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jonss1948

Modern Aircraft Paints.

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I was contemplating. Do modern aircraft paints, impart a positive aerodynamic effect on the hull of say, a 747 and does the extra weight of the paint, cancel out any efficiency advantage? The reason I ask is because there must be a lot of titanium dioxide in those paints and it's heavy stuff. It could be merely an advertising thing but with fuel burn paramount, these days, do airlines consider this?

 

Jon

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I've never run an airline, but if I had to speculate, I'd say the paint might be there for corrosion control. Also I think it might be easier to keep a painted aircraft clean. As you pointed out the paint adds significant weight which I'm sure the airlines do consider, so I'm sure they believe they derive some benefit to their bottom line which makes the weight worthwhile.

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Yes paint does have weight and will increase fuel costs and increase take off weight. Remember it was American Airlines that didn't use paint for decades, mostly because Cyrus Rowlett Smith hated painted aircraft. Robert Crandall justified this by saying less paint reduced the aircraft's weight, thus saving fuel costs.

 

A painted 747-400 with logos will add just over 555 pounds to the aircraft. A polished 747-400 with logo's adds only 55 pounds to the aircraft.

 

Check out this chart from Boeing:

http://www.boeing.com/commercial/aeromagazine/aero_05/textonly/fo01txt.html#table1

 

Read through the rest of that link and a lot of your answers are on there.....Cheers


Matthew Kane

 

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I seem to recall a few years back now Cathay Pacific used some kind of experimental coating on one of their aircraft, I think it was an A340 that was supposed to reduce the drag on the fuselage and thus improve fuel efficiency. I think they found the cost/trouble of maintaining the coating was greater than the amount of fuel saved.

 

I also remember reading somewhere that the pigment used in red paint is quite heavy and adds a lot of weigh to a large aircraft - hence you don't see many liveries that have lots of red in them.

 

Finally, I think the reason why the USAAF stopped painting so many of its aircraft in 1944 was to save weight. On an aircraft the size of a B-17 or B-24 the weight saving was very significant.

 

Then of course there's the corrosion control aspect. I work on a ship and we paint absolutely everything to stop corrosion. I'd imagine it's very much the same with an aeroplane. Also bear in mind modern aircraft with a high degree of composites would look absolutely awful and ramshackle if they weren't painted.


Nick

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"Finally, I think the reason why the USAAF stopped painting so many of its aircraft in 1944 was to save weight. On an aircraft the size of a B-17 or B-24 the weight saving was very significant."

 

 That was more for time savings during the build process. We had acheived air superiority by 1944 over Europe and we were at peak production rates in '44 as well. So USAAF made the decision to for-go the paint altogether as a way to save time. Given the speeds of the time, any weight savings would be neglible for the mission being flown. Saving fuel wasn't high on the list during wartime.

 

 Composites have to be painted, or at least some sort of topcoat applied. They are too porous to be left bare, unlike aluminum clad skins.

 

"I'd imagine it's very much the same with an aeroplane."

 It is. If you have bare metal, out comes the Alodine, and the paint brush. Conversion coat first, then you apply the polyurethane paint to touch up.

 

 Raptor

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From Boeing's website:

CORROSION PROTECTION

Polished and painted airplanes both need to be washed regularly to preserve their exterior surfaces. However, for the sake of appearance and image, it is not uncommon for polished airplanes to be washed twice as often as fully painted airplanes. Regular washing protects against corrosion by removing contaminants. It also gives maintenance personnel the opportunity to assess the surface condition of an airplane, which permits operators to predict the date and extent of future maintenance required for corrosion and erosion. A mild alkaline detergent and pure warm water should be used. It is particularly important to wash new airplanes, because the protective oxide film that naturally forms and grows on aluminum with age is relatively thin and provides little protection. Both painted and polished surfaces can be adequately protected from corrosion. Fuselage skins are made from Alclad aluminum that consists of a high-strength core alloy bonded to a thin layer of pure aluminum or aluminum alloy. Wing skins are made of bare aluminum and are protected by an impact-resistant paint system. Polished surfaces are protected from corrosion by regular buffing after washing. Painting protects against oxidation, salts, and jet fuel spills. However, unrepaired chips and cracks in paint collect dirt and moisture and so may become corrosion sites. Painted surfaces are also susceptible to filiform corrosion, or worm corrosion, which begins between metallic surfaces and paint and erodes both. It creates hydrogen and lifts up the paint layer as it travels across the surface.[/size]

So the savings from a polished aircraft opposed to a painted aircraft will increase costs in corrosion prevention. A trade off from one for the other


Matthew Kane

 

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That was more for time savings during the build process. We had acheived air superiority by 1944 over Europe and we were at peak production rates in '44 as well. So USAAF made the decision to for-go the paint altogether as a way to save time. Given the speeds of the time, any weight savings would be neglible for the mission being flown. Saving fuel wasn't high on the list during wartime.

