Painting composite structures
Ken Bolvin
that I heard that composite structures have to be painted a light color or
they lose structural integrity, delaminate, etc. He said that was a bunch
of hooey (well not quite that word). He also stated that Rutan did some
research on it that proved any color will do. I'd really like to have a
black Glassair or Lancair (a white plane non-conformist). Anybody else
know if the A&P instructor is correct?
--
Ken Bolvin
Qualcomm Inc.
kbo...@qualcomm.com
Roy Hann
: Ok all you composite gurus, I was asking my A&P teacher about the theory
I am not a composites guru, but I have a graph in front of me here that
purports to be from the September 1975 Soaring magazine. It shows that
at at ambient air temperatue of 100F, a white fiberglass coated foam
box had a surface temperature of 150F, while a black box was tad
over 220F.
Unless you have EVIDENCE that your epoxy can take the heat, I think
you'd be a fool to use any colour but white. Most manufacturers of
epoxy concede that their products are seriously weakened at even
just 175F. I recently read a claim by a local builder that a glue
called Araldite is good even up to 600F! However Ciba-Geigy (who
make the stuff) deny that Araldite has extraordinary high temperature
properties. Who are you going to believe?
How many red or black Rutan-built composite aircraft have been flown?
Be cautious and paint it white; or locate credible test results that
show darker shades are OK, or do your own testing. When it comes to
heterodoxy in aircraft structures, I wouldn't just take someone's word
for it.
--Roy Hann
B Lacovara
kbo...@qualcom.com (Ken Bolvin) writes:
Is the A&P instructor correct? Well, it's not a black and white issue :)
Here's the deal: Any decent high performance epoxy will normally handle
the ambient heat from outdoor exposure. On a 100 degree F day, in the
southwest at noon, a black or dark green surface will reach about 175
degrees F. Temperatures of 175 degrees F will not cause a loss of
properties or delamination of a well bonded structure. However...
These elevated temperatures may cause some surface distortion due to a
phenomenon known as post cure. As the resin cycles through high
temperatures a slight amount of shrinkage may take place which could lead
to anything from a slight cosmetic rippling on the surface to something
severe enough to effect the airfoil shape in gliders. In addition, a dark
colored surface will highlight surface flaws that would be overlooked in
white. All things being equal a light colored (white) airframe will appear
to have better surface conoturs than a dark colored surface.
Bottom line: If you choose to go with a dark color the "fairness"
(contour) will have to be execptional to look good and there is no
guarantee the surface will stay distortion free.
Bob Lacovara
Technical Director
Composites Fabricators Association
Roy Hann
: In article <kbolvin-2608...@kbolvin.qualcomm.com>,
:
: Is the A&P instructor correct? Well, it's not a black and white issue :)
: Here's the deal: Any decent high performance epoxy will normally handle
: the ambient heat from outdoor exposure. On a 100 degree F day, in the
: southwest at noon, a black or dark green surface will reach about 175
: degrees F. Temperatures of 175 degrees F will not cause a loss of
: properties or delamination of a well bonded structure. However...
Since your posting flies (ha ha ha) straight in the face of my
earlier one, can you suggest published findings which we might
consult in oder to better understand the testing you refer to
above (and therefore the conclusion)?
I'd also be interested if you could support the claim that 175F
will "not cause a loss of properties." Common sense suggests that
if epoxy DOES soften as it gets hotter, and I think we agree that it
does, then it should have lost SOME strength at 175F. I recently
read one claim that Chem-Tech T-88 has only 25% of its peak strength
at just 150F! If that is true, then frankly I would be terrified of
the stuff. Can you elaborate/refute?
--Roy Hann
John Hamilton
(Roy Hann) wrote:
>
> blac...@aol.com (B Lacovara) writes:
> : In article <kbolvin-2608...@kbolvin.qualcomm.com>,
> :
> : Is the A&P instructor correct? Well, it's not a black and white issue :)
> : Here's the deal: Any decent high performance epoxy will normally handle
> : the ambient heat from outdoor exposure. On a 100 degree F day, in the
> : southwest at noon, a black or dark green surface will reach about 175
> : degrees F. Temperatures of 175 degrees F will not cause a loss of
> : properties or delamination of a well bonded structure. However...
> I'd also be interested if you could support the claim that 175F
> will "not cause a loss of properties."..
> --Roy Hann
Common homebuilt resin systems, ie room cure or slightly elevated, will
have a loss of properties at 175-200 degrees. Definitely the foams have
reduced integrity as well. The temperatures are reaching the 'cusp' where
properties can drop significantly. Thermal stress from the outer skin
versus the inner due to a high thermal gradient, can also set up shear
which is additive to flight loads.
