Kitfox Series 7 Super Sport - Show Me Fox

[Jason Murphy]

10 ga is overkill for the pitot heat. You will probably have difficulty terminating that large of a wire. I think 14 ga is commonly used with a 15 A fuse or breaker.

Yeah yeah yeah. They've always worked well for me as long as I don't ask them to do something they weren't designed for. Just kidding with you Harlan

Yup. The Stewart brothers who started the company still live close by. Really good guys who are willing to share their experiences.

These comments are right on Jason. I used 14ga on mine and it works perfectly as far as I can tell. I say that because the controller varies how much current actually goes to the heater based on OAT. I'd be really surprised to ever see the system ask for full current but even if it did, 14ga is good. While I don't expect to fly mine in that kind of cold where I need a lot of heat, my training was that if you flew into rain - turn on the pitot heat. Doesn't take a lot of heat to deal with the rain but still helps keep water out of the system.

Like Alex, I love how your kids are involved in the build. The time spent now are the memories you have later. Those are priceless.

Geek

Agree. 10ft of 14AWG will have ~0.025Ω of resistance. At the full 10A, you'll see 0.25V drop at the pitot tube. Insignificant.

10ft of 10AWG will have ~0.01Ω of resistance and 0.1V drop at 10A. It will weigh about 2.5 times as much as 14AWG.

I wanted to thank everyone for the incredible responses and discussion, I would like to discuss the topic a little further and gather additional thoughts from you.

For those of you who are running the 14 ga wire how are your routing the wire?

I have not actually measured the total length of the wire run but I estimate if you ran the wire down the spar tube and back to the pitot probe you would have at least 18 ft and that doesnt count running the wire through the cabin to the power source. P. 75 of the G3x install manual calls for 10 g wire for distances of 20 to 30 ft.

I purchased the unregulated pitot so unfortunately I do not have anything which would decrease the demand of the heater. Perhaps Stein would work with me on this and I could trade up.

[Eric Page]

For those of you who are running the 14 ga wire how are your routing the wire?

Some of my wires go through the spars (wingtip lights, mostly), but some others for items mounted closer to the cabin went through a small gap between the spar tube and the fuel tank. I held them in place with small dabs of latex caulk. The wires are below flush and won't print through the fabric.

...I estimate if you ran the wire down the spar tube and back to the pitot probe you would have at least 18 ft and that doesnt count running the wire through the cabin to the power source. P. 75 of the G3x install manual calls for 10 g wire for distances of 20 to 30 ft.

If it's an unregulated heater, then Garmin probably wants 10AWG for longer runs because they rely on a minimum voltage across the fixed resistance of the heater to produce the promised heat output. Less voltage = less current = less heat. In the grand scheme of things, <1lb of extra wire in one wing isn't going to make your plane fly crooked! Whatever keeps Garmin's warranty department happy...

Are you building an IFR airplane?

[Geek]

I wanted to thank everyone for the incredible responses and discussion, I would like to discuss the topic a little further and gather additional thoughts from you.

For those of you who are running the 14 ga wire how are your routing the wire?

I have not actually measured the total length of the wire run but I estimate if you ran the wire down the spar tube and back to the pitot probe you would have at least 18 ft and that doesnt count running the wire through the cabin to the power source. P. 75 of the G3x install manual calls for 10 g wire for distances of 20 to 30 ft.

I purchased the unregulated pitot so unfortunately I do not have anything which would decrease the demand of the heater. Perhaps Stein would work with me on this and I could trade up.

