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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).

 

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Journal Archive (Newest First)
Thursday
Dec132018

Using OEM Panels in the MIP

The introduction of the Boeing 737 Max has meant that many carriers are updating their fleets and retiring earlier production 737 NG airframes.  This has flow on benefits for flight simulator enthusiasts, because more and more OEM NG parts are becoming available due to NG airframes being stripped down and recycled.  

LEFT:  OEM Captain-side DU panel.  Note the thick engraving and specialist DZUS fasteners (click to enlarge).

Although some items, such as high-end avionics are priced outside the realm of the average individual, many other parts have become reasonably priced and are often a similar price to the equivalent reproduction part.

This article primarily relates to the panels used in the Main Instrument Panel (MIP), and lower kick stand.  The term panel means the aluminum plate that is secured to the framework of the MIP, and lightplate refers to the engraved plate that is secured to the panel.

Do You Notice The Difference

This is a common question.  The resounding answer is yes – the difference between OEM and reproduction parts can be noticed, especially if you compare the identical parts side by side.  This said, some high-end companies manufacturer panels that are almost indiscernible from the OEM panel.  These panels are bespoke, expensive, and usually are only made to a custom order.  Therefore, it really depends on which manufacturer/company you are comparing the OEM panel against.

By far the biggest difference between an OEM and reproduction panel, other than appearance, is the tactile feel of a knob, the overall robustness of the panel, and the firmness felt when rotating a commercial-grade switch; the later feels very accurate in its movement. 

LEFT:  Close up detail of OEM lightplate and general purpose knobs (click to enlarge)

There is litle compromise with backlighting as an OEM panel has a consistent colour temperature and intensity without hot and cold spots.  

Using a real panel helps to provide immersion and, as your're using a real aircraft part there is no second-guessing whether the panel is an accurate copy; using an OEM panel is literally 'as real as it gets'.  Furthermore, it’s  environmentally friendly to use second hand parts.  New parts (reproduction or otherwise) are made from  finite resources. 

Limitation

Not every OEM part can work in a home simulator.  For example, the OEM potentiometer responsible for the dimming function in the lower kickstand DU panels cannot be used.  This is because Boeing use a rheostat instead of a potentiometer.  Without going into detail, a rheostat is designed to take into account 115 volts AC commonly used in aircraft.  If using these panels. you will need to change the rheostat to a high-end commercial potentiometer.  

Table 1 outlines 'some' of the main differences between the OEM panels and their reproduction equivalents.

Table 1:  Main differences between OEM and reproduction panels (MIP only).

The information presented in the above table, should not be taken in a way that reflects poorly on the manufacturer of reproduction panels.  There are a few high-end companies whose panels are indiscernible from the real item; it’s the purchaser’s knowledge and the manufacturer’s skill that will define whether a reproduction panel replicates the real item.   ‘Caveat Emptor’ should always be at the forefront of any purchase decision.

Potential Problems Using OEM Panels in the MIP

Potential problems often surface when attempting to mate OEM parts to the framework of the MIP.  This is because reproduction MIPs rarely echo the identical dimensions of their OEM counterpart. 

It's not possible to document every potential problem, as all reproduction MIPs are slightly different to each other.  However, some issues encountered may be the misalignment of screw holes between the MIP framework and the OEM panel, the inability to use the panel's DZUS fasteners, the panel being too large or too small for the MIP in question, and the open framework structure at the rear of the panel (which incorporates the wiring lume and Canon plugs) interfering with the infrastructure of the reproduction MIP, or the mounting of the computer screens.

In general, OEM panels cannot be mounted to a reproduction MIP without major work being done to the framework of the MIP.   The solution is to use a MIP that has been designed 1:1 with the OEM MIP, or fabricate a MIP in-house to the correct dimensions.

Specifics to the FDS MIP

The MIP used in the simulator is manufactured by Flight Deck Solutions (FDS), and although the MIP is made to a very high quality, the dimensions of the MIP are not 1:1. 

LEFT:  OEM Stand-by instrument panel. Although difficult to see from a picture, the overall robustness of this panel surpasses all but the very best reproductions (click to enlarge).

The most problematic issue is that the MIP length is slightly too narrow to enable the OEM panels to be fit correctly to the front of the framework.  For example, the OEM chronograph panel is 1 cm wider than the FDS chronograph panel.  Furthermore, most of the OEM panels (such as the standby instrument, chronograph and landing gear panel) measure 130 mm in height as opposed to the FDS panels that measure 125 mm in height.  This causes problems when trying to line up the bottom of each panel with the bottom of the display bezels

The standby instrument panel does fit, however, there is a few centimeters of space between the panel and the adjacent display bezel frame.  In the real aircraft, the display bezel and the edge of the standby instrument panel almost abut one another.  The autobrake panel does fit as do the lower kickstand panels.

FDS use screws to attach their panels to the upper MIP framework, however, OEM panels use DZUS fasteners.  The screw holes on the FDS MIP do not align with the position of the DZUS fasteners in the OEM panel.  The lower MIP panel (kickstand) in the real aircraft also incorporates a DZUS rail to which the panels are attached.  The FDS kickstand does not use a DZUS rail, and screws or reproduction DZUS fasteners are needed to secure the OEM kickstand panels.

The above said, FDS does not state that their MIP is I:1, and when asked will will inform you that OEM panels will not fit their products without considerable fabrication.

