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sidsel.svein(at)oslo.onli
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 Posted: Sun Jul 15, 2012 3:02 am Post subject: Cockpit cover - Any colour as long as it's white |
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On our recent trip to Venezia where we had 35 degrees during takeoff at 9:30 AM, Stephan and I were quite puzzled by the negative effect our metallic-grey cockpit covers had when it came to keeping the heat out. The temperature inside the cockpit was HIGH.
I have now received the report from the Norwegian Institute of Advanced Europa Cockpit Cover Research. The reason it took so long, was that only today has the sun been out sufficiently long to carry out such an important field study. Here is the summary of the institute’s findings (temperatures in degrees Centigrade):
<![if !supportLists]>- <![endif]>Ambient air: 23.5
<![if !supportLists]>- <![endif]>Under car window sun protection material (I have now made covers to place inside all windows from a set purchased at auto supply store): 26.9
<![if !supportLists]>- <![endif]>Under white pillow case material (single sheet cotton, thinner material than the metallic-grey cover, tight weave): 38.7
<![if !supportLists]>- <![endif]>Under metallic-grey cockpit cover, made professionally to many Europas: 58.7
All cases: Temp. sensor held up against the underside of the test piece by pins, to ensure minimum ambient air influence. All test pieces at right angle to the sun’s rays. No wind.
It is evident that the metallic-grey material is totally unsuitable for sun heat protection. The colour is just for show, and has the opposite effect of what we common folks believe. It is of course water tight, but I am sure there is also white fabric available that keeps the water out.
If you see a Europa at Popham next year, all covered in white bed sheets, it’s mine!
May the sun shine every day the rest of the summer,
Svein
LN-SKJ
[quote][b]
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kevinmarie(at)blueyonder.
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| Posted: Sun Jul 15, 2012 4:25 am Post subject: Cockpit cover - Any colour as long as it's white |
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Sun covers so far this year have not been needed in the UK but floats are looking likely 
Kevin Challis
On 15 Jul 2012, at 12:01, "Sidsel & Svein Johnsen" <sidsel.svein(at)oslo.online.no (sidsel.svein(at)oslo.online.no)> wrote:
[quote] <![endif]--> <![endif]-->
On our recent trip to Venezia where we had 35 degrees during takeoff at 9:30 AM, Stephan and I were quite puzzled by the negative effect our metallic-grey cockpit covers had when it came to keeping the heat out. The temperature inside the cockpit was HIGH.
I have now received the report from the Norwegian Institute of Advanced Europa Cockpit Cover Research. The reason it took so long, was that only today has the sun been out sufficiently long to carry out such an important field study. Here is the summary of the institute’s findings (temperatures in degrees Centigrade):
- Ambient air: 23.5
- Under car window sun protection material (I have now made covers to place inside all windows from a set purchased at auto supply store): 26.9
- Under white pillow case material (single sheet cotton, thinner material than the metallic-grey cover, tight weave): 38.7
- Under metallic-grey cockpit cover, made professionally to many Europas: 58.7
All cases: Temp. sensor held up against the underside of the test piece by pins, to ensure minimum ambient air influence. All test pieces at right angle to the sun’s rays. No wind.
It is evident that the metallic-grey material is totally unsuitable for sun heat protection. The colour is just for show, and has the opposite effect of what we common folks believe. It is of course water tight, but I am sure there is also white fabric available that keeps the water out.
If you see a Europa at Popham next year, all covered in white bed sheets, it’s mine!
May the sun shine every day the rest of the summer,
Svein
LN-SKJ
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rob(at)hyperion-ef.com
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| Posted: Tue Jul 17, 2012 8:20 am Post subject: Cockpit cover - Any colour as long as it's white |
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What these measurements tell us is what we knew before making any measurements – that darker colors absorb the sun’s radiant energy more than light colors. This is why the Europa factory correctly advises that white is the only acceptable color for the fiberglass airframe. What these measurements do not tell us is how much of the sun’s energy is reflected from the outer surface of the cockpit covers, only what heat is transferred by conduction through the cover. The metallic grey material is probably a very good reflector of radiant energy in the part of the spectrum most important for reducing the temperature within the cockpit.
