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Mission Statement 

The purpose of FLAPS-2-APPROACH is two-fold:  To document the construction of a Boeing 737 flight simulator, and to act as a platform to share aviation-related articles pertaining to the Boeing 737; thereby, providing a source of inspiration and reference to like-minded individuals.

I am not a professional journalist.  Writing for a cross section of readers from differing cultures and languages with varying degrees of technical ability, can at times be challenging. I hope there are not too many spelling and grammatical mistakes.

 

Note:   I have NO affiliation with ANY manufacturer or reseller.  All reviews and content are 'frank and fearless' - I tell it as I see it.  Do not complain if you do not like what you read.

I use the words 'modules & panels' and 'CDU & FMC' interchangeably.  The definition of the acronym 'OEM' is Original Equipment Manufacturer (aka real aicraft part).

 

All funds are used to offset the cost of server and website hosting (Thank You...)

No advertising on this website - EVER!

 

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Journal Archive (Newest First)

Entries in OEM (22)

Friday
Apr072017

Alternate Use for OEM Rudder Pedal Circuit Breakers

The picture at left is of an OEM circuit breaker that has been removed from an OEM rudder pedal control mechanism.  The front plate of the control mechanism has several circuit breakers on the Captain and First Officer-side of the flight deck.

LEFT:  OEM circuit breaker switch.  The two connectors on the rear of the switch are very easy to connect to an interface card for push/pull functionality (click to enlarge).

Although connection of the circuit breakers, to the original functionality that was assigned to the switch in the aircraft, is not necessary (unless wanted), there is no reason why the circuit breakers cannot be used for additional functionality outside of the simulator environment.   Many enthusiasts have specially made panels that reside in the center pedestal to address such a need. 

The circuit breakers are basically an on/off push/pull switch.  Each switch can be easily wired to a standard interface card, such as a Pokeys or Leo Bodnar card, and then configured in ProSim-AR to a particular function.  If using FSUPIC, the functionality of the switch can be assigned to any on/off function.

For example, using FSUPIC (buttons) it is possible to assign each circuit breaker to a simulator function such as: pause, sim acceleration, jetway extension, etc.  The list is almost endless.

In my simulator, I have the Captain-side circuit breaker switches configured to simulator pause and simulator time acceleration.  These commands are readily accessible within the FSUPIC framework.

The circuit breaker switches are aesthetics, therefore, configuring the switches to regularly used commands is a way to minimize keyboard usage, and declutter the flight deck.

Friday
Mar242017

OEM Rudder Pedal Mechanism and Handles

The OEM rudder handle mechanisms have been sitting in storage for considerable time, and I thought it was time to add them to the simulator and replace the very poorly made and ‘cheesy’ reproductions that I was using.

LEFT:  OEM rudder handles and mechanism installed to Captain-side kickstand.  The stick shaker can be seen in the foreground (click to enlarge).

The rudder mechanism is not a small item that you can easily screw to the kickstand.  Each handle attaches to a 8-inch-long box, that houses the various circuitry, cabling and a dozen or so aircraft circuit breakers. 

Connection to the aircraft’s system is via two Canon plugs at the rear of the unit, while movement of the pedals forward or aft is facilitated by a long metal cable that connects to the rear of the handle.

The mechanism is not light-weight and weighs in at just over 1 kilogram.

The rudder handles do nothing other than add to the aesthetics of the simulator.  However, if wanted the various circuit breakers can be connected to an interface card (something I will not be doing).

LEFT:  Rudder handle mechanism (prior to cleaning).  The long metal cable that connects to the rear of the handle (enabling the forward and aft adjustment of the pedals) has been removed.  The white handle hangs loose and needs to be attached to the box using plastic fasteners (empty holes).  The black circular pull on/off circuit breakers can be seen below the white handle  (click to enlarge).

Installation to MIP

There are several methods that can be used to install the mechanism to the Main Instrument Panel (MIP).

If you are using an OEM MIP, then connection of the mechanism to the kick-stand is a matter of using the existing bolts and placement holes.  Fitment to a reproduction MIP is accomplished differently and depends upon how the MIP is constructed. 

