Simulator subjects

Dzus or not to Dzus? 

Dzus rail Dzus rail or Dzus receptacle rail and its corresponding fasteners can be found on all commercial and military aircraft including helicopters. it is usually present as long strips on overhead panel frames and is identified as a silver or aluminium strip with multiple holes.The receptacle rail is pretty useless without appropriate fasteners to use with it. Receptacle rails come in both single hole and strip configurations. The strip configuration acts as a supporting frame for the panels or removable parts to be fastened, with continuous holes for stud engagement and rivet mounting on 9.525mm(3/8”) centres. The strip is riveted to a support member and the stud panel rests against the strip face having the stud holes. The strips are aluminium alloy with a continuous rigid stainless steel wire staked across the underside of the stud holes. The fastened panel rests on the strip and its captive quarter-turn studs engage the rigid wire.

pa-3500smallExamples of Dzus receptacle rail and fasteners.


William Dzus saw a need for a new type of fastener to meet the requirements of the Aircraft Industry – a quick-acting, self-locking device. From this idea he invents and develops the well-known Dzus Fastener, with capability to withstand vibration and a tolerance for high stress and strain. Manufacturing begins as a one-man business in a small garage in West Islip, New York. The shear merit of the product creates a wide-spread market and the company grows. (courtesy DFCI Solutions inc)

So, what does this mean to the constructor?
Chances are that when you install a panel in say your overhead rack, it will be removed and put back in place many times. When it is removed for repair, modification or service, you will want a system that allows you the ability to quickly remove and replace a panel or module. On a motion based simulator, it is imperative that the simulator is equipped with a system that will not have panels or modules dropping to the floor during the transition through a storm or while traversing a rough runway. On a simulator with the Dzus fastener system installed, all you need to remove a panel is a single blade screwdriver.

The alternative.
The cheapskate way to fix your panels into an overhead panel frame is to use aluminium angle with threaded holes in it. Yes, this method is very cheap and in the short term effective, but I can assure you that as the aluminium threads slowly strip and flog out, you will be faced with panels that dont secure in place and drop out just as you are negotiating that wind shear on short final.

dzus-rail A close up of the precisely placed fastener holes and the securing wire running the length of the rail.

The costs. Both Dzus fasteners and receptacle are expensive.Typically, a single Dzus fastener will cost between 3 and 7 dollars (you usually need 2 to 4 per panel). On top of that you will need some specialised tools to fit the fasteners to the panel. Aircraft panel thickness is mostly 1.6mm (.062"), so you need to be careful what type of fastener you purchase because they come in varying types depending on your panel thickness. Receptacle rail comes in lengths of 3m (10ft) and costs about $200 per length. It is precisely machined and provides a consistently accurate placement process for your panels. All of the above cost big bucks, but provides a beautiful and professional system for your simulator.
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If you are one of those crazy people out there considering making your simulator in the 'old school' way with analogue gauges, then you may not care too much for this article, but for others wanting to build a modern and reliable simulator, read on; MIP DUs is just an abbreviated way of writing 'Main Instrument Panel Display Units'. DUs now replace a myriad of instruments that once cluttered the Main instrument panel. Most modern airliners have replaced the old 'steamgauges' with CRT or LCD flat panels. Analogue gauges had a curious relationship with pilots because pilots absolutely relied on them, but never always trusted them. A pilots instincts would always tell him that he was right if there was a disagreement between what the pilot thought and what a gauge was telling him. This was evident in a pilots habit of tapping a gauge if he/She did not agree with a reading. Digital displays did away with the problem of mistrust and disbelief as all the important information was now displayed in graphical format and the days of sticky pointers and mechanical failures have largely gone. Dont be fooled into thinking that the elements that drive the modern pilot displays are somehow different and foolproof. The PFD in an A320 still relies on measuring air pressure , both pitot and static. Even some light aircraft are fitted with 'glass cockpits' to make the job of reliability and maintenance easier.

Understanding ratios
If you have decided to install LCD monitors into your instrument panel, you have stumbled across the first difficulty in creating you glass cockpit. You have probably worked out that a single DU measures 7.5"x 7.5". In ratio terms this is a 1:1 ratio, but no matter how hard you look and no matter how many times you trawl through the web, you cannot find a display that is as wide as it is high. This is because a modern display of any type has a ratio of 4:3 in other words, it is wider than it is high. You can purchase 1:1 ratio LCD flat panels from Honeywell, but at last enquiry the price was about $20,000 USD each. There was a guy who patented the process of cutting a standard LCD panel down to a 1:1 size, but the process is very complex and can only be performed on certain brand flat panels.

