Winter Build 2018/19: Hangar 9 P-47D Razorback

[wilmracer]

Excited to see how you tackle the retracting landing light. The retraction method would be relatively straightforward for someone with your mechanical skills. Have you thought about how to activate the light when it drops? I haven't seen the inner workings of too many folding landing lights. I know some have used contact plates for power, others have used radio controlled switches, and I know some lighting boards have options for landing lights included.

You thinking 3D printed for the whole light assembly? Or use a found part from a flashlight? Watching with interest

 

[willsonman]

The simple way to tackle it is to use an offset door hinge. You can pick up a contact switch pretty easy from Mouser, Jameco, or digikey. It would be the kind where it is on in the open position... most switches operate in the closed position. If it is positioned right on the lip of the balsa skin then when the light is retracted it will compress the switch and turn off the light. Light comes down and it will complete the circuit. A 3D printed part will work perfectly for this and a LED will keep it light and simple. 9g servo should be enough for this work.

 

[wilmracer]

The simple way to tackle it is to use an offset door hinge. You can pick up a contact switch pretty easy from Mouser, Jameco, or digikey. It would be the kind where it is on in the open position... most switches operate in the closed position. If it is positioned right on the lip of the balsa skin then when the light is retracted it will compress the switch and turn off the light. Light comes down and it will complete the circuit. A 3D printed part will work perfectly for this and a LED will keep it light and simple. 9g servo should be enough for this work.

Awesome. Sounds like you already have this figured out. Can't wait to see it implemented.

 

[willsonman]

Got everything sanded down last night. There were just a couple of spots that required some elbow grease but nothing too major.


Having an option for droppable items from the pylons is always a favorite of mine. The 76 gallon fuel tanks were a perfect option as they are fairly small. This is good for two reasons. 1: They can easily fit on a standard 220x220mm print bed and 2: the smaller profile equates to less drag. The teardrop shape is also good compared to the lager bullet-shaped tanks. Only took about 20 minutes to draw it up and there are two halves that are easily glued together with CA. First test print in PLA was OK. I set the wall thickness to the minimum to help save some weight but at some angles this is just too extreme. I've doubled the wall thickness and will do a test print again to confirm this is the appropriate action.


I also got the reference drawing printed. It is formatted for 44"-wide paper so if you choose to use it at a copy center, be prepared for some crazy costs. What is nice about these prints is that I can take precise measurements for reference lines for panel lines, rivets, and placement of panels. Placement of the inner gear doors and landing light can also be easily extrapolated from the drawings as well.

 

[willsonman]

All the wood has now had a single coating of sanding sealer. This simply is a coating to prevent soaking of additional WBPU for glass application and resin to fill the weave. It also hardens the wood surface a bit while I go through modifications.

With the wood more stiff, I took to removing the wheel well liners. They are simple polystyrene that has been vacuum formed and glued inside. You can see the amount of glue is good and removal was pretty easy however, they were not salvageable after removal.


Further still, after having to rebuild the hotend of my printer, I got good flow of the filament and I was ready to do an ABS print of the fuel tank. This is just the bottom half but the thicker wall seemed to solve all of the issues I encountered on the test print. With the ABS print it will withstand summer heat better and also be able to be sanded/treated with acetone to be super smooth.

 

[willsonman]

Nothing done over the weekend. I did get another box of parts from HH that will allow me to refine some detail points now. I need to get the glass applied before I tackle them. Our club needed a new shed to store our mower so we constructed that and I'm also working on moving the shop around for some logistical reasons. After working in the shop for a couple of years now and looking at video work, I need to re-arrange to allow for better work flows to keep everything more organized.

 

[DamoRC]

Looking forward to seeing this one shine in the sun. Gonna be great!

DamoRC

 

[willsonman]

I got the bulk of the shop reorg done last night. Lots of cleaning done and some organizing yet to do but there are a couple of changes that were needed:

1: The location of my printer previously was across the room from a vent duct located on the ceiling. I often had issues with ABS prints lifting from the bed because the cooler air from that vent would make it's way over and cool the part too much and lift. I do not have an enclosure to regulate the temps but the simple solution was to move it to a corner, behind the path of the vent and where less turbulent air would be.