I fabricated an aluminium cradle (saddle) that is attached by two nuts and bolts to the lower portion of the kickstand (under the kickstand out of sight).  The rudder mechanism slides into the cradle and a small screw holds the mechanism in the correct place.  A similar assembly could easily be made from wood and painted Boeing grey.

Read about an alternate use of the circuit breakers.

Wednesday
Mar082017

OEM B737 CDU Conversion - Introduction

One of the slower projects is the conversion of two B737 CDU units.  The two units were purchased from an aircraft scrap-yard in the US and were formally used in a Boeing 737 operated by United Airlines.  

LEFT:  Straight from United Airlines to me.  Two OEM CDU units.  The rear unit has already had its CRT display removed and is partially  'gutted' (click to enlarge).

The two CDUs came from an airframe of a B737-500, which in 2008 was retired along with other Boeing classics, due to United Airlines decision to adopt the Airbus A-320.

The rear of each unit has a chronometer showing the hours of use - one unit has 5130 hours while the other has 1630 hours.

The CDU presently used in the simulator is manufactured by Flight Deck Solutions (FDS) and although I have been pleased with its operation and reliability, there is little resemblance, other than appearance, to the OEM unit.

LEFT:  Detail of the keyboard and DIM knob.  Interestingly the DIM knob dims the actual screen and not the backlighting (click to enlarge).

The prominent difference is external build quality and the tactile feeling when depressing the keys on the keyboard; the keys don't wobble in their sockets, but are firm to press. 

There is also a strong audible click when a key is depressed.  Furthermore, the backlighting is evenly spread with each key evenly lit.

The OEM CDU is large and VERY heavy.  I was surprised at the weight - a good 6 kilograms.  Most of the weight is made up by the thick glass CRT display screen and other components that reside within the sturdy aluminium case.

LEFT:  The casing removed to show the electronic boards that are secured by lever clips.  Like anything OEM, the unit is made very well from solid components (click to enlarge).

Like the casing, the internal structure is also made from aluminium and has four rails to enable the electronic boards to be installed and secured into place. 

Whenever I look at anything OEM, I am amazed at the workmanship that has gone into producing the item; the CDU does not fall short in this area.

A myriad number of small screws hold together the aluminum casing that protects the internal components.  Not only screws are used, but also special miniature DZUS fasteners than enable the side of the casing to removed easily for maintenance.

Nomenclature

When discussing the CDU there are three similar terms that are often used interchangeably: CDU, FMC and FMS.  In this website, I use the terms CDU and FMC interchangeable which is not quite correct - let me explain.

LEFT:  Protective cover removed to show the main pin-out board, rear of the CRT display, power supply, and electronics.  These parts cause the CDU to be quite heavy.  The two Canon plugs  are just visible at the right of the picture enable connection to the aircraft. (click to enlarge to see detail).

The Control Display Unit (CDU) is the interface that the flight crew use to interrogate the data from the Flight Management Computer (FMC); it's basically a screen and keyboard.  The FMC in turn is but one part of a complex system called the Flight Management System (FMS).  The FMS is capable of four dimensional area navigation.  It is the FMS that contains the navigational database.

CDU vs. MCDU

The older units used in the classic airframes are always referred to as a CDU, while the NG units are called a MCDU.  M stands for multipurpose or multi-function.  Basically, the MCDU has a different key called a menu key.  This key, when pressed, accesses another layer of information that is not available in the earlier CDUs.

For those more military-minded, the CDU in military parlance is called a mission computer.

Aesthetic Differences

The CDU dates from 2008, therefore; it is not exactly identical to the CDU used in the Next Generation airframe, however, it is very close.

Main Differences - 500 series to NG

(i)    The dim knob is a slightly different shape;

(ii)   The display screen is rounded at the edges (the NG is more straight-edged);

(iii)   The absence of the horizontal white lines located on the inside edge of the display frame bezel; and,

(iv)   The display screen is different - cathode ray tube (CRT) verses liquid crystal display (LCD).

(v)   Two of the keys are different.  The NG has a menu and space key whilst the older CDUs have a DIR INTC and a blank key (no lettering on key). 

Other differences, not important in the simulator environment, are the colour of the fonts used; older units have black and white or green font while later model NG units use multi-coloured font.