The LCD solution.
a 17" LCD panel can be positioned on an instrument panel to represent 2 DUs. On a 737 simulator, the flat panels have to be positioned so that when the bezels are fitted, they will cover up the 'ugliness' of the installation. There are no specific instructions on the positioning of the flat panel installation as it varies wildly with your own instrument panel construction and design. Don't worry about the positioning of the graphics when you locate your flat-panels as programs like PM will allow plenty of adjustment to correctly position the graphics
in the centre of the viewing area.When choosing an LCD with a VGA or DVI interface, check critical specifications like contrast ratio and viewing angle.Without a good contrast ratio your PM installation may have blacks that are really just dark greys instead of true black. The human eye has a hard time distinguishing between differing shades of grey and the black area of that LCD monitor may be just a read dark shade of grey. A good way of testing blacks on a monitor in a brightly lit department store is to take a small piece of black card. Place it alongside of the black areas of a monitor you are looking to buy for your simulator, it will soon be obvious how black the monitors blacks really are. On older technology LCD panels you had to face the monitor square on to get the best image.The more of an angle you viewed the flat panel at the more washed out the image became. On a good quality TFT LCD flat panel, you should still be able to view the screen images of angles up to 80 degrees. This means that from the captains seating position, you should be able to comfortably read the FO's displays without the graphics washing out or blurring.

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One of the major considerations when taking on simulator design is how to get devices input or changes to the host program and vice versa. One of the first concepts that first time simulator constructors try to get their heads around is how to make your computers aware that controls and switches are being used. There are two primary data streams in every simulator. The first is the stream that makes the host computer(s) aware that controls are being manipulated and used. The second is a stream back to various displays, controls and indicators throughout the flightdeck.The devices that use employed as interface control devices are generically referred to as i/o interfaces or input/output devices.The following list and descriptions are a basic selection of the i/o cards available on the market today. What i/o devices are available? You have the following readily available options for i/o devices;

Phidgets are a family of modular USB devices that come with a set of terminals that you can wire switches and a bunch of other devices to. When a switch is thrown, the phidget reports via USB the port where the switch activation took place. You can then programatically decide what action the host computer should take when port x is on. Phidgets come in different modules that are designed to monitor different input types. They can handle pure digital i/o while some modules are designed to monitor analogue i/o such as potentiometers. These is a Phidget card designed specifically to accept input from a rotary encoder. While the phidget system is very fast and modular, it does have its failings. It requires the user to be able to program in one of the mainstream languages such as C, Java or VB. Cards are designed in 'types' for specific jobs such as digital and analogue i/o, so you may need several card types for a single panel. Phidgets were primarily designed for the robotics community, but if you think about it, a simulator is just a big robot.

The EPIC system appeared in the late 90's and was designed by a guy called Ralph Robinson. It has a central processing board that runs a program written or designed by the user (you). Connected to central processor board are many different wiring boards designed to accept a variety of digital and analogue inputs. The central processor board is run by a flashed program so that it is officially embedded computing. EPIC requires no special tools to program ,Just Windows notepad. Probably the biggest failing of EPIC is that it uses pseudo C language to program it. While C is a powerful language it is also hard to learn and makes using EPIC hard to use without a substancial programming background. On the upside, it is a fast system with speeds comparable to more professional i/o systems. There are now bridging routines that allow VB programmers to implement EPIC without having to go elbow deep in C.

Brew your own
If none of the i/o devices out there blows your skirt up or their specifications dont meet your requirements, then you can choose to produce your own boards. If you have the capability and knowledge to do this then you certainly dont need to be reading this article. With today's Atmel and PIC systems, making your own i/o boards is a very real possibility with some caveats; You will need an intimate knowledge of electronics and programming. Unless you are developing a seriously expensive simulator wIth very specific needs, it would be much cheaper to use an OTS (off the shelf) solution to the i/o issue. Like a new religion, do we really need another standard to confuse the issue of data i/o?

Centralised Design and Architecture
If you are designing a system and phidgets is your choice of I/O device, there is a temptation to centralise all of the i/o in an attempt to save money. Centralising means that you are attempting to maximise the use of your i/o cards by running all wiring back to one central point. While this is a efficient use of the cards it has two major flaws.
Flaw #1. Since each panel is hardwired back to a group or cluster of I/O cards, if you require to remove a panel from say your overhead panel collection, it means that you have to unwire every device from the panel you are removing in order to remove the panel from the frame it was fastened to. The solution to this is to install a quick release plug such as a DB25 or cannon.
Flaw #2 Since multiple panels may be dependant on a single card in the centralised design, if one card fails, it may take out 2 or more panels thus, rendering the simulator unusable. That is unless your simulator has a MEL that excludes multiple vital panels.

Panel specific i/o
If your budget will allow, a far better way is to opt for a panel specific i/o system where you have i/o boards mounted on and dedicated to each panel. The real value in this system is reliability and speed. If you ever need to remove a panel from its frame, its just a matter of just unplugging the power supply to the panel and remove the panel. Because each panel has localised wiring, there is nothing to disconnect. This system has several flaws;
Flaw #1
Since each panel requires its own card or set of i/o cards, this system can get pretty expensive. The tradeoff is that wiring remains localised and is easy to trace in case of a fault; if a card fails, only that panel fails.
Flaw #2
Whereas the centralised system may only require 6-8 USB connections back to the host computer, the Panel specific system may require 20-30 connections back to the host to allow the host computer to receive communications from all of the panels.

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