2: I added a table. With the computer to focus on print work (3D and plans) I needed a more dedicated spot that would not be cluttered with sharps and other building activities. So a smaller table was set up to support some new computing equipment and the 3D printer. This required that I move the large-format printer across the room.

With these activities done, I started my first final print of the oil cooler/ waste gate. It came out perfect. I used 0.1mm layers on the part with 0.2mm layers on the supports. ABS does not bridge well so supports were required. I wanted to test the printer's new location and performance and I was right... no lifting or any hint of it.

I have also drawn out the location of the inner wheel well flaps on the wings. Using the reference drawings and making them slightly smaller to accommodate the way the wings plug into the fuselage, it will look and operate seamlessly. I also took a look at the wing pylons again. I need to wrap up my ABS print work for now and print my release mechanism to see if it will even fit in the pylon. It's done with PLA to avoid the part shrinking. The tolerance inside the mechanism requires it.

 

[willsonman]

I thought I should update this thread so that anyone following along will know that I'm not dead. It's pretty unusual for me to provide updates that are a few days apart, let alone nearly a month! Life has been off-axis as of late but I have been making SLOW progress.

First off, I did manage to complete organization and cleaning after shifting things around in the shop.


In terms of work done on the aircraft, I've been able to print off the top portion of the fuel tanks. I still need to glue the two halves together but they are done. I've purchased a set of new nozzles, including a 0.2mm one for the high-detail work that needs to be done. I've been doing test prints to dial in the settings on the smaller nozzle. Things like wipe, retraction, and extrusion percent all need to be dialed in to make the print quality the best it can be.

As I've been fiddling with the printer, I've been glassing all of the wood parts. The H-stab, elevators, ailerons, flaps, hatch, and fuselage have all been glassed with WBPU. The glass was applied AFTER I had applied a single coat of WBPU and allowed to fully cure. This was done to help save some weight as I did not want to saturate the wood with an excess of WBPU or epoxy. All I have left to do is the wings however I do need to add balsa skin material to the openings on the bottom. Before I can do that I need to install the navigation lights in the wingtips, work out the wheel well doors, and finally figure out the drop mechanism for the pylons. Having access to the interior of the wing just makes these additions easier.



I've also looked into the fuselage side intercooler doors. I'm pretty sure I can animate these as well and will likely be 3D printed along with some other hardware.

 

[willsonman]

Coming back from my conference for work I felt much more rejuvenated to work on this project. So, lets get into it.

The fuselage requires the most amount of re-work. It needs details that are lacking in the base version so it was time to cut. First off was the exhaust scoop. the stock one is shaped fine but the stock location was a bit too far aft from what my 3-view indicated. I measured for the location and traced the part on the center line. I cut out an undersized hole and used my dremel to create a recess for the fiberglass part to seat into. I used a sanding wheel on the dremel to remove excess material from the scoop to make it functional to vent air out of the fuselage. There will be more of this later. Some CA affixes the scoop after roughing up the surface and spackle applied to blend it into the balsa.


Moving along, the OCWG part needed its hole and again, using my reference 3-view I measured for its location and began cutting the balsa with a razor blade. As you can see, there was a ply former along with a corner of the equipment tray in the way. Since this was fairly minor structure, I decided to just cut it away with my razor saw. The fitment will be blended but I'll need to make the functional waste gate valve and oil cooler door for each side.


Also of note, I measured and penciled the location of the intercooler doors on the sides of the fuselage. This feature is entirely lacking in the stock model. This will be functional as well providing additional venting for the fuselage. More development on this later.

 

[PsyBorg]

I just caught up with this and may be a tad late with this info but have you looked into the foam inserts used for rc monster truck tires? The have different densities and could easily be formed to match the rubber for this build.

Also I was thinking. If you use rubbing compounds alot on the finish eventually that will wear thru. What about finish shining and maintainance using Mothers like we did for car and motorcycle chrome and polished aluminum.

