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RE: Martin Mars Build Thread (ivansplans.com) - 2/18/2013 4:56 PM   
Roger Gray


 

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Status: offline 		Just another thought-1/16 ply to cover the forward bottom, would not add much weight and much more durable.  I have a source for 2' x 4' sheets resonable. 

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RE: Martin Mars Build Thread (ivansplans.com) - 2/18/2013 7:34 PM   
Mustang Fever



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Status: offline 		They're off by less than 1/8", front to rear. I thought maybe my centerline was off, so I checked it with a string stretched from one end to the other, no worries there.

As far as the hull bottom, I'm going to cover it all in 1/16 balsa as called for, but then I'm going to glass the whole thing to about an inch above the waterline, using very light glass and finishing epoxy. Ends up being about the same weight as 1/16 ply, but very water tight and dent resistant.

Kerfing is not bad if you have a scroll saw or a band saw with a very wide mouth. For the longer stretches I have to use my scroll saw. Takes about 2 minutes per stick, max. It's really the only way to get long balsa sticks to give you the nice curves shown on the plans. It's either that or pre cut the curved sections out of sheet stock. Problem with that is these plans have a lot of disputes. There are two places where the crosspiece lengths can be measured off the plans, and they do not agree. I decided to stick with the top view, using the distances between the various longerons, which are clearly identified. I don't think my bird matches the drawing, but it looks right, so like you said, sometimes you gotta shoot the engineers an proceed with production. I like my birds to look nice, but I'm not a fine scale type, and I'm far from being a perfectionist. I strive to achieve the "airshow/ARF" appearance. Slick, glossy and pretty. Example attached. F4H-1 bashed from a Savage Light Industries F-4C/D kit.

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RE: Martin Mars Build Thread (ivansplans.com) - 2/19/2013 5:58 PM   
Mustang Fever



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Status: offline 		Only thing left to do on the basic hull frame up is the secondary step.

I almost missed the fact that the stern tapers from bottom to top. The two halves are glued directly together at the top, but are separated by the width of the bottom former at the bottom. I made a 1/8 balsa triangle to go in the gap and make everything nice and even.


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RE: Martin Mars Build Thread (ivansplans.com) - 2/19/2013 9:25 PM   
Roger Gray


 

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Status: offline 		I can see the next construction step in the aft bottom will be very interesting.  I'm trying to mentally see the shape of how it will connect with the upper long section.  Are there any compound surfaces between the two to sheet?

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RE: Martin Mars Build Thread (ivansplans.com) - 2/19/2013 11:36 PM   
Mustang Fever



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Status: offline 		Roger:

This is a common process when building a scale flying boat. I had to do much the same when I attempted a PBY years ago. The larger flying boats all have secondary steps below the aft fuselage. Ivan included two pictures with the plans that illustrate the process. (First two below) Essentially, you sheet the curved bulkheads that are below the upper hull, then sheet straight up from the lower hull such that the sheeting intersects. It sounds complex but it's not.

Here's the last of what I did today. The hull and hull bottom are framed up. I'm now putting in 1/16" balsa gussets in all the corners so that the hull won't change shape on me when I start sheeting it.

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RE: Martin Mars Build Thread (ivansplans.com) - 2/20/2013 4:43 AM   
Roger Gray


 

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Status: offline 		 Well, that turned out very simple!  Looking GOOD!

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RE: Martin Mars Build Thread (ivansplans.com) - 2/20/2013 4:46 AM   
Roger Gray


 

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Status: offline 		Well, that turned out simple.  Looking GOOD! 

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RE: Martin Mars Build Thread (ivansplans.com) - 2/20/2013 2:09 PM   
Mustang Fever



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Status: offline 		Thanks, mon.

I did a twist test this morning, and she's a lot less flexible than I thought she would be, so no more gussets. I'm going to put her back on the 2x4s and sheet the bottom, then tackle the secondary step/upper hull.

