Fairings

[Bcone1381]

I’ve been fabricating fairings over the past few months. I’m on the home stretch. I just made these H-stab fairings. Having a foot long sample every type of rubber channel Aircraft Spruce has available came in handy. Next time I will put one more nut plate close to the h-stab trading edge to better secure the aft ends of these fairings.

Additionally, the fabric contacts the outboard edge of the fairing and so it needs to be protected.

 

[Bcone1381]

Here are some shots of my wing root fairing. Spinningwrench and I discussed this and I followed his lead. EAA SPort Air Workshop called Composites for RV's is a good class to take that teaches a lot of these techniques.

The leading edge fairing is made of 3 layers of 8 oz bi-directional fiberglass cloth and one layer of Carbon Fiber. The top fairing is just fiberglass. Making the top wing root fairing of glass was more effort I think than making it of aluminum.

Fabricating the raw form is fun and easy and pretty quick. Getting the raw part finished is more work. I like coating the raw part with epoxy, then frosting it with epoxy-microballoon mix. My favorite mix has about 80% of the weight as dry epoxy-micro. I get a better finish with fewer air pockets with that mix. It still sands really nice. So I frost the part with the micro, let it cure, then sand off almost all of the cured microballoon frosting, then fix all imperfections. Sometimes I use Bondo to fix small imperfections becuase of its fast cure time.

I like to leave the part in place on the aircraft as I finish the raw surface. I get better results. One of my gear leg fairings warped. I did the finish work off the airframe on the workbench and I think bondo or microballoons might shrink a bit and caused some warpage.

I like Aerpoxy epoxy products, but also use West Systems. Microballoons and Flocked Cotten are two addatives we add to epoxy to do this stuff. Epoxy is expensive, but the addatives are very cheap and they open up a world of possibilities for little monitary value. Learn to use them....experiment. I can make small batches of Aeropoxy so I have less waist. But West (uses a pump) is faster...saves time.

 

[Redneckmech]

Beautiful work, those turned out really nice!

 

[rodsmith]

I was amazed at how much time went into making the fairings. I thought the stabilizer fairings would be very simple and quick. Turns out it was a major pain to match the countour of the fabric and other cover plates. If doing it over I would have started with poster board templates. Here is a picture of all the completed fairings.

 

[Bcone1381]

Ha ha! Rod, I know what you mean. I think My first stabilizer fairing was satisfactory after four unsatisfactory attempts! I discovered the fabric has a slight bow in it adjacent to the stabilizer…that was version 2.

 

[Bissetg]

That’s looking really good Brooks, you might have a market for them!

 

[RickG]

Great work Brooks make some molds and start selling parts so the rest of us don't have to go through what you just had to.. (please)

 

[Bcone1381]

Great work Brooks make some molds and start selling parts so the rest of us don't have to go through what you just had to.. (please)

Thank you for the compliment.

ya know, this prompts a few thoughts. A component of building our aircraft build could be described as “Custom Hand Crafted.” All of our windshields get trimmed. Mine was trimmed 1/4” further than what is ideal. Darn! I used cardboard from Kellogg’s Raisin Bran Crunch and simple artist modelers clay to form the mold then taped it up with packaging tape prior to laying up the impregnated fiberglass.

So mine won’t fit anyone else’s. And if a builder trims the windshield correctly a cardboard template will fit nice and it can be used to form a fairing from aluminum in 25% of the time.

so Bearhawk building combines science and art and skill and knowledge. I am taking too long to build. But I enjoy it. I like the results I’m getting.

 

[Nev]

Very nice work.

 

[arborite]

Beautiful as is all of your work Brooks. stop setting the bar so high;-)

one question though - are the horizontal stabilizer to fuselage fairings required? all of my old Pipers just left the gap exposed. i didn’t realize i need to make fairings back there. of course the Patrol is much higher performance than my old Pipers or my LSA project, so maybe different needs? i guess with the stationary tail (as opposed to the jack screw setup in the pipers) it would clean thing s up nicely back there.

 

[Bcone1381]

one question though - are the horizontal stabilizer to fuselage fairings required? all of my old Pipers just left the gap exposed. i didn’t realize i need to make fairings back there. of course the Patrol is much higher performance than my old Pipers or my LSA project, so maybe different needs? i guess with the stationary tail (as opposed to the jack screw setup in the pipers) it would clean thing s up nicely back there.

The gap on my Patrol Kit was about an inch. I have no experience yet. But I suspect the benefit of the H-stab fairing is noticeable and beneficial Because I once flew a glider that did not have a .125" gap at the wing root sealed with tape. I bet I lost 20% performance in its glide ratio. I could also hear the air turbulence.

Also, I've not seen a flying Bearhawk without that fairing installed.

 

[spinningwrench]

Brooks your wing root fairings look familiar and great. I haven’t tackled the tail but intend to make them all composite. No two airplanes are the same especially regarding the windshield mount so I doubt a generic version of these would work for everyone.

