Bulkhead cutout finishing

[Sammac91]

What do builders normally do with the bulkhead cutouts, do they leave the exposed foam or put something like food in the channel for durability?

[Jon Matcho]

You definitely don't want to put "food" in there! 

 

Do you mean the inner edge of the bulkheads where the holes are cut? Most leave the foam exposed in anticipation of bonding to something else.

 

However, in cases where that will not be true (leg holes), you could put a small amount of micro in there to keep the edges smooth (possibly to find out months later that you'll want to widen this area by 1/4" on each side  ).  

 

I'd wait until finishing and until you are certain it's worth doing, otherwise you're adding weight where it may not even be visible.

[Sammac91]

Hi Jon, It's the leg cutout I was thinking about. Just seems it's a high traffic area with the chance of being chipped out over time plus the foam is just exposed there. Nothing is mentioned in the plans and I guess paint somewhat fills and seals off the foam.

Cheers,

Sam

[macleodm3]

Like Jon said, you can just the leave leg cutouts as is.

If its going to be exposed to weather (like the fuselage sides at the canard cutout) then its good to seal it.  

 

Keep it light and simple (to help assure you get it flying someday and so that it flies light and fast).

[Jon Matcho]

It's the leg cutout I was thinking about. Just seems it's a high traffic area with the chance of being chipped out over time plus the foam is just exposed there.

 

For reasons I share with Andrew (weight and being drawn into the weeds of perfection), I suggest not doing anything until you realize you're certain that you know the best time to address.

 

With that said, I plan on digging a shallow cavity in the leg holes and filing with micro for the "high traffic" reason you identified (and it will look better).  I won't do it now because I just may increase the width and/or height of the area slightly when it's time for avionics, etc.  The more material I have to work with, the better.  

[SteveJ]

Not mentioned...

My experience/policy dealing with foam and fiberglass construction is that before paint, at the latest, ALL foam MUST be sealed. Too many primers/paints out there that eat too many foams otherwise.

[Jon Matcho]

On 3/22/2019 at 7:21 PM, SteveJ said:

Not mentioned...

My experience/policy dealing with foam and fiberglass construction is that before paint, at the latest, ALL foam MUST be sealed. Too many primers/paints out there that eat too many foams otherwise.

 

There's nowhere that you should see exposed foam.  It would be temporary if you did while waiting for a part to be assembled later.  Most often you have foam + a micro slurry + at least 2 layers of fiberglass + more micro and then paint.  The foam is well protected.

With that said, and back to the original 'bulkheads' topic, I HAVE seen exposed foam on flying planes (albeit rough-finished) within the inside cutouts of bulkheads.  A fix is to fill with 'micro'.

You don't want to let fuel get near foam, which is another topic...