Wiring Your Plane with the Vertical Power VP-X

Marc Ausman of Vertical Power demonstrates a basic aircraft electrical wiring setup using the new VP-X solid state electronic circuit breaker system.

EAA Hints for Homebuilders: ELT Installation and Testing

EAA Tech Counselor Dick Koehler discusses the federal regulations and installation techniques for emergency locator transmitters (ELTs).

EAA Hints for Homebuilders: The Homebuilder's Library

EAA Tech Counselor Dick Koehler recommends a few must-have books for every kitplane builder’s library.

EAA Hints for Homebuilders: AN Hardware Basics

EAA Tech Counselor Sam Coates reviews the basic nomenclature and proper installation of AN threaded fasteners.

EAA Hints for Homebuilders: Riveting with a C-Frame

EAA SportAir instructor Wally Anderson demonstrates a backriveting technique using a C-Frame Bench Riveting Tool and a 12″ backrivet set, both from Cleaveland Aircraft Tool in Boone, Iowa. This technique seems virtually foolproof, and the results are sharp and consistent. I think I’ve just decided which C-Frame to buy.

EAA Hints for Homebuilders: Cutting Aluminum on a Bandsaw

Sam James demonstrates a technique for safely cutting aluminum sheet using a bandsaw.

EAA Hints for Homebuilders: Rivets 101

In this segment of EAA’s “Hints for Homebuilders” series of instructional videos, Tech Counselor Jack Dueck reviews the basics of driven rivets.

EAA Hints for Homebuilders: Sheet Metal Tools

Here’s a quick introduction to aircraft sheet metal tools, from the EAA’s “Hints for Homebuilders” series of instructional videos, featuring EAA Technical Counselor and SportAir Workshop superhero Jack Dueck.

Four Methods of Flush Riveting

I recently stumbled across this old Lockheed/Walt Disney Industrial Training animation which demonstrates four common methods of flush riveting used in aircraft construction. It reminded me of those tedious film strips we used to watch in fourth-grade science class. But hey, guess what? I learned something.

According to Wanttaja, “Every item made from 2024 or 7075 alloy should be cleaned, etched, alodined, and primed before assembly.”

• Cleaning
• Etching
• Alodining (Chemical Conversion)
• Priming
• Sealing the Faying Surfaces

You could probably condense the first three processes and just call them “Surface Preparation.”

Some Initial Thoughts

There seems to be a sort of continuum that defines the “RV Internal Priming Theory” spectrum, which runs from “No Primer” on the one end, to “Scotchbrite/Alumiprep/Alodine/AKZO” on the other. If it can be reasonably argued that the AKZO, etc. method offers the most thorough protection, and if a case can also be made for doing no priming whatsoever without the airframe turning to dust in your hands, then it’s safe to say that several adequate “middle roads” exist.

I’m finding several builders whose process is similar to this:

1. Abrade with maroon Scotchbrite pad, household detergent and water.
2. Degrease with MEK, acetone, PPG DX330, Coleman lantern fuel, or something similar.
3. Prime using whatever brand, toxicity, and style of application best suits the builder.

I think that’s what I’m going to do. But just for kicks, let’s go over the range of possibilities.

Cleaning

Cleaning means the removal of surface grime and corrosion. Exposed aluminum surfaces quickly form an oxidation layer, which, ironically, helps avoid further oxidation, but it needs to be removed before primer is applied. To break the corrosion and lift surface grime, try a mildly abrasive household cleaner (Dawn?) and Scotch-brite pads. When finished, wipe it down with MEK or acetone to get rid of fingerprints.

Sherwin Williams R1K213, Martin Senour 6387, PPG DX330, DuPont 3939S, BASF 901

First of all let’s clear up a few things; Lacquer thinner, acetone, MEK, and enamel or urethane reducers are NOT surface cleaners.

Source

Then, list specific product options usable for each step, including (especially) enviro-friendly solutions like Citra-Safe/d-Limonene instead of MEK or acetone.

As a straight solvent, d-Limonene can replace a wide variety of products, including mineral spirits, methyl ethyl ketone, acetone, toluene.

Etching

Primer doesn’t like to stick to the smooth, shiny aluminum surface, so we etch the components by hand, with Scotchbrite, or with a weak acid solution called an etchant.

Scotchbrite Pads

• Type I – Aluminum oxide (minimum of 94% ALO3 and a hardness of 9.4 Moh’s) Color: Maroon.
• Type II – Natural silicon dioxide (SiO2) (hardness of 6.8 to 7.0 Moh’s). Color: Tan.
• Type III – Silicon Carbide (minimum of 97% SiC and a hardness of 9.6 Moh’s) Color: Gray.