It is erroneous to conclude that “the metallic-grey material is totally unsuitable for sun heat protection” because cockpit air temperature is not a function of the temperature of the heat shield, and cockpit air temperature was not measured. At the temperatures involved, radiant heat transfer is inconsequential so therefore the measured temperature on the interior side of the cover material is insignificant and irrelevant
Now, having said that the conclusion was erroneous I should point out that the cover in question may indeed be a rather poor means of reducing the cockpit temperature. We simply do not know from the available information. As with academic studies, here we must conclude that further research is necessary.
For the absolutely best reflection of infrared energy use a gold coating on the metallic shield.
Best regards,
Rob Housman
Irvine, California
Europa XS
Rotax 914
S/N A070
Airframe complete
Avionics soon
From: owner-europa-list-server(at)matronics.com [mailto:owner-europa-list-server(at)matronics.com] On Behalf Of Sidsel & Svein Johnsen
Sent: Sunday, July 15, 2012 4:02 AM
To: europa-list(at)matronics.com
Subject: Cockpit cover - Any colour as long as it's white
On our recent trip to Venezia where we had 35 degrees during takeoff at 9:30 AM, Stephan and I were quite puzzled by the negative effect our metallic-grey cockpit covers had when it came to keeping the heat out. The temperature inside the cockpit was HIGH.
I have now received the report from the Norwegian Institute of Advanced Europa Cockpit Cover Research. The reason it took so long, was that only today has the sun been out sufficiently long to carry out such an important field study. Here is the summary of the institute’s findings (temperatures in degrees Centigrade):
<![if !supportLists]>- <![endif]>Ambient air: 23.5
<![if !supportLists]>- <![endif]>Under car window sun protection material (I have now made covers to place inside all windows from a set purchased at auto supply store): 26.9
<![if !supportLists]>- <![endif]>Under white pillow case material (single sheet cotton, thinner material than the metallic-grey cover, tight weave): 38.7
<![if !supportLists]>- <![endif]>Under metallic-grey cockpit cover, made professionally to many Europas: 58.7
All cases: Temp. sensor held up against the underside of the test piece by pins, to ensure minimum ambient air influence. All test pieces at right angle to the sun’s rays. No wind.
It is evident that the metallic-grey material is totally unsuitable for sun heat protection. The colour is just for show, and has the opposite effect of what we common folks believe. It is of course water tight, but I am sure there is also white fabric available that keeps the water out.
If you see a Europa at Popham next year, all covered in white bed sheets, it’s mine!
May the sun shine every day the rest of the summer,
Svein
LN-SKJ
| Quote: | | http://www.matronics.com/Navigator?Europa-List |
0123456789
[quote][b]
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rob(at)hyperion-ef.com
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| Posted: Mon Jul 23, 2012 11:18 am Post subject: Cockpit cover - Any colour as long as it's white |
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Please don’t take offence, all I want to do is clarify the science involved
Your reply convinces me that you do not understand any of the mechanisms of heat transfer applicable to keeping the cockpit relatively cool when the airplane is left in the sun. That is forgivable for folks that are not educated in the science of heat transfer, but what is unforgivable is the manufacture’s mistaken belief that UV has something to do with heat, and that conduction is a significant contributor to increasing the temperature in the cockpit. UV is at the opposite end of the electromagnetic spectrum from infrared, and while all of the spectrum contributes something to heating the further we get from infrared the less the contribution.
Briefly, there are three means of heat transfer, radiant, conductive, and convective.
Radiant heat transfer predominates when the temperature of the source, in this case the sun, is very high. This is because the radiant energy is proportional to the absolute temperature (Kelvin or Rankine scale) raised to the fourth power. We experience radiant heat transfer from everyday things like the heating elements on an electric range, from a flame, or even a tungsten light bulb, all of which are sources at relatively high temperatures.
