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Jun 07, 2007, 10:51 PM
start slow and taper off
falconhob's Avatar
Discussion

Martin Mars slow build thread


Well, after stumbling across Perry's Mars Build Thread a few months ago, and then following Luke's wonderful Solent thread, I went ahead and ordered a set of plans for the Martin JRM Mars.

I've loved these planes for a long time - we used to summer vacation up at Sproat lake when I was a kid, and every time I heard the big radials fire up, I FLEW down to the beach as fast as my 5 year old legs could carry me so I could to watch them taxi down the arm of the lake.

Since then, I've been flying r/c for 25 or so years, the last 10 primarily in pattern Some of us pattern guys actually love scale, indoors and sailplanes too! The one thing about pattern is you learn to build LIGHT. Really light. Stupidly, expensively light... the primary difference being the strength required is quite a bit different in a model like the Mars, so the techniques donít carry over all that well, however the obsession with grams never goes away.

Anyway, it's been at least 10 years since I built a kit, and the closest thing to scratch building would have been a SIG King Kobra "craftsman's kit", where (presumably to save money) they just print the parts on the wood and you get to cut them out thus proving that you were indeed a craftsman. I've never scratch built anything like this, but I figure if Iím going to try it, I might as well do it on a project that I find inspiring. Of course, that logic is on par with sitting down at the piano and attempting a Mozart piece with no previous training, but I figure the downsides are about the same; some modest embarrassment for me and a general discomfort for those unfortunate enough to be in the audience.

The other thing about this project is that Iím going to take my time. I figure this is going to take at least a year to build- I'm not in any rush! If it's a while between posts, it's because life is getting in the way again. I'm also pretty green at posting pics and such to the forum, so please bear with me.
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Jun 07, 2007, 10:57 PM
start slow and taper off
falconhob's Avatar
First, to get a quick win, I chose to start with the tail feathers. It was at this point that the first obstacle presented itself - I had to figure out how to copy the parts from the plans to the wood. After researching on the net and finding the acetone rub technique and the photocopy/ironing technique, along came Perry (with the first of many project saving tips) to the rescue. He suggested cutting out patterns from light acetate. After rummaging through our local Michael's I found a 10 pack of plastic "portfolios" artists use to cart around their work. The package was $5, and provides enough sheet plastic to easily do 3 planes this size (or one, if you goof up as much as I do). The cool thing is if I ever want to make up an entire Mars out of acetate, I just have to glue it together!

After tracing and cutting out the plastic patterns, I snagged a felt marker from my kidsí massive collection of ďscrap bookingĒ supplies to trace the patterns onto the wood. Fortunately, I have a rather large stash of contest grade balsa on hand, (one of the other reasons I undertook this project Ė no wood costs!) so I should be able to get this thing in at a reasonable weight.

I should mention that while at Michaelís, I nabbed a 2x3 cutting matt, and a box of 100 #11 blades., which makes cutting out the pieces much easier as they donít shift around.

After tracing the ribs and end pieces onto the wood I used the exacto to cut around the inside of the marks, lightly sanded them to get the shape correct, and after some fiddling to get everything to fit, glued them together. Later Perry mentioned to me that the structure needs to be reinforced a bit, so Iíll be installing some 45í lattice pieces to strengthen things. Iíve also not finished sanded them as experience has shown that Iíll bonk the things into the wall or doorways several times before I reach the covering stage.

https://www.rcgroups.com/forums/show...=1342873&stc=1
Last edited by falconhob; Jul 22, 2007 at 01:05 AM.
Jun 07, 2007, 11:00 PM
start slow and taper off
falconhob's Avatar
With that ďquick winĒ under my belt, I opted to start the fuselage next. The key to success here is a balsa stripper (I have a master airscrew, however there are others available that may be even better) and the cutting matt. Most of the construction is 3/16Ē by ľĒ sticks, so strip up a couple of 1/4Ē sheets to 3/16Ē wide. Just my preference; the narrower the strip the better the cut.

You can frame up each of the sides in two or three pieces; I opted for the 2 piece approach. If you prefer, you can build the lower rear frame of the hull step seperately and glue it on later. The rear top of the fuse is in this picture just for information. In hindsight I would recommend not gluing the 1/8Ē ďstripe stripĒ until you get the upper rear fuse glued on, as itíll be easier to keep it straight.

https://www.rcgroups.com/forums/show...hmentid=&stc=1
Last edited by falconhob; Jul 22, 2007 at 01:06 AM.
Jun 07, 2007, 11:04 PM
start slow and taper off
falconhob's Avatar
Basically, itís just a box, and after a couple hours of cutting and gluing, youíll end up with something like this. Iím using a magnetic building board (no, theyíre not just levitatingÖ) which makes life way easier for lining stuff up. No pins! The standups are a little short, but they get the job done. And yes, I keep my laptop screen saver running through 30 or so pictures of the Hawaii Mars to stay inspired.

