1/12 C 47 Feasibility

[bpeltzer]

Thinking about building a 1/12 scale C-47 from Balsa. I'm currently working out the details in my head, but I need some help. What should I expect the weight of such a plane to weigh if crafted of balsa, ply, and some kind of film covering?

Some of the details that I am thinking of right now:

- 95.5 inch span
- 67 inch length
- 17 inch height
- Electric powered
- Controlled by a DX6i and AR 6200
- Retracts and flaps
- Removable wings just outboard of the engine nacelles

Questions/suggestions are welcome regarding what peple think regarding:

- The weight that I will be able to achieve
- How many watts of power I should have for good flying characteristics (trying to fly scale at 1/2 to 5/8 power so that I have some in reserve in case i get in trouble)
- Recommended motor/ESC/battery if someone has done this before
- System/method for removing and attaching wings
- Any other suggestions regarding building materials.

[GordonTarling]

I'd suggest you take a look at the KMP DC-3/C47 for some guidance, it's just over 100" span - there's a thread over on RC Universe about it. I think you should budget for a weight around 20 pounds. A 3 piece wing seems the most practical to me, but a lot depends on your own storage and transport facilities. Electric power is VERY practical for this model, I was playing around with it in Motocalc the other day and found several motor/battery combinations that would work well. I think I ended up with a 6S lipo pack and around 1500 Watts per motor. The limiting factor, at least with the KMP one, seems to be the prop diameter, which needs to be less than 13", but Motocalc showed that a 12.5 x 8 3-bladed prop would work well. Here's a link to the RCU thread - http://www.rcuniverse.com/forum/m_7025866/tm.htm

[eflightray]

I would say it depends how much scale you want to build into the model, it's often the detail that weighs.

I have a 93" span B25, weighs 10lb-8oz and a 100" span B17, weighs 12lb-1oz ready to fly. Both are scratch built to fly scale like, not for up close scale detail that just adds weight. So depends.....

[Zipman]

Hi bpeltzer,
Here is something to start with other than 3 views. Also search for DC-3/C-47 here and on RCUniverse for threads.

There are (3) - R/C DC-3/C-47 plans that I know about in the 1/12th size. In no particular order here they are. I have the first 2. The Model Airplane News plan is more scale than the Flying Models one but the FM one is easier to build. Neither plan has estimated finished weight. The Flying Models DC-3 came out 13 lbs dry. I read on one forum the MAN DC-3 was about the same. Keep the tail light and you won’t have to put a ton of lead in the nose to balance it. The FM plan is fixed gear and the MAN one has retracts. Both plans are balsa/ply construction fully sheeted and glow powered. The Traplet model is electric. This should be your first starting point. I want to build one electric also and I will probably buy this plan. Good Luck.

Stan

Flying Models Magazine - http://www.flying-models.com/
Plan – CF454, Douglas DC-3, Stand-off scale, by Tony Lombardo, engine - .45, span 96 in, Nov 1977 issue, price $15.00.

Model Airplane News - http://www.modelairplanenews.com/ME2/Default.asp
In the description the fuse length is wrong.

Douglas DC-3
Category: Giant Scale
This Paris White design features fully planked and sheeted fuselage
and flight surfaces. In flight, the plane is stable enough
to match the skills of infrequent fliers; it hasn’t any bad habits.
WS: 94 in.;fuse: L: 49 in.; engine: (2) .50 to .60; 6 channels;
2 sheets.
X06711 29.95

Traplet Publications - http://www.rcmodelworld.com/issue/issue.aspx?cid=4226
The plan was just published in the September 08 issue and is not listed in their online catalog yet. I sent their Customer Service an email inquiry a few days ago but no response yet. I will post more when I get a response.

Douglas DC-3 Dakota
Build and fly this impressive 96" span transporter design by Robin Fowler for twin-electric power and 4-6 function R/C

[eye4wings]

Sorry for the delay,
Zipman sent me a PM asking for a few details of my DC-3, informing me that Traplet are not listing the plan yet although it is published.

