by Jonathan M. Stern
Because conditions are standard (29,92" sea level pressure and 15° C temperature very close to sea level), your density altitude at your cruising altitude of 6,000 feet can be expected to be 6,000 feet. Although there are many different ways to approach performance calculations, I like to use density altitude. By selecting the performance chart for a 6,000 foot density altitude, I select cruise performance data of 72 percent BHP, 151 KTAS, and 13.0 GPH. According to the chart, this performance is achieved using a manifold pressure of 22" and 2,300 RPM. You enter these data on the left side of the log under CRUISE.
The winds aloft are reported relative to true North. Your courses, as taken from the LAE chart, however, are based on magnetic North. Before you can use the winds aloft data with your magnetic courses, you need to convert the winds to magnetic. This is done with the correct figure for magnetic variation, which is found at both the top and bottom of the LAE chart. The magnetic variation in Boston is almost 16° West. At Bradley, it's about 14° West. For simplicity's sake, use 15° West for the whole trip. For longer East/West trips, you can use different variations along the way.
To convert true winds to magnetic winds, you add Westerly variations to, or subtract Easterly variations from, the wind direction. This can be remembered by the saying "East is least, and West is best." Accordingly, wind direction along the route of flight is shown in the flight log as 115° (100° + 15°).
Wind correction angles, which keep the airplane flying on course in a crosswind, are calculated using a flight computer or trigonometric formula and entered under WCA in the flight log. Likewise, groundspeed is calculated with the flight computer using wind, TAS, and magnetic course. The result, in this case 178 knots, is entered under GS in the flight log. The estimated time enroute, or ETE, between each fix is then calculated from the groundspeed and the distance using a simple time, speed, and distance calculation.
The calculation for ETE to the first fix is complicated by the time, fuel, and distance to climb calculation. The distance covered in the climb must be subtracted from the distance to the first checkpoint. Then the remaining distance to the first checkpoint is used to calculate additional time enroute and fuel burned to the first checkpoint.
The fuel burned and time elapsed in the climb is added to the remaining fuel burned and time elapsed to the first checkpoint. Finally, the time enroute is totaled and entered next to TTL ETE and the fuel burned is totaled and entered to the right of T.F.R., which stands for total fuel required. The T.F.R. includes one gallon for approach and landing and 9.75 gallons reserve, which represents 45 minutes at cruise airspeed with the specific power setting selected for this flight from the cruise performance charts.
IFR flights require sufficient fuel to reach the destination, the alternate (if required), and to fly for 45 additional minutes at cruise airspeed.