FUEL IS A FLUID; IT FLOWS, BUT IT DOES NOT STRETCH
Fuel goes only so far
The distance from Campbell Airport (C81), a little north of Chicago, to St. Pete-clearwater International Airport (PIE) in Florida is about 920 nm.
A Piper PA-28-181 Archer has two 25-gallon tanks, but is officially credited with 48 gallons of usable fuel. The pilot’s operating handbook says that at 75 percent power and best-power mixture, it burns 10.5 gallons an hour and cruises at 125 knots. The required fuel reserve for night VFR is 45 minutes at a “normal” power setting. Since a more conservative setting than max cruise certainly qualifies as normal, the reserve might arguably be six gallons. In addition, some extra fuel is required for taxi, run-up and climb; let’s say 1.5 gallons.
Question: Ignoring wind, how would you plan this trip? Would you choose to make one fuel stop or two?
This is the kind of problem that might be presented to a student preparing to earn his private pilot license. The arithmetic is simple. Although in level, coordinated flight you probably have access to almost the whole 50 gallons, we’ll go by the book and start with 48. Subtract 1.5 for taxi and climb, and six for reserve. That leaves you with 40.5 gallons. Divide by 10.5 gph, and you can fly for three hours and 50 minutes, covering about 480 nm.
So you could make the trip in two legs, provided that one was not shorter than 440 nm (because 440 plus 480 equals 920). Or you could make two stops, in which case leg length would be of less concern. Or you could lean the mixture and slow down to, say, 115 knots. That would reduce your fuel flow to around 8 gph and prolong the flight by 40 minutes, but it would increase your maximum leg length by 100 nm.
Such was the calculation that presented itself to a father who intended to take his 15-year-old daughter and her best friend from chilly Illinois to Florida for their spring break. The 53-year-old businessman, a 1,600-hour pilot and, according to an obituary, a “larger than life” figure and pillar of his community and church, had owned the Archer for seven years and probably had a pretty good idea of what it could and couldn’t do — including some notion of how the fuel gauges behaved. The Archer, not a lightning-fast airplane, would require at least 7 hours and 20 minutes to cover the distance. Throw in a meal or two and the time to refuel and stretch your legs, and just getting to Florida and back was going to eat up two days of the nine-day vacation.
Perhaps it was with this in mind that he decided — or they decided, since his daughter liked to call herself his copilot — to leave Friday night, fly all night, and be in Florida to greet the semitropical sun. It was an ambitious plan, and could be pretty exhausting for all aboard; and so it was perhaps natural that the pilot might choose to cruise at 75 percent power and best-power mixture.
What was harder to understand was why he made the first stop in Nashville, Tennessee, after flying only 366 nm, 74 nm short of the minimum leg length for a one-stop trip. He now had either to throttle back and slow down, or to make a second en route stop.
He did neither. Instead, at 4 in the morning, after 4 hours and 21
QUESTION: IGNORING WIND, HOW WOULD YOU PLAN THIS TRIP? WOULD YOU CHOOSE TO MAKE ONE FUEL STOP OR TWO?