Reinstalling the Landing Brake for Glassing

I’m going to try to make my posts a little shorter, as I think most people don’t want to read a novel when they visit construction blogs, and it may help me get more posts out more often.  Heather and I just got back from Oshkosh 2011, and met a lot of you that visit this site.  Having met more people who check the site regularly, I feel more obligated to update more often, if that makes sense.

We’re still in the “trying to catch the site up with the progress” mode here, so this step happened well over a month ago.  Again, this is not my official build log, I’m keeping that in a notebook, so I don’t feel too bad that my post dates are a bit off.

Prior to glassing the bottom, the landing brake needs to be reattached.  This is so that you can glass over the entire bottom and have a smooth transition with the landing brake closed. The first thing you do is sand a 1/16″ depression around the cutout, as seen below.

depression sanded around the brake cutout

This allows space for the flange around the landing brake.  As it says in the plans, this will all make sense in chapter 9, during the finishing of the landing brake.  I accomplished this task using the fein tool with a sanding head.  Helped a lot for sanding through the micro from the foam I had added to ease the transition to the naca scoop / landing gear area.

The next order of business is to vacuum the brake depression, then you glue it down with a few small dabs of 5-minute epoxy.  I generally don’t like the idea of using 5-minute epoxy on foam because of the damage it causes during removal, but I went ahead and did it anyway.

Glued Down!

Once the brake was glued back in, the last step is to create a mold for the flange around the brake with duct tape.  This took a LOT of tape, and is intended to be flush with the brake, and 1″ wide.

Tape Buildup

That’s it for this post.  Stay tuned!

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Contouring the Fuselage Bottom

Here is a most exciting step.  Contouring the fuselage bottom felt like a huge milestone.  Previously, the fuselage has been looking a little… square. Yeah, I know the sides have some complex curvature to them, and the bottom is slightly curved, but all the joints are these ugly sharp corners.  After this step, no more!

I was lucky enough to be tackling this post when my parents were up for a visit, so Dad and I tackled the airplane while the ladies were out shopping or talking about girl stuff or whatever it is they do. 😉  I tell ya, it’s great to be doing work on the plane with another engineer around!  Dad’s always got a good perspective on these things.

Anyway, when first setting about carving the sides, the bulk of the material is supposed to be carved away with a jig saw set at 45 degrees.  Problem is, the area it has to cut through is about 6″ to 7″ wide.  The little 2″ jigsaw blades I had would never get it done.  So I took a hacksaw blade, traced the end of a jigsaw blade in it, and cut it out with a dremel and my permagrit tools.

Making my Own Jigsaw Blade

 

It Fits!

The problem with using a jigsaw blade, while it’s long enough, is that it is rather flexible.  In order to make it come out where it was supposed to, and maintain a 45 degree cut, dad had to walk along with a scrap piece of metal and keep pressing the blade one way or the other to keep it straight.  We had previously drawn the lines on the bottom and sides of the fuselage to mark the cuts, so it wasn’t really a big deal, but like the plans say… GO SLOWLY.

Here goes nothin'

It’s also nice to have the Dad man around to take picture of me working… most of the pictures have been just the pieces and parts, or heather working.

Rough Cut Almost Complete

Once the rough cut was done, I decided to take the simple route for sanding the bottom shape.  I simply took my 2 foot permagrit sanding board, and went at it, checking against the template every once in a while.  For some reason, I find this type of work immensely satsifying, which is probably a good thing considering the amount of finish sanding these planes take!

Sanding Away

A lot of people have put a lot of thought and effort into contouring their fuselage bottoms, and make sanding blocks from the templates, or use a specially made tool that has been passed around the community for years.  I found that all to be overkill, and just stuck to the plans. At any rate, I’m quite happy with how mine came out doing it the old fashioned way, and I got it done very quickly.

As many builders have, I had a gap back near the landing gear bulkheads between the sides and bottoms, outboard of the longerons.  This is where we get a bit of foreshadowing of the contouring process to come.  I mixed up some dry micro, filled the gap with it, and came back and sanded it to the right shape.  After three rounds of this, it was perfectly smooth, and close enough to the right shape for me!

Contouring the back third of the plane is the trickiest part of the procedure, and I don’t have any pictures of it, unfortunately.  I just imagined a hotwire cutter pivoting around a forward point, and pinned up against the firewall (as is called out in the chapter 7 FAQ on cozybuilders.org), and sanded away.  The big part that confuses people is the way the foam is supposed to be cut out around the spar cutout. (I cut out the spar cutout at this point, which was dead simple.) The plans are a bit confusing on this point, but I found the pictures at the following link most helpful:

http://www.stealthturtle.com/index.php/Ch-7-Fuselage-Exterior/64-chapter-7-step-2-contouring-the-bottom

The only thing I did differently at this point was leave the section cut next to the vertical part of the spar perpendicular to the fuselage, instead of sloping it.  Later on, when I was getting ready to glass the sides, I made some rounded slopes down to the glass at LWX and the longeron, but I didn’t see much point in sloping the foam down to nothing in the spar cutout.  The idea behind sloping in this area is to allow you to make a glass to glass bond with the glass that was laid on the inside of the sides back in chapter 5.  All will be clear by the end of the chapter.

