Thu May 17, 2012 3:59 pm
#1066360
Simple Factors
Pilot X figures that a half-full tank will still leave him plenty in reserve − but are there any factors he hasn’t taken into account? By Adrian Bleese
Pilot X could remember with pride all of his aviation firsts: his first flight, his first solo, his first cross-country, his first trip with a passenger… yet here he was on the day of his very first solo glider land-away and he wasn’t feeling proud at all. He had to admit that this was probably due to the fact that it had begun as a local flight in a Cessna 150 and the gliding element was entirely unintentional.
He ran through the checks to determine the reason for the unrequested silence: primer, mags, throttle, mixture and somehow he found that he also had time to reflect on the events which had brought him here…
It had all started in the pub, the night before, when he’d agreed to take his friend, Ed, for a flight, meeting him at a farm strip close to Ed’s home. Pilot X had phoned the flying club early on the Saturday morning to arrange not only the hire of an aeroplane but of one with significantly less than full tanks. He’d had to do some quick maths because, while Pilot X was obviously a CAA standard 90kg, Ed was 16 stone in just his pants and Pilot X had no wish to see him in his pants. The club’s Cessna 150L weighed 1,127lb with just its oil; so, with both of them on board, Pilot X made a quick mental calculation that he could afford to have just 50lb of fuel in the tanks for their trip.
A check of his PPL notes showed that a gallon of fuel weighs 7.2lb but that was as good as seven gallons and he’d always planned for five per hour during his training. That meant that he could afford to fly Ed for 45 minutes and still have two or three gallons, giving him half-an-hour’s reserve, just in case. As they were meeting at a farm strip which was 20 minutes flying time away, he could also afford to put in another gallon-and-a-half which he should have burned off by the time he got there. That was his plan, then: eight-and-a-half gallons would give him 20 minutes to the strip and 45 with Ed, leaving a more than adequate reserve. He could then top up before flying home again; the maths worked.
Just enough fuel
It was mid-afternoon before he got to the airfield. He’d not only left plenty of time for last night’s couple of pints to wear off but had had to placate his girlfriend about disappearing again. It took a promise of dinner and a movie to get him out of trouble, meaning that he had to be back home by 6.30 or face the prospect of finding somewhere new to live. He found the little Cessna with quarter tanks, which was ideal. His walkround confirmed that three-quarters of the dipstick was dry; with a capacity of 26 gallons it must currently have six and a smidge, so Pilot X needed just two-and-a-half.
He taxied to the pumps and shut down. He’d always filled aeroplanes to the top before and hadn’t realised that the pump was in litres, but someone had very helpfully written the conversion factor on the cover of the refuelling log; one gallon equals 3.785 litres. A scribbled calculation later and, adding half-a-gallon for safety, he was pumping just under eleven-and-a-half litres in.
As he taxied to the holding point, the gauges still showed less than a quarter full,
but then everybody knew how unreliable they were, he must now have nine gallons, more or less. It was a beautiful early spring day, a powder-blue sky and some high up, puffy cirrocumulus. It was one also of the first times this year that the sun warmed the side of his face as he flew. Twenty minutes later he was rounding out at the gorgeous, wide green farm strip to pick up Ed.
He could tell that his friend was a little nervous and so decided not to mention the
fuel calculations and just get on with flying him over his house and bringing him back to earth without too much of a bump. Ed said that he enjoyed himself, but his colour suggested that half-an-hour was enough and Pilot X rejoined the circuit.
Ed’s colour returned as Pilot X’s drained − there was no fuel, apparently there never was, people sorted themselves out. Well, usually they did. It was after five in the afternoon and finding the owner of a high-wing aeroplane with a syphoning tube and a jerrycan was a non-starter.
Think seriously
OK, time to think seriously. He had started with six gallons and added three; at five gallons per hour that was enough for almost an hour-and-fifty-minutes and he’d flown less than an hour. Even being pessimistic, he needed just two gallons to get him back to the airfield and he had at least that. It was now nearly five-thirty but he might still be home in time to save his relationship, if he got straight off.
Ten minutes later and almost in sight of home he heard the first cough from the engine, then another, which he felt…
Carb heat didn’t seem to help. The third cough was the last, then silence. He stared in disbelief at the slowing propeller and time stretched to allow him to watch in wonder as it windmilled uselessly. The primer is locked, mags are on both, throttle is open, carb heat is on hot and the fuel… ah, the fuel.
The bubble of extended time seemed to focus the world outside. He now remembered that an imperial gallon weighed 7.2lb but a US gallon weighed just six, because it was smaller and, while the C150 had two 13usg tanks, there were one-and-a-half somewhere, which were unusable. He didn’t need to do any more maths or any more checks… he picked his field.
