INSTALLATION OF BALLAST

Ballast is used in an aircraft to attain the desired CG balance. It is usually located as far aft or as far forward as possible to bring the CG within limits using a minimum amount of weight. Ballast that is installed to compensate for the removal or installation of equipment items and that is to remain in the aircraft for long periods is called permanent ballast. It is generally lead bars or plates bolted to the aircraft structure. It may be painted red and placarded: PERMANENT BALLAST - DO NOT REMOVE. In most cases, the installation of permanent ballast results in an increase in the aircraft empty weight.

Temporary ballast, or removable ballast, is used to meet certain loading conditions that may vary from time to time. It generally takes the form of lead shot bags, sand bags, or other weight items that are not permanently installed. Temporary ballast should be placarded: BALLAST _____ LBS. REMOVAL REQUIRES WEIGHT AND BALANCE CHECK. The baggage compartment is usually the most convenient location for temporary ballast.

The places for carrying ballast should be properly designed, installed, and plainly marked. The aircraft operation manual must include instructions regarding the proper placement of the removable ballast under all loading conditions for which such ballast is necessary.

Controlling CG Position With Ballast

Figure 3-12  shows an example aircraft whose CG exceeds the forward CG limit under certain loading conditions. The forward weight and balance check proves that with only the pilot and minimum fuel aboard, the forward CG is exceeded.

Without ballast placed somewhere aft to bring the CG within the designated limits of +16.5 in to +20.0 in, the aircraft is unsafe to fly when loaded with the pilot and minimum fuel. The problem of determining how many pounds of ballast are needed to move the CG within the approved limits can be solved by using the following formula:  

Ballast weight needed:

Inserting in the formula the applicable values:

Weight of the aircraft as loaded = 1907.5
Distance out of limit = +1.7 in
Arm from variable weight location to the limit affected = 53.5 in

We obtain the following:

When the mathematical computation ends in a fractional pound, use the next higher whole pound as the actual ballast weight. Consequently, 61.0 pounds must be placed in the baggage compartment to bring the CG safely within the CG range.

A final forward weight and balance check should be made to prove that by adding 61.0 pounds of ballast in the baggage compartment, this aircraft could be safely flown with minimum fuel aboard. Place a placard in the cockpit in a conspicuous place for the pilot, or anyone concerned, to see. The placard should read: FOR SOLO FLIGHT CARRY A MINIMUM OF 61.0 POUNDS IN BAGGAGE COMPARTMENT.

Maximum Load Conditions

A rearward weight and balance check will determine whether the airplane shown in figure 3-12 can be flown safely when fully loaded without exceeding the aft CG limit or its maximum gross weight.

The CG is well within the CG range when fully loaded; however, the maximum allowable gross weight is exceeded by 10.5 pounds. In this case a number of alternatives are available to remedy this overloaded condition without appreciably reducing the aircraft payload or flight range, as follows:

Alternative No. 1 - reduce baggage by 10.5 lbs.
Alternative No. 2 - reduce fuel by 10.5 lbs, or 1.75 gals.
Alternative No. 3 - reduce passenger load by one passenger.

Each alternative listed will require a placard stating the loading arrangement by which the gross weight and CG will be retained within their designated limits. Compute a new CG position for each alternate loading arrangement.