I'm not going to write a thesis, but there is NO WAY I'd fly in a
homebuilt, painted black, on a hot sunny day. PERIOD.
John G. Hamilton,
Lockheed Space Systems, Structures Engineer, Composites Technology.
Larry Elie
>From: blac...@aol.com (B Lacovara)
>Subject: Re: Painting composite structures
>Date: 28 Aug 1994 00:59:03 -0400
>In article <kbolvin-2608...@kbolvin.qualcomm.com>,
>kbo...@qualcom.com (Ken Bolvin) writes:
>>Ok all you composite gurus, I was asking my A&P teacher about the theory
>>that I heard that composite structures have to be painted a light color
>or
>>they lose structural integrity, delaminate, etc. He said that was a bunch
>>of hooey (well not quite that word). He also stated that Rutan did some
>>research on it that proved any color will do. I'd really like to have a
>>black Glassair or Lancair (a white plane non-conformist). Anybody else
>>know if the A&P instructor is correct?
>Is the A&P instructor correct? Well, it's not a black and white issue :)
>Here's the deal: Any decent high performance epoxy will normally handle
>the ambient heat from outdoor exposure. On a 100 degree F day, in the
>southwest at noon, a black or dark green surface will reach about 175
>degrees F. Temperatures of 175 degrees F will not cause a loss of
>properties or delamination of a well bonded structure. However...
>These elevated temperatures may cause some surface distortion due to a
>phenomenon known as post cure. As the resin cycles through high
>temperatures a slight amount of shrinkage may take place which could lead
>to anything from a slight cosmetic rippling on the surface to something
Post cure is real. ALL composite structure exposed to light face it. It
usually is 'cosmetic' in that the structure is only affected a few thousandths
of an inch from the surface. I have seen it in other structures as well. If
the structure is thick; you loose aerodynamics and finish. If the structure
is thin; it may warp, it may even fail. Bob is right here. Leave the dark
colors to the F-117.
>severe enough to effect the airfoil shape in gliders. In addition, a dark
>colored surface will highlight surface flaws that would be overlooked in
>white. All things being equal a light colored (white) airframe will appear
>to have better surface conoturs than a dark colored surface.
>Bottom line: If you choose to go with a dark color the "fairness"
>(contour) will have to be execptional to look good and there is no
>guarantee the surface will stay distortion free.
>Bob Lacovara
>Technical Director
>Composites Fabricators Association
Larry Elie
le...@smail.srl.ford.com
Bob Kirkpatrick
It has been shown that composites are sensitive to UV light, and will
deteriorate over time. Also, some epoxy materials may become semi vis-
cous when they get hot. As a result, it's usually recommended that any
composite planes be hangared, and spend as little time under the sun
as possible. Also, it's suggested that those which use epoxy resins
not be painted dark colors because of their greater heat absorbtion.
I've never built a composite plane, but have used composites for a few
projects, and in each case there have been manufacturers warnings on
protection from sunlight and excessive heat.
---
Bob Kirkpatrick -*- bo...@dogear.com -*- Dog Ear'd Systems of Spokane, WA
"Who... are you?" asked the caterpillar. Smoke rings issued as he spoke."
Richard Lanning
With all the discussion on painting composites I was wondering
what limitations there are to the Reaction Injection Molding process?
This is what the BD-12/14 aircraft will be made of which I believe is
graphite based so it is my understanding that the finished pieces
actually come out black. Will RIM material have the same heat
constraints? How about UV light, is this a problem?
Rich
Larry Elie
>From: lan...@acc211.vf.ge.com (Richard Lanning)
>Subject: Re: Painting composite structures
>Rich
It depends. How long will the parts cure in the mold? Will they be painted
later? (Bumpers on some Fords are RIM then painted, I think black, grey and
yellow RIM are common) If so, how long will they cure before painting? If
post painted, not allowed to cure, and painted dark (to UV), the surface
finish may deteriorate, the paint peal, and a wavy if not rougher surface may
result. If the paint reflects UV, no problem is likely.
Larry Elie
le...@smail.srl.ford.com
SidLloyd
writes:
>It has been shown that composites are sensitive to UV light, and will
>deteriorate over time. Also, some epoxy materials may become semi vis-
>cous when they get hot. As a result, it's usually recommended that any
>composite planes be hangared, and spend as little time under the sun
>as possible. Also, it's suggested that those which use epoxy resins
>not be painted dark colors because of their greater heat absorbtion.
It is my understanding that glass/resin is impervious to UV light, but
foam will breakdown. It is therfore important that paint contain a UV
barrier.
For molded and cured (baked in oven) composite kit planes, colors other
than white seem to be OK. It is also recommended (by Stan Montgomery from
Alexander Airplane and Gary Hunter from Shell) that all homebuilt parts be
post cured to about 150 degrees (3-8 hours). This can be done via
electric heaters in an enclosed space or by wrapping the part in black
plastic and putting it in the sun. Monitor the temperature as some foams
can melt at 170 or so. Post curing can markedly increase the strength of
the part.
