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Feb 06, 2016, 09:51 AM
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Phaedra's Avatar
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Build Log

Maratuka DC3 kit


I have been looking for a good DC3 model for quite a while now, and never really found what I was looking for. Most of the models I found were either too small (foamies), not really scale, or both.
Then, in December, I found an old unbuilt Maratuka kit, straight from the seventies, for sale. Because the asking price was too high for me, I placed my bid, and waited patiently. And so, after about a month, the seller was willing to lower the price. I finally caved in, and upped my bid to his new asking price, and we immediately agreed on the sale.
And so today, I drove all the way to his place and picked up the model. And I must say, I'm quite happy with this; it's a real builders model...the only thing non-balsa in the box, are two aluminium (!) engine cowls.
I'm afraid I can't start the build right away, due to other priorities, and I will already have a hard time waiting until at least next winter before I can begin this one.
I will do this model in the Sabena livery:



Next step is to look for the Robart retracts for the Top Flite version, which has approximately the same wing span. I plan on converting the to electric, instead of pneumatic.

Stay tuned...
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Feb 07, 2016, 02:19 AM
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Concordefan3's Avatar
You got a great kit to make a very scale and authentic model of DC3. I have been looking for one myself and haven't come across one in last 4 years!. You are right prices for these kits are quite high and it's hard to get one at reasonable price...Topflite kit doesn't cut it, this is ur ticket....

Will you be powering it with glow or electric power plants? I would suggest to go with electric with same size of motors as glow and you will get more power and reliability out of them....
Feb 07, 2016, 02:53 AM
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Phaedra's Avatar
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I never fly glow, always use electric. I am thinking towards Eflite Power 32 or the likes, but I haven't done the calculations yet.
Last edited by Phaedra; Feb 07, 2016 at 02:59 AM.
Feb 07, 2016, 09:08 AM
Skylar's People
cwrr5's Avatar
I think the power 32's are going to leave you a bit short on power... my best guess based on the size would be a pair of good 60-size on 6 cells minimum.

Great project, watching with interest!

Feb 07, 2016, 10:50 AM
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Phaedra's Avatar
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According to the specifications of the kit, weight would be 4 to 4,5 kg. No idea how accurate or realistic that is, but the full box weighs about 4,2 kg, and I still need to add servos, retracts, wheels, motors and batteries to that. So let's say I get to 5 kg, if I don't do any effort to reduce weight while building.
I read here and there that this kit is largely over-engineered, with sheeting in 3mm all over the thing, so I guess there is some weight gain to be achieved after all.

When I put into eCalc the motorisation of my Hangar 9 Twin Otter (don't recall the AUW of that one, but it should be around 4 kg...), 2 x Eflite Power 32 with 3-bladed MAS 12x8 propellers on 4S, I get a calculated thrust of 3,3 kg per motor. The Twin Otter is way overpowered with that combo (it takes off on half throttle), so my gut feeling is that this calculation is somewhat realistic, and it would put this model on the good side of the performance chart.

I will do more simulations before I ever order motors and props for this model, but first I want to do a bit more research on actual flying models of this rare type, to get more accurate and realistic numbers.
And that is the hard part, because this model was more popular when the Internet wasn't yet around...so not much build logs or flight reports to be found....


EDIT:
I just found a mention of this model somewhere, and the owner claims he has an AUW of 3,6 kg with 4-stroke engines...he did do quite an effort to save weight while building it, though. But at least it is possible to keep the weight acceptable, and that is reassuring.
Last edited by Phaedra; Feb 07, 2016 at 11:52 AM.
Feb 07, 2016, 03:20 PM
Brooklynite In Texas
Hello

The kit you have is a good one, the marutaka Kit is a Royal design and they fly quite well.

The last one I saw used 35 Two strokers for power and that was all one needed, I flew the B-25 on the original wankels with plenty of zip. If the model is assembled with common sense with out a lot of added weight you will be fine.

Just for the record, plans for the C-47/DC-3 can be found on the OUTERZONE.com free plans site there are several plan sets available in various sizes but you may have to do a little searching for them.

