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Defrost fan

Jrskygod

Well Known Member
I have seen several builders that have installed a fan in the top of the panel to blow air on the windshield for defrost. How effective is this solution? Did you duct any heat to that area? What size fans are being used and how many CFM. Your input would be most appreciated. Thanks
 
An alternate approach would be to simply not install such a fan.

I had considered doing so, but on the advice of other builders around the great white north (MN) who said I wouldn't need it, I didn't install one. After a couple of winters and flights with OATs well below zero, I can't say I've ever had a fogging/frosting problem.
 
An alternate approach would be to simply not install such a fan.

I had considered doing so, but on the advice of other builders around the great white north (MN) who said I wouldn't need it, I didn't install one. After a couple of winters and flights with OATs well below zero, I can't say I've ever had a fogging/frosting problem.

All depends on the actual condition of the air.
Here in the Pacific North (wet) West we have a lot of days during the year were the temp. / dew point spread is rather small with somewhat higher relative humidity. It is not uncommon to climb in and close the canopy and have the interior side immediately start to fog over.
The RV-14 has this feature incorporated into the design and will be standard with the kit.
Computer fans just moving the ambient cockpit air seem to be enough to take care of it.
 
Rv14 Defrost

All depends on the actual condition of the air.
Here in the Pacific North (wet) West we have a lot of days during the year were the temp. / dew point spread is rather small with somewhat higher relative humidity. It is not uncommon to climb in and close the canopy and have the interior side immediately start to fog over.
The RV-14 has this feature incorporated into the design and will be standard with the kit.
Computer fans just moving the ambient cockpit air seem to be enough to take care of it.

I have been studying all the different threads on defrost options. Fogging the interior of the windsheild can be a problem where I live. Based on the bolded part, it seems I should just build on since Vans has anticipated my needs:)
 
Here in the mtns of Colorado it is common to fly at zero or below and the canopy will always fog up while on the ground. To solve this problem I mounted two computer fans below the glare shield. Worked like a dream. Once airborn the fan are not needed.
 
I run the fans all the time, they do double duty as defrosters, and pulling air out of the avionics area.
 
An alternate approach would be to simply not install such a fan.

I had considered doing so, but on the advice of other builders around the great white north (MN) who said I wouldn't need it, I didn't install one. After a couple of winters and flights with OATs well below zero, I can't say I've ever had a fogging/frosting problem.

Brad, you must be not breathing or not carrying passengers! I have always had problems while taxiing (with a passenger - solo no real problem) when OAT near the 0F range. It is especially bad when dewpoint spread small, and the taxi or delay time is long. I took off last month with a px and the only view I had was through the windscreen, where my fans were blowing. Everything always clears up a minute or so into the flight. Of course, you can go sporting and taxi with the canopy open... Keeping inside surfaces of plexi clean helps also, by reducing nucleation sites.

I was not on of the MN builders who said you won't need fans:eek:
 
Brad, you must be not breathing or not carrying passengers! I have always had problems while taxiing (with a passenger - solo no real problem) when OAT near the 0F range. It is especially bad when dewpoint spread small, and the taxi or delay time is long. I took off last month with a px and the only view I had was through the windscreen, where my fans were blowing. Everything always clears up a minute or so into the flight. Of course, you can go sporting and taxi with the canopy open... Keeping inside surfaces of plexi clean helps also, by reducing nucleation sites.

Wow, I had no idea it was that big of a problem. Seriously, I usually fly alone but sometimes bring a friend and I'm also usually breathing but I've never had an issue with it. It might be that the inside of my canopy is pretty clean - I'm a little ... obsessive ... about that and clean both inside and out on a pretty regular basis.

I was not on of the MN builders who said you won't need fans:eek:

Nope!

I'd add that my hangar mate, Vince, came up with a compromise that he seems pretty happy with: he wired a computer fan to a cigarette plug so he has a portable defrost fan when he wants it. He seems pretty happy with it; perhaps he'll chime in.
 
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I wired 2 computer fans to my master switch, they help defrost the windscreen in the winter and cool my avionics in the summer. A cheap and easy option to add, and yes even the heat from the avionics and fans alone is enough to make a big difference while taxing on the ground in my environment.
 