Traplet Plan Number MW3303. Cost £25+p&p (£7.00 UK)
ABS set CA3303SET. Cost £30.50+p&p (£7.00 UK)

The model spans 96" and demounts in four sections for transport - Centre section includes nacelles and nose, plug in wings outboard of nacelles, tail section (with dowel and piano wire pin fixing) is fuselage aft of main spar.
AUW is 9 pounds 2 ounces.
Power train (2 - of course!) Tower Pro TP2915-930 (revs/volt) 40 amp ESCs, 3s LiPo packs 4000 mah, props DIY wooden 3-blade 12 x 8.
Home-built retract system operates in scale time-frame of 5-6 seconds.
Flies at a nice scale speed, looking bigger in the air as a consequence.

Hope this helps.

[eye4wings]

Having re-read Gordon's post I was a tad shocked at the motor power capacity he suggested and realised that I hadn't stated the power that I used on my DC-3 design.

The TP 2915 is rated at a maximum of 400 watts per motor and the model flies at 1/2 to 3/4 throttle. I measured the maximum current draw on the 3s pack of 27 amps - therefore 320 watts flat out on fully charged cells - so total of about 600 watts easily flies the model.
The larger motor rated at 600 watts (TP3520-670 (revs/volt) - same price £20 from allelectricrc.co.uk) is slightly more efficient but would require an extra cell to get the revs on the same props.
I use the larger motor in my Q6 (shown in my avatar) which is 112" span and 12 pounds AUW. In neither models do the motors break into a sweat!

Sorry Gordon, but the sort of watts you're talking would have my DC-3 accelerating in the vertical!

[Zipman]

Robin (eye4wings).

Thanks for the info on your DC-3. That is a light airframe for the size of the model. Less than half the weight of the KMP DC-3/C-47 that Gordon was using as a basis for his recommended power setup. Is your model fully sheeted both fuselage and wings to reflect the scale type covering?
I am looking forward to purchasing the plans, parts and the two issues of the magazine covering the build. Can you post a picture of the completed model here?
One more question. Do the plans show the details of the home-built retracts( a must for this model). Thanks again for your input.

Stan

[bpeltzer]

Thanks for the info guys. I'm just starting my first scratch build, the Boeing L 15 in FLY RC recently. I've always loved the C-47, and have been thinking about scratch building one ever since I started flying RC. Good to know that something like this can be done with electric power. At this point I'm giving myself till I'm 40 to build this aircraft, so I got 9 years +/- to get it done.

[eye4wings]

Stan,

I didn't draw up the plans for this model. I was asked to develop it from outline drawings already done and the draughtsman visited me to check details of the model. He then completed the drawings - which are larger than I can cope with on my drawing board!

Yes the drawings show the layout and sizes for the UC. They are a little vague on the operation system (which changed as the model was developed) but I used a torque bar from the centre line out to each wheel, operated first by an old servo which had a dead (and removed) amp and which I put a couple of extra stages of gearing on. This gave scale retraction times but suffered reliability problems because of the ens micro switching system I used. I later substituted this for a (working!) SuperTec 136GH which operates through horns, sacrificing scale time. This servo is the slowest I can find at 1.5 seconds end to end.
Retract systems are the bane of my life!
But I have recently found a sail winch which I have got working for the current build. This operates in 5 seconds - just right.
You might like to have a look at the thread 'retract servos too fast?' under 'Scale electric planes' for a whole lot of info on how other modellers do the job.

And yes, the model is fully sheeted (except for wing undersides), sheeting as soft as will do the job (of course) particularly at the tail end.

I'll have a look at what pics I have available and post them later.

[eye4wings]

Okay so here are 3 pictures, two of the completed model in the drab livery that was pretty much standard dress for the majority of RAF 'Dakotas' and one that shows the original retract setup in construction.

The view showing the wing is included because the washout at the tip is clear to see. This is why the handling in the air is so nice. No danger of tip stalling.

Hope this helps.

[Zipman]

eye4wings,

Thanks for the update and pictures. Nice job on the Dakota.
I have been thinking of a similar central retract setup for the Cessna Bobcat. The gear retraction geometry is very similar in both aircraft. I will check out the link 'retract servos too fast?' you mentioned for further ideas. Great, I think I got more out of this thread than bpeltzer did. Thanks to all for the responses.

Stan