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RE: Martin Mars Build Thread (ivansplans.com) - 2/20/2013 4:59 PM   
Roger Gray


 

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Status: offline 		I didn't know you were Jamacian?  Sorry bad joke-your last greetings.  That thing will end up tight and strong.

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RE: Martin Mars Build Thread (ivansplans.com) - 2/20/2013 5:14 PM   
Mustang Fever



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Status: offline 		Yeah, 25 years in the service will do that to you. I don't use pure "American" English anymore. Kind of a mixture.


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RE: Martin Mars Build Thread (ivansplans.com) - 2/21/2013 12:54 AM   
Roger Gray


 

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Status: offline 		Question: Do have to wet the balsa stick in the Kerf cut sections when you complete your bends?  Sorry, I told you I would be a pest.  It's just that that was the first time I have seen the technique used.  You must be retired or semiretired like I am.  I'm a Striped bass fishing guide(since 1981) and during the winter months I have the time to build and I love it!  I sold a business that was related in the fishing business and bought a small farm moved to the lake I love to fish/fly and my wife and I are 66 yrs of age and 45 yrs married.  Life is good.  I love the planes, love to fly, but really love to build from scratch.  I am going to have to start selling some of the ARF and kit planes to fund other builds.  I'm lucky that Lone Star Balsa is about twenty miles from my home.

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RE: Martin Mars Build Thread (ivansplans.com) - 2/21/2013 1:12 AM   
Roger Gray


 

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Status: offline 		This was a foam build with lots sanding and glass. 

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RE: Martin Mars Build Thread (ivansplans.com) - 2/21/2013 3:09 AM   
Mustang Fever



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Status: offline 		The kerfing is enough to make the balsa plenty flexible. Neat part about using it, once everything's lined up and sheeted, you can go back inside the hull and dribble CA or Elmer's onto the cuts and "freeze" it into position.
I generally make the cuts no more than 1/4" inch apart, and about halfway into the thickness of the material. Kerfing on two sides is tricky- you're going to have some breaks now and then, but it generally works well. My advice- take a 1/4 square stick and practice.

I'm 65 and have been retired since age 53. My wife's a little younger, and we've been married 41 years. I do all kinds of building- ARF, kits, plans, scratch. Fixed wing and helis, slow flyers to high performance. My only "job" is AEO at the local CAP squadron. I give the Cadets dual instruction on an electrified Aerostar 40, and we build and launch lots of model rockets.

Really like the Mariner. I had the plans for that for a very long time. Saw one fly at a lake a long time - ago. Pretty airplane. I think the designer lives here in Michigan. I think Jimmy Buffet has one, or used to. Big flying boat nut, that guy.


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RE: Martin Mars Build Thread (ivansplans.com) - 2/21/2013 4:07 AM   
Roger Gray


 

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Status: offline 		Going to be gone for a few days maybe, maybe you'll be able to get somemore done.  Later-have fun. 

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RE: Martin Mars Build Thread (ivansplans.com) - 2/21/2013 4:21 PM   
Mustang Fever



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Status: offline 		Be careful out there. I'm off building for a few days, anyway. Sprained my foot and can't get down the stairs.


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RE: Martin Mars Build Thread (ivansplans.com) - 2/25/2013 12:40 AM   
Mustang Fever



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Status: offline 		Finally got the bottom all sheeted. (Back to the secondary step, anyhow.)

Will start sheeting the semi circular parts of the aft step tomorrow. I plan to use 1" wide strips of 1/16 balsa, almost a strip planking operation.

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RE: Martin Mars Build Thread (ivansplans.com) - 2/25/2013 3:45 AM   
Roger Gray


 

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Status: offline 		Looks like the foot is better, that's good.  The next phase is going to be interesting.  Keep her coming.

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RE: Martin Mars Build Thread (ivansplans.com) - 2/27/2013 3:00 AM   
Mustang Fever



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Status: offline 		Well, the 1 inch strips did not work out, so I tore them off and started over.

