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Tip: Defroster-system on a RV-7

A

ao.frog

Well Known Member
We're just about finished with our homemade defroster-system, so I'm posting a few pics.

The basics are two computer-fans which have the same size as Vans flanged ducts, some airhose, hoseclamps, a flanged bulkhead penetration, and "Y" duct connection and a three flanged ducts.

On my first -7, we used only one computerfan but the airmass is alittle too low, so on this -7, we've installed two fans and connected their airflow. Hopefully that'll give more defroster-function.



Here's an overwiew:







The fans are mounted on each side of the hot air outlet by the FF:







Then, the two hoses are joined together:







Then through a couple of bulkheads:







And finally up towards the outlet:





Overhead the outlet, we've made a hole in the glareshield in the same size as the outlet.
The airflow will then clear a hole in front of the pilot (the plane has the right seat as pilot seat) enough for taxing and departure.


PS: wr're in the middle of wiring now, so the "wire-madness" will hopefully be done with soon... :)
 
Thanks for the pictures of your defrost system Alf. Pretty simple way of picking up the warm air as it enters the cabin from the heat muffs. I've been spoiled with a liquid cooled engine for the last 13 years and it's oversized cabin heater. It will be an adjustment going to heat muff, maybe electric underware will be required.
Cam Andres
RV9A with IO360 -down to the last 100 items
CH701 with EA81 C-FCAM
 
Axial fans are not typically used in applications with ducting. You will get flow separation or stall not unlike our wings. If you want to increase static pressure you can run those two axial fans in series instead of parallel as you have them now.

Here is an example of a better centrifugal option...like in your car or home central heating and air conditioning.

http://www.skycraftsurplus.com/dcfbbloweriiifan12vdc.aspx
 
If you want to increase static pressure you can run those two axial fans in series instead of parallel as you have them now.

Correct,Intel runs them on their 2U and 1U rack mount servers to cool the processors and they produce huge air and reside in a duct system
 
Also it will be great if you can set it to blow the air at more than one spot. Pilots don?t look out only directly in the front of them but thru the range of canopy.
 
Thanks for the input regarding two fans in series.
It'll be pretty simple for me to buy two more fans and install them in series at this point of the build, so that's exactly what I'll do.

Just so I don't misunderstand: you guys mean that I schould install two more fans, one on each side and on top of the ones which are there already, and that there schould be no spacer or spacing beetween the two fans?
 
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Yes, try it with the two hooked to temporary power then add two more and note the difference in output volume. Two pull about 0.6 Amps, two more won't quite double your current draw due to the help from the upstream fan. Let us know your results.
 
It looks like it will interfere . .

It looks like the tube flange on the instrument panel will interfere with the tube on the canopy frame. I am building a 7 also and had two similar fans, but switched to a 9 CFM blower from Mouser. I was surprised at the restricted area that is available for passing defrost air with the canopy frame lowered. The aft tube on the frame snugs close to the back of the instrument panel, and below it's plane.

On the flow. or stalling, you might just test the fans for flow with expected backpressure installed and see how it flows before making changes.

Good Luck! I like the basic idea.
 
Ok, I'll report back when I have installed two more fans.

Bill; Thanks for the warning, but it'll be no interference with the canopy frame-tube, because the hole in the glareshield will be forward of that tube. (beetween the tube and the canopy support flange)

What we might have to do however, is to move the duct outlet flange outboard of the right canopy-"bar" (the right one of the two ribs which go into the holes on the fuselage)
This means that the outlet flange will have to be outboard of the right hand instrument panel support rib.

For now, we'll try this location and see how airflow which will be blocked by the right canopy-"bar".
 
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Flange moved

Hi again folks.

We've moved the defroster outlet flange outboard now. It's now sitting just outside of the right hand instrument panel rib.







PS: The hoseclamps are missing in these two pics. The hose is just put in place temporary.




The airflow restriction from the right hand canopy "bar" where too big with the outlet flange on the previous position. (inboard of the right hand instrument panel rib)

As already mentioned, I've built the plane so the right seat is pilot seat, but I guess you'll have the same case with the defroster outlet on the left side.


