how can you figure out how many gallons of fuel are needed to go a certain distance or range in an airplane.?

Question

I meant to say small airplane.Manybe this will help, how many gallons of fuel cover a mile in a airplane? can you increase range that the airplane can travel?

Answer 1

That depends on many factors, such as the size of the plane, VFR/IFR, alternates, the type of engines, the wind, altitude, humidity, gross weight, hold times, taxi time, and of course how far you are flying. It also depends on what country you are flying in, as different countries have different regulations for reserve fuel.

You said a "small airplane" but that's all relative. After 22 years as a captain on a B767 heavy passenger jet for a major airline, a Lear or a Caravan is a small plane to me, but they may be a large plane to somebody else.

Let's keep this simple and I will propose some basic parameters for your question.

Let's assume we are flying a Cessna 185 on floats 120 nautical miles (about 200 km) in a zero wind condition. We are taking off from a salt water bay at sea level and landing in a lake at 1000 feet ASL with no mountains in between.

The 185 will burn about 15 US gallons per hour (57 l/hr) and cruise about 120 knots. So that means it will take 15 gallons to complete the flying portion of the flight, or 15/120=0.125 gallons per mile or 8 miles per gallon. (note that is nautical not statute miles).

The formula you need to calculate nautical miles per US gallon is:

MPG = V/F
where V is the speed of the plane in knots
and F is the fuel burn in US gallons per hour

But we need extra fuel for:

- warm-up
- taxi
- pre-landing reconnaissance
- taxi and docking
- and you need at least a 45 minute reserve for most VFR flights in ICAO member states

So all in all the plane should not depart the hypothetical bay with less than 30 useable gallons in the tanks. The actual fuel consumption when you allow for the time the engine is running will probably be around 6 nautical miles per US gallon in our scenario. A Cessna 185 has a fuel flow guage, showing pounds of fuel burn per hour, and we need to convert that to gallons which depends on the temperature of the fuel.

Every aircraft has different speeds for different efficiencies. The maximum speed (VNE) is not likely your maximum endurance speed (hours) or maximum range speed (miles). The max endurance speed (measured in hours of flight time) is probably just above the stall speed of the aircraft when its in "clean configuration." That is when the engines produce the least amount of power to remain airborne, and the aircraft creates the least amount of drag - drag increases as the square of the speed. The max range speed is going to be a lot faster than that, as it becomes a function of burning less fuel per mile travelled, as the plane needs to move faster to achieve that. Most commercial planes fly 10-20% faster than their maximum range speed because time is money, both for the airline and for the passengers.

I don't have a flight manual for a Cessna 185 in front of me, but I think the maximum range speed is going to be around 90-100 knots.

Most airplanes will have these speeds specified in the flight manual, and they are determined by mathematical modelling and also by actual flight testing by factory test pilots before the airplane is certified. Flight manuals and some company operations manuals also have specific speeds listed for various unusual flight conditions, such as landing gear failures, one engine inoperative, flap malfunctions, depressurization etc.

Also remember that an airplane's speed is always the airspeed, and the only time that is equal to ground speed is in a zero wind condition.

Answer 2

depends on the plane, the wind direction and velocity, the altitude where the plane starts, the altitude where the plan stops, the altitude that the plane flies at, how fast the plane flies, and more. It takes more fuel to climb than it does to fly level, but it usually takes less fuel to go a given distance when flying at a higher altitude. If the wind is blowing away from the destination, then the plane has to work harder or fly longer than if the wind was blowing towards the destination.

Answer 3

It depends upon the weight and speed the plane is travelling as well as the pressure (altitude), temperature, humidity of the air.

There is a "most efficient" air speed for a plane. It's not full speed nor is it as slow as possible. It depends upon the factors mentioned above.

If you are figuring ground distance travelled, then you have to factor in wind velocity as well.

Answer 4

choose an altitude from terrain and atc requirements.

choose a power setting from flight experience. my usual plane (piper cherokee 140) cruises nicely at 65% power.

determine your air speed from your chosen power and altitude using the airplane's flight manual.

add in wind speed and direction to determine your ground speed.

from the length of the leg and ground speed determine the time en route.

use fuel consumption figures from the flight manual to determine the fuel for the leg.

repeat as necessary.