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Fiberglass emp fairing plan of attack

PaulvS

Well Known Member
The fibreglass intersection fairing F-694B for the empennage on my -6A project does not appear to fit at all well, at least initially, and the gelcoat is rough. There are old posts on this problematic part and what other builders previously did but unfortunately many of the pictures have become lost.

I'm wondering what is the best plan of attack and whether to buy a new and hopefully better F-694B-1 fairing from Vans, or try to fix the existing part, or to make a new part from scratch?

I haven't done any fiberglass work for a while (built a sailing dinghy in my teens) and assume that fixing the current part would mean removing the gel coat and then cutting it up some and making various lap joint extensions around the edges before smoothing with micro. This could well be as much work as making a new part, I guess.

I would like it to end up looking like the fairing in this thread:
https://vansairforce.net/community/showthread.php?t=22931

Thanks for any suggestions.

Paul
 

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Hi Paul,
Before cutting it up, I would tape it down as best as you could and use a heat gun to get the fibreglass to “relax” and take up the new shape. I did this with a few 7 parts, including the empennage fairing. Any gaps I had along the edges, I taped the aluminium surfaces, clecod the fairing on and filled with flox, then sanded in a new edge until I was happy.
End result was not as good as Dan’s masterpieces, but good enough for me.
Good luck with it.
 
Or

Or you can apply clear packing tape to the empennage where the fairing fits, then apply epoxy/flox/cabo to the fairing flanges, and install the fairing. When the epoxy had cured, remove the fairing and sand edges to shape. A perfect fit will be the result…
 
This is what I did to fit the empenage fiberglass fairing.

For the leading edge of the horizontal stabilizer, I laid down a few layers of fiberglass to fill the gap. I bonded the extra layer to the existing fairing and trim to fit.

In some sections between the screws, you see some billowing because of the compound curve as the fairing wraps around the vertical and horizontal surfaces. In this case, use a hack saw or something with a similar kerf thickness, make slit cut into the fiberglass. This should remove the billowing effect as the material fills into the empty space of the kerf. Then cover the kerf from the bottom with fiberglass and smooth the outer surface with micro.
 

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Do what Dan did....you will be happy.

I did it........let the front hook under the leading edge of the HS.
Only screws holding it on are 4 screws in the rear, 2 each side.
Very clean looking.
Lots of work......very messy either way...good luck.
 
Paul, that part is made with the mold on the outer surface, but it is the inner surface that controls the fit. Mine fit badly too (circa 2003 part) and before making mods, I sanded all the inner contact areas so there were no ripples, runs, extra thickness etc as it is a layup. That solved 90% of the issues, and then split some places to shrink it with a trough and lap patch on the outside. I taped the area and used some micro to fill some gaps and sanded exterior (gel coat) to restore thickness.

You might talk to Vans, it seems the later parts with gray gelcoat seemed to fit pretty well. I can't address availability and current sourcing.

I did use heat to get some other parts to fit better, but not this one. Heat rarely worked for me. YMMV
 
I think you want to trial test it using clecos as I have done first before declaring it unworkable. You can always trim the excess and fill in the void with fiberglass parts that are non-structural. It is not one and done like metal. It took a few weeks for this part to fit on my RV8 but I wasn't as concerned working with fiberglass as some. Give it a try. You will be surprise how well it will come out in the end.
 
I have an RV8 with a Showplanes Fastback and the Van's fairing didn't work at all with the modified rear deck. I ended up destroying it trying to cut it to fit so I hit the internet and came across this wonderful video from Stu's Aircraft Factory of a carbon fibre empennage fairing from scratch. Here it is https://www.youtube.com/watch?v=T3486oE0ge8 I watched it a few times and emboldened by how easy Stu made it look I got some carbon fibre and proceeded to lay it up. I ended up throwing the first one away but I learned a great deal and the second was very satisfactory. Very stiff, held on by two screws. As mentioned in a previous post, it's really important to get the underlying shape correct. Correct in the sense that it's the shape you want. I used pouring foam as it has more consistency. I used the same technique for my upper intersection fairings. I was very happy with the result overall but it was a lot of work. The second one was much better with half the time.
 

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Mine was terrible (early 2000 part) and made worse by sitting in an odd position for a decade. As Bill said, you need to clean up the inside surface, then go to town with a heat gun. Use the heat to get the general shape you want then force it into position and get the holes drilled and clecos in. Then keep using heat to get it into its plastic state and it should take a set in the right form. Sometimes it best to get a couple clecos in and heat before the next two, etc.

