How to Calculate the Wing Loading of a Flying Model Aircraft

The wing loading of an aircraft is the measure of weight carried by each given unit of area.

For model aircraft, wing loading is expressed as ounces per square foot (oz./ft²).  Experience with different models will make this figure more meaningful to you.

Why Wing Loading is Important

• Wing loading is the only indicator of how "heavy" an aircraft is.  The actual weight of an aircraft is meaningless.

  A 50 lb model having as many square feet of wing area is a lightweight.  A 6 lb model having 2 square feet of wing is very heavy and will fly like a sledgehammer (or maybe not quite that well).

• The lighter the wing loading, the slower the aircraft can take-off, fly and land.  It will also have a better climb.

• A larger model can have a higher wing loading and fly comparably to a smaller aircraft having a lower wing loading due to differences in the aerodynamics of different size aircraft.

  For example, let's say we have two aircraft that are absolutely identical except for physical size.  The smaller model has a 36" wing span while the larger aircraft has a 108" wing span.

  The smaller model may have a wing loading of 8 oz./ft² and the larger aircraft may have a wing loading of 35 oz./ft².  Both of these aircraft may perform nearly identically at substantially different wing loadings due to the difference in size.  Note that these figures are off the top of my head and not meant to be taken literally.

It is a good idea to inform the person who is test flying your model as to the wing loading so they have an idea of how long of a take off run it will need to build air speed.  This is something that comes with experience because there are no stall warning indicators in model aircraft as there are in full-scale aircraft.

How to Calculate Wing Loading

In this example, we will use an aircraft weighing 5-1/2 lbs (5 lbs 8 oz.) with 600 square inches of wing area.  Calculating the wing loading requires that the wing area be converted to square feet (ft²) and pounds to ounces.

1)  Convert the area to square feet.  There are 144 (12 x 12) square inches in a square foot.

600 in² ÷ 144 = 4.17 ft²

2)  Convert the total empty weight (ready-to-fly with no fuel) to ounces.  There are 16 ounces in a pound.

5.5 lbs x 16 = 88 oz.

3)  Divide the weight by the area:

88 oz. ÷ 4.17 ft² = 21.1 oz./ft²

Using round numbers, this gives the aircraft a wing-loading of 21 oz./ft² or

You can perform the entire calculation in one shot using simple substitution:

(Weight x 2304) ÷ Wing Area

Where weight is in pounds and wing area is in square inches

Plugging the numbers from this example into the above formula gives us this:

( 5.5 x 2304 ) ÷ 600 = 21.1 oz./ft²

For multi-wing aircraft, divide the overall weight of the aircraft by the total wing area for all wings.

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Copyright © 2003 Paul K. Johnson