Ch 9.1: Main Gear Reinforcements (3 of 3)

Last But Not Least

Ok...down to the last strength reinforcements of the landing gear bulkheads.  This one beefs up the area between the forward and aft LG bulkheads themselves.   This is the area where the main gear bow will actually be installed.

Piecing together the template

The last reinforcement went so well using the template, I decided to try it again on this one.  I thought it might be the only way I was going to get the glass fibers running the correct direction all the way around.

I first pieced together a template using pieces of paper and tape.  I used a sharpie to mark the corner areas and planned to trace these on to the plastic before I wet the glass so I could get it positioned correctly on installation..

Since the area to be glassed has a major bend in it  (see right side of pic), I had to decide where to cut it in order to get it to lay flat for cutting the glass. It is mentioned in the plans that you'll have to cut the glass somewhere and overlap it or it will otherwise bunch up....but make sure you don't overlap on the hard points...these need to be flat.

Paper template
(as if looking down at the copilot's side).
Note the triangle cutout (top) where
the glass  will fold and overlap in the bend.

Looking around at other builder sites, I came across Charles Fernweger's builder site.   He showed a template that looked a lot like mine...giving me a little confidence that I was on the right track.  He cut his from the front corner, where the three separate planes come together, diagonal up the 90 degree inside corner in the forward bulkhead.  When the template is laid flat, you get something like the top picture to the left.  The cut I made is represented by the open triangle.

Paper template
(as if looking down at the pilot's side)
Note the triangle gap is closed.

I closed this gap up with another piece of paper running horizontal until it met the other side of the open triangle like in the 2nd pic.  Note this is flipped as if for the other side.

When cutting the wet glass to shape, I made one cut from the location of the sharpie in the 2nd left pic, to the 4-way intersection.  The 4-way intersection is the corner where the three planes meet  (fwd upper bulkhead, fwd lower bulkhead, and fuselage side).  Now when I installed the glass, and it folds up, I had a side of excess glass to overlap onto the angled upper portion of the fwd bulkhead for a strong bond.  I hope that makes sense...EZ to do, hard to explain.


After the "all over" reinforcement is complete, there is one more 2xBID that goes over the hard points just like the other reinforcements.  Using the same process, I cut 2xBID 19"x 6" and laid it in from hard point to hard point.  EZly done.  (OOPS: The next morning when I completed the pilot's side I realized that I had accidentally made this lay-up with 3 ply's instead of 2...oh well...I guess a few extra once's wont hurt.)

Reinforcements Complete
Pilot's side, between the fwd & aft LG Bulkheads

Reinforcements Complete
Copilot's side, between the fwd & aft LG Bulkheads

All the fuselage main landing gear reinforcements are now done!  It's time to start working on the main gear bow itself.

Onward.
cab

Ch: 9.1: Main Gear Reinforcements (2 of 3)

Center NACA foam between the
Firewall (left) and Aft LG Bulkhead (right)
(view is looking from right side of the a/c)

Adding strenght between the firewall and aft LG bulkhead.  

First the center foam piece is glassed w/2x BID (left).  This is the foam that forms the top side of NACA Scoop.  Easy enough.

Paper template used for second layup.
The sharpie lines mark the corners
of the layup area to help align it when installed.

Second, each side is glassed with 3xBID that wraps from the back of the aft LG Bulkhead, around the side, and on to the fwd side of the Firewall.  I followed the plans method for these pieces...make a paper template, wet out the glass on 3 mil plastic over the template, cut out the glass to match the template, install, squeegee  air out, pull plastic off. Voila!
Installing the glass this way made these layups pretty easy and were probably some of the best layups I've done...too bad they won't be visible as this area will end up being covered by the main spar.  One template will work for both sides but it is not symmetrical so remember to flip it over before you do the other side.  Peel ply from hard point to hard point as there is one more layup that covers that area.  You could do this layup and the next one all at one time, but with the tight space, I was afraid I would mess up the work I'd already done.  So I waited for this one to cure before going on to the next layup.

