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  #1  
Old 06-05-2022, 05:48 AM
GrinchF16's Avatar
GrinchF16 GrinchF16 is offline
 
Join Date: Jan 2020
Location: Indiana
Posts: 140
Default Defrost Fan

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

Completely informal poll:
Do most of you have Defog Fans?
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  #2  
Old 06-05-2022, 06:37 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,661
Default -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.
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  #3  
Old 06-05-2022, 08:10 AM
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AlexPeterson AlexPeterson is offline
 
Join Date: Sep 2005
Location: Ottertail, MN
Posts: 2,533
Default

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.
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  #4  
Old 06-05-2022, 08:11 AM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest
Posts: 2,328
Default 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.
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WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

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  #5  
Old 06-05-2022, 10:04 AM
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plehrke plehrke is offline
 
Join Date: Sep 2006
Location: Defiance, MO
Posts: 1,935
Default

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.
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  #6  
Old 06-05-2022, 10:55 AM
terrye terrye is offline
 
Join Date: Feb 2010
Location: Vancouver, BC, Canada
Posts: 998
Default Defrost Fan

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.
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  #7  
Old 07-02-2022, 03:29 PM
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1001001 1001001 is offline
 
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Location: Just Minutes from KBVI!
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Default

Quote:
Originally Posted by terrye View Post
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.
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  #8  
Old 07-02-2022, 03:50 PM
rocketman1988 rocketman1988 is offline
 
Join Date: Jun 2010
Location: Sunman, IN
Posts: 3,058
Default Fans

I have two Noctua 120mm fans installed and they work great…
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  #9  
Old 07-02-2022, 04:30 PM
abwaldal@gmail.com abwaldal@gmail.com is offline
 
Join Date: Jan 2017
Location: Battle Ground WA
Posts: 529
Default

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
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  #10  
Old 07-02-2022, 05:04 PM
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GalinHdz GalinHdz is offline
 
Join Date: Mar 2010
Location: KSGJ / TJBQ
Posts: 2,349
Default

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.
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