Defrost Fan Install - OK to cut holes in skin?

[IowaRV9Dreamer]

I'd like to install 1 (or 2) lightweight fans in the forward top skin to blow unheated air up onto the inside of the windscreen. The intent is to keep air moving for defrost purposes on the ground in a cold cockpit (I fly a lot in winter).... not for deicing purposes. I know others have done similar.

My question regards cutting holes in the skin for the air to blow through. I was thinking of just punching a 2" round hole and mounting the fan underneath, with some sort of finger guard. Position for the pilot side would be as shown, with the firewall on the left side of the pic and the panel on the right side:



Should I be concerned about cutting such a large hole here for structural reasons? Should I add a doubler?

BTW - fan is 60x60x25mm, from "Jamicon" moves 21 cfm, draws 0.23 Amp and weighs < 3 oz! Its seems to move an adequate amount of air and is also pretty quiet (not that fan noise matters).

Datasheet here for interested parties.

http://www.jamicon.com/spec/DC/JF0625-00.pdf

Thanks for any help, and have a Happy Thanksgiving!

[avee8tor13]

Dave,

I drilled holes and than riveted one of the scat vent tubes on the inside to accept a 2 inch scat tube.

http://avee8tor.smugmug.com/Airplane...56979222_T4gcx

I am from Boone just outside of Ames by the way. Good luck on your build.

Tim

[mcencula]

Originally Posted by IowaRV9Dreamer

Should I be concerned about cutting such a large hole here for structural reasons? Should I add a doubler?

Dave,

I see you've built a slider. Here's my line of thinking: Since the canopy skin on a tip-up isn't really attached to the airframe (except for the pivots), the airframe is strong enough with no skin there at all. Thus, on a slider, a couple holes won't hurt anything (and will still probably be stronger than a tip-up).

Final recommendation should come from Van's, of course.

Good luck!

[IowaRV9Dreamer]

Originally Posted by mcencula

Since the canopy skin on a tip-up isn't really attached to the airframe (except for the pivots), the airframe is strong enough with no skin there at all.

That's a really interesting thought. I looked at the tip-up plans (which I'd never really done before) and it looks like Vans separated the forward top skin into two parts. One part is between the firewall and the subpanel and that is stationary. The second part is between the subpanel and instrument panel and that part moves with the canopy.

Since my holes would be in the aft part, I think you are probably right about that part of the skin being non structural.

I still may put a doubler, however.

dave

[RV7AV8R]

Dave, I made mine exactly like you are considering. I rarely need it but when I do it works fine.

[Snowflake]

Just a thought, but if you put the fan over the top of your radio/gps stack, you could suck some of the heat out from there to help defrost. Some louvers in the skin to direct the air out across to the pilot's side may be needed if you put your radios off to the right like many people.

Could be useful in summer too, to help cool the radio stack on hot days. On one really hot day this year after being parked in the sun, my iCOM started rebooting when I tried to transmit. It fixed itself after a few minutes of flying though.

[Bob Axsom]

I located one 2" hole on each side of the center post (two holes) in the skin forward of the instrument panel under the windshield as you are considering for you airplane. I also cut two rings to back up the skin around the holes and sandwiched some screen wire that I bought from Aircraft Spruce across the holes to prevent foreign objects from falling down through the holes. This was done to vent the heat from the avionics during operation. I have an "Ice Box" cooling fan blowing cool air through small diameter SCAT tubing onto the avionics boxes. Later I thought about the defrost needs of the windshield and I routed a 2" SCAT tube from a valve in the heater system to the edge of the left side hole in front of the pilot. It is flattened and strap clamped in place. I found it essential on several winter flights. It works very well and there have been no problems in 6-years (600+ hours) of operation. I don't see any structural risk at all. I have no fans blowing air onto the inside of the windshield.

Bob Axsom

[yakdriver]

On my 7 I punched a 2" hole and mounted the fan with a screen to keep the big stuff out. It works really well as we get a lot of cold damp days here in the winter. On the Cub I'm building I plotted out a grid and drilled #41 holes. I would do the same on the 7 if I could do it over. It looks great. Don

[Mark Burns]

Dave,
Here's a link to a thread on this.
See my post #9

http://www.vansairforce.com/communit...OST+FAN&page=2

I've had my 7A flying for two years and have only turned the fan on a couple of times, and didn't need it then But I do live in Louisiana.

Mark

[IowaRV9Dreamer]

Hi Mark - I saw your post with the awesome cutouts and I didn't think I could replicate it... but maybe I'll try!