To a purist, these differences are probably important, and if so, you will have to contend with a reproduction MCDU or pay an exorbitant amount for an NG unit. 

Software

The software used in the OEM CDU is not used in the simulator.  The CDU functionality is dictated by the avionics software (ProSim-AR) in use.  This is also true for the font type and colour.

LEFT:  Completely gutted.  All unnecessary and unusable electronic components have been removed.  These two CDU units will soon operate flawlessly with ProSim-AR and flight simulator (click to enlarge).

Converting the CDU

I am liaising with an Australian company that specialises in converting avionics components used in commercial flight simulators.  This company has had considerable experience converting B747 avionics and is keen to see if their expertise will similarly work with the B737.

In a second article, I will explain in more detail how the conversion was done, and examine some of the problems that needed to be resolved.  I also will discuss the mounting of the unit into the CDU bay. 

More photographs of the CDU are located in the image gallery.  Additional images will be added to the gallery in due course.

Glossary

OEM - Original Equipment Manufacture (aka reral aircraft part).

Friday
Aug262016

Assembly of Forward Overhead Panel

Construction of the simulator began in 2011.  It is now 2016 and I am perplexed to why the build has taken so long to complete.   Of course, opting to try and use OEM (Original Equipment Manufacture) parts whenever possible has added significant time to the project -  especially the procurement of parts.

LEFT:  Forward overhead using OEM parts (click to enlarge).

Most of the parts that make up the forward overhead have now been obtained and assembly of the components is well advanced.   Very soon the wiring from the panels to the Phidgets cards will begin.  This will be followed by several hours of testing to check correct functionality and to ensure perfect harmony between components and systems. 

A basic frame has been constructed to enable the overhead to be easily positioned to enable the wiring to be done with a little more ease.  After the forward overhead is completed, work on the aft overhead will commence.  Rome, it seems, was not built in a day.

Certainly, completion of the forward overhead will be the major project over the next few months.

Wednesday
Jul012015

Throttle Quadrant Rebuild - Parking Brake Mechanism Replacement, Improvement, and Operation

In the previous system, the parking brake lever was controlled by a relay and a 12 volt solenoid.  The mechanical system worked well, however, there were some minor differences between the simulated system and that of the system used in the real Boeing aircraft.

LEFT:  Parking brake lever in the UP engaged position.  The red incandescent bulb is 28 volts, however, a 12 volt bulb can be used.

There has been minimal change to the mechanical system, with the exception that, the solenoid has been replaced by a 12 volt actuator, and to engage the parking brake lever to the UP position the toe brakes must be depressed. 

Navigate to this published post that has explained the earlier conversion of the parking brake: B737 Parking Brake Mechanism.

What is an Actuator

An actuator is a type of motor that is responsible for moving or controlling a mechanism or system.  It is operated by a source of energy, typically electric current, hydraulic fluid pressure, or pneumatic pressure, and converts that energy into motion.

Almost every modern automobile has a door lock actuator which is responsible for the locking and unlocking of the door locks.  This website 'How Stuff Works' provides a very good overview of how an actuator works.

The actuator is responsible for maintaining the parking brake lever in the UP position.  This occurs when the circuit is closed and 12 volt power is briefly directed to the actuator to lock the device into the engaged position. 

LEFT:   The actuator is the blue plastic coated mechanism.  The parking brake vertical control rod, micro limit switch and upper part of the high tensile spring can be to seen to the lower right (click to enlarge).

System Overview

The actuator is the mechanism that enables the parking brake lever to be locked into the UP position.  Without power, the actuator is in the resting position and the parking brake lever is pulled to the DOWN position by a high tensile spring. 

The unit, operates on 12 volt power and is mounted horizontally on the Captain-side of the quadrant. 

In addition to the actuator, a micro limit switch and relay (on/off) are also used. 

Micro Switch and Relay

The micro switch is mounted proximal to the vertical control rod, and when the parking brake is is in the DOWN position, the connectors from the micro switch are touching a flange that has been attached to the rod, however, when the parking brake lever is moved to the UP position, the connection is severed. 

