PLT239: Forces Acting On A Balloon
What code PLT239 covers, why the FAA tests it, and how to study Forces Acting On A Balloon before your checkride.
Recall forces acting on aircraft - buoyancy / drag / gravity / thrust
What this means for your checkride
For a balloon the primary forces are buoyancy acting upward and gravity, the weight of the balloon and its load, acting downward, with the balloon in equilibrium when the two are balanced. Drag acts to oppose vertical motion through the air, damping how quickly the balloon climbs or descends. Unlike powered aircraft a free balloon has no thrust of its own and no way to steer laterally, because it simply travels with the surrounding wind.
Understanding which forces act, and that a balloon lacks thrust, explains why altitude is the only direct control a balloon pilot has.
A balloon is not steered like an airplane. With no thrust, horizontal travel is entirely a matter of choosing an altitude with a favorable wind.
Where to study it
A code on your test report is an area of deficiency. An authorized instructor must review it with you and endorse that review before you take the practical test, and the examiner may revisit it during the oral. Study it until you can explain it out loud, not just recognize the answer.