Wayne, thank you for the response. Couple of follow up questions for you.

Re-grounding, for the autopilot servo's would you run a dedicated line for them or could I just ground to the metal frame?

Electrical connect/disconnect for the wings. Do you have a part number or link for the shielded connectors that you are talking about?

Finally, what aircraft are you building? How far along are you?

Cheers,
Matt

I’m building a Bearhawk LSA, the smallest of the BH fleet.

I’m not doing the autopilot, so I’m not much help there, but in general, the power ground to the chassis should work if the other end at the control boxes are also grounded to the chassis. I have a ground junction box right next to the master power bus that everything ties to.

One thing I learned from Garmin about the CAN bus wire, though. For a simple system, using the regular shielded MIL C 27500 should be fine, but for more complex systems, they definitely recommended the Gigaflight wire. The data traffic for a complex system could sometimes have trouble on the 27500 wire. With an autopilot, you’re getting into the complex system zone.

I haven’t picked the shielded connector yet but give me a little time and I’ll share where I am on that one. Basically a shielded DB-9 connector pair should work, but they are kind of big. I’m looking for something smaller, like a Deutsch sealed connector.

I bit the bullet and went with the Garmin recommended canbus wire. I'm probably going to introduce enough issues into the system as a first time builder that I didn't want a third party issue causing me issues when I was trouble shooting. Wire and equipment arrives on Friday, going to be an exciting weekend.

Excellent strategy. There will probably be problems and you don’t want to give anyone an excuse to run you around with someone else. Kind of like when Gateway computers wouldn’t talk to Epson printers: “it’s not our issue, it’s theirs. Have you installed the right driver? Oh we don’t know which driver you should use, you’ll have to talk to them….”

Figured I'd hit the brain trust up over here as the Kitfox forum doesn't have the traffic.

I'm planning my wiring. Installing a 915, G3X and a GEA 24 for the connection. I know if I hook up the CAN line from the rotax I get: RPM, Manifold, Manifold Air temp, Oil Pressure, Oil Temp, Exhaust Gas Temp, Coolant Temp, Fuel flow, ECU bus Voltage, Throttle position and Percent power. I was surprised CHT wasn't in there at first glance. This is my first experience with a rotax so I don't even know what I don't know. Coming from the certified world with a Turbo on a IO550 I would want Turbine inlet temp, All my CHT's, Current Amps on top of the others mentioned. Plus nice to have if it even matters on a rotax is Induction air temp and compressor discharge temp. I've used those in the past with some trouble shooting issues.

Am I over thinking this? Also, where is the best place to learn about operating a rotax? I took a flight yesterday and it was 28 degrees in the morning. I turned the pad heater on the night before and would never start my continental at that temp without preheating. Is that something I have to be concerned with on a rotax?

Appreciate all the help.

Having built / been involved in building a few experimentals, a few thoughts/recommendations:

1. Lockwood Aviation in Sebring, FL has tremendous expertise (as well as a full parts/maintenance operation) when it comes to Rotax. They are a great resource.

2. SteinAir (steinair.com) is a great resource for any and all avionics / wiring related needs. They have a very good online store, sell the absolute highest quality tools and products (like wire, crimpers, heat guns, strippers, solder sleeves, dsub pins/connectors, Garmin parts to build up connectors, etc). They have a series of YouTube videos that is a tremendous resource for doing all manner of avionics wiring. Not cheap but absolutely rock solid quality including full harness/panel builds for those willing to spend the $.

3. Vic Syracuse of Base Leg aviation (https://baselegaviation.com/) has done a series of books/videos on the fundamentals of experimental airplane building. Big focus on safety. Invaluable stuff - mostly focused on Van's but Vic has built at least one KitFox as well as many other experimentals including a helicopter.

4. AEA (https://aea.net/training/courses/basicinstall/) has a fantastic avionics course a few times a year near KC. They teach all the wiring skills needed to build up avionics harnesses with a focus on Garmin (including Garmin staff doing guest appearances) - includes a tremendous knowledge base/training on canbus wiring/gounding/troubleshooting etc, and a training manual that covers all the topics taught - I used it extensively as a reference.

5. Polyfiber is a great fabric system - helped with a build using this system. Another good system is called Airtech, based out of Arkansas. (https://airtechcoatings.com/) Lots of videos on the website to familiarize. (This may be what was referred to earlier in the thread as "Airtex"). I'm not as paranoid as others (as an ED doc with decent experience) about the "toxicity" of its solvent system. Do your own research - but mine says it's mainly a respiratory irritant with the worst toxic effects shown in those exposed to high airborne concentrations for long periods of time (or those dumb enough to ingest it). Good ventilation overcomes most of the issues. MY OPINION ONLY, make your own decisions based on your own research. I'm way more afraid of metals/metal salts used in airplane builds (lead, cadmium, mercury etc), take a great deal more care with those.

6. The most easily overlooked tools (in terms of quality) in building harnesses are strippers and crimpers. Get a Daniels (DMC) AFM8 (good ones used on eBay) and buy the right positioners (there's a brand sold on Amazon - JReady - that's pretty good, cheaper than OEM, but I wouldn't cheap out on the crimper itself). Get the good strippers and good coax crimpers on SteinAir's site, you will not regret it. Easy to sell the Daniels crimper when you're done with it, but I won't sell mine...

7. Molex/molex style connectors will cause pain and will be unreliable long-term. Where possible replace with better connectors. I'm a huge fan of Deutsch DTM (smaller size) connectors. Not cheap, requires buying some specific crimper tools (decent kit sold on Amazon) - or you can buy the right positioners for the Daniels crimper. These are similar to connectors used in high-end applications and include silicone seals to keep the water/salt out. I would not buy the cheap knockoffs (JReady), the good ones can be bought here: https://theelectricaldepot.com/deutsch- ... 5a8baec5ac

8. Bring all grounds that involve audio or avionics signals back to a single grounding point whenever possible (this applies to non-canbus stuff - as a digital bus, canbus rules are different). The Carbon Cub I helped build had a single ground point for this but I like the "forest of tabs" method better. Here's a photo of one pending installation:



9. Shielded wires mainly protect from higher frequency signal leaks into/out of wires - not as effective for low-frequency magnetic induction. The best way to protect from magnetic induction is twisting the wires (or buying twisted multi-conductor wires: twisted/shielded is belt and suspenders, at a cost of weight). It's important to understand the difference between high frequency (audio/signal) interference and magnetic induction (not to mention digital vs analog signals/wiring) in wiring applications.

PM me if I can be of assistance. Not an expert on KitFox by any means but I know the fundamentals and have a particular interest in avionics / wiring related topics.

Not familiar with Rotax, but they have water cooled heads so CHT is probably not as critical to monitor. It probably has a water temp input, right?

8:50’s are a great compromise size for that plane.

Yeah I got that wrong. AIrtech is correct name for the fabric and paint process not Airtex!

Thank you for the super helpful post. I sent you a PM as well.

I think you are probably right on that one given the water jacket for cooling.

I think that is where we are going to start given it's my first tail wheel. I think it will be a while before I'm going to need a bigger tire based on where we are trying to land it. Pavement and manicured grass is going to be my wheel house for a while.

Matt

8.5's will do a hell of a lot more than manicured grass. Before the big balloon tires came on the scene, that was the go-to tire on a lightweight plane for pretty much anywhere.

if you are sticking to pavement & cut grass, then try a 6x6, no point in lugging around any more weight than you need