STANDARD FUEL LOADING Total Outboard Center Total Outboard Center Fuel Tanks Tank Fuel Tanks Tank Load 163 2 Load 163 2 29,550 9,850 9,850 40,000 11,600 16,800 30,000 10,000 10,000 40,500 17,300 30,600 10,200 10,200 41,000 17,800 31,050 10,350 10,350 41,500 18,300 31,500 10,500 10,500 42,000 18,800 32,100 10,700 10,700 42,500 19,300 32,550 10,850 10,850 43,000 19,800 33,000 11,000 11,000 43,500 20,300 33,600 11,200 11,200 44,000 20,800 34,050 11,350 11,350 44,500 21,300 34,500 11,500 11,500 45,000 21,800 35,000 11,600 11,800 45,500 22,300 35,500 12,300 46,000 22,800 36,000 .. 12,800 46,500 .. 23,300 36,500 13,300 47,000 23,800 37,000 13,800 47,500 24,300 37,500 14,300 48,000 .. 24,800 38,000 14,800 48,500 25,300 38,500 15,300 49,000 25,800 39,000 15,800 49,700 11,600 26,500 39,500 16,300 50,000 11,750 26,500 50,526 12,013 26,500 FIGURE 61. Fuel load distribution table.
job in determining in-flight c.g. travel if standard burn-out procedures are followed.
When the aircraft is loaded ready for takeoff, the total weight of the aircraft is called taxi gross weight or ramp gross weight. Because of high fuel consumption during ground operation, this weight may be 500 to 1,000 pounds more than takeoff weight.
Maximum takeoff weight is the maximum allowable just before brake release. This weight may be limited to a lesser weight for any particular takeoff by many factors related to aircraft performance.
The actual takeoff weight limit is calculated by the use of various performance charts, taking into account such factors as: Runway length, temperature, density altitude, runway slope, and wind conditions.
Maximum landing weight is a structural limit and is the maximum weight authorized at touchdown.
All weight in excess of maximum landing weight must consist of disposable fuel. A fuel dumping system is required on the aircraft if the maximum takeoff weight is more than 105 percent of maximum landing weight.
Conditions may arise during flight, such as engine failure or an aircraft system failure, which may require a landing sooner than originally planned In this event, fuel may have to be dumped to reduce weight to maximum landing weight. If the fuel dumping procedures contained in the aircraft flight manual are followed, c.g. travel will remain within prescribed limits. Calculations of the effects of fuel dumping are similar to those used for fuel burn.
Use of the fuel-load table moments makes the calculations simple. Some manuals will provide a fueltank centroid as a single arm, then the effect of fuel dumping can be calculated by a single remove weight formula such as the one which follows:
EXAMPLE:
STAB TRIM ENTER AT 25% MAC, PROCEED TO DIAGONAL LINE, READ RIGHT OR LEFT, 2 UNITS NOSE UP AIRPLANE NOSE DOWN -1- AIRPLANE NOSE DOWN LIMIT -1-1
PILOT'S TRIM SETTING UNITS - AFT
- MID 4 & FWD.
.......
• 10
AIRPLANE NOSE UP LIMIT'
AIRPLANE
NOSE UP 15 20 25 30
CENTER OF GRAVITY - PERCENT MAC FICURE 62. Stabilizer trim.
Weight before dumping. 160,000 lb. at Ve) ; or on the other hand, the nose may pitch
c.g. before dumping -Sta. 615.5 up uncontrollably depending on which direction the Fuel to dump 40,000 lb. stabilizer is out of trim. Once the aircraft is air- Centroid of fuel tanks -Sta. 750.2 borne, the trim is adjusted by the pilot to a setting Find c.g. after dumping. which will enable him to fly with minimum control Use remove weight formula: pressure. The only acceptable procedure for takeoff Wt. removed New total wt. - Dist. from c.g. to tank Ac.g.
120,000 - 484,7 Ac.g. = 44.9
c.g. after dumping = 615.5-44.9=570.6 in.
STABILIZER TRIM SETTING Before starting a takeoff in a large turbojet aircraft, the stabilizer trim must be placed in a position dictated by the c.g. location. An improperly set stabilizer trim may have such a powerful effect that it cannot be overcome by elevator control. During takeof, it may be difficult to raise the nose (rotate is to set the trim according to c.g. location before the takeoff roll is started.
Some of the c.g. control systems previously explained (see Convair 880M loading. summary, fig.
53) provide a stabilizer setting directly when the total weight c.g. is calculated. Other systems require the use of a simple chart to couvert from c.g. in % MAC to stabilizer setting for a particular takeoff weight. A typical chart from an aircraft flight manual is illustrated in figure 62.
• When the c.g. is determined to be located at a particular station, that location must first be converted to % MAC to use the stabilizer trim chart.
A typical problem follows:
Given: 2. Cargo:
Takeoff c.g.-Sta. 575.0 Fwd. ... Aft ... .. 3,000 .. 900........***** MAC -Sta. 540.0 to Sta. 745.0 3. Passengers:
Stabilizer trim chart (fig. 62) Fwd. 20 ..
Find: Stabilizer trim setting for takeoff Aft 40 (Winter wt. = 165 + Solution: 5 lb. carry-on baggage)
1. Determine c.g. in % MAC: 4. Fuel load:
c.g. % MAC= C.g. -LEMAC Tank 1 .20,000.
Tank 2 . ..20,000.
MAC = 575.0-540.0 5. Average fuel consumption to point of first intended Tank 3 .20,000
205.0 landing-3,600 lb./hr./engine. Three-engine op- = 205 35 = 17.1% MAC fuel management for entire flight. eration for 2:30 hours. Straight tank to engine
2. Determine stabilizer setting to nearest ½ 6. Limitations: a. Max. ramp wt.-165,000 lh.
unit: b. Max. zero fuel wt.-110,000 lb.
Enter chart at bottom on 17.1 % line. c. Max. landing wt.-135,000 lb.
Proceed upward to diagonal line. Read stabilizer setting = 5 nose up. d. c.g. limits-15% to 35% MAC e. MAC-Sta. 750.0 to Sta. 955.0 Find:
Ramp and landing weights and c.g LARGE AIRCRAFT LOADING PROBLEM Investigate if limitations are exceeded.
Stabilizer trim setting.
Given: An air carrier aircraft has the following load condition: Solution:
Weight Index moment/ 1,000 Use loading tables-figure 60.
1. Basic operating weight .85,000 65720.0 Use stabilizer trim setting chart-figure 62.
Complete the loading form below:
Takeoff conditions check Load item Weight Index Basic operating weight Payload:
Cargo:
Fwd.
Aft Passengers Fwd.
Aft Sub total (zero fuel weight) Fuel load:
1 Main 2 Main 3 Main Total (ramp and takeoff wt.)
Ramp c.g.-% MAC Stabilizer trim setting Landing conditions check Load item Weight Index Zero fuel weight Remaining fuel load:
1 Main 2 Main 3 Main Total (landing wt.)
Landing c.g. % MAC Notice that the fuel arms (fig. 60) vary with weight because the aircraft used in the problem is a swept-wing type. The correct procedure is to add a new fuel index to the ZFW index. Subtraction of index units for fuel burned will not properly account for the change in arm.
Using the principles explained in the preceding chapters, you should be able to solve the sample problem. As a spot check, here are several answers:
1. No limits are exceeded.
2. Stabilizer trim for takeoff is one-half nose up.
3. C.G. at landing weight is 22.2% MAC.
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