EAA Sport Aviation - October 2009

members forum
Cable Fitting Errors

I read Mike Cushman’s article in the September Sport Aviation, and I have several problems with it. The process and materials he uses are notably different from how I do it, and I think that more research into what the CAA and FAA said about this process would’ve been a good idea.

First off, all of the FAA manuals and textbooks like Brimm and Boggess (Aviation Maintenance) specify using an iron or a soldering trough; flames are not recommended because heat is less controlled with them.

Next, modern solder may seem like a good idea, but it’s overkill for one thing, and more importantly it flows at 475°F and the FAA says max temp allowable is 450°F. CAM 18 specifies 50/50 lead/tin with a melting point of 390°F max. Worse than this is the flux. FAA says use a combo of rosin and stearic acid, which is a mild fatty acid that is edible and used in candy manufacture. It warns specifically against mineral acids like the hydrogen chloride and zinc chloride in the No. 4 Comet flux, which says right on the bottle “Corrosive Material.” There is no way to guarantee that there isn’t a pocket of this stuff inside the finished splice.

Finally, the splicing diagram is an important part of this process and should have been included with the article. I will attach a copy to this e-mail. It is very specific regarding wire size, length of wraps, and size of inspection openings.

I would not recommend the process as written in this (your) article.

Andrew King, EAA 275985

Vienna, Virginia

More About Cable Fittings

Regarding the article on “ Wire-Wrapped and Soldered Cable Fittings,” I have some concerns about the safety of this method of making these terminal ends. Some time ago I read a report concerning the failure of aircraft bracing cables with soldered terminals. Essentially two manufacturing processes contributed to the failure of the soldered terminal ends. First, excessive heat used in making the solder joint. The recommended method was to heat the wire with a soldering iron rather than a torch. Failed cable ends had used a blowtorch to heat the cable for soldering. The heat generated by the blowtorch destroyed the strength of the cable. Even careful use of a propane torch is likely to cause the same heat-related failure.

The second contributor to cable failure was the use of a corrosive flux in making the joint. In other writings, a sal ammoniac type flux was considered unacceptable as a flux in soldering cable terminal ends. The manufacturer of the Comet No. 4 flux that you recommend describes it as corrosive to steel and solder joints.

(In the report I read) while the cables initially appeared strong, improperly made cable failed prematurely, often with catastrophic results.

In the early days of aviation, cables were tinned prior to assembly and final soldering. As early as 1917, alternatives to soldered cables were being explored and recommended. You may be interested in reading the following NACA report from 1917:

Sunderlang, C C Horn, H J Green, D; Report on investigations of aviation wires and cables, their fastenings and terminal connections; NACA Report - 3; 1917.

I think that it is unlikely that soldered terminal ends would have been used by the Pietenpol era.

Another method of making cable terminal ends was by splicing the cable. Directions for splicing can be found in Aircraft Mechanics Handbook, Paul Van Winkle, editor, The Manual Arts Press, Peoria, Illinois, 1944. This book is available in electronic form through Google Books.

On a side note, after my father graduated from high school he was employed as an apprentice cable splicer for the Army Air Corps before being drafted.

Robert Luken, EAA 598460

Dayton, Ohio

Corrections

Unfortunately in the editing of my GlaStar completion in the August issue, it left the impression that it flies 175 mph while burning just 6 gph of fuel. While I wish that were true, it isn’t.

Here is the original text about my project: “Now with over 165 hrs flown, I can say the XP-360, with an AirFlow Performance fuel Inj., and LightSpeed CDI in place of a right Mag. has worked very well behind the 74” Hartzell blended airfoil CS prop., delivering either a top speed of 175 mph, or sipping 6 gph while running LOP at an economy cruise of 130 mph.”

Dustin Paulson, EAA 480819

Mora, Minnesota

Gone West Error

Because of incorrect information, we mistakenly listed Omer Benn, EAA 444649, as being deceased in the Gone West listing in the July issue (subsequently repeated in the September issue to correct city/ state errors). Omer contacted us to let us know he is alive and well in Champaign, Illinois. We apologize greatly for the error.

Pober Baby Ace Not Super Ace Chuck and Bonnie (Poberezny) Parnall called our attention to the fact that we incorrectly identified the airplane hanging in the Founders’ Wing on page 35 of the September issue. We called the airplane a Pober Super Ace. It is in fact a Pober Baby Ace, the airplane built for a Mechanix Illustrated magazine feature.