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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)
« 2012 - 2013: Seasons Greetings, Thank You & 2013 Plans | Main | Digital Chronometer Running ProSim737 Software »
Monday
Dec102012

Genuine B737 Control Columns - A Closer Look

The two control columns have been refurbished and installed into the simulator.  The control columns previously were used in a B737-500 operated by Croatian Airlines.  I was fortunate to have been able to secure these columns, and although there is some wear on the yokes, all buttons, electric trim switches, chart holders and trip indicators are as used by the airline and are in good condition and are operational.  Furthermore, a working stick shaker is attached to the captain-side control column.

Mechanical Set Up

To allow the two columns to be fitted to the 5 inch high platform, the lower cogs have been removed and replaced with bearings.  The bearings support a high strength stainless shaft that connects to a rotating disc beneath each of the columns; whatever movement is made to one control column is mimicked on the other and vice versa.

LEFT:  Genuine B737-500 control column (captain-side).

Physical movement of the control column is registered by high-end potentiometers and movement converted to an electrical signal that can be read by the interface card.  The interface card used is a Leo Bodnar 836X joystick controller.

The interface card, electrical wiring and potentiometers are installed on a piece of plastic board that is attached to the platform superstructure beneath the floor.  Although everything is out of sight, they are easily assessable should the need arise.

Push and Pull Pressures

In the real Boeing 737 aircraft the control columns are hydraulically driven, and a fail-safe cable mechanism provides redundancy should the hydraulics fail.  The B737 is rather unique in that, although hydraulics control movement of the control column, the pressures needed to manipulate the columns are still quite stiff, therefore; flying a B737 can be quite tiring - you must use a little muscle to move and then  old the controls in place.

The specifications for the real aircraft state that the control column has a 37 pounds push/pull value +- 4 pound, while the roll pressures are 12 pounds +- 3 pound.  These pressures can differ from aircraft to aircraft, but fall within the published specifications. To replicate the push, pull and roll forces as accurately as possible, four heavy duty springs have been fitted to the column mechanism. 

The control column pressure can be adjusted by either replacing the springs with higher or lesser tension springs, or by disengaging the outer springs.  A pressure test determined that push/pull pressure is 20 pounds and roll pressure 15 pounds.  The push/pull pressure is on the low side, however, will be left as is for the time being.  Springs have been used rather than hydraulic rams due to a springs simplicity.

The video at the bottom of this post demonstrates the linkage mechanism and springs in motion.

Configuration - Movement and Buttons

Configuration of the control columns is straightforward. Although there are two control columns, each column is linked to the other; therefore, only one interface card is required. 

Configuration of the yoke is initially set up in the Windows joystick calibration software, and buttons on the yoke are connected to each button output on the interface card.  Further registration and calibration is then completed in the set-up menu of flight simulator (FSX) and further fine-tuning using FSUIPC.  Although it is possible to assign buttons directly via the flight simulator set-up menu, I prefer to use the more sophisticated and reliable FSUIPC to assign button functionality.

Back Lighting (Trip Indicators)

The yoke does not have any back lighting; any illumination of the yoke is achieved by focusing the map light which is attached to the overhead panel.  The back lighting for the trip indicators, to illuminate the numbers, is the only back lighting.  Trip indicators are not a standard component of a Boeing yoke but are a special order item specific to an airline.  Pilots use the trip indicator to 'scribe' the flight number of the flight, however, more often they are not used at all.  I often use the trip indicator as a ready memory pad to scribe in the landing speed (VREF+5) for an approach.  The back lighting for trip indicator is powered by 5 Volts.

Chart Holders

The chart holder is used to secure the approach plate or paper chart, in an area that it can easily be read during flight operations.  The chart holders have a folding type mechanism beneath the plate that allows the holder to be either pushed flat against the yoke, or positioned at a user-selected angle. 

Another function of the chart holder is to provide a ready memory jogger for specific flight operational modes (check list).  The adhesive transfer on which this information is printed is specific to each aircraft type.  illumination of the chart plate, like the yoke, is achieved using the map light.

OEM verses Reproduction

There are several control column reproductions on the market: Precision Flight Controls (PFC), CH Products, Revolution-Sim and Ace Engineering to name a few.  Over the years I have used products from ACE, CH Products and PFC.  Without transgressing into a tit for tat argument, you get what you pay for.  

