Martin 167 Maryland design and build. - Page 5 - RC Groups
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Dec 08, 2008, 08:42 PM
scratchnhover's Avatar
Look for "A" grain stock if they have it. The nose piece looks like C grain which doesn't conform well to curving surfaces and snaps easily when doing so.

The A grain will have long, straight grain running lengthwise down the board.

Planking works out well for shapes like these- especially ones that are complex curving surfaces (like a dome) rather than simply a curving surface (like a cylinder).

Typically the material suppliers will send you a mixture of A, B and C grain unless you specify otherwise (and typically pay a premium).

Our LHS usually has the A grain but it is often quite hard and heavy wood. If you can't find it, use your coupon to order from Balsa USA!

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Dec 08, 2008, 08:47 PM
Two left thumbs
Here's a site showing grain types: See both pages one and two.

Dec 08, 2008, 09:33 PM
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RyanPSU21's Avatar
Thanks for the link. I'm kind of aware of the 3 types.

This is a sample of the end of one of the sheets. This is typical of the end maybe 15 sheets that I got from Lonestar. They were all already split about a foot from the end that is like this. As you can see in the picture it is more or lass A grain along the bottom inch here and C-grain in the top going to the right. The rest of the sheet is going to the left and is mostly A-grain. In the split region the lower half below the split is very flexible. Above the split is very stiff. The nose section sheeting is from one of these pieces of wood from the 6 inches next to this section where the flexible portion was aligned to the fuselage side and stiff section is on top. Whenever I pull these sheets out I have been cutting off the 12 to 14 inches that is split and tossing it in the scrap bin for whenever I need to cut a small part.

The sheeting on top of the fuse behind the cockpit area came from a different sheet that was A-grain that came from the LHS. I can usually find okay 1/16" sheeting there. I've found I dread 3/16" or thicker coming from there as it always has a strip somewhere down the sheet that is maybe 3/8" wide on a 3 inch sheet that is rock hard and nearly impossible to cut with a #11 blade short of grabbing the knife and using a stabbing motion to saw bit by bit past it.
Dec 08, 2008, 10:02 PM
scratchnhover's Avatar
Yeah, those are tough to work with for sheeting Ryan. Typically in an order you'll only get a couple really good ones for this- truly straight A's- and the rest are marginal and not up to the task you have at hand. I wouldn't want to say anything negative about the company that suffered the loss but I've been happy ever since I switched to Balsa USA!
Dec 10, 2008, 08:50 PM
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RyanPSU21's Avatar
Yesterday and today I got the rest of the top sheeting done. Today I started making the bottom fuselage formers. I made one plywood for the tailwheel support. I am just going to either go with a small nosewheel bracket or brass tubed stuck to the plywood former. Every picture I've found showing a Martin167 in the air shows the tailwheel hanging down so I'm assuming from that it either didn't retract or tailwheel retract wasn't used for whatever reason.
Dec 10, 2008, 09:00 PM
Übung macht den Meister..
Deuce's Avatar
Originally Posted by RyanPSU21
... Every picture I've found showing a Martin167 in the air shows the tailwheel hanging down so I'm assuming from that it either didn't retract or tailwheel retract wasn't used for whatever reason.
Interesting, as the last pic clearly shows an opening, that might be a wheelwell!

Nice work and good progress so far!

Dec 10, 2008, 09:39 PM
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RyanPSU21's Avatar
The plastic kits I have pictures of and a few full scale pictures show a small well there. The last picture kind of shows the fuselage where the tailwheel is attached but in that photo there doesn't appear to be any well at all. Some drawings I have clearly mention a retractable wheel. But all in flight pictures and most of the artist drawings I could find all show a tailwheel hanging out there.