Aluminum oxide, silicon dioxide, and silicon carbide are classed as ceramics. Although one aerospace manufacturer specifies aluminum oxide pads for cleaning before chemical film treatment, I have it on good authority that all three ceramics are okay for aluminum.

Scotch-Brite™ Hand Pads 7447 or at Cleavland Tool: Scotch-Brite Red Hand Pad

Stewart Systems EkoEtch

Chemical Conversion Coatings (Alodining)

Alodining chemically changes the outer layer of aluminum to make it more corrosion-resistant. The end result is a golden-brown tint to the aluminum.

Although I believe the best corrosion control is produced by starting with a chemical conversion coating, very good corrosion control can be had by using two coats of corrosion inhibiting primer in place of the chem film. — Lee H. Erb, EAA Chap 1000 Det 5, Arlington TX; EAA Chap 34, June 1997

“The simplest way to prep the aluminum is to wet abrade with Scotchbrite and water, followed by solvent cleaning with acetone, or MEK, or toluene. The alternative is alumiprep 33 acid plus alodine 1201 conversion coating. This is NOT preferred because of the hazardous chromates in alodine.

In either case, before priming, it is essential to remove the thin oxide layer that forms on aluminum. Scotchbrite or acid etch will accomplish this.”

– John Griffin, Sales Manager Akzo Nobel Aerospace Coatings

That’s all I need to hear to skip the alodine process. My new process will be to wipe the parts down with acetone or laquer thinner to remove the oils, then alumiprep, and finally prime. That seems to be the least hazardous method to using AKZO. Source.

PreKote^®

This cool product might just take the place of the first three steps altogether, and is non-toxic to boot.

PreKote can be used on a wide range of surfaces including aluminum, steel, magnesium, titanium, CRES, galvanized surfaces, composite and plastic surfaces. Consistent, high performance results are achieved with a variety of paints and primers.

PreKote is non-toxic, non-corrosive, non-flammable, CFC free, ODS free, odor free, and readily biodegradable upon disposal. PreKote eliminates the forced air containment suits required for traditional chromated conversion coatings. Simple rain gear and goggles are all that is needed.

“For airframe construction, I’m going to try AKZO purchased from Aircraft Spruce and a product called PreKote as a pre-prime surface etch prep. For mixing and cleanup considerations, I’m going to try the 3M Paint Preparation System.” — Scott Card

Priming

Generally, it is accepted that two-part epoxy primers provide the best corrosion resistance. However, they are expensive, toxic, heavy and dry slowly all of which makes them problematical for the home builder. If you can tolerate those issues and want your RV to be in good shape when your grandchildren inherit it, they may be “best” for you. — Section 5A, Van’s RV-8 Preview Plans

Self-Etching Aerosol Primers

• Sherwin Williams GBP-988
• NAPA 7220
• MarHyde (light gray)
• Tempo A-880 (gray)
• SEM Self-Etching Primer

SEM Self-Etching Primer (Amazon.com)

• 39683 Gray, Aerosol
• 39684 Gray, Quart
• 39681 Gray, Gallon

Randy Lervold’s notes on interior priming on his RV-3B:

In deciding on the SEM for interior use I did consider the more thorough processes such as acid etch, alodine, and epoxy primer. In the end however, I decided that the materials listed above represent the best balance between the time investment and the protection they afford. I did informal testing with most of the commonly available self-etching rattle cans and found the SEM to be at least as durable as any of them, but left a nicer finish. [emphasis mine] — Randy Lervold

Sealing the Faying Surfaces

Fayed Surfaces of Similar metals – Seams and joints that possess fayed surfaces of similar metals shall be protected, at a minimum, by application of primer coating to each surface.

Just before riveting two pieces together, brush (spray or lightly wipe) the faying surfaces with primer, then install the rivets “wet.” If the rivets are inside and not exposed to weather, the “wet” can be primer. If one end of the rivet will be in the “weather,” then use sealant. Use a “Q” tip to put in a lot of primer just before placing the rivet in the hole. If you are using sealant, experiment a bit so that you don’t get too much squeeze-out. It is a skill.

Why the rivets should be installed wet: After drilling the holes of both sheets, the holes need to be deburred. We always used a large twist drill. The deburring leaves a small chamfer which may or may not be filled with rivet when it is installed. Installing “wet” pretty well ensures that there will be no void for electrolyte (water) entrapment.

Source

Cabin Interior

• Sherwin Williams Jet Flex
• DeVilbiss GTi 620G Millennium HVLP spray gun

References

• AvWeb.com Corrosion Control
• Muroc EAA 1000 Corrosion Control Articles
• Aviation Maintenance Technician Handbook, Chapter 6