16 Jul 2016 - Auto Pilot Wiring

Today I think I have come very close to finalising the autopilot wiring. I say I think as I am on about the third major revision of this.

On finally getting on to wiring up my servos which I bought years ago to do the physical mounting work; I found one was misbehaving when I tested them in the system. After consulting with my supplier (Mendelssohn Pilot Supplies) I was very pleased with Danny's prompt service and soon had news that I could return my servo under warranty - that's great service from both Mendelssohn's and Dynon thanks guys if you are reading this! So at the moment I am waiting for word back and am in possession of only one servo.

Here is a drawing of my auto pilot wiring scheme


I am installing two Dynon autopilot servos one for pitch and one for roll. The skyview system talks to them over the two twisted pairs (I think 2nd pair is for redundancy) that it uses on all other network nodes. The servos need an independent power supply each which comes from two channels of my VP-X electronic fuse system they also need a ground return which I decided to run back to the firewall forest of earths rather than ground locally at each servo. Finally the servos require an autopilot disconnect which is a common signal sent to both and is active low. This signal will come from one of three sources either P1 Stick Switch, P2 Stick Switch or Panel disconnect Switch. I am planning to splice the P1/P2 stick signals together in the wing central spar area before feeding the common signals forward to the panel - more on that later.

To get all these signals to each servo you need some sort of splice as outlined in the dotted lines on the diagram. I went for locating this close to the branching point in the aircraft under the P2 seat. I originally made my splice using 9 pin D-Sub connectors but found them rather large and difficult to secure together and mount. After the problems with one of my servos I also decided there was also potential for plugging one in the wrong position and then opted for Molex Minifit-Jr connectors as shown.

I made a couple of angles fitted nutplates to them and made a mounting plate:


I have learnt that it is easier to have nutplates facing forwards in these tight spaces just the two central holes are used to secure the plate the smaller ones are drilled in error (unintentional lightening holes) I may remake this plate if the cosmetics get to me but it will do for now.

Pop riveting the angle brackets in place was very challenging as there is very little space for the tool:


I ended up using a 08 screw and nut in the top right position (just visible) after a lot of cursing. I would recommend mounting further forward in hindsight. wanted this removable for access to wiring and also if I ever need to go behind the plate for an unforeseen reason; eg if a part rolled under there.


I then crimper and wired it as per the drawing using twisted wire solder joints with heat shrink for all the 3-node joints:



Then I cut to length and crimped all the cables that plug into here double checked the wiring visually for consistent colours into and out of the connectors:




Here is the final assembly in place.



The pitch servo runs out to the right on the picture into the central tunnel and the up aft to the servo.
The roll servo cable runs out to the right wing (to left in picture) and was terminated with 20cm of loose lead on a free hanging receptacle as I have yet to site the Panel mount Plug side in the wing root.

I also made up the length of cable that runs up in the wing and terminated the ends to use as a test cable for my one servo which I tested in both roll and pitch positions and worked OK in both. Hopefully I will hear back about my faulty servo soon and will be able to test both together but don't anticipate a problem.

30 May 2016 - Tail Nav Light and Strobe Wire Routing continued

So today I was carried  on with the tail light wiring.

I decided to go with a ground point on my left longeron as my wire run is getting a bit full in places.

I drilled out a rivet in a spot that looks convenient to get to but out of the way too. I tried tapping for an 8-32 screw but the hole was already too big so opened it out for an AN-3 bolt thread tapping size.

I didnt have a tap for the AN-3 bolt and I really want a good electrical connection through the threads so unwilling to let that stop me yet again I made one from a bolt by first tapering the end on my lathe then cutting flutes with a grinder. Tested it on some scrap and then went for it.

The wire was terminated with a ring crimp and I added a couple of washers to make up the thickness for the unthreaded section of the AN3-3 bolt I used this was fitted below tightened up in the longeron thread then a nylock was added to the top to lock it off in my home-made thread.

Before cutting the wire to length I ran the full length rool of wire back to my earthing point at the firewall and did a conductivity test - Looks good to me.

You can see my VP-X Electronic Circuit Breaker System just behind and my forest of earths shorted onto the firewall and this is connected directly to the batter negative on the other side.




Well that is one less wire to run but I haven't run the strobe sync signal wire yet so time for some fuselage diving.


Above is as far as I need to go as I can reach the rest from aft you can see the black white wires leading to my outside air temperature probe that I have located just under the tailplain on the right side.




Above my hand is the anchor point for the passenger shoulder straps and below is the standard install for one of the two static air vents. A tube stuck on a pop rivet which has it's centre knocked out then glued in place for security.



I made little clips and riveted them in with the skins in the more forward section getting a bit full now.

Finally cut the wires to length and terminated them in a 4-way Mini-Fit Jr connector. They need to be long enough to come out of the rudder fairing to attach the connector but not so long they might feed back and obstruct the rudder movements in the hinge area.

29 May 2016 - Tail Nav Light and Strobe Wire Routing

Today I wanted to end up with wire runs completed for the tail lights that's going to be a Navigation position light and a strobe light.

I haven't purchased anything yet but I know I will need two power wires and a ground return and possibly a strobe sync signal wire too so I need a four pin connector.

I decided to make a hole in the aft bulkhead right of central in the lowest rudder hinge bracket. A place used by other builders too. I fitted a snap bushing, The wires are going to run over the top of the fiberglass rudder bottom fairing so my plan was to cut this away more to clear the wires for full deflection of the rudder. I also planned to slide on extra protection in he form of some air line which would guide the wires through the gap and restrain them too.

