Center that Gravity

Longitudinal balance affects the security of the longitudinal axis that the glider. To accomplish satisfactory pitch attitude handling in a glider, the CG the the correctly loaded glider is front of the facility of press (CP). Once a glider is produced, the manufacturer offers glider CG limitations, which call for compliance. These restrictions are generally uncovered in the GFM/ POH and also may also be discovered in the glider airframe logbook. Addition or removed of equipment, such as radios, batteries, or flight instruments, or airframe repairs can have an result on the CG position. Aviation maintenance technicians (AMTs) need to record any changes in the weight and balance data in the GFM/POH or glider airframe logbook. Weight and also balance placards in the cockpit must also be updated.

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Problems linked With CG forward of forward Limit

If the CG is in ~ limits, pitch mindset control stays within acceptable limits. However, if the glider is loaded so the CG is front of the forward limit, managing is compromised. The glider is stated to be sleep heavy. Sleep heaviness makes it complicated to advanced the sleep on takeoff and also considerable earlier pressure on the manage stick is forced to control the pitch attitude. Tail stalls occur at airspeeds greater than normal and also are adhered to by a quick nose-down key tendency. Restoring a typical flight perspective during stall recoveries take away longer. The landing flare is more daunting than normal, or perhaps even impossible, due to nose heaviness. I can not qualify to flare could an outcome in a hard nose-first landing.


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The adhering to are the most usual reasons for CG front of front limit:

Pilot weight exceeds the maximum permitted pilot weight.Seat or sleep ballast weights are installed yet are no required as result of the weight of the pilot.

Problems connected With CG Aft that Aft Limit

If the glider is loaded so the CG ar is behind the aft limit, managing is compromised. The glider is said to be tail heavy. Tail heaviness can make pitch control of the glider complicated or also impossible.

The fundamental problem with a CG aft that the aft border is the designed function of the horizontal stabilizer and also elevator. Fixed wing plane are generally designed so that the horizontal stabilizer and also elevator provide a down force to respond to the slightly nose forward CG such the the aircraft often tend to resume a level pitch mindset after one upset about the lateral axis. As the airspeed changes, the pilot alters the trim or trims the aircraft so the down force precisely balances the forward CG in ~ limits. Need to the aircraft be upset and also the sleep pitches upward, the resultant slower airspeed results in less down force created by the horizontal stabilizer and elevator. This decreased down force lets the nose reduced so the airspeed retains to the pre-upset value. This is dubbed positive stability. Conversely, if the upset areas the aircraft in a nose down attitude, the increased airspeed will rise the under force and raise the sleep to the pre-upset balanced condition. However, if the manage surface is in a stalled condition, this stabilizing activity will not start until the manage surface regains un-stalled airflow and begins creating down force again.

The adhering to are the most typical reasons for trip with CG situated behind permissible limits:

Pilot load is less than the specified minimum pilot seat weight and also trim ballast weights necessary for the lightweight pilot room not installed in the glider before flight.Tailwheel dolly is quiet attached, much aft ~ above the tailboom that the glider.Foreign matter or debris (water, ice, mud, sand, and nests) has accumulated in the aft fuselage of the glider and was not discovered and removed before flight.A heavy, non-approved tailwheel or tail skid was mounted on the aft tail boom of the glider.

Sample Weight and also Balance Problems

Some glider manufacturers carry out weight and balance details in a graphic presentation. A well designed graph gives a convenient way to recognize whether the glider is in ~ weight and balance limitations.

In number 5-19, the chart indicates that the minimum load for the front chair pilot is 125 pounds, and also that the maximum is 250 pounds. It additionally indicates that the maximum behind seat pilot weight is 225 pounds. If each pilot weighs 150 pounds, the intersection of pilot weights falls within the envelope; the glider load is within the envelope and also is safe for flight. If each pilot weighs 225 pounds, the rear seat maximum fill is exceeded, and the glider fill is external the envelope and unsafe for flight.

Figure 5-19. Weight and balance envelope.

The CG position can additionally be determined by calculation utilizing the adhering to formulas:

Weight × eight = MomentTotal minute ÷ total Weight = CG place (in inches aft of the recommendation datum)

The computational an approach involves the application of straightforward math functions. The adhering to is an example of the computational method.

Given:
Maximum gun weight1,100 lb
Empty weight600 lb
CG range14.8–18.6 in
Front chair occupant180 lb
Rear chair occupant200 lb

To determine the invited weight and CG, follow these steps.

List the empty weight of the glider and also the weight of the occupants.Enter the moment for each item listed. Remember, load × eight = moment. To simplify calculations, the moments might be divided by 100.Total the weight and also moments.To recognize the CG, divide the moment by the weight.

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NOTE: The weight and balance documents for a certain glider carry out the empty weight and moment, and also the info on the arm distance.

Figure 5-20. Weight and also balance: front and also rear seat pilot weights and moments.

In figure 5-20, the weight of each pilot has actually been entered into the correct block in the table. Because that the front chair pilot, multiplying 180 pounds by +30 inches returns a moment of +5,400 inch·pounds. Because that the behind seat pilot, multiply 200 pounds by –5 inches yields a moment of –1,000 inch·pounds. The following step is to uncover the sum of all weights (980 pounds) and record it. Then, find the amount of all moments (+16,400 inch·pounds) and also record it. Now, discover the arm (the CG position) the the loaded glider. Division the complete moment by the full weight to discover the CG of the invited aircraft glider in inches native the datum:

+16,400 inch·pounds ÷ 980 pounds = +16.73 inches

The final step is to determine whether total weight and also CG place values are within agree limits. The GFM/ POH lists the maximum gross weight together 1,100 pounds. The operation weight the 980 pounds is much less than the 1,100 pounds maximum gun weight. The GFM/POH perform the authorized CG variety as between +14.80 inches and +18.60 inches from the datum. The operating CG is +16.73 inches native the datum and also is within these limits. The weight and also balance are within operation limits.

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