I'm using a technique I had thought about before starting- to only sheet between each pair of bulkheads instead of trying to go the whole length of the aft hull. I now wish I had followed my inclination to make the half round bulkheads out of 1/8 balsa instead of 1/16th as called for. Now I've got to paste 1/8 doublers onto each one so that they'll be wide enough to glue the sheeting onto from both directions.

Ivan's pics make this look very simple, but the constantly changing shape and volumes involved make it really tough. For me, anyway. However, once I get out from under the secondary step, I might be able to go the rest of the distance to the stern with a single piece.

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RE: Martin Mars Build Thread (ivansplans.com) - 2/27/2013 3:45 AM   
Roger Gray


 

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Status: offline 		It will all work out no matter which way you do it.  How long is the section at the point of the triangular sheet piece you show installed to the the very end of the bottom of the hull?  The more seams the more filling and sanding.  I HATE SANDING!  It gives me sinus problems.  Keep her going.

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RE: Martin Mars Build Thread (ivansplans.com) - 2/27/2013 1:07 PM   
scale only 4 me



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Status: offline 		Bob, When I've built round planes and floats I use 3/32 balsa cut into about 3/8" strips planking. It's pretty easy to get the 3/8 strips to bend and go where you want them to and the 3/32 thickness leaves enough to sand for a rounded shape.. IMO getting large piece to conform to compound curves is impossible to make look good.

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RE: Martin Mars Build Thread (ivansplans.com) - 2/28/2013 6:01 PM   
Mustang Fever



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Status: offline 		I realize now I had got into the habit of sheeting fuses with the largest possible pieces, front to rear. Don't know why or how. The instructions for my last build, the Phantom, had me do the sheeting between pairs of bulkheads only, and it really came out nice.

Seems to be working nicely, here, too. I'd post a picture, but RCU is being crappy and I'm out of patience at the moment.

The problem with doing any kind of full length sheeting or strip planking on this model is that the hull framework is so flexible at this point. It's a real challenge to keep it straight, and any kind of pressure applied while doing large pieces of sheeting is going to distort it.




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RE: Martin Mars Build Thread (ivansplans.com) - 2/28/2013 11:54 PM   
Roger Gray


 

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Status: offline 		Are you doing some on each as you go or just one? 

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RE: Martin Mars Build Thread (ivansplans.com) - 3/1/2013 12:58 AM   
Mustang Fever



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Status: offline 		I've got 5 pictures showing the process, but RCUs stupid server isn't working right. Maybe tomorrow.


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RE: Martin Mars Build Thread (ivansplans.com) - 3/4/2013 2:37 PM   
Mustang Fever



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Status: offline 		Well, that's it. I'm done with RCU. This weekend I couldn't even sign in, and the upload just burned up a meg from my data plan and still doesn't work.


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RE: Martin Mars Build Thread (ivansplans.com) - 3/8/2013 1:49 PM   
Mustang Fever



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Status: offline 		Well, the photo upload started working again, so here's the progress to date. I think I remember the steps I took for these pictures. I've not been working on this bird for awhile as I was finishing my Phantom.

The first thing was to get all the half round bulkheads sheeted so that sheeting is under the entire outside edge of the aft step.

Next I put a straight edge alongside the aft step and measured down to the half round section at one inch intervals. This allowed me to draw a sort of pattern. It didn't fit perfectly at first, but didn't require too much modification.

You can see, though, that somewhere I went wrong as by following the shape of the aft step with the sheeting, I didn't get anywhere near the actual aft end of the structure and it didn't look right at all.

So, I put in a cheater piece on each side, and played around with filler and small pieces of balsa until it looked right. I think you can just make out the forward edge of the cheater piece in the fourth pic.

The Futaba 8J radio arrived yesterday, and for fun I went ahead and set up a file for the Mars, and established the three mixes necessary to get differential thrust for steering when taxiing on the water. I selected one of the switches to enable and disable the mixes. It was easy. The jog dial system Futaba uses is very intuitive, and anyone who's played around with computers at all can easily handle the menus.



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