Wind Shield heat/defogger

Does anyone have a windshield defogger/heat system?

I have a RV-7A at Flying Cloud and despite misgivings when we built it, never put in a defroster/defogger.

Turns out it's never needed one. Any slight fogging I've seen goes away immediately after takeoff or is obviated by leaving the canopy cracked open a small amount (it has a slider). We kept a cloth in the cockpit in case it was needed to wipe off condensation but have never had to use it.

Bob, I am planning one, but interested in the answers you get. I am building a tip-up. I was planning for two axial fans, but they were too large to fit in the space. I now have a radial blower that will get mounted and pickup air from the heat box. The plan is a 1.25 inch tube blowing through two 3/8 x 2 1/2 inch slots. I tried this with a test setup and it seems to blow nicely.

I suppose one could look at temperatures, humidity, and mass transport phenomenon, but I am not. Just making sure the air blows across the pilots viewing area primarily. Possiblly I'll do both sides.

Here is a Bob Axsom comment:

http://www.vansairforce.com/community/showpost.php?p=672224&postcount=6

Thought about simply drilling a row of holes under the windshield but never did. I have used a clean microfiber rag on two occasions to satisfy my wifes desire to see. I am fairly confident the fog would have abated by the time I was ready to take off.

First plane (7a slider) just cut 1/2 x 5" openings above avionics letting their warm air rise thru to the w/shield. Worked great except on real cold days where w/shield would fog up in the corners when first taxiing, but clear when flying.
Next plane (7 tip up) used complicated ducting & fan from heater & required connectors between airframe & tip up. Fear that a concentrated hot spot may damage the w/shield drove us to restrict/reduce airflow 90% and gave satisfactory performance.
Since then I've resorted to using a simple computer fan, square duct/fan mount, below a slot cut in the glare shield. Excellent results.

I installed a simple 2"-Y from Aircraft Spruce under the subpanel and connected it to the air inlet. One scat goes to the air outlet on the right side panel and the other scat tube goes to an outlet on the left forward skin under the windshield. Even with idle power there is quite some air moving and I can adjust or close the outlet under the windshield. The air is not heated with this arrangement but normal fogging is easily removed.

Dash Defrosters

I mounted 2 small computer fans in my RV9A tip-up. They are controlled by a single switch. I've used them twice so far. Both times it was morning and my tip-up started to fog up. Turn on the fans and the moving air clears up the canopy. Works great. I'll try and get some pictures tomorrow if I go out to the airport.
Russel
RV9A, not quite finished, but flying

I didn't add any type of defogger. On the few occasions when the canopy started to fog up, I popped it open and started the engine. The air moving through the canopy, even on a cold day, was enough to clear it in short order.

Why add the weight and complexity?

we had thought about some kind of defogger for our tipup for quite a while but in the end decided against it.

200hrs of experience now affirm this decision. i keep a towel or kleenex ready in case the canopy fogs somewhat up (only on ground, only before takeoff, in winter with cold outside temps).

never ever has it happened in flight and even a quite fogged up canopy with only a smal patch wiped clear lookin forward will clear up right at/after takeoff.

also, flight visibility tends to be even worse when flying through rain without any inside fog on the canopy than in clear weather but with some fog inside. and there's no wipers either :-(

Our two 80 mm computer fans run continuously for avionics cooling. We have used them as a defogger on many winter flights.