Martin Mars XPB2M-1R Scratchbuild - 1943-123 inch Wingspan

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Neons
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Re: Martin Mars XPB2M-1R Scratchbuild - 1943

Post by Neons » Sat Mar 24, 2012 10:13 pm

Mid Wing Assembly
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This is how far I got fabricating the middle wing portion in the last 2 days. I am giving this wing a rest while I do the 2 outer wings next. I want to get the plug in spars working before any covering takes place. It will be easier this way. The clamps on the wing are holding elastic pressure while the Elmers Poly glue cures tonight.
Attachments
3-24-12 Mid wing Assenbly.jpg
Middle 4 ribs and outer ribs are ply. The spars are hardwood. Leading and trailing edges are balsa. The rest are foam ribs.
3-24-12 Mid wing Assenbly (1).jpg
Bob Pacheco

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Neons
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Re: Martin Mars XPB2M-1R Scratchbuild - 1943

Post by Neons » Tue Mar 27, 2012 10:43 pm

Wing Outer Plugins
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2 days work getting them framed. I put 5 degrees washout in the wing plugins. Still have to do the ailerons and servo planning, wing float mounts, and the wing plug sockets. Use of hard woods is extensive. There will be a load of stress on these outside wings. I have also been informed my new foam sheeting is back ordered and no shipping in site. I may have to revert to 3mm foam and epoxy and glass it.
Attachments
3-27-12 Wing Outers (0).jpg
10 foot spanning a chair, stool , and onto my saw.
3-27-12 Wing Outers (1).jpg
Ailerons have to be cut free yet
3-27-12 Wing Outers (2).jpg
That is 2 Honda Wings it is spanning.
Bob Pacheco

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Neons
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Re: Martin Mars XPB2M-1R Scratchbuild - 1943

Post by Neons » Fri Mar 30, 2012 7:11 pm

Wing Joints Outdoor Size Display
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This is what I got done today. The joints are hardwood. They are boxed in for a snug fit the male parts. I had to square them to the rib surface and build as it went. I am going to put a push wire in from the leading edge in a brass tubing that goes through the male plugs. This will hold them in place securely while in flight.

Next is the wing float mounts and a sub surface box for the servos. Then back to the mid wing.
Attachments
3-30-12 Wing Joints (1).jpg
The right wing had to be carefully fitted to the male on the left. It required routing and then filing the rectangle slot with a square file. .Then fabricating the boxes to snug fit and glued then clamped.
3-30-12 Wing Plane Display (1).jpg
My garage door is 10' L X 8' H
3-30-12 Wing Plane Display (3).jpg
Dropped on the plane. A lot to go yet.
3-30-12 Wing Plane Display (4).jpg
Bob Pacheco

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Neons
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Re: Martin Mars XPB2M-1R Scratchbuild - 1943

Post by Neons » Sat Mar 31, 2012 10:28 pm

I got my float mounts and servo boxes done in the wings today. I made the wood strut frames with hardwood and balsa. Then I set them up for angle and glued them together. I guess i just had to find something more to do for tonight.

After a supper break I did start the floats. I find working with foam so easy and fast. If you looked over the float plans you would be there for a couple days with the small frames and formers let alone the finishing.. You can see them sitting on the foam block pictures. I roughed them out on my bandsaw. I think they will be done tomorrow and ready for glass cloth. I'll add some pics here when done.
Attachments
3-31-12 FoatsPrep (0).jpg
Start by tracing patterns slightly oversize on a couple a foam rectangles.
3-31-12 FoatsPrep (1).jpg
Cut one side with some edge to spare. Put the etra back and flip the block. Cut the other side out. Ready to sand to shape next.
Bob Pacheco

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Neons
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Re: Martin Mars XPB2M-1R Scratchbuild - 1943

Post by Neons » Mon Apr 02, 2012 6:29 pm

I started my sanding at 12:00 Noon here. I was done at 13:30 hours. Very easy to do. I believe yesterday I got 1.5 hours getting the rough shapes done. 3 hours total. I can also say that foam allows you to sand a nice concave shape to the bottom . Can't do that with balsa either unless it is thick or a block. I am so happy for foam. Way stronger than a balsa build up float. The 2 floats weigh in at 1.6oz. (45 grams). Time saved? Enormous. I am next going to put the hardwood screw mount in. Then work on the plywood strut mounts.
I glued in the mount stick. It just took about another hour. I am working the V strut mounts now.
Attachments
4-1-12 Foats Sand (0).jpg
Here is one float sanded to the lines. Time - 40min.
4-1-12 Foats Sand (1).jpg
Here are both. ime 1hr. and 30min. Try to build a balsa float in that time
4-1-12 Foats Stik Mount.jpg
Added a hardwood stick mount foe the V mount to secure too. I marked the float and the channeled a dado to take the stick. I used a Dremel with a 3/8 inch stone to route the channel. I glued it in with Poly glue and taped to hold it
Last edited by Neons on Mon Apr 02, 2012 6:38 pm, edited 1 time in total.
Bob Pacheco

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Neons
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Re: Martin Mars XPB2M-1R Scratchbuild - 1943

Post by Neons » Mon Apr 02, 2012 6:35 pm

Floats Assembled
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I sanded the V struts mounting sticks and screwed the V strut to the floats. I am done for now on the 2 plug in wings. The floats will be epoxyed when I do the fuselage. The floats weigh 2.9oz. each now. I have started getting the middle main wing leading edge and sheeting ready for nacelles. There is sheet balsa in this area also.The nacelles will be foam and balsa with fiberglass cowls.
Attachments
4-2-12 Floats Assmbled (0).jpg
The float is lined up and just sitting in place. The servo compartment alomgside.
4-2-12 Floats Assmbled (1).jpg
Bob Pacheco

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Neons
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Re: Martin Mars XPB2M-1R Scratchbuild - 1943

Post by Neons » Tue Apr 03, 2012 11:23 pm

Wing Plug Lock - Nacelle Blanks
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Here we have 2 operations. I like the the push in wire through the spars plugs. Planning is essential for placement. I moved them in about 3/4" from the wing joint. Better holding power for the dihedral position. Also it moves the holes away from the joint to help stop a crack across the hole and a weak spot near the joint. I used 3/32" tubing that allows a 1/16 inch piano wire to pass through.

