Defroster?

I'm thinking of Two heater control valves in the firewall. One for heat, one for a defroster. Like a pair of TG-10's

Anyone do that?

Dkb

Defrost

Computer fans are common.

I use two valves but only one is on the firewall

If I were doing it now I think I would work it out where I had zero control boxes on the firewall but alas if a frog had wings ...

My one on the firewall has the function of 0 = dump heated air overboard and 1= heated air enters the cockpit on the passenger side to a "Y" duct. Out of one leg of the "Y" a duct takes heated air to the passenger foot area. A duct on the other leg of the "Y" routes heated air to the left side of the cockpit behind the instrument panel to the second control box. This has a function where the 0 output = heated air routed to the pilots foot area and 1 = heated air to the windshield on the pilot's side. There are two control cables with knobs on the upper right and left portions of the instrument panel which can be called R and L respectively. Knobs in = 0, knobs out = 1. In the following logic map, effect state 0 = off and 1 = on. Pah = passenger heat, Pih = pilot heat and Pid = pilot windshield defroster:

Control/Effect
L R /Pah Pih Pid
0 0 /0 0 0
0 1 /1 1 0
1 1 /1 0 1
1 0 /0 0 0

All functions perform very well as intended and have been used several times in the past eight years.

Bob Axsom

I just used a computer fan to pull heat from behind the panel. No piping is connected, and it's worked fine.

Just use a computer fan. It solves two issues. The first is to function as a defroster and the second is to move warm air away from you avionics. Your avionics will heat the air warm enough to function as a defroster. many RV-10 folk, leave these on all the time to keep there stack cooler.

If you use a line from the heater, that air is too hot and you'll risk melting and/or distorting your canopy.

On a Cherokee, the defroster is fed from the heater and the vent is directed aft across the glare shield. I've seen some pretty ugly results from folks that think that the vents are on backwards and flip them toward the window. The acrylic starts turning yellow pretty quick.

Absolutely disagree

rleffler said:

Just use a computer fan. It solves two issues. The first is to function as a defroster and the second is to move warm air away from you avionics. Your avionics will heat the air warm enough to function as a defroster. many RV-10 folk, leave these on all the time to keep there stack cooler.

If you use a line from the heater, that air is too hot and you'll risk melting and/or distorting your canopy.

On a Cherokee, the defroster is fed from the heater and the vent is directed aft across the glare shield. I've seen some pretty ugly results from folks that think that the vents are on backwards and flip them toward the window. The acrylic starts turning yellow pretty quick.

Click to expand...

I do not usually disagree with Mr. Leffler but I have the system, I have the experience with the defroster in the RV and I believe he and the previous poster are wrong! I also have a avionics cooling fan that operates continuously as soon as I turn on the avionics master switch and two large vents in the sheet metal below the windshield behind the instrument panel. If the windshield is fogged over with frost or whatever IT WILL NOT BE REMOVED BY OPERATION THE AVIONICS FAN! It is not often needed here in northwest Arkansas where we have a nice hangar and the climate is mild but when we need it our defroster system is turned on and it clears the windshield in front of the pilot only. Once in route I turn the defroster off providing heat for me and the the windshield remains clear. My routing and flattened end shape is positioned at the edge of the left avionics heat vent on the forward side pointing back toward the pilot very similar to the configuration on the Piper Archer II which we owned for 22 years that I often used the defroster on with no detrimental effects. I have 8 years of operation on our RV-6A with effective operation and no detrimental effects. I am far more concerned about capturing the heat around the exhaust system and routing it into the cockpit than I am about damaging the windshield from the minimal heater system in our RV. In over 30 years of ownership of aircraft with this exact type of defroster I have never experienced a problem but I have a friend who owned a Cessna 182 that barely got the plane landed before passing out from CO. The other three in the plane were incoherent, one collapsed on the ramp after getting out of the plane and everyone in the plane had to be taken to the hospital for recovery. As you might guess I don't use the heater unless it is necessary and if I don't enable the heat system the defroster is not enabled either. If you can't see out of the windshield it is a problem that needs a system that will clear it reliably. If you are not a traveler faced with all of the different conditions and demands of serious travel then you don't need a heater system or a defroster system and you will be safer without them. If you need them, I have built this system and it works!