I wired 2 computer fans on the glare shield ducted to the cabin heat box with some SCAT tubing.
70-GlareShieldFormFitted_zpsfddc61ba.jpg


I recently placed real fan covers on the glare shield instead of just holes. Makes the installation look more professional.
71-CompletedGlareShieldWithDefrostFanHoles_zps9cc3d74a.jpg


The fans are controlled via a panel on/off switch.
51-SwitchPanelCloseup_zps351168d8.jpg


In winter, with the heat box SCAT tubing connected, they help defrost the windscreen. In the summer, with the cabin heat box SCAT tubing disconnected, they help cool the avionics. They work GREAT.

:cool:
 
Pictures?

Cool!

Can we see pictures?

CC
I wired 2 computer fans to my master switch, they help defrost the windscreen in the winter and cool my avionics in the summer. A cheap and easy option to add, and yes even the heat from the avionics and fans alone is enough to make a big difference while taxing on the ground in my environment.
 
Defroster is a must for me

On my first -7, I used one computer cooling fan.
Allthough this is usable, I used four fans on my second -7 (2+2) installed on each side of the inlet for cabin heat.

For fans, I used the expensive type so the bearings would have better quality.

w7n5hi.jpg






Here's a closeup of one of the dual fans installation:

2uz6zcj.jpg





And here's the air outlet:

9toj1i.jpg


BTW: all hoses where secured with clamps after the install.

The defroster are wired to a separate switch.

I only need it on the ground, because once airborne, the canopy clears quickly.


I have not installed any "air-spread" outlet, because I didn't want to restrict the airflow.
Th right seat is pilot seat so I've installed the outlet in front of the pilotseat.
The top of the windshield is painted flat black so noone sees the hole anyway, at least not on a TW.

The defroster works great for me, and I'm VERY I installed it! I'm using it on every startup from Fall until Spring.

The best reason I can think of for installing a defroster system, is that it would be a VERY difficult job to install it after the plane is done.
In fact, I can't imagine how it'd be possible...
 
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Triple Duty !!!

I have 2 computer fans installed, drawing air out from behind the avionics
And de fogging the windshield at the same time.
The fans draw very little power and I decided to wire them permanently on when the master switch is on.
Triple duty, cooling avionics bay, keeping fog off the windshield and reminding me to turn the master off.
In the old days we had a whining gyro telling you the master was still on.
 
I went with just a single fan, small computer supply style, more so to draw heat away from the avionics than any perceived need for defrost, since I live in west Texas. I took a 12-volt power supply fan that draws only 190 milliamps, put it in series with a 15-ohm 5-watt resistor mounted immediately below the fan in the airstream for cooling, and wired that to my avionics master with a 1-amp fuse. The 15-ohm resistor gives me a voltage drop of roughly 3.5 volts which slows the fan speed to the point that it's barely audible without a headset and I'll never be bothered by the fan noise.

I think my 430W fan is louder than this defrost fan now.
 
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Being in Florida I was more worried about the avionics heat. So to kill both birds I installed just two grills. The convection though these is good so I get some defrost and a lot of cooling for the avionics.
 
You want fans with good pressure

I'm not flying yet so I don't know for sure how well this works but for most fan installations you want a fan that has a good pressure/flowrate curve. This is especially true if you use any type of ducting. I plan on using two ebm-papst 8312H fans mounted on the F-7106 Forward Top Skin. They work as combination defog/avionics cooling fans. These are 80mm X 32mm fans. They have good flowrate and pressure. Digikey has them in stock for $33.22. Not cheap but these are really nice fans. If you ever need a more powerful fan, the ebm-papst 8212JH4 fan is a 80mm X 39mm fan that has much more flowrate and pressure and will bolt in the same place as the lower power fans. You can find the specs for these fans by doing an online search.

I hope this helps.

Jeff
 
I opted for a radial fan.

http://www.mouser.com/ds/2/310/1337705601m1_odb9733_series-476196.pdf

30CFM with no back pressure, the link above has the flow curve.

I plan to have the suction side to come off the top of the heat distribution box. In past posts, Bob Axsom, ( http://www.vansairforce.com/community/showpost.php?p=12004&postcount=3 )he says without heat it won't work in certain conditions, but with heat, works in all conditions.

The plan is to blow at a with a shallow incidence angle for best velocity across the canopy. A test by blowing into a box and cutting slots and holes, left slots as being the best approach. YMMV.

That ebm-papst 8212JH4 fan is impressive. I might rethink this selection.
 
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It is a frequent occurance here in the NW. I installed a 72" fan from HartZell. I open the slider about an inch and it is gone in a few sexonds. Never an issue in the air, only on the ground.
 
