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Heliograph

V

Vlad

Well Known Member
For couple years I was puzzled how my brand new glare shield got a burnt spot. I didn't solder anything in the cockpit and my passengers usually don't smoke. Then I got another a bigger one. Then one day I returned to my aircraft to see a touch of smoke coming out of the cockpit. Now I know why. Ever heard of a heliograph or sunshine recorder? Your RV bubble canopy can be one of these.


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Watch the sun at your six thirty.


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Your bubble canopy (tip up in my case) becomes a powerful magnifying glass. Your finger won't stay like this for too long you feel the heat right away.


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These marks I acquired through 4 years of flying without even knowing the cause. Only last year I was able to figure it out after seeing a smoke. Did anybody experienced something similar? What would happen if your glareshield is other then aircraft designed part?


Heliograph%20-%201%202.jpg
 
From your experience, would you say that your RV should be parked in a certain direction if outside or rather to NOT park it facing a certain direction.... (such as never park facing north during the day)?
 
Vlad,
Fascinating!

You have one smoking hot airplane! You'll just have to fly inverted to avoid additional burn marks while in cruise. :D
 
There is another variation of this. IIRC it was Dave Saylor who had a polished -10, until the reflection off of his wing melted one of his side windows. His wing is now painted.
 
This is a common problem for gliders with tip up canopies. Often find a spot burned in the glare shield if not careful and the sun shines through the tipped up canopy.
 
cmmguy said:
From your experience, would you say that your RV should be parked in a certain direction if outside or rather to NOT park it facing a certain direction.... (such as never park facing north during the day)?
Click to expand...

Certainly. If possible avoid sun position between 5 and 7 o'clock with tip up canopy open or propped.


drill_and_buck said:
Vlad,
Fascinating!

You have one smoking hot airplane! You'll just have to fly inverted to avoid additional burn marks while in cruise. :D
Click to expand...


:D:D:D A good one Mike! But why are you getting all awards and trophies? :D:D:D
 
Well, the science is well known, but the discovery of it in an RV is amazing. I guess that the sun comes in at that angle frequently. I have a tipper, so it looks like parking in the sun without a cover is not recommended.

What is declination and heading (relative to the fuse) of the sun to create this issue? Any way to avoid it?

Edit: Good timing on the answer above. Thanks
 
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Meske tip-up/slider mod also

I saw the Meske tip-up/slider mod being demoed at Sun-n-Fun some years back, when someone pointed out to the owner that the sun was burning a hole in his seat. Same thing the angle of the canopy was a big magnifying glass.
 
Haven't seen it happen in an airplane (yet) but my brother in law lost a pickup to this. He had some 5-gallon jugs of clear glass full of water in the bed of his truck sitting on a rubber bed mat, it smoked and eventually ignited the rubber bed mat, which ignited the two fuel jugs also sitting in the bed of the truck, and it was all over but the cryin'...
 
Just to clarify, the canopy is believed to focus the sun's energy (a) like a parabolic reflector (sunshine reflects off the inside of the canopy to a focal point), or (b) by refraction (sunshine passes through the plexiglass at an oblique angle, probably twice, to a focal point, much like a magnifying glass)?
 
DanH said:
Just to clarify, the canopy is believed to focus the sun's energy (a) like a parabolic reflector (sunshine reflects off the inside of the canopy to a focal point), or (b) by refraction (sunshine passes through the plexiglass at an oblique angle, probably twice, to a focal point, much like a magnifying glass)?
Click to expand...

"B". Not believed, but empirical data as it has been observed many times as the sun is refracted by the canopy.
 
parabolic reflector

DanH said:
Just to clarify, the canopy is believed to focus the sun's energy (a) like a parabolic reflector (sunshine reflects off the inside of the canopy to a focal point), or (b) by refraction (sunshine passes through the plexiglass at an oblique angle, probably twice, to a focal point, much like a magnifying glass)?
Click to expand...

Based on personal experience with a Sport Criuser, the interior surface of the open canopy reflects and focuses the sun's rays in a concentrated spot that melts/burns the top of the glareshield. Only occurs with tip-up canopy OPEN and tail toward the sun. Sun has to be at relatively high angle, IIRC, at least in the Sport Cruiser geometry. Happens in the blink of an eye. Pick your combustables carefully...

With regard to the question of reflection vs. Refraction... the relatively low angles of incidence leads me to believe that the phenominon is based on reflection rather than refraction. Refraction at shallow angles dissipates so much energy within the plexi. I have not done any ray tracing to verify this.

Roger
 
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I was sitting in my truck having lunch one day and noticed smoke rising from the console. A partially filled plastic bottle of water refracting the sun's rays to a point was the cause...
 
one more casualty

.....so my starboard nav light lens catches the sunlight just right, & melted the wingtip plexi light cover.
.....can't really park differently, so just replaced the cover, and put some green tape over the nav lite, at least until I need it for night flying! ( not happening this century!)

darn parabolic geometry eh?
 
...And yet another casualty

I found two parallel deep burnt gouges in the upholstery of one of the seats in my RV6. One was about 4" long and the other a little shorter. Had to reupholster the seat.

Steve
 
I always said I wasn't going to be one of those guys that flies my airplane somewhere, parks it, and then covers it up with a cover - but I just ordered a cover.
 
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