Reinforcing the Glass Strut Fabricating NG-30 Installing Worm Drive Assembly Box Assembly
Nose Floor & Sides Rudder Pedals Master Brake Cylinders Completing Nose Gear
Pitot & Static System Closing the Top Nose Door
I decided to shape the nose sides first before the nose bottom because I figure I will have a greater chance of bumping / scratching the nose bottom when working on the sides instead of visa versa. I also decided to make a shaping jig to guide my sanding - so that both sides of the nose will have the same curvature. The question is - how do I determine the nose sides curvature? Here's what I did:
First, I make sure the fuselage is leveled from side to side and front and back. Then I firmly attached the nose cone that I purchased from FeatherLite to F-0 with duct tape. I taped a large piece of paper on the floor underneath the nose. Using a plumb line, I marked several data points on the paper along the curvature of the fuselage before the foam. I repeated the process with the data points along the edge of the nose cone. Then I connected the data points with a long flexible aluminum strip as shown. This line forms the curvatures of the nose sides. My next step was to make two wood templates with its edge shaped to the same curvature.
Once I made the templates, I turned the fuselage over to its up side down position. I mounted the templates level and parallel to each other as shown. I used clamps at the front and hot glued at the back to keep the template in place during the sanding. I definitely do not want them to move on me at this time. The rest is just sanding the sides with a long sanding block along the template curvatures. However, I took time with this process because mistakes will be costly down the road. I repeated the other side with the same approach.
I removed the NG-5 plate from the top of the strut so that I can sand the bottom without obstruction. Then I made a couple long and wide sanding blocks for shaping the bottom. I used the strut cover as a guide for sanding. However, MKNG-3 gave me a slight problem which I have to do a bit of local sanding. In the end, it worked out OK. I was surprised how sharp the corners turned out though.
I contemplated to make a jig to shape the corners but decided against it because the corner curvature will not be constant from the fuselage to the nose. I decided to shape it by eye. I made the rough cut with a hacksaw blade. I held the hack saw blade at both ends (without the hacksaw mounting frame), bent it a bit and scraped the foam off the corners with long strokes - from nose to fuselage. Once I got the rough cut, I switched over to the sanding belt I used for shaping the fuselage bottom sides. Again, with long strokes from front to back (NOT as polishing your shoes), to smooth out the corners. Its a messy task and you'll get foam dust all over the place. Fortunately, the foam was so easy to shape, it took me about 3 hours to complete.
One of the steps involved in glassing the nose is to cut the strut loose after the bottom is cured. I was concerned about cutting 'around' the nose cover (from Featherlite) and that the cut should be symmetrical. Since it would be difficult to find the cut line afterwards, I decided to make a paper template first. As shown, I drew a center line down the strut and at every inch, I took an equal distance left and right from the center line (yet clears the nose cover). Once done, I joined the dots with a French curve on one side. Then I fold the template over at the center line and traced out the other side.
I laid the glass over the nose bottom and pre-cut the glass (2 layers) prior to applying micro onto the foam. I also removed NG-5 (but taped over the foot print) before glassing. I then applied dry micro over the dents and gaps between the nose cone and F-0. I also taped down the sides per plan as well. I almost missed the 3rd ply and caught it at the last minute.
I traced out the cut lines with the template (above) and it looked OK. The seam between the nose cone and nose bottom turned out OK as well. However, the seam between F-22 and the nose bottom probably needs some micro filling down the road.
Notice I did not have the birch plywood support for the nose bumper because I plan to do something different than plan. See the bullet shape marking in front of the strut?
According to the plans, the nose bumper is made out of a hockey puck and glassed under the nose. The main function of the hockey puck was to protect the bottom of the nose when the plane is parked in its nose down position. However, as the 'Gear Up Landing Club' members have grown in size at an un-controllable rate , discussions (in the Cozy Forum) have turned to replacing the hockey puck with some serious hardened materials. They include maple wood, Kevlar, hardened stainless steel and others... including a piece of truck tire from the freeway by Bill Therringer... what??? That caught my attention because it sounds like it can be free .
I sent Bill a private e-mail and asked for specifics. He responded with clarifications and a picture showing his battle scars (left)! If I remember correctly, he 'tested' this truck tire contraption 3 times and he thinks it should be good for two more times. He also stressed that flox worked surprising well in bonding old tires onto fiber glass. When asked about how to replace the old tire - the answer was 'I got a monster grinder'! Well the truck tire material makes sense to me as far as wear resistance to the runway surface is concerned - I am sure we all had a few hard brakings (or fast starting for the young builders) one time or another - and above all, his contraption was proven! Thanks Bill, for this practical idea...