Hey Jason - I did not route my pitot wiring up to the spar and then down the spar due to the added length. Mine runs down to and then behind the fuel cell where it comes out very close to the rest of the wiring/pitot tubing that is running down the spar. So on mine it's not the 18 feet you were looking at. The real reason I went with 14ga is that the current draw vs temp is not 15 amps. (I also put a 15A breaker inline so the wiring is protected). Second part would be how cold is it where I am going to fly at? When it's freezing outside you will find me in front of the fireplace with a good book and a bourbon. But I did test it when the OAT here in WA was -12 degrees F this last Winter and my 15A breaker didn't pop and the probe was warming. To illustrate why I am not a big fan of the G3X install manual, the information on the actual current draw is Table 2-1 on page 2-16 (rev AT manual) and not where you were looking (but where you, me and everyone else would think it would be). Here's a mock up of the table (it didn't want to copy nicely on here)

"Table 2-1 GAP 26 Initial Current Draw vs Probe Temperature (-10, -20 units only)
Probe Temperature -40°C (-40°F) - 12A, 0°C (32°F) - 9.25A, 50°C (122°F) - 7.3A, 100°C (212°F) - 5.85A, 175°C (347°F) -4.36A
Notes (from the table in the manual)
Table 2-1 refers to probe temperature at initial turn-on. For example, upon turn-on at -40°C, the standard
(-10) or regulated (-20) heated probes will initially draw 12 amps, but will draw less current as they warm
up.
The -10 non-regulated probe draws current proportional to the probe temperature as shown in Table 2-1.
The -20 heated regulated probe uses similar power to the -10 probe when airborne, but will limit the
current to regulate the probe temperature to ~75°C (167°F) when the probe temperature reaches this
value."

So two takeaways for you from the table are that the 12A draw is start up current and not constant and the second is that you are probably OK with the -10 version probe. The -10 version does draw current proportional to the temp based on the temp. The -20 regulated version regulates the current based on actual probe temp. (If I had read this before I ordered mine I probably would have gotten the -10)

Keep up the great work Jason. Like following your build.

Gary

[Jason Murphy]

It has been a minute since I have posted an update. I have been very busy working on multiple facets of the project over the past 2 to 3 weeks. This entry will be a little all over the place.

Before I do I would like to thank Gary and Eric for their responses. They were informative and contributed to the conversation.

I was able to find the chart you had mentioned in your response. I don’t think I would have ever looked in that section to find that information unless you had mentioned it.

Eric, I am considering making the airplane legal for IFR flight. The goal would not be for flying in any type of adverse weather but to remove barriers and increase safety over scud running if there were to be a low ceiling layer. In addition I could use use the airplane to maintain instrument currency.

I ordered the materials to begin covering with Stewart Systems. I also ordered an Air Compressor which should be able to handle operating the spray gun.

Since I am going for a little different look with my build I decided on ordering a 2 blade prop from Sensenich. I have not committed to a length at this time but I had ask on Facebook and was provided with an incredibly objective response supported with a research study suggesting 75” would have the best overall performance. I still need to review the research article and decide if it is applicable to my situation.

I have also found a new flight instructor to assist me with my initial CFI training and we have had several sessions in the last 2 weeks. I am glad to feel like I am making progress in that area of my life as well.

I am also making plans to attend the Reno Air Races. I plan on driving west and stopping in Homedale and exchanging my plain firewall for one that has been burnished by the factory. They use their CNC tooling and burnish the stainless prior to bending it to shape. This is an option that there is an additional charge for on the FWF kits but not something that’s published anywhere. An example is the firewall on Brandon’s airplane. So mid September I will be making my rounds through the Western US. Lots of new states for me. We have not figured out if I will be solo or have my wife and daughter with me.

Back to the build. There was not a lot of action here. The last few weeks have involved several sessions of fabricating new false ribs to replace the ones I had removed with the heat gun. I realize the ones which I had removed and had been slightly burnt were probably fine. In fact the dark roasted outside could be pretty easily sanded off. Regardless it made me feel better on the inside to drive to St Louis and get a sheet of 2.5mm aircraft grade Finnish Birch for $30 and time. I contacted Kitfox they quoted close to $1000 for a set of top and bottom ribs which was double of what I actually needed. I used my original factory ribs as a template and simply traced around them and finished cutting them out with a scroll saw.

