Primers - Airliners

Kind of wondering out loud here - I notice that Boeing apparently uses primer inside of their aircraft structure. Most airliners are scrapped in 20 years or so - so why does Boeing use primer inside? And what do they use? Does anyone have this knowledge - I'm interested to learn the answers.

Most big planes corrode from all the soda "pop", puke, urine, fish, salt and other yummy stuff that gets spilled. The Zinc based primers help to slow things, but are generally insufficient. Still, most Boeing airframes outlive the fuel efficiency of the engine technology. That is, most are scrapped because the engines burn too much fuel. Metal fatigue from thousands of cycles also is a problem. Corrosion isn't the cause of any retirements that I can think of. Well except Aloha.

E. D. Eliot said:

Kind of wondering out loud here - I notice that Boeing apparently uses primer inside of their aircraft structure. Most airliners are scrapped in 20 years or so - so why does Boeing use primer inside? And what do they use? Does anyone have this knowledge - I'm interested to learn the answers.

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Ooooh goodie, a chance to reignite the primer wars.

The short answer is that Boeing prime their aircraft because they are professional, they are smart, they have enormous experience, and they know that unprotected or alclad aluminium in certain enviroments can start corroding almost immediately.

The VansAirforce archives are full of reports of RV builders developing corrosion on bare alclad components....during the build process!!! They come up all the time. So much for unprotected Alclad. Here's a thread posted just a couple of weeks ago:

http://www.vansairforce.com/community/showthread.php?t=79813&highlight=corrosion

It should tell you something when even Scrooge McVan uses a primer on his quickbuilds (not much of a primer mind you).

On aluminium components Boeing actually uses a Boeing Spec product, namely BMS 10-11 Type 1, which is a two-pack epoxy primer and typically comes in a green or yellow colour.

In reality virtually all of the reputable general aviation manufacturers now use the same BMS 10-11 spec product including Piper and Cessna.

It is relevant that decades ago many major GA aircraft manufacturers, including Piper and Cessna, never used any primer at all. The end result has been an international fleet of GA aircraft with massive corrosion problems which have left today's owners with a corrosion repair bill that totals literally hundreds of millions of dollars annually.

You'll hear anecdotal reports from some owner living in the Mojave Desert about how good his non-primed alclad-only Cessna from 1975 looks...but the truth is that a large percentage of the ageing GA fleet are now virtual rust buckets. You only have to pop a piece of alclad aluminium in a 5% saltspray cabinet for a mere couple of days to realise that alclad (a thin, pure aluminium coating) alone provides extremely limited corrosion protection. It's better than nothing....but not by much.

You may ask yourself why so many RV builders do not properly prime their aircraft given the experience of major GA players such as Piper and Cessna. The reasons are many but I will list a few.

1. Ignorance of the limited protective capabilities of Alclad.

2. Desire to save money.

3. Desire to save construction time.

4. Building for their own limited flying future rather than the possible extended flying future of the aircraft.

5. Encouragement from other builders who are influenced by 1-4 and feel the need to rationalise their "easy option" building technique.

E. D. Eliot said:

Kind of wondering out loud here - I notice that Boeing apparently uses primer inside of their aircraft structure. Most airliners are scrapped in 20 years or so - so why does Boeing use primer inside? And what do they use? Does anyone have this knowledge - I'm interested to learn the answers.

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The AKZO primer a lot of us use was started by Steve Barnard (of the CAFE RV-6A and first quickbuild kits) when he worked for MacDonald-Douglas in Long Beach.

At that time it was made by Dexter and the specification was a MacD-Doug specification. The manufacture has changed (bought out IIRC) and of course McD-Doug was bought out by Boeing and company specs combined.

At first it came from the local aerospace paint distributors in the LA area - then someone persuaded Aircraft Spruce to stock it. It was around $80 a kit back then.

Captain Avgas said:

...The short answer is that Boeing prime their aircraft because they are professional, they are smart, they have enormous experience, and they know that unprotected or alclad aluminium in certain enviroments can start corroding almost immediately.

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And their planes still corroded!

E. D. Eliot said:

Kind of wondering out loud here - I notice that Boeing apparently uses primer inside of their aircraft structure. Most airliners are scrapped in 20 years or so - so why does Boeing use primer inside? And what do they use? Does anyone have this knowledge - I'm interested to learn the answers.

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Since I was a production worker for McDonnell-Douglas/Boeing, I came into direct daily contact with and am reasonably familiar with the primer practices used by the giant defense contractor. I can assure you that a robust corrosion control program is paramount and no expense is spared to stave off the effects of corrosion. In addition to epoxy primer, all salt water aircraft such as the FA/18 and T45 also feature proseal between every part before being joined, I mean everything including something as dimunitive as a small electrical clip.

For a time, I also did modification work on Hornet flaps that came back to the factory after years of operational service with the fleet. Amazingly, despite those flap assemblies employing the toughest corrosion control measures and methods known to man, even still, due to the effects of salt water some of those flap assemblies became hopelessly corroded and as a consequence, scrapped.

