Van's Air Force
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Cowl Fabrication
- Thread starter BruceMe
- Start date
smokyray
Well Known Member
Old vinylester or new pre-peg? If it's a new one, here is a link to an RV4 facelift project with a new cowl:
http://www.firebirdaviation.com/FA1_content/Rbrthull_e.pdf
http://www.firebirdaviation.com/FA1_content/Rbrth%20Full_e.pdf
If it's an old one, my gel coat cracked under the paint after a few hundred hours on the upper cowl from the latent heat after shutdown. When I refinished it I stripped it down below the gelcoat, used vari prime and epoxy filler and PPG DGHS with good results so far. There are some very good pin hole filler primers out there. Glass in the air dams under the upper cowl intakes if you haven't, they help. One cool thing I thought of after mine was done was to lay up a sheet of carbon fiber underneath the upper cowl above the engine for extra strength. Make sure your oil door is big enough to get your hand through. Also make sure the lower cowl fits over the exhaust pipes where they exit. I trimmed 3 inches off the lower lip for my Vetterman 4 pipe. Some people have glassed in fairings over the pipes...
I used rolled hinge material throughout, a good call if you haven't already. I also ended up using DZUS fasteners on the rear upper cowling where it joins the fuselage in front of the avionics panel. The hinge kept breaking there on mine. Other than that, sand, fill, sand fill. When you get tired of that just paint it and go fly!
RR
http://www.firebirdaviation.com/FA1_content/Rbrthull_e.pdf
http://www.firebirdaviation.com/FA1_content/Rbrth%20Full_e.pdf
If it's an old one, my gel coat cracked under the paint after a few hundred hours on the upper cowl from the latent heat after shutdown. When I refinished it I stripped it down below the gelcoat, used vari prime and epoxy filler and PPG DGHS with good results so far. There are some very good pin hole filler primers out there. Glass in the air dams under the upper cowl intakes if you haven't, they help. One cool thing I thought of after mine was done was to lay up a sheet of carbon fiber underneath the upper cowl above the engine for extra strength. Make sure your oil door is big enough to get your hand through. Also make sure the lower cowl fits over the exhaust pipes where they exit. I trimmed 3 inches off the lower lip for my Vetterman 4 pipe. Some people have glassed in fairings over the pipes...
I used rolled hinge material throughout, a good call if you haven't already. I also ended up using DZUS fasteners on the rear upper cowling where it joins the fuselage in front of the avionics panel. The hinge kept breaking there on mine. Other than that, sand, fill, sand fill. When you get tired of that just paint it and go fly!
RR
BruceMe
Well Known Member
I've got the old vynel ester. I may go with a holy cowl some time later on.
1 - Did you scratch up the gelcoat well before painting over it?
2 - I will do the air-damns.
3 - Has anyone installed a exit air lip like on the newer RV models? Any improvements from that?
-Bruce
1 - Did you scratch up the gelcoat well before painting over it?
2 - I will do the air-damns.
3 - Has anyone installed a exit air lip like on the newer RV models? Any improvements from that?
-Bruce
Steve Sampson
Well Known Member
Smokey - can you expand on a couple of points.
1. Is 'Rolled hinge' what VANS supply or is this stronger?
2. Can yo uexplain what yo umean by " glassed in fairings over the pipes..."
Thanks, Steve.
#4478
UK
1. Is 'Rolled hinge' what VANS supply or is this stronger?
2. Can yo uexplain what yo umean by " glassed in fairings over the pipes..."
Thanks, Steve.
#4478
UK
smokyray
Well Known Member
Steve,
I'm not sure what Van supplies now for hinge material, but rolled hinge has no separation where the actual small hole is formed. In other words, the hole where the wire slides through is solid wall throughout the circumference of the hole. The old hinge material had a separation gap there and yes, that's where they broke.
The exhaust fairings I spoke of were seen on several RV-4's over the years. Where I cut back the lower cowl lip to allow the pipes to exit freely, several "glass masters" made exit fairings similar to the fairings where the rudder cables exit, except large enough to cover an exhaust pipe. These are glassed onto the lower cowling and subsequent notch cut into the lower cowl underneath them. What this does is fair in the exhaust pipes into the slipstream, maybe good for a half a knot or so. Being a fiberglass cripple, my zip saw made the modification to the lower cowl lip in 30 seconds.
As far as the gel coat prep, originally, I 500/1000 grit sanded the gelcoat vinylester cowl, tips and wheelpants, primed with Kry-lon and painted with sillver/red Dupont Centauri Acrylic enamel. I flew it polished with painted fiberglass for 3 years (picture still on Van's website in "RV4 section") After a FBO guy in KS stated: "paint or polish, make a decsion"...ow. I decided to paint. Big Job! Needless to say here is a very quick and dirty: I Etched, alodined, epoxy primed (no self etching primers due to high corrosion area I live) The interior structure was primed with Zinc Chromate rattle cans. Overall: PPG paints rule! I used DGHS polyurethane and it still shines after 8 years.
Good Luck!
RR
I'm not sure what Van supplies now for hinge material, but rolled hinge has no separation where the actual small hole is formed. In other words, the hole where the wire slides through is solid wall throughout the circumference of the hole. The old hinge material had a separation gap there and yes, that's where they broke.
The exhaust fairings I spoke of were seen on several RV-4's over the years. Where I cut back the lower cowl lip to allow the pipes to exit freely, several "glass masters" made exit fairings similar to the fairings where the rudder cables exit, except large enough to cover an exhaust pipe. These are glassed onto the lower cowling and subsequent notch cut into the lower cowl underneath them. What this does is fair in the exhaust pipes into the slipstream, maybe good for a half a knot or so. Being a fiberglass cripple, my zip saw made the modification to the lower cowl lip in 30 seconds.
As far as the gel coat prep, originally, I 500/1000 grit sanded the gelcoat vinylester cowl, tips and wheelpants, primed with Kry-lon and painted with sillver/red Dupont Centauri Acrylic enamel. I flew it polished with painted fiberglass for 3 years (picture still on Van's website in "RV4 section") After a FBO guy in KS stated: "paint or polish, make a decsion"...ow. I decided to paint. Big Job! Needless to say here is a very quick and dirty: I Etched, alodined, epoxy primed (no self etching primers due to high corrosion area I live) The interior structure was primed with Zinc Chromate rattle cans. Overall: PPG paints rule! I used DGHS polyurethane and it still shines after 8 years.
Good Luck!
RR
