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Jim Meade

N521CT Crashed Racine WI 17 May 21

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We had several throttle breaks with training at the club I am at, and I was able to get it standardized to review the procedures if the airplane is unresponsive to power change commands, and we replace the throttle cables when there's more than a couple thread breaks, or if it's really looking rather mangled.

The throttle cable damage is a result of people going far too tight on the nut, it pinches the cable so hard that it actually starts to cut it.

The rotax carb engine is very forgiving to stops and restarts, but one additional caution: if the throttle is left open and the ignition is off, it will continue to draw fuel through the system, and it will coat the exhaust with fuel after a little while. A restart could result in an afterfire. More than likely it will just be a little one, but big bangers are not out of the question. Just don't freak out if it happens, it's more important that you stay focused on getting down safe and not about the big scary sound that happened.

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What concerns me here is the vibration. How bad is it?

We pay a high price to have two carbs for redundancy. That price includes initial aircraft cost, added aircraft weight and field service costs associated with balancing the carbs. And in providing dual carbs, Rotax has departed from standard aviation design.

But unlike dual ignition systems, which keep all the cylinders operating pretty darn well in the event of a single failure; the carbs cut the boxer in half, right and left. In the event of a carb failure, one side of the engine is punching... against nothing. (Maybe the cylinders should have been divided fore and aft).

If one side can get you home, or at least keep you out of the trees, then the price we pay is probably worthwhile. And congratulations to Rotax.

But if it is vibrating so bad that its going to rip the engine off the mounts, what's the point?

How bad does it vibrate?

It sounds like this pilot probably had only one side of the engine operating throughout the landing side of six patterns (6-12 minutes total?). And it looks like the engine stayed put to the end.

Does anyone now how long we can expect our engines to continue operating, and remain in place, on one carb?

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You still have use of both carbs at high throttle settings. There is no problem at cruise, just when going to low throttle as in landing.  At this point you have one carb at high throttle and one at low throttle. It shakes like a paint shaker because it is unbalanced. The only fix is to shut the engine off and glide to the runway.

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Just happened to read this thread today.  This is a major "must read" for all Rotax owners.  Thanks to Al for posting and for the others who have actually done dead stick landing to join in.  Although some say this is a "no brainer" and easy to figure out, like Tip and Garza, I envision not being able to diagnose the problem because of ensuing confusion and my thoughts going to mush when confronted with my normally great running Rotax instantly going haywire.  Failed electrical, broken engine, broken prop, bad fuel, broken carbs??  Don't see me sorting thru these possibilities while in this confused state.  Now that I have read this post, I believe that I will be able to recall and react as needed, should I be confronted with this. 

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11 hours ago, Mike Koerner said:

What concerns me here is the vibration. How bad is it?

We pay a high price to have two carbs for redundancy. That price includes initial aircraft cost, added aircraft weight and field service costs associated with balancing the carbs. And in providing dual carbs, Rotax has departed from standard aviation design.

In my mind at least the two carbs are not for redundancy. They are there because it is less complex in design and implementation. 

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