Specialist DZUS Fasteners

The OEM panels used in the upper MIP incorporate into the panel a specialist DZUS fastener.  This fastener is used to tightly secure the panel to the framework of the MIP; screws are not used.  Screws are only used to secure the lightplate to the panel. 

LEFT:  DZUS fastener that secures DU panel to the MIP framework (click to enlarge).

The DZUS fastener is shaped differently to the fasteners used to secure the panels located in the lower kickstand, overhead and center pedestal, and these parts are not interchangeable. 

Reproductions rarely replicate these DZUS fasteners.  However, like many things it's often the small things that make a difference (at least aesthetically).

LEFT:  Rear of OEM Captain-side DU panel.   Note heavy duty rotary switches (Cole & Jaycor brand), neat and sturdy wiring lume, and easy connect Canon plug.  The use of the correct bracket in the panel enables the AFDS unit to fit snugly to the panel.  Note the depth of the external frame which can cause placement issues (click to enlarge).

Advantages Using OEM Wiring Lume and Canon Plugs

A major plus using any OEM panel is that the part usually includes an expertly-made wiring lume that terminates at Canon plug.    If possible, the original wiring lume should be kept intact and additional wiring should be done from the Canon plug.  It’s very difficult to duplicate the same level of workmanship that Boeing has done in relation to the wiring.  Furthermore, the wire that has been used is high-end aviation grade wire.

The Canon plug deserves further mention, as the use of a Canon plug (or any connector for that matter) enables you to easily remove the panel for service work should this be required.  If at all possible, the original Canon plug (and wiring) should be used because it’s neat and tidy and ensures a good connection.  However, if the correct Canon plug cannot be procured then a reproduction plug should be fabricated.  There is nothing worse than having to disconnect wires from an interface card to remove a part.

Configuring an OEM Panel

Configuring an OEM panel to use in flight simulator depends on which panel you are referring to. 

LEFT:  OEM landing gear panel. Like any OEM part, the neatness in relation to the wiring is immaculate.  A Canon plug enables the panel to be connected to a lume which then connects with whatever interface card is in use (click to enlarge).

Panels with knobs, toggles and switches are relatively straightforward to interface with a respective interface card (Phidget card, PoKeys card, FDS SYS card or similar).  Determining the pinouts on the Canon plug that control backlighting requires the use of a multimeter, and then connection to a 5 volt power supply.  If the panel includes annunciators (korrys), then these will need to be connected to a 28 volt power supply (using the correct pinouts).

Technology is rarely static, and there are other ways to interface and configure OEM panels.  The ARINC 429 protocol is becomming inceasingly common to use along with specialist interface cards, and these will be discussed in separate articles.

The Future

The FDS MIP can, with some work, be modified to mount the OEM panels.  However, an easier option is to find another MIP that has been designed to mount the panels, or fabricate a MIP in-house to OEM dimensions.

LEFT:  Rear of DU panel showing korry connections and AFDS bracket (click to enlarge).

Final Call

Aesthetically, nothing beats the use of an OEM panel, and the panels used in the upper MIP and lower kickstand offer little comparison to their reproduction equivalents, with possible exception to bespoke reproductions. By far the biggest challenge is determining the pinouts for the Canon plug, but once known, configuration using a Phidget or other traditional card is relatively straightforward. 

As straightforward as it may seem, potential problems surface when attempting to mate OEM panels to an existing reproduction MIP.  To resolve these issues, often a replacement MIP is needed that has been made to the identical dimensions of the OEM counterpart.

Additional Information

The following articles may provide further information in relation to using OEM parts.

Note that some of these articles are to be reviewed and brought up-to-date (technology and ideas are rarely static).

Acronyms

ARINC 429 - Aircraft communication protocol
DU - Display Unit
Lume - A harness that holds several wires in a neat way
OEM - Original Equipment Manufacturer
MIP - Main Instrument Panel

Thursday
Aug232018

Adding Liveries to ProSim737 Flight Model

Flight simulator enthusiasts enjoy flying the livery of their choice, whether it be a cargo carrier such as FedEX, or a livery from one of the many passenger airlines that fly the Boeing 737 airframe.  

LEFT:  The livery for the JAL TRANSOCEAN Air, which depicts a whale shark is spectacular.  Why would you not want to use liveries when some look like this.  The whale shark inhabits the waters that this particular airline fly to (southern Japan) - © DavE-JetPhotos.

Airlines have unique liveries that identify the carrier.  Often the design is specific to the country or to a particular motif unique to the airlines.  For example, QANTAS depicts a red kangaroo on its tail and Aeroflot always depicts the Russian flag on its tail wing.  Some liveries relate to airline branding, others can be nationalistic (those carrying flags on their tail wings), and others can be just for fun - such as Taiwanese airline's Eva Air 'Hello Kitty' liveryWikipedia has an interesting list of airlines that have liveries that relate floral emblems, animals, flags and the like.

Some software companies, for example PMDG, have developed livery add-ons that can be installed by a self-extractable.exe file;  it’s only a matter of clicking the .exe file and following the prompts, and the information, textures and changes are automatically installed behind the scenes by the software.  

The ProSim737 flight model (developed by ProSim-AR) does not at the time of writing provide a self-executable file for add-on liveries; users must install liveries manually.  Thankfully, the steps to install a livery are generic, and have been more or less the same since FS9 and FSX.

This article will address how to install an aircraft livery to the main aircraft folder for ProSim737 using the ProSim737-800-2018 Professional aircraft (Version 3 flight model) using Prepar3D (P3D).

