60″ Do 335 Progress

Work is proceeding slowly on the fiberglass fuselage. I have built up the forward fuse structure, which fits inside the glass fuse. Plan is to glue it in place and then cut out the hatches and doors.  The rear fuse is also shown with former F19 being fitted just forward of the stab leading edge.

Fiberglass fuse and parts

Closer view of forward fuse structure

Rear fuse with former F19

 

 

 

 

 

 

 

 

 

The standard retacts will be Spring Air 100 series units.  The nosegear unit is shown being fitted.

Spring Air 100 series tricycle retracts

Nosegear unit mounting position

 

 

 

 

 

 

 

 

I’m in the process of designing scale gear for this model in Solidworks.  Here is a sample:

Scale main landing gear

Scale nosegear

Main landing gear yoke

 

 

 

 

 

 

 

 

So far I’ve only built the nosegear strut.

Gary

Fuselage done

The fuselage is finished. We’ll leave the forward top open until we arrive at a final configuration.

I put a neon yellow covering on the underside of the stab for enhanced visibility. I was a little concerned it would look funny, but I actually like it. Not sure if Dean will agree

Dean is going to be travelling for two weeks, so the first flight on solar will have to wait until he returns.

Completed Fuselage

Neon yellow stab underside

Gary

Wood Construction Complete

Here is the complete airframe. That’s Dean on the left and me on the right. Dean has done all the work on the electronics and motor/prop calculations. He’s also discovered a cool trick with the electronics to make it all work better. That wing is something! Also shown is the full 30-cell solar array and the motor/prop we are going to use.

Complete airframe

Gary

Wing panels done

The three center wing panels are done. Here is a shot of them put together with the new fuse.

Center wing panels

The outer (tapered) panels are done also, Dean built those. We’re going to do a trial fit today. The stab is also done. The tail will go together quickly. Should have the airframe done to bare wood in the next few days.

Dean is working on some mods to the electronics so that a trickle charge can be applied to the receiver battery (we’re not using the BEC). This thing will be able to fly for hours, so the receiver battery will be the main limiting factor. Sort of like *food* is the main limiting factor in a nuclear submarine patrol

Gary

Flying Solar

My friend Dean and I have been studying solar power, so we decided to build a solar powered glider. The AutoCAD workspace is below.

Solar Glider AutoCAD Workspace

Here is a picture of the new fuselage with the center wing panel with solar cells.

We should be finishing the primary wood construction in the next few days. Estimate a week to 10 days to begin flight testing. The glider will feature wingerons in addition to standard rudder and elevator. For the uninitiated, that means that the outer wing panels are all-flying control surfaces. With such a long wingspan, a glider like this can be hard to maneuver! Not sure how this part will work out yet, we’ll see.

Gary

Completing the Molds

After the plug and flange are cleaned up, you can see the flange came out PERFECT! I’m really happy with the results. Worth all the effort I think. After that we spray the plug and flange once more with PVA, and begin the process all over again, just like the first half.

High-res shot of flange

PVA applied

One more time...

The last step is to attach supports to the mold halves so they sit flat and stable on the workbench during layup. I’ve used 1/2″ plywood in the past for this. I’m trying 1/8″ lite ply this time. It’s easier to cut and just as strong when reinforced with 9 oz cloth & resin on both sides. I also make fillets of thickened epoxy before the cloth goes on.

Freshly cracked open

Mold supports added

Front supports

Gary

Mold Layup Begins

Now that the parting board is done, we can begin the mold making process. I start by placing the plug into the parting board, trying to get the best fit possible. As I mentioned before, there is a small gap in some areas, but only 1/64″ or less. I filled this gap all the way around the parting board with Silicone RTV. After that a coat of PVA mold release is sprayed on with an automotive touch-up gun.

The first two pictures show the plug and parting board after PVA has been sprayed on them. The greenish tint you see is the PVA.

Plug with PVA

Close-up showing RTV filler

The next three pictures show the first coats of epoxy going on. I use West Systems epoxy exclusively. These first two coats use a black dye and enough colloidal silica powder to thicken the epoxy to a ketchup-like consistency. The black color is to make it easier to spot bubbles when laying up in the mold later. I do two coats of this, the second slightly thicker forming fillets in the corners. After this gels, I add a layer of 9 oz. cloth and normal epoxy (no dye or thickener).

