Having finished setting up the forward structure, I decided to scale back my project slightly. As I had the galley and the lav, I had planned to use the full length of the remaining floor to extend out the back. When I saw how much space the forward section occupied, I decided to stop the sim at station 277, which is about 8 inches behind the cockpit door frame. This will leave space for a combination of shelves and remote displays mounted aft of the circuit breaker modules on either side of the door. I plan to leave some of the Boeing structure exposed so that visitors can appreciate the engineering.
Station 277 turned out to be about 18 inches aft of the section I had set up, so I spent a few days cutting the aft section pieces down to this uniform length. I reassembled the previously divided floor with screws and nuts, then built up the ceiling in four sections. The reassembled structure came within about 2 inches of my basement ceiling, so it was definitely a good place to stop.
I had a lot of leftover aluminum structure that was aft of station 277, so cut it into small enough pieces to fit in the bed of my pickup, and drove off to the scrap metal dealer, who gave me 40 cents per pound. I’ve decided to sell the galley and lav on eBay. It will be interesting to see if there’s some other person crazy enough to want these things.
The next phase of the reassembly involves shoring up all the structural connections in the cockpit shell. In total there are eleven major sections, and I took advantage of existing rivet holes whenever possible to allow for precise realignment. For the connections between the sides and flight deck, I used steel mending plates of various sizes found with the hinges at Home Depot. The resulting assembly is very solid, with virtually no movement between pieces.
The real test of the fit will come when I mount the circuit breaker walls and the cockpit door, but that point will probably not come for several months yet as I have to mount a lot of avionics before I close up the back. Next up: fitting the main instrument panel and mating the bottom of the Boeing FMC bay to the top of the FDS one.
In this post I will describe how I figured out the wiring diagram for a real Boeing 737 landing gear lever mechanism, including the solenoid and Korry lights.
I’ve seen (and even owned) several landing gear levers that were designed and marketed for the home simulation market, but they just don’t have the heavy tactile feel of the real thing, and I’ve never seen any that have a working solenoid or override lever. The cockpit I bought fortunately still had the original gear lever still in place, complete with the six Korry annunciators that serve as gear position/transit lights.
The solenoid is a 28 volt device that, when energized, allows the lever to be pulled up to initiate a gear-up cycle. In the real aircraft, a number of logical conditions must be met for the solenoid to be activated, which prevents the gear from being raised while the aircraft is on the ground. The gear handle itself is equipped with an override trigger that allows to pilot to raise the handle in the event that the solenoid fails.
The solenoid wiring was easily determined as there were only two wires, one of which had to be 28 volt and the other a ground. The position switch wires were also easily traced back to the cannon plug. I was surprised on initially removing the assembly that only the gear down position had a switch installed. Although holes were present for mounting a gear up switch, the switch itself was missing. I can only assume that in the real aircraft the up position is read somewhere along the cable that runs to the actuator. For my simulator I just added an identical switch scavenged from another part of my project.
There are several manufacturers of annunciators for the home simulation market, but once again, there’s nothing quite like the real thing which have the press-to-test function available.
The wiring of the model 319 type 1 Korry annunciators have been described by David Allen. These are ground-seeking type circuits with 4 terminal lugs. Terminal 1 is the 28 volt input voltage. Ground terminal 2 to illuminate the indicator. Terminal 3 is grounded for a ‘test all’ function that lights the indicator, but extinguishes the light when pressed. Terminal 4 is grounded for a press-to-test function.
The wiring scheme is as follows:
24-pin cannon plug:
Pin 3: common to all terminal 3’s (test all function)
Pin 4: nose red terminal 2
Pin 5: nose green terminal 2
Pin 6: right red terminal 2
Pin 7: left red terminal 2
Pin 8: right green terminal 2
Pin 9: left green terminal 2
Pin 10: common to all terminal 4’s (press-to-test function)
Now that the floor is level, it’s time to start building up the cockpit structure. The second forward level consists of three sections: left, right and center, with the vertical divisions roughly in line with the inboard rudder pedal linkage on each side.
All three pieces are made of aluminum, but there are thick spars that Boeing designed to protect the pilots, and the sections are bulky and heavy. So I enlisted the help of Elmer and Andy, who came over to help me hoist these pieces into place. The sides were easy enough, but lifting the top onto the structure required some planning.
For some reason I must have been in a hurry on the day that I cut these some three years ago, because I completely neglected to make any indexing brackets. Not really a problem because the windows are structural, and I have an almost complete set of Boeing windows. By mounting these windows and using an awl to line up the bolt holes, I aligned not only the left/right/center sections but also the top to the sides.