Note that ProSim-AR produces two flight models – Version 2 and Version 3, and unfortunately, the liveries made for Version 2 (of which there are many) do not work with Version 3.

For those users who use the ProSim737 Version 2 flight model, the process of installing liveries is similar, however, the ProSim737 folder structure is different.

Back-up

Before proceeding with any amendment to the aircraft folder, make a backup of the ProSim737 aircraft folder BEFORE making changes.  It’s also wise to copy the default aircraft configuration file.  This can easily be done by right-clicking the file and saving as a copy.  The copy can reside in the same folder, as it will have the word ‘copy’ annotated to the file name.

It’s good policy to do this just in case a problem is experienced.   If a problem presents itself, it’s an easy matter of deleting the aircraft folder and replacing it with the original, or replacing the aircraft configuration file.

The Basics

We are interested in three components:  

(i)      The ProSim737 default aircraft folder;
(ii)     The add-on livery texture folder; and,
(iii)    The aircraft configuration file (aircraft.cfg).

Note that the default ProSim737 aircraft is installed via a self-executable file that installs the default 738 aircraft to the correct folder.

File and Folder Structure

The ProSim737 aircraft software installs the aircraft to the following folder: D://Documents/Prepar3D V4 Add Ons/ProSim-AR/Simobjects/Airplanes/ProSim737-800-2018 Professional.  

This folder falls outside the main P3D folder architecture, however, various files are automatically linked to P3D so they aircraft can be flown and seen in the game.  In my setup I have two drives, which is why the Prepar3D folder is located on D Drive rather than C Drive.  Your dirve may feature a different drive letter.

LEFT:  One interesting livery is British Airways (BA).  All BA aircraft depict the Union Jack on their tail.  In the 18th Century, England had colonies throughout the world and it was often stated that ‘the sun never set on the Union Jack’.  With the loss of her colonies the sun definitely now sets on the Union Jack, however, it probably never sets on British Airways as there is always a BA aircraft somewhere in the world.  Screen grab of ProSim737 BA livery. © Matthew Fitzjohn (click to enlarge).

Livery Texture Folder

An add-on livery is usually downloaded from the Internet in zip file format.  Once the zip file is extracted, you will see a number of folders and files.  At the very least there will be a texture folder, in which is stored the various bitmaps and images necessary to amend the default aircraft with that livery.   There may also be a thumbnail image of the livery and a ‘read_me’ file.

The ‘read_me’ file is important, as this often will contain the correct edits for the livery that need to be added to the aircraft configuration file.

Non-mipped Images

The developer of the livery may also have included additional folders such as non-mipped images.  Opening this folder will reveal an alternate texture folder.  

Textures developed from non-mipped images are displayed differently by P3D and often provide slightly better detail that standard textures.  This may be advantageous if you often zoom into the aircraft to view close-up detail.  There are many variables that affect the appearance of non-mipped textures, including graphic card settings, computer specifications, and P3D settings.  For most users, the use of non-mipped textures in not necessary.  However, ‘horses for courses’, so test and choose whatever is appropriate to your circumstances.  

If you open the ProSim737 aircraft manual (found with the original default aircraft download) there is a section that addresses the differences between mipped and non-mipped textures.

Aircraft Configuration File

The aircraft configuration file is important as it contains, amongst other things, the necessary instructions to display whatever aircraft has been selected from the P3D aircraft list.  

The configuration file is set out logically with higher-level entries (top of page) identifying the various liveries that have been included in the main ProSim737 aircraft folder.  By default, the ProSim737 flight model installs a number of liveries to the aircraft folder and automatically amends the entries in the configuration file.

BELOW: Text that relates to an aircraft livery in the aircraft configuration file.  Bolded sections need to be edited for each livery.

[fltsim.XX]
title=Prosim_AR_737_800_PRO_2018_Virgin_Australia
sim=Prosim738_Pro
model=
panel=
sound=
//sound=cockpit
texture=VIRGIN
atc_heavy=0
atc_flight_number=209
atc_airline=Velocity

atc_model=737-800
atc_parking_types=GATE,RAMP
atc_parking_codes=VOZ
ui_manufacturer="Prosim_AR"
ui_createdby="ProSim-AR"
ui_type="737-800"
ui_variation="PROSIM_AR_Pro_2018_Virgin_Australia"
ui_typerole="Commercial Airliner"
atc_id=PS209
visual_damage=0

Installing Textures to ProSim737 Aircraft

A: Copy the aircraft texture folder for the livery (from the download) and paste the folder into the ProSim737-800-2018 Professional folder located in simobjects/airplanes.

B: Open the aircraft configuration file (for editing). This file is located in the main aircraft folder.  Make sure you back-up this file or copy it BEFORE making changes.  This will enable to you to revert to the original file if a mistake is made.

C: Copy the aircraft details from the downloaded 'read_me' file and add them to the configuration file.  The correct place to add the details is below the last aircraft listed.  If the ‘read_me’ file does not have this information, then it will be necessary to add the information yourself.

By far the easiest method to do this is to copy/paste the last aircraft listing, and then re-name the segments accordingly.  In the example above, I have bolded the sections that need to be edited.

