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.

Testing Elevator Trim 26 May 2016

Testing Elevator Trim 26 May 2016

Today I fired up my system and tried out the Elevator trim. I dont have the stick wired up yet so used the controls through my Skyview unit. It moved up and down fine but the trim widget didnt reflect the movements.

After a lot of poking around and disassembly of the tail I traced the fault back to the D25 connector at my VP-X Sport. I had the blue and green wires swapped on both the elevator and aileron trims. Ray allen dont seem to document what the wires are too well and when I wired the connector I just used a reasonable wiring scheme and planned to copy it all along but then I would end up with a blue goes to green and a green goes to blue somewhere.

I decided to swap at the connector at the VP-X and stay consistent. this is not an easy fix getting the pins out.

Swapping Wires at J01 at the VP-X D25 Connector

I updated the drawing with the wire colours for later reference after lesson learnt:

Updated VP-X Schematic

I will share my full drawings when I have finalised them.

Bingo - I can now see data in my skyview. Spent a lot of time reading up on how to get the widget working. You have to calibrate it and set it to VP-X in skyview. Turns out you don't have to swap the up/down wires if you have them wrong as the calibration process sorts this out for you. After calibration you can see a little bar and a green mark for Take off trim too.

This may be the last time I open this D25 connector - the Spiral wrap is temporary as it would smoke if there was an electrical fault, it will be tied the old fashioned way with waxed line once I know I am done with it. 

So now the widget looks like this (2nd from bottom right:

Wiring Elevator Trim

Ok so my build project hasn't been the Fastest RV-7 Build in the world, but today I decided to turn over a new leaf and get cracking on what is left to do.

I also decided the reason for my stalled project was the lack of details on the avionics stage of the build, so I have resolved to document best from here on I can so others don't have to reinvent what I have done if they want to follow my example.


Wiring Elevator Trim 24 May 2016

Today I did some final wiring for the Elevator Trim.

The design was prompted by helping with an RV8 tail repair when the tailplane needed to be removed. Because of the wiring it was necessary that the the trim servo hatch was opened and disconnected then the elevators were split then the left elevator removed. Then the stripped down connector could be threaded through the holes before the remaining section of the Tailplane could be removed.

I decided adding an extra connector would be worth it even with the downside of an extra potential failure point. This would enable the entire tailplane to be removed in one piece.

Here is the extra connection fully installed:

Elevator Trim Connection

I made a little bracket to guide the cable up through the Aft Deck. This was from a strip of aluminium formed around a drill bit fitted with a nutplate. I used a few inches nylon airline to guide the cable and prevent chaffing.

I made another bracket with two plate nuts attached to carry the panel mount Plug. After spending an hour or two making it I found the hole for the plug was a little too big and the plug rattled about a bit so I backed up the push fit ratchet with epoxy glue to stop the rattling.

Others have used soldered or crimped 9 way D-types here. I chose Molex Mini-Fit-Jr. for the connector you are looking at the back of what they call the free hanging receptacle. part nr 39-01-2065 and this mates with the Panel Mount Plug PN 39-01-2066.

You can buy a kit of these connectors from RS/Allied here is mine with some extra 22-26 AWG Male/Female Crimp Terminals that you need for these smaller gauge wires:

Molex Mini-Fit Jr. Connector Kit P/N 76650-3011 with extra 22-26 AWG Male/Female Crimp Terminals

You will need also the correct crimping tool tool see in top right of next shot it is called an "Engineer PA-21 Universal Crimping Pliers" don't use any old crimp tool for this you will get unreliable crimps. It is a none ratchet type and sells for £20-£40 on amazon and Ebay.

PA21 Crimp Tool

Next I set about making off the connector and the wiring section.
There are moving parts all around here so the less unrestrained cable the better. fitting the trim servo assembly through the hatch is a challenge as there are mm of clearance if done in the correct sequance - have fun!

I decided on another bracket to restrain the connectors here. The only place to put it is on the back of the trim servo. There is extra heat shrink for the section that passes between the elevator and the tailplane.

Trim tab Servo Assembly

Trim tab Servo Connector Bracket

Spot the deliberate mistake - the tie wrap should pass under the latch clip which then stops the clip springing open even when pressed. Here it is over it which will release the latch.

Don't do this!

here is the servo fitted into the elevator

Threading Elevator trim wires

I fitted a bushing into the hole in the trailing edge of the tailplane and had to put two flats on it as it is a very tight fit - At least I know that will not work free and jam the elevator. Hole is too small for threading the connectors so had too make up pins and thread this way. you need tree hands for this offering up the elevator into the bearing joints whilst poking the wires  in through the small hole one at a time. Don't forget to have the elevator hinge pins to hand after you have done it too.
Note to self check why rear rivet hole is left open.


Here is a pic of my bracket with all pins pushed in. There are two white wires on this cable which I have designated servo up down. This is where I will come to swap them if they are wrong way round.




Now I need to produce an up to date drawing of this wiring...


Updated the Wiring Schematics 25 May 2016
So here is a draft of the wiring page for the elevator trim. This is a draft and I need to update the Roll trim details.

I have been using ExpressSch which is part of ExpressPCB this is a free design package that I have used elsewhere on this project to design circuit boards but more of that later.