Part of what I was looking for was an idea of the size of fan and the cfm that would be used. I'm thinking a 3" dia. and about 80 or so cfm but thats just a wild guess.
 
Mine is a used 3" fan from our first computer. If it fails we have another from our second computer. Didn't even think about buying one new...

No idea of cfm but with only avionics as a heat source it clears the windscreen very quickly. I can just feel the moving air as it hits my face.

It doesn't take much if you put it on as soon as you get in. The aircraft is an -8 so a side by side would probably take two fans to clear the entire windscreen...

I did paint the "grill" flat black so it wouldn't reflect in the windscreen...
 
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Our GTX330 is recommended to have cooling air supplied (not absolutely necessary but in high-density traffic areas where the XPDR is getting lots of interrogations, the life of the box will be extended by keeping temps cooler with some pressure airflow through the box).

I was only able to find an avionics cooling fan with 3 outputs. Hmmm... 3 outputs, only one avionics box connected... that leaves two outlets unused. Seems like they might be able to provide some flow up to the windshield. Since I'm running the fan all the time anyways, plumbing the spare outputs to the defrost vents just seems natural, and it will help get rid of some warm air from under the glare shield.
 
I'm curious... how are some of you guys with tip-up canopies mounting your fans? I bought a pair of 3" computer fans to mount underneath the glare shield, but I'm running into problems. They will run into the top flange on the panel when the canopy is lowered. They can only be mounted so far forward under the glare shield before running into the canopy braces.

Does anyone have some ideas to share? Better yet... any pictures? It looks like I'll either have to get much smaller fans, or mount them on top of the glare shield (I really don't want to do that, if I can help it).
 
I'm curious... how are some of you guys with tip-up canopies mounting your fans? I bought a pair of 3" computer fans to mount underneath the glare shield, but I'm running into problems. They will run into the top flange on the panel when the canopy is lowered. They can only be mounted so far forward under the glare shield before running into the canopy braces.

Does anyone have some ideas to share? Better yet... any pictures? It looks like I'll either have to get much smaller fans, or mount them on top of the glare shield (I really don't want to do that, if I can help it).

I found the same issue on my tipper. I purchased squirrel cage blower style and plan to use some scat hose with slots. The plan is to pull from the heater box. It is not installed, so that could change.

I have seen the smaller fans installed neatly in the glare shield, don't know the size, or have a reference, sorry. I have extra axials :D
 
Bruce,
A 3 inch fan is probably too big. Here's a pic of my 60mm fan. It overlaps the brace a bit, but it doesn't need to be perfect to move the air. It has to be back far enough so it doesn't hit the panel when the canopy is closed.

Note that I cracked the housing when I tightened the screws, but it still works fine. I already have a new one to replace it when it fails. They only cost $5 on ebay.

DSCN0794_zpsdd3jcibb.jpg


DSCN0797_zpspottdkdg.jpg
 
The fans are controlled via a panel on/off switch.
51-SwitchPanelCloseup_zps351168d8.jpg



GalinHdz,

Where did you source the switches, cluster and labeling?

Looks great!
 
Any recommendations for solving the foggy windscreen problem for an already flying slider? Installing a fan after the fact sounds very painful! I'm thinking that rigging one of those computer fans with a cigarette lighter adapter and then setting it atop the panel for a few minutes might work. Thoughts?
 
Any recommendations for solving the foggy windscreen problem for an already flying slider? Installing a fan after the fact sounds very painful! I'm thinking that rigging one of those computer fans with a cigarette lighter adapter and then setting it atop the panel for a few minutes might work. Thoughts?

Have you ever had a foggy windscreen? Inquiring minds and all that . . .
 
DeFog Fan

I don't tend to have foggy windshields here in Florida but I find the defog fans useful for moving air from behind the panel and reducing temps for the avionics. (I think this was suggested in another thread).

I have a Troll Avionics fan electrically plumbed behind the panel. But I have not routed the scat lines to the avionics. I'm concerned that it would just move the hot air behind the panel to the avoinics; hot air blowing on the avonics does not seem like a useful cooling approach.
 
The canopy of my -4 would fog up in the winter every time I got in the plane.
Its a fairly small cockpit and after pulling the plane out of the hanger, I guess I was generating a lot of steam :D

Once I got the engine running, it would clear up fairly quickly, but I had to delay taxi by a few minutes till it cleared up.

I did not have a fan in the -4, but thought it was pretty easy to put one in my 7, so I did it. Just started flying so I have not used it yet. Will see how it does this winter.
 
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