The most important edits are the texture= ?, title= ? and ui_variation= ?. These three entries directly influence whether you will see the livery in the P3D aircraft list and in the game.  It’s very important that the texture= ? be the exact name of the texture file in the aircraft folder; your livery will not be able to be seen if this is not done.  In some instances, the name of the texture folder may be an airline’s name (texture.virgin) or a three letter aircraft code such as texture.ual (United Airlines).  

D: The FLTSIM number also needs to be edited to reflect the correct sequence order in the configuration file. Make sure each aircraft has a sequential number. If you have three aircraft liveries, the files will be [fltsim.01], [fltsim.02], [fltsim.03].  Be especially vigilant to copy all brackets, equal signs and commas (syntax) as these are necessary to see your aircraft in P3D.

Problems and Troubleshooting

By far the easiest way to troubleshoot a problem, such as the aircraft not being visible in the P3D aircraft folder, is to delete the aircraft configuration file and reinstall the original backed up file.  Then redo your work ensuring there are no mistakes.  If your mistakes relate to the actual texture folders, then delete the complete folder and reinstall the original backed up folder and start again.  Most problems relate to typo errors such as forgetting to include the correct syntax (punctuation marks).

Setting Up the P3D Aircraft Folder for Ease of Use (favourites and type)

When you open P3D to select an aircraft, a graphical user interface (GUI) screen displays  the aircraft and liveries that are installed to the aircraft folder. 

LEFT:  Screen capture showing the P3D aircraft selection folder.  Note the ‘show only favourites’ star, which when selected, will cause that livery to be displayed in the list at the expense of liveries not selected by the star.  Also, note the additional identifier in the vehicle type column (737-800 CARGO) - click to enlarge. 

This list can be long and unwieldy to navigate with the mouse, not to mention time consuming - you want to be able to identify your 738 liveries quickly and not wade through several versions of the aircraft you do not use.  To prune the number of aircraft you need to sort through, you can delete the unwanted aircraft from the aircraft folder, however, an easier method is to use the favourite functionality.

Select the favourite star for those aircraft/liveries you want to be see displayed in the aircraft list.   Once an aircraft /livery has been allocated as a favourite, it will always be displayed in the list, while those aircraft not ‘starred’ will not be displayed.  

If you have both cargo and passenger aircraft (or military versions of the B737), you may also want to segregate these aircraft by type.  This makes it easier to find a particular aircraft type.   This can easily be done by editing the title= ? and the ui_type= ? for that aircraft in the aircraft configuration file.  

BELOW:  An example in which the type has been edited to reflect the aircraft is a cargo aircraft (Aloha Air Cargo).  Editing the title is obvious as this changes the name in the P3D aircraft list.  However, editing the ui_type= ? enables you to change the aircraft type.  In the example below, I have included the word CARGO to differentiate cargo liveries from passenger liveries.  I have bolded the entries that need altering.

[fltsim.XX]
title=Prosim_AR_737_800_PRO_2018_Aloha_Air_Cargo
sim=Prosim738_Pro
model=
panel=
sound=
//sound=cockpit
texture=AAH
atc_heavy=0
atc_flight_number=211
atc_airline=Aloha
atc_model=737-800
atc_parking_types=GATE,RAMP
atc_parking_codes=AF
ui_manufacturer="Prosim_AR 2018"
ui_createdby="ProSim-AR"
ui_type="737-800 CARGO"
ui_variation="PROSIM_AR_Pro_2018_Aloha_Air_Cargo"
ui_typerole="Commercial Airliner"
atc_id=PS211
visual_damage=0

Livery List

Liveries for the Version 3 flight model can be downloaded from the ProSim-AR website:  Version 3 ProSim737 Liveries and Version 3 ProSim 737 Liveries.

Final Call

Adding various liveries can be fun and adds a element of realism, especially if you fly in different regions and enjoy looking at the aircraft, or are a videographer that creates flight simulator videos.   Paring down the aircraft list in P3D to display only the aircraft and liveries you want to see, and then segregating aircraft based on type, can save considerable time and mouse use.


ABOVE:  The livery for the JAL TRANSOCEAN Air – another viewpoint.  There is also a pink coloured livery.  Japan is one of my favourite regions to fly.  © Keishi Nukina - KN Aviation
Sunday
Jul152018

String Potentiometers - Are They Worthwhile

A flight simulator enables us to fly a virtual aircraft in an endless number of differing scenarios.  The accuracy of the flight controls when the aircraft is flown manually (hand flown) comes down to how well the aircraft’s flight controls are calibrated, and what type of potentiometer is being used to enable each control surface to be calibrated.

LEFT:  Custom-made box housing Bournes string potentiometer.  Note cable, dog lead clip, and JR Servo connection wires (click to enlarge).

This article will examine the most common potentiometers used.  It will also outline the advantages in using string potentiometers instead of inexpensive linear and rotary potentiometers.

What is a Potentiometer

A potentiometer (pot for short) is a small sized electronic component (variable resister) whose resistance can be adjusted manually, either by increasing or decreasing the amount of current flowing in a circuit.

The most important part of the potentiometer is the conductive/resistance layer that is attached (printed) on what is called the phenolic strip. This layer of material, often called a track, is usually made from carbon, but can be made from ceramic, conductive plastic, wire, or a composite material.  

The phenolic strip has two metal ends that connect with the three connectors on the potentiometer.  It’s these connectors that the wires from a control device are soldered to.  The strip has a wiper-style mechanism (called a slider) that slides along the surface of the track and connects with two of the potentiometer’s connectors. 

