CHI Aerospace

# Calculating Weight & Balance

Calculating weight and balance is essential for flight safety. Different points on the plane hold various items (baggage, fuel, pilot, passenger, etc) and if the weight is not equally distributed, it could result in compromised safety. Read through the example below to understand how to compute weight and balance to ensure a safe flight.

**Prior to preflight inspection, we provide students with a weight & balance worksheet to fill out specific to the aircraft they will be flying. This example is based on flying our Van’s RV-12 N922CA.*

**Fuel Calculation**

**How many gallons of fuel will you use?**

To find this, you’ll need to know how many gallons you burn per hour, and the amount of time you’ll be flying. Flying at an altitude of 2,500 feet with a power setting of 5,000 RPM burns 4.4gals/hr. In this case, we'll be flying for 2.5 hours:

*fuel burned gal/hr × flight hrs*

*4.4gal/hr × 2.5hrs*

*11 gallons *

**How many gallons of fuel will you have when you land?**

First, you’ll need to know your takeoff gallons and your gallons used, which we just calculated above. Let’s say we’re taking off with 15 gallons of fuel. Subtract the total amount of fuel you have on takeoff from the amount you will use during your flight.

*takeoff gallons - gallons used*

*15gal - 11gal*

*4 gallons remaining*

**Fuel Weight Calculation**

**What will be your takeoff fuel weight?**

To calculate your takeoff fuel weight, multiply your takeoff gallons by the weight of fuel.

*Note: Avgas weighs 6lb/gal

*takeoff gallons × fuel weight*

*15gal × 6lb/gal*

*90lbs takeoff fuel weight*

**What will be your landing fuel weight?**

To find this, you’ll need to know your landing gallons, and multiply this by the weight of fuel.

*landing gallons × fuel weight*

*4gal × 6lb/gal*

*24lbs landing fuel weight*

**Weight & Balance Table**

Note: in the tables below, the **bold** numbers are values that have been pre-calculated and provided by the aircraft manufacturer and can be found in the __Pilot’s Operating Handbook__ (POH). The aircraft weight can also be found in the POH.

This example is calculated for a pilot who weighs 120lbs, a passenger who weighs 180lbs, and they have a combined baggage weight of 50lbs.

**The aircraft arm value (80.5452in) was retrieved from the *__weight & balance worksheet for Van’s RV-12 aircraft N922CA__* and can be found on our website under Flight Training>Pilot Resources.*

** Arm:** A horizontal position on the aircraft. It is the distance measured from a reference point, also known as the “datum.”

** Moment:** the product of weight and arm, measured in inch-pounds.

**1. Center of Gravity (CG):** position at which the airplane would balance if it were possible to suspend it at that point. Aircraft have specific CG ranges to be considered safe to fly. CG is calculated by moment divided by weight and this aircraft has a CG range between 80.49in and 85.39in. The CG is within range after calculation for this example.

**2. Zero Fuel Weight:** The weight of the plane loaded with pilot, passenger, baggage, without any fuel. The zero fuel weight is calculated by finding the sum of the total weight in Table 1. We also found the zero fuel weight CG and the zero fuel weight moment from Table 1.

*Zero Fuel Weight CG*

*moment / zero fuel weight*

*92,463.75in-lb / 1,135.5lbs*

*81.43in CG*

*Zero Fuel Weight Moment*

*zero fuel weight × fuel arm*

*1,135.5lbs × 81.43in*

*92,463.75in-lb*

__3. Usable Fuel:__ The aircraft fuel tank has usable fuel and unusable fuel. The fuel tank can hold 19.8 gallons, but 4 gallons are unusable when the aircraft is in a pitched up position. In this example, we took off with 15 gals.

*3. Usable Fuel Weight*

*usable fuel × weight of fuel*

*15gal × 6lb/gal*

*90lbs*

*Usable Fuel Moment*

*usable fuel weight × fuel arm*

*90lb × 110.28in*

*9,925.20 in-lb*

*4. *Ramp Weight:** **The weight of the plane fully loaded with pilot, passenger, baggage and fuel. This is calculated by adding the zero fuel weight plus the usable fuel weight (see sum in Table 2). Please note there is a maximum weight limit of 1,320lbs, so you couldn’t put two 200lb pilots, 50lbs baggage, and full fuel tanks, as this would exceed the maximum weight.

*4. Ramp Weight*

*zero fuel weight + usable fuel weight*

*1,135.5lbs + 90lbs*

*1,225.5lbs*

*5. Ramp Weight Moment*

*zero fuel weight moment + usable fuel moment*

*92,463.75in-lb + 9,925.20in-lb*

*102,388.95in-lb*

**6. Taxi Fuel: **This is the amount of fuel you burn while taxiing. In this example, say we burned 0.5gal (and don’t forget to multiply by the weight of fuel!).

*6. Taxi Fuel*

*fuel burned × weight of fuel*

*0.5gal × 6lb/gal*

*3.0lbs*

*7. Taxi Fuel Moment*

*taxi fuel weight × fuel arm*

*3.0lbs × 110.28in*

*330.84in-lb*

__8. Takeoff Weight:__ The weight you takeoff with; calculated by ramp weight minus taxi fuel weight (see difference in Table 3). The CG is within range after calculation.

*8. Takeoff Weight*

*ramp weight - taxi fuel weight*

*1,225.5lbs - 3.0lbs*

*1,222.5lbs*

*9. Takeoff Weight Moment*

*ramp weight moment - taxi fuel moment*

*102,388.95in-lb - 330.84in-lb*

*102,058.11in-lb*

*Takeoff Weight CG*

*takeoff weight moment / takeoff weight*

*102,058.11in-lb / 1,222.5lb*

*83.48in*

__10. Fuel Burn:__ The fuel you burn during flight, calculated by gallons used (calculated above) multiplied by the weight of fuel.

*10. Fuel Burn Weight*

*gallons used × fuel weight*

*11 gal × 6lb/gal*

*66 lbs*

*Fuel Burn Moment*

*fuel burned × fuel arm*

*66lbs × 110.28in*

*7,278.48in-lb*

**11. Landing Weight:** The weight you land with; calculated by takeoff weight minus fuel burned. The CG is within range after calculation.

*11. Landing weight*

*takeoff weight - fuel burned*

*1,222.5lbs - 66lbs*

*1,156.5lbs*

*Landing Weight Moment*

*takeoff weight moment - fuel burned moment*

*102,058.11in-lb - 7,278.48in-lb*

*94,779.63in-lb*

*Landing Weight CG*

*landing weight moment / landing weight*

*94,779.63in-lb / 1,156.5lb*

*81.95in*

Remember that the Van’s RV-12 aircraft have a CG range between 80.40in to 85.39in, so be sure to double check and verify that all calculations are within that range.

There you have it - the weight and balance calculations explained! Try it for yourself and see if you understand where these numbers are coming from and if you get the same answers. We also have quizzes on our web page under “__Pilot Resources__” with word problems on weight and balance calculations among other flight training resources. If you have any questions, this is a great topic to bring up with your instructor. Good luck!