A CH yoke retailing at $100.00 cannot be compared with an ACE yoke retailing around $1300.00 and both products have been manufactured to cater towards differing segments of the market.  This said, the difference between ACE and PFC is very marginal.  I cannot comment on Revolution-Sim having not used their products. 

So what is the different between a high-end reproduction yoke and a genuine B737 yoke and column?

The main difference is the feel and finesse of the genuine item which is difficult to replicate in a reproduction unit.  Boeing has spent a lot of money (more than PFC, ACE or Revolution-Sim combined) in the development and engineering of the control column, and this is very difficult to replicate in a reproduction unit.

The genuine yoke and column is engineered to provide faithful service for many years.  It is also built to suffer use and abuse from real-world pilots, and I am certain anything a virtual pilot can throw at it, will not cause any damage.  The buttons and electric trim switches are solid, feel good to manipulate and are very reliable.

Performance

The control wheels and columns have zero slop in movement - to explain, the yokes move left and right with a smooth silky feel and there is absolutely no staggering, binding or rough patches as the yoke moves across its full range of movement.  Likewise, the columns move forward and aft very smoothly.

The electric trim switches are far more responsive than reproduction switches I have used.  A slight application of pressure on the switch activates the electric trim.  The electric trim switches response is a akin to a hair trigger on a firearm - it only needs a light touch to activate. 

The control columns, once fine-tuned in FSUPIC,  are very responsive and any movement is accurate.  If the control wheel is turned 15 degrees to the left, the measurement on the aileron tape is exactly 15 degrees..

Synchronization

I was concerned that synchronisation between the two control columns would not be perfect, however, my concerns were short-lived.  The use of high-end bearings at the end of the control linkages removes any slop that may have been apparent if bearings had not been used. 

Appearance of Yoke - Used Look

If you carefully study the pictures of the control column - especially the control wheels, you will observe that the yoke is not pristine but shows solid use (and probably abuse when it was striped from the aircraft).  The baked-plastic covering of the yoke shows scratches and some of the metal has been rubbed clean of paint.  Some simmers dislike this look and prefer a brand new 'out of the showroom' appearance.  If this is you, then I suggest that a genuine yoke may not be for you, unless you wish to completely overhaul the yoke and pay the large amount of money required to re-bake the plastic coating.

I like the 'used' look and feel it adds to the simulator.  I have been in many cockpits and very rarely do you find a flight deck in brand new condition, other than in the first few months of flight service.  More often than not, gauges, yokes and panels are scratched, dented and stained from many hours of sustained use from individuals that are more interested in flying and going home after the flight, than maintaining the desk!

To view detailed pictures of the control columns, mechanism and interface card, navigate to the image gallery (flight controls and platform construction).

Below is a short video showing the under floor mechanism, springs and linkage rods.  If you listen carefully you will hear the springs creaking.  This is not an issue when the simulator is running as any noise is cancelled out by the noise of the engines.

 

  In a latter post we will discuss the rudder pedals.

Glossary

Control Wheel - Yoke.

FSUIPC - Flight Simulator Universal Inter-Process Communication (interface software that provides a bridge between flight simulator and outside programs).

OEM - Original Equipment Manufacturer (aka real aircraft part).

 

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Reader Comments (7)

Fantastic! Have you studied mechanical engineering before?

I am just wondering how your managed to come up with such an ingenious design. I don't think yoke schematics for the home user are easily available!

December 10, 2012 | Unregistered CommenterBen

Thanks Ben. I had help - it wasn't just me :) Building is often a team effort. F2A

December 10, 2012 | Registered CommenterFLAPS 2 APPROACH

Awesome, what specific potentiometers do you use?

November 20, 2015 | Unregistered CommenterChris

Greetings

This company sells various pots that can be used. Military specification pots are best as they are more robust

http://au.mouser.com/Passive-Components/Potentiometers-Trimmers-Rheostats/Potentiometers/_/N-9q0yp

Cheers, F2A

November 20, 2015 | Registered CommenterFLAPS 2 APPROACH

Helpful article - I loved the insight

May 8, 2016 | Unregistered CommenterBibi Grundy

Hello
Very nice job
Do you have a diagram of the mecanism as I owna pair of original yokes and would like to check if it can be done by myself
Thanks

Jacques

November 23, 2016 | Unregistered CommenterJacques

Hello Jacques

Thanks. I do not have a diagram - sorry. There are many ways to interface and connect the yokes, F2A

December 3, 2016 | Registered CommenterFLAPS 2 APPROACH

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