Cessna 172 SP GA Cockpit Project

Rory Gillies, August 2003

Introduction

The range of hardware available to MSFS users has never been better, with a whole host of specialised products available to enhance the simming experience. Along with the GoFlight (http://www.goflightinc.com) range of avionics, I had been keeping a close eye on The Real Cockpit (http://www.therealcockpit.com) range of training devices. Unfortunately, even their Basic Training Device was well out of my price range.

Recently an off-shoot of The Real Cockpit, SimKits (http://www.simkits.com), was formed, providing a nearly full set of C172 instruments in kit form. This opened up the option of building a complete cockpit simulator to augment my WidevieW (http://www.wideview.it) system. With a budget of £1,000.00 (GBP) I set out to build a fully functional 172 panel complete with avionics and all switches, effectively making the keyboard redundant during all stages of flight. This article will document the project.

Planning

The SimKits range contains just about every gauge you need for a full IFR 172SP panel. They also supply a panel and case, but as I was on a limited budget I decided to build my own panel from plywood. The savings made here enabled me to purchase three GoFlight modules for avionics and switches: the GF-P8 and GF-45PM for avionics and the GF-T8 switch module. As the panel had to integrate with my existing set up building it from scratch would make this easier.

With the intention of spreading the cost over several months, I ordered the ASI, Attitude and Altimeter gauges along with the central control unit from SimKits. I sourced the HS322 servos from a UK company, Helicopters Online for £8.81 including VAT. Some gauges require the servos to be modified for continuous rotation. These can be bought pre-modified from SimKits, or you can download instructions from the website and modify them yourself - I chose the latter route.

Construction of the Panel

SimKits provide an Autocad template for the panel, which I had printed to 1:1 scale. I purchased a half sheet of 4mm ply and cut it to size, using the Autocad drawing as a template.

The large instruments are 79mm dia. and the small ones are 56mm. After accurately marking out the gauge positions It was off to our local tool store to pick up the hole saws. Unfortunately, these sizes were not stocked by any tool shop in Shetland, so they had to be ordered. With the holes cut, the panel was really starting to take shape.

The Instrument Panel taking shape.

To obtain a good finish the plywood was coated with a plastic film and shrunk on with a hair dryer. The whole thing was then sprayed with a matt grey acrylic paint (designed for vinyl and car bumpers).

The final bit of work with the panel was to build the avionics stack, designed initially for the GF-45 and GF-P8, but with room for a GF-166 radio modules and another GF-P8 pushbutton module that would be added at a later date.

The Panel complete with avionics stack.

Construction of the Gauges

I decided to build the Airspeed Indicator first as this was a simple kit with a single normal servo and only consisted of nine parts. The kits are very well made with clear and concise instructions. The ASI took only ten minutes to put together, and once I had dug out an old AT power supply I hooked up the CCU (Central Control Unit) and calibrated the instrument. No problems there, so it was on to the Attitude Indicator, with 22 different components and two servos.

The Attitude Indicator during assembly.

The gauge was again simple to make, taking about 1½ hours to complete and calibrate. I left the Altimeter until last, as it was the most complex kit with a plethora of gear wheels, soldering and a servo to modify. This instrument took over two hours in total, but when completed the gauge refused to calibrate. The SimKits website has a very active technical forum which is a great source of help and information, and the SimKits support department is very quick to help out. I eventually traced the problem to the servo I modified. This involves cutting the top of the potentiometer shaft inside the servo and then gluing it centrally. As there was a lot of grease inside the servo mechanism the glue had not stuck, and a tiny shard of plastic on the output shaft was turning the pot shaft when the servo ran. Clearing out the grease and gluing properly cured the problem.

The next consignment of instruments arrived from Simkits enabling me to nearly complete the panel – VOR 1 and 2 gauges will be installed at a later date. I had few problems building any of the rest of the gauges, although I managed to break the bulb on the turn coordinator! This gauge really needs a person with three hands to position the front plate, as very accurate alignment is required to ensure the slip ball fits exactly over the eccentric shaft.

One other issue was slipping of the heading bug on the Heading Indicator. A quick visit to the SimKits forum found a solution, and highlighted that you should never glue the units face plate on until it is fully tested. Although the face plates can be removed, the noises the plastic makes when breaking the glue weld is very disconcerting!

Installation

With the instrument panel largely complete it was time to calibrate and test it with my WidevieW system. Up to this point testing each instrument had been done with my laptop as there was no room to fit the panel into the final position.

The panel sitting on top of the yoke, a temporary arrangement until modifications were made to the cockpit.

