken in the air, and it is the reason the vehicle on the roads below has been following you the whole time.

And why the crew matters more than passengers expect. The ground crew tracks the balloon by road, gets to the field, helps pack a very large envelope into a very small bag and drives everyone back to where they started. That drive is part of the 4 h 30 m in the listing, and it is why a Napa Valley air balloon morning takes half a day even though the time off the ground is a fraction of it.

What the valley gives it. Fifty kilometres of floor between two ranges, running from the city of Napa in the south to Calistoga in the north, with Highway 29 on one side and the Silverado Trail on the other, the towns of Yountville, Oakville, Rutherford and St Helena in a line, and Mount Saint Helena at the far end. It is a long, narrow, flat-bottomed space with plenty of open ground to come down in, which is exactly the kind of place ballooning works.

For the flight, book $288. The only balloon listing over this valley, at 4.8 across 128 reviews, Small group, 4 h 30 m, Free cancellation.

For the highest-rated day on the ground, add $750 at 5.0 across 6 reviews, or $635 at 5.0 across 46.

For the most evidence behind a wine day, add $165. 4.7 across 1,294 reviews, ten hours, with the redwoods on the way in.

For a seat and a table instead of a vehicle, add $410. Three hours, 4.9 across 9 reviews.

For the lowest fare on the site, add $99. Nine hours, 4.9 across 20 reviews.

Read as a whole, the machine explains the product. A Napa Valley air balloon is a bag of warm air with two controls, drifting with whatever the morning air is doing above fifty kilometres of vines, followed by a vehicle that will collect you from a field somebody else chose. That is why the booking is half a day for an hour of flying, why the hour is at dawn, and why $288 buys a window rather than a timetable.