My Sonex Project

[Matt541]

Almost forgot, I can't say enough about joining your local EAA Chapter. I've been an EAA member since 2015, but didn't attend a chapter meeting until March of this year.

In the last 2 days, 5 different guys from the chapter helped with the move and getting it back together. Couldn't have done it on my own, and it was much easier than when my wife and I brought in back in the U Haul truck.

[Matt541]

Got that Revmaster engine purring again!

When I replaced the mixture control, it looks like I didn't have it set correctly. The carb wasn't actually getting a full rich mixture even though the knob was pushed in all the way. I even had the lever positions marked on the carb body correctly... Plus I needed to revamp my start procedure.

Ts and Ps all looked good so I moved on to taxi testing. May have played with the smoke system during a run up too..... (I hear it did well, but no pics.)

Found a few things I need to tinker with yet. For example, I have an extra CB box under the right side of the panel for the wig wag system. It turns out that if you try to open the RS vent, your hand touches the exposed contacts and wakes ya up a bit! Surprise! I'll be fashioning a guard for that.

Hopefully finishing the condition inspection this weekend.

Debating if I'll move on to "high speed" taxi testing then or just say a prayer and fly it. Thoughts?

[WesRagle]

Hi Matt,

I wouldn't try high speed taxi on a proven design. If the W&B is good and the plane has flown previously I don't see what high speed taxi tests would teach you.

What I decided when it came time for my first Onex flight was:

1) Tie the tail down and run the engine full power. I learned that I couldn't get the engine to die and I found out what static RPM to expect and that that RPM was in a good range as far as power is concerned.

2) I did a lot of medium speed (20 -30 mph) taxiing. That got me used to the direct steering and got me used to the sight picture for landing. It also trains your hand to move naturally between the throttle and brake.

Of course the danger of high speed taxi is that you might get airborne. If you've ever aborted a takeoff just after getting airborne you already know it's not like a normal landing. No time to get set up, and you're slow and nose high and ... Very easy to mess up.

If you do decide to do high speed taxi tests, I would suggest that if you do get airborne add full throttle and complete a successful takeoff :-)

Best of Luck,

Wes

[Arjay]

Hi Matt:

Back in 1982 my wife surprised me with a Baby Lakes for my birthday. As a very small single seat taildragger, there was no way to get transition training in it so I had to figure it out on my own. Very early on I was doing some medium speed taxi familiarization runs down the runway at about 1/2 throttle when the little devil jumped about 6 inches off the runway. Very quickly, I was faced with a huge decision. But, by that time I was anxious to fly the thing, so I let my training and instincts take over, dropped the nose slightly to remain in ground effect and pushed the throttle wide open. That little rascal dropped about 3 inches, then gained some speed. After a second or two, I pulled back slightly on the stick and she rocketed toward the sun. What an amazing feeling-- I was climbing like a bat out of hell.

Now, what do I do? Sooner or later I will have to land this thing. Having no training in this bird, and certainly no owner's manual with operating instructions, I have no idea what approach speed to use or what the numbers are for a stabilized approach. Should I go ahead and try to land, or fly it for a while. Decisions! Decisions!

But, I figured I can land any time. Might as well fly for a while and see what this bird is like. So, I flew her for about an hour, then took her in for a landing. It was then I discovered the airspeed indicator was not working properly, as it was indicating much slower than I knew was correct. Sooooo, it's a landing totally by feel. Wouldn't you know that landing was just about the best one I ever made in that airplane.

Moral is: go with your instincts and let your training guide you. And, by all means fly as much as you can.

Blue skies and cavu weather

Ron
Lagacy Sonex taildragger with Aerovee and Aerocarb.

[Matt541]

Thank you Wes and Ron for your input on that. Since then, I've only gotten it up to about 20mph just to feel it out.

While working on the condition inspection this weekend, the last spark plug I removed also brought the threads with it. So now it's either Time-Sert or new head time....

Not a trace of anti-seize on the bottom plugs...

Although not my Sonex, i did get some flight time in a Rans S-7 over the weekend. Was good to just get back in the sky, take some of the pressure off from working on 541.

[Matt541]

My engine can now hold all 8 spark plugs again, many thanks to Mike Smith for letting me borrow his Time-Sert kit.

And I got the new Sonex machined tailwheel installed to boot. I like the extra ground clearance for the tail, but I honestly feel like it turns just a bit sharper too.

Sittin' pretty on the new tailwheel...

Still going through some things before attempting Round 2 of the condition inspection.

Honestly though, the last couple weeks have had more of a focus on family than the airplane. Guess it's good to take a step back now and then.

It's old news now, but for posterity's sake, I finally put a video together about moving 541:



(You can plainly see the difference in tail clearance between the old and new versions. Old version in the video thumbnail.)