Bob Axsom

I'm not looking to start a debate. I can't speak for the other RV models, but in the RV-10 the heaters work quite well. Some believe they produce too much heat and don't hook up both sides. Van's has a sb that shows how to mix cold air to reduce the heat temps. Just search on tunnel heat for more details.

I wasn't referring to an avionics fan, i have one of those installed too. Garmin requires them on two pieces their gear that I have installed.

What I was recommending putting a pair of computer fans in the glare shield to exhaust warm air from behind the panel to the windshield. Most RV-10s may have more avionics than some of the other RV models.

There are many RV-10s flying with this configuration, many in the northern us and canada. I'mnot aware of any icing issues with this configuration.


I will agree if you let it get to the stage that your windscreen is frosted over, then a lesson in risk management is in order. Like I mentioned, many RV-10s have these fans blowing all the time (even in summer) and frost doesn't form. I'll stop short of stating it can't , but I'm not aware of it happening with this configuration.


This works for RV-10s, but I'm am willing to concede that in other RVs with minimal avionics configurations and/or steam gauges it may not work.

Bob Axsom said:

I do not usually disagree with Mr. Leffler but I have the system, I have the experience with the defroster in the RV and I believe he and the previous poster are wrong! I also have a avionics cooling fan that operates continuously as soon as I turn on the avionics master switch and two large vents in the sheet metal below the windshield behind the instrument panel. If the windshield is fogged over with frost or whatever IT WILL NOT BE REMOVED BY OPERATION THE AVIONICS FAN! It is not often needed here in northwest Arkansas where we have a nice hangar and the climate is mild but when we need it our defroster system is turned on and it clears the windshield in front of the pilot only. Once in route I turn the defroster off providing heat for me and the the windshield remains clear. My routing and flattened end shape is positioned at the edge of the left avionics heat vent on the forward side pointing back toward the pilot very similar to the configuration on the Piper Archer II which we owned for 22 years that I often used the defroster on with no detrimental effects. I have 8 years of operation on our RV-6A with effective operation and no detrimental effects. I am far more concerned about capturing the heat around the exhaust system and routing it into the cockpit than I am about damaging the windshield from the minimal heater system in our RV. In over 30 years of ownership of aircraft with this exact type of defroster I have never experienced a problem but I have a friend who owned a Cessna 182 that barely got the plane landed before passing out from CO. The other three in the plane were incoherent, one collapsed on the ramp after getting out of the plane and everyone in the plane had to be taken to the hospital for recovery. As you might guess I don't use the heater unless it is necessary and if I don't enable the heat system the defroster is not enabled either. If you can't see out of the windshield it is a problem that needs a system that will clear it reliably. If you are not a traveler faced with all of the different conditions and demands of serious travel then you don't need a heater system or a defroster system and you will be safer without them. If you need them, I have built this system and it works!

Bob Axsom

Click to expand...

Defroster...

Bob Axsom said:

If I were doing it now I think I would work it out where I had zero control boxes on the firewall but alas if a frog had wings ...
Control/Effect
L R /Pah Pih Pid
0 0 /0 0 0
0 1 /1 1 0
1 1 /1 0 1
1 0 /0 0 0

All functions perform very well as intended and have been used several times in the past eight years.

Bob Axsom

Click to expand...

Greeting Bob, Bob, et al!

My boolean arithmetic is still good, but it is my mechanical engineering that is a little light.

My original plan was two heater control valves in the fire wall, but folks say a fan would do. I'm using Skyview avionics (and I hope Dynon nav/comms) so I figure avionics heat will be at a minimum anyway.

So: Maybe one punched hole in the firewall for the TG-10 operated by a single cable. After that a "Y" with one leg to the footwell, and the second leg, via an axial fan and a flat tip a la "Cessna" to a defroster slit on the glare shield. (Think crevasse tool on a vacuum cleaner) I do not think I want to punch a 3" to 5" hole in the glare shield.

Bob Leffler raises an important point about too much heat on plastic wind screens. My Skyhawk did not have a fan on the defroster, and seems to work OK. Bob L: How about an air door at the heat inlet: one way to footwell and one way to defroster?

Does anyone have pics?

advTHANKSance!

Dkb

comfortcat said:

Bob Leffler raises an important point about too much heat on plastic wind screens. My Skyhawk did not have a fan on the defroster, and seems to work OK. Bob L: How about an air door at the heat inlet: one way to footwell and one way to defroster?

Does anyone have pics?

advTHANKSance!

