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N91CZ

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Nov 19, 2013
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11
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Woodland, CA
Perhaps not a project for everyone, but I swapped my two elevator push-rods for carbon units after someone asked if it might save weight. Indeed it did. ~50%, 2 lbs vs 4 lbs. The larger the tube, the easier it is to save on weight. The tubes are roughly 5' and 6' in length. Primary load is compression. Can hold 9x 6G flight load (compression).
End plugs are aluminum with a spiral groove for gripping. Fittings are centered in tube with a precise bondline thickness of .010"
Weak link in tension is the threaded rod.

 

Victor Bravo

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KWHP, Los Angeles CA, USA
- 50 feet of 5/8" x 0.035" aluminum tubing - a bit over 4 lbs.
- If I could cut that in half I'd be saving about as much weight as I gain Thanksgiving day.
If you ate at our house you could use cast iron pushrods.

BTW Bob, off topic and unsolicited, have you looked into grant funding or gov't contracts to support your akafliegs? There may well be some funding there, because you have the capability to train in job skills, re-training, youth development, etc.
 
Last edited:

proppastie

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Feb 19, 2012
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NJ
Perhaps not a project for everyone, but I swapped my two elevator push-rods for carbon units after someone asked if it might save weight. Indeed it did. ~50%, 2 lbs vs 4 lbs. The larger the tube, the easier it is to save on weight. The tubes are roughly 5' and 6' in length. Primary load is compression. Can hold 9x 6G flight load (compression).
End plugs are aluminum with a spiral groove for gripping. Fittings are centered in tube with a precise bondline thickness of .010"
Weak link in tension is the threaded rod.
Really nicely done

...however looks like your aluminum tube is .065 wall, Bobs is .035 wall......His weigh 1/2 as much......If we use your numbers and assume a linear relationship (which may or may not be true) Bob's tubes would have weighed 2 lbs and you would of saved 1 lb.
 

Jonny o

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Oct 31, 2015
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Location
Fairbanks, AK USA
Perhaps not a project for everyone, but I swapped my two elevator push-rods for carbon units after someone asked if it might save weight. Indeed it did. ~50%, 2 lbs vs 4 lbs. The larger the tube, the easier it is to save on weight. The tubes are roughly 5' and 6' in length. Primary load is compression. Can hold 9x 6G flight load (compression).
End plugs are aluminum with a spiral groove for gripping. Fittings are centered in tube with a precise bondline thickness of .010"
Weak link in tension is the threaded rod.





Would post a picture of the spiral groove and give a description of your bonding technique. Thank you for the pictures and dialog.

Jonny
 

Marc Zeitlin

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Dec 11, 2015
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Tehachapi, CA
End plugs are aluminum with a spiral groove for gripping....Weak link in tension is the threaded rod.
In the short term, the weak link may be the steel rod-end threaded portion. However, as has been mentioned numerous times in this thread and many others, having aluminum in contact with carbon is a recipe for long-term corrosion of the aluminum. Depending upon the environment where you live and fly, "long-term" may be 1 year, 10 years, or 100 years - hard to say. But if any moisture ever gets in there (and humidity counts), galvanic corrosion will start.

I would also be concerned, with such a very thin bond line, with CTE issues between the AL and carbon. Again, depending upon the altitudes and environments in which you fly, you could develop large bond line stresses due to extreme cold shrinking the AL and not shrinking the carbon. If you've done the calcs, and a 0.010" bond line (with whatever adhesive bonding agent you used) can withstand say 150F temperature differential (100F max to -50F min, as an example) then maybe you're OK, but it would be chancy to use such a system without verifying bond line stresses at the extremes of temperatures and temperature differences. If you put a few rivets through there as a backup, this question becomes less safety critical, as it can be a checklist item at the CI, rather than a "hey, why doesn't moving the stick move the elevator anymore?" issue.

My $0.02.
 

Richard6

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Aug 14, 2010
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707
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Plymouth, MN USA
You may want to rethink the aluminum part in the carbon fiber tube.

Galvanic Corrosion could be an issue:

Galvanic Corrosion
The process of galvanic corrosion occurs when two different metals are touching each other in the presence of an electrolyte, a fluid that allows the flow of electrons from one metal to the other. As the process continues, one of the metals will deteriorate quickly as its electrons flow steadily to the other metal. When you fasten aluminum using screws made from a different metal, especially in situations where the metal is exposed to salt water, galvanic corrosion may cause significant deterioration of the aluminum base metal.

Aluminum Screws
Because galvanic corrosion happens when dissimilar metals come into contact with each other, the simplest way to prevent the process is to use screws made from the same metal as the metal you're fastening. Aluminum screws will not cause corrosion in aluminum base metal, even if the screws aren't plated or treated with any corrosion-resistant material.

Carbon Steel Screws
Unplated steel screws will cause corrosion in aluminum in a wet environment. They'll rust quickly themselves, as well, so they're not a good choice for fastening aluminum. Galvanized steel screws, however, are plated with a corrosion-resistant coating, usually consisting of zinc, that is not nearly as reactive with aluminum. The zinc plating prevents the underlying steel from coming into contact with the aluminum, and the risk of corrosion of the aluminum is reduced significantly.

Stainless Steel Screws
Stainless steel is an alloy of carbon steel that is, itself, resistant to corrosion. However, stainless steel is reactive with aluminum, and when a stainless steel screw is in contact with an aluminum base metal, the aluminum is likely to corrode. As is the case with carbon steel screws, a plated stainless steel screw is less likely to corrode aluminum; screws treated with a high-quality coating consisting of zinc and aluminum flakes are especially resistant to corrosion.

Brass Screws
Brass is very reactive with aluminum, and brass screws will cause substantial corrosion of an aluminum base metal in a wet environment. The process of galvanic corrosion depends on the presence of an electrolyte, though, so in a totally dry environment the risk of corrosion is low, even if you use uncoated brass screws.
 

Gareth

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Joined
Oct 14, 2018
Messages
21
Location
Brisbane
Thanks everyone you have answered my question, seems to much work for carbon system so will go with aluminium,cut to length,insert end threaded plugs ,bolt or rivet ,screw rose joint in and finished ,did 1 today after measuring it took 7 mins to finish
cheers gareth
 

autoreply

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Jul 7, 2009
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10,762
Location
Rotterdam, Netherlands
In the short term, the weak link may be the steel rod-end threaded portion. However, as has been mentioned numerous times in this thread and many others, having aluminum in contact with carbon is a recipe for long-term corrosion of the aluminum. Depending upon the environment where you live and fly, "long-term" may be 1 year, 10 years, or 100 years - hard to say. But if any moisture ever gets in there (and humidity counts), galvanic corrosion will start.
I regularly see damage due to galvanic corrosion, sometimes as soon as a week in.

Typically polyester bushings with a small %wt amount of graphite powder for lubrication. In salty offshore environments the aluminium structure around the bearing (the wear causes the graphite to spread out) often looks like it has been attacked by savage chemicals.

Even applications that are inside a heated space (factories etc) regularly show galvanic damage on the alu structure due to condensation.
 
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