PLT181: Physics Of Hot Air Lift
What code PLT181 covers, why the FAA tests it, and how to study Physics Of Hot Air Lift before your checkride.
Recall balloon - hot air / physics
What this means for your checkride
A hot air balloon works by heating the air inside the envelope, which causes that air to expand and become less dense than the cooler surrounding air. Because the heated air weighs less than the ambient air the balloon displaces, the balloon reaches positive buoyancy and rises. The greater the temperature difference between the air inside the envelope and the outside air, the faster the balloon climbs, and heat lost through the fabric and top must be replaced to sustain flight.
The heat, expansion, and density relationship explains why temperature control is the pilot's primary tool for lift.
The balloon does not rise because hot air is weightless. It rises because heating makes the enclosed air less dense than the air it displaces.
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.