Where did winter 2020 go? [100.0 hours]

I got an E-mail from someone wondering why I stopped posting.

I’ve been steadily working the project, but having reached the “90% done, 90% to go” stage, it’s been hard to progress many tasks through to completion. Winter down in Tassie was long and cold as usual, and the short days tend to slow down workshop hours. Thankfully that’s now behind me for the year.

The inlet plenum 3D printing work reached a stalemate. After many Covid delays, I received the second prototype and it was damaged in transit due to poor packing. I worked with the vendor and insurance to have it replaced, and after yet more Covid delays the replacement arrived, also smashed in shipment. I was able to tape together enough pieces from the two parts to decide that the shape was going to be correct; however, I lost faith in the high temperature epoxy material – it was clearly too brittle. The correct material is ASA, but the quality of the first prototype was not good enough. In order to compete in online 3D printing services you need the lowest price, and there’s a big difference between how this first prototype was printed and how I would want it done. I talked to a few vendors in Australia, and it was clear that the cost would rapidly escalate into the thousands of dollars, for each printing, and I might want to do more adjustments yet. I decided to shelve the work, and ordered a commercial grade large form 3D printer. After months of delays, some again due to Covid-19, this thing will arrive here next week. The only problem is it arrives in 8 boxes and I have to assemble it. Once I get it up and running, I’ll be able to print the plenum as many times as I care to, with the quality I want, before calling it right.

I designed all the overhead panels, some auxiliary panels for headset connections etc, and settled on the replacement lower panel arrangement for the Aerosport 310, which was previously incorrect. I worked with AFS to get these designs finalized and the panels are being cut and printed at this time. In the meantime, I made some cardboard replicas and used these to do most of the overhead wiring. I’m not willing to post a photo of that.

I’ve been doing the wiring, which is a big job for an RV-10 made bigger by my choice of 2 batteries, 2 alternators, a 3 screen panel, A/C and SDS EFI. The wiring is about half done overall, and currently looks like a disaster. I started out wanting to simply do the wiring behind the baggage bulkhead and through the overhead, so that I could finish up the tail and put the final skin on. This plan rapidly devolved into an acceptance that I had to do all of the wiring, there are too many interactions to lock up one part before all parts of the puzzle are solved.

Associated with the wiring are some custom electronics. These pieces are:

  • Backup EFIS power. The backup EFIS power nominally comes from the second battery/alternator supply. However, what is the action in the case of an electrical fire and smoke starting to fill the cabin? It has to be “both masters off”, there’s no time to figure out which system is the problem. The engine will keep running because the EFI system is separately powered, but in order to keep minimal EFIS functionality, the regular backup battery must be used. So, I designed a board which will supply backup power to the AFS system, which will come from the secondary battery/alternator system if it is running, otherwise will come from a backup battery. Changeover is automatic, and the functions are ground tested as part of the runups.
  • SDS EFI power. Although the ignition systems, the two fuel pumps and the two ECU’s are on physically redundant battery+alternator systems, there is only one set of injectors so I needed what some would call an “essential bus” to run the fuel injectors. Any place physically redundant systems have to come together is a problem so I’ve applied some effort to this which I’ll post more about in a few months time.
  • Monitoring and logging. Between the extra TFT display on the panel, the EFI power system, the battery backup system and the A/C there are various sensors and data monitoring that I wanted brought back to a central non-essential point. A small embedded computer system sits under the pilot’s seat and has various communication methods to collect data and present information on the extra TFT display. This may eventually be a last resort backup EFIS, but not initially. I needed a set of interfaces for this embedded system that went beyond what is commercially available, so I’ve done a board for that as well. The prototype worked OK with a couple of jumpers and I’m re-spinning the board now.

In between all these activities, I found I was missing various miscellaneous/low-cost parts, which I’ve procured on a slow track with a few consolidated shipments from the US, again affected somewhat by Covid delays.

Reading through all of the above, it’s clear that I’ve done quite a bit over the past few months, but haven’t managed to actually finish anything. When I finally do manage to finish something, I’ll put up a celebratory post that will include some photos.

I have no idea how many hours I’ve spent on the above over winter – quite a lot – but I’m just going to log 100 hours because I really haven’t kept track of it all.

SDSEFI flywheel modification [4.5 hours]

In order to use SDS EFI &/or ignition products, it is necessary to modify the ring gear to insert magnets for timing sense. This is a straightforward procedure, but not commonly done for dual pulley ring gear as used when an A/C compressor is fitted to the engine.

My ring gear (flywheel) was supplied by Airflow Systems as part of the A/C kit, and uses a serpentine belt for the A/C compressor drive. The magnet insertion points wind up in the middle of the serpentine belt area, which changes how things need to be done compared with the standard procedure published by SDS. Here’s what I did.