Just wanted you all to know so don't install it like the first pics in this post.


PS: another update will come as soon as we've installed double fans on each side.
 
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I've got a defrost fan in my RV-8, and it is very useful in the winter, on the ground. Without the fan, after I get in and close the canopy to keep the cold air out, the windscreen fr ostsup very quickly. The defrost fan clears the windscreen in less than a minute if I select it on as soon as I see frost forming on the inside of the windscreen. Once I am flying I don't need the fan, as there is enough air circulation from the cockpit heat.

My installation is much simpler - the fan is bolted directly to the forward fuselage skin, with a grate above it to keep it from chopping up fingers, etc.
 
Any photos Kevin? Are you using hot air or just air from the Instrument Bay?

I often need to open my canopy while taking position and scoop cold air from outside with a gloved hand to clear the inside just before take off.

It sounds like you have a better solution.
 
The only photo I have readily at hand is on my web page, here. That's the same one as in the link in my original post. I'll look in my photo archive tonight to see if I can find other shots.

The fan is just a 12v computer case fan. There is no duct. The fan draws air from just below the upper skin, behind the instrument panel. That air must be pretty much the same temperature as ambient when I first use the fan, but it still does a great job. It has never failed to clear the frost well before I am ready to taxi.
 
best POH ever!!!

Kevin, I haven't looked at POH's for a few years, and I'm not sure I ran across yours...but I'd love to see you get ramp checked, and you hand the guy your 148 page binder! :)
But on a safety note, I'm rehashing my checklists to fit my new Kneepad, and I like to see what a real test-pilot has come up with...I'm sure I can improve mine!
thanks for sharing!
 
More air with double fans

Hi RV-ators in colder climates:

We've installed two more fans on each side now; one on top of the other, as suggested here in the forum.






The airflow is quite higher now, so the defroster-function must be better too.

What we found when testing the system on the bench, was that the RPM of the top fan increased when it was placed on top of the lowest one.

When you think about it, that's pretty natural, and this higher RPM must also be helping with increasing airflow.

All-in-all: an easy mod which I'm glad we did because it was easy to do at this stage of the build.

BTW: we'll also make holes in the glareshield just above the two avionics stacks as someone else here suggested.
That'll help cool the avionics and also hopefully provide some defroster-function the left side of the windscreen.
 
You should stick an eyeball vent in the glare shield so you can deflect the airflow in various directions.
 
Here is what I did: I used an eyeball vent from Vans as Dbro172 suggested, however only on the left side. I used one out of the kit as I used aluminum eyeballs on each side. The air is coming from the right (passenger) air inlet through a Y pipe. No fan (and no heat) so it is only working when the engine is running. At this time I only have 23 hours logged but mostly in our humid and foggy cold winter weather and i can say it works really good. I was surprised how good the airflow is with the engine on idle power only and it is easy to direct the airflow with the eyeball vent. I found that I even can defrost - or defog - the right side of the windshield.
Two more things to see on the second pic: A hook for a headset, in the shade and out of direct view. Also an external power plug so I can jumpstart alone should it be necessary.


IMG_1411edit_zps879cb2fa.jpg


IMG_1735edit_zps48e7d4e1.jpg
 
Kevin Horton said:
I've got a defrost fan in my RV-8, and it is very useful in the winter, on the ground. Without the fan, after I get in and close the canopy to keep the cold air out, the windscreen fr ostsup very quickly. The defrost fan clears the windscreen in less than a minute if I select it on as soon as I see frost forming on the inside of the windscreen. Once I am flying I don't need the fan, as there is enough air circulation from the cockpit heat.

My installation is much simpler - the fan is bolted directly to the forward fuselage skin, with a grate above it to keep it from chopping up fingers, etc.
Click to expand...

I did the same kind of thing for my RV-6. Very easy to install. And works great. I'd say it clears it up in 30-45 secs.
 
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