Page 22 - Sept23T

Parked in a line of tail draggers.
pilot in Alaska, to join me, and we set the date. With an experienced back- country pilot on board (my son) and me not wanting to look bad, I started to pay attention to the myriad de- tails involved in this kind of flying in piston single-engine aircraft. After flying mostly turbines for the past 20
years, the details were fortunately still in my memory, but rather distantly so. One of the most important details is the effect density altitude has on non-turbocharged airplanes. Den- sity altitude is the pressure altitude corrected for temperature. The high- er the temperature, the higher the
density altitude, even though the pressure altitude remains the same. Density altitude is a critical factor when flying in and out of the high backcountry, so much so that many of the airstrips have signs that warn about high density altitude next to the departure end of the runway. It is so crucial that in non-turbocharged airplanes, arrival and departure times are usually planned for the cooler times of day.
For example, the temperature in that part of Idaho is usually in the 50s at night but then jumps to the high 90s during the latter part of the day. The density altitude at Flying B can be above 7,000 feet if taking off in the afternoon, making a high gross- weight takeoff on a short runway and a confined area just plain hazardous. A non-turbocharged piston engine loses about one inch of manifold pres- sure or about 3.1 % of the engine’s total horsepower per thousand feet of density altitude, which means that at
20 • TWIN & TURBINE / September 2023