Flywheel Cap Screw Failure

[gammaxy]

If the regulator ias seeing a need to charge the battery and the alternator go low in voltage I think the current curve woulkd be inverse to the voltage.Pete

The way the permanent magnet alternator and linear voltage regulator on the Aerovee works is by clipping the voltage to some level (around 13.8 volts) to avoid over-charging the battery. The voltage from the alternator and regulator must be greater than the battery in order to charge it. Once the alternator drops below the battery's voltage, there is nothing that would cause current to increase and flow "uphill" into the battery.

[tomwasser]

Mike Smith,
Fast forward from your post May31, 2015 to my last flight in my Sonex with Aerovee engine built 2013, flown since April 2019 with 87 "perfect" hours AND EXACTLY THE SAME SERIES OF EVENTS OCCURRED on a delightful early evening flight 7/6/20, EXCEPT, I had 2-4 minutes to land, (as the cockpit was filing with black acrid smoke and loosing power), off airport on a remote country road, 2 miles north of Lyons, NY., 6 miles from the closest grass strip.

I could have copied and pasted your description and just put my name at the end. Readers can reference your complete description.

Sonex and Kerry were very supportive and cooperative but in my humble opinion this secondary ignition system is an engine failure waiting to happen.

I received my parts exactly as your parts and am rebuilding. I am addressing the fact 5/8 inch flat head cap screws attach the small magnet flywheel ring to the main flywheel as an assembly provided by Sonex. There are 16 screws in this secondary ignition any one of which can be a source of failure in my opinion.

How, how do we Aerovee owners assure this not happening again since "glue" in the form of locktite is holding this area of our precious engine together?

I am not upset as much as incredulous that this area of the Aerovee build has not been given more attention than gluing 16 screws to the AFT end of the engine build. And I am thankful to be alive.

Tom Wasser

[tomwasser]

Sorry, there are 18 screws in this secondary ignition area, 4 of which are part of the flywheel assembly provided by Sonex. These 4 cap screws are short 2-3 threads from being flush on the other side of the flywheel.
Tom Wasser

[tomwasser]

I called Locktite, owned now by Henkel corporation, a German company and spoke to an engineer, who was very knowledgeable about Locktite and primers. Bottom line is that Locktite red 263 has primer and there is no need for a separate primer. Locktite blue 242 and red 262 do not have a primer so primer can be used, either 7649 or the 7471 suggested by Sonex. Permatex formerly owned by Locktite has a different number for their red sealer and he would not comment. Also if one uses a primer with Locktite you have the additional possibility of an error not using it correctly.

Why use two products either Locktite 242 or Locktite 262 and a primer, when Locktite 263 has the primer. I may be wrong but I used Locktite 263 on 14 screws for assembly of the secondary ignition. I decided not to mess with the 4, 5/8 inch screws that attach the secondary smaller flywheel to the larger primary ignition flywheel provided by Sonex since they have never seen a problem with these screws backing out.

If someone has different or new information, please respond.

Tom Wasser

[tomwasser]

Help, you electronic geniuses! I am trying to understand why my Aerovee stator alternator, upon destruction, (due to ONE cap screw backing out), put out excessive current and burned up my Dynon amps shunt rated up to 60 amps and popped the 30 amp circuit breaker simultaneously within 2-4 minutes forcing immediate landing of my Sonex on a road 7/6/20. Why did the 30 amp breaker not protect the shunt from excess current from the alternator? It appears all other wires are intact. I replaced the coils and voltage regulator as a precaution.

I have downloaded the last hour of Dynon's SV engine data and am trying to display this in Excell.

Neither Dynon nor Sonex has any explanation for why the 60 amp shunt was destroyed except to say there was excessive current output.

The 30 amp breaker was installed inline after the alternator, shunt, and with aircraft loads to protect this circuit in the event of excess alternator current output. Apparently this happened! When I get my new shunt from Dynon should I do anything differently to protect this circuitry, while at the same time using Dynon's shunt to monitor amps with their Skyview system.

Thank you all.
Tom Wasser

[sonex1374]

Hi Tom,

Pictures of the failed shunt would be helpful to see how and where it failed. Additionally, we'd need to see your electrical system diagram to understand how everything was wired in your airplane. With it we could probably construct a reasonable hypothesis as to what happened, but without the diagram it's more random guessing.

Having said that, the first thing that comes to mind is that the alternator was damaged by the screw head creating an internal short between the windings. The short then sucked down battery voltage and a whole lot of current, causing damage to the shunt. It's also worth noting that if the 30 amp breaker opened first (say after a momentary short circuit and high-current rush from the battery) then the alternator would (assuming the shunt was located on the alternator/voltage regulator output line) try to supply full alternator output to the shunt and have dumped all this output into the sensing wires of your Skyview EMS module that was monitoring the shunt. It's an unlikely scenario, but possible. If this happened, it would fry the EMS module (so if the EMS is OK, then it didn't happen, but you may want to check the EMS out).

[edit - philosophical thought here. I'm not a fan of using shunts. They are relatively fragile, and don't really provide all that useful of info to the pilot. If the bus voltage is high, then the alternator is working. If the bus voltage is low, the battery is draining. What more info can the shunt actually give you that the volt meter can't?]

Alternatively, a failing alternator *could* produce some nasty voltage spikes as windings randomly made and broke contact, but this wouldn't be my first guess as to what caused the problems.

I'd also be interested in seeing your skyview data. We might be able to deduce what happened from that.

Jeff

[XenosN42]

I have downloaded the last hour of Dynon's SV engine data and am trying to display this in Excel.

Hi Tom,

An easier why to view your Dynon SkyView data is to use 'The Flight Data Viewer'. https://www.JASFlyer.com The app allows you to view all the detailed values, plus graphs and an animated EFIS view. For a demo see https://www.youtube.com/watch?v=82WYZXPpCoc&feature=youtu.be

Cheers

[mike.smith]

Help, you electronic geniuses! I am trying to understand why my Aerovee stator alternator, upon destruction, (due to ONE cap screw backing out), put out excessive current and burned up my Dynon amps shunt rated up to 60 amps and popped the 30 amp circuit breaker simultaneously within 2-4 minutes

Hi, Tom:

I'm not an electronics genius, so I can't answer your question, but I can tell you my electrical system had only a 30amp fuse along that circuit, and when the alternator went crazy that fuse blew, and everything downstream was protected.

I'm really glad to hear you made it down safely!!

It does suck that there is no way to check those bolts during an inspection, unless you want to half-remove the engine to take all that stuff apart. And as I think you are surmising, if you check the bolts by trying to turn them, you may very well break the hold of the Loctite even if they were all tight and locked in place. So you're damned if you do and damned if you don't.

If it's any consolation, that happened to me some 400 hours ago, and no issues since.

[inventor]

My first thoughts about this is that the windings in the alternator shorted the battery to ground.

[tomwasser]

Not very sophisticated but .png is my wiring. Also 2 wires from the shunt to pins 24/25 of the Dynon EMS to read amps and display on engine data screen; since incident are x'd out. If, if my EMS took a hit and partially failed it is just the amps area because all other engine parameters are functional, although just today my first flight since alternator failure showed excess voltage 14.9 when before it was around 13.2-4. Thanks.
Tom