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Doug G.

Sinking Floats

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Hello all,

I have been in a conversation on a Facebook group where an individual claims to have received 17 bad (sinking) brand new floats for 912 Bing carbs.

I know there was an issue that led to an exchange and the required weighing of floats on inspection, but has anyone heard of an issue with newly purchased floats?

Thanks

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No on the new floats. It was a different company and float material composition. I would have a hard time believing any single individual had 17 bad floats. yes there were some that had a bad couple of floats while they were trying to work this out, but 17?

If the new floats were bad this would be all over the internet, but this has calmed down since the latest model. 

With the new Rotax checklist the floats are supposed to be weighed every annual.

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The new floats out of the box weigh a tad more because of the new composition. To keep these within spec they actually trimmed down the brass insert on the ends that stick out flush on the older floats. The brass sleeve is still down inside just not as long to reduce the overall weight.

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I have rejected two pairs of floats of the new floats that have been in service for about 6 months. One set has gone over the 7 gram limit, the other is approaching. I'm already in the process of reporting it and doing a warranty claim.

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While discussing floats, I have a new theory why one could have a sinking problem and others may have not.

Premise:

  1. The floats are made of foam, which is closed porous.
  2. Airplanes cycle between different altitudes which leads to different atmospheric pressure between takeoff, cruise and landing.
  3. If the inner pressure of a foam bubble in relation to the outer atmospheric pressure exceeds a certain limit, the foam structure, building up a bubble, will crack.

Conclusion:

If an airplane is operated often at high altitudes while the departing and landing fields are at low elevations, this might lead to sinking floats more often, than in the other case.

 

What do you think? Is this theory intelligent or completly idiotish? I think, this could explain why some Rotaxes has problems with floats regardless the float generation used.

 

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Actually it was poor chemical composition compared to previous years. The closed foam pours were supposed to resist fuel absorption, but due to their chemical compound fuel was allowed to penetrate the pours. This is why earlier engines rarely had issue like we saw a while back. This has been changed over the years and looks like the ones they had a while back wasn't working out. This hopefully should now be corrected. The new floats when made like the old ones with the hollow brass insert were too heavy. So the brass insert was cut down and that's why you don't see it protruding out the ends anymore. They trimmed the float weight.

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I’ve been having good results with the current floats. However they seem to be on the heavy side out of the box even with the weight shaving. The last 8 sets I’ve gotten have come in around 3.1-3.2gms out of the box as opposed to the 2.9-3.0gms on the last few 2 dot and 3 dot versions. Ive cheaked on a few that have been in there for 6 months or so, and so far so good. 

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