At this point in the build I am rediscovering many items that have been in storage for a few years. I had an unwelcome surprise when I pulled out my windows to find what had been advertised as a full set actually consisted of two FO side P1 windows, a matched set of P2 slider windows, and only one of the P3 windows that I needed. Luckily there was a captain side P1 window for sale on eBay at a reasonable price, but the only source of an FO side P3 window is for new old stock at a somewhat less reasonable price. Through one of these window deals I wound up with an extra pair of P2 slider windows, so hopefully these will fetch a good price online and allow me to purchase what I need. For now, I plan to use the captain side P3 as a template to make a plywood insert for the P3 window opening on the FO side. Even the full-motion level-D sims black out these rear windows, so I don’t feel like I’m detracting from the experience by doing this.
Having overcome the major hurdle of implementing dynamic force feedback, I have been busy performing other tasks that will be most easily accomplished while the floor remains in vertical position. These include wiring the brakes and stick shakers, as well as rewiring the throttle quadrant with salvaged AMP cannon plugs that allows the interface cards to easily detach from the mechanical parts of the unit. I used a 55 pin plug for the switches and pots, and a separate plug with larger 16 gauge pins for the power connections.
I spent at least a week going over the underside, testing all the functions and tidying up cable runs. Once this section is put down into its final horizontal position, there will be only 20 inches between the flight deck and the floor of the basement, so I will still be able to get in and work on things, but it will be a lot less convenient and probably a lot more likely to induce neck and shoulder pain. Twenty inches seems like a lot, but that’s the distance from the flight deck to the floor, and there are a lot of mechanical parts in between, such that there won’t even be room for a creeper.
The day finally came, and after one final cleaning, I cut the heavy cable ties holding the floor section to the ceiling joists above, and started sliding the section as far forward as it would go in the room. I called my buddy Adrian, a senior F/O at jetBlue, to come over and help me lower it. I figured it would be pretty easy for two of us to lower it down, as it seemed to me that most of the weight was concentrated in the yoke and rudder mechanisms located fairly far forward. It wasn’t that hard, but the aft end was quite a bit heavier than I thought. Luckily Adrian’s fiancee Kelly, herself a Captain and check airman at Frontier, was there to help place the aft floor supports, which I had made from short sections of 6×6 and 2×6. Once we got it down, a quick check revealed that the flight deck was perfectly level in all directions. Looks like my cuts and indexing were precise enough!
I know, I know…it’s been over a year since my last update. I have been working on implementing dynamic force feedback, a slow but steady process that required designing, and sometimes redesigning, custom made transmissions for driving all three control axes.
I am happy to report that I now have all three axes working after a great deal of calculation, consultation, and trial-and-error experimentation with various transmission designs intended to mate the BFF do-it-yourself force feedback interface cards to the original Boeing flight control structures. There were several examples of such implementations out there on the web, most of which involved expensive custom gearing and none with an original 737 mechanism.
The designer of the BFF cards is extremely helpful with the installation and operation of the cards themselves, but leaves it to the simulator builder to come up with the proper mechanisms for driving the controls. My first step was to consult my pilot buddy Andy Schwartz (of the mechanical engineering firm SSA Engineering) for some badly needed help with the engineering. Armed with some actual Boeing flight control tension specifications from David Allen, Andy confirmed that the specified motors, gears and belts that I had dreamed up would supply the required forces at the man-machine interface.
The BFF card designer specified a particular motor from an Italian manufacturer, which does not accept credit cards, Paypal or Bitcoin and required an international wire transfer for payment. The motors themselves arrived almost a month later, and only then was I able to start designing custom motor mounts to fit onto the existing Boeing structure. One of these was fairly simple but the other two were complex shapes that required some time to fabricate using my old friend, the electric 4.5 inch angle grinder. After cutting the shapes from 3/16 inch steel plate, I cleaned up the sharp edges with a polishing disc attached to the same tool. As the steel was not stainless, I applied several coats of gray primer to prevent corrosion before installing into the floor structure. The motors themselves were mounted through a hole drilled in each plate. A rubber/cork gasket cut from a sheet obtained at my local auto parts store was used to help reduce noise and vibration from the motors. A large number of fasteners was used for each mounting plate with the same goal in mind. The largest plates, the one used for the pitch and roll axes, serve double duty as structural supports since they cross the midline and connect and maintain the proper spatial relationship between the two halves of the divided flight deck floor.
