General enquiry

[Guest Redair]

Greetings each, well as my hunt for the pefect aircraft continues, I find that I am puzzled, with regard to construction of kit aircraft. Having looked at many websites and magazines, I would like opinions of those who have been there and done it, on whether or not, complete painting of the inside surfaces of metal aircraft is required during construction.

 

It seems that some just use a sealing agent or primer on the contact areas of the various metal parts, whilst others paint everything in sight.

 

Is there a recommended procedure, or is it just down to personal choice/cost?

 

Regards, Redair.

 

 

[Case]

Good question Redair. I'd also like to know what people are using eg. brand names. I would have thought contact surfaces would be the primary concern.

 

 

[Guest Flyer40]

It seems you can go further than that. I've been reading about hard case builders who rig up large acid baths to anodize their components prior to assembly and now I'm less clear on what constitutes adequate corrosion protection.

 

Acid wash, Alodine, zinc chromate primer, etch priming.......... I've had difficulty grasping what's what because every article I've read seems to assume some prior knowledge, which I don't have.

 

Is there an authoritative reference suitable for dummies?

 

Would a can of green spray paint do if I matched the colour? ;)

 

 

[Ultralights]

Standard procedure for Boeing, Airbus, BAE and Augusta westland is..

 

1 treat all aluminium parts with an alodine or alochrome solution, some are brush on and dry others are a 2 part mix which is rinsed off with water.

 

2 parts are then painted completely in a zinc chromate primer

 

3 parts are installed/joined using a sealant or joining compound, sealant is a must on all areas exposed to air flow, rain, heat, oils and other fluids, otherwise just a joining compound will do.. joining compound is to ensure gaps and between metal parts are filled so water cant condense in the voids

 

final parts are painted in a interior or external paint.

 

when an aircraft is "marinised" all components are painted in 2 part polyurethane paint before being assembled "wet" with sealant on all components.

 

Titanium and steel components are treated by Passivation instead of Alodine/alochrome solution.

 

we are currently modifying the Navy Sea King fleet to improve crashworthiness, even though these helicopters are reasonably old, and have spent most of their operational lives at sea or flying low over salt water, we are yet to find any trace of corrosion anywhere. yet the Bae Hawk 127 aircraft built in williamtown, were all test flown with only a coat of primer, after their testing flights, they were panted in RAAF blue and grey camouflage, these aircraft are only just 6 yrs old now, and are riddled with corrosion, some to the point of complete part failure.

 

if at a minimum, paint every part!!

 

anotehr thing i have been thinking independently is, corrosion needs 3 things to start, but an electrical current is the primary cause, i am wondering, instead of wiring earth connections to the airframe, then the battery, wouldnt the risk of corrosion be reduced if the earth was routed directly from the component, to another bus to the battery? as this would remove the electrical path from the airframe? and no, im not an avionics expert. just structures.

 

as for making large baths for treating, in the field we use a large plastic bin, and to spray bottles, one with the solution, and the other with water, and spray the parts while they are in the bin using appropriate PPE of course. or you can purchase the alochrome pens which is a wipe on and let dry solution.

 

 

[Guest Redair]

Just as I feared... more involved than I could ever hope to comprehend with my minature brain!!! Looks like I'll be doing a lot of research in this area now, and there was me thinking the only thing I had to worry about was which aircraft to go for;)

 

As for the elastic-trickery being a cause for concern, an earth bus or a hard wired return seem like an excellent idea.

 

Thanks, Redair.

 

 

[Case]

Eddie Seve is a Zodiac builder on the web (Kitlog). He has just used Cortec primer. Don't know much about it and can't find a supplier in Australia. I think Eddie imported it from the US.

 

 

[Guest disperse]

Negative earth

 

anotehr thing i have been thinking independently is, corrosion needs 3 things to start, but an electrical current is the primary cause, i am wondering, instead of wiring earth connections to the airframe, then the battery, wouldnt the risk of corrosion be reduced if the earth was routed directly from the component, to another bus to the battery? as this would remove the electrical path from the airframe? and no, im not an avionics expert. just structures.