My flywheel had timing marks on the front side only. This confused me for a long time because the timing marks didn’t line up with the tooling holes as described in the SDS procedure. It turns out this was all because of my ignorance about Lycoming engines. When timing marks are on the front side of the flywheel, the TDC #1 mark lines up with the small hole at about the 2 o’clock position (viewed from the front) of the starter motor. When timing marks are on the aft side of the flywheel, the TDC #1 mark lines up with the vertical split at the top of the casing. So, with the flywheel lined up at TDC #1 (which I confirmed by looking at the #1 piston through the top plug hole), I marked the rear TDC #1 mark, and the tooling holes then matched up as described in the SDS instructions.

There is a difference though – the tooling holes in the Airflow Systems flywheel are 3/16″, whereas those in the standard flywheel are 1/4″. Ross at SDS kindly made me a drilling jig to suite the flywheel I have.

I then went ahead and drilled the flywheel exactly as per the SDS instructions, using a new #29 cobalt split point drill and plenty of cutting fluid. By sheer good luck, the holes wind up exactly centered in one of the grooves for the serpentine belt – see the pictures. This is lucky because it means it isn’t necessary to rebuild the “crest” of the grooves on the flywheel, just fill in material that has been removed inside the groove.

I tapped the holes #8-32, again as per the standard instructions, and carefully de-burred the sides of the holes in the micro-V groove using needle files, sandpaper and a magnifier. I then cleaned out the holes thoroughly with acetone. At this point though, it is necessary to deviate from the SDS procedure.

There isn’t enough depth to insert two grub screws as well as the magnet, only one grub screw will fit. Here’s what I did:

  1. Each hole contains the magnet, and one grub screw. I soaked the grub screws in acetone to remove any grease or oil, then set the four grub screws aside on a clean, dry tray.
  2. For each hole, I picked up a grub screw with an Allen key, applied red loctite (these aren’t ever coming out) to the grub screw threads, and inserted the grub screw to a bit short of the right position from the outside, leaving the Allen key still in place.
  3. I then mixed up some 5 minute epoxy, filled the hole per the standard instructions (the plastic shaft of a Q-tip with the head cut off works well for this), and inserted the magnet from the inside. The magnet gets pulled in and smacks against the grub screw.
  4. Now carefully wind the grub screw further in, until the magnet is at the desired position, just inside the inner surface of the flywheel. Remove the Allen key. Wipe off the excess epoxy with some acetone on a clean rag.
  5. Clean off the red loctite from the serpentine pulley groove with acetone. I used a piece of paper towel with acetone, and a clean feeler gauge to get right down to the bottom of the groove. Then I used a Q-tip dipped in Acetone to get down and clean the loctite out of the threads in the hole, above the grub screw, while holding the flywheel so that the acetone would run out of the hole rather than down around the grub screw – so as not to displace any loctite around the threads.
  6. Do one hole at a time – go back and repeat steps 2-5 another three times, making sure to get the magnet orientation right. Then set everything aside for a few hours or overnight for the epoxy and loctite to cure.

Now it is necessary to “rebuild” the damaged groove. I used a product called Devcon Titanium Putty to do this. It’s an expensive product and you only need a small amount, I was able to borrow some from a friend that is a commercial user. There are other metal repair products around that would also be suitable.

Mix a small amount and force it down each hole so that there is a continuous layer of putty around the top of the grub screw out to the bottom of the groove, and use a fine knife to roughly shape the two sides of the groove, ensuring the threaded hole is fully filled up to the top of each side of the groove. I then let the Titanium putty cure for 3 hours. Don’t let it go much longer – after about 6 hours it gets a lot harder to work.

Three hours after applying, I used a combination of tiny needle files and various fine grades of sandpaper to rebuild the groove in each of the four hole positions. I started with the files, then switched to 120 grit paper to get each position nearly done. I wore a magnifying headset to do this, so that I had good vision for this micro-surgery. When I got close to the final result, I set the flywheel aside for another few hours for the putty to harden a bit more.

After about five hours total, I did some further sanding using 240, 400 and finally 800 grit paper to polish each side and the rim of the groove to complete the rebuild. The Titanium putty is well secured by the threads of each hole – see the final picture. The job is done when each side of the groove is smooth and flat, and you can run your fingers across the top of the groove with your eyes closed and not be able to tell when you run across where the hole was.

  • f50a
    f50a
    #29 hole drilled in Airflow Systems dual ring gear
  • f50b
    f50b
    Hole tapped 8-32, not yet de-burred
  • f50c
    f50c
    Mixing Devcon Titanium Putty
  • f50d
    f50d
    Titanium putty applied
  • f50e
    f50e
    After filing and sanding Titanium putty