Chuck and Ryan's Build Tips

[PBY Catalina]

How is your EXcoming along? Ready for paint??

Almost !

[ceslaw]

Extra Fabric Stuff. A few little fabric additions were added to the fuselage based on experience gained from a prior build.

1. A fabric oval was cut from a tape and applied over the end of the bottom stringer aft end point. There is a noticeable bump which may need a bit of extra protection.

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2. A second round access port was added on the bottom aft of the extended baggage opposite the access port for the fuel drain. There is a 90-degree fuel line connection, ELT antenna, and fuel drain in this area and someday that additional access point may be useful. It will not be cut open unless and until it is needed.

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3. Two-inch circles were cut from tape and placed in the area where the brake lines will emerge. We will be using stainless steel lines and thought a bit of reinforcement was warranted.

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4. A piece of fabric was used to cover the metal on the forward side of the door opening. The reason for this addition is to provide a surface that is the same material as the aft and bottom sides of the door opening so the paint will be uniform.

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5. An access port was added on the right side below the elevator corresponding exactly to the access port on the left side. There is a lot of stuff going in inside that part of the Cub and being able to access it from both sides can make life easier. It will not be cut open unless and until the need arises.

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6. In a post last November a chase was described which provides a means of extending a cable or wire from the forward to aft end around the extended baggage after the aircraft is completed. A two-inch circle cut from a tape was added on the left side, bottom aft corner. This will provide reinforcement for the hole if a cable it added for a lockable tail wheel.

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[PBY Catalina]

Extra Fabric Stuff. A few little fabric additions were added to the fuselage based on experience gained from a prior build. ...

Thank you DAN,

Useful to me, I’m at the same stage. !

[ceslaw]

Bubbles Revisited. Solidly adhering the fabric to the concave surface under the ailerons can be a challenge. Long ago a post described a method for sealing larger bubbles:

https://forum.cubcrafters.com/showth...ll=1#post13544

On the current plane there were no large bubbles, but a couple of small ones, a half inch or smaller, popped up. Fixing little bubbles is easier than big ones. The repair was done after they emerged following the application of the Poly Spray. An Exacto knife was used to open the bubble after which a dilute mixture of Poly Brush was injected with a cheap syringe. A bit of touch up with Poly Spray and the bubble was gone and the incision nearly invisible.

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[ceslaw]

Spray Materials Mixing.

Keeping track of the mixing of the various products can be a hassle with repeated references to the Poly Fiber book or some website. A little chart was put together and stapled to the wall with a photo shopped picture for inspiration of what the cub should eventually look like.

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Mixing the Aerothane was a bit more complicated so a diagram with illustrations was made which even a seasoned citizen can understand at a glance.

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If anyone is interested, here is a legible version:

Spraying, General
- 30 – 35 PSI at gun. 40 PSI per Poly Fiber manual
- Air flow adjustment on gun set for max.
- External gauge adjustment set at max
- Hold gun 8” from surface, 50% overlap, move rapidly to avoid runs.
- Wipe lightly with C-2210 Paint Cleaning Solvent between coats of material

Poly Brush
- Strain with 60 x 48
- Thin 3 parts to 1 part reducer
- Four coats overall
- Extra coat on leading edge of wing
- 2.0 tip

Poly spray
- Strain with 60 x 48
- Thin 4 parts to 1 part reducer
- Four coats, extra on top surfaces
- 2.0 tip

Paint, Poly Tone (on fabric)
- Strain with 60 x 48
- Spray when under 70 degrees for best finish.
- Thin 4 parts to 1 part reducer
- Start painting on the edges of wing and tail feathers first to avoid over spray on flat surfaces
- Four coats: tack coat, at least two hours apart, remaining medium coats.
- 1.4 tip

EP-420 Primier
- 2 parts EP-420 primer with 1 part EP-430 catalyst
- Allow 30 minutes induction time before thinning
- Thin with E-500 Epoxy Reducer, 2 parts Catalyzed primer to 1 part reducer.
- Ratio: 2 Primer: 1 Catalys: 1 ½ Reducer
- Light tack coat, followed by two medium coats at 10 – 15-minute intervals.
- 1.4 tip