Pilot's side firewall (left)  to
aft LG bulkhead (right) layup

Copilot's side firewall (right)  to
aft LG bulkhead (right) Layup

The last layup in this area is another 3xBID that wraps from the firewall, across the floor, and up the aft side of the aft LG bulkhead hard point.  In total, this whole reinforcement places an additional 6 ply's of fiberglass over the aft gear hard points and the bottom engine mount hard points of the firewall.  Again, I peel ply'd the hard points and the edges of the glass which you can see in the pics.



With this area now protected, it's time to move on the "hell hole" between the forward and aft landing gear bulkheads where the main gear will actually be installed.

Onward.

Ch 9.1: Main Gear Reinforcements (1 of 3)

By the time I'm done with Chapter 9, I'll have the main landing gear, wheels, brakes, and speed brake installed.  It starts with reinforcing the area around the landing gear bulkheads so it can hold the main gear bow and take loads from landings.

Strength in Numbers...of plys!
This will be a three part post because there are 3 areas that are reinforced.  #1, the front of the Forward Landing Gear Bulkhead; #2, the area between the Aft LG Bulkhead and the Firewall, and #3, the area in the middle between the Fwd and Aft Landing Gear Bulkheads where the gear bow will be mounted.  These are tricky to glass because of the number of corners to glass around and the limited space to work in for the latter two areas.

Fwd LG bulkhead
For the front most reinforcement, I followed the technique used by Bernard Siu.  Instead of making paper templates and trying to cut the glass to fit, I cut three 10" x 24" rectangle of BID and laid it in starting from the bottom/forward and working aft/up being careful to keep the glass pinned in the corner.  Additionally there are two additional BID plys that cover the hard point up to the bottom of the tall tabs for a total of 5 plys over the hard point.  In the pictures, the sharpie marks outline the reinforced area.

Pilot side reinforcement looking aft.  Stray
sharpie marks are misaligned edges of glass

Fuselage, back seat looking aft at the Fwd Lnd Gear Bulkhead.
The reinforced areas are at each side, extending from 2"
on the side, along the floor 6",  then back to the bulkhead
and  all the way up the tall tabs. 

With a little patience, and slow curing epoxy (I used the Aeropoxy 3665 hardener which has a little
longer working time than the 3660 I usually use), I got all 5 plys down and peel ply'd in 2.5 hrs.  The copilot side went slower...but that was because I had a six month lapse in working on the project and had lost a little glassing efficiency.

As I was wrapping this reinforcement up, I came across an archived email discussion from Marc Zeitlin.  The plans, Ch 9, figure 1, shows an additional 2xBID tape to be run from the floor to the fwd bulkhead...but the text never discusses it.  I thought it was because this layup was already done in Ch 6 when the fuselage bottom was attached.  According to the email however, Marc Z stated that the additional 2xBID tape should be done.  He said that this far into the plans, it assumes you know to 2xBID tape any place two parts come together.  So if it actually shows one, even if it's an additional tape, do it....so I did.

The plans have you reinforce the area between the bulkheads next, but you need to turn the fuselage on its side.  So I went ahead and did that while I had easy access.

Onward.

Ch 8.1 - 8.5: Headrest - Part 2/2

Return to the Headrests
Ok...back to finish the first 5 steps in Ch 8.  Note it's been 9 mths since part 1 of this post.  Mostly because I wasn't working on the Cozy for about 6 months while involved in some other projects, retiring from the USAF, securing a new job, honey-dos, etc.

Since I'm not using the plans version of headrests, I can skip part of step 1 and all of step 4 but of course that work will be replaced with other work to install custom headrests.  At the beginning of Ch 8, I already cut the shoulder support.  I also ordered and received my Saab headrests and the adjustable headrest guides from a Saab dealer.  Now it's time to get it all together.