Sid Lloyd
Art Utay
In general, the epoxy systems used by homebuilders are room temperature cure,
meaning cured system degredation will occur with sunlight (temp and UV
exposure). The way around this is to use a 250 F or 350 F system with a UV
resistant epoxy. These systems are in widespread use in the aerospace industry.
The only requirement is an autoclave or oven to run the cure cycle (typically
6-8 hours)
Unfortunately, the capital costs will be considerable.--
********************************************************************************
Arthur W. Utay, Senior Aerospace Specialist | Your mileage may vary
B18...@vaxb.phx1.aro.allied.com |
(602) 231-1321 |
Cessna 180 N2362C ASEL, Com'l Inst, Comm'l Glider |
********************************************************************************
Cole Larson
: Ok all you composite gurus, I was asking my A&P teacher about the theory
Many years ago, when I was a student at the University of Nevada in Reno,
I worked at the Atmospherium there. It was heated using solar
collectors. We painted them black on one side and white on the other.
The collectors could rotate either side out. To our amazement, the white
side collected more heat!!! After some research, we discovered that the
particular white we picked absorbed more infrared than the black did!
If this principal works in general, I think that some aircraft paint
company could clean up making infrared reflecting low temp coatings in a
variety of colors.
I bet someone ambitious could find a brand or two that worked better than
others.
G A Venkatesh
>It is also recommended (by Stan Montgomery from
>Alexander Airplane and Gary Hunter from Shell) that all homebuilt parts be
>post cured to about 150 degrees (3-8 hours). This can be done via
>electric heaters in an enclosed space or by wrapping the part in black
>plastic and putting it in the sun. Monitor the temperature as some foams
>can melt at 170 or so. Post curing can markedly increase the strength of
>the part.
How soon after the construction should the part be post cured? Or more
useful to me, how long can you wait before the post cure is no longer useful?
venky
Charles Crosby
>In article <33p5in$k...@search01.news.aol.com> blac...@aol.com (B Lacovara) writes:
>>>Ok all you composite gurus, I was asking my A&P teacher about the theory
>>>that I heard that composite structures have to be painted a light color
>>or
>>>they lose structural integrity, delaminate, etc. He said that was a bunch
>>>of hooey (well not quite that word). He also stated that Rutan did some
>>>research on it that proved any color will do. I'd really like to have a
>>>black Glassair or Lancair (a white plane non-conformist). Anybody else
>>>know if the A&P instructor is correct?
>>Is the A&P instructor correct? Well, it's not a black and white issue :)
>>Here's the deal: Any decent high performance epoxy will normally handle
>>the ambient heat from outdoor exposure. On a 100 degree F day, in the
>>southwest at noon, a black or dark green surface will reach about 175
>>degrees F. Temperatures of 175 degrees F will not cause a loss of
>>properties or delamination of a well bonded structure. However...
---snip---
>>severe enough to effect the airfoil shape in gliders. In addition, a dark
>>colored surface will highlight surface flaws that would be overlooked in
>>white. All things being equal a light colored (white) airframe will appear
>>to have better surface conoturs than a dark colored surface.
>>Bottom line: If you choose to go with a dark color the "fairness"
>>(contour) will have to be execptional to look good and there is no
>>guarantee the surface will stay distortion free.
The people with most experience of composite planes are the German
sailplane manufacturers and certification authorities. As far as I
know, they have a requirement that all composite gliders MUST be white,
except for the bright red (or whatever) anti-collision wingtips.
Untill the Germans start approving black gliders (now wouldn't that look
sinister :-) , I would stick to light colours for composite homebuilts.....
Charles Crosby e-mail : cro...@fanella.ee.up.ac.za
Dep of Mech and Aero Eng meg...@upvm2.up.ac.za
University of Pretoria Phone : (012)-4202861 (w) (012)-3451586 (h)
South Africa Fax : (012)-436540 (w) (012)-3451586 (h)
SidLloyd
Venkatesh) writes:
>How soon after the construction should the part be post cured? Or more
>useful to me, how long can you wait before the post cure is no longer
useful?
Gary told me that post curing is always useful, regardless of how long
after the layup has been made. I don't know any specifics in terms of
percentage increase of strength though.
Sid
Bob Kirkpatrick
> I'm not going to write a thesis, but there is NO WAY I'd fly in a
> homebuilt, painted black, on a hot sunny day. PERIOD.
I assume, John, you meant a COMPOSITE homebuilt. My Pitts is black
and it hasn't seemed to affect the tube and fabric structure at all.
:-)