Defroster

15 Jul 2005 Defroster

On 14 Jul 2005, at 12:05, Mickey wrote:

>> I’m thinking about a kind of defrost vent in the
>> glare shield. I think a couple of PC muffin fans
>> would be perfect, but before I start cutting, I
>> am wondering if this is really needed. Is it a
>> common problem for the front windshield to become
>> fogged up?
>>
The messages I have read suggest that it is a big problem if you want to operate at temperatures of 10 deg F (-12 deg C) or colder (reported by RV-6A builder Alex Peterson on the RV-List). If you close the canopy (which you will want to, because of the cold prop blast), the moisture in your breath will tend to freeze on the inside of the canopy and windscreen. He said:

“Either a fan of some sort or keeping the canopy cracked open on the ground is necessary when the temps are at or below say 10F. One has time to study these things in MN winters.”

Jim Cone suggested that even muffin fans may not be adequate:

“I have two 4 inch fans for windshield defog in my RV-6A that take air from the footwell. This past September, on a flight from Gillette, WY, in a driving rain, my canopy fogged up inside before takeoff and as soon as I wiped it off, it fogged up again. I could see well enough to take off IFR and went into the soup at 300 feet AGL. It took almost two hours before the canopy was clear inside even though I had the cabin heat on full hot and the fans running. It was not a problem because I didn’t see the ground until 600 feet on final approach at Sioux Falls, SD. I am building a 7A (my third RV) and am putting a second heat muff on the other exhaust and routing the air from that to two 3 inch vents pointed at the windshield. I want some real heat to defog the windshield.”

Curt Reimer from Winnipeg (where they have very cold winters) said:

“I’d recommend them for sure. I wouldn’t be comfortable flying in cold weather without some kind of defroster, and that’s just with one person on board. They’re fairly light and they don’t cost much. They work very well in simple “freestanding” mode like most people install them – you don’t really need to duct any heat to them. I generally still leave the canopy cracked until I’m warmed up and ready for taxi. I keep the vent open a bit as well just to keep lots of airflow until I’m airborne. Once in the air the canopy clears right up and the fans aren’t even required, though I still keep them on. Coldest flight so far -29F.

I don’t know how long they will last though. Mine are from the surplus store and don’t sound as healthy as they used to. I think they were designed for the easy life of a heated office, and here we are using them in a cold airplane, pulling 6Gs with a shaky ‘ol Lyc up front. Mine are still working so far.”

Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://www.kilohotel.com/rv8