L-1011 Weight and Balance: Take-Off Trim

The Horizontal Stabilizer takeoff trim settings as shown are good for all flap takeoff settings. It might be noted the range is from about 1.8 units to about 5.3 units depending on the percent of MAC normally in the are of 3 to 4 units.

To use the graph simply enter the graph at percent ofMAC, move up to slope line, and across to the left to get the trim setting.

This trim setting will also be shown on load sheet and can be checked with digital chart in GRN. This will be discussed more in performance. 

L-1011 Weight and Balance: Center of Gravity

L-1011 Center of Gravity

Looking at the operating envelope we can identify the limiting factors. Across the top we indicate the percent of the Mean Aerodynamic Cord. Across the bottom we indicate the index units. The chart also gives the in-flight and taxi forward and aft limits as well as the zero fuel weight forward and aft limits. 

L-1011 Weight and Balance: Maximum Useful Load

Maximum Payload (Weight Limited)

This is the difference between the maximum design zero fuel weight (MZFW) and operational empty weight (OEW). Payload consist of passengers, baggage and/or cargo.

Maximum Useful Load (Weight Limited)

This is the difference between the maximum design takeoff weight (MTOW) and operational empty weight (OEW). Useful loads consist of payload and usable fuel. 

L-1011 Weight and Balance: Weight Limitations

Maximum Design Taxi Weight (MTW) 225,900 KG 498,000 LBS

This is the maximum weight for ground maneuvers as limited by aircraft strength and airworthiness requirements. The weight of taxi and engine run-up fuel is included.

Maximum Design Takeoff Weight (MTOW) 225,000 KG 496,000 LBS

This weight must not be exceeded at the start of takeoff run. Any weight in excess of MTOW must be consumed during taxi and/or ground maneuvers.

Maximum Design Landing Weight (MLW) 116,900 KG 368,000 LBS

The maximum weight at which the aircraft may land without exceeding its structural limitations. Prior to landing, any weight in excess of MLW must be in the expendable fuel.

Maximum Design Zero Fuel Weight (MZFW) 153,300 KG 388,00 LBS

The maximum weight of the aircraft before expandable fuel is added. It is also the maximum sum of operational empty weight and payload.

L-1011 Weight and Balance: Arm Calculation

To facilitate calculation in the development of loading system the moment is reduced to a more workable magnitude by the following index equation:

Weight x (Arm - 1216.4)
--------------------------------
10,000 lb. in. or kg. in.

What we have done in this case is to change our frame of reference from the leading edge Mean Aerodynamic Cord (MAC) to the quarter cord, 25% of the Mean Aerodynamic Cord. All movement forward of the quarter cord will be negative numbers; all movement aft of the quarter cord will be positive numbers. The reason for using the quarter cord is that it is the approximate center of pressure on the wing. The aircraft will normally be operated at the center of gravity very close to the quarter cord.

Additionally, it is by convention, that is most if not all manuals are manufactured and indexed so that they refer to the quarter cord. By using the index system we simply add and subtract Index units, taking the and resolute and ensuring that it is within the operating envelope of the aircraft.

L-1011 Weight and Balance: Overview

Looking at the Lockheed L-1011 plan form view, we can see that the leading edge Mean Aerodynamic Cord is at the fuselage station 1143.0. The length of the cord, that is from the leading edge MAC tot he trailing MAC, is 293.5 inches long. For convenience of operation, then, we convert fuselage stations into percent of the Mean Aerodynamic Cord, 1,430, dividing that by the length of the Mean Aerodynamic Cord, 293.5. To convert the end result to a percent we will move the decimal point two places the left, and divide by 2,935. This will yield a percent of the Mean Aerodynamic Cord. If we wish to go the other way, that is find the arm; we would simply take the percent of the Mean Aerodynamic Cord and multiply it times 2,935 of the Leading Edge Mean Aerodynamic Cord of 1,143.0 and would have the original arm.

All this, of course, will lead to us being able to compute the center of gravity of the aircraft for any given arm.