I did have to use flox in several areas for an eye pleasing fit. Where mine wrapped around the leading edge was terrible, so once the heat forming was done, I loaded this up with flox and cleco'ed it in place. Then come back and make the outside look good with your old friend the sandpaper. Also practice with the heat gun on some scrap. Not a lot of room between hot enough and burning the material.

Larry
 
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Paul, choosing an attack plan here is arguably a case of desired result...physical configuration, not quality.

If you're going with rows of screws along the edges and metal close-outs under the HS per plans, heat, some back side reinforcement, and liquid shim can net a nice result. The screw rows pull it tight; your primary goal is to fit and reinforce so it doesn't pillow up between screws.

If you like the minimal screws approach, it has to fit from the start, and needs to be a little thicker/stiffer. It's also easier to flow it into a glass fairing under the HS. You get choice of materials. If the 6 fairing is old, it may be polyester/glass. An epoxy/glass or epoxy/carbon fairing can be stronger and/or stiffer.

Not much time difference either way, and a good craftsman can make either work.
 
I have lots of photos of what I had to do with my fairing here.

Heat helps, but in some areas just cut off the non-fitting surfaces, or build up with some additional layers or flox/micro.

Mine fits nice and tight now, and is only held on with about a dozen screws. I personally think that you really don't need all off the screws that Van's calls out along the VS and HS skins.
 
I have an RV8 with a Showplanes Fastback and the Van's fairing didn't work at all with the modified rear deck. I ended up destroying it trying to cut it to fit so I hit the internet and came across this wonderful video from Stu's Aircraft Factory of a carbon fibre empennage fairing from scratch. Here it is https://www.youtube.com/watch?v=T3486oE0ge8

The fairings do require quite a bit of massaging to get to fit nice. The keys are a nice firm base unlaying structure that will not move. Rigid (which is why I like carbon fibre) if you don't want pillowing between fasteners. The existing fairing may be a nice start with the desired contour shape but I found in most cases I had to cut off the edges and make my own.
 
Emp fairing

Paul, choosing an attack plan here is arguably a case of desired result...physical configuration, not quality.

If you're going with rows of screws along the edges and metal close-outs under the HS per plans, heat, some back side reinforcement, and liquid shim can net a nice result. The screw rows pull it tight; your primary goal is to fit and reinforce so it doesn't pillow up between screws.

If you like the minimal screws approach, it has to fit from the start, and needs to be a little thicker/stiffer. It's also easier to flow it into a glass fairing under the HS. You get choice of materials. If the 6 fairing is old, it may be polyester/glass. An epoxy/glass or epoxy/carbon fairing can be stronger and/or stiffer.

Not much time difference either way, and a good craftsman can make either work.

Dan
I read your Tips more times than I can count. I see your Emp Fairing goes down and under the HS a little.
Is there anything else under the HS?
Where are the few screws you used?
 
Cut it up, glass it, redo as needed for a tight, long term fit. (like others have said) Its a right of passage for an RV build.
 
Call me old-school but I'm going to weigh in here on, modify as needed.
The "heat it up" trick may well work - if so then you're golden. In my case it wasn't enough so I cut and laid up new to fit around the HS leading edges, and cut and re-layup the top edge of the fairing along the VS. It's just sanding and fitting fiberglass work, part of the build.
 
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Dan
I read your Tips more times than I can count. I see your Emp Fairing goes down and under the HS a little.
Is there anything else under the HS?
Where are the few screws you used?

Upper fairing has (each side) one at the front and two at the rear. Doesn't actually need screws at the front because it hooks around the leading edge of the HS.

The fairing under the HS is just 4 plies of tape. Use tape somewhat wider than the finished part...cure it and then trim the width. I don't often recommend glass tape, as novices tend to use it everywhere, with terrible results. However, here it is the right choice.
.
 

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Emp Fairing

Upper fairing has (each side) one at the front and two at the rear. Doesn't actually need screws at the front because it hooks around the leading edge of the HS.

The fairing under the HS is just 4 plies of tape. Use tape somewhat wider than the finished part...cure it and then trim the width. I don't often recommend glass tape, as novices tend to use it everywhere, with terrible results. However, here it is the right choice.
.

Thanks
Exactly what I needed.
I use the rolls of fiberglass 1", 2", 3" & 4" when it fits the bill, but I trim the edge off.
 
Thanks all for the guidance and info, which gives me a clearer understanding of the best plan of attack.

I spent some more time trying to get the existing fairing to fit better, including heating it with a gun and removing high spots, but haven't had much joy, the gaps are just too big. It probably doesn't help either that it has been sitting on a shelf in the shop for 20 years.