The initial trials of the system were very encouraging. The fact that your eyes have to refocus from the monitors to the gauges makes the effect very realistic, and much greater eye movements are needed to scan the instruments.

With the panel largely complete, modifications to the system unit were required to fit it properly. I had decided not to modify the CH yoke at this time, as there is a possibility SimKits may release a yoke compatible with their CCU (Central Control Unit). As the attitude and direction indicators had to be central with the yoke, the avionics panel would sit out to the right hand side. To accommodate this, the Wideview monitors had to be offset to one side, with the added advantage of creating a more “left hand seat” feel to the cockpit view.

The panel in place (without IFR instruments). Note the slight offset of the monitors to the right creating a “left hand seat” impression.

The main and avionics panels were mounted to a wooden frame constructed over the existing yoke, fixed with small self tapping screws. I played around with the eyepoint, and with the panel assembly sitting directly above the yoke the forward view and instrument height were almost identical to a real 172. The CCU was mounted directly behind the panel giving easy access to all the connectors.

With the GoFlight GF-45 and P-8 (push button unit to control the GF-45) modules installed in the avionics stack I now had a capable VFR panel. Although some mouse and keyboard actions were still required – typically at start up and shut down – the feeling was much closer to sitting in a real aircraft. To complete the panel the two VOR instruments plus another GoFlight GF-P8 and a GF-166 Versatile Radio Panel were ordered. The GF-T8 toggle switch unit was installed to the left of the yoke to operate most of the electrical equipment.

IFR Fit

The GF-166 and P-8 units were ordered from Canada at a considerable saving, even including import tax and shipping, and I was fortunate to receive a $35.00 (US) discount on the two VOR gauges from SimKits. The servos were again ordered from Helicopters Online in Farnborough, and most of the kit arrived about the same time.

The VOR gauges were easy to build, although the VOR 1 gauge was a bit fiddly positioning the top plate so the needles engaged on the servo eccentrics. There was also a problem that developed with the OBS gear wheel slightly fouling the casing, which resulted in the gear shaft on the cap shearing – the OBS turned fine clockwise but anti-clockwise seemed very stiff. As luck would have it there was an extra gearwheel cap (part S) included in the kit – the only duplicate part I’d ever received! The bezels of the two VOR gauges were painted with silver enamel, and the black anodise was sanded off the rim of the aluminium OBS knobs to reflect the look of the real instrument.

Once tested and calibrated the VOR gauges were installed in the panel, along with the GF-166 radio panel and associated GF-P8 to control the functions (more on this later). I moved the clock/timer unit (a UWIN multi-function clock/stopwatch) from the position of VOR 1 to the correct location above the engine instruments. I hadn’t done this before as it would not fit into the smaller instrument recess, and a special mounting had to be made for it. The GF-45 in the avionics stack was moved down, with the radio installed below the top GF-P8.

The completed IFR fit. Note the GF-T8 switch unit to the left of the yoke and the repositioned clock.

Panel and Avionics Layout

The main panel instrument layout is exactly as you would find in a real 172SP (or the FS2002 panel for that matter). With the avionics panel I tried to create a realistic arrangement, mounting the GF-P8 push button unit above the GF-166 radio that it controls. The second GF-P8 sits above and controls the GF-45, along with autopilot functions.

The GoFlight GF-P8 push button modules allow you to assign various functions to the GF-166 radio and GF-45 device. The top buttons assign Com 1; Com 2; Nav 1 and Nav 2 to the GF-166 along with DME 1 and 2 to the GF-45. The remaining two buttons are currently used for the magneto positions, allowing me to start the engine without using the keyboard. The lower GF-P8 assigns Transponder, ADF, AP Settings and Instrument Settings to the GF-45. The remaining four buttons control Autopilot Master; Altitude Hold; Heading Hold and Nav 1 Hold functions. The buttons on the GF-166 control active/standby frequency toggle plus NAV 1 & 2 Ident.

The cockpit layout and aircraft controls.

As well as the control surfaces, the CH three-lever yoke operates the throttle and mixture, flaps, trim and parking brake. The centre lever (normally used for prop pitch) is not used at the moment.

To the left of the yoke is the Main Switch Panel, a GoFlight GF-T8 toggle switch module. As there was not enough room to mount it below the main panel (it sits where the circuit breakers should be) I had to make a mounting for it: it could not be mounted flush into the panel due to the support frame behind. From left to right: Alternator Master; Battery Master; Avionics Master; Landing Lights; Taxi Lights; Nav Lights; Beacon/Strobe Lights; Pitot Heat. The alternator and battery master switches will be replaced by more appropriate switches at a later date.