To ensure and proper orientation I used a small carpenter square and bridged the cap strips of the ribs with a level. It may not be a perfect process but much more repeatable than using the calibrated eyeball.

Last night I finished up installing the bottom ribs. When I fabricated them I made them stand a little proud. Now I just need to use my sanding block and sand them down flush with the adjacent cap strips.

I still need to install the No 2 rib, false ribs under the wing tank, reinforce the No 1 rib and dress up the junction of the leading edge. I will also fill the low spots in the wing tank.

There are some odds and ends I need to do before covering but I am making lots of progress towards covering.

[Jason Murphy]

Getting ready for a trip out west for the Reno Air Races. I plan to stop in at Homedale to exchange my plain firewall for a burnished firewall.

Applied a dollop of Superfil that had been thickened with micro balloons to the wing tank. Used levels to bridge the space between the No 1 and No 3 ribs. Used tongue depressors and index cards for spacers to match the contours of the adjacent ribs.

Applied extra superfil to the false ribs. Mixed another small batch and filled behind the antenna plate and the front of the vertical stabilizer.

I would be interested in hearing from other people areas they had filled or wish they had filled.

[Jason Murphy]

Sanded the forward edge of the vertical stabilizer. I was concerned about how the weld bead would show through the fabric. I believe it blended in well with the Superfil body filler.

I also finished bonding the No 2 rib and sanded the transitions between the lower false ribs and the leading edge of the wing. I will need to return with my 3/8” rod and work on the sides.

After all the thought and planning regarding the heated pitot I decided that I didn’t want to go that route. I reached out to Stein Air and they will exchange it with an untested pitot. Realistically the cost savings will be chewed up by shipping. I will be packing it up and sending it back after I return from Reno. This will slightly simplify the build. I was also under good advice that I probably will never fly the thing in a situation I would actually need the anti ice / de ice capability and if I do things have seriously gone wrong.

[bbs428]

You’ll be glad for the simplification of your build.
I think back to all the stuff I did or wanted to do and now that I’m flying, all the gizmos seem not that important.
If I were to build another Kitfox it would be a bare bones style VFR with a few steam gages and an I-fly.
Going with the streamlined metal wing strut would be a good upgrade as it’s handy to push and pull on when jockeying the aircraft around. The fairing’s over the tube lift-struts are fragile. Too bad it’s such an expensive upgrade!

Keep up the great work Jason!

[Jason Murphy]

It has been a hot minute since working on the project. I have had a lot of irons in the fire keeping me away from the project.

I have been doing some organizing in my work area. I purchased a warehouse shelf to put things away on. I also purchased a 60 gallon Air Compressor rated for 13.2 CFM which I need to find a home for and get it hardwired in place, run some plumbing for the air lines and declutter the work space. This compressor should be adequate despite what the air compressor sales people claim who want to sell me an industrial unit. I will be borrowing a devilbiss spray gun which uses 14 to 15 CFM.

Received confirmation from the aircraft registration division that my special N Number I had requested has been reserved in my name.

I felt the urge today to at least get something done on the project.

I sat down and finished sanding the superfil creating the transition to my false ribs on the bottom side of my wing.

I moved onto prepping the underside of the wing tank to install the filler ribs on the bottom side of the wing tank. I have decided I am going to take the same strategy as I did the false ribs and cut them proud and sand them flush with the adjacent ribs.

I will need to add a touch of filler to the No 2 cap strip to bring it up to where it needs to be. I will recheck the left wing after this one is complete and see if it needs some additional loving which it undoubtedly will.

[Geek]

Good to see you back at it Jason!!! You're doing great work.

Gary

[Jason Murphy]

Thank You Gary! It’s good to be back!

I am hoping things will slow down a bit around the 20th of next month and I can go back to focusing on the project with another rating under my belt.

I saw in another thread a yaw dampener was released for the Model 7. I am hoping to integrate that into my current avionics kit. I need to spend some time catching up with my colleagues and see how their builds are progressing and get some good ideas while I am at it.