The use of a micro switch facilitates a second line of containment.  What this means is that the circuit will only remain open, when both the relay is open (toe brakes depressed) and the connection from the micro switch is severed - both variables must be triggered for the mechanism to operate.  This can only occur when the toe brakes are depressed whilst simultaneously pulling the parking brake lever to the UP position.

The relay, either enables or inhibits 12 volt power to flow into the circuit, and this is dependent upon the whether the toe brakes are depressed.

The reason for this set-up will be understood shortly.

Toe Brakes

In the real aircraft, the parking brakes can only be engaged or disengaged when the Captain-side or First Officer-side toe brakes are depressed.  This has been faithfully replicated in the simulator using a mechanical system.

How It Works

The actuator will only engage when the toe brakes are depressed.  This means that the parking brake cannot be engaged (lever locked in the UP position with red annunciator on) or disengaged (lever in DOWN position with red annunciator off) unless the toe brakes are depressed. 

Two items are needed to engage the parking brake lever.  A relay to signal open or close (on/off) when the toe brakes are depressed, and the micro limit switch discussed earlier.

Depressing or releasing the toe brakes opens or closes a relay which in turn enables 12 volt power to reach the annunciator.  However, the system is only 'live' (closed system) when the parking brake lever is moved to the UP position, severing the connection between the flange on the vertical control rod and the micro limit switch, enabling power to flow unhindered through the circuit.  When the toe brakes are released, the circuit is open and the actuator remains in the engaged locked position with the parking brake lever locked in the UP position.

To release the parking brake lever, the opposite occurs.  When the toe brakes are depressed, the relay opens directing power to the actuator which disengaged the actuator lock.  The parking brake lever is then pulled to the DOWN position by the tensile spring.

Two Methods of Connection Can be Used - Full Mechanical or Part-Mechanical Software

There are two methods that can be used to connect the actuator to the parking brake mechanism.  The first is a straight physical method - the toe brakes are connected to a relay which in turn is connected to the actuator and micro switch. 

The second method is part-mechanical and software controlled and involves using the ProSim737 avionics suite.  Using a Phidgets 0/0/4 relay the USER 1 interface in the configuration menu of ProSim737 is programmed to read the movement offset for the toe brakes.  When the toe brakes are depressed, the software detects and reads the offset which in turn opens the relay enabling power to flow to the actuator.  The actuator will be engaged (circuit closed) only if the connection between the vertical control rod and the micro switch is severed (parking brake lever is in the raised position).

The power for the actuator is connected from the 12 volt busbar in the Throttle Communication Module (TCM) and then, via a straight-through cable, to the Throttle Interface Module (TIM).  The relay for the parking brake mechanism is located in the TIM.

How To Engage The Parking Brake

The method used to engage the parking brake is as follows:

(i)        Slightly depress the toe brakes.  This will open the relay and enable 12 volts to engage the actuator;

(ii)       Raise the parking brake lever to the UP position and hold it in this position; and,

(iv)      Release the toe brakes.  Releasing pressure on the toe brakes causes the actuator to lock into the engaged position.

To release the parking brake, the toe brakes are depressed.  This will cause the actuator to unlock and return to its resting position.  The high tensile spring will pull the parking brake lever to the DOWN position with a loud snapping sound.

Actuator Caution LED

The design of an actuator is such, that if power is continuously applied to the mechanism, it will burn out.  If operating correctly, the actuator will onlt receive power when the toe brakes are depressed and the parking brake lever is raised at the same time.

To combat against the unforeseen event of power being continuously supplied to the actuator, for example by a relay that is stuck in the open (on) position, a coloured LED has been incorporated into the three LEDs that are fitted to the front of the Throttle Communication Module (TCM).  This flashing LED illuminates only when the circuit is closed and the actuator is receiving 12 volt power.

Additional Information

Like many things, there are several ways to accomplish the same or a similar task.  The following posts located in the ProSim737 forum discuss the conversion of the parking brake lever.

How To Make Your Own Parking Brake Release

Parking Brake Logic

Glossary

Two terms often confused by beginners are open circuit and closed circuit.

Any circuit which is not complete is considered an open circuit.  Conversely, a circuit is considered to be a closed circuit when electricity flows from an energy source to the desired endpoint of the circuit.