[Matt541]

So my last few weeks have been diagnosing and hopefully fixing some ignition issues with my Revmaster CDI. Although the reality is that I've been lucky if I get one day a week to work on it...

This setup utilizes coils on top of each plug, kinda like an LS1 V8. Four, yes 4, ignition switches on the panel. The CDI box is wired with 4 circuits coming out of it, companion cylinders for the top and bottom plugs. i.e. 1T and 3T, 2B and 4B

My problem has been an excessive "mag" drop on switches 1 and 2, which basically means one whole ignition system was not firing. Switch wiring and grounding was all correct, as was the wiring out of the CDI box to the respective cylinders. Dig a little deeper.

A known potential issue with the Revmaster CDI is the use of these Molex connectors.

Molex Connectors

Other owners have been plagued with issues and stumped for months, only to find that one single terminal had worked loose and backed out ever so slightly. But just enough to break contact. Backprobing the connector with meter would temporarily make contact and make it check out ok. So that was job # 1. I inspected all of the connectors and wiring and found not only loose terminals but multiple spots of bad wiring as well.
Including this doozy:

Only a single strand left together...

Got it all back together temporarily with Wagos (Diagnostic purposes only) and fired it up to find that the drop on switch # 2 was cured. I systematically removed a set of connectors and replaced wiring, running the engine in between, to see if I could find the issue on switch # 1, but no joy.

Finally, after exhausting all other possibilities I removed the CDI box from the back of the engine. Simple job with 4 allen cap bolts, but something I was reluctant to do.

CDI Box Internals

I immediately found one issue, a loose wire on one of the resistors that lead to the switches. Loose enough that I could easily pull it off:

Shouldn't that be connected?

Certainly an issue, but I wasn't convinced it was the issue. Then I found this:

The smoking gun?

Broken solder connection on the board itself. That's got to be it right?

How did this happen? Funny thing is I was recently reading about a NASA study concerning solder connections and how they fail in air and space craft. (Maybe in the rabbit hole on the opposite end of this forum...) If you look closely enough at the picture, you will notice a few things.
First off, these board connections have not been potted to give them ANY sort of vibration resistance.
Next, the leads coming out of the CDI box have no strain relief to protect them from moving around or getting yanked on.
Combine those two factors and the outcome is no surprise.

Now, I want to be clear that I'm not dogging RM for this, this is clearly an early version of their CDI system and later boxes have both of these points addressed. But if you're flying behind a RM CDI and you haven't done so, you might want to check the age and condition of your system as well. There is a lot of redundancy built into the system, but ya know Murphy's Law, something something...

I've repaired the box and will be heading to the airport today to see if it that did the trick. Wish me luck!

[Matt541]

SUCCESS!

Reinstalled the box, fired it up, and no more HUGE rpm drop.

Next up is rewiring everything and replacing the Wagos with Seal All Connectors from ACS. These are basically the same thing as the Delphi Weather Pack connectors we used at the dealership.

With any luck, I'll get the condition inspection done next weekend.


Put a video together on diagnosing the problem:

[Matt541]

New wiring and connectors are done, but I didn't make it out to the airport to install it.

Well worth the effort.

I'll be up there at some point this week though. This coming weekend is looking REAL good, so got to be ready for it.

In the meantime, I did get the Pt 2 video together on my ignition:



If you have a Revmaster with the CDI ignition, it may be worth ditching the Molex connectors all the way around and take a good look at your CDI box.

[Matt541]

Almost a month later, finally got to fly 541!



Was all set to fly it at the end of November, warmed up the engine, all good. Fired up again to make the flight and I had ZERO oil pressure indicated. Oil temp was good, but I just couldn't take the chance since I was still safely on the ground. Turns out it was just a faulty VDO sending unit, but of course it would wait until then to go. Anyway, I installed a mechanical oil pressure gauge to make sure and sure enough, oil pressure was still good.

Then it was a matter of waiting for the winds, weather and my schedule to all come together. I have limited myself to "winds calm" until I can get more comfortable with the airplane. I'll take a 35kt direct crosswind in a 182 in Alaska (done it, don't recommend), but I won't chance 5kts across yet in this. (Up until this point, I had never soloed a taildragger.) IT took a couple weeks, but I finally had my moment.

It flew great! Responsive, but not twitchy. Easy to fly, but it will take some time before I feel I can fly it WELL. (in my book.) I overcontrolled twice, both on takeoff and transition to 3 point attitude. I didn't realize it, but the video revealed that I touched tail first.

But at the end of the day, this was the result:

My first Sonex smile!

Thanks for everyone's advice and insight getting to this point!