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Building the NACA Scoop

I apologize to my loyal readers, it would seem that I’ve been slipping again in updating the site.  The only thing I can say in defense is that I’ve been building like mad!  Now if I could just get the site caught up while I’m waiting for epoxy to cure…  if you were to look at the date stamp on the pictures, you’d see that this is being posted over a month after the work was actually done.

I was quite excited to tackle the step of building the NACA scoop!  Something about the challenge of sanding a huge block of foam down to a small triangular shape that fits just right scratches my itch for sculpting things.  This is the beginning of chapter 7, and the whole chapter involves a lot of adding pleasing shapes to things by hand.  Loads of fun!

The NACA scoop is built up from the bottom of the fuselage as it was left in chapter 6.  Up meaning up with the fuselage upside down on the table. To accomplish this, we put a 2″ thick block of urethane up against the front side of the bottom of the forward landing gear bulkhead, then put a 1″ urethane block in front of it.  There are actually 4 blocks in total, 2 on each side of the center line.  The template from the plans for the NACA scoop is used to trim the inside edges of the blocks, and what you wind up with looks like what you see below:

Foam laid out with NACA cut out

Then you take the blocks off, butter them up with micro, and put them back in place, with plenty of weight to make sure they stay flush with the bottom.

Weighed down

The bulk of the construction of the NACA scoop is then sanding the foam blocks down to be flush with the fuselage near the landing brake, and flush with the bottom of the forward landing gear bulkhead (LGB).  As many builders have found, I needed another foam block added on to the front side of the NACA scoop buildup, in order to make the foam flush with the rest of the bottom.  I added another 1″ block of foam extending up to the rear edge of the landing brake.

Flush with forward LGB

As is hinted at in the picture above, we also installed the plywood pieces called out in the plans between the landing gear bulkheads, and between the …. firewall?!  We hadn’t installed the firewall yet!  After a review of the plans, I found we were supposed to flox in the bottom half of the firewall at the end of chapter 6.  That was easy enough, after cutting the holes in the firewall for the lower longerons and LWYs, chapter 6 was officially in the bag!

Unfortunately, we don’t have too many pictures of the plywood pieces. Here’s a shot of Heather cutting them out of birch plywood:

 

Heather cutting wood

Here’s a top down shot of the area in question, you can see that additional urethane foam is used to fill the gap between the firewall and the rear LGB.  More blue PVC foam is used to form the channel for the NACA scoop in that area as well.

You may also notice in the above picture that the port side foam block doesn’t have a seam in it.  What gives? Well, I got a little too excited in my sanding, and wound up with a sizable depression in the foam.  I microed on another 1″ sheet of urethane from a pretty much trashed sheet, and sanded it level.  I can’t recommend this approach, as the edge of the sheet wound up being in the section of the fuselage to be rounded, but that’s a story for the next post.  Just take my word for it for now.  If you’ve gotta add foam, you can do it, but it might be easier to just use dry micro.

Also in the above picture, you may notice some stirring sticks wrapped in packing tape against the sides of the scoop.  Those are there because of more nicks in the urethane (man this stuff is a pain), and were used pretty successfully as dams for micro to fill in the nicks without messing up the bottom of the scoop. This worked a lot better than I thought it would, I apologize for the lack of after pictures.

 

Tongue depressor micro dams.

See the nicks?!

As an editorial note, it really bugs me when I visit other cozy build sites and can’t find much evidence of mistakes being made.  I like to think I’m doing a pretty good job putting this thing together, but I think that sharing the MANY mistakes I make along the way is much more interesting, and MUCH more helpful than writing a blog about how perfect my construction is.  Yes, it’s an airplane.  Yes, precision counts.  No, you’re not perfect.  For those out there pursuing a perfect airplane, good luck, but I intend to fly my cozy someday! *gets off soapbox*

Up next: Contouring the bottom!

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Bottom Installation

Once the bottom cures, installation is pretty straightforward. A block is glued in to support the foam at the landing gear bulkhead, then flox is spread on every mating surface, and the bottom is put in place and weighted down.