Having finished mounting the motors, I was able to start the task of wiring the cards. Ian provides extensive instructions with the cards, and suggested an inline circuit breaker for each axis to use as a ‘kill’ switch in the event of undesired behavior. I happened to have about ten 28-volt circuit breaker switches lying around as a result of the circuit breaker switch airworthiness directive that became effective for piston Beechcraft aircraft in 2010. The FAA forced operators of these aircraft to replace thousands of these switches with newer models after a few reports of failures and resultant smoke in the cockpit episodes. So I chose three of these with appropriate amperage ratings and installed them in an existing structural support under the FO side left rudder skid. I left enough slack in the wiring to allow them to be repositioned to the underside of the main instrument panel after that component is installed later. These switches are not airworthy per the AD, but perfectly functional for this purpose.
I would have preferred to have mounted all three BFF interface boards somewhere above the flight deck to facilitate their maintenance, but practical concerns prevented me from doing so. Because the motors have integrated position sensors, the signals carried by the small gauge wires back to the interface boards are very low voltage and Ian recommends not extending the shielded wire bundles coming from the motors. The cable bundles are short, no more than three feet. As there are also large heat fins on the cards, they could not be located in an enclosed part of the cockpit without complex cooling systems including ducting. So I had no choice but to mount the cards underneath the floor in areas that would be relatively accessible with a mechanic’s creeper.
The BFF cards can be daisy chained together in order to allow the use of a single USB interface cable. This is advantageous because the boards were designed to use a specialized USB PICAXE cable that uses a 1/8 inch mini stereo jack that costs $30 and must be ordered from the UK. The software identifies the different control axes by the use of jumper pins that are set on each board. Ian recommends that all three interface cards be co-located, so that each length of daisy-chain serial cable between boards are no more than eight inches to eliminate noise. I could have achieved this by mounting one card above the roll axis motor mount plate, but this would have made it very difficult to access from the underside, so I elected to purchase a second PICAXE cable to allow me to locate one interface card about 12 inches away from the other two. As also recommended by Ian, I installed two cooling fans, one for the pitch axis and one that is shared by the roll and yaw axes.
It took a few weekends to cut, crimp and run all the wire between the wall outlet, power supplies, and interface boards. I took advantage of some existing Boeing light fixtures used by mechanics when accessing the forward flight control bay, using another old Beech circuit breaker switch in the process. I will be happy to have these lights operational the first time I have to venture under the flight deck on the creeper.
When I first applied power and fired up the BFF test software, all three axes moved, but not very much. After a few emails exchanges with Ian, I got the pitch and roll axes moving but it was clear the yaw axis, with the belt-driven design that I came up with initially, was never going to work because the motor needed to make at least 120 degrees of revolution in order to achieve initial calibration. So I elected to relocate the yaw axis motor from the midline to a place just outboard and forward of the rudder crossover linkage. I was hoping to build a transmission with spare parts on hand, but a brief experiment with direct drive with a pushrod and the largest gear I had in stock resulted in the same problem: not enough rotation to pass the calibration routine. So I ordered two additional timing belt pulleys, fitting the small one to the motor and the large one to a custom fabricated shaft/plate assembly that attached to the Boeing mechanism. This replaced an original autopilot component made out of plastic, which was apparently designed to shear in the event of a control jam.
The roll axis is controlled by a motor mounted in the midline, fitted with a timing belt pulley and long belt with a number of flat pulleys to correctly set the tension. I was able to find some blocks online that were cut with the timing belt pitch, through which the ends of the belt were sandwiched. I then drilled a hole through the end of each block, passing an existing Boeing cable already connected to the aileron/spoiler controls.
This axis initially had too much slack to calibrate the motor. A call to David Allen revealed that there is a spring inside the FO side aileron hub that allows the Captain and FO side aileron/spoiler controls to decouple in the event of a control jam. Conveniently, there was a rigging pin hole in the mechanism used to immobilize the spring. After testing out what David promised me was true, I simply tapped some threads with a 3/8-16 tap, cut a countersink, and inserted a screw, locking the aileron and spoiler hubs together, resulting in a much smoother mechanism.
The pitch axis motor is fitted with a NEMA 34 planetary gearhead with a 10:1 reduction ratio, a simple, cost effective alternative to building a custom transmission. The planetary gearhead was then fitted with a large pulley which was then attached via a pushrod to a pair of existing tabs on the elevator torque tube.