Conductive heat transfer predominates in solid materials such as the cockpit covers in question, and at lower temperatures. Conduction is what makes the handle of a pot on the stove get hot after the pot is heated by radiation from the burner and heat is transferred (conducted) through the aluminum, cast iron, or copper pot, to the handle
Convection, either natural or forced, transfers heat by moving a fluid (either a gas or liquid) from a higher temperature location to a lower temperature location. We use this method to cool both liquid and air cooled engines.
So, getting back to my original point:
The best way to keep the cockpit cool is with a material that reflects the sun’s radiant energy. A layer of aluminum foil will do this quite well. Gold foil will be better still but a bit more expensive (check out the amount of gold you see in pictures of satellites). Since the interior surface of the cover in question is a few degrees warmer than ambient, and nowhere near the temperature of a light bulb for example, there is virtually no radiation from the interior of the cover to the cockpit, hence my assertion that the measurements you made are meaningless. If anything, the cover with the highest interior temperature might actually help reduce the temperature in the cockpit because it is a demonstrably poor insulator which means that once the cockpit is hotter than the ambient air the heat can be transferred by conduction to the surface of the windows and from there convection will remove heat to the air.
Further comments below…
Best regards,
Rob Housman
Irvine, California
Europa XS
Rotax 914
S/N A070
Airframe complete
Avionics soon
From: owner-europa-list-server(at)matronics.com [mailto:owner-europa-list-server(at)matronics.com] On Behalf Of Sidsel & Svein Johnsen
Sent: Wednesday, July 18, 2012 9:44 AM
To: europa-list(at)matronics.com
Subject: SV: Cockpit cover - Any colour as long as it's white
Rob,
With respect, I wish to comment some of your statements:
>What these measurements do not tell us is how much of the sun’s energy is reflected from the outer surface of the cockpit covers, only what heat is transferred by conduction through the cover.<
What is of interest is not what is reflected (per se), but what is transferred by conduction. No – see above. The temperature on the underside (shadow side) of the material was measured, and this gives indeed a good indication of the heat transferred – the higher the temperature, the more heat is transferred. True as far as it goes. Whether the heat that reaches the underside is a result of low reflection from the outside surface or high conductivity (low insulation) in the material is irrelevant. Sort of true but it is indeed heated by conduction through the cover as a result of minimal reflection.
>The metallic grey material is probably a very good reflector of radiant energy in the part of the spectrum most important for reducing the temperature within the cockpit.<
If this is the case, the material must have a very high conductivity/low insulation, since it gets really warm on the underside, meaning that the energy not reflected passes easily through the material. The cover manufacturer stated the following in an e-mail to me yesterday: “These covers will reflect UV radiation, but this is not the only way that heat is tranferred. Conduction is likely to be a major factor. No - see above We have not designed a product to protect and insulate from the heat of the sun (insulation would surely be needed outside the glass).” Did they really mean that the cover is useless for keeping the cockpit cool? Again they demonstrate their ignorance by recommending insulation outside of the glass (sic) because the polycarbonate-cover “system” would work the same whether the insulation is outside or inside.
>It is erroneous to conclude that “the metallic-grey material is totally unsuitable for sun heat protection” because cockpit air temperature is not a function of the temperature of the heat shield, and cockpit air temperature was not measured. At the temperatures involved, radiant heat transfer is inconsequential so therefore the measured temperature on the interior side of the cover material is insignificant and irrelevant<
How can cockpit air temperature NOT be a function of the temperature on the inside of the cover? See above. Consider the following – case 1: The entire aircraft is covered, and the temperature on the inside of the total cover is 58.7 degr. C – constant over time. When the cockpit air temp has stabilized, it will be 58.7 degr C. Case 2: The inside of the total cover is 38.7 degr C. When the cockpit air temp has stabilized, it will be 38.7 degr C. In the real case, where parts of the structure surrounding the cockpit are not covered, the inside air temperature will be different from the temperature on the inside of the cover. However, the higher the cover inside temperature is, the higher the cockpit temperature gets. Further, the structure (e.g. fuselage skin) is in direct contact with the underside of the cover, and I can assure you that the white skin under the cover was significantly hotter than the white skin exposed to the sun, which felt cool in comparison. Perhaps I should not have said “insignificant” in my original message. That temperature would be a significant indicator of cockpit temperature when at equilibrium but your report of the original measurements did not indicate that equilibrium had been attained. The white skin under the cover is an indication of the temperature of the cover after the cockpit has already been heated by radiation, and the cover’s interior heated by conduction, and the white skin of the aircraft is cooler because it has efficiently reflected the radiant energy of the sun.