Since I am using Jack Wilhemson's nose lift that includes a pedestal to be mounted at the base of the strut for nose down parking, it basically replaces the original function of the nose bumper. Therefore, the function of the nose bumper (in my case) would be purely protecting the bottom of the nose in case of gear up landing. I like the tire materials for my 'gear up bumper', but, I prefer to make it replaceable and a bit more pleasant to the eye than an exposed tire from Freeway I-60. So here's the plan:
My nose bumper will consist of a 16 ply BID base (like the sole of a shoe), which will be shaped to the curvature of the fuselage for good contact against shear forces. This BID base will be bolted tightly to the bottom of the nose & fuselage with (5) T-nuts and 1/4" bolts. It can be removed for repair after a gear up landing or whatever reason. The 5 anchors (for the bolts) are made out of a set of 16 BID 'L' brackets, epoxied against the sides of F-0 and NG-30 respectively. I got this idea from reading Wayne Hick's site (BTW, he's got a gorgeous looking nose bumper). A bullet shaped 1/2" thick rubber bumper will be floxed onto the BID base (taken from Bill's approach). The entire contraption will be enclosed by 2 BID plies, like the upper cover of a shoe. This 2 ply BID serves two purposes - 1) It covers up the rubber tire material so that the bumper looks like it is part of the plane and 2) It provides additional enforcement to keep the rubber from peeling off (in addition to the flox surface).
[Hindsight: I added an aluminum spacer (tube) between the 16 BID anchor and the 16 ply BID base to prevent compression of the foam when tightening the bolts. More discussion 2 paragraphs below.]
In the event of a gear up landing, the very top part of the 2 ply BID will make contact and I suspect, it will last about 2 seconds, then the tire will hit the road. However, most of the surrounding 2 plies should remain in place. Since the rubber is secured to the 16 ply BID by flox as well as the remaining 2 BID glass enclosure, it should stay put. As there is no bolt protruding above the rubber, the grinding will have to take 1/2" of tire rubber before reaching my second and third line of defense (i.e. the nose strut plate and the 16 ply BID. I plan to strengthen the nose strut skid plate either with SS or maple wood.
First, I drew up a bumper base pattern (paper template) similar to Bill's contraption (bullet shape) and traced it onto the desirable location (2 pictures above). Then I laid a 16 ply BID (at 45 degrees) large enough to cover the entire pattern. Do not forget to cover the pattern area with packing tape prior - or it'll give you a really bad day! This BID layer forms the removable bumper base. The reason for using the BID tape is that it conforms perfectly to the curvature of my nose bottom. It will be difficult to carve anything else that 'hugs' the mating surface.
Once the BID layers cured, I traced the bumper base pattern onto the top of the BID with the same paper template. Then I popped it off the fuselage and trimmed it to shape with a band saw and various sanding sticks. Note I have a smaller one close by... that was one of those measured ONCE and end up cutting too short kind of part ! I ended up re-doing the 16 ply BID...I match drilled 5 holes through the bumper base as well as the BID anchors (discussed below).
I also built up (5) 16 ply BID anchors on the opposite side of the bolt holes (for the nose bumper base to bolt to). These L-shaped BID anchors are mounted with its vertical leg against either F-0 or NG-30 as appropriate. The largest BID tab is at the inside of the nose cone - right in front of F-0. If you look close, you can see its silhouette in the above picture. With these 5 bolts and nuts, the bumper base can be held tightly against the strengthened underside of the fuselage and nose cone.
[Hindsight: I received a suggestion from Wayne Hicks that I should add some structure between the tabs and the 16 layer BID base such that the foam will not compress when tightening the bolts. Thanks Wayne, for the advice! Since my tabs are already in place, it would be difficult to hog out the foam underneath them and fill in with flox (to prevent compression), unless I turn the plane over (again) and open it up from the fuselage bottom. I really didn't want to open up a sizable hole in the fuselage bottom because when I patch it back up, I may end up changing the surface profile of the fuselage (where my BID base fits onto). I decided to open up the bolt holes a bit to 3/8" diameter (from 1/4") and fit an aluminum spacer in between. After cutting the spacers to length, I floxed the spacers in the holes - making sure I waxed the bolts while the flox cures. It turned out OK.]