The strip enables the potentiometer to transport current into the circuit in accordance with the resistance as set by the position of the potentiometer on the phenolic strip. 

As the potentiometer moves from one position to another, the slider moves across the carbon layer printed to the phenolic strip.  The movement alters the current (electrical signal) which is read by the calibration software.

Types of Potentiometers (linear, rotary and string)

Potentiometers are used in a number of industries including manufacturing, robotics, aerospace and medical.  Basically, a potentiometer is used whenever the movement of a part needs to be accurately calibrated. 

LEFT:  Inexpensive rotary potentiometer.  This pot used to control the ailerons.  The pot was inserted into the base of the control column and held in place by a fabricated braket (click to enlarge).

For the most part, flight simulators use adjustable type potentiometers which, broadly speaking, are either linear or rotational potentiometers.  Both do exactly the same thing, however, they are constructed differently.  Another type of rotary potentiometer is the string potentiometer.

A linear potentiometer (often called a slider) measures changes in variance along the track in a straight line (linear) as the potentiometer's slider moves either in a left or right direction.  A linear potentiometer is more suitable in areas where there is space available to install the potentiometer. 

A rotary potentiometer uses a rotary motion to move the slider around a track that is almost circular. Because the potentiometer's track is circular, the size of a rotary potentiometer can be quite small and does not require a lot of space to install.

Potentiometer Accuracy

The ability of the potentiometer to accurately read the position of the slider as it moves along the track is vital if the attached control device is to perform in an accurate and repeatable way. 

LEFT: A very inexpensive linear potentiometer ($3.00).  The tracks on this pot are made from carbon and the body is open to dust and grime.  They work quite well, but expect their life to be limited once they begin to get dirty (click to enlarge).

The performance, accuracy, and how long that accuracy is maintained, is governed by the internal construction of the potentiometer; in particular the material used for the track (carbon, cermet, composite, etc).  Of particular importance, is the coarseness of the signal and the noise generated (electrical interference). when the potentiometer has power running through it.

For example, cermet which is composite of metal and plastic produces a very clean low noise signal, where as carbon often exhibits higher noise characteristics and can generate a course output.  It’s the coarseness of the signal that makes a control device easy or difficult to calibrate.  It also defines how accurately the potentiometer will read any small movement.

Potentiometers that use carbon form the mainstay of the less expensive types, such as those used in the gaming industry, while higher-end applications that requite more exacting accuracy use cermet or other materials. 

Essentially, higher end potentiometers generate less noise and produce a cleaner output that is less course.  This translates to more accurate calibration.  This is seen when you trim the aircraft. 

A quality mid to high-end potentiometer, when calibrated correctly, will enable you to easily trim the aircraft, insofar that the trim conditions can be replicated time and time again (assuming the same flight conditions, aircraft weight, engine output, etc).

Simulators, Dust, Grime and Other Foreign Bodies

Flight simulators to control a number of moving parts, generally use a combination of linear and rotary potentiometers.  For example, a rotary potentiometer may be used to control the flight controls (ailerons, elevator and rudder) while a linear potentiometer may be used to control the movement of the flaps lever, speedbrake and steering tiller. 

Any component that has a current running through it will attract dust, and the location of the potentiometer will often determine how much dust is attracted to the unit.  A potentiometer positioned beneath a platform is likely to attract more dust than one located behind the MIP or enclosed in the throttle quadrant.

A rotary potentiometer is an enclosed unit;  it is impervious to dust, grime and whatever else lurks beneath a flight simulator platform.  In comparison, a linear potentiometer is open to the environment and its carbon track can easily be contaminated.  Once the track has become contaminated, the potentiometer will become difficult to calibrate, and its output will become inaccurate.

Sometime ago, I had a linear potentiometer that was difficult to calibrate, and when calibrated produced spurious outputs.  The potentiometer was positioned beneath the platform adjacent to the rod that links the two control columns.  When I removed the potentiometer, I discovered part of the body of a dead cockroach on the carbon track. 

This is not to say that linear potentiometers do not have a place – they do.  But, if they are to be used in a dusty environment, they must have some type of cover fitted.  A cover will minimise the chance of dust adhering to the potentiometer’s track. 

I use linear potentiometers mounted to the inside of the throttle quadrant to control the flaps and speedbrake.  The two potentiometers are mounted vertically on the quadrant’s sidewall.  This area is relatively clean, and the vertical position of the mounted potentiometers is not conducive to dust accumulation.

Ease of Installation

Both linear and rotary potentiometers are straightforward to install, however, they must be installed relatively close to the item they control.  Often a lever or connecting rod must be fabricated to enable the potentiometer to be connected with the control device.

String Potentiometers (strings)

A string potentiometer (also called a string position transducer) is a rotary potentiometer that has a stainless steel cable connected to a spring-loaded spool. 

LEFT:  Cross section diagram showing internals of string potentiometer (click to enlarge).

The string potentiometer is mounted to a fixed surface and the cable attached to a moveable part (such as a control device).  As the control device moves, the potentiometer produces an electrical signal (by the slider moving across the track) that is proportional to the cable’s extension or velocity.  This signal is then read by the calibration software. 

The advantages of using string potentiometers over a standard-issue rotary potentiometer are many:

(i)        Quick and easy installation;

(ii)       Greater accuracy as you are measuring the linear pull along a cable;

(iii)      Greater flexibility in mounting and positioning relative to the control device;

(iv)      No dust problems as the potentiometer is enclosed;

(v)       No fabrication is needed to connect the potentiometer to the control device (only cable and dog clip) and,

(vi)       Greater time span before calibration is required (compared to a linear potentiometer).

