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| cutting prop hub hole |
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| mounted on engine |
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| side view |
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| 3/4 view |
that's it for now.
COWL AND SPINNER PROGRESS
I had just laid up the Spinner and Spinner backing plate. I had to wait 72 hours for my resin system to cure sufficiently to be able to trim and sand it. That is very important!! I mounted the spinner backing plate on my Lathe. I then made a self centering coupler for the tip of the Spinner. I used this coupling to mount the spinner to the arbor. After a little tweaking I was able to dial the spinner in with less than .004" of run out.
this is a live shot of the running lathe. I am cutting the prop hub centering hole. I mounted the backing plate between two wooden plates. The hole in the plate was larger than the center shaft. This allowed me to adjust the outside run out with a dial indicator. once it was perfect, I drilled 4 holes and bolted the plate to the wood backing plate. this locked it in for good. Once the backing plate was spinning true, I set the spinner in position.
Unfortunately I don't have any pictures of this procedure. but the idea was to get it true and mounted then drill 4 holes for a 3/16" cleco and locate the parts. Here its shown mounted on the engine.
here is a side view. I couldn't locate the cowl until I had the spinner mounted. The top surface needs to fair cleanly into the spinner loft.
this is my favorite view. The inlet is still rough trimmed, and the cowl has not been sanded. You can see the witness line where the upper cowl mold was attached to the lower cowl mold.
that's it for now.
that's it for now.
LOWER COWL AND NEW SPINNER
I prepped the lower cowl for layup by applying 7 coats of Carnauba mold release wax. Followed by a buildup of Rexall Partall 10 PVA release film. Since the lower cowl needs a surface extension into the upper cowl, that mold was also recoated.
After both molds are joined together I shot more primer onto the surfaces. You want to be ready to do the layup immediately after the primer flashes off. This will give you the best mechanical and chemical bond to the resin.
The seam between the molds is stuffed with modeling clay.
The clay is pushed into the seam and then gently scraped off with a sharpened tongue depressor. nothing will stick to the clay because its an oil base clay. This will keep the laminate near this joint from becoming porous and it makes a smooth transition between the mold halves.
As I mentioned earlier in this blog, I need to make an inner flange that will be secondarily bonded to the lower cowl and form a flange that the upper cowl will sit on. In order to do this, I need to lay up the lower cowl at least 2 inches beyond its normal trim. Remember the actual parting line between both cowls is etched into the upper cowl surface. This is the reason I needed to join the upper cowl. Here is an image of the initial lay up. the surface is covered with polyester fabric, the same fabric I cover the plane with. In this case its functioning as Peel ply. I like to lay a final layer of Peel ply on my wet lay-ups especially at any ply splices. The peel ply beautifully transitions these ply's together. The other reason is in the area of the overlap flange, I want a smooth surface with no rough ply edges.
Its HOT today in Texas, humid too. after I finished the lay up, my tee shirt was soaked clean thru. I actually wrung a cup of sweat out of this thing!!! I can hardly wait for fall. The high temp keeps dropping one degree per day. By mid October, it will be wonderful again in Texas!!!
I released the upper cowl and here is what is left. Even in this high heat, I needed to let the laminate cure for 48 hours. Its important that the resin become fully cured almost to the point of being brittle. The tool I like using for trimming is a vibrating multi tool. I use a grout cleaner as a cutter. There is carbide grit bonded to a steel disk. This will wear thru beautifully and with very good control. The actual final trim of the cowl is one inch below the trim that you see.
Here you can see the secondary flange lay up I did on top of the original cowl lay up. I laid 7 layers of wax on the inside of the cowl before I laid up the inner flange. Here I am parting the inner flange from the cowl. once I have released the inner flange, I will re trim the cowl an inch lower at the scribed trim line.
here is another view of the inner flange. You can see that it will lock in and "key" perfectly to the inside surface (IML) of the cowl.
Here is the inner flange being bonded to the IML of the cowl. you want to make sure you use an actual structural adhesive here and not thickened laminating resin. . Structural adhesives all have an elastomeric polymer added to the matrix. This dramatically increases the peel strength of the bond. This will keep the flange from peeling away from the cowl. I used T-88 structural adhesive.