 

[Bcone1381]

When using clay, I found the better practice is to apply too much clay then remove excess to get a desired shape. Applying and buildig up clay to match the desired shape is inferior.


This is what a piece looks like in raw un trimmed. I then frosted it with "Dry Micro" aka epoxy with microballoons mixed to a peanut butter texture. It cures then it gets sanded with 80 grit and 220 grit.


This is just popped off and is untrimmed.

This top shock strut fairing has a flaw, do you see it?

Now it's fixed.

 

[RickG]

Really nice work Brooks!!

 

[Pbruce]

Brooks, your root fairings look great. Did you also use modelling clay to mould your wing root fairings? Seems like it would be a lot of clay. Was there any tendency for it to sag due to being such a large mass? Is this the process?: tape to protect the margins, clay for shape, glass and carbon layers, then epoxy/micro to fill and final shape?

 

[rodsmith]

I wouldn't mix glass and carbon cloth. You could use carbon but it doesn't save much weight on parts that you aren't vacuum bagging.

 

[Pbruce]

I just like the extra stiffness. It seems to integrate well within layers of glass. And I have some on hand. Probably not necessary though, except where I’m extending the fairing in over the egg-sized hole at the wing root cutout. I’m going to apply a few layers of 4 oz cloth and carbon inside and out beyond the margin of the damage by about 3/4”.

Until now didn’t know about using clay. I always used foam in the past. But Bcone and Spin Wrench are turning out really nice fairings using clay. Looks like it’s the way to go for complex shapes.

 

[Bcone1381]

When it comes to bridging the wing root, I find myself resorting to simple materials and techniques, almost like a five-year-old. I use scissors, cardboard, and tape to get the job done.

I only encountered some issues with sagging when I used heavy clay on my top Wing Strut Fairings. To address this problem, I had to embed/hide aluminum angles to prevent further sagging. On the other hand, I used a minimal amount of clay on the wingroot fairing.

To bridge the gap between the wing and the windshield, I employed poster board and recycled cardboard from a Kellogg Raisin Bran box. Once the gap was adequately bridged, I covered the windshield with blue painter's tape, followed by a layer of clear, smooth 3M packaging tape. This packaging tape is the same kind I use for sealing boxes before shipping. Its slick surface allows for easy removal of epoxy-cloth layups. This tape can be waxed to achieve similar results. However, it's important to note that applying 3M packaging tape directly to paint may cause it to peel off. In the case of the wing root fairing, only a small amount of clay was used to create a smooth transition (fillet) where the cardboard meets the windshield.

Regarding the layups, Rod, I incorporated a layer of carbon to enhance stiffness. If I recall correctly, I used three layers of glass along with one layer of carbon. While I haven't encountered any issues with this approach, I could be mistaken, as I often am. I would appreciate it if you could share any concerns you may have about my layups, as I don't want others to receive incorrect information from my post.
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[rodsmith]

Somewhere I had heard it's not a good idea, but I don't remember why. I'm no expert on the subject, your reasoning for the carbon makes sense.

 

[BravoGolf]

Those are beautiful. Really nicely done.

 

[Pbruce]

Now that you mention it Rod, I remember that carbon is electrically reactive with aluminum. In view of that, I’ll make sure to keep any carbon cloth away from the margins of the fairings where they might touch the windshield top channel, aluminum-strip wing top fairing and the wing skins. Maybe any screw holes too. Any carbon will be sandwiched between layers of epoxy-glass so will be isolated on the inner and outer surfaces. Thanks for mentioning possible issues. Interestingly, my factory wing tips are 100% carbon/epoxy.

 

[Bcone1381]

This is what I ended up with for my lower wing strut faringing. Since the gear is hinged and articulates, I pulled the gear together with ratchet straps to simulate zero weight on the wheels when I fabricated everything. But geometery changes when the landing force spreads out the gear. I nice fix I saw on one bearhawk is a sliding strut faring that is spring that keeps it tight to the airframe. I am not a designer and tried then gave up. I took my faring over the band saw and cut the bottom off and riveted silicone baffle material. I like how if fills the gap, flexes, and avoids moving parts.

Here's what I came up with for the lower wing strut fairing. Since the gear is hinged and I want to build the fairings as though it was in flight, I used ratchet straps to pull the gear together prior fabricating these. I saw a clever solution on another Bearhawk aircraft where they used a sliding strut fairing with a spring mechanism to keep the fairing tight against the fuselage irregardless of the weight on wheels. As I'm not a good designer and found it challenging to mimic that and eventually gave up. Instead, I took my fairing to the band saw and cut off the bottom, then riveted silicone baffle material onto it. I like how it fills the gap, provides flexibility, and eliminates the need for moving parts.

 

[rodsmith]

Beautiful work Brooks.