>Now, having said that the conclusion was erroneous I should point out that the cover in question may indeed be a rather poor means of reducing the cockpit temperature. We simply do not know from the available information. As with academic studies, here we must conclude that further research is necessary. <
Ref. the above quote from the manufacturer with respect to the cover not being suitable for heat reduction. I’ve already pointed out that the manufacturer is simply ignorant of heat transfer mechanisms. There is, however, another manufacturer who claims to have better suited material (ref. Gerry’s posting on Monday). I have asked for a sample of that material, and will make a comparison of the underside temp of that and the metallic grey that I presently have.
The best practical heat protection of the cockpit is to cover the windows on the inside by auto heat shield (the foam layer offers effective insulation = low conductivity). See my comments above about the relative contribution by conduction. The problem arises when you also need to cover the cockpit and engine top (ref. air intake location for 912 UL/ 912 ULS) against rain.
If the white cover shows lower temperature on the underside than the metallic-grey cover, this is either due to different radiant heat reflection definitely or different conductivity through the fabric minor contribution , or a combination of both. How much is actually caused by one or the other is beyond the scope of my interest in this subject – I only wish to find a lightweight, water tight cover that is noticeably better than the metallic-grey that I now have. White colour is in all likelihood better than metallic grey. Definitely, and something metallic is better still. Reflectivity in the infrared is a function of the material alone, specular or diffuse. Aluminum is better for reflectivity than painted anything, but I don’t want a corroding airplane.
On a sunny day, check on cars in a parking lot: White is definitely coolest to the touch (most heat reflection = least soaking up of heat into the car body metal). Correct Yellow, green, grey, red, blue: Much hotter. Correct again. Silver metallic: Almost as bad as any of the darker colours. Reason according to paint manufacturer: The special “sheen” of metallic paint is created by particles reflecting light in different, arbitrary directions – also down towards the surface on which it is painted. We don’t care where the reflected energy goes as long as it leaves the surface we want to keep cool, and since the angle of reflection equals the angle of incidence there is no way for the energy to be reflected below the surface. This is why our aircraft made of epoxy must not be painted silver metallic, while aircraft (and cars) made of polyester may have this type of paint but that’s because of the glass transition temperature, and entirely different concern. I am not saying that the “metallic” grey cover has the same properties as silver metallic paint, but grey is still not white. Yup, any color as long as it’s white.
Regards,
Svein
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Paul M 383
Joined: 19 Mar 2012
Posts: 97
Location: United Kingdom
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craigb(at)onthenet.com.au
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| Posted: Tue Jul 24, 2012 12:33 pm Post subject: Cockpit cover - Any colour as long as it's white |
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Maybe a space blanket with a cotton backing would be ok
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Remi Guerner
Joined: 14 Dec 2010
Posts: 284
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| Posted: Wed Jul 25, 2012 3:34 am Post subject: Re: Cockpit cover - Any colour as long as it's white |
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From my experience, anything white will keep the cockpit cool and will not cause damage to the fiberglass skin. Better to have cotton cloth inside to avoid scratching the perspex and some sort of vinyl outside to prevent the cloth to absorb water in case of dew or rain.
Personally I am using a homemade cover made of the sort of cloth used to make day light blocking curtains. It is very effective for keeping the cockpit cool but is not waterproof.
Remi Guerner
F-PGKL
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rob(at)hyperion-ef.com
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| Posted: Wed Jul 25, 2012 1:48 pm Post subject: Cockpit cover - Any colour as long as it's white |
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To avoid offending anyone else I will opt out of further discussion on this
subject, so others will have to answer your query.
Best regards,
Rob Housman
Irvine, California
Europa XS
Rotax 914
S/N A070
Airframe complete
Avionics soon
--
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