Nicopress fitting failure report

[dewi8095]

Thanks, Ron.

Don

[Racegunz]

After reading this thread I just had to go and try to destroy one of the first cables I made with my cable swager, (it was loose according to the guage) I clamped the cable end to my welding table and put a 10" long drift punch in the eyelet and levered it under the tubing on the extremely heavy table. I literally stood on the drift punch and bounced on it until it bent some, this is way more tension than you could pull on a stick or push on a rudder pedal. It held, didn't even look like it was stressed. When I get back to work I'll do a more scientific test with our hydraulic ram press and let you know when the same cable fails (if it does). Long story, but I have new confidence in my cables. I can only imagine how bad this crimp must have been to be pulled out like it was.

[bwilson4web]

I have a 1940 edition of "Aircraft Maintenance" by Daniel J. Brimm, Jr. and H. Edward Boggess. They don't mention nicropress fittings but instead have a section titled "HOW TO MAKE A WRAPPED TERMINAL" (pp. 377.) The short version is they put the thimble in a 'splicing clamp' and run the cut end 21 times the cable diameter. This is wrapped in soft steel wire and soldered with three, 7D wrappings, and an 'inspection' gap. Then everything is soldered. Soldering cable, especially if it has any plastic coating or core, is not going to be practical. Also, the labor per termination is going to be higher than pressing a slieve. But is there there a strength problem with the old style, wrap-and-solder? This is followed by sections "HOW TO MAKE A FIVE-TUCK NAVY SPLICE" and "HOW TO MAKE A ROEBLING ROLL SPLICE" . . . Thanks, Bob Wilson

[Dana]

My 1941 Taylorcraft still had the old woven eye splices on some of the control cables. Properly done they're very strong, but they're also very labor intensive and require a high degree of skill from the mechanic. It was state of the art back then... Nicopress didn't exist yet.

P.S. I have the same book... and the companion "Aircraft Engine Maintenance" volume.

[Tom Downey]

Inspect cables old enough to have woven splices, very well they are subject to corrosion and wear, AC 43-13 has a very good inspection criteria for this.

[Dana]

I know this is an old thread but there is a discrepancy between Hangar10's checking figures and Ron W.'s ShopSheet figures... which is correct? I need to check the swages I did on new 3/32" rudder cables for my Kolb.

Hangar10 says:
1/16" sleeve - .190-.195" go dimension
3/32" sleeve - .255-.265" go dimension
1/8" sleeve - .343-.353" go dimension
5/32" sleeve - .380-.390" go dimension

but Ron W says:

1/16" .1908 max
3/32" .2674 max
1/8" .3532 max
5/32" .3965 max

[RV8505]

As A Tech Counsler and Airline Mechanic I discourage the use of home made cables! It is bad genral practice to use uncalibrated tooling to crimp your fitting and then not load test it on a calibrated load testor. This is just an example of why I discourage it.

For example:

Moreover, completed cable assemblies in certified aircraft are required to be tested prior to sale or installation. That test load or proof requires that the cable be pulled from the attachment pin, eye, or other fitting to at least 60% of ultimate cable load, or at least 1200# (WITHOUT SLIPPAGE OF THE FITTING!). ALL FAA-PMA cables are produced to this standard, which is difficult if not impossible to meet in a field environment where a simple nicopress tool is used to fabricate the cables.
(Classic Aero LLC and Univair both produce cables to this OEM standard)

The point I want to reinforce, is that you can make cheap cables for about $25-28 each, And, the untested failure rate is relatively high. In the alternative one can buy certified cables for twice to three times the home-made cost which have been pull tested for slippage to more than 1200#- and you will be assured of proper, long-term, safe operations without cable failure.
Is the loss of control in your aircraft worth the additional $300-400? For most of us it is.

[Racegunz]

As A Tech Counsler and Airline Mechanic I discourage the use of home made cables! It is bad genral practice to use uncalibrated tooling to crimp your fitting and then not load tested on a calibrated load testor. This is just an example of why I discourage it.


, And, the untested failure rate is relatively high. .

Really? relatively high? until this thread I had not heard of a homemade cable failing and this threads example was just a ridiculously bad job. What is relatively high? do you have any NTSB reports verifying your stance?

[RV8505]

Really! All it takes is one to ruin your day! By not using the proper equipment your rolling the dice and gambeling with your life and the life of your passengers. Here is one example, google the internet you won't have to go far.

On August 21, 2011, at 1514 central daylight time, a Hendryx/Wiley Super Rebel experimental amateur-built single-engine airplane, N540AF, sustained substantial damage during a forced landing following an in-flight failure of the aileron cable near La Porte City, Iowa. The private pilot, who was the sole occupant and registered owner, sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the 14 Code of Federal Regulations Part 91 personal flight. The flight departed the Nichols Airport, La Porte City, Iowa, approximately 1425.

According to the pilot, the accident flight was the third flight into the Phase 1 flight test program. While maneuvering the airplane at 2,500 feet above ground level through a series of turns, the pilot noticed the control stick force increase, and then he heard a bang. Following the bang sound, the pilot had no aileron control authority. The pilot maintained some control via rudder inputs and executed a forced landing to a field. During the forced landing, the airplane nosed over and came to rest inverted.

A postaccident examination of the airplane revealed the firewall and fuselage were buckled. One of the aileron cable swages failed, which resulted in the loss of aileron authority. According to a Federal Aviation Administration inspector who examined the airplane, the cable swage failed due to an improper crimp. The cable was manufactured by the builder during the airplane build process.

From the NTSB Docket
Steve Johnson

[Frank Giger]

That's why EVERY swag has to be checked with a go/no go gauge, which takes just a second to do.

For my aircraft, buying pre-crimped cables is changing one problem for another - the drag/anti-drag cables in the wings, for example, are tensioned in situ to ensure both tightness and to keep the wing square. Using pre-measured cables would mean introducing a turnbuckle, which wouldn't be seen again once the wing is covered.

The fewer parts to break or loosen the fewer points of failure.

I got a friend of mine with the right tools to take one of my oopsy cables (nothing to do with the swags) and take it to failure. The cable failed before the swag, breaking well away from it, which made me pretty happy.