Weight and Balance Data

This information is one of the most important pieces of aircraft data you enter because Center of Gravity affects flight characteristics. Fill in this information carefully. Weight and Balance data is used in fuel consumption, flight time, and other calculations for flight planning and reporting. The more accurately you enter information, the more accurately JIFP can reflect your aircraft flight performance.

NOTE If you want to edit the weight and balance information for a trip, see Trip Weight and Balance.

Viewing the Weight & Balance Data

If you are editing an existing aircraft model, access Weight and Balance by performing the following actions:

  1. Select an aircraft model:

  1. Select the Weight and Balance tab in the Edit Aircraft Model or the Edit Default Aircraft Model dialog box.

The Weight & Balance window contains two sections. The right side of the window displays the Center of Gravity (CG) Envelope. The CG stations are listed in the left half of the window.

Center of Gravity Limits Envelope

The CG envelope is drawn using the information in your Pilot's Operating Handbook (POH). The horizontal axis shows aircraft CG arm limits in inches aft of datum. The vertical axis displays the loaded aircraft weight (gross weight limits). If you are entering a new aircraft, no envelope displays here.

Center of Gravity vs. Moment

JIFP uses center of gravity, not moment, information. Ensure that you are using the correct data to create your envelope. Depicting aircraft loading in CG terms give you a more intuitive picture of how the aircraft is loaded. In the days before JIFP, the only reason a pilot really needed moment was to calculate the loaded center of gravity.

Moment Envelope Center of Gravity Envelope

Converting Moment Data to Center of Gravity

Check your POH carefully to see if the manufacturer used Moment or CGs for weight and balance information. Some aircraft manufacturers try to save you the trouble of calculating CG by directly providing moments in their tables and charts. You might have to look hard to find the CGs, or you might have to calculate them yourself from the moments. If your POH gives weight and balance information in moments, you must convert it to CGs before entering it into JIFP.

Also, watch out for moment indexes, when aircraft manufacturers try to simplify the large numbers by dividing the moments by 100 or by 1,000. Add back whatever zeros were removed from those numbers before you do the following calculations.

Below is a sample loading problem from a Cessna manual:

Item

Weight

Moment

You Compute CG
(Moment ¸ Weight)

Empty Weight

1467 lbs.

57,300 LB-inches

39.0 inches

Fuel

240 lbs.

11,500 LB-inches

47.9 inches

Pilot/Passenger

340 lbs.

12,600 LB-inches

37.0 inches

Rear Passengers

340 lbs.

24,800 LB-inches

72.9 inches

Baggage Area

20 lbs.

900 LB-inches

95.0 inches

The POH from Cessna gives you Moment, but you need Center of Gravity. Divide each Moment by the corresponding weight to get CG. You can use the worksheet below to help you compute your CG's.

Working with Loading Graphs

If you have this information only in a loading graph, read the moments and weights from the graph before doing your calculations. Each of the points on the envelope must be converted from Moment to CG. Write down the weight and moment at each breakpoint in the envelope, and then divide moment by weight to get CG.

Worksheet for Converting Moments to CGs

Use the worksheet below to figure the centers of gravity for each loading station in your aircraft and each point defining your limits envelope.

Item

Weight

Moment

You Compute CG
(Moment ¸ Weight)

Empty Weight

Lbs.

LB-inches

Inches

Fuel

Lbs.

LB-inches

Inches

Pilot/Passenger

Lbs.

LB-inches

Inches

Center Passengers

Lbs.

LB-inches

Inches

Rear Passengers

Lbs.

LB-inches

Inches

Baggage Area 1

Lbs.

LB-inches

Inches

Baggage Area 2

Lbs.

LB-inches

Inches

Other

Lbs.

LB-inches

Inches

Other

Lbs.

LB-inches

Inches

Other

Lbs.

LB-inches

Inches

Envelope Point 1

Lbs.

LB-inches

Inches

Envelope Point 2

Lbs.

LB-inches

Inches

Envelope Point 3

Lbs.

LB-inches

Inches

Envelope Point 4

Lbs.

LB-inches

Inches

Envelope Point 5

Lbs.

LB-inches

Inches

Envelope Point 6

Lbs.

LB-inches

Inches

Envelope Point 7

Lbs.

LB-inches

Inches

Envelope Point 8

Lbs.

LB-inches

Inches

Entering a New Envelope

You should enter a new envelope whether putting in a new aircraft or changing an existing aircraft. Since weight and balance specs change from year to year, even the envelope for an aircraft similar to yours might not be accurate.

Clearing the Existing Data

To clear the existing data:

  1. Click Delete All to clear the existing envelope. If you are entering a new aircraft, no envelope exists to clear, and the Delete All button is unavailable.