The plans say to hot glue a block to the forward side of the forward landing gear bulkhead, in order to keep the foam 1/8″ higher than the NACA scoop.  I glued this block in place before installing the bottom, but later realized that I shouldn’t have bothered.  The 1/8″ offset is to help in carving the joggle for the landing gear cover, but I later decided I would follow Wayne Hicks’ method, which doesn’t require a joggle.  If you are building your own, I would suggest researching the landing gear cover construction before you flox in your bottom.

Heather and I spread flox all over the mating surfaces, then set the bottom in place.  Unfortunately, I didn’t think to take any pictures of the weighted down bottom, but we used about everything heavy that we could lift!  I crawled underneath and wiped off the excess flox, but saved the taping for later.  It’s a good thing too, there is a lot of taping to do, and it would be very tough to do over your head while on your knees.

The next day I went to set about taping, and found we had made a mistake in the glassing of the bottom.   The front edge of the bottom is supposed to be rounded over, and have glass on the front face.  This face floxes on to the bottom of F-22, and you want to have a flox to glass bond there, not flox to foam.   The shear strength of the foam alone is not nearly strong enough, the flox would separate very easily, destroying the joint.

Fixing the improper glassing took a day of my working time.  First I cut the flox joint with the fein tool and a hacksaw blade, then I cut a 45 degree bevel on the corner with the fein tool, and sanded it round.

Once that was done, I pulled a sheet of plastic into the joint so that I wouldn’t get micro on F-22, and spread micro on the now exposed foam, using one of my mixing sticks.

Plastic barrier

I then made a 2-ply BID tape about 4 inches wide, pried F-22 off as far as I could, and laid it around the corner (very successfully, I might add). I then removed the plastic, spread flox in the joint just as I had done with the micro, and put a 2″ 2-ply BID tape over the corner and peel plied the joint.

Completed joint repair

As you can see in the pictures above and below, I used a couple clamps to make sure that the bottom stayed flush with the bottom of F-22.

Joint repair outside

The next day I removed the peel ply, trimmed up the fiberglass, and was quite pleased with how the joint turned out.  I proceeded to do about half of the joint taping, and half of the joint taping the next day.  I had the fuselage laying on it’s side for most of this procedure, and was amazed at how difficult it was to get the BID tapes to stick to the joints that were upside down.  Doing this with the whole fuselage upside down would have been a real chore.

Fuselage on its side for taping

Front joints

Forward side of instrument panel joint

It was quite exciting to see the fuselage interior come together like this.  Looking just at the inside, it’s starting to look like a plane!!

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Building the Bottom

Building the bottom of the fuselage is much like building the sides, only the jigging isn’t nearly as complex.  The first thing you do is glue several 3/8″ sheets of PVC foam together, just like building the sides.  This is trimmed to fit between the forward landing gear bulkhead and F-22.

Once the foam is trimmed along the longitudinal axis of the plane, it is weighted down, and you trace out the longerons, and where all the other pieces of structure contact the foam.  While the foam was upside down on the fuselage, I used a combination of Bondo and hot glue to build a frame on the bottom to maintain the curvature of the bottom when the foam was flipped over on the table.  Once it was back on the table, I trimmed the outside of the foam to match the outside of the lower longerons, per plans.

Foam in frame

As you can see in the picture below, I traced out the landing brake.  What you can’t see is the pretty good job I did cutting it out with a 45 degree bevel all the way around with a jigsaw.  I wish I had gotten some pictures of that before it all got fiberglassed.  Oh well, there will be plenty of pictures of the landing brake in the future.

Landing Brake traced out

Just like with the sides, the contoured shape of the inside of the bottom is created by carving many pieces of urethane foam.  Also like the sides, this was the most time consuming part of the process, and took all the cozy working hours of a weekend.

Laying out contour pieces

Here’s the whole bottom, ready to be glassed, after microing all the contour pieces in place:

After work the following Monday, Heather and I tackled glassing this thing.  First all the foam had to be microed, and it seems I never ever mix enough of the stuff.  The whole bottom is then covered in 2-plies of BID, and the rear seat area is covered in an additional ply for supporting people standing in the back seat.

Performing this layup was quite the challenge, as it was with the sides, because of the difficulty associated with getting the fiberglass to lay down in the corners of the contour pieces.  We exacerbated the level of difficulty by running out of BID just as we were finishing the second layer.  The second and third layers of BID in the back seat area are now a patchwork of the BID scraps we had left over from all of our progress thus far.  We made sure to overlap each scrap by an inch, as is standard procedure, so strength shouldn’t be compromised.  However, because there was so much overlapping, and so much epoxy was retained by the peel ply in smoothing all the transitions, our fuselage bottom is probably a little heavier than average.

Fiberglassing the bottom took Heather and me 3.5 hours just to do the glass work.

Stay tuned for installation of the bottom!

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