It was a stint on the C-17 program that sold me on AKZO epoxy primer. If that tough primer is good enough to meet Boeing's uncompromising specifications, it is good enough for me.

apkp777 said:

Most big planes corrode from all the soda "pop", puke, urine, fish, salt and other yummy stuff that gets spilled. The Zinc based primers help to slow things, but are generally insufficient.

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You're probably referring to the famous yellow/green "zinc chromate" primer adopted for use in aircraft during WW2. It's still available but no longer very popular.

I doubt that any serious aircraft manufacturer today would still be using that product for general priming...certainly not Boeing.

The Boeing BMS10-11 specification contains either barium or strontium chromate and has far superior adhesion properties to the old zinc chromate products.

Captain Avgas said:

You're probably referring to the famous yellow/green "zinc chromate" primer adopted for use in aircraft during WW2. It's still available but no longer very popular.

I doubt that any serious aircraft manufacturer today would still be using that product for general priming...certainly not Boeing.

The Boeing BMS10-11 specification contains either barium or strontium chromate and has far superior adhesion properties to the old zinc chromate products.

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They were still using gallons of Zinc Chromate 20 years ago. That along with the BMS 10-11. And yes, the Zinc Chromate was not nearly as effective, but the 10-11 wasn't a cure either.

My point is, nature wins. Like it or not. When it comes to primer people just need to do whatever it takes to ease their conscience. I personally have treated, primed, top coated, Dynoled, sealed, taped, waxed, vapor barriered, and still spent years (literally) grinding corrosion and doing repairs.

Rick6a said:

....
It was a stint on the C-17 program that sold me on AKZO epoxy primer. If that tough primer is good enough to meet Boeing's uncompromising specifications, it is good enough for me.

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Err, minor detail Rick, but shouldn't that be good enough for McDonnell Douglas?....

The C-17 was designed in Long Beach, correct? ...and the primer spec was a McDonnell Douglas specific specification before it was adopted by Boeing.

Is the same AKZO (nee Dexter) product now being used on Boeing designed planes with the merged in McD specification?

apkp777 said:

My point is, nature wins. Like it or not. When it comes to primer people just need to do whatever it takes to ease their conscience. I personally have treated, primed, top coated, Dynoled, sealed, taped, waxed, vapor barriered, and still spent years (literally) grinding corrosion and doing repairs.

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I'm not sure exactly where you're coming from on this issue.

Are you suggesting that any steps taken to prime and prevent corrosion from the outset are simply futile because in the end "nature wins". Surely not.

Perhaps you can elaborate.

Captain Avgas said:

I'm not sure exactly where you're coming from on this issue.

Are you suggesting that any steps taken to prime and prevent corrosion from the outset are simply futile because in the end "nature wins". Surely not.

Perhaps you can elaborate.

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Whatever it takes to ease your conscience. Some guys prime everything, some only certain areas (what I did). Some prime nothing. I really don't think there is a right or wrong answer to the priming question. Just don't think that priming is the corrosion "solution". Certainly helps, so does alclad, so does corrosion inhibitors. I am sure the epoxy primers are likely the best choices. Boeing did not solve corrosion with BMS 10-11 epoxy primer. I doubt any of our RV's operate in the environment that airliners operate in. Still, spill one Coke in your plane, primer or no primer, in a few years, you'll be amazed. I for one don't allow sugar drinks in my plane. I primed all the inaccessible areas and top coated most of them as well. In wet areas, I also used Corrosion X. When I move to Florida (soon), I will probably Corrosion X the whole plane. Maybe use T-9, haven't decided for sure.

I understand priming makes some feel warm and fuzzy, it just doesn't help me forget the barrel areas and "penthouse" in DC-10's, the keel's of 727's, and the cargo pits in 747's. I admit, my only experience is applying "FR" primer in the form of Zinc Chromate. In hind sight, if I built another plane, perhaps I'd get my hands on something better. For the record, I used DAP self-etching primer on my RV. It was cheap, convenient and seemed like a reasonable choice.

az_gila said:

Err, minor detail Rick, but shouldn't that be good enough for McDonnell Douglas?....

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Gil,

I never could get used to being a "Boeing" employee. I hired in at McDonnell Aircraft. In 1967 it morphed into McDonnell-Douglas. In 1997, I suddenly became a Boeing employee. How the big boys divvy up business spoils on that level is way beyond my depth.

Rick6a said:

Gil,

I never could get used to being a "Boeing" employee. I hired in at McDonnell Aircraft. In 1967 it morphed into McDonnell-Douglas. In 1997, I suddenly became a Boeing employee. How the big boys divvy up business spoils on that level is way beyond my depth.

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I know how that goes, I went from Hughes Aircraft to GM Hughes Electronics to Raytheon without moving...