  2. Main Envelope should be selected.

Setting the Envelope Range

The numbers in the fields around the envelope define the scale for the envelope graph. The ranges entered into JIFP need to be slightly larger than the limits indicated in your POH. A good guideline for the Gross Weight Limits in the vertical axis should be 100 lbs. above and below the CG envelope. Allow two inches on either side of the envelope for the CG arm limits (in inches from the datum) used in the horizontal axis. If you do not like the way the envelope looks in the graph after you draw it, you can rescale it by typing different numbers in the scale fields.

  1. Click in the field in the upper left corner of the graph. Enter the upper Gross Weight Limit for vertical axis. Press the TAB key.

  2. Enter the lower Gross Weight Limit. Press TAB.

  3. Enter the lower CG limit in inches from the datum for the horizontal axis. Press the TAB key.

  4. Enter the upper CG limit. Press the TAB key.

NOTE Ensure that you press TAB after typing numbers in fields. This action tells JIFP to recalculate the items affected by the new number.

Entering the CG Envelope

This method uses your mouse to draw the CG envelope. If you prefer to type in the values for the points or need more precision than is supported by drawing the envelope with your mouse, see Editing the Envelope below.

  1. Move the mouse pointer into the graph. Notice the numbers at the bottom and to the left of the box. These numbers indicate the position of the mouse pointer (77 inches and 2,000 pounds in the example below).

  2. Move to the point matching the lower left corner of your CG Envelope and click .

  3. Move to the point where the edge of the envelope first changes direction. Click again, and JIFP draws the first side of the envelope.

  4. Move around the envelope, stopping and clicking at each corner, and ending at the point where you began in the lower left corner. If you make a mistake, click Delete Last to erase the last segment. To start over, click Delete All.

Editing the Envelope

You can create or modify the envelope by typing in the numbers. This action lets you define the envelope with greater precision than is possible by drawing it with the mouse

Click Edit Envelope. This action opens the Edit CG Envelope dialog box.

The first point on your list is the lower left corner point of your envelope. Points are listed in order as you move clockwise around the edge of the envelope. Envelope points must be added in order. The graph is empty if you are creating a new envelope.

TIP To make a closed shape, ensure that your last point is the same as your first point.

Deleting an Envelope Point

To delete an envelope point:

  1. Click the point that you want to delete in the Edit CG Envelope dialog box.

  2. Click Delete to remove it from your list.

  3. Click OK.

  4. Click OK again to accept your change and close the Weight & Balance screen, or Cancel to close the screen without saving changes.

Adding or Modifying an Envelope Point

To add or modify an envelope point:

  1. To open the Edit CG Point dialog box, click Add or click on a point you want to change, and choose Modify.

  2. Enter or modify the Weight and the Arm. Ensure that you use CG data, not moment data).

  3. Click OK when you have finished adding or modifying points.

CG Stations

When the CG envelope is complete, you can begin to add or modify the list of CG stations on the right side of the Weight & Balance window. In the example below, the CG stations have already been filled in. The window might look this way if you are modifying an existing aircraft. The buttons at the bottom add new stations, and modify or delete existing stations. If this aircraft were being entered from scratch, no stations would be in this window; the Add button would be the only available choice.

JIFP sorts the stations in order of Center of Gravity with the empty stations appearing first.

Adding or Modifying a CG Station

To add or modify a CG station:

  1. Click Add to add a station or click a station, and then click Modify to change data for that station. The Edit Moment Item dialog appears (for Variable or Fixed Arm). You can also double-click any station on the list to modify it.

  1. Enter the Description.

  2. Type in the Default Weight.

  3. Select the Minimum Weight and Maximum Weight check boxes, and type in the limits if you want JIFP to impose minimum and maximum weights for this station when you enter your Preflight > Weight & Balance.

  4. Type in the Arm in inches for the station. Ensure that you use CG data, not moment data.

  5. Select the item type (Fixed Weight, Pilot/Crew, Passenger, Baggage/Cargo, Fuel, or Other). Fixed Weight items cannot be changed in Preflight > Weight & Balance. Fuel items are figured in the weight of the starting fuel when planning the trip. You can choose any of the other types for any other items.

  6. When you are satisfied with the data for this CG station, click OK.

Repeat these steps, adding or editing other stations, until the Weight and Balance setup is complete. You must use the Empty Weight and Center of Gravity from the aircraft's most current weight and balance form.

Troubleshooting Weight & Balance Data

If your weight and balance calculations appear questionable, the first thing to check is the Center of Gravity envelope. Verify that you did not use Moment information where CG information belongs. You can also view your weight and balance data by opening the Preflight Menu and selecting Weight and Balance. See Preflight > Weight & Balance for more information.

When you have entered weight and balance information, save your edited fields, or click Cancel to revert to the original data. If you are creating an aircraft model from scratch, click Next to continue to ICAO Flight Plan Information.