After looking at some of the good examples that people posted and watching Stu's youtube videos I am going to try moulding a new fairing that will curve around the leading edge and be attached with a minimal number of screws.

There seems to be a few options for building up the surface to mould over and I'm going to try first with the old fairing by cutting it down to fit inside the gap between the HS and VS and use modelling clay or tape to smooth around the edges. If that doesn't work out then I will try spray foam as per Stu's video.

The last resort if the above fails will be to order a new fairing as some have suggested, although it looks like there would be some work involved with that too.

At least this should be a good learning experience in preparation for the other fibreglass work that is ahead.
 
I used clay and carbon fibre which is very stiff so minimal screws required. I just watched Stu’s video and my method was very similar. One thing that stands out is that he was using the west system epoxy pumps. As Dan has pointed out, they can be very inaccurate. I got a small digital scale from Horror Fraught which I tested and found to have good repeatability. I used it to check the epoxy pumps and found them to be considerably off, like 15%. So I ditched the pumps and I use the scales only.
 
As follows

Mine turned out pretty good. I started with a Fairing Etc fairing. (My first 7 was used for the prototype for the fairing). I'll admit I like fiberglass work and find it oddly satisfying. And, the end result.

Taped off the vertical fin above and below the contact point. Same with the horizontal stab and turtle deck.

Used West Systems epoxy with micro fill mixed in. Mixed it thick like peanut butter.

Smear it liberally at the contact points.

Smoosh the fairing down and duct tape in place. Let cure for 12 plus hours.

Remove duct tape and check fit. Lather, rinse repeat as necessary.

Sand to proper tapers. When happy with the fit I laid a 2 ounce glass trip over the edges to further bond the epoxy mix with the fairing.

I only used 5 fasteners per side for the main fairing. I bonded Tinnerman washers into the glass so the fasteners would be fastening to metal and not glass. So, there is one under the front side, one on the horizontal in back, two on the back edge on the vertical fin top and bottom and 1 at the inspection plate. Minimal fasteners and the fit doesn't lend to any puckering.

Call me a little nuts but I miked the front edge so I had a consistent thickness around the turtle deck.

I'll see if I can post some pictures. Don't hesitate to shoot me an email with any questions. [email protected]
 
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This is what a Fairings-Etc tail fairing looks like. RV6 in this case. I’ve only done some minor trimming to get the shape I want, and glassed a little extra material on the part that grabs the HS leading edge. I wanted a little more purchase in that area. I’ve drilled 3 holes on each side where my fasteners will go. Before I install the nutplates for those fasteners, I’ll underlay fiberglass cloth and epoxy along the contact areas on the HS and VS where is stands a little proud. This will stiffen the somewhat flimsy edges and make it lie perfectly flat on those skins. Since the leading edge wrap on the fairing makes it difficult to remove the fairing because the aft end hits the elevator horn, I’ve cut that part off. I made a separate aluminum part that will take that cut off part’s place which has a riveted aluminum ‘clevis’ that the shortened aft fiberglass fairing just slips into snugly. Makes removal easy and secures that little tail nicely. Oh ya - the Fairings-Etc fairing also includes the fiberglass fairing for the under side of the HS. Mine is trimmed and ready to be bonded in place. I will use an epoxy structural adhesive and just drill a few small holes for clecoes to be used to hold it in place while the epoxy cures.

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Toss it

Paul,
You have the same fairing I got (early 6A kit). Frankly it is a piece of trash, like most of Van's early polyester parts. Yours looks better than mine did out of the box. After trying for two weeks of heating and shaping, heating and shaping, it still looked like a potato chip. You can heat and bend polyester fiberglass and after a couple of months it tries to resume its original shape. Only by sanding off the gel coat and applying epoxy glass will it stay.

As I see it you have two choices. 1) buy a good part from one of the aftermarket sellers and do some minor fitting, or 2) Read all the posts and study all the pictures that Dan H. put on this site showing how to make an empennage fairing. And make your own. I cut up the old fairing into pieces and trimmed them as needed to form the base for an "in place" mold. Add some foam pieces, some clay here and there, cover it with packing tape, and lay up a new fairing. You can do it. When you,re done it will fit and drop in place like a watchmaker putting together a Swiss watch.

My web site is gone but I can send you some pictures if and when you decide to become proficient at fiberglass. A very well fitting empennage fairing showcases your plane.
Dave A
 
Design consideration

Beware that if you make a beautiful wrap around the leading edge that the back leg that drops down around the torque tube has to have enough gap to push the fairing forward for removal. I did this and later removed the large wrap under in favor of not making the aft section two piece (really three). I realized that my removal was going to be a problem after paint. YMMV

Making a new fiberglass intersection fairing from HS to Fuse is highly recommended. You can mate it to the upper fairing and makes a much easier transition than stock Vans.
 
