Free sim
Density Altitude
Your airplane doesn't care what the altimeter says — it performs at the altitude the air feels like. Set the field elevation, temperature, and altimeter, and watch the ground roll stretch past the sea-level baseline: the engine makes less power, the prop grips less, and the same lift-off airspeed takes longer to arrive.
Live readouts of pressure altitude, density altitude, and the ground roll as a multiple of the sea-level standard-day book number, computed from the field elevation, temperature, and altimeter setting sliders.
The airplane performs as though it were at the density altitude, no matter what the field elevation says — thinner air means less power, less prop grip, less lift, and the same lift-off airspeed arriving later. The multiplier applies to yourPOH's sea-level standard-day number; the POH always wins. Charts don't include humidity, so a muggy day is worse than the math above.
Drilling for the checkride?
Chapter 4 of our ACS-organized Private Pilot Quick-Review Study Guide covers the whole performance story — pressure vs. density altitude, the weight-and-balance math the examiner walks you through, and the CHECKRIDE TRAP answers for hot-high-humid days.