Questions
1 What factors were detrimental to Pilot X’s decision making?
2 At what point should he have admitted that the maths just didn’t work?
3 What other factors added to his confusion?
Pilot X figures that a half-full tank will still leave him plenty in reserve − but are there any factors he hasn’t taken into account? By Adrian Bleese
Pilot X could remember with pride all of his aviation firsts: his first flight, his first solo, his first cross-country, his first trip with a passenger… yet here he was on the day of his very first solo glider land-away and he wasn’t feeling proud at all. He had to admit that this was probably due to the fact that it had begun as a local flight in a Cessna 150 and the gliding element was entirely unintentional.
He ran through the checks to determine the reason for the unrequested silence: primer, mags, throttle, mixture and somehow he found that he also had time to reflect on the events which had brought him here…
It had all started in the pub, the night before, when he’d agreed to take his friend, Ed, for a flight, meeting him at a farm strip close to Ed’s home. Pilot X had phoned the flying club early on the Saturday morning to arrange not only the hire of an aeroplane but of one with significantly less than full tanks. He’d had to do some quick maths because, while Pilot X was obviously a CAA standard 90kg, Ed was 16 stone in just his pants and Pilot X had no wish to see him in his pants. The club’s Cessna 150L weighed 1,127lb with just its oil; so, with both of them on board, Pilot X made a quick mental calculation that he could afford to have just 50lb of fuel in the tanks for their trip.
A check of his PPL notes showed that a gallon of fuel weighs 7.2lb but that was as good as seven gallons and he’d always planned for five per hour during his training. That meant that he could afford to fly Ed for 45 minutes and still have two or three gallons, giving him half-an-hour’s reserve, just in case. As they were meeting at a farm strip which was 20 minutes flying time away, he could also afford to put in another gallon-and-a-half which he should have burned off by the time he got there. That was his plan, then: eight-and-a-half gallons would give him 20 minutes to the strip and 45 with Ed, leaving a more than adequate reserve. He could then top up before flying home again; the maths worked.
Just enough fuel
It was mid-afternoon before he got to the airfield. He’d not only left plenty of time for last night’s couple of pints to wear off but had had to placate his girlfriend about disappearing again. It took a promise of dinner and a movie to get him out of trouble, meaning that he had to be back home by 6.30 or face the prospect of finding somewhere new to live. He found the little Cessna with quarter tanks, which was ideal. His walkround confirmed that three-quarters of the dipstick was dry; with a capacity of 26 gallons it must currently have six and a smidge, so Pilot X needed just two-and-a-half.
He taxied to the pumps and shut down. He’d always filled aeroplanes to the top before and hadn’t realised that the pump was in litres, but someone had very helpfully written the conversion factor on the cover of the refuelling log; one gallon equals 3.785 litres. A scribbled calculation later and, adding half-a-gallon for safety, he was pumping just under eleven-and-a-half litres in.
As he taxied to the holding point, the gauges still showed less than a quarter full,
but then everybody knew how unreliable they were, he must now have nine gallons, more or less. It was a beautiful early spring day, a powder-blue sky and some high up, puffy cirrocumulus. It was one also of the first times this year that the sun warmed the side of his face as he flew. Twenty minutes later he was rounding out at the gorgeous, wide green farm strip to pick up Ed.
He could tell that his friend was a little nervous and so decided not to mention the
fuel calculations and just get on with flying him over his house and bringing him back to earth without too much of a bump. Ed said that he enjoyed himself, but his colour suggested that half-an-hour was enough and Pilot X rejoined the circuit.
Ed’s colour returned as Pilot X’s drained − there was no fuel, apparently there never was, people sorted themselves out. Well, usually they did. It was after five in the afternoon and finding the owner of a high-wing aeroplane with a syphoning tube and a jerrycan was a non-starter.
Think seriously
OK, time to think seriously. He had started with six gallons and added three; at five gallons per hour that was enough for almost an hour-and-fifty-minutes and he’d flown less than an hour. Even being pessimistic, he needed just two gallons to get him back to the airfield and he had at least that. It was now nearly five-thirty but he might still be home in time to save his relationship, if he got straight off.
Ten minutes later and almost in sight of home he heard the first cough from the engine, then another, which he felt…
Carb heat didn’t seem to help. The third cough was the last, then silence. He stared in disbelief at the slowing propeller and time stretched to allow him to watch in wonder as it windmilled uselessly. The primer is locked, mags are on both, throttle is open, carb heat is on hot and the fuel… ah, the fuel.
The bubble of extended time seemed to focus the world outside. He now remembered that an imperial gallon weighed 7.2lb but a US gallon weighed just six, because it was smaller and, while the C150 had two 13usg tanks, there were one-and-a-half somewhere, which were unusable. He didn’t need to do any more maths or any more checks… he picked his field.
Questions
1 What factors were detrimental to Pilot X’s decision making?
2 At what point should he have admitted that the maths just didn’t work?
3 What other factors added to his confusion?