I also had a heck of a time getting the nose trapezoid size correct Ė the two views on the plans are quite different. In the end I wound up with this, which seems to look about right.

https://www.rcgroups.com/forums/show...=1342888&stc=1

https://www.rcgroups.com/forums/show...=1342889&stc=1
Last edited by falconhob; Jul 22, 2007 at 01:06 AM.
Jun 07, 2007, 11:07 PM
start slow and taper off
falconhob's Avatar
Next up is the top cross ribbing, which was pretty straight forward, and the joining of the rear fuse step lower sections. I neglected to snap any pictures between the box stage and this stage, so by this point Iíve added the top rear fuselage side pieces, the front and rear top formers, flight deck, and roughed out the battery hatch. I didnít like the profile of the hatch as it didnít have the slope of the real mars, so I changed the formers a bit.

*edit - in hindsight, I would suggest using a light balsa block in front of the flight deck, as it will be much easier to shape properly later on.

https://www.rcgroups.com/forums/show...=1342891&stc=1

Next up is building the flight deck superstructure, which I tried several different ways before finally just building the thing in place. I still have to put the top pieces on, and then figure out a way of getting the windows in place!

https://www.rcgroups.com/forums/show...=1342892&stc=1
Last edited by falconhob; Mar 26, 2008 at 04:57 PM.
Jun 07, 2007, 11:13 PM
start slow and taper off
falconhob's Avatar
For a little inspiration, I put the pieces together to see how it looked. Pretty cool! Youíll note the sheeting on the upper rear of the fuse; this comes after installing the lower rear formers and applying plenty of windex to the sheeting before bending into place.

https://www.rcgroups.com/forums/show...=1342895&stc=1

That pretty much brings things up to date; itís now sunny and warm so Iím out flying my GP 182 electric conversion or practicing for the Fatherís day pattern contest. If the rain returns, Iíll probably start on the wing, as it would be nice to get the whole structure looking like a plane for our public air show in August.

https://www.rcgroups.com/forums/show...=1342896&stc=1
Jun 08, 2007, 12:13 AM
AMA 670207
Rudderman98's Avatar
Lookin Good!

Perry
Jun 08, 2007, 01:34 AM
Registered User
LukeZ's Avatar
falconhob, very nice work indeed! Welcome to the group and I'm definitely signed up for this ride.

It's very exciting to see another of Ivan's birds being built, and what's more you're in the Northwest so you can bring it to Chilliwack! Maybe next year we can have three Mars and three Solents lined up on the beach.

Your work looks first rate to me, though I certainly know how it is to feel a bit inadequate for such a massive job. But you've made a cracking start and looks to me like you're on a roll. How long have you been at the build?

Very smart too, waiting until you have a bit to show to begin the thread. This gets all your viewers excited, who in turn will keep you at it when you get worn down.

Here's a picture of the Mars to motivate you; I thought at first this might be the same one as in your avatar but I believe it's slightly different. I need to see if I can order a print of this one as it's so spectacular.



Luke
Jun 08, 2007, 02:27 AM
Registered User
LukeZ's Avatar

double post - oops


...
Jun 08, 2007, 03:18 AM
Student of Ivan
mountainman2442's Avatar
Nice to see another one of Ivan's plans coming together! I'll be watching this thread as well. My Mars plans are in line to be built, just not sure of when...need to finish the Solent first.

John
Jun 08, 2007, 05:31 PM
CP140 NAVCOM
knight of Ni's Avatar
Lookin good!... just remember not to overbuild it... Most people look at the finished structure and think that it's too flimsy (like there's not enough there). This is the magic that is the guru Ivan... it'll fly just beautifully if you keep the weight down.

Mike
Jun 08, 2007, 08:45 PM
start slow and taper off
falconhob's Avatar

plan to keep it light...


Thanks for the advice and support! I know I'll be needing it over the course of the build...

After researching the 600 series motors and gearboxes, then hearing that Ivanís Mars had been re-powered with the Jamara 480 pro BB and MP Jet gearbox setup, I decided to go that route. I contacted John Swain at Fanfare Electric flight supplies and ordered the motors and gearboxes. He knows his stuff, as we went through several possible motor / gear combos before deciding on 4.09:1 with the Jamara pros. As an added service, if you order both the gearbox and motor set from John, he runs in and assembles them for you, which is a nice free service.

