Ban the Bonk!

Posted June 2019

Helped the A&P with the condition inspection last week, no issues.

Yesterday, I took the plane up for the first post-inspection flight.  I prefer to wait a day or so after the inspection, and preflight the plane with fresh eyes in case anything was forgotten during the reassembly.

Fuel float showed the tank was getting low, but still at the point where I could fly for a bit and still keep the required reserves. So up I went for a bit, flying over a couple of folks houses, checking out the RC flying field, etc.  Come back, shoot some touch and goes, then land.

Noticed something as I taxied up to the gas pumps.  I could hear an irregular mechanical "bonk" as the engine idled.  Damn.  Something coming loose in the engine?

I leaned forward, holding the brakes and tried to isolate the sound.
Bonk...bonk.... then nothing for a few seconds.

I switched off the mags, and the engine spun to a stop.  I started unbuckling the seat belt.


What the pluperfect hell....?  I jiggled myself up and down a little.

Bonk.  Bonk.

Then it came to me.  I was hearing the cork of the fuel float bump into the finger strainer on the bottom of the tank.  The largely empty tank was an echo chamber, giving the cork-to-brass thud a more metallic sound.

The builder of my plane build the filler neck of the tank a bit too close to the axis of the finger strainer below.  The cork does clear, but there's enough play to let them occasionally contact.

But I'd heard the bonk and immediately came to the worst conclusion. Thought I was going to have a heart attack....

Don't normally run the tank as low as I did...usually make a run over the car gas place and buy five gallons.  But I like to put an occasional load of leaded fuel in, and yesterday was a good opportunity to run the tank a little lower.

For those who are wondering, it took 10.1 gallons to fill the tank.  16 gal capacity, about two gallons unusable....

Ron Wanttaja

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