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RV-8 NACA ducts: Screens?

goatflieg

Well Known Member
I'm thinking about installing my NACA ductwork in my QB wing, and this seems to be another potential pitfall for novice builders such as myself. No mention in the builder's manual, and the instructions that come with the duct kit are purposefully vague. I'm wondering if anyone has installed screens in the inlet of the duct? I know bugs aren't an issue at altitude... but I'm leery of having an unscreened opening that accesses the fuselage. I'm wondering if any other builders have thought of this, and what they might have done.
 
Study the plans carefully. A lot of builders miss the snake guard.
 
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I put a stainless screen in my air vent systems, front and rear. Not at the NACA inlet opening, but at the SCAT tube connection on the front inlet and just below the eyeball vent in the rear. No univited bugs coming in through the fresh air vents.
And BTW I've hit bugs at 12k ft altitude
 
I used a piece of honeycomb aluminum I had on hand from an EMI fan grill. 1/8" holes, about 1/2" thick. Cut it slightly oversize on the bandsaw, pushed it in, and secured it with some RTV or proseal. Kinda cool and works great. You can pick up small pieces on eBay.
 
Yes but first you have to get the correct RV ducting.



I used some screen material from an old sliding door my dog went through and then captured it at the NACA duct with the RV hose pictured above.


(Click to enlarge)

To secure the NACA duct to the inside of the fuselage, I used Pro-seal. Almost 10 years later, I haven't had an issue with the screening or the ducts.
 
Just did this 3 days ago.

Not an 8, but I just formed a cup of aluminum screen over 1 1/2" ID PCV and the cup fit perfectly inside the scat tube, secured it with RTV (X2).
 
Years ago, one summer day flight in my 8 I am getting sand blowing in my face. I think, that's strange, it is coming out of the vent and I am at high altitude, how can this be. Back on the ground I find a big mud dobber nest in the scat tubing, no screens. My solution was to cut some foam rubber plugs for the vents that I installed after each flight just like I habitually install a pitot cover. On a new build, I think screens would be a good idea.
 
Find some PVC pipe a little larger OD than the ID of the NACA vent

Cut 2 rings for each vent and cut each lengthwise, to allow insertion and give some spring tension to hold in place

Sandwich your chosen screen between the rings

Add a couple of drops of thin CA

So far so good @ 300 hrs...



 
Some good ideas here. Actually, I was thinking of something like this... sealing the screen across the initial opening and sandwiching it between the sheet metal and the duct with RTV & blind rivets. Not sure if the screen layer would influence how much air would enter the duct. Permanence vs. repairable is also an issue. Some of the solutions here are repairable... but the opening is still an invitation to nesting critters. Will wait to hear more feedback before committing to this plan. The photo is for illustration only. Obviously I would trim and seal it before installing. Also going with synthetic mesh, rather than metal. Not as durable... but no corrosion issues.
FP28032017A0002E.jpg
 
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Consider maintenance (replacement) down the road. Peeling the duct off to replace a broken screen (some kid will poke at it) won't be fun.
 
So, just a quick thought. how about a magnet with the same diameter as that screen (Ron's duct with the round screen above) attached to one of those 'remove before flight' bright red lanyards. Seals the opening on the ground, super easy off/on and storage??
 
Not an 8, but I just formed a cup of aluminum screen over 1 1/2" ID PCV and the cup fit perfectly inside the scat tube, secured it with RTV (X2).

My RV-6 has similar. I used EPOXY to glue the screen cut round to fit in at the SCAT tube clamp location.
 
I went for a local flight one day and had water? coming out of the vent. I was a little puzzled as I keep the plane in a hanger. For a couple of seconds I suspected my hanger mate had washed my plane. As I reached forward to close the vent a very large slimy tree frog exited backwards along with a lot more water/slim.
Its funny how well these vents work to keep water out. I have flown in heavy rain and never had water come out of a open vent. Sometimes a little water if it has been outside in the rain but then it is still very little. A guess a nose wheel model would not even have that issue.
 
So, just a quick thought. how about a magnet with the same diameter as that screen (Ron's duct with the round screen above) attached to one of those 'remove before flight' bright red lanyards. Seals the opening on the ground, super easy off/on and storage??

Last I checked, magnets don't work so well on aluminum and plastic.
 
Highly recommend. Hit a swarm of honeybees one day in a 172 just as the front wheel left the ground. My 4 and 8 year olds in the back seat began screaming at the top of their lungs as about 15 bees were suddenly flying/crawling on them as the air vents were pointed at them to keep them cool. A real test of your concentration. I put screen door screen over the circular end of the NACA inlets prior to sliding the SCAT on . works great and is difficult to see from the outside. Minus one reason for potential chaos.
 
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