Cruising range at 75% power at 8,000 ft with 24.5 US gallons of fuel with 45 minutes reserve is how many nautical miles?

Cruising range at 75% power at 8,000 ft with 24.5 US gallons of fuel with 45 minutes reserve is how many nautical miles?

• A. 260 NM
• B. 340 NM
• C. 300 NM
• D. 320 NM

Answer: (D)

Range equals speed times endurance. To get endurance, you use the fuel you actually have for cruise (after setting aside reserve) and divide by how fast that fuel is burned. Total fuel is 24.5 gallons. The 45-minute reserve at this power level uses about 8.5 gallons per hour × 0.75 h ≈ 6.4 gallons. So usable fuel for cruise is roughly 24.5 − 6.4 ≈ 18.1 gallons. If the burn rate at 75% power is about 8.5 gallons per hour, the cruise endurance is 18.1 / 8.5 ≈ 2.1 hours. The cruising speed at 75% power and 8,000 ft is about 150 knots. Multiply by endurance: 2.1 h × 150 knots ≈ 315–320 NM. The closest value is 320 NM.

Range equals speed times endurance. To get endurance, you use the fuel you actually have for cruise (after setting aside reserve) and divide by how fast that fuel is burned.

Total fuel is 24.5 gallons. The 45-minute reserve at this power level uses about 8.5 gallons per hour × 0.75 h ≈ 6.4 gallons. So usable fuel for cruise is roughly 24.5 − 6.4 ≈ 18.1 gallons.

If the burn rate at 75% power is about 8.5 gallons per hour, the cruise endurance is 18.1 / 8.5 ≈ 2.1 hours.

The cruising speed at 75% power and 8,000 ft is about 150 knots. Multiply by endurance: 2.1 h × 150 knots ≈ 315–320 NM. The closest value is 320 NM.