 

A very good point. The negative would be the weight of the extra cable. also with painting. The weight.. sounds silly but just pick up a 4L tin

 

What if you were to run a thin copper strip down one side ? would only have to be less then 1" wide and could be wired direct to the negative terminal?

 

 

[Ultralights]

another little thing i have discovered and looked into with my Vampire, after i bought it, i gave it a good going over, and discovered quite a few rivets have failed. not because of corrosion, but the rivet head had work right through the aluminium skin, creating a hole the same diameter as the rivet head itself. after talking to the NDT guys at work, i have been told the cause is, being a polished metal finish, is the polish itself, when the aircraft has been polished, and it has on a regular basis, the polish which is an abrasive, is forced under the rivet heads, where is stays and through the movement and flex of the skin in flight and handling, the abrasive polish has worn a hole through the skins!!

 

so now after replacing a few wing skins on the vampire, polish is kept well away, and i now use a non abrasive Wax to maintain the shine..

 

i was thinking about the paint weight drawback, i was thinking, if a 4 ltr tin of paint weighs 4 kg, how much of this paint actually is added to the part, i know when i spray paint things, im sure 90% of the paint doesn't ever reach the job, and is lost as overspray or just ends up on the filter paper in the booth.?

 

 

[Guest Redair]

Indeed, the extra weight was something that I was thinking about when I posted the question, but over the years, I have seen so many metal aircraft that have been painted that nice shade of washed-out green on the inside, that I began to wonder if it was just fashion or there was a good reason to do it... and I quite like the colour!

 

As for polish... well apart from the fact that I would be too lazy to do it, I think that a nice coat or two of shiny paint would be an advantage when it came to helping seal up any gaps/joints in the skins.

 

Redair.

 

 

[Guest ozzie]

Just a point for those who are puting an electrical system in their aircraft. it is best to try and avoid using the aircraft as an earth point. try and isolate all the components from the airframe (lights,panel engine ect) lot of work but if you are going to keep it for a long time it will help reduce corrosion in your airframe and around the earth wire connectors on the mounting points. this is what usually gives you high resistance makes your battery and alt work hard and components not working at their best due to voltage drops ect. learnt this when working on ali boats. if you do use your airframe as an earth make sure you use stainless for both the wire and connectors as some of the others actually encourage corrosion.

 

just some tips

 

ozzie

 

corrosion prevention and painting prep. i use Henkel Alumiprep 33 for cleaning and conditioning followed by Alodine 1201 a chemical etch coating then followed by a two pak zinc chromate etch. if applying a finshed coat over this i would use something like Almigrip two pak primer followed by Almigrip two pak colour.

 

Note: zinc chromate will not stay on unprepared and unetched surfaces. if you are going to farm the work out to an automotive refinisher make sure they are experienced in painting aluminium. most are not.

 

avoid automotive paints as they are not subject to the rapid tempeture changes that an aircraft is subjected to. ie parked on the ground in 30+ then several minutes later it can be minus somthing. auto paint will crack and craze within 12 months.

 

of course plastic parrots are a diffferent case when prepping.

 

plenty of good books on these subjects.

 

 

[Guest Flyer40]

Excellent advice from the pro's, thanks. It sounds like being a metal worker means necessarily having secondary skills and equipment in spray painting.

 

I have to say plastic is starting to look less unappealing. Especially with the earthing issue that ozzie pointed out which is no longer an advantage to metal.

 

 

[Guest Redair]

Excellent advice from the pro's, thanks. It sounds like being a metal worker means necessarily having secondary skills and equipment in spray painting. I have to say plastic is starting to look less unappealing. Especially with the earthing issue that ozzie pointed out which is no longer an advantage to metal.

Quite so, and this is why I am finding it so hard to choose the right aircraft.... every time I look into one area or another, more potential problems seem to be waiting there for me. There appear to be that many drawbacks to each style/design, that I might just end up buying a kite and waiting for a windy day!!!

 

Thanks for the advice from those in the know though.... without your input to my sometimes odd questions, I might otherwise end up making a very expensive mistake, or series of mistakes.