First coat of epoxy

2nd coat of epoxy

2nd coat of epoxy

After the first layer of cloth and resin gels, I lay on a thick coat of epoxy. This coat is thickened to a cake frosting consistency. It is layed on about 1/8″ thick. While this is still wet, I lay on a second layer of 9 oz cloth and resin. This completes 1/2 of the mold.

Completed mold half

Completed mold half

After the first mold half cures overnight, I flip the whole thing over and remove the parting board. I’m really pleased how the first mold half came out. The flange came out perfect! All the work on the parting board payed off. The Silicone RTV filler worked perfectly. There was no seepage of epoxy. I’ll take some close-ups of the flange area after it’s cleaned up so you can see how perfect it turned out. My iPhone camera doesn’t do too well with close-ups.

Parting board removed

Parting board removed

Flange close-up

I did have a little bit of damage to the plug were a scribed area was a bit weak and some of the primer came off. I’m going to repair that before making the second mold half.

Gary

Finish Work on Parting Board

After the microballoons fillet and fiberglass band has cured, I remove the plug.  Some cleanup is needed to get the PVA mold release off of everything. Just a damp towel does the trick.

One tip if you try this — the fillet of microballoons needs to be pressed firmly into the gap. I discovered after breaking it loose that I hadn’t completely filled the gap in some areas, causing voids.

Next I sand the parting board smooth, sanding off the fillet on the molding side.

sanding the fillet off

Once the fillet is sanded off and the parting board is smooth, I mask off the plug contact area and spray a coat of primer on the parting board, see below.

Tape applied

...and removed

close-up

After the first coat of primer dries, I use some automotive spot putty to fill any gaps or sinks, then sand smooth and apply a second coat of primer. Now the parting board is nicely finished. Ready for final sanding with 800 grit and waxing.

after 2nd coat of primer	close-up	with plug in place
fit is near perfect	close-up

I’ve tried this method before on smaller parts (cowls) with excellent results. I can see that this time with a much larger part, a perfect fit between plug and parting board is harder to achieve. I can see that there is a small gap (1/64″ or so) in some areas, so I’m going to use some filler for this small gap. I’m thinking either latex caulk or RTV Silicone. The caulk is easier to work with, so I think I’ll try that first. It’s important that this material have low shrinkage, since that will prevent a “sink” forming. But — the gap is very small so it probably isn’t that critical. Main thing is to prevent epoxy from seeping into the crack.

Parting Board Work Continues

This is the first conventional two-part fuselage mold I’ve done.  I’m trying out a method for achieving a perfect molding seam with no pegs used to support the plug in the parting board.  If this is successful, the molds should produce perfect parts with little flash and no pegs to sand off.

Work on the parting board continues. First the plug is final sanded with 800 grit sandpaper.  Then four coats of Johnson’s Paste Wax.  Wax on, wax off   Then the plug is fastened to a board with drywall screws. The screws go through holes in the board and into the end of the wing stub. Then PVA mold release is sprayed on the plug in the area around where the parting board will be.  After that dries, the parting board is set in place on the fuse center line. The parting board is supported by stacks of paper cups, adjusted to the proper height. There is a gap of about 1/8″ to 3/16″ between the parting board and the plug all the way around.  Next a fillet of epoxy with microballoons is applied on both sides of the parting board, pushing it into the gap between the parting board and the plug.  This makes for a perfect fit between the parting board and the plug.  No clay will be necessary.

Plug fastened down

Parting board in place

Microballoons application

The epoxy/microballoons is allowed to gel, then a strip of fiberglass cloth and resin is laid down on the plug and parting board. This strip of fiberglass will support the plug when it is set into the parting board for molding.

Fiberglass strip

Close up

Close up #2

Gary

Fiberglass fuselage work begins

The fuse plug is nearly ready for molding. All of the 1/64″ chart tape has been removed. After final sanding, we’re ready to make a mold!

First step in making a two-part mold is the parting board. I’m using a brown pressboard, more on that later. First step is to transfer the outline of the fuselage onto the parting board so a hole can be cut. Here are the plans laid on top of the board. Nails are used to transfer the outline.

Parting board layout

Front part

Gary