Tail Lights Routing

The snap bushing is out as it is a tight fit and compresses the tube and makes threading the wires difficult.

I made a second hole in the next bulkhead for the bulkhead for the wire run and used the tube to guide the wires passed the right rudder control wire.

These wires are running down the right fuse side

note the small green bracket in the aft end I made to support them on route.


Under the passenger area they go via a connection block to similar wires which will run to each wingtip and will be fed from behind the panel routing through the footwell centre tunnel.

I have yet to decide to run a ground wire or use the aircraft structure. A good site for the tail lights ground point would be at a removed rivet point on the longeron here:

Proposed grounding point

It would offer reasonable access and good conductivity.

The reason for not doing this is I came up against an unexpected snag. My rudder bottom does not clear the exit of the tail wheel spring tube. I am building a tail dragger and it looks like these parts are cut for a RV-7A with the nose wheel.

It looks like I need to trim a taper section off the rudder bottom for tail wheel clearance.

 Time to re-read the instructions for the rudder and/or phone a friend...

28 May 2016 - More Trim Servo Work

Wanted to take the tailplane off today for storage and remove the elevator from it. When I came to threading my new connector out I discovered the hole was too small in the trim tab so had to take all the pins out to remove it.

After measuring the diagonal I decided to open out the hole. Some have made a separate hole to avoid having the jack screw sharing the hole and coming close to the cable. If I use the same hole as is standard, having a bigger hole can only help.

I found my 3/4"step drill bit would just fit through the slot in the leading edge of the trim tab and having a hex shank I could extend it.

Deburring the hole was more of a challenge. Here is a pic of the servo jack screw and the servo cable sharing the enlarged hole.

I have become an expert a removing the Sero assembly from the trim tab now. The big tip is you must fully wind the servo jack screw into the servo before disconnecting it. Fully in = fully down on the trim tab. Then you have the problem of an elevator with a trim tab in the fully down position if you want to store it. I made a 6 pin mini fit Jr extension lead that I put on to enable me to straighten it up after putting the servo back in for storage.

Back to the Aileron servos. Instructions call out for Safety wire for the linkage to the springs. I am not too keen on this and may re-make later using RC servo linkages and piano wire (as others have done), when I aquire the parts so for now a trial run with undersize wire to help me decide.

But for now I followed instructions but added heat shrink.

• With the stick central set the servo central over the center pitch crank bar.
• Everything is symmetrical so linkages should be the same length.
• You need to choose a length that so the springs never go slack on one side and start flapping about with full side sick applied.
• I found 8cm seemed about right for both sides.
• Made my first wrap for the spring side 3cm long and heat shrinked
• Slid other sides heat shrink on
• Measured and formed a bend at 8.5 cm (0.5cm taken up in twisting)
• With wrap removed from spring threaded wire linkage onto servo tab and twisted it
• slide heat shrink up and heat shrinked second end.
• Mate wire link with spring
• Repeat for other side.

Everything Central

Central servo with full left stick

Central servo with full right stick

When I get the correct size locking wire or RC servo linkages I will take a look at the unlikely event of full left trim full right stick later when I have aileron limits fixed as I don't want to over extend my springs.

Here is a video clip of the effect of applying trim full each way. Rather shaky as I am using a phone and operating the SkyView at the same time:

Next I want to finalise wiring for the tail light I havent got. I am running a strobe and a Nav
 Position light to the rudder bottom position.

It is interesting that there are precise light angles specified for the light which means you cant use any old light but then you mount it on a moving part! Seems like we ar paying alot of money for aircraft spec parts for no good reason here.

To measure and mark things off with the tail and on with The Fin and Rudder

You cant fit the bottom fiberglass rudder fairing to the rudder with the rudder fitted so of and on again.

Need to find a spot for the wire penetration. Some have brought them out just above the faring so need to mark up that spot.

It is a bit close to top of hinge bracket, I may cut some meat off the fiberglass and drop it a little.

Some builders have made a hole much lower down and made another slot in the fiberglass for the wire. I will sleep on that decision.

27 May 2016 - Aileron Trim Wiring, Final Fit and Calibration.

Today it was the turn of the aileron trim.

Nut Plate Brackets on the Aileron Trim Servo

First I dug out my parts and assembled the servo and linkages. I didnt relish the idea of struggling with the supplied small nylock nuts while contorting and levitating in the confines of the cockpit so I made a couple of  brackets with nutplates to make the job easier.

I final assembled the servo linkage assembly:




Then I attached a connector just like the one on the Pitch Trim Servo in the comfort of a chair at my bench:




The next connector was made off in the cockpit floor and the assembly was fitted to the center section of the floor. Even with the nut plate bracket it is not easy working on this. Would definitely recommend spending the time making them




Tested it without the springs attached to the joystick plenty of travel from the white lever:

Full Travel For Right Wing Up 

Mid Position

Full Travel For Left Wing Up

As for the Pitch trim you need to calibrate it befor the position shows up on the widget this time I took a few snaps. Poor quality due to glare and protective plastic on screens but you get the idea:

Aileron  Trim Widget Before Calibration

Calibration is done with Skyview while moving the trim servo










And now I have a working widget indicating both Pitch and Aileron trim with green takeoff indicators visible too

Functioning Trim Widget

You can see I have already got my flaps widget indicating too - I will post a few snaps of the installation shortly when I finalise the wiring for it.