Pull Those Cowlings Off, Folks--And Have a Close Look!

[drdehave]

My policy is to the pull the cowlings off my Sting Sport every 3-4 hours for a detailed exam; I never go longer than 5 hours.

In 1,250 hours of flying 1MZ, I'd guess I've found at least 10 potentially important issues or already-critical items when doing this.

Today was another "find." My muffler bracket attaches to the back of the engine (magneto case) with three M6 x 1.0 bolts. The head of the lower right bolt was sheared off, so there was nothing holding the bracket at this point. Leaving this to fester, it very likely would have set up vibrations leading to more sheared bolts and/or cracked exhausts--or who knows what else.

Anyway, given what I've found in 3.5 years by regularly removing my cowlings, I can't believe there are some LSA folks around me here, who consider it too much of a bother to remove their cowlings more frequently than about once every 25-50 hours; One guy I know once went almost 100! (because he lacked cam-locs and cowling removal entailed taking out 40 screws)

I don't care how many screws there are (yeah, I can say that, with my sweet little cam-locs) or how long it takes, it just makes good sense to Pull Those Cowlings Off, and Have a Close Look ---frequently!

Rich

[drseti]

My upper cowling is secured by 11 CamLocks. I pull it every couple of days, and give things a look-see. 15 screws hold the lower cowling, and it in turn is the only thing supporting the radiator, which needs to be bungeed up when the lower cowl comes off - so removing that happens far less frequently. But, I can see a lot with just the upper one removed. And, yes, I've caught quite a few squawks before they became problems.

[sandpiper]

Magnetos? What engine do you have?

[drdehave]

Magnetos?

Indeed...Just a Senior Moment, sir. Let's just say..."the muffler bracket attached at three points to the rear of the engine."

[drseti]

Actually, Rich, you spoke correctly. At the back of the Rotax 912, where your muffler bracket attaches, is the flywheel housing. Embedded in the flywheel are a bunch of permanent magnets. Around the plastic housing are three pairs of fixed coils. As the magnets spin, the lines of flux pass the coils, inducing a current into each. One pair of coils connects to the voltage regulator, powering the bus. Each of the other two pairs of coils provides raw power to one of the capacitive discharge ignition modules. Those spinning magnets and fixed coils are certainly a magneto, aren't they?

[sandpiper]

Actually, Rich, you spoke correctly. At the back of the Rotax 912, where your muffler bracket attaches, is the flywheel housing. Embedded in the flywheel are a bunch of permanent magnets. Around the plastic housing are three pairs of fixed coils. As the magnets spin, the lines of flux pass the coils, inducing a current into each. One pair of coils connects to the voltage regulator, powering the bus. Each of the other two pairs of coils provides raw power to one of the capacitive discharge ignition modules. Those spinning magnets and fixed coils are certainly a magneto, aren't they?

Here I am, trying to be a S.A. and you kick the legs right out from under me.

[drdehave]

I really thought someone would say, "Now, that's unusual, Rich. Why the heck do you suppose that bolt-head would shear off?"

You know why? Because that little M6 came loose. Then, the bracket-arm it was holding, went into harmonics with it. That in turn make the area just below the head turn into jello, the bent-spoon-effect, you know? Then, it was soon bye-bye-bolt-head. At least that's my take, since I was able to remove the headless bolt with just my fingers, it was so loose!

So, safety lesson Number Two: Paint-mark ALL your fasteners, so spotting stuff coming loose--or about to--is real easy! Saves me grief all the time!

Rich

[drseti]

Rich, there's a torque spec on every fastener in a Rotax engine. Even that little M6 bolt has a torque specified in the Rotax maintenance manual. So, I presume you used a calibrated torque wrench.

John, it's OK; you're still a smart arse.