Start Circuit Test

Time: 0.5hrs

I put together a test circuit of how I’m thinking of doing the start circuit wiring for my Sling. The issue is that I’m not totally sure if I’ll be using the Rotax 915 (which isn’t available yet) or the standard 914. If I use the 914 then the typical master switch (keyed or not) and an aviation start switch could be used in place of all this. It would take a little less panel space and simply things a bit. However, if I use the 915 then a standard aviation switch can’t be used since it will use electronic ignition. The problem comes down to this. If I end up getting the panel cut and installed and then I choose to use the 915 then I need to rework the panel and probably get a new one and cut with different holes and layout. This circuit though would work for both engines so I’m thinking it may be the safest route, plus you get the cool glowing start switch. I also like the idea of the keyed master. If I have the key then I know I turned off the master.


I made a quick panel mock up to hold the switches. I mentioned in the video that the master solenoid is incorrect. I purchased one that needs power supplied to the coil to operate rather then just simply grounding the coil. Not a big deal, but typically you use the later as your master solenoid. The actual circuit can be found on the Resources page. It’s actually very simple, it just looks a lot worse with all the clip leads being used.

Here’s a short video that shows the circuit working. Sorry I suck at making videos and this is actually the first time I’ve every posted anything on line.

It’s been a while

Well I still don’t have my parts so I’ve been working to clean up the electrical diagrams and panel layout. I created a bunch of new objects for the panel so it’s looking pretty close to what it will look like in reality. I’ve also been contemplating whether I will wait for the 915is or use the 914UL. In either case I’m trying to design the electronics and panel so that it can easily accommodate both. For example I added separate mag switches rather then use the aviation type start switch. This layout will work with the mags on the 914UL or the A/B ignition units (ECU’s) on the 915is. I also like the idea of having a keyed master switch rather then a simple switch.. if I have the key then I know the master is off. This idea is used on the Sling 2’s that use the 912is and I didn’t like it as first, but now that I think about it more I kind of like it. The one thing I don’t like about the Sling electronics design is that they put the full load of the system through the master switch. I’d rather do the more traditional Battery Contactor and use a low current switch. For this reason I couldn’t find a keyed switch that was both the master and the start switch so I opted to do a separate start switch, but the cool part is I can use one that’s illuminated and it’s pretty easy to make the light come on when everything is switched on correctly (mags, master, etc) for the engine to start. Also I’m thinking of installing capacitive fuel level sensors in addition to the resistive floats. If I do I’ll need another way to read that level so I added in the separate 2.5″ gauge for that. Once I figure out which one is more accurate then I can wiring that one into the Garmin GEA24. I’m thinking maybe to put the separate gauge in the throttle quadrant so that if I don’t want to keep it I can just replace that part and not have a hole in the instrument panel.

Here’s the new panel layout.


Here’s the PDF of the electrical diagrams. Just email me if you want the Visio since WordPress won’t let me upload that file type


Search for things to do

Time: 2 hr

Did some random stuff on the plane in an attempt to keep busy while I wait for my parts.

Things done today:

  • Ran wiring for AP servos
  • Drilled out two holes for battery reinforcing bracket
  • Notched top of battery reinforcing bracket
  • Riveted battery reinforcing bracket to firewall
  • Installed a few rivnuts in firewall
  • Riveted top front rib
  • Put a few rivets in the seat rails
  • Installed M3 screws into throttle assembly
  • Installed edge grommet on rear bottom seat section


I did a rough run  of the wires to the roll and pitch servos (which I don’t have yet… Hey Christmas is coming so I can hope). I will daisy chain the power, ground, AP disconnect, and CAN bus from the roll servo over to the pitch servo. The roll servo also gets an extra 22-2 for RS-232 to the GMA307 AP Controller. The pitch servo will eventually have an additional (2) 22-2 runs for the pitch trim motor. The pitch servo is also the end of the CAN bus so will have to jumper some pins on the connector when I wire that up. I also need to install some adel clamps or the like to keep the cables in place.


