Windshield defroster

I have just finished installing the hot air valve in the cabin of my 9a, and I am wondering if anyone that flies in the colder temps has installed or felt the need for a windshield defroster. It seems like it would be feasable to route hot air to the glareshield at this stage of construction, but I wonder if there is a need. Thanks Bob Collins

YES I WOULD INSTALL I DEFROSTER

I had two ocassions when the windshield was so fogged up that I couldn't see anything but the instrument panel. This was on the ground getting ready for takeoff. Problem was that I had a very nervous passenger that was breathing more hot steam than the titantic produced. No I do not have a defroster but I'm making revisions for one soon. We had to leave the slider canopy open for quite awhile to clear things up in 30F air,,,burr..... Once we got into the air we had no problem after air movement in the cabin stopped the problem. I would install one if your in that stage. I'm sure others will relate to similar times but it doesn't happen very often, mostly while on the ground is when I had problems. AJ

I installed a defrost System

I installed a defrost system and I use it. The windshield fogged up on Sunday before taxiing out to the runway for our flight to St. Louis. I turned it on and the windshield cleared up nicely as I have many times before. If you plan to fly IFR I think you should have it. I can't imagin trying to fly in cold weather IMC without it.

Bob Axsom

Have one, wouldn't do it again

I put a defroster in my tip up -6, made of two computer fans. I live/ fly year-round in Wisconsin. When flying solo, I've never had a windshield fogging problem. With a passenger (and lots of conversation) it does fog up during taxi on cold days. The fans do an OK job of keeping it clear, but, on the coldest days, cracking the canopy for 15 seconds does the same trick just fine. I've never had it fog up in flight, even with lots of yaking with a pax.

My -8 will not have any defroster. KISS whenever possible.

Bob Axsom said:

I can't imagin trying to fly in cold weather IMC without it.

Click to expand...

I've never noticed a fogging problem in flight in cold weather, only on the ground. Cold weather IMC= icing, which is a much bigger potential problem. I've only got a little bit of experience with flying in icing in the RV, and while performance was not noticably effected, I wouldn't want to push it. If you are counting on the defroster to melt ice accumulation on the canopy, I think you are in for a nasty surprise.

Bob, as stated already, ground ops are the issue. I have consistently found that when the OAT is below about 15F with no sun, and two people are on board, frost will form. Keeping the canopy open willl keep it clear, but will not clear it up once frost has formed for quite some time. I keep the fans blowing air from behind the instrument panel until in flight. Even once in flight, any frost allowed to collect will not clear for several minutes after takeoff. I'd put it in if you plan any flying at or below about 15F.

A couple of RVs at my home field (Pontiac, Michigan) have the two computer fans installed and they seem to work very well in either tip-up or slider. I have had only some minor fog issues in my tip-up 9A and am considering cutting and screening two holes in the glareshield to allow convection heating of the canopy. If this doesn't work, I plan to install the fans using the same holes.

I agree with KISS principle

My system is purely mechanical and it is basically on or off. I have a controll box mounted on the firewall with two ports that controls the flow of the heat from the heat muff. One port is routed to the cowl outlet with SCAT tube as a heat dump when off. The other port routes the heated air inside the cockpit to a "Y" fitting behind the instrument panel. One outlet of the "Y" is routed down the firewall to the area of the passenger's feet. The other output of the "Y" routes to another control box like the one on the firewall with two outlets. One outlet is routed to the pilot's feet area and the other is routed to the edge of one of the two the large screened (2 to 3 inch dia.) avionics vent holes (the one on the pilot's side) of the forward fuselage upper skin that extends under the windshield (I have a slider). The latter hose is flatten on the end where it is clamped by the edge of the hole to fan out the air. The control knob (cable) for the first valve is on the passenger's side of the instrument panel and it is the main cockpit heat control. Against the panel is OFF and pulled is ON. The second control knob is on the pilot's side of the instrument panel and it is the defrost control. this knob against the panel is normal heat for the pilot but pulling it out diverts heated air to the inside of the windshield. There are no fans on this system and because heated air rises, it works quite well.