I used a 1/16 wire on a drill and drilled the holes through the both wing spars from the leading edge. The wing has to be held in the non sagging dihedral position before drilling. The brass tube is marked and cut with a Dremel cuttoff tool. They have to be longer than the space it will fit by at least 1/8" each end to set in the wood and glued. Two plugs and 2 pieces of brass. After secured the wing is renoved and 2 small cut pieces of brass are made 3/16"long to go into the holes on the plugs. The plugs are 1/4" wide. I pushed them in with help of needlenose pliers. These prevent wear in the wing plug tips and take out any slack in the dihedral. All that is needed now is to make 2 pieces of 1/16" wire with a bend on the end. Push it all the way in. The brass guides make it line up and go right on through. Shown in the picture with a 1mm carbon rod going through. I sharpened a point on it. The brass sticks out the leading edge. I have to add another leading edge balsa molding and then fair it to the edge.

Next is my start on a sample nacelle block. I used 1 inch foam and a piece of 2 inch foam cut into a horshoe shap near the wing end. I oversized the outside diameter to 4 inches. This gives me a square inside opening about 2 inches. Two 1/4" sticks will go from the main wing spar to the firewall plywood from inside the square hollow. I will have air space for my Esc's also with motor plugs. I will shape and test fit tomorrow as this is the initial test nacelle. II could put a dowel through the nacelle and shape it in the drill press or lathe also. I may just hand shape it. If it works out I will make the other 3 nacelles. I think it is going to be a go.
Attachments
4-3-12 Wing Plug Locks.jpg
Brass tube guide and it will have piano wire rod push in and through the plugs. Locked!
4-3-12 Motor Nacelle Start (0).jpg
Rough 1" foam cut to 4" outside and 2" inside. Cut it oversize allowances.
4-3-12 Motor Nacelle Start (1).jpg
Poly glue clamped and setting up.
Bob Pacheco

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Neons
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Re: Martin Mars XPB2M-1R Scratchbuild - 1943

Post by Neons » Wed Apr 04, 2012 4:58 pm

Making My Nacelles using a Machine
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This is my first machine made nacelle. It comes out to a true shape. I found that hand sanding can be done just about as easy but takes longer. The glue lines make shaping harder to do. I have to stop and sand the glue down then continue shaping. Doing a glued up block on the drill press would have been real hard to do. A solid block with a 1/2 inch dowel glued in deeper would be easy on either machine..

I think a solid block of blue foam would have been a good way to go. I would then split in half and re-glue together again after hollowing with a Dremel or hot blade. It is possible to hollow without splitting also.

Emily nacelles were made in a solid block and sanded to shape. Works well for hand sanding. These were a piece of cake.
http://www.rcgroups.com/forums/showp...8&postcount=55
Attachments
4-4-12 Making Nacelles (0).jpg
I used a squaer foam driver with a dowel. I also put a nail across and through the dowel drive. Hot glued into the blue block A wood screw and a dowel glued in place on the tapered end.
4-4-12 Making Nacelles (1).jpg
Setup in drill press if it was to be done there.
4-4-12 Making Nacelles (2).jpg
Setup in my lathe. It has to be knife cut first to near shape.
4-4-12 Making Nacelles (3).jpg
Finished. I found my sanding bloch on the corner took it down good. Glue lines present problems.
4-4-12 Making Nacelles (4).jpg
Done!
4-4-12 Making Nacelles (5).jpg
The nacelle fit to the wing and shortened to length.
Bob Pacheco

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Neons
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Re: Martin Mars XPB2M-1R Scratchbuild - 1943

Post by Neons » Wed Apr 04, 2012 5:02 pm

This is about the foam I am using for making parts. They are both made by Dow Corning. The blue is heavier density thus slightly heavier. Found in Loew's. The pink from Home Depot is very light and low density. The both sand very well if you pay attention to sanding and the grit. I like #36 - 60 grit to rough it in.

I first use a small break a point knife fully extended and attack the foam part I am making. Stay away from drawn lines. These knives are a must have with thick foam.

I use #100 to get closer. This is where you may get scrapes and pieces if you do not clear the dust load up in the paper. If you get chunking, it is because there is grain in foam. Sand single strokes toward you or away. Change down grit size. I finish shaping with #150. This puts it smooth enough to be epoxy/glassed.

I use home made 1/2 sheet block with different grits. You may see them in some pictures. There is a new screen type sandpaper at Home Depot that sheetrock drywallers use. I may try it some time. The dust goes through it.

When possible do the sanding and roughing outdoors on a breezy day to blow the dust away from you. Shaping round objects is best done on a lathe or drill press spinning fast. . Sand lightly so it does not destroy itself in your face. Use a center dowel glued in to keep the work held steady or else something bad can happen to the part. You may not be happy about it.
Bob Pacheco

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Neons
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Re: Martin Mars XPB2M-1R Scratchbuild - 1943

Post by Neons » Fri Apr 06, 2012 10:16 pm

I got the 3 other nacelles done today. The epoxy was not totally hard but I went ahead anyway to get them done. Mounts and firewalls are next. I see wiring also coming up before I can finish the sheeting under the nacelles.
Attachments
4-5-12 Making Nacelles (6).jpg
Not glued up yet.
Bob Pacheco

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