I figured it was safe to install the battery reinforcing bracket. There were two holes that got covered by the top firewall reinforcing channel so I needed to drill those out. Also the bracket overlap the top bracket (grey bracket in photo) so I made a small notch in the battery bracket so it sits flat on the firewall.

I also received the M3 socket cap screws from BoltDepot today so I loosely installed those for the throttle stops in where I think they need to go. I added some heat shrink on the screws just so the throttle lever wasn’t hitting the threads of the screw. It took some experimenting, but what I ended up doing was to cut a piece of heat shrink and put it on the smooth end of a 7/64″ drill bit then heated it to lately shrink to that size. I then removed the heat shrink from the bit and slid it over the screw threads when installing the screw. I probably could have just shrank it right on the screw after it was inserted, but I was worried that for one the heat gun would bubble the primer and two the heat shrink would stick to the screw making it very difficult to remove the screw if I needed.


Installed some edge grommet to the seat belt holes in the rear seat bottom section. The paint came out pretty good too… not too bad for a table in the back yard with a can of rustoleum from HD.

Carpeting and mockups

Time: 3 hrs

Things done today:

  • Covered the rear under seat close off panels with carpeting (speaker cover)
  • Made cardboard/wood mockups of various remote avionics
  • Worked on figuring out placement of avionics

I’ll be heading out to San Francisco on Thursday to do the Napa Ragnar 189 mile relay so I won’t be working on the plane much this coming week. I’m hoping to get a few hours in on it before now and then. I want to try to get the first coat of grey paint on the seats before I leave.


Some mockups of Garmin avionics that I made from what I had laying around. They’re a tad bit heavy so tape doesn’t like to hold them in place for too long. I made them the size that includes the connectors so I can fit they somewhat close if needed and not have to worry if the wiring is going to get in the way. It was good to see what some of the avionics is going to be like. I really wanted to mount the Transponder under the rear seat but there’s just not enough room.


Proposed placement of the avionics. There’s not a whole lot of room. I think the GTR20 (Comm 2) and GTX45 (Transponder) will have to mount on rails. I’m thinking I may be able to mount them on the right side one on top of the other, but the way pictured should work as well.


Pretty happy with the way this came out. I used Krylov adhesive which may not be “industrial strength” enough for this. I order some V&S 2028 Industrial Adhesive from which may be better. The Krylov isn;t bad, but I’m sure the kids feet will catch and edge and start sealing the covering off.


Panel Mock-up

Downloaded X-Panel software to do some panel design. The software is pretty decent though I’ve found a few bugs already. The big bummer is that even though you can print out full size technical drawings of your panel it says to not use them for cutting the panel. I suppose if you verify the measurements for accuracy then you’d probably be OK to use them. I was planning on loading this into a CNC FlowJet machine and having the main openings in the panel cut. Well still a long ways away from having to worry about this. Anyways here’s what I came up with so far. I had to create the AirMaster AC-200 and Garmin GMC-307 equipment so if anyone needs those for X-Panel just let me know and I can send them to you.


Preliminary Electrical Drawings

I’ve been working on some Visio diagrams for the electrical. Not sure how much of this is going to change, but have been learning a lot about the avionics in the process. It seems like the Garmin G3X is going to come out a little cheaper then some of the others out there, plus I’m familiar with the G1000 and 430 as well. The big cost is the certified GPS unit (Garmin GTN650), but I really want to be able to do some light IFR in this airplane (we don’t get too many storms here in SoCal, just marine layer). I’ll be using a Vertical Power VP-X Pro which has some good and bad points. Also am still working on how to do the charge system. I read that you can run the two alternators (well generator and alternator) at the same time to increase capacity. What I’d also like to do is be able to disconnect the 18A generator (hence the charge relay) to just power the engine electronics and main fuel pump should there be any issues were I need to isolate that from the rest of the electrical equipment. I used the Rotax and Sling wiring diagram as a basis, but not really sure if this approach is good or not.

Sling 4 Wiring