The importance of point (iii) cannot be underestimated.  The string can be extended from the potentiometer within a arc of roughly 60-70 degrees, meaning that the unit can be mounted more or less anywhere.  The only proviso is that the cable must have unimpeded movement. 

Attachment of the string to the control device can be by whatever method you choose.  I have used a small dog lead clip.  As the potentiometer is completely enclosed dust is not an issue, which is a clear advantage in that once the potentiometer calibrated, the calibration does not alter (as dust does not settle on the track).

I have used string Potentiometers to calibrate the axis on the ailerons, elevators and rudder (one potentiometer per item).  I have also used a dual-string potentiometer in the throttle quadrant to calibrate the two thrust levers.

Fabricate Your Own String Potentiometer

Whilst you can purchase ready-made string potentiometers, their cost is not inexpensive.  As a trial, a friend and I decided to fabricate our own string potentiometers.

LEFT:  String potentiometer.  This pot connects to the ailerons.  The stainless cable can be seen leaving the casing that connects with the aileron controls.  An advantage of string pots is that they can installed more or less anywhere, as long as there is unimpeded access for the cable to move (click to enlarge).

The potentiometers used are manufactured by Bourns (3590S series precision potentiometer).  These units are a sealed, wire-wound potentiometer with a stainless steel shaft.  According to the Bourns specification sheet these potentiometers have a tolerance +-5%. 

LEFT:  Diagram showing spring-loaded spool (click to enlarge).

The potentiometer is mounted in a custom-made acrylic box in which a hole the size of the potentiometer's end, has been drilled into the lid.   Similar boxes can be purchased in pre-cut sizes, but making your own custom-sized box enables the potentiometer to be mounted inside the box in a position most advantageous to your set-up. It also enables you to place the mounting holes on the box in strategic positions.

Another small hole has been drilled in the side of the box to enable the stainless steel cable to move freely (see image at beginning of article).  If you want to allow the cable to move through an arc, this hole must be elongated to enable the cable to extend at an angle and move unimpeded. 

The cable (string) is part of a self-ratcheting spool (also called a retractor clip) which is screwed to the inside of the box and connected directly with the stainless steel shaft of the potentiometer.  The cable when attached to a solid point is kept taught by the tension of the self-ratchet spool (an internal spring controls the tension).   Ratchet spools are easily obtainable and come in many sizes and tensions.   Three standard JR servo wires connect the potentiometer to a Leo Bodnar BU0836A 12 bit Joystick Controller card.  A mini dog lead clip is used at attach the cable to the control device.

One of the major advantages when using string potentiometers is that the actual potentiometer does not have to be mounted adjacent to, or even close to the device it controls.  The line of pull on the cable can be anything within roughly a 70 degree arc. 

Additional Information

This website (no affiliation) has an excellent overview on potentiometers.  The video is very interesting.

http://www.resistorguide.com/potentiometer/

Final Call

Previously, I used inexpensive linear and rotary potentiometers to control the main flight controls.  I was continually plagued with calibration issues, and when calibrated the calibration was not maintained for more than few months.  Furthermore, manual flight was problematic as the output from each of the  (cheap) potentiometers was course, which translated to less accuracy when using the ailerons and elevators.  Trimming the aircraft in any condition other than level flight was difficult.

Without doubt, the use of quality string potentiometers have resolved all the earlier calibration and accuracy issues I had been experiencing.  With the replacement potentiometers, the aircraft is easily hand-flown and can be trimmed more accurately.

Perhaps in the future I will ‘up the anti’ and purchase two commercial high-end string potentiometers and dedicate them to the ailerons and elevator, but for the time being the Bourne potentiometers suit my requirements.

Monday
May282018

FMC Software and its Relationship with LNAV and VNAV

The procedure to takeoff in a Boeing 737 is a relatively straightforward process, however, the use of automation, in particular pitch and roll modes (Lateral and Vertical Navigation), when to engage it, and what to expect once it has been selected, can befuddle new flyers.  

In this article I will explain some of the differences between versions of software used in the Flight Management Computer (FMC) and how they relate to when you engage  LNAV and VNAV.  I will also discuss the autopilot and Auto Flight Direction System (AFDS) and explain the Flaps Retraction Schedule (FRS).

It’s assumed the reader has a relatively good understanding of the use of LNAV and VNAV, how to engage this functionality, and how they can be used together or independently of each other.

FMC Software Versions

There are a several versions of software used in the FMC; which version is installed is dependent upon the airline, and it’s not unusual for airframes to have different versions of software.

LEFT:  A mundane photograph of the CDU page displaying the U version of software used by the Flight Management Computer.  The page also displays the current NavData version installed in addition to other information (click to enlarge).

The nomenclature for the FMC software is a letter U followed by the version number.  The version of software dictates, amongst other things, the level of automation available.  For the most part, 737 Next Generation airframes will be installed with version U10.6, U10.7 or later.

Boeing released U1 in 1984 and the latest version, used in the 737 Max is U13.

Later versions of FMC software enable greater functionality and a higher level of automation – especially in relation to LNAV and VNAV.

Differences in Simulation Software

The FMC software used by the main avionics suites (Sim Avionics, Project Magenta, PMDG and ProSim-AR) should be identical in functionality if they simulate the same FMC U number.  

