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Searching for a lost winglet

I read online that a passenger airplane lost its winglet in turbulence while crossing Alabama and had to land early in Birmingham. I was unable to find any news about where the winglet fell and decided to see if I could figure it out from FlightAware’s ADSB data.

Shows route airplane took before and after losing its winglet.

When displayed on Google Earth, the track of N233NN looks almost perfectly straight, so I wrote some code to take the long, straight segment across Georgia and Alabama and compare it to a perfect great-circle route. Viewed this way, there is a very sudden 75m deviation to the right followed by a recovery. This seems like it could be consistent with losing a winglet.

If my observation is correct, the winglet most likely fell off between the labeled point and Millerville which corresponds to the maximum deflection on the graph.

I spent half an hour flying over the area and was unable to locate the winglet.

Secondary Ignition Current

I measured this on my workbench with a magnet attached to a drill spinning next to a spare ignition trigger. I measured the coil as 3.2 ohms and set my power supply to 14v. I used a shunt resistor at the output of the power supply to measure the current draw of a single coil/trigger combo. I expected to measure a peak current of about 14v/3.2ohms = 4.4 amps. It turns out the trigger applies only 11.4v across the coil, explaining why I only see a peak of ~3.5 amps.

The ignition spark is generated when the current drops sharply to 0. There’s a period of almost zero current lasting 2.5ms while the magnet is still close to the trigger. This period is longer at slower RPMs and I believe it gets shorter at higher RPMs. I wasn’t able to test higher RPMs with my drill setup, but I did move the magnet far enough from the trigger that it was barely triggering and saw periods of ~1ms at the same RPM.

Using this data, I simulated the expected waveform at a range of RPMs to show how the average current draw decreases as RPMs increase. It’s only about a 13% decrease in current and probably not enough to be readily noticeable.

While investigating this, I noticed the triggers de-energize the coils after about 2 seconds without a trigger. This greatly reduces their drain on the battery while the engine isn’t running.

Dynamic Propeller Balancer

I’ve been curious about the balance of my propeller/engine combination.  Rather than find someone with access to a dynamic balancer, I decided to design and build my own.

Balancer setup on bench

Moving to the airport

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Cockpit mostly complete

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Throttle, electrical, and fuel

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Attaching engine mount

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Riveting fuselage former

Archie came over again and helped me rivet the last two fuselage formers in place.

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This week I completely disassembled the forward fuselage, deburred them, and added a hole for the rear spar on the left side.  I then reattached the sides, bolted, and riveted the skins.  I started riveting the spar tunnel in place with flush rivets.

Forward fuselage deburring, dimpling, and countersinking

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