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DIY LED landing light -- Wing skin as heat sink?

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finn.usa(at)gmail.com
Guest

Posted: Sat Oct 31, 2020 7:14 pm Post subject: DIY LED landing light -- Wing skin as heat sink?

Might say the most critical thing for LED life and high lumens output is 

conducting heat away from the LED.



That usually means attaching heavy heat sinks.



Could we save weight by using the wing skin as a heat sink?



I understand it would present problems in adjusting (pointing) the light.



But, could we bond/attach the LED to a (alum?) plate that is then 

bonded/riveted/screwed to the leading edge wing skin?



Let's say we use a 100W LED (~13,000 lumens). We'd have to remove 70 to 

80W of heat from the LED. LED doesn't like more than 150°C and it would 

be better to keep it cooler. LED area 34x34mm.



I don't have a good grasp of thermal conductivity (conductance?). How 

thick would the mount plate have to be? How much area would be needed 

where the mount plate contacts the wing skin (using some kind of heat 

sink compound/adhesive between the plate and skin)?



Am I right in assuming the plate has to be thickest were the LED is 

mounted and then taper down in thickness as it expands out in width and 

height?



Perhaps tapered layers of carbon fiber (with thermal epoxy) would be 

better as the LED mount plate? (After a diamond, graphene or graphite 

apparently has the best thermal conductivity.)



Any (thermal) engineers here that could enlighten me?



Finn

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bartrim(at)gmail.com
Guest

Posted: Sat Oct 31, 2020 11:59 pm Post subject: DIY LED landing light -- Wing skin as heat sink?

Hi Finn;  This may not be using the skin as a heat sink, but it works great and is lightweight.

I bought some of these lights from Amazon and took them apart to make my landing lights.

https://www.amazon.ca/Lightfox-Driving-Offroad-Waterproof-Warranty/dp/B01M98GWR2/ref=sr_1_2_sspa?crid=31MNRKKNOSJAA&dchild=1&keywords=led+spot+lights+offroad&qid=1604214923&sprefix=led+spot+%2Caps%2C274&sr=8-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEySTdLUVhZSDFQQTEmZW5jcnlwdGVkSWQ9QTA2NDM1NzcyUVdZV1QyR0tJS1dRJmVuY3J5cHRlZEFkSWQ9QTAwNzU1NTUzSzVRRTYzNTZSUjZHJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

this is from Amazon's Canada site, but I'm sure you can find them even cheaper on the US site.

Then I took them apart as you can see in these pictures posted here on Google photos

https://photos.app.goo.gl/S68h3zpVy7RVJDTT8

I can't remember how much weight I discarded from the parts I removed, but it was most of the weight of the light.

The mounting plate was originally part of the Duckworths landing light that I wasted my money on. That is a simple part to make. I have 2 of those mounted mid wing and are pointed down for use as taxi lights, then I mounted 2 into the wingtips (required some fibreglass work) and have them pointed straight ahead for landing lights.

These lights are very durable and bright. I must have bought more than a dozen so far as I've put some on my truck, my son's Jeep, my skidsteer, 4 on the plane and probably the harshest duty is the pair I put on my ATV, which are thoroughly abused. They are extremely bright in the bush with very little current draw so my ATV has no problem running them continuously. I think those ones are at least 4 years old and are still working great despite the abuse.

  It looks like there are even better versions of these lights now, that appear to be the same construction so you can still dismantle them to get the good parts only.

Todd Bartrim

RV9

13Bturbo 

On Sat, Oct 31, 2020 at 8:20 PM Finn Lassen <finn.usa(at)gmail.com (finn.usa(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: Finn Lassen <finn.usa(at)gmail.com (finn.usa(at)gmail.com)>

 

 Might say the most critical thing for LED life and high lumens output is 

 conducting heat away from the LED.

 

 That usually means attaching heavy heat sinks.

 

 Could we save weight by using the wing skin as a heat sink?

 

 I understand it would present problems in adjusting (pointing) the light.

 

 But, could we bond/attach the LED to a (alum?) plate that is then 

 bonded/riveted/screwed to the leading edge wing skin?

 

 Let's say we use a 100W LED (~13,000 lumens). We'd have to remove 70 to 

 80W of heat from the LED. LED doesn't like more than 150°C and it would 

 be better to keep it cooler. LED area 34x34mm.

 

 I don't have a good grasp of thermal conductivity (conductance?). How 

 thick would the mount plate have to be? How much area would be needed 

 where the mount plate contacts the wing skin (using some kind of heat 

 sink compound/adhesive between the plate and skin)?

 

 Am I right in assuming the plate has to be thickest were the LED is 

 mounted and then taper down in thickness as it expands out in width and 

 height?

 

 Perhaps tapered layers of carbon fiber (with thermal epoxy) would be 

 better as the LED mount plate? (After a diamond, graphene or graphite 

 apparently has the best thermal conductivity.)

 

 Any (thermal) engineers here that could enlighten me?

 

 Finn

 

 

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bartrim(at)gmail.com
Guest

Posted: Sun Nov 01, 2020 12:02 am Post subject: DIY LED landing light -- Wing skin as heat sink?

Ooops, that was the link for my own collection of reference photos,

This is the one you need to see how I did the lights

https://photos.app.goo.gl/wQvyosNK1QBFjz7c8

Todd Bartrim

On Sun, Nov 1, 2020 at 12:54 AM Todd Bartrim <bartrim(at)gmail.com> wrote:



[quote] Hi Finn;

   This may not be using the skin as a heat sink, but it works great and is

 lightweight.