 

Redair.

 

 

[Guest ozzie]

Please don't let my comments scare you away from what you wish to build. just pointing out that if you wish to build an aircraft that will still be in great order when you pass it to your grandson you really have to pay attention to not only the construction but also the quality of finish.. if you want an aircraft that will work when you flick a switch then you have to spend the time and go a little futher and think of the future, the area you operate in and other parameters. some people build an aircraft for experience only and just throw it together, when it is finished they will start on something else and the other aircraft is retired with low hours on it and engine and other parts used on the new one. and the cycle goes on. If on the other hand that it will be in your flying life for ever, then it is a different story. do you wish to spend more time maintaining or flying. The finish is personal as well as preventive and just painting and going for a high standard of corrosion prevention may take as long as it did to assemble the kit.

 

The owners of earlier GA spam cans have just been asked to inspect their airframes fully for corrosion as the manufacturers did not expect them to have a high life time and this reflected the way parts were preped. if you have ever had the chance to look fully inside a cessna wing you will notice that there was not one bit of corrosion prevention done during manufacture. These are the aircraft that look like finding there way onto the RAAus register in the maybe near future. Soon A C150 may be the same as a DC3. you can pick them up for a song but your 100 hourlies will kick the crap out of you..

 

ozie

 

 

[Guest Redair]

Ozzie, thanks, but do not be too concerned... you haven't scared me off (yet!) it's is just that my list of priorities and requirements keeps getting re-arranged due to the extra, or hidden little details that come to light as I look deeper into each type of construction. I guess that in the end, I have to weigh up all the extra costs, (money and time) of each type until I can decide what is going to best suit my needs and my abilities. Sadly I am the sort of person who cannot just throw something together. I'd rather take twice as long looking at the instructions and three times as long on the construction, to know that I have done something as well as I possibly can. And, more to the point, know that I will not have to start pulling things apart shortly afterwards to re-do them to a better standard. There will be a large amount of time and money invested in whatever I choose, and I want to get the right aircraft first time round, and hopefully keep it.

 

Like it says at the bottom.... "So much to learn"

 

Redair.

 

 

[old man emu]

Regarding polishing the finished surface of arcraft:

 

When we do an Annual/100 Hourly, we finish off by cleaning the aircraft. We use good old Turtle wax, applied with a moist cloth. and polished off with a soft, dry cloth. We use Turtle wax on composites (Jabs etc) and aluminium (Cessna & Piper). Turtle wax is a good, soft polish for windows.

 

I'm off work until Thursday, so when I get there, I'll get the details of the chromate we use as a coating for metal airframes. I'll post my findings on Thursday night.

 

Old Man Emu

 

 

[Wilfred]

I have read about how they get olive oil and baby oil

 

I just hope they don't injure any turtles getting that turtle wax.

 

 

[Guest Redair]

Thanks Mr Emu, I look forward to your next post, as I need all the help I can get if I'm ever going to come to a decission on an aircraft, although having said that there is one which is very near the top of my list now, so fingers crossed.

 

Just one other question... Turtle Wax is a good, soft polish for Windows... would that be the XP Home Edition or Professional?

 

Redair.

 

 

[Yenn]

Do not mix copper and aluminium, as an ex yachtie I know this is a sure fire recipe for corrosion. A copper coin dropped in the hull of a tinnie will quickly eat it's way through.

 

The weight of paint includes a lot of volatile compounds that evaporate, reducing the weight. I don't know the actual ratio.

 

 

[Thruster87]

[Soon A C150 may be the same as a DC3. you can pick them up for a song but your 100 hourlies will kick the crap out of you..] LOOKY HERE!!!!! the DC3/C47s are around 60yrs OLD and are still flying with VERY little corrosion on our two at HARS.They where made in a hurry during the war years but they where primed with zinc chromate and it has made all the difference. Cheers T87

 

 

[slartibartfast]

Like this one.