I wanted the mounting bolts to stay flush with the fiber glass bumper base because if the grinding ever gets down to the bolt heads, the bumper base will come off in record time. I found some tee nuts from McMaster-Carr, but they only handle 1/4" 20 bolts only (I would prefer 10-32 threads). I had to shorten the tee nut necks to match the thickness of the bumper base. I also had to open up the thru holes to accommodate its 5/16" neck diameter. Then I applied a bit of flox to hold the tee nuts in the holes. With the bolts coming up from the inside of the fuselage, I can pull the bumper base tightly against the fuselage bottom (as shown). The surface of the BID is just about level with the 1/4" aluminum strut plate.
Hunting for the tire materials was an adventure in itself - I caught myself jogging for position, looking for retreads, while driving down Interstate I-60 at 70 mph. After several days of retread gathering, measuring and cutting, I was not happy with the loot (BTW, the Freeway cleaning crew should thank me for this !!!). Most of the tire strips I picked up had either weird patterns, wide gaps between threads or uneven surfaces. If you wanted to see sparks flying, try cutting one of these truck tires with your band saw. Their steel belts are much heavier than passenger cars.
I finally decided to buy the tire rubber and go for solid rubber instead. I did a bit of research through Google and learned that the two types of rubber that have the highest abrasive resistance properties are natural gum rubber and SBR (tire) rubber.
I ordered a SBR loading dock bumper from McMaster Carr the next day and it arrived promptly - this thing is monstrous !!! By the looks of it, it will never wear out as a nose bumper and with its weight, it will probably work as a counter weight to keep the plane from tipping backwards as well - a real dual use potential ... I attempted to cut it to sheets with little success because the material is so tough. I finally gave up and looked for alternative rubber format.
Fortunately, McMaster-Carr also sells both Ultra-Strength Natural Gum Rubber and High Strength SBR in 12"x12"x1/2" sheet form. I bought one of each ~$20/sheet and put them to the test. I clamped one down and put a belt sander with 60 grit to it. It smoked, it smelled, got hot (only at the contact surface), some hot black dust flying out but no major wear - definitely not 1/2" worth in a hurry. Both materials look and feel pretty much the same. I decided to use the Ultra-Strength Natural Gum Rubber because it sounded tougher ...
I made another paper template for the tire materials - just a bit smaller than the bumper base. I traced it out onto the rubber sheet and rough cut it out with my band saw (4 TPI blade). Then I shaped the edges with my table belt sander and various sanding sticks. This material was difficult to shape, as expected, but eventually, the nose bumper took shape. I further cut out small pockets at the underside of the bumper to accommodate the slight protrusions of the tee nuts.
After I put wax over the bolts and on top of the tee nuts, I applied flox on the mating surface of the rubber and bumper base. I must have used 9 clamps to hold the two pieces together for complete bond and cure. For a test sample, I floxed a small piece of rubber to a cut out piece of the bumper base (16 ply BID) to verify its adhesion later on.
After the flox cured, I clamped the the test sample at the base and took my belt sander to it. This time I was looking for tear and separation of the rubber from the fiber glass. They stay bonded quite well - I think it will take a lot of shear force to separate the two. I do not know how much because I was not able to do so... Note the little bit of flox along the edges probably helped as well. However, I was able to separate the two by prying them apart (peeling). But I have to break through the flox first, that's why I'll be floxing down the edges of the rubber and enclosing it with 2 ply BID. If you look close, you can see part of the rubber at the top was removed by my belt sander.
My next step was to enclose the entire assembly with 2 plies BID. I first shape the edges of the fiber glass to conform to the slope of the rubber bumper. Once completed, I applied dry flox all around its edges, filling in any gaps and irregularities. Right before I laid the 2 BID layers, I brushed over the dry flox with epoxy, making it nice and smooth. The flox, in some way, encased the rubber in place inside the 'shoe'. Then I laid on the 2 ply BID and peel plied. Once it cured, I trimmed off the overhanging glass. Total weight of the nose bumper is 14 oz. Since it is at the nose, maybe I can reduce some ballast instead.
Here's a picture of my completed nose bumper. Once it is painted to the same color of the plane, it should be less 'visible'. I also made a nose strut skid plate out of maple wood. I was surprised how hard the wood is and its resistance to sanding. It gets hot, but localized - nothing like a metal plate. Note I extended the length of the maple wood strut plate so that it covers up the hole forward of the plate - but you need to slope the front edge so that it does not interfere with the bumper edge.
Between this nose bumper, Jack Wilhelmson's auto nose gear extension and a voice prompt (planned future addition), I may have a chance to avoid gear up landing and subsequent damage. We'll see...