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Late summer weekday flying in South Auckland, New Zealand

Posted: Wed Mar 13, 2019 3:04 am
by Odakyu-sen
Went for a flight with another FLPHG pilot at the Drury airfield.

After my second flight, I noticed a crack next to the bolt hole in the end of the exhaust manifold supporting strap (that bolts to the engine casing on the port side, near the starter motor). Later, when I removed the exhaust for repair, I found that the crack had gone completely through the end of the strap, and only the bolt washer was retainig the broken end of the strap.

I've since had the strap tip welded back on. I'll put the exhaust back on the Mosquito tomorrow.

Pre-and post-flight checks for fatigue cracks (especially around the muffler and its fittings) are essential. Although I safety-wired both exhaust manifold bolts after I tightened them up a couple of months ago, when I removed the safety wire yesterday, the bolts were not tight at all. Only the safety wire was preventing them from unscrewing and falling out.


Re: Late summer weekday flying in South Auckland, New Zealand

Posted: Wed Mar 13, 2019 8:59 am
by red
Odakyu-sen wrote:
Wed Mar 13, 2019 3:04 am
Pre-and post-flight checks for fatigue cracks (especially around the muffler and its fittings) are essential. Although I safety-wired both exhaust manifold bolts after I tightened them up a couple of months ago, when I removed the safety wire yesterday, the bolts were not tight at all. Only the safety wire was preventing them from unscrewing and falling out.
Odakyu-sen,

Good catch. I have been involved with aircraft for most of my life, and I have a real appreciation for safety wire. Certain parts of my motorcycle are safety-wired, which surprises some riders, but that doesn't stop me. If certain OEM bolts are not drilled for safety wire, I will drill them myself. That said, what you found should not have happened. There is a certain "science" to the use of safety wire, and if done correctly, it will prevent any loosening of the bolt. The wire exiting a bolt head should bend in a clockwise direction (for right-hand threaded parts), then proceed to the attachment point. This method prevents the bolt from even starting to loosen. It would take lots of words to explain the techniques, but Google can find dozens of images of safety wire installed correctly, for almost any drilled fastener.

Safety-wire pliers will twist the safety wire in a professional manner, with an easy pull or two on the "twister" handle. (Hand twisting of the safety wire pair is okay, too.) Safety wire pliers will clamp on, twist, and cut wire cleanly. They usually cost a dozen (or two dozen) dollars, although you could spend far more. They do come in large and small sizes, also. I have full-sized and hand-sized versions; the small one works in tight places.

Re: Late summer weekday flying in South Auckland, New Zealand

Posted: Wed Mar 13, 2019 11:29 am
by DMarley
Odakyu-sen wrote:
Wed Mar 13, 2019 3:04 am
... I noticed a crack next to the bolt hole in the end of the exhaust manifold supporting strap (that bolts to the engine casing on the port side, near the starter motor). Later, when I removed the exhaust for repair, I found that the crack had gone completely through the end of the strap, and only the bolt washer was retainig the broken end of the strap.
...
Hi Odakyu-sen
This potential problem is timely to me, and probably to many other FLPHG's. Are you a member of FLPHG group on FB? Pilots share a lot of information on that forum. Sadly, the yahoo FLPHG group is pretty silent. Do you have pictures of the problem?
viewtopic.php?f=27&t=36089&p=404116#p404116

I am in the process of reconditioning an older Explorer harness (made in Australia and very similar to an older Mosquito). Upon starting it for the first time after I purchased it, the combustion gasses were escaping quite loudly from the RedHead and cylinder interface (no gasket is required there). The head/cylinder bolts were not quite finger-tight!

So at this stage, there is little semblance to a power harness, as ALL the parts are scattered about, everything getting reconditioned and double and triple checked. Found lots of little problems stemming from previous owners' lack of good understanding. Oh the joys of the 2-stroke. They're amazing little engines... iff fed and cared for properly.

The prop that came with the unit was 'modified' likely by interference with a glider's keel. So I'm looking at appropriate prop possibilities as well. Folding (Bolly) or non-folding.... hmmmm.

I could have taken the easy route and purchased a new unit, but this way I have a real education regarding the proper feeding and care of these potentially-fickle portable mountains.

Really appreciate you posting your experiences, the good and the not-so-good!

Re: Late summer weekday flying in South Auckland, New Zealand

Posted: Thu Mar 14, 2019 1:15 am
by Odakyu-sen
I've applied to join the Facebook FLPHG group.
I put my exhaust back on and lock-wired the manifold bolts. My Mosquito NRG uses these offset custom-made hex-nuts to retain the manifold bolts. I understand that the more modern NRGs allow the exhaust manifold bolds to screw directly into the cylinder head.
I should be okay for now.
The newer exhaust that I bought after the original one failed (and took out my prop) is much more robust. (Here's the video of my emergency landing:
)