Dkb

Click to expand...

You don't mention which RV that you have. You will need to make a determination if the heat temps are appropriate for your model RV. I only have experience with RV-10s, which has too much heat being produce. Judging from Bob's comment, the other models may not be so efficient.

If you do it like a Cherokee and the slot opens towards your face and not the windscreen, you'll probably be ok. Just don't aim it directly at the windscreen.

rleffler said:

You don't mention which RV that you have. You will need to make a determination if the heat temps are appropriate for your model RV. I only have experience with RV-10s, which has too much heat being produce. Judging from Bob's comment, the other models may not be so efficient.

Click to expand...

With my "six" and approx. 4" computer fan, frost was never a problem. And this is flying winters in the mountain west. I have a "kind of a" tee setup that blew straight down on the passenger side, and a 2" pipe towards the pilot side. All air through the defrost fan was picked up from behind the panel, with no ducting. As to the 4" hole in the glare shield, it's about a 2/3rds semi circle with a flat edge against the windscreen. I cut these with adjustable drill routers that us heating A/C installers use. They are available at Home Depot.

Decision Timeframe

Bob Axsom said:

If you are not a traveler faced with all of the different conditions and demands of serious travel then you don't need a heater system or a defroster system and you will be safer without them. If you need them, I have built this system and it works!

Bob Axsom

Click to expand...

I am just now getting going with plans to build a 9A. At what point do I have to make a decision about including a heater in the build? Planned use includes trips back to IL, but mostly any XC would be in the Southeast to Mid-Atlantic and only rarely in the winter.

I live in Central FL where I rarely need a jacket. I haven't done almost any flying since the mid-90's, but I seem to recall using the cabin heat quite frequently during training in So. IL. Even in summer once we got off the ground and to training altitude of 3,000'. Maybe I am not remembering correctly.

-Matt

With all four of us in the plane before startup at 20*F, we have to leave my door cracked a little to reduce fogging up the inside. Once started and taxiing out, we have front/rear heat fully open and two 80mm computer fans running above a full panel. There is barely enough warm air to prevent windshield fogging during taxi/runup, but once full power for takeoff is applied there is more than enough. The side windows take longer to clear completely, sometimes 10-15 minutes if climbing into colder air. If we have low humidity, then we open eyeball vents partially, which helps dry it out inside. If leaving our home airport then I pre-heat the cabin as well as the engine and the family is strapped in before I pull the plane out. This slow pre-heating helps prolong fogging. I would not recommend this setup for frost removal or cold, moist climates, but works great for us here. Like Bob mentioned, our heat is about double what it needs to be, so even while taxiing we get a fair amount.

If you had the heat spread across the bottom forward edge of your glareshield using a homemade fiberglass duct with holes in it and an adjustable venturi to
mix in cabin air, you might be okay. I just would not want to direct the 180*F heat from my outlet on the windshield and crack it about the time I get to 5,000' AGL.

Cabin heat

Another option that I would do next plane.

Heated seats. Simple. They work wonderful in my truck, even when I take off in the winter before the engine warms, the seat heaters are worth every penny. Love them.

Gloves, hat and good socks and shoes are smart in case of an off airport landing.

Must have

I intend to put a defroster in mine. Once after ice fishing, I pulled the engine blanket off my Chief and started up. The windshield up front was clear, until about the time I became airborne. It was zero to 10 below. It frosted instantly. I was able to maintain a horizon reference out the side window by looking at the lake shore until the windscreen cleared. The other lesson I learned was to have a horizon (tree line)out the side, as sometime flat light conditions can be quite dangerous.
I am thinking about closing all the lightning holes in the tip up structure with ceconite, running hot air mixed with cabin air, push it in with a fan, and have it directed out through a bunch of small holes.

I chose a rather simple solution. Probably is not defrost, but more like a De-mist function. I put six 3/4 inch holes in my glare shield behind the windshield. I am relying on convection from the radio stack and the heater to de-mist the windshield. So far it works well. On those cold misty humid mornings hear in the Pacific North West, it only takes a minute or so for it to clear the fog off the inside of the windshield.

Probably not great for Icing conditions, but as a VFR pilot, I avoid those conditions. If this is not adequate, I have plans to install a muffin fan.

Keep is simple.

Here's...

... what we've done:

http://www.vansairforce.com/community/showthread.php?t=95632