As at 2018, ProSim-AR uses U10.8A and Sim Avionics use a hybrid of U10.8, which is primarily U10.8 with some other features taken from U11 and U12.  Precision Manuals Development Group (PMDG) uses U10.8A.  

Therefore, as ProSim-AR and PMDG both use U10.8A, it’s fair to say that everything functional in PMDG should also be operational in ProSim737.  Unfortunately, as of writing, PMDG is the only software that replicates U10.8A with 97+-% success rate.

To check which version is being used by the FMC, press INIT REF/INDEX/IDENT in the CDU.  

Writing about the differences between FMC U version can become confusing.   Therefore, to minimise misunderstanding and increase readability, I have set out the information for VNAV and LNAV using the FMC U number.   

Roll Mode (LNAV)

U10.6 and earlier

(i)    LNAV will not engage below 400 AGL;

(ii)    LNAV cannot be armed prior to takeoff; and,

(iii)    LNAV should only be engaged  when climb is stabilised, but after passing through 400 feet AGL.

U10.7 and later

(i)    If LNAV is selected or armed prior to takeoff, LNAV guidance will become active at 50 feet AGL as long as the active leg in the FMC is within 3 NM and 5 degrees of the runway heading.  

(i)    If the departure procedure or route does not begin at the end of the runway, it’s recommended to use HDG SEL (when above 400 feet AGL) to intercept the desired track for LNAV capture;

(ii)    When an immediate turn after takeoff is necessary, the desired heading should be preset in the MCP prior to takeoff;  and,

(iii)    If the departure procedure is not part of the active flight plan, HDG SEL or VOR LOC should be used until the aircraft is within range of the flight plan track (see (i) above).

Important Point:

•    LNAV (U10.7 and later) can only be armed if the FMC has an active flight plan.

Pitch Mode (VNAV)

U10.7 and earlier

(i)    At Acceleration Height (AH), lower the aircraft’s nose to increase airspeed to flaps UP manoeuvre speed;

(ii)    At Thrust Reduction Altitude (800 - 1500 feet), select or verify that the climb thrust has been set (usually V2+15 or V2+20);

(iii)    Retract flaps as per the Flaps Retraction Schedule (FRS); and,

(iv)    Select VNAV or climb speed in the MCP speed window only after flaps and slats have been retracted.

Important Points:

•    VNAV cannot be armed prior to takeoff.

•    Remember that prior to selecting VNAV, flaps should be retracted, because VNAV does not provide overspeed protection for the leading edge devices when using U10.7 or earlier.

U10.8 and later 

(i)    VNAV can be engaged at anytime because VNAV in U10.8 provides overspeed protection for the leading edge devices;

(ii)    If VNAV is armed prior to takeoff, the Auto Flight Direction System (AFDS) remains in VNAV when the autopilot is engaged.  However, if another pitch mode is selected, the AFDS will remain in that mode;

(iii)    When VNAV is armed prior to takeoff, it will engage automatically at 400 feet.  With VNAV engaged, acceleration and climb out speed is computed by the FMC software and controlled by the AFDS; and,

(iv)    The Flaps should be retracted as per the flaps retraction schedule;

(v)    If VNAV is not armed prior to takeoff, at Acceleration Height set the command speed to the flaps UP manoeuvre speed; and,

(vi)    If VNAV is not armed prior to takeoff, at Acceleration Height set the command speed to the flaps UP manoeuvre speed.

Important Points:

•    VNAV can be armed prior to takeoff or at anytime.

•    At thrust reduction altitude, verify that climb thrust is set at the point selected on the takeoff reference page in the CDU.  If the thrust reference does not change automatically, climb thrust should be manually selected.

•    Although the VNAV profile and acceleration schedule is compatible with most planned departures, it’s prudent to cross check the EICAS display to ensure the display changes from takeoff (TO) to climb or reduced climb (R-CLB).  

Auto Flight Direction System (AFDS) – Operation During Takeoff and Climb

U10.7 and earlier

If the autopilot is engaged prior to the selection of VNAV:

(i)    The AFDS will revert to LVL CHG;

(ii)    The pitch mode displayed on the Flight Mode Annunciator (FMA) will change from TOGA to MCP SPD; and,

(iii)    If a pitch mode other than TOGA is selected after the autopilot is engaged, the AFDS will remain in that mode.

U10.8 and later

(i)    If VAV is armed for takeoff, the AFDS remains in VNAV when the autopilot is engaged; and,   

(ii)    If a pitch mode other than VNAV is selected, the AFDS will remain in that mode.

Preparing for Failure

LNAV and VNAV have their shortcomings, both in the real and simulated environments.

To help counteract any failure, it’s good airmanship to set the heading mode (HDG) on the MCP to indicate the bearing that the aircraft will be flying.  Doing this ensures that, should LNAV fail, the HDG button can be quickly engaged with minimal time delay; thereby, minimising any deviation from the aircraft’s course.

Autopilot Use, Flap Retraction and Eliminating Unwanted Pitch

When the aircraft is in manual flight (hand flying), the trim setting should be set correctly so that forward and back pressure on the control column is not required.  If the autopilot is engaged when the trim is not correct, the aircraft will suffer unwanted pitch movement as the automated system corrects the out of trim condition.

Adhering to the following recommendations will reduce the likelihood of unwanted or unexpected deviations from the desired flight path.

