How much fuel to buy to complete a trip?
That’s the question. How you calculate the fuel needed, is explained here.
So grab your calculator and do the exercise.
As a sample we take the Carenado AC 11 Commander 114. In the specifications of this aircraft we discover a maximum range to fly of 730 nm.
The cruising speed is 150 kts. These 2 figures show us the max. time to fly with full tanks. Divide the specific range by the cruising speed and we get the “Endurance”.
:: the Endurance is 730 / 150= 4,8 hrs; this means that you could fly ~4,5 hours with maximal fuel loaded. But what is max. allowable fuel?
In the specifications of this aircraft we learn that the max fuel allowed is 408.00 pounds.
With this information we can calculate that
:: the Average Fuel Consumption per hour is the (Fuel capacity in USG) divided by the (Endurance) 408 / 4.9 ~ 83 pounds/hr
Now the trip:
If you want to fly a trip of say: 114 nm with an average speed of 150 kts, your Flight Duration is:
:: Flight Duration= Distance to fly in nm divided by Average Speed in kts equals 114 / 150 = 0.76 hrs (45 min)
Your Fuel Needed = Flight Duration x Average Fuel Consumption per hour and in this case: 0.76 hrs * 83 pounds/hr = 64 pounds
In case of emergency there is a 45 minutes rule, saying that you need extra fuel for 0.75 hrs; in conclusion we need 0.76+0.75 hrs x 83 ~approx. 125 pounds of fuel to buy.
Now get in the plane and select Vehicle/Fuel and Payoad.
To change the fuel and payload, press Change Fuel in the Aircraft and Fuel and Payload menu and calculate with how many percentage each tank must be filled. Max. volume was 408 pounds, we need in each tank max 204 pounds; Change the values and check the outcome.
OK….where there is fuel weight needed for the flight, you cannot stiff the aircraft with passengers and/or luggage as far as you like…
So we check:
the maximum gross weight is 3140 lbs, we have 155 pounds on board as fuel, we got 2 passengers added to the payload (200 lb each) and we see that the baggage weight remains 195 lbs only. And since the passengers have 150 lb for luggage…Houston…we have a problem…
For your convenience some conversion factors are below:
1 Gallons [US] = 3.7854118 Liters
1 Gallons [US] = 8.3452641093 Pounds
1 Kilograms = 2.20458 5379 Pounds
1 Liters = 0.26417205124 Gallons [US]
1 Pounds = 0.11982844244 Gallons [US]
1 Pounds = 0.4536 Kilograms
How much fuel to buy?