Weight Limits & Balance

Weight limits apply to aircraft for three main reasons

  1. The aircraft can only perform as required below certain weights
  2. The aircraft is only strong enough to withstand forces under a certain weight
  3. The aircraft needs to be balanced and weight incorrectly placed in the aircraft, can cause irrecoverable losses of control

The weight limits you must know are:

  • *MTOW – maximum takeoff weight – this is in the POH and under RAA rules is required to be on display on the dash of the aircraft. Never exceed MTOW
  • *Empty Weight – The aircraft’s empty weight prior to any fuel persons, equipment or luggage being put into the aircraft
  • Pilot weight, passenger weight
  • Fuel weight is approximately 0.73 kg / L
  • Baggage each bag needs to be weighed in case they go in separate locations

Balance

When an aircraft is within its weight limits and has the weight correctly placed for safe flight, this is called the safe flight envelope, or sometimes referred to as “within the envelope”.

The envelope is a box that has the top line as MTOW, the bottom line as Empty Weight and the two sides of the envelope represent the safe limits of how far forward or back the weight can be in the aircraft at any given weight.

 

weight-and-balance-chart

Note that as weight increase the C of G moves towards the rear of the aircraft in most aircraft.

The smaller area within the envelope is called a utility envelope and is sometimes shown to represent a certain use for the aircraft. For example an aircraft may only be allowed to carry cargo, or perform mustering work within that envelope.   Most RAA aircraft only show the one large envelope.

The bottom axis indicates how far back the C of G is from the datum point.

The datum point is a reference point that we use to measure where in an aircraft a weight is located. Usually its the firewall or the tip of the spinner.

If for example it was the fire wall and the pilot weighing 100kg sat 1.0m from the datum point. The weight is 100kg and the length of the moment arm is 1.0 m or 100cm. How we graph this weight is explained in each POH.

You will learn this in detail with your instructor and in your navigation endorsement for your aircraft.

For your pilot certificate be sure to know that you can only put items in the aircraft in specified locations below the weight limits on those placards. Know MTOW and Empty Weight.

If in any doubt go to your POH and check before adding any weight to the aircraft or check with the instructor.