 

Very true, I forgot about saving time in building the aircraft. However, the weight saved - approx 500lb on a B-17 - would allow either more bombs or more fuel to be carried. That's not to be sniffed at.

 

More info here:

 

http://www.taphilo.com/history/WWII/USAAF/Boeing/index.shtml

 

Interesting also they say by sanding the paint as smooth as possible they could achieve a 5mph increase in speed. That reminds me of how they would use putty to fill the panel lines on the first 1/3 chord of the wing on the P-51 and then polishing the airframe to get maximum speed. As a scale modeller there's always plenty of people queueing up to tell you about it when someone builds a model of a P-51D and leaves the panel lines on the wing.


Nick

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Interesting also they say by sanding the paint as smooth as possible they could achieve a 5mph increase in speed.

Goes to show how much an effect Parasitic drag (skin friction) can have.

Matthew Kane

 

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Very true, I forgot about saving time in building the aircraft. However, the weight saved - approx 500lb on a B-17 - would allow either more bombs or more fuel to be carried. That's not to be sniffed at.

 

More info here:

 

http://www.taphilo.com/history/WWII/USAAF/Boeing/index.shtml

 

Interesting also they say by sanding the paint as smooth as possible they could achieve a 5mph increase in speed. That reminds me of how they would use putty to fill the panel lines on the first 1/3 chord of the wing on the P-51 and then polishing the airframe to get maximum speed. As a scale modeller there's always plenty of people queueing up to tell you about it when someone builds a model of a P-51D and leaves the panel lines on the wing.

Good points.

 The fill in is still done today. We call it aero-sealing for aero smoothing and for it keeps out the weather too. 

 

 Raptor

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In war time those marginal differences actually meant life or death in some circumstances.


Matthew Kane

 

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Very interesting and informative replies. Thank You and I've been reading those links for what feels like hours. This running an airline business is getting complicated if obscure factors like this can affect their bottom line. You'd have to be an Actuary to figure out the cost index.

 

Regarding wartime use of paint and that figure of 500lbs for the B17 amazes me, there was an Australian Pilot based in the UK who would totally disarm his Spitfire, putty and sand all the rivets, shove a couple of cameras in it and then perform high speed, low altitude, photo reconnaissance flights over Germany. The aircraft was faster than the ME/BF 109. I'm not so sure if it would have been faster than a BF 109 that had the same treatment.

 

Jon 

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Regarding wartime use of paint and that figure of 500lbs for the B17 amazes me

I was thinking the same considering a 747-400 uses 555 pounds of paint. The difference is most likely better uses of paint on modern assembly compared to 1943. Automation paint compared to manual spray bombing back then

Matthew Kane

 

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I was thinking the same considering a 747-400 uses 555 pounds of paint. The difference is most likely better uses of paint on modern assembly compared to 1943. Automation paint compared to manual spray bombing back then

The science of modern paint technology is a source of wonder. I used to mix specialised paints and the range of chemicals used is considerable. viz: 30 ml of a certain chemical affecting the viscosity of a complete 300 ltr batch. I'd love to see the paint recipe on the Blackbird but I think it might be classified.

 

Jon

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The science of modern paint technology is a source of wonder. I used to mix specialised paints and the range of chemicals used is considerable. viz: 30 ml of a certain chemical affecting the viscosity of a complete 300 ltr batch. I'd love to see the paint recipe on the Blackbird but I think it might be classified.

 

Jon

In 1943 the B-17's were most likely painted like tractors or cars as people were shifted from civilian production to war time production. Eventually the engineers made improvements along the way.

 

You are correct, today Paint is more of a science. Things like Led are now removed and other additives are used, in high heat applications it is becoming even more challenging.


Matthew Kane

 

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I also remember reading somewhere that the pigment used in red paint is quite heavy and adds a lot of weigh to a large aircraft - hence you don't see many liveries that have lots of red in them.

True and Black, any of the darker pigments really but they've got the technology now where colour is achieved through miniscule additions of pigment to a 20 ltr bucket so the weight is not such a factor. The amount of pigment used on a 747, say Dark Blue, would be quite heavy. I think they'd use a few more than 2 x 20 ltr buckets to do a complete hull and engine cowl paint.

 

Jon

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