 I bought some of these lights from Amazon and took them apart to make my

 landing lights.



 https://www.amazon.ca/Lightfox-Driving-Offroad-Waterproof-Warranty/dp/B01M98GWR2/ref=sr_1_2_sspa?crid=31MNRKKNOSJAA&dchild=1&keywords=led+spot+lights+offroad&qid=1604214923&sprefix=led+spot+%2Caps%2C274&sr=8-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEySTdLUVhZSDFQQTEmZW5jcnlwdGVkSWQ9QTA2NDM1NzcyUVdZV1QyR0tJS1dRJmVuY3J5cHRlZEFkSWQ9QTAwNzU1NTUzSzVRRTYzNTZSUjZHJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

 this is from Amazon's Canada site, but I'm sure you can find them even

 cheaper on the US site.

 Then I took them apart as you can see in these pictures posted here on

 Google photos

 https://photos.app.goo.gl/S68h3zpVy7RVJDTT8

 I can't remember how much weight I discarded from the parts I removed, but

 it was most of the weight of the light.

 The mounting plate was originally part of the Duckworths landing light

 that I wasted my money on. That is a simple part to make. I have 2 of those

 mounted mid wing and are pointed down for use as taxi lights, then I

 mounted 2 into the wingtips (required some fibreglass work) and have them

 pointed straight ahead for landing lights.

 These lights are very durable and bright. I must have bought more than a

 dozen so far as I've put some on my truck, my son's Jeep, my skidsteer, 4

 on the plane and probably the harshest duty is the pair I put on my ATV,

 which are thoroughly abused. They are extremely bright in the bush with

 very little current draw so my ATV has no problem running them

 continuously. I think those ones are at least 4 years old and are still

 working great despite the abuse.

   It looks like there are even better versions of these lights now, that

 appear to be the same construction so you can still dismantle them to get

 the good parts only.



 Todd Bartrim

 RV9

 13Bturbo



 On Sat, Oct 31, 2020 at 8:20 PM Finn Lassen <finn.usa(at)gmail.com> wrote:



> 

>

> Might say the most critical thing for LED life and high lumens output is

> conducting heat away from the LED.

>

> That usually means attaching heavy heat sinks.

>

> Could we save weight by using the wing skin as a heat sink?

>

> I understand it would present problems in adjusting (pointing) the light

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Ceengland

Joined: 11 Oct 2020
Posts: 391
Location: MS

Posted: Sun Nov 01, 2020 12:37 pm Post subject: DIY LED landing light -- Wing skin as heat sink?

On Sun, Nov 1, 2020 at 12:59 PM Finn Lassen <finn.usa(at)gmail.com (finn.usa(at)gmail.com)> wrote:



 	  Quote: 	
		                     



          

     On 11/1/2020 12:03 PM, Robert L.       Nuckolls, III wrote:

     

      	  Quote: 	
		                 	  Quote: 	
		  

           

           Trying to wrap my head around the transition from flat contact           area under           the LED chip to the heat sink plate as it expands out in area.           Seems           mounting it to an infinite piece of alum foil would not be the           same as           mounting it to 10x10" 0.063" thick alum plate           ... 	
       

         But the sheet has thermal resistance too. And

         rate of dissipation is a function of temperature

         differential. As you move out onto the sheet,

         the fastest transfer is right around the base

         of the LED; temperatures fall as you move

         out hence energy dissipated per unit area 

         declines.

       

         Intuitively, it makes sense that 'sink'

         temperature at the base of the LED will

         be much higher than at a remote location.

       

         Are we talking about landing lights?

       

       

                

             Bob . . .                     	
     Yes landing lights.

     

     So my understanding is right. Thicker plate near LED base, then     tapering out. You'll also see that in old big heat sinks: thick base     then fins tapering out.  I guess optimal design is  total surface     area versus enough material to conduct the heat to the entire     surface (when designing for least weight). Some newer heat sinks     I've seen have numerous rods sticking out from the base. Perhaps     (for least weight) the rods should actually be tapered.

     

     This my original question: "Am I right in assuming the plate has to     be thickest were the LED is mounted and then taper down in thickness     as it expands out in width and height?"

     

     Another interesting item from Googling "best thermal conductivity":

     "Along with its carbon         cousins graphite and graphene, diamond is the best thermal         conductor around room temperature, having thermal conductivity         of more than 2,000 watts per meter per Kelvin, which is five         times higher than the best metals such as copper."

     

     leading to my: "Perhaps tapered layers of carbon fiber (with thermal     epoxy) would be better as the LED mount plate? (After a diamond,     graphene or graphite apparently has the best thermal conductivity.)"

     

     One could shape the carbon fiber layup to closely fit the leading     edge skin.

     

     I guess I'm thinking way, way, way too far out of the box 

     

     Finn



	
Jim Weir has a couple of articles in Kitplanes magazine that give a 'cookbook' method of figuring heatsink size.  I don't know, but strongly suspect that the epoxy used as a binder in a typical carbon layup will more than kill any thermal advantage of the carbon. How about some aluminum flashing sheet? Bend up multiple ' [ ' channels with increasing center widths, stack up up 'concentric' drill for the LED base, then reassemble with heat sink compound. Not perfect, but a lot faster/cheaper than carbon, and you get the extra thickness next to the LED. 

Of course, by the time you do all that, you'll have spent more in parts/labor than the FlyLEDs light we talked about, off-line.  I doubt it will be much lighter, either.

Charlie

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