Tuesday, 25 August 2015

Some basic terms related to Aircraft - Part 7 - Wing Loading

11. Wing Loading

  • This is one of the main factor we will be dealing with when we actually scratch build a RC Plane.
  • When we deviate from the material and ways specified by a designer, we are going to change the wing loading of the original design.
  • If we are not taking this seriously, it will affect the performance of the aircraft. So be familiar with this term.

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 RC model aircraft, wing loading is expressed as ounces per square foot (oz./ft2).
  • When you actually have experience with different models you will understand this figure more meaningful and know 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 1 kg model having as many square meter of wing area is a lightweight.
  • A 1 kg model having 0.5 square meter of wing is very heavy and will fly like a heavy hammer.
  • The lighter the wing loading, the slower the aircraft can take-off, fly and land.  It will also have a better climb.
  • It is a good idea to know about the wing loading of your model so you will have an idea of how much long ground is required to build air speed for take off.
  • This is something that comes with experience because there are no live indicators in model aircraft to show you the speed and give stall warning as in a real aircraft.

How to Calculate Wing Loading.

We will take example of an aircraft weighing 6 lbs with 700 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.
      700 in2 /144 = 4.86 ft2
2)  Convert the total empty weight (ready-to-fly with no fuel/battery) to ounces.  There are 16 ounces in a pound.    6 lbs * 16 = 96 oz
3)  Divide the weight by the area:  96 oz / 4.86 ft2 = 19.753 oz/ft2
So the aircraft  wing-loading is  20 oz / ft2.
We can do the entire calculation by using simple substitution:  (Weight x 2304) ÷ Wing Area
Where weight is in pounds and wing area is in square inches
Putting the numbers from the above example into the simple formula gives us this:
(6*2304)/700 = 19.7485
For multi-wing aircraft, divide the overall weight of the aircraft by the total wing area for all wings.
Scratch built SPAD Demon - Low wing Trainer -  Coroplast and Balsa wood

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