Tom 4536

Braking After Landing

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15 hours ago, kortopates said:


You'd bet wrong. There was more than one version of single pick brakes used between your C and the midbody. The long bodies and Encore use a double puck brake. However, this doesn't improve braking action like you might think. It mainly improves how long the pads last. Same tires with same contact area, albeit more weight.

Same frictional area, more weight. The burden of being frequently correct is a heavy one.

  • Haha 2

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I've owned the M20M for three years and was never satisfied with braking.  I had almost accepted that the performance was due to the gross weight of the long body but continued looking for an answer given that I work (towards my own A&P rating) in a shop that specializes in Beech.  Last fall while doing the annual my plane I noticed some very tiny bubbles (almost invisible) in the brake fluid line from the master cylinders to the reservoir.  I back bled the brakes until I no longer saw this in the line but still was not happy with the results.  

Two weeks later, I decided to flush the entire system.  I back bled all the way through the system.  Dark red/brown fluid came and then new fluid from both sides.  Finally I have the brakes that I expected.

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Back up a little bit, GA aircraft brakes use mineral based hydraulic oil which is not hygroscopic but hydrophobic. Long story short, it will not absorb water like older automotive brake fluid.

Second, if your brake oil is thick/gooey, you also need new o-rings. Cleveland brakes don't have return springs and they rely on "o-ring roll" to return the piston. Get your hangar fairy to hang the calipers over a small bucket with the pads removed. Depress each brake pedal and the pistons will come out with a gush(or blob) of oil. Aeroshell 41(mil-5606) is cheap, let it run out and start fresh. You can then take them to your local mechanic to get them flushed and replaced with new seals.

After reassembly, fill up from the bottom and enjoy good brakes that also release properly.

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Over the years, I have tried several techniques to keep the brake fluid bright and shiny. What seems to work well for the hangar elves is, each year, to just drain a few ounces of fluid from each caliper and then refill the reservoir. 

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On 6/22/2018 at 2:54 PM, Hank said:

Nope. But people here are saying to change the brake fluid in cars and planes every few years. I don't spend money for the sake of spending it, and try not to fix things that aren't already broken or giving indications that they may break. The brakes in my cars ans Mooney work just fine. I probably use the emergency brake in my truck every month or two (but used it parking in my driveway in WV), but have yet to use the parking brake in my Mooney in the eleven years that I've owned her.

  Automobiles use a completely different formula for their brake fluid than whats recommended for your plane (5606 Hydraulic Fluid)  Just about every owner's/maint manual I've seen for an automobile will recommend brake fluid flush and renew between 80k-100k miles, some sooner than that.  I don't think "every few years" is applicable in either case, but if you are having braking issues in your Mooney then fixing any leaks, replacing the $6.00 worth of fluid and bleeding properly will usually solve better than 90% of these issues.

 

My .02,  

Ron

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Also as a matter of practicality don’t undervalue aerodynamic braking - pull that yoke back and save your pads. 

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