The Avionics Stack

GF-P8 assigns Com and Nav functions to GF-166 and DME to GF-45
GF-166 Versatile Radio Panel. Controlled by the GF-P8 above this device acts as Com 1, Com 2, Nav 1 and Nav 2.
GF-P8 assigns ADF, XPDR, AP and INST functions to the GF-45, along with autopilot master switch and functions.
GF-45 via GF-P8 above acts as ADF, XPDR, AP and DME 1 & 2 (via top GF-P8)
IPAQ Pocket PC running Memory Map Navigator software. This moving map display uses CAA digitised 1:250,000 and 1:500,000 aeronautical charts with GPS data supplied from FS2002 using Pete Dowson’s GPSOut utility.

WidevieW System

During the construction of the panel I carried out some upgrade work on the WidevieW system, building a new server and making the front view a client. This enabled me to reduce the work the server had to do by not displaying high resolution and quality graphics – all the sliders were set at minimum and FS was run in a 640x480 window.

Schematic Diagram of the entire system. Note how the server no longer displays an outside view.

The current WidevieW system comprises a 3.1GHz P4 with 1GB DDR RAM running Windows XP Professional. The five clients are mostly 2100XP Athlon units with 512MB DDR RAM and GeForce 4 Ti4800 graphics driving 19” Iiyama screens. The clients all run Windows ME.

Each computer is equipped with an Intel PRO/100 Fast Ethernet NIC connecting to a 16 port unmanaged Fast Ethernet switch. TCP/IP is used for file sharing, and WidevieW runs on the IPX protocol. Not shown in the above diagram is the file server, not actually integral with the WidevieW system. This holds a complete copy of all the add-on scenery and scenery config in a shared folder: any additions to the scenery library is added here first then copied to all the WidevieW PC’s via a mapped drive. This ensures all the computers in the system have an identical scenery library and layering – very important to ensure identical views.

Connected to the server (or flying PC) via USB is the TRC Central Control Unit, the GoFlight avionics and the CH Yoke and Pedals. All the GoFlight units are connected into a high power USB hub, with the controls and TRC CCU plugged directly into the PC’s ports. The iPAQ is connected via a 115200 bps serial link into COMM 1.

Operation and Flying

As the system has evolved, so has the complexity of operation. As the startup and shutdown sequences have to be performed in a specific order I have created a simple checklist for the purpose. From cold it takes around 10 to 15 minutes to make the system flyable.

The Startup and Shutdown Sequence Checklist.

A typical flight proceeds as follows. Firstly the master power switch is set on providing power to the entire system. The monitors are then switched on (if they are left on there is quite a power surge when the master switch is turned on). I then check that the LED on the TRC Central Control Unit is steady red – if the LED is flashing the unit still has an active configuration which can prevent the instruments working correctly when the link to FS is started. I then check all the USB connections are secure for the GoFlight units.

After the initial checks each computer is switched on, and TRC CCU power supply is turned on. FS is then started on each PC (six of them!) and the weather is set on the server. After setting the time the default flight is started on each PC (normally saved from the previous flight), and as all my flying takes place within the area covered by the Visual Flight/GetMapping VFR scenery volumes it can take several minutes for the flight to load.

Once the flight has loaded on the server I start the TRC Link software that links the CCU with FS, via FSUIPC. As the panel boots, each client has to be set to WidevieW client mode with blocking mode (WidevieW Config). If the computers are left as clients at the end of the previous flight it can take over 10 minutes just to load the flight in the VFGM VFR scenery areas, and sometimes they can get stuck in a loop and not start at all.

After the clients are set the altimeter correction has to be adjusted on the TRC Link software – the altimeter does not auto zero, and may be one or two thousand feet out at startup, although it is always complete thousands. The sub base unit under the seat is switched on, and finally WidevieW is started on the server. This loads the current server weather on the clients and synchronises the time. At last it’s time to go fly!

Once “in” the aircraft – always the RealAir Simulations 172 re-registered G-JHML – it’s time to pre-flight and fire up the engine. After checking the parking brake is set the battery master is switched on followed by the beacon. When the aircraft is fitted with a working fuel selector I will switch the fuel on at this point, but for now the fuel is left on “both” at all times. The throttle is opened ½ an inch, mixture full rich, and after a virtual “Clear Prop” I advance the magnetos until the engine fires into life.

Checking the oil pressure, I set the RPM at around 1100 for the warm up then flick on the alternator and avionics master switches. The radios and selector buttons are then all checked and set, clock set, altimeter subscale set, DI synched with the compass, and after another check of the T’s and P’s it’s time to move to the engine run up area.