First I located where the birch hard points for the shoulder harness attachments would go.  The plans call for 8.5" apart.  This was a change made in Newsletter #50 which reduced the spacing from 11.5" based on a European safety study that gave 8.5" as the max safest distance for shoulder harnesses.  I ended up adding 1/2" and making them 9" apart.  At 8.5" they were just a hair too close to my neck...and I don't have a big neck.  Researching the archives, I found that many builders questioned the change since there was no accident evidence to really drive it.  Some chose to leave them at 11.5" and use an "H" cross piece to ensure the harness stays on the shoulders in an accident.

Shoulder Brace, inverted,
w/ birch hard points curing with 1 ply BID

With that decision made, I cut the birch hard points and glued them in with 5-min epoxy.  Then I glued the two halves of the shoulder brace together.  I decided to go ahead and glass the inside...but not leave an overhang since I'm not installing it on the seat back yet.  This allowed me to have a more solid structure to work with while I figured out how to support the headrest.  (Post build note:  as it turned out, waiting to do this after I designed my headrest supports would have been better and saved me a little weight.)

Deviation Time...
At this point I had to start doing things a tad different.  I couldn't install the shoulder brace onto the seat back until I designed the support structure for the headrests.

After some thought, I decided to install aluminum tubing for the headrest guides to slide into.  This will provide more support than just gluing the headrest guides in place.  My fear is that someone will grab the headrest and lean on it while getting into the plane so I want to make sure there's enough support in case that happens.

After ordering tubing with the wrong wall thickness twice, I finally got the right size to fit the headrest guides...3/4" OD w/ .049" wall.  I located the holes for the tubes in the shoulder brace and drilled and glassed receiving holes for the tubes into the seat back w/ 1 BID to provide a more solid hold at the bottom.  The holes aligned with the front inside edge of the shoulder brace.  Later in the build, I'll adjust the length of the tubes if needed based on where I want the center of the adjustment travel to be...then they will be floxed in place.

Pilot side holes for
headrest support tubes

Tubes used to form glass
 down into the holes

Next I cut some leftover 1/4" birch to provide support structure for the tubes on the inside of the shoulder brace.  These support the top of the tubes while the holes in the seat back support the bottoms.  The tubes go through the birch right up against the front of the shoulder brace.  The back is cut to match the angle of the seat back so it will flox to the seat back just like the rest of the brace.

Birch supports for top of headrest
guide tubes

Checking everything before glassing
in the birch supports in place w/1 BID

Next I prepared the nut plates for the harness bolts.  I followed the recommendation in the FAQs to flox/screw the aluminum squares with the nut plate permanently to the bottom of the harness hard points instead of the hokey way the plans directs you to do it.  Each nut plate is secured to the aluminum with rivets.  Holes were then drilled in the opposite corners from the rivets for #4 screws to secure them (with Flox) to the underside of the birch hard points installed earlier.

Inside of the shoulder brace.  Headrest supports glassed
in place, ready to secure the 4 nutplates with
flox & #4 screws before installing in the plane

The shoulder brace was then installed per plans and taped at the adjoining sides.  Next I sanded a the sharp back corner of the seat back round to allow the 3 ply UNI reinforcements to take the corner properly.  They were installed longer than plans at 17" instead of the plans 13".  Since these are "reinforcements", I felt I wanted a little more than a couple of inches overlapping the seat back and behind the seat.

And here is the result with headrests temporarily installed and showing different adjustment heights. What you can't see in the pic are the black plastic adjusters at the top of the tubes.  During the finishing process, I'll flox in the support tubes and hide them in a small contour of some sort on top to make it look nice.  All you'll see then is the adjusters on top.


 Another chapter down...on to chapter 9 and the main landing gear.

Ch 9.2: Preparing the Strut

Main Gear Strut, sanded, cut to 95" total length w/legs cut at
8 degrees up at the trailing edge.

Jumping ahead, I started step 9.2 because my shop heater is broken and I can't do any layups in the current temps.  Step 9.2 is the prep of the main gear strut.  It involves sanding the strut to a dull finish so it will take epoxy, cutting excess length from the strut legs, and cutting an angle in the strut legs to match the angle that it will be installed in the fuselage.  This was all very straight forward with no issues and took about 3 hours or so total.

The rest of 9.2 will be tackled later.

Onward, cab