Bob Axsom

Defrost fan

I ordered a 3-1/2" 12volt computer fan.
http://www.computercablesource.com/detail.aspx?ID=46

Then I drew a grill pattern in AutoCAD. Printed out a full size template, and about an hour and a half later I had this!



It turned out better than I was expecting. It will probably look better when painted flat black.

If anyone wants the drawing I can email it to you. ACAD or .pdf.

Mark

Wow! Nice cut job. I have a great appreciation for just how difficult that must have been. It looks CNC good.
Don

fan?

I live in Ottawa, Canada, and it can get quite cold here. Question about the computer fan idea... is the fan fed by some hot air source, or is it just to circulate cabin air around, blowing it past to the canopy?

Mark, what kind of tool did you use to do that cutting job?

Tools used

Phil,

I punched center marks from my template, and scribed the cut lines with a divider.
I used a unibit to drill 7/16" holes at the end of the slots.
Then a hand nibbler to open up the slots. Then filed to final shape.


Mark

Looks good Mark. Getting close to attaching the canopy so if I'm going to do this, now is the time. A pdf copy of the cutout drawing would be great if that's OK.

Clive Whittfield

Defog fan

Mark, I would like a pdf of the drawing.
Thanks,
David Maib
[email protected]

Mark Burns said:

I ordered a 3-1/2" 12volt computer fan.
http://www.computercablesource.com/detail.aspx?ID=46

Then I drew a grill pattern in AutoCAD. Printed out a full size template, and about an hour and a half later I had this!

It turned out better than I was expecting. It will probably look better when painted flat black.

If anyone wants the drawing I can email it to you. ACAD or .pdf.

Mark

Click to expand...

Defog fan

Mark, I would like a pdf of the drawing.
Thanks,
Matt

'Matt and Jana [email protected]

Defrost vent

Mark,

What did you use to cut with. Nice job.

See post #12

dadroot said:

Mark,

What did you use to cut with. Nice job.

Click to expand...

Tommy (dadroot),

Scroll up to post #12. I describe how I did it there.

Thanks,
Mark

Mark,

Do you have a slider or tip up? I was working on laying my vent out last night, and I'm gonna run in to the interference with the reinforcement braces for the tip up frame... If I move it aft a bit, my EXPBUS board will cause problems...that's my fault tho...

cjensen said:

Mark,

Do you have a slider or tip up? I was working on laying my vent out last night, and I'm gonna run in to the interference with the reinforcement braces for the tip up frame... If I move it aft a bit, my EXPBUS board will cause problems...that's my fault tho...

Click to expand...

Chad,
I have a slider.

I hope you can find a place to put it!

Mark

I went with a very simple defrost method that seems to work well. I installed a 1" flange between the heater vents. Then used some 1" SCAT tubing to another 1" flange mounted on the glare shield in front of the pilot. When the heat is on, air flows up along the inside of the windshield. There are no flaps, levers, or motors. It may not work in an area with high humidity, but it worked in Michigan and now in the Sierras in California.

Mark, Please send me a copy of the autocad drawing. If you can send the actual autocad file, as I use this.

Thanks

[email protected]

Another option!

On my first plane, I installed some muffin fans in a couple of soffit vents that were made of aluminum. They were louvered. They just set in the holes that I cut in the glareshield. They can be pointed where you need them, and they really seem to help keep the radios and other stuff behind the panel cooler since they pull the heat out the top of the panel.

They have worked flawlessly for eight years, and I am going to do it again if I can find the soffit vents.

Compass affected?

Anyone have issue with the compass reading when installing the muffin fan? ... when operating the muffin fan?

Am considering window defogger as well, since I live in a fairly cold winter climate.

avionics affected?

Yes I was wondering the same thing. Are the radios or the compass affected by these fans while they are on?

Christopher.