The airfield I usually fly from is Eddsfield, a small grass strip in East Yorkshire. As I can be pretty sure there’s no other traffic about I usually do the run up at the threshold, a short distance from the parking area. Setting the parking brake the RPM is gradually brought up to 1900, and then the magnetos are checked: first the right on its own, then the left, looking for about a 50 rpm drop (it never really varies from 50 rpm but it’s good practice for the real thing!). The throttle is then retarded fully for the idle check before setting at 1100 rpm again. The final cockpit checks are made (trim, flaps, fuel, mixture full rich, T’s & P’s), landing lights on and a virtual blind call on the Eddsfield frequency to announce “Golf-Mike Lima ready for take off runway two-seven, right hand circuit to full stop landing” and we’re away.

The parking brake’s released, and counting to three the throttle is advanced to fully open. Keeping straight with the rudder and holding the weight off the nose wheel with some back pressure on the yoke we soon reach 55 Kts on the downhill runway, and the aircraft gently un-sticks. Holding off just above the strip I let the speed increase to 75 Kts before climbing out over the fence. The after take off checks are completed (flaps, throttle full, mixture full rich, airspeed, T’s & P’s) and the aircraft is trimmed for around 75 to 80 Kts, switching off the landing lights at 500’ AAL and turning right for the crosswind leg.

The climb continues to 1000’ AAL where we level out, reduce power, turn downwind and trim. A quick scan of the engine instruments to check the T’s & P’s, the throttle and trim is adjusted to maintain around 90 Kts, and a downwind call is made when abeam the 09 threshold. As we pass the 27 threshold I reduce speed to 80 Kts and re-trim, before turning base when the threshold is about the eight o’clock position. At this point the first stage of flaps is dropped and the aircraft re-trimmed, then the landing checks are completed – fuel, altimeter, DI, mixture full rich, T’s & P’s, brakes off and landing lights on – and the base call is made.

By this time the speed has dropped back to about 70 Kts with the first stage of flaps, and a slight reduction of the throttle pitches the nose down to commence the descent. At about 700’ AAL the turn to final is commenced, lining up with the runway at about 550’ AAL and dropping the next stage of flap. I trim the aircraft for 65 Kts and call “Golf-Mike Lima final Eddsfield two-seven”. If the wind is light I may drop the last stage of flap at about 300’ AAL and re-trim. The throttle is hardly touched during descent unless large corrections in the approach path are required. Airspeed is controlled by pitch, and once trimmed the aircraft will almost fly itself right down to the threshold.

As we approach the threshold I ease the nose up slightly aiming for around 60 Kts over the fence. The flair is initiated, and the aircraft held a few feet off the runway until the airspeed decays (this is easy with the peripheral vision from the side views). Just as the stall warning sounds the aircraft lightly settles onto the runway, and I keep the nose wheel off the grass and gently ease it down as the speed reduces. Once all three wheels are on the ground the aircraft comes to a stop with little or no braking required.

As there’s no taxiway at Eddsfield I turn to backtrack the runway, running through the after landing checks – flaps up, transponder standby, landing lights off and taxi lights on – on the way. At the parking area the parking brake is set, RPM set at 1000 to cool the engine, avionics master off, mixture idle cut-off to shut down the engine then turn off the magnetos. Once shut down the beacon, alternator and battery master switches are turned off and the flight is complete.

As you can see from the above the realism of the system is absorbing, and you feel like you are actually flying. With the peripheral vision the feeling of motion is quite surprising – some people who have flown the system for the first time have actually felt slightly nauseous! You pay far more attention to real instruments than those displayed on a screen, and because most of the systems are in place you tend to follow accurate procedures. It’s not the sort of setup you can jump into for a quick flight as there is so much preparation, and as a training aid for real world flying I personally find it invaluable.

Once the flying is over the system needs to be shut down correctly following the checklist. The most important thing is to reset the clients to server mode, otherwise the next session can take a very long time to start.

The Future

As with all projects like this it's never really finished! I'm very happy with the system as it is at the moment, but improvements could be made in areas such as trim and flap control, yoke and pedals, throttle and mixture, magneto and starter switch... the list just goes on!

The development of WidevieW progresses, and to keep up with new features the inevitable switch to FS2004 will eventually happen as any further developments for FS2002 cease. On a system such as this upgrading to a new sim version cannot be taken lightly, and compatability issues can become a real headache. For the moment anyway I intend to stick with FS2002, and when the time is right to upgrade I'll document the project - watch this space!

More pictures and info here.