Progress update

Here is a work-in-progress update. The info and videos that people here posted gave me the confidence to attempt molding a new fairing, so thank you. Most of the detail of what I did is in the attached pics.

The first mold was made from laminated timber and it was a failure because I did not understand the compound shape of the rear tail cone and couldn't get the form right. I also tried foam but did not have any adhesive that would adequately glue styrofoam.

The next mold is made from sheet aluminum and is better.

I've applied around 4 layers of overlapped BID cloth using West Systems epoxy. Some more cloth is still required around the edges and at the base of the vertical stabilizer. I used polyester fabric from the dressmaking shop as peel ply. I takes a bit of effort to rip it off, I'm not sure if that is normal, I've got some proper peel ply and crowsfoot fiberglass cloth coming in the mail. So far, so good, I'm looking forward to finally removing and then trimming the part.

I thought this would be an easy part to practice fibreglass because it is small. It was actually a bit more difficult than I thought, due to all the compound curves and corners. The fiberglassing process was messy and chaotic!
 

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I've had some difficulty with my FG work too. It matters how cloth is oriented when it is laid out on a complex surface with compound curves. It will form nicely if the bi-directional twill cloth is cut on a 45 degree bias,

I hate wasting cloth, if you cut it off the roll on a 90 degree like I do with wrapping paper at christmas time the cloth wont want to form nicely around those curves. So, I just sacrifice a triangle then cut my strips off the roll on that bias 45 angle.
 
Fiberglass

Here is a work-in-progress update. The info and videos that people here posted gave me the confidence to attempt molding a new fairing, so thank you. Most of the detail of what I did is in the attached pics.

The first mold was made from laminated timber and it was a failure because I did not understand the compound shape of the rear tail cone and couldn't get the form right. I also tried foam but did not have any adhesive that would adequately glue styrofoam.

The next mold is made from sheet aluminum and is better.

I've applied around 4 layers of overlapped BID cloth using West Systems epoxy. Some more cloth is still required around the edges and at the base of the vertical stabilizer. I used polyester fabric from the dressmaking shop as peel ply. I takes a bit of effort to rip it off, I'm not sure if that is normal, I've got some proper peel ply and crowsfoot fiberglass cloth coming in the mail. So far, so good, I'm looking forward to finally removing and then trimming the part.

I thought this would be an easy part to practice fibreglass because it is small. It was actually a bit more difficult than I thought, due to all the compound curves and corners. The fiberglassing process was messy and chaotic!

You're pretty far along but if I may...
Go to Home Depot and buy a sheet of pink construction foam. I have a friend in construction who saves me the scraps.
Buy a can of 3M 77 spray contact cement.
Cut and glue pieces then carve and sand to shape.
Boards or PVC pipes wrapped with 40-80 grit gind through it like a hot knife through butter. Takes very little time.
Cover everything with heavy packing tape.
Wax the tape.
Lay up the fiberglass.
If the weave won't conform, use strips overlapping edges and ends. It's not a wing spar. Four or five layers thick will be plenty strong.
The fairing is a "one and done" part so no need for a reusable mold.
Sorry, just my humble opinion.
 
Update

Thanks Brooks and Larry.

The part came off the mold with a little effort overall and the areas that were coated with furniture wax came off easily. Some parts of the tailcone I covered with clear packaging tape for protection and this worked also, but left a sticky residue that was difficult to clean off.

The sheet metal mold itself worked very well and the fairing fits like a glove, much better than the old Vans kit polyester part. The surface is a bit uneven though because I lost track of the overlapping strips of BID cloth that were needed to cover the complex shape.

I have set up the mold again to make a second part using the crowsfoot weave fabric. I also got some proper peel ply that is finer than the polyester suit fabric.

I found that the tailcone intersection area is tricky to carve from foam block or wood because the aft 4 inches is flattish surfaces that intersect at 90 degrees and then forward of that the mold needs to take the form of a cone that meets up with the tailcone skins ahead of the VS and HS. The attached pic shows what this intersection looks like with the sheet metal and duct insulation tape mold.
 

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Fairing

That's very nice. The overlaps are easily fixed. I use some flox under a fiberglass layer. Apply the flox, lay down the fiberglass then peel ply. Use a credit card to squeegee the flox underneath. Low spot gets filled and the outer layer is flat.
 
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