Design Study: L-1011 Flight Simulator

(C) Terry Jones

Got this image from Terry Jones (retired Delta) showing the Lockheed L-1011 flight simulator at Delta Airlines as it existed until a few years ago. The unit is no longer installed with Delta and Terry is trying to identify what happened to it after it was de-installed. The image nicely shows the hydraulic system for the motion platform as well as the analog projection system.

Great image .. thank you Terry!

L-1011 Weight and Balance: Mean Aerodynamic Cord

The Mean Aerodynamic Cord (MAC) by definition is the cord of an imaginary air foil which throughout the flight range has the same force vectors as the three dimensional wing. In the example above, we have a rectangular wing with a cord root of 100 inches and a tip root of 50 inches. In order to graphically locate the MAC, we simply add 50 inches to the lower half of the cord root and 100 inches to the upper half of the cord tip. The line connecting the two extremes will intersect a line drawn from the center of the root to the center of the tip. The point of intersection then represents the Mean Aerodynamic Cord, at the trailing edge we have the trailing edge MAC. At the leading edge we have the Leading Edge MAC. Note that the MAC is not the average cord, but is the cord to the centroid of area. Centroid is the center of mass. 

L-1011 Weight and Balance: Aircraft Dimensions

Thinking in terms of weight and balance, note the the main landing gear is some 1280 inches back from the forward portion of the aircraft. The leading Edge Mean Aerodynamic cord (LEMAC) is 1143 inches aft of the datum. The lateral balance is measured in inches and is referred to as buttline. There is a right buttline and a left buttline. Note that the landing gear is some 432 inches from center to center. The wingtips are 1864 inches from tip to tip. This is certainly a consideration in terms of lateral balance when dealing with fuel management and ground handling. 

L-1011 Weight and Balance: Overview

Over the next few blog posts we will take a look at the weight and balance limitations of the L-1011 and how to compute them. This is actually quite an interesting exercise in flight simulation since it also validates the physics model of the flight simulator. Load and Balance data is importation so that the flight crew and other personnel operate the aircraft within its operation envelope.

There are a few basic concepts that are used when calculating weight and balance of the Lockheed L-1011. To start with we will have a look at the profile of the aircraft (see above). Everyone is familiar with the basic size of the L-1011, but perhaps not how that can relate to weight and balance.

You might note form the diagram above that Station 0 is some 183 inches forward of the nose of the aircraft. This is designed that way so that if additional structure is added to the nose, the radome is changed or other things we will not end up with a negative number.

Additionally, you'll notice that the main floorboard of the aircraft is water line 200. The pavement on with the aircraft sits is water line 19. That means that water line 0 is some 19 inches below the surface of the earth! :) Again, this is done to avoid negative numbers. Working form forward to aft you might note that the landing gear is sitting at Station 540 when extended, and will retract to about Station 440 ... some 100 inches! This will have to be accounted for in the operational loading limits.

You might also note the relative position of the cargo compartments to the landing gear and wing arrangement.  In terms of weight and balance we can see how easy it is to have rather large moment changes on the L-1011. The overall length of the aircraft is some 164 feet, 2 inches which amount to 1970 inches !

L-1011 Engine: Reverser System

The reverser system if for ground use only and is used to slow the aircraft. The revers are operated by a separate set of levers forward of the thrust levers:

1. Forward thrust levers at idle 
2. Lift reverse thrust lever to reverse idle detent
3. Autothrottle clutch and cable system moved in direction for reverse thrust operation

There are a number of switches that are actuated by the reverser: The switch module actuals switches to:

1. Select flight idle RPM
2. Energize dual selector valve reverse thrust solenoid 
3. Power control mechanism actuates mechanical input to dual selector valve 
4. Translating cowl moves to deployed postion
5. Further movement of reverse thrust lever increases rpm through cables and tele flex cable

When the thrust levers are stowed the following actions happen:

1. Grund idle circuit energized
2. Dual selector valve solenoid de-energized 
3. Mechanical input returned to forward thrust selection 
4. Translating cowl moves to stowed postion 
5. Increased forward thrust is again available

L-1011 Engine: Ignition Schematic

The L-1011 has a dual ignition system used on each engine. The features of the system are:

• Two igniters per engine 
• Two ignition units
• Systems identified as A and B

Each unit is capable of high and low energy output.