I really like the scale look of the varioprop 4 blades on Perryís Mars, however it turns out they donít make them for a 3.0mm shaft, which is what the MPJ gearboxes have. A polite email to Christian Ramoser at Varioprop was all that was required for him to do a custom run of four 8B hubs drilled for the 3.0mm shaft. I think he charged an additional 5Ä for the service. Through an error (completely on my part) I managed to order left hand rotation props, when I wanted RH rotation. I shipped them back and they swapped them for me no problem - Iím very happy with their service. Iím running the 10.4Ē diameter blades, and will be pitching them at 6Ē as airspeed is not the goal here, static thrust is. Not sure what the load will end up like, but weíll soon find out! Worst case is I have to drop to the 9.9Ē or smaller diameter blades.

Last up is the power end of the equation. After hunting high and low for a brushed controller which could handle 6S lipo (i.e. 18v under load) and 30 amps in the series-parallel wiring configuration, I settled on the Jeti JES 450. This unit is rated at 30 cells and 45 amps, so it should be good. However, it is not lipo friendly, hence my next acquisition, the Dimension Engineering SmartBEC. This little gem saves me the weight of an rx pack, switch, etc., and also has a feature which allows a non-lipo friendly ESC to behave like a lipo enabled unit. As a bonus, it is also lighter than the UBEC, and their shipping is cheap! (sorry, my inner accountant is showing through again). Iím going to get one of these for my 182 as well.

The final piece will be the battery, and for that I need to determine what capacity I need. Once I have that figured, IĎll look for a 6s pack that has the C rating to handle the anticipated 24A load, and look for the lightest pack.

Given the large amount of wire in this model, I did spend some time working through what gauge of wire would offer the best weight/power delivery compromise. I want to get the max out of these motors, so I traded some weight for power delivery, and ordered up a few packages of Astroflight 13g wire, as it seemed to be the best deal per foot. I do still need to source some ferrite chokes, and would appreciate any advice on running the wires (twist them? If so, how tight?)

As you may have noticed, the underlying theme here is light, since I want to run the lower power system. Hopefully I can get this project in under 10 lbs. No small challenge, but I think it may be possible if Iím VERY careful.

For covering Iím going to try the Doculam and paint; I snagged 3 rolls of 1.5 mill 27Ē off ebay (1500í!) so Iím set for several lifetimes. For painting, Iíll be using the acrylic enamel apple barrel paints applied with my CO2/Paasche airbrush system. The CO2 ensures absolutely no moisture in the paint and applies the product cold; this seems to really reduce the overspray issues compared to using an air compressor system. Itís a simple system, a CO2 bottle, a co2 valve assembly from your local u-brew beer store, and some adapters to get to your airbrush.

Servos and receiver Ė I have a few of the Berg 4L receivers, however Iím not sure if theyíre up to the task. I may go with a 7 channel or a programmable frequency unit. For servos, Iím wide open. I've used load calculators that indicate as little as 2 oz/ins of torque would be required to move the surfaces at the speed the mars will fly. Any recommendations (with supporting rationale...) would be welcome.
Last edited by falconhob; Jun 08, 2007 at 09:08 PM.
Jun 08, 2007, 08:52 PM
start slow and taper off
falconhob's Avatar
Quote:
Originally Posted by LukeZ
Maybe next year we can have three Mars and three Solents lined up on the beach.
That's my idea of heaven at this point!

Quote:
Originally Posted by LukeZ
How long have you been at the build?
about 2 months

Quote:
Originally Posted by LukeZ
Here's a picture of the Mars to motivate you; I thought at first this might be the same one as in your avatar but I believe it's slightly different. I need to see if I can order a print of this one as it's so spectacular.
Another beautiful pic for the collection. Thanks!

Wayne
Jun 08, 2007, 09:42 PM
Registered User
RiBell's Avatar
Quote:
Originally Posted by LukeZ
Maybe next year we can have three Mars and three Solents lined up on the beach.
Luke
So Luke: what your telling me is that I need to get busy and start building as well.
Going to watch this one come together. I have Ivan's plans for the Mars; however I think that I'll build the Solant first.
Rick
Jun 08, 2007, 10:45 PM
start slow and taper off
falconhob's Avatar

bass vs. plywood


I've started working on the wing, and notice that there is a lot of basswood called for. I have oodles of ply, light ply, 3, 5, 7 ply, you name it, but no basswood. Is it OK to substitute ply for the bass, or should I procure some basswood?

It's used for spar joiners to plug the outer wingtips onto the center section. Most kits I've built use plywood joiners. Is it a weight thing? Is there any strength relationship between ply and bass?

While I don't want to overbuild, I really don't want to underbuild!


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