yet another windshield fairing question

[Desert Rat]

hey guys- I'm laying up a one piece windscreen fairing to be bonded on with the Sika process.

As of right now, I've got it about .10" thick at the hoop that goes across the top. This is kinda what I was shooting for since that area is prone to people grabbing it and needs to be a bit more robust.

The sides and forward perimeter that wrap around the windshield base are about .070" at the edges, obviously quite a bit thicker toward the middle of the radius.

Since the windshield is bonded in with Sika, theres nothing really structural about this area, but I don't want it so thin that it flexes and the paint cracks.

What say you? Is .070 thick enough or should I go with another ply or two?

 

[PaulvS]

I think I would make it a bit thicker because the aft edge is vulnerable to knocks and needs to be strong enough to take it. Van's recommends 0.08 in the construction manual. A buddy cracked a piece out of the corner right above the track on his.

I just finished laying up the aft skirt with epoxy. Initially it was .060 thick and that would've been OK however I put on a couple more plies to 0.080 and it feels more robust (and is heavier, that's the downside).

What's the rationale for attaching with Sikaflex vs epoxy like G/flex? Sika needs to be a certain minimum thickness, so that is going to add bulk to the fairing?

 

[Desert Rat]

I think I would make it a bit thicker because the aft edge is vulnerable to knocks and needs to be strong enough to take it. Van's recommends 0.08 in the construction manual. A buddy cracked a piece out of the corner right above the track on his.

I just finished laying up the aft skirt with epoxy. Initially it was .060 thick and that would've been OK however I put on a couple more plies to 0.080 and it feels more robust (and is heavier, that's the downside).

What's the rationale for attaching with Sikaflex vs epoxy like G/flex? Sika needs to be a certain minimum thickness, so that is going to add bulk to the fairing?

Thanks Paul. The aft edge is already about .10" for the reason you identified. Well, that and I have no confidence that people won't grab it getting in and out, even if I tell them not too.

As far as why Sikaflex? I guess no reason really. I used it to bond the canopy to the frame and later the canopy skirts and windscreen and it worked well in that application. Due to the way I bridged the gaps where the windscreen meets the fuselage with packing tape prior to laying up the fiberglass there's about a 1/16" cavity in there already to allow for a nice thick bead toward the center radius of the fairing. I figure with that, it can fair out to almost nothing at the edges, then a nice fay seal at he edge to seal it all up.

Seems like there might be some small advantage to sticking with one adhesive for everything so that everything has the same expansion coefficient, but I might be wrong about that.

 

[PaulvS]

Ah OK maybe I misunderstood about the thickness, it sounded like .010 at the top of the roll bar where somebody might (will) grab it but only .070 lower down at the base of the windscreen. If however that aft edge is .010 all the way around from longeron to longeron I think it will be strong.

 

[Desert Rat]

yeah, sorry, I probably didn't explain it very well. The entire aft "hoop" is about .10" The wrap around part that runs fwd from the corners and covers up the intersection between the windshield base and the upper fuselage fwd skin is currently about .070".

 

[krhea]

fairing thickness

This is going to be my best estimate but my original fairing was 8 or 9 layers of 9 oz 2" wide fiberglass strips. I actually bent that by grabbing it or sitting on it right at the center, then when doing the paint i added a few more layers and don't touch it.

I think .100 is too light but your welcome to look at mine. Or i'll take a photo and send or best yet. RViators meeting my hanger KEGT 900am 18th Nov.

Keith Rhea
RV7
2023 donation