• High energy used for engine start 
• Low energy used for continuous ignition requirements 

The every modes are selectable and are:

• Armed by the ENGINE START panel switches 
• Initiated by FUEL AND IGNITION switch on the center console 
• Automatically terminated by switches in the N3 tachometer
• Start and continuous ignition cannot be energized simultaneously  

Avionics Bending: S.F.E.N.A. ADIs - Working

A few months ago I shipped a set of SFENA ADI's to an extremely talented student at the Universidad de Las Palmas de Gran Canaria (ULPGC). The Spanish Wizard, as I would like to title him now, Javier Pérez and his team got the SFENA ADIs to work by creating a very neat integration of the ARINC 429 protocol with X-Plane. Javier sent me the short youtube video link below. Amazing work! The ADIs will stay on loan with Javier for more time until he can do more work with them and also aid them in his research work. Once the ADIs return to Atlanta, they will become part of the L-1011 simulator exhibit at the National Museum of Commercial Aviation. 

L-1011 Engine: Engine Fuel System

Low Pressure Pump

Receives fuel from aircraft system and ensures satisfactory pressure to the high pressure pump. Has a scroll type impeller working on an induction and centrifugal principle.

L.P. Fuel cooled Oil Cooler 

Engine oil system uses low pressure fuel as an oil cooling medium Conversely maintains fuel temperature above 0ºC for fuel heating.

High Pressure Pump

Delivers the required fuel flow to the combustion chamber as scheduled by the fuel regulator. A gear type pump.

Fuel Regulator 

Controls the high pressure pump output according to signals received from the pressure ratio control and HP shaft speed. A mechanical unit driven but he external gearbox.

Pressure Ratio Control 

Tells the fuel regulator the fuel flow required to achieve the P4/P1 pressure ratio selected by the pilot's throttle lever. It is part of the fuel regulator.

Control Signal Amplifier

This unit signals the high pressure fuel pump when N1 & N2 or TGT reach predetermined maximums. The HP fuel pump then controls fuel flow to prevent here maximums from being exceeded.

Starting Fuel Regulator 

Ensures a suitable fuel flow for light up and acceleration under all conditions.

Manual Enrichment Solenoid 

Provides extra fuel during the start cycle. Selected by the pilot through the Start/Fuel/Ignition switch.

H.P. Shutoff Valve 

Controls the fuel flow to the fuel spray nozzles when starting and stopping the engine. Electrically actuated valve.

Fuel Flowmeter

Provides signal of engine fuel flow and fuel used to the flight deck instruments. 

L-1011 CPT Retrofit Project Kick-Off

The first collaboration project with the National Museum of Commercial Aviation will be the restoration and retrofit of a Lockheed L-1011 Cockpit Procedures Trainer. The equipment was given to the museum by Delta Airlines here in Atlanta. While the CPT was still working during de-installation, the original computer hardware is very old and very hard to maintain. Therefore, the idea will be to de-construct the original CPT hardware and re-build it using the x-plane software and National Instruments (NI) hardware stack. I will document the project efforts on the L-1011 CPT here with this blog as well as in the museum blog. Below is the proposed timeline that would make the L-1011 CPT ready for display by summer of 2013 which is an ambitious, but realistic timeline:

The procedures trainer uses flight simulator specific instrumentation and does not have instrumentation in place for every system. Instrumentation that does not exist will be augmented with real flight hardware flown on a L-1011-1. Also, as typical for CPTs the instrument plates are not Type IV light plates. However, to make the CPT a more interesting exhibit item we will replace the simulated plates with light plates flown on an actual L-1011-500. 