Good luck and joy to you
Feb 07, 2016, 03:31 PM
Brooklynite In Texas
I just checke the outerzone site and found these, There are more! FREE!
Feb 07, 2016, 03:50 PM
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Phaedra's Avatar
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Thanks for the links!
My kit is from the era before Maratuka was taken over by Royal, and as such the plans included appear to be different from the ones you referred to.
Very interested to find the differences between my kit and the Royal plans...
Feb 07, 2016, 07:55 PM
Registered User
PC Pilot's Avatar
This DC-3 has E flite 32s. Be sure to see the short, high angle take off in post 94.
https://www.rcgroups.com/forums/show....php?t=2090742

This a Top Flight kit also with Eflite 32s.
https://www.rcgroups.com/forums/show....php?t=2203843
Feb 07, 2016, 08:52 PM
Skylar's People
cwrr5's Avatar
ok...
Feb 07, 2016, 10:38 PM
Registered User
AntiArf's Avatar
Good to see these old kits built and good subject. You're probably thinking along the right lines as far as not overpowering, given the twin efficiency and the efficient wing. I built a Guillows some years ago, and was not only surprised with how well it flew, but on low power. The model is not light at 19+ oz AUW, but will take off and fly at an incredibly low speed, given it's small size and weight. The model uses approximately 20 gram outrunners, which I had questioned being sufficient at the time. My last twin experience with a 36" Miles Aerovan was similar, where the 20 gram outruners had sufficient power on 2s, again not a feather light model either.
Feb 08, 2016, 03:16 AM
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Phaedra's Avatar
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Thanks all for thinking along. You guys are making it very hard for me to put this model away until I have time to build it
But a little research won't hurt...

It seems that a 10" prop would be closest to scale. With an Eflite Power 32 motor turning a 3-bladed 10x7 prop, I would get a static thrust of 2,1 kg per motor at full throttle, but about 1,9 kg at 95% throttle and max efficiency.
Since I have no real idea yet on how much weight I will achieve, it's still hard to take definite decisions about this.

A bigger problem to tackle is related to the CG, more precisely: where to put the batteries. I will need to make an access hatch somewhere to get the batteries in and out easily, and of course, given the age of this kit, this was never foreseen. I am trying to get in touch with Jan Karlsson, who built this model very lightweight, but powered it with 4-stroke engines. I'm hoping he can give me some more information about this.

Meanwhile, I also already ordered the Robart retracts from the Top Flite kit, almost identical in scale (1:14 versus 1:13,7 for my kit). The only online shop in Europe that I found that carried them only had one set lef in stock, and so I didn't want to take any chances with this.
I already has a pneumatic cilinder included, but I also saw videos where they are being operated via a "muscle-servo". My tinkering brain is also thinking about converting a standard servo into a linear servo that would drive the retract via a worm wheel, which would cause less stress in the servo. I could do this via either a linear potentiometer, or endpoint detection via micro switches. Just ideas....
Last edited by Phaedra; Feb 08, 2016 at 03:23 AM.
Feb 25, 2016, 05:00 AM
Registered User
lionel_69's Avatar
Quote:
Originally Posted by Phaedra
My tinkering brain is also thinking about converting a standard servo into a linear servo that would drive the retract via a worm wheel, which would cause less stress in the servo. I could do this via either a linear potentiometer, or endpoint detection via micro switches. Just ideas....
Hi Phaedra, I got the same idea once ago, but It is soooooo slow. (I hacked some old 9g HXT-900 servos to try that).

Train atterrissage à vis sans fin (3 min 23 sec)
Feb 25, 2016, 05:11 AM
An unexpected error occurred
Phaedra's Avatar
Thread OP
Now THAT......is slow

Maybe if I can eliminate part, or all of the gearing from the servo, things might speed up a bit. But the gears are there to increase the torque, so I have to take care that I don't burn the motors doing that.
Thanks for the very useful input Lionel, that was what I was fearing.....
Feb 25, 2016, 02:55 PM
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Phaedra's Avatar
Thread OP
Meanwhile, I received the Top Flite retracts.
Looks pretty good, not really fine scale, but close enough for me.
Looks like very nice workmanship, and seems sturdy enough.
This goes upstairs now, awaiting the build.....


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