Aerothane (on metal and carbon fiber)
- Strain with 60 x 48
- 3 parts Aerothane with one part U-865 Catalyst.
- Allow 20 minutes induction time before thinning
- Thin 3 parts catalyzed Aerothane to 1 part UE-820 reducer
- Ratio: 3 Aerothane: 1 catalyst: 1 1/3 Reducer
- 1.4 tip
- Flattener, four parts paint with one part flattener (8 ounces per quart of paint). Then catalyze and thin normally

[ceslaw]

ELT Antenna Check. Last October a post described adding a simple radial 23 ¼” in length to the base of the ELT antenna to correct the mismatch caused by the mounting bracket design. At that time a near perfect SWR was confirmed by this solution.

https://forum.cubcrafters.com/showth...ll=1#post27698

What was not known was what affect, if any, covering and application of the Poly Spray, with its aluminum powder for UV protection would have on this solution. So, with the multiple coats of Poly Brush, Poly Spray, and Poly Tone we checked it again.The SWR remains virtually perfect. The fabric and application of the Poly system coatings did not affect it at all.

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The addition of this single radial would seem to be the most effective and simplest solution to the mismatch issue.

[Andy]

The addition of this single radial would seem to be the most effective and simplest solution to the mismatch issue.

It looks like a good fix for 121.5 MHz but what is the match at 406 MHz? It may be degraded and it may not be. The only way to know is to measure it.

Can you borrow an analyzer that covers 406 MHz?

[ceslaw]

Yea, I wish there were someone nearby here in rural southern Illinois that had a tuner that went up to 406 MHz, but alas, no such luck.

My impression / assumption is that the antenna is internally balanced on the 406 MHz band, although I have not found any specs confirming that. CC tested the system and it passed the 406 MHz test installed per their specs, further leading me to believe it is internally balanced and/or the mounting system they use does not adversely function at that frequency.

Regardless, I also added a radial for the 406 MHz band just to make sure we were balanced if the foregoing impression / assumption is flawed.

So much thought and analysis for something that will, hopefully, never be used.

[ceslaw]

The Perfect Hole. We decided to upgrade to stainless steel covered brake lines and larger calipers. The stainless-steel line is a bit more abrasive to the fabric than plastic, so steps were taken to protect the fabric.

In a prior post we noted the addition of a 2” round grommet where the brake line passed through the fabric. With the plane painted, it was time to add the hole to pass the line.

https://forum.cubcrafters.com/showth...ll=1#post28424

Masking tape was applied to a 5/16” washer and using an XActo knife a hole cut in the tape. It was then stuck on the plane at the point where the brake line exits the fabric. Using the washer as a guide a perfect 5/16” hole was cut with a fresh XActo knife. We now had a perfect hole.

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After the brake line was passed through the perfect hole, a six-inch length of ¼” protective covering was placed, two inches above and four inches below the fabric. After the protective covering was cut to length a soldering iron was used to slightly melt the ends to prevent fraying.

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[ceslaw]

Brake Line Covering. The placement of the protective covering on the stainless brake lines was previously described. Now it is time to clean up the ends of the protective wrap (Part#05-12893) to prevent fraying and hold them in place.

Half inch heat shrink was ordered from Aircraft Spruce, both adhesive lined (Part #11-11540) and plain (Part #11-01300). The adhesive lined shrink was cut in 1 ½” lengths and applied at the end points of the protective covering, starting at the top. A silver Sharpe was used to mark the end points so it would be centered. This heat shrink material is heavy and does a nice job. The adhesive holds the protective covering in place tightly

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The non-adhesive heat shrink was cut in 1 ¼” lengths. Before passing the brake line through the three supports the non-adhesive heat shrink was partially shrunk so it could be squeezed in place. After the brake line was secured to the brake caliper the three partially shrunk sections were carefully centered on the supports and shrunk with the heat gun.

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