Video - Intersection Fairings

[sjhurlbut]

Couple days ago there was a thread on intersection fairing and them getting beat up. Well I've experienced that before. Check out this video of how to make them from scratch (not that hard) and so they don't get beat up.

Hope you all have a great holiday season.

https://youtu.be/lgMvfysThlQ

[FLY6]

Steve, very well done, I find videos like this very informative. As I am not the builder of my plane, I enjoy construction videos such as this as I may someday have to rebuild my intersection fairings. This takes some of the mystery and fear out of tackling such tasks.
Thanks for taking the time to do the video

[DanH]

All the basics are there.

Do remember the Golden Rule of Forms and Molds....time spent creating a really accurate, well finished mold or form pays large dividends later...less sanding, less filler, and less weight. A lumpy form makes a lumpy part.

Using little strips of fiberglass tape for this layup is not a good idea. Tape has a thick selvage edge, a knit ridge sometimes twice as thick as the base tape. The selvage tends to form voids in stacked layers, not a problem if epoxy filled, but heavy. The selvage also locks the warp and fill fibers, so tape doesn't conform to compound curves very well....which is why it's being used in short bits in this example. Last, short tape lengths usually result in a layup with uneven thickness.

Much better to do the layup with a stack of pre-wetted cloth. Cut one ply as a pattern while taped to the airplane, then two or three more using the developed pattern.. Stack 'em, wet 'em out between 4 mil plastic, squeegee out the excess resin, peel one side, and wrap the form, using gloved hands to smooth it into place. 9oz plain weave is surprisingly conformable, and 8-harness satin is even more so.

BTW, the time to do an upper intersection fairing on a Grove gear is when the fuselage is upside down for gear alignment and mounting.

Here's an oil cooler duct. Not an intersection fairing, but illustrates the principles.

Pattern development, single ply of 8.9 oz 8-harness satin. The 8-harness weave allows the warp and fill fibers to slide around in relation to each other.
The wrap will conform better and better as the excess fabric is cut away:



One ply, dry wrapped, cut to pattern shape. The single overlap seam is under the neck:



Three plies, cut using the pattern, stacked and wetted, about to get a top plastic sheet followed by a roller to push all the excess epoxy to the perimeter:



All three plies wrapped and smoothed on the form. A strip of polyester peel ply keeps the wet glass from unwrapping at the neck. See the glass tape added to form a mounting flange? That's a good use for tape.



Finished parts. Note how little fill (zero) is needed for shape. Any filler will be weave filling only. That's the beauty of a good form, and a one piece wrap.

[Bavafa]

Originally Posted by DanH

All the basics are there.

Do remember the Golden Rule of Forms and Molds....time spent creating a really accurate, well finished mold or form pays large dividends later...less sanding, less filler, and less weight. A lumpy form makes a lumpy part.

Using little strips of fiberglass tape for this layup is not a good idea. Tape has a thick selvage edge, a knit ridge sometimes twice as thick as the base tape. The selvage tends to form voids in stacked layers, not a problem if epoxy filled, but heavy. The selvage also locks the warp and fill fibers, so tape doesn't conform to compound curves very well....which is why it's being used in short bits in this example. Last, short tape lengths usually result in a layup with uneven thickness.

Much better to do the layup with a stack of pre-wetted cloth. Cut one ply as a pattern while taped to the airplane, then two or three more using the developed pattern.. Stack 'em, wet 'em out between 4 mil plastic, squeegee out the excess resin, peel one side, and wrap the form, using gloved hands to smooth it into place. 9oz plain weave is surprisingly conformable, and 8-harness satin is even more so.

BTW, the time to do an upper intersection fairing on a Grove gear is when the fuselage is upside down for gear alignment and mounting.

Here's an oil cooler duct. Not an intersection fairing, but illustrates the principles.

Pattern development, single ply of 8.9 oz 8-harness satin. The 8-harness weave allows the warp and fill fibers to slide around in relation to each other.
The wrap will conform better and better as the excess fabric is cut away:



One ply, dry wrapped, cut to pattern shape. The single overlap seam is under the neck:



Three plies, cut using the pattern, stacked and wetted, about to get a top plastic sheet followed by a roller to push all the excess epoxy to the perimeter:



All three plies wrapped and smoothed on the form. A strip of polyester peel ply keeps the wet glass from unwrapping at the neck. See the glass tape added to form a mounting flange? That's a good use for tape.



Finished parts. Note how little fill (zero) is needed for shape. Any filler will be weave filling only. That's the beauty of a good form, and a one piece wrap.

Now this is a work of art which Dan has many examples of it.

Dan, I assume this is for the in portion of the duct and not the exit air, correct? If this was for the exit air, would you have any concerns about the hot air if this was West system?

[DanH]

Mehrdad, the specification of interest for a hot application would be Tg, the glass transition temperature of the epoxy in use. It's the temperature at which the solid epoxy changes from hard to rubbery. My notes show a lot of 145-165F oil cooler exit air temperatures, and I have recorded lower cowl air at over 200F. That's a lot higher than the stated Tg for West 105.

So why does it work? Obviously rubbery epoxy would not be suitable for a structural composite part, in particular if loaded in compression. However, a duct like this isn't very structural. So, think of it this way...if you could substitute a moderately stiff molded rubber part with glass fabric reinforcements molded in, would it work ok? If the answer is yes, then Tg isn't much of a concern.