AF­TER­MATH

FUEL IS A FLUID; IT FLOWS, BUT IT DOES NOT STRETCH

Flying - - Contents -

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?

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