From what I can tell in the pictures and drawings that maybe there is a small well there for servicing the tailwheel mechanism or steering but not a retractable tailwheel.
Dec 18, 2008, 08:15 PM
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RyanPSU21's Avatar
I finally got some more done on it tonight. I got all the bottom fuselage formers on, made the tailwheel mount and added some reinforcements. I added some of the stringers but ran out of wood tonight before I could finish all of them. I need 2 more sticks from the LHS tomorrow so I can finish the stringers.
Dec 22, 2008, 08:39 PM
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RyanPSU21's Avatar
I got some more done. I made the front wing hold down plate for the dowl to go through. I haven't quite decided exactly how the back of the wing will bolt on. Probably I will cut out some sections of the 1/4" balsa saddle and glue in some hardwood blocks. I threw some 1/64" plywood reinforcements on in the areas where the 1/4" square fuse longerons have joints in them and around the front and back of the wing saddle. I got the bottom fuselage sheeting in place so the fuselage is essentially finished now until I have the wing and tail feathers ready to mount. I weighed what is done so far and it came in at 10.5 ounces. Not too bad considering the size of the fuselage.
Jan 05, 2009, 08:41 PM
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RyanPSU21's Avatar
I finally had a chance to get some more work done tonight. I was gone in South Carolina to visit my parents for Christmas week and then got Food Poisoning right after getting back here the day before New Year's Eve and am finally feeling okay enough to get back to work.

I got the horizontal stab parts cut out and setup ready to get gluing tomorrow.

I got the motors and ESC's for Christmas for this from my Dad. The powersystem, retracts and radio parts are all accounted for and ready to go on this now.
Jan 06, 2009, 06:47 AM
eye4wings's Avatar
Those ESCs are pretty chunky! I bought a couple from GiantCod but haven't used them yet. Very cheap anyway.

FWIW my 96" DC-3 uses scale three blade props and 3s lipos with the smaller, slightly higher revving TP motors - it has more than enough power for scale-like flight at about 40A. So with 4 A123s you should be well powered.
I make up my own three-bladers from two blade for cheapness - especially when I need two. There's a photo with the first part of the published article in September 2008 RC Model World if you are interested in the jointing.
Jan 06, 2009, 06:15 PM
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RyanPSU21's Avatar
I've got one extra of these ESC's that was in my Albatros Dva. Part of the reason I went with these so I'd have a spare already. They are big but the plane should have plenty of space for it.

That magazine is very hard to find over here. How hard is your Hub to make? If it involves any kind of machine or most power tools beyond a dremel or hand drill I don't have access. I may still go with some APC or MA 3bladers when I am further along and have something to mount the motor to, to test things with.
Jan 11, 2009, 02:49 PM
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RyanPSU21's Avatar
The horizontal stab and the vertical fin are mostly done today. The horizontal still needs some sheeting in the center section. They both need a heavy dose of 80 grit to get the leading edge shaped and trailing edge tapered down.
Jan 12, 2009, 11:36 AM
What could possibly go wrong?
nickchud's Avatar
Wow! this is serious! What a project. Good luck!

Jan 12, 2009, 08:33 PM
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RyanPSU21's Avatar
Originally Posted by nickchud
Wow! this is serious! What a project. Good luck!


The wing has been started now. I decided to go with 3/8"x1/8" spruce for the rear spar and 1/4"x1/8" basswood for the front spar. My B24 with about the same wingspan and quite a bit higher wing loading had just single set of 1/4"x1/8" spars so I should have more then enough. The wing root ribs on this are about 3 times the size of the B24 ribs so that should help a lot structurally as well since the spar moment of inertia should be quite a bit larger. There will be a 1/16" ply joiner on each spar set going out to the 5th rib where the engine nacelle and landing gear mounts will be. The spars are tapered a little bit at the center so that the ply will go around the curve that is at the center section. Due to the landing gear wheel location spars that were straight at the center section wouldn't work. Another bit of fun tonight was that the spars especially the rear spar are quite a bit off the ground. I am really glad I put in the alignment tab at the back of the ribs as otherwise trying to get the ribs glued onto the spars straight would be a real chore. That was one bit of unhappiness with last year's B24 build was that the trailing edge was not quite straight due to not really having a good way to keep the ribs aligned while gluing onto the spars and putting the sheeting on.

I am hoping to get both ESC's, the retract air cylinder and the retract valve and servo all mounted to the wing so that it minimizes the number of connections to be made and to avoid needing a disconnect in the air system for the retract. I am not sure where that would then leave the fill valve at though I think I could hide it coming out the bottom of the fuselage or atleast have it not that noticable.

The other thing tonight I am looking at is how hard it would be too add the bomb bay to this and have the ability to drop a few 500lbers with it. In looking at the photo and the bottom of my fuselage it looks like the 4 500lb bomb load will fit without going into the bottom wing sheeting or not much anyways. Looking at the photo it looks like the scale location of the bombs when loaded is probably 2 rows of 2.

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