Two tone balloons.

How can the balloon be kept in the air? That's the problem facing every balloonist who wants to make a really long flight. Giving the balloon a two-tone, silver and black colour scheme doesn't solve the problem, but it certainly can help!

First across the Atlantic - Double Eagle II

The first balloon to cross the Atlantic (Double Eagle II) had a silver and black colour scherne. It was crewed by three Americans, Ben Abruzzo, Max Anderson, and Larry Newman. The crew, their equipment and bags of sand ballast were carried in the balloon's gondola, a small steel and fiber glass boat. The gondola and its contents were kept in the air by the balloon's envelope.

This was made of nylon, and filled with helium, a gas much less dense than air. The helium gave the balloon its lift.

On August 11th, 1978, with weather forecasters predicting air currents moving steadily eastwards over the Atlantic, the balloon took off from Maine, U.S.A. Getting the balloon into the air was relatively easy. Keeping it flying evenly, however, was much more difficult. Although the size of the envelope had been carefully matched to the gondola's weight, the balloon's height changed frequently. Temperature changes were to blames. The heat of the day made the helium expand and become less dense. This increased the balloon's lift, causing it to rise. At night, the gas cooled, contracted and became more dense. The balloon fell.

In order to keep the balloon in the east-moving air, its height had to be controlled. When the balloon rose too far, helium was allowed to escape through a valve. When it fell too far, sand ballast was thrown overboard to lighten the gondola. Unfortunately, each cubic meter of helium released and each sand bag thrown overboard brought the end of the flight nearer. That's why the colour scheme was important. The silver upper part of the envelope reflected the Sun's heat during the day, preventing the helium from overheating. The black lower part of the envelope absorbed heat radiating from the Earth at night, and from the

early morning Sun, preventing it from cooling too much. This saved precious helium and ballast, prolonging the flight. Helped by the colour scheme, Double Eagle II did stay in the air long enough to make the crossing. 137h, 5 min, 50 s after takeoff, 5001km from its launch, it landed in France.