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Defrost Fan

GrinchF16

Well Known Member
In redoing my panel, we discovered a wired labeled “Defog Fan”…. Attached to nothing.

Completely informal poll:
Do most of you have Defog Fans?
 
-7 tipper

I have the switch . . . . does that count? Never installed a delivery system.

On clear days below 20F I get fogging on the canopy both solo and dual. It occurs on the shady parts at the wrong sun angle. Pretty persistent too, when it ices. Only once ( of many many events) I had to lift the canopy with some rpm to allow clearing for TO. Brrrrr. After 230 hrs and it is still on the list but has not made it to the top. It would have been better to do in build stage. If it happened in a busy airport situation it definitely would be a factor.
 
Anyone who has taxied their planes, especially with two on board, in OAT's colder than about 5F, with DP not much lower, either has a fan or wished they did. Once in flight, I've never needed it more than for the first minute or two after taking off.
 
Just me

I wired the panel for a defrost fan just to have it. I had no intention of hooking it up. But when I got to the glare shield install, I realize it will be really hard to drill the holes once the windscreen was in. In addition, some others wrote here the real use of the defrost fan is to move the warm air from the heater outlet to the top of the cabin; it allows the cabin heat to be more even. So I installed the fan.
 
I installed two fans, left and right. Use them even in summer to pull air from behind panel for avionics cooling, not that is really needed.
 
Yes, I've installed LH and RH 3" computer fans. I've labelled the switch "AVIONICS/DEMIST FAN". Even when not running the vent holes provide an outlet for avionics heat. In summer, electronics like to be kept cool so the fans would normally run. In winter the inside of the windshield can mist up, fans intended to run during ground operations and as required in flight. My Cessna 150 doesn't even have a demist vent (although later models did) much less a fan. PITA trying to wipe the inside of the windshield with shoulder harnesses on.
 
Yes, I've installed LH and RH 3" computer fans. I've labelled the switch "AVIONICS/DEMIST FAN". Even when not running the vent holes provide an outlet for avionics heat. In summer, electronics like to be kept cool so the fans would normally run. In winter the inside of the windshield can mist up, fans intended to run during ground operations and as required in flight. My Cessna 150 doesn't even have a demist vent (although later models did) much less a fan. PITA trying to wipe the inside of the windshield with shoulder harnesses on.

I have a ton of old computer parts lying around, and among them are a few big (130mm) PC power supply cooling fans. The power supplies kicked the bucket years ago, but the fans were fine, so I saved them for this purpose. I never really test fit them until today, and now it seems they are quite huge. They'd need a nearly 4.7" hole in the panel top cover.

I'm wondering if this is just a little *too* big. Others have mentioned using 3" or 3.5" fans. Any thoughts on whether a big hole like 4-3/4" is just too much? On one hand I can see that they'd be quite prominently noticeable, but on the other hand, they will push a ton of air at the windshield, which may be helpful.

Here in western PA, it's pretty common to have fogging problems in small aircraft when flying in the cooler months, mostly when taxiing or before the engine has really warmed up and is heating the cabin.
 
I too think computer fans work great. Come in many different sizes.
But as for the unfinished switches. I have one that says BOMBS on my panel.
Just never finished the rest.
Ha Ha.
Art
 
I also have 12v computer fans for "defrosting" in my panel with scat hose connected to the cabin heat box. In summer I pull the scat hose off the fan and they become avionics cooling fans.
 
Yup, got a “defrost” fan on the glareshield. Helps draw some of that hot air from the cabin heat coming out around my feet up and aft around the canopy. My bride claims it does indeed make it warmer in the back of my -8. I’ve never ridden in the back of my -8 but I have to say, her temperature sensor is very particular :D
 
Anyone with a FB -8 care to comment on installing these fans? We have the lower, glareshield and the upper portion of the canopy frame right on top of it. So, I'd guess the fans would have to be mounted on the lower glareshield, and then a vent installed over them on the canopy frame?
 
Anyone with a FB -8 care to comment on installing these fans? We have the lower, glareshield and the upper portion of the canopy frame right on top of it. So, I'd guess the fans would have to be mounted on the lower glareshield, and then a vent installed over them on the canopy frame?

Manufactured a bracket to hold the fan and mounted it under the glareshield.

49903E6F-803B-42F0-A07A-A2242BEC9891.jpeg

I made four slits on the glareshield as far forward as possible aft of the windshield portion of the canopy.

A22C67CE-C4C7-4F0C-ABDC-2EA9E39C722F.jpg

It’s surprising how much air this little fan moves. Like I mentioned before, works great for defrosting if you happen to fly into icing conditions (happened once to me), but more importantly, it moves the hot air coming out by your feet up, across the inside of the canopy and to the back seat.

This computer case fan works great. I chose one with the highest CFM capacity. I’m sure with today's processors you can get a fan that moves even more air.

50FB6A6C-8A87-4E7F-895C-A86A078CD66F.jpg
 
I had some overheating on hot days with my Dynon D-100 so I put a Y connector in the NACA duct tubing and ran a tube up behind the panel and the D-100. I also cut a 1 inch hole in the dash just behind the windscreen. Now get cooling for the avionics and it defrosts the windscreen also. Seems to work fine.
YMMV
Figs
 
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