Windscreen Defrost Vents - No Fans

[jerry98b]

Hello all. I'm getting closer to putting my windscreen in place and wondering if I should add some small defrost vents. It doesn't get very cold where I'm at, but sometimes windshields will fog up a bit on cool mornings.

I'm thinking about cutting a single small "U" slit on both side of center into the glare shield to make vents similar to what is on the firewall heat inlet cover. There wouldn't be fans, just heat rising through from below heater and avionics. Thoughts?

 

[wirejock]

The fans are an excellent cooling system for the electronics.

 

[larrynew]

Thoughts?

I would be worried about dropping things through the slit onto your avionics and wiring without a screen.

I installed two computer cooling fans (with screens) in my 7A like many have done and about where you’re showing. Very happy I did for the times (maybe a dozen in 1000 hrs) when a foggy windscreen would have been a problem.

If you go with fans, don’t mount them too far forward. Hard to tell without the windscreen installed but they will be difficult to service or replace. Ask me how I know .

 

[MarkW]

I felt there would be avionics heat build up underneath and I wanted the ability to defrost or more correctly de-fog the windscreen. Also didn't wan the complexity of fans so I cut round holes and used the screens/grills from computer fans. Only wish I has panted them black. The rest of the glareshield is flat black an d the chrome stands out.

 

[larrynew]

Maybe size vent holes to fit fans if you decide to add them later. And move them back about 1-2 inches from here.

 

[skelrad]

I'm torn on putting in fans myself. With a tipup, the space between the canopy skin stiffeners and the top panel brace is pretty limited, so the fans have to be pretty tiny! I seem to recall someone mentioning they used 52 mm fans, or somewhere in that neighborhood. Do two fans that small really move enough air to matter? I suppose I could put more than two fans in, but I don't really want to turn my glare shield into swiss cheese.

 

[eavila1]

Jerry, I'm wiring two cheap but sufficient defrost fans on the top skin. A buddy of mine says they work well and they help with avionics and distributing some heat.

On another note, your top skin looks good. Question. My fuse is a quickbuild and I'm having a heck of a time getting the left and right lower holes to line up. It almost seems too tight or something is going on with alignment or something. How did yours go on. Ok, or was it a challenge? Anything you did to ease installation?

 

[jerry98b]

Ok, you guys talked me into it. I ordered the following. These will easily plug into the back of my HDX screens and will power on when they do; ordered set of 4 to have a couple extras.

 

[SuperCubDriver]

I just put a vent like the ones on the side just below the windshield on the pilot´s side. It is fed cold air from the outside via a Y-Tube from the left vent line. It works quite well for defrosting, even idling on the ramp. Of course the engine must run to move air. I was surprised how well the NACA inlets work. With the cowling removed they won´t work but who flies without.

 

[rv6n6r]

I have a windscreen vent without a fan and it helps a bit but could use more on damp mornings when the inside fogs up. I would recommend a fan. My vent is a bunch of small holes evenly spaced using an Adafruit through-hole breadboard as a template.

 

[Ralph Inkster]

I’ve cut vent slots in every build, some with fan motor, some without. The planes without fan might fog up a bit during cold weather operations taxiing out to the runway, but as soon as I push the throttle in, the w/shield clears up.

 

[Desert Rat]

Ok, you guys talked me into it. I ordered the following. These will easily plug into the back of my HDX screens and will power on when they do; ordered set of 4 to have a couple extras.
View attachment 72753View attachment 72754

I put a couple of those in the glare shield as well although mine are switched. FYI. you can't make them run backward by switching polarity. As I recall, mine suck from the side that has the label in the center. At any rate, make sure when you install them that you have them oriented properly so they aren't blowing down.

 

[rdamazio]

I cut simpler holes on the glareshield, added doublers with the correct shape for the fans I have, and then will add the nicer-looking covers from the Aerosport glareshield cover.

 

[alcladrv]

In my -7A slider, I cut a 3/4" wide vent slot about 3" long for defrost. It's off-center to the left side. Pro-sealed a screen on the underside. It's connected to a 2" SCAT duct that runs all the way to the baffle ramp forward of cylinder #2. The spinning prop becomes my fan.

 

[F18Sailor]

Any thoughts on how to do this to an existing glareshield? Instrument departure in very light rain, occasional mist resulted in the windshield fogging up from the inside-that was worse than the actual weather! It would be nice to have some airflow over the inside of the windshield, I was thinking to port it from the NACA cooling duct, but hesitant to cut the glareshield with it firmly installed.

 

[71459]

The planes without fan might fog up a bit during cold weather operations taxiing out to the runway, but as soon as I push the throttle in, the w/shield clears up.

This is how it goes. No need for fans - keep it simple.

 

[BobTurner]

Unintended problems: For those thinking about ducting external air to under the glareshield, remember that years ago Cessna did exactly that. And years after that, there were all sorts of issues with corroded avionics. Rain was getting inside in flight. For the person mounting a fan on the back of a piece of avionics: Does the avionics already have an internal fan? Make sure your new fan doesn’t work against the internal one. And such a fan is for cooling avionics only. If you want defrosting/defogging the fan has to be close to the grill/holes.

 

[rv6n6r]

Any thoughts on how to do this to an existing glareshield? Instrument departure in very light rain, occasional mist resulted in the windshield fogging up from the inside-that was worse than the actual weather! It would be nice to have some airflow over the inside of the windshield, I was thinking to port it from the NACA cooling duct, but hesitant to cut the glareshield with it firmly installed.

I did this before the windscreen was on, used a computer busboard as a template (e.g. this) to drill the holes but you should be able to use a tight angle drill and do it after the fact. For me it didn't work very well without a fan so I put one in - no duct, just put a fan under to get warm-ish air from the avionics bay, so no real worries about contaminants or hot air messing up the plexi.