(i)    The autopilot should not be engaged before passing through 400 feet AGL;

(ii)    The flaps should not be retracted before passing through 400 feet AGL; and,

(iii)   The autopilot should not be engaged before flap retraction is complete, and then only engaged when the aircraft is in trim.  

If this procedure is adhered to, the transition from manual to automated flight will be barely discernible.  

Regarding point (iii).  I have used the word ‘should’ as this is generally a preferred option, however, airline policy may dictate otherwise.  

Flap Retraction Schedule (FRS)

The flaps on the Boeing 737 should be retracted per a defined schedule.  Failure to follow the FRS may cause excessive throttle use and possible flight path deviation.

LEFT:  Flap Retraction Schedule from FCOM (click to enlarge).  Copright FCOM.

Selection of the next flap position should be initiated when reaching the manoeuvre speed for the current flap position. 

Therefore, when the new flap position is selected, the airspeed will be below the manoeuvre speed for that flap position.  For this reason, when retracting the flaps to the next position, the airspeed of the aircraft should be increasing.

Said slightly differently, with airspeed increasing, subsequent flap retraction should be initiated when the airspeed reaches the manoeuvre speed for the current flap position.  

The manoeuvre speed for the current flap position is indicated by the green-coloured flap manoeuvre speed bug.  The bug is displayed on the speed tape of the Primary Flight Display (PFD) and is in increments that replicate the flap settings (UP, 1, 2, 5, etc).

Acceleration Height

Flap retraction commences when the aircraft reaches Acceleration Height, which is usually between 1000 and 1500 feet AGL (this is when the nose of the aircraft is lowered to gain airspeed).

However, often there are constraints that affect the height at which flap retraction commences.  Determining factors are: safety, obstacle clearance, airplane performance, and noise abatement requirements.  At some airports, airlines have a standard climb profile that should be followed for their area of operations

White Carrot

Located on the speed tape of the PFD is a white-coloured marker called a carrot (the carrot looks more like a sideways facing arrow).  The position of the carrot indicates V2+15.

LEFT:  Captain-side PFD showing white carrot.  Image from ProSim-AR 737 avionics suite (click to enlarge).

If you look at the Flap Retraction Schedule in the FCTM (see above image from FCOM), you will note the airspeed that is recommended to begin retracting flaps is V2+15 (the position of the carrot).  The white carrot is a very handy reference reminder.

Important Points:

•    The minimum altitude for flap retraction is 400 feet AGL.  

•    Selection of the next flap position should be initiated when reaching the manoeuvre speed for the current flap position.

•    Airspeed should be increasing when retracting the flaps.

•    The white carrot is a handy reference to V2+15.

•    Acceleration Height can differ between airports.

Summary

I realise that some readers, who only wish to learn the most recent software, will not be interested in much of the content of this article.  Notwithstanding this, I am sure many will have discovered something that may have been forgotten or overlooked.

The content of this short ‘function specific’ article came out of a discussion on a pilot’s forum.  If there is doubt, always consult the Flight Crew Training Manual (FCTM) which provides information specific to the software version used at that particular airline.

Glossary

AFDS – Autopilot Flight Director System
CDU – Computer Display Unit
EFIS – Electronic Flight Instrument System
FMA – Flight Mode Annunciator
FMC – Flight Management Computer
LVL CHG – Level Change
LNAV – Lateral Navigation
MCP – Mode Control Panel
ND – Navigation Display
PFD – Primary Flight Display
 VNAV – Vertical Navigation

Sunday
Apr292018

ISFD Knob Fabricated

The Integrated Standby Flight Display (ISFD) is mounted in the stand-by instrument cluster in the Main Instrument Panel (MIP).  The ISFD provides redundancy should the Primary Flight Display (PFD) on the Captain or First Officer fail. 

LEFT:  OEM ISFD (Image copyright Driven Technologies INC).

The ISFD is not a common panel to find second hand, and working units are expensive to purchase.  I don't  have an OEM ISFD, but rather (at least for the moment) use a working virtual image displayed by ProSim737. 

Conversion of an OEM unit is possible, however, the unit would need to be fully operational, and  finding a working unit at a reasonable price is unlikely.  ISFDs are expensive and reuse is common.  If a unit does not meet certification standard, it's disposed of because it's broken and cannot be economically repaired.

ISFD Knob

LEFT:  ISFD knob.  Two versions: one replicates the taller NG style while the other is slightly shorter.  Although not functional, they provide a better representation of the plastic knob that previously was installed.  (Click to enlarge).

The ISFD knob that came bundled with the MIP I purchased is very mediocre in appearance – in fact it's a piece of plastic that barely looks like a realistic knob.  I purposely have not included an image, as the design would be an embarrassment to the company that produced the MIP.

LEFT: Knob being fabricated on a lathe.  This photograph has been taken by another person and is not my property (click to enlarge).

A friend of mine is a bit of a wizard in making weird things, so I asked him if he could make a knob for me.  He made two knobs – one based on the standard design seen in the Next Generation airframe and the other knob a shorter version of the same type. 

Attention to Detail

Attention to detail is important and each knob has the small grub screw and cross hatch design as seen on the OEM knob.  The knobs have been made from aluminum and will be primed and painted the correct colour in the near future.

A 2 axis CNC lathe was used to fabricate the knobs.  The use of a computerised lathe enables the measurements of a real knob to be accurately duplicated, in additiona to any specoifc design (such as cross hatching or holes to install grub screws).