 

[willsonman]

Both are good questions.

I’ve observed that you can make neoprene discs as tire inserts and you can increase the amount of resistance by adding layers of it. This also will increase tire bounce so you have to balance out what you add.

The rubbing compounds will not be used to continually re-finish the surface. It’s a one time deal. You can seal it with a clear coat but you can still get oxidizing under that. Mother’s polish could be used as well but I will be adding details in paint so that’s a no-go as well. My plan is to use a product called sheila shine. It’s an industrial metal cleaner and polisher in one with no abrasive properties. It’s also not oil-based so there is no risk of it creeping under the paint.

I know the finish will not be perfect forever but that’s not really the point. The point is to provide a systematic and comprehensive approach for all to learn. I still have yet to find this in any RC repository. Tips and tricks for application as well as step-by-step instructions all in one place as a reference. Snippets here and there are fine but a single location of information is invaluable for such a difficult technique.

 

[wilmracer]

Those look SO much better than stock and the fact that they will be functional is sweet. Intercooler doors will add a lot of scale to it too.

Also super interested in your results and thoughts with your aluminum application. Flite Metal looks great but is $$$$. One day I want to do a bare metal finish like this and I'm eager to see how yours turns out

 

[willsonman]

Yeah, I think there is a LOT of interest in this aluminum covering but again, there is so much sporadic information out there it does not lend itself to be very approachable. I really hope I can make a good attempt to address this.

 

[PsyBorg]

I have been pondering the metallic coverings. I am bored today with the lack of parts for repairs and the rain stopping more plank attempts at flying.

I am going to carefully cut some scale size panels out of aluminum foil and see if working that small allows for smooth application. Might even be able mate edges in a way to accurately reproduce seams.

Then may be even try adding grains of salt in a rivot pattern in the spray glue before adding each foil plate.

I know I am goofy but as I said it's one of those days where creating something to do is a necessity.

I have plenty of scrap foam as well as a few cheap balsa panels from tangerine crates to mess with so we shall see what comes about.

 

[willsonman]

I had minimal time to work on this last night but I have finally gotten my printer to the point where I can actually print again. During moments of heat-up of the bed and head, I assembled the drop tanks. Sanded the lip and thin CA.


As you can see from this pictured print, there is a tad bit of retraction work to be done but using the 0.3mm nozzle is working to get this smaller part more accurate and less work in post-processing.

 

[willsonman]

Update of the sporadic progress I've made over the past several weeks.

 

[willsonman]

While running the printer I started on prototyping the OCWG animations.

A cardstock template was generated for the OC door and then traced onto a Mountain Dew can. A small tab extension was added on one side for a control arm. Fitting was good so I moved onto the waste gate valve as it was trickier.


I started off by placing the print over the can, tracing the circle size for the valve, and cut out circles that were needed. I used a cotter pin from my stash to provide a means to sandwich the circle in and provide the scale look. Using a dremel, I removed some material from the print to drill holes into the print for the cotter pins to pivot inside. I got good rotation with minimal resistance. I needed an extension for coupling to the servo so I cut a small piece of brass out and brazed it to the end of the cotter pin.


I had to play a little with the pivot point but hinging in the middle got the movement that I was after. I'm fairly sure I can remove the ink from the can material with acetone too. What is not shown here, but at the end of the video posted above, is a linking wire between the door and the valve. While this was not how it actually functioned, It was simple to just have the movements tied together. I've got a good idea for servo placement and I'll set it up so that the servo for each side is in a Y to operate off of the throttle channel.

 

[rockyboy]

At the club auction last weekend I was almost able to pickup this exact ARF to follow along, but I already had a couple other purchases on my tab and stepped out of the bidding at $80. I think it went for $130 final sale. It's a good looking plane even stock

 

[wilmracer]

At the club auction last weekend I was almost able to pickup this exact ARF to follow along, but I already had a couple other purchases on my tab and stepped out of the bidding at $80. I think it went for $130 final sale. It's a good looking plane even stock

Even at $130 that is an amazing deal. The ARF retails for $399!