 

[ATTACH]4911.vB[/ATTACH]

 

She arrived from South Africa some time ago and has been sitting around at Goulburn in the elements for ages. Now she's getting a little engine work and will soon be winging her way to Bankstown for the next stage of her life.

 

Great to see.

 

 

 

[old man emu]

Just one other question... Turtle Wax is a good, soft polish for Windows... would that be the XP Home Edition or Professional?Redair.

Nahh! It's for Vistas :clown:

 

Old Man Emu

 

 

[old man emu]

Redair,

 

I took your question to work today, and this is the answer I got:

 

Because we are in the Parts & Hardware supply business, we don't make recommendations about paints or surface preparation products. We gladly will direct you to the sources of information which will allow you to make an informed decision. Having made your decision, we will help you obtain the products you require at the best price.

 

The reasoning behind this policy is that there is a lot of subjectivity in these decisions, as well as a lot of objectivity. Sometimes people make subjective decisions in buying paint, then when it doesn't please when the paint is applied, they try to shift it back onto the supplier.

 

Anyhow, our first bit of help is to direct you to FAA Advisory Circular No 43-4A, "Corrosion Control for Aircraft". You can find this on the 'Net if you Google "Advisory Circular". You can mouse thru the Index until you find the Circular, then download it in pdf format.

 

You can get the product Alodine through Aviall. 2-Pac chromate paint can be obtained from a business caller Volmar, which is in Sydney.

 

If you need any further directions, or contact details for suppliers, don't hesitate to ask.

 

Old Man Emu

 

 

[Guest Redair]

Many thanks Mr Emu.

 

Redair.

 

 

[bushcaddy105]

Gooday Redair- I have just come across your thread, and have found all the replies interesting, as none seem to distinguish between the different alloys or alclad. I, too, went through the investigation process before building my BushCaddy, and decided that as 6061 alloy was the predominant material, and that it has good corrosion resistance, I would just prime both surfaces of all laps before final assembly, after thoroughly solvent cleaning these surfaces. To keep weight down, I brushed only along the joint lines rather than spraying, and left the rest raw. As zinc chromate seems to be a definite health hazard, I used a single pot epoxy etch primer (the fumes of which are probably equally toxic!) and had no trouble with adherence. Quite the opposite - stray dribbles on external surfaces due for future painting took some hard scrubbing with thinners to remove. Time alone will tell if long term protection is up to scratch, but after 2 years no problems are evident.

 

Just another approach to confuse you!

 

 

[old man emu]

The decision on how much corrosion prevention you do whilst building an aircraft falls squarely into the "penny wise, pound foolish" category.

 

30 odd years ago, Piper and Cessna were pumping out aircraft like crazy. They didn't expect the aircraft to remain in service for as long as they have - planned obsolecence. Therefore, they didn't corrosion proof their products satisfactorily. At the maintenance facility I work at, we are seeing the result of this type of thinking in a number of aircraft. Owners are dropping their planes in for Annual Inspection, expecting the aircraft to be returned in a day or so, but finding the aircraft needs major restoration work, costing a substantial percentage of the value of the aircraft. And the market value of the aircraft after restoration does not reflect the cost of it.

 

How much weight will you add to your aircraft by applying corrosion protection? Probably not as much as added by tie-down kits, tow bars, and other assorted junk that finds its way into cabin space. Sure, a four litre can of chromate paint weighs about 5 kilograms, in the can. But a lot of paint is lost to the atmosphere during application AND during drying off of the thinners and carrier fluids in it.

 

One thing I urge you to do when purchasing any kind of chemical product you intend to use on your aircraft, is to ask the supplier for the Material Data Safety Sheets applicable to the product. Read through them before opening a can of anything. The information will protect your health so that you can enjoy the fruits of your labour well into the future.

 

You are investing a lot of your life into building your plane, and buckets of TLC. Your aircraft will have a higher quality finish than any factory built job because the finished product will reflect your personal standards. For you, it's a labour of Love. For the factory employee, it's a means to an end. You can be "pennywise" and save a few dollars by ignoring corrosion prevention while building, but in a few years' time your savings may be "pound foolish"

 

Old Man Emu