Time for a trial fit up. I joined both halves and temporarily attached them with Clecos. Eventually I will replace each Clecos with a bonded nut plate. Before I can actually set the position of the cowl, I need to mount the spinner and backing plate. The cowl must sit with a 3/16" gap between the outer surfaces and the spinner. the surfaces must all be true and faired. So before I can finish mounting the cowl, I had to lay up a new spinner and prop backing plate. Fortunately I already have the molds.
The cowl I about 6 inches too long, this is why I made the extension surfaces on the master model. I wanted to be sure I had more than enough excess.
here is the backing plate mold. This will get 3 ply's of .014" thick Graphite. The Lathe will be used to true it up and trim it.
here is the spinner laid up in its mold. the white fabric is peel ply. This is a very hard mold to release because you cant start a edge peel. But I coated the mold with Wax and PVA. Once cured, I will submerge this mold overnight in water and hopefully it will float out after the PVA dissolves.
I made two wooden backing plates and clamped the backing plate between them. The hole in the backing plate is much larger than the center bolt. This is so I can use a dial run out gage and adjust the position of the backing plate until it runs true.
More in a few days or so!!!!
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| upper and lower molds joined |
After both molds are joined together I shot more primer onto the surfaces. You want to be ready to do the layup immediately after the primer flashes off. This will give you the best mechanical and chemical bond to the resin.
The seam between the molds is stuffed with modeling clay.
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| modeling clay |
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| final layup |
As I mentioned earlier in this blog, I need to make an inner flange that will be secondarily bonded to the lower cowl and form a flange that the upper cowl will sit on. In order to do this, I need to lay up the lower cowl at least 2 inches beyond its normal trim. Remember the actual parting line between both cowls is etched into the upper cowl surface. This is the reason I needed to join the upper cowl. Here is an image of the initial lay up. the surface is covered with polyester fabric, the same fabric I cover the plane with. In this case its functioning as Peel ply. I like to lay a final layer of Peel ply on my wet lay-ups especially at any ply splices. The peel ply beautifully transitions these ply's together. The other reason is in the area of the overlap flange, I want a smooth surface with no rough ply edges.
Its HOT today in Texas, humid too. after I finished the lay up, my tee shirt was soaked clean thru. I actually wrung a cup of sweat out of this thing!!! I can hardly wait for fall. The high temp keeps dropping one degree per day. By mid October, it will be wonderful again in Texas!!!
 |
| multi tool trimmer |
I released the upper cowl and here is what is left. Even in this high heat, I needed to let the laminate cure for 48 hours. Its important that the resin become fully cured almost to the point of being brittle. The tool I like using for trimming is a vibrating multi tool. I use a grout cleaner as a cutter. There is carbide grit bonded to a steel disk. This will wear thru beautifully and with very good control. The actual final trim of the cowl is one inch below the trim that you see.
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| inner flange being released |
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| more inner flange |
here is another view of the inner flange. You can see that it will lock in and "key" perfectly to the inside surface (IML) of the cowl.
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| bonding the inner flange |
Here is the inner flange being bonded to the IML of the cowl. you want to make sure you use an actual structural adhesive here and not thickened laminating resin. . Structural adhesives all have an elastomeric polymer added to the matrix. This dramatically increases the peel strength of the bond. This will keep the flange from peeling away from the cowl. I used T-88 structural adhesive.
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| Trial Fit |
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| Another view |
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| Backing plate mold |
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| Spinner mold laid up |
here is the spinner laid up in its mold. the white fabric is peel ply. This is a very hard mold to release because you cant start a edge peel. But I coated the mold with Wax and PVA. Once cured, I will submerge this mold overnight in water and hopefully it will float out after the PVA dissolves.
 |
| Backing plate being trimmed |
I made two wooden backing plates and clamped the backing plate between them. The hole in the backing plate is much larger than the center bolt. This is so I can use a dial run out gage and adjust the position of the backing plate until it runs true.
More in a few days or so!!!!