L-1011 Engine: Airflow Control

The engine fuel system is completely self-contained and delivers fuel at the proper pressure and flow to satisfy engine pressure ratios selected by the throttles. It then maintains the set power irrespective of ambient temperate up to a specific ISA limit during takeoff, climb and cruise. Above these temperatures it may be necessary to restrict engine power to prevent exceeding RPM or TGT limits. 

L-1011 Engine: Vibration Indication

To measure the RB.211 engine vibration several sensors are used to feed the indicator systems on the L-1011.

Vibration Pickups

• Two pickups utilized
• Both pickups located on top of IP compressor case
• The pickups are identified as A and B
• The pickups provide signals for the signal conditioner unit

Signal Conditioner

• Contains rectifiers and filters for processing signals from pickups. 
• Contains level detector which operates warning light on respective engine indicator
• Provides three frequency bands that correspond to vibration frequencies of the N1, N2 and N3 stages.

Project Collaboration: National Museum of Commercial Aviation

Great meeting with the people from the National Museum of Commercial Aviation here in Atlanta. The museum has a number of simulators and is interested in keeping them in working condition for an exhibit that will be focused on the history of commercial flight simulation. I believe that in partnership with the museum the L-1011 cockpit project will find a permanent home which will allow many people to enjoy the simulator and get engaged in the project. 

L-1011 Engine: RPM Indication System

FAA regulations quire that all three engine rotating assemblies shall have an RPM indicator in the flight station. The three indicators are:

• N1 - LP (fan) shaft speed
• N2 - IP compressor shaft speed 
• N3 - HP compressor shaft speed

N1 and N2 shaft speed signals are generated by phonic wheel and magnetic probe systems. The N3 shaft speed is measured by a conventional tachometer generator.

Two identical probes are located inside the front bearing housing in line with each phonic wheel. One probe is connected to the indicator circuits; the second may be utilized if the first fails. 

L-1011 Engine: TGT Indicating System

The Turbine Gas Temperature (TGT) indicating system is a rapid response type system indicating the temperature of the hot gas stream entering the first stage of the LP turbine. All thermocouples are wired in parallel to provide an average temperature indication. TGT signals are connected to the respective indicator located int he flight station and to the engine fuel control amplifier for an over temperature signal.

L-1011 Engine: EPR Indicating System

The Engine Pressure Ratio (EPR) system provides an indication of the inlet to exhaust pressure ratio and is used as the primary thrust setting indicator. The Turbine Gas Temperature (TGT) indicating system displays the temperature of the exhaust gases entering the LP 1 nozzle guide vanes. Three %RPM indicating systems are provided one for each engine rotating spool.

L-1011 Engine: Flight Engineer Engine Instruments

The flight engineer station of the L-1011 features the remaining engine instruments. The Engine indicators  located on the Flight Engineer's panel are:

• N2 RPM Indicators
• Engine Vibration 
• Engine Oil System Instruments (Oil Quantity, Oil Temperature and Oil Pressure)

L-1011 Engine: Engine Indicators - Center Panel

The Pilot's Engine Indicators are located on the Center Instrument Panel forward of the throttle levers and quadrant. These instruments are:

• EPR indicators 
• N1 indicators
• TGT indicators
• N3 indicators 

L-1011 Engine: RB.211 Airflow Controls

The air flow control system of the RB.211 engine improves the surge margin at low power acceleration and deceleration.

Variable Inlet Guide Vanes for the first stage of IP vary from -7.5º to 33.5º full close at idle. They open with increasing power.

Two IP and two HP stages. One IP and both HP valves are controlled by the VIGV control unit. The other IP has a separate control unit which closes the valve at a slightly higher pressure ratio than the first three.

When the engine is off the valves are in the following stage:

• VIGV's are Closed
• Bleed Valves are Open

When the engine is running at specific EPRs:

• EPR 1.12 both HP Valves are RH IP Closed
• EPR 1.23 LH IP closed 
• EPR 1.6 VIVG's full open