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Jun 03, 2017, 01:06 AM
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david.ingham's Avatar

Line powered control line, for the minnimal space

(I think I started a thread somewhere but I can't find it.)
This is the only thing I can fly much in the little park across the street. It has the battery in the handle, so it is even lighter than other control line models. The lines are less than 12 feet long. I did one loop and crashed the second time I tried.
It weighs around 70 grams, while the only RC I have flown there is 25 grams.

The RTF toy itself is much cruder than the 25 gram two channel RC foamies.
The main problem out of the box was that the weight on the outer wing was less than half the weight of the lines. The second problem turned out to be that the lines were too stiff between the bell crank and motor, so the bend of those wires affected the trim. I eventually spliced in soft silicone wire to reduce that problem. The pictures show replacement and reinforcement.

Here is the BangGood link for the original model:
Last edited by david.ingham; Jun 03, 2017 at 01:23 PM.
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Jun 03, 2017, 02:59 PM
coriolan's Avatar
Bang_Good re-invented RTP flying!
Please report on the performance with such long lines (4 meters)considering the low voltage and small wires. Some sites of interest:
Jun 03, 2017, 03:15 PM
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david.ingham's Avatar
Thanks, I will have a look.
As I said, I managed one loop and crashed on the second try. That was with one lithium ion cell. It is very tame, about right for beginners with all 6 NiMH cells. My guess is that I can keep adding voltage without burning out the motor quickly. It is very easy to adjust the voltage, because 14500 lithium ion cells have the same size as AAs, a bit longer with protection circuit, but they fit.
Jun 03, 2017, 04:22 PM
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david.ingham's Avatar
I don't see any there with the lines for both control and power. I am thinking that if I add a potentiometer, I will have a full proportional two channels (without a single transistor).

Its awfully nice not having to recharge a battery every time. I just push the button to start, cycle it to slow down and release it to land. A 14500 will last maybe half an hour to an hour of flight time and a NiMH twice that. The BangGood RTF is not more than a proof of concept, it needed modification to be flyable. But I could start with a kit intended for 020.

Magnet wire would be the thing to use if one had a dedicated space, but insulated stranded wire is more manageable and safer with children around. One can use thin long wires and more voltage to cover the loss. This looks like maybe an ohm total in the wires.
Jun 03, 2017, 05:00 PM
coriolan's Avatar
With pure RTP there is no control (early one were rubber powered), with electric RTP the voltage is varied to alter speed, climb and decent. Now R/C RTP is being used which offer more option (retract,flaps etc...)while doing away with power through the wires, Outerzone has many RTP plans:
RTP Avro Lancaster (1 min 2 sec)
Jun 05, 2017, 12:18 AM
Design is everything.

RC plane in RTP mode

My first RC plane the "Piper Cub" arrived in the mail the other day. Unfortunately I do not have access to a football field, more like a basketball court sized area next door. After a flew straight flights and crashes, I reverted to plane B: RTP mode.

The model is simply too fast to fly in a 10m x 10m space, but flies fine in RTP mode, using a 10m string. (Visible in picture). It will just take off in half a circle and then climb well, no elevator control, which I miss very much. I had to add weight and a makeshift aileron to the outside wing to make it stay flying in a circle when the breeze whipped up a bit. Very tough plane - will survive brick walls and brick pavement.

With proper elevator and aileron control, flight in a limited area will not only be possible but enjoyable as well, I think. This is a real cheap $18 alternative to an RTP system. Of course one could run a thin power wire to the model to power it during flight. Cheaper alternative to the Fly line RC though that system has elevator control for loops.

The model was purchased to sped up my project tp test my idea of RTP in racetrack pattern, so that's next.
Last edited by Designer2010; Jun 05, 2017 at 12:21 AM. Reason: Clarity
Jun 05, 2017, 12:22 AM
Design is everything.
Model weights 26g like it says and generates about 20g of static thrust from those motors. Maybe it can be converted into an SU-27.
Last edited by Designer2010; Jun 05, 2017 at 12:22 AM. Reason: Smiley
Jun 05, 2017, 10:23 AM
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david.ingham's Avatar
I have a similar RC airplane and i might use it that way, thanks. That isn't in principle as much fun as line powered CL because it has no elevator control and needs frequent recharging, but that is a much better engineered and tooled model. Rather than use a post, I guess I would tie a thread to the transmitter.
The standard is tip weight equal to half the weight of the lines, but I like more than that in small models. Sometimes it is possible to offset the wing to avoid adding weight.
Jun 05, 2017, 08:34 PM
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david.ingham's Avatar
(I tried tying thread to my 25 gram RTF RC, but it was too windy for it to fly.)

With an eye to building a new model, with new or the old electrical parts, I took some measurements of my BangGood line powered CL:

Total weight of the airplane, not including the lines, but with increased wing weight, reinforcements and patches: 63 grams
Weight of the bare motor: 18 g.
(A brushless motor could decrease the weight, but it would need an always on controller.)

Voltage to motor, motor disconnected (= battery voltage 6 s NiMH): 8.2 volts
Across motor, motor running: 4.2 V
Resistance at battery connector, motor shorted out (resistance of both wire lines): about 1. Ohm
Current at motor, motor running (through cheap multi-meter): 2.1 amp.
So two or three volts is lost in the lines and one or two volts to the internal resistance of the six good Eneloop AA cells. Since cooling is good, a 3 V motor should work. Run time must be most of an hour, with small decrease in power. (Power would vary much more with alkaline cells. It would probably droop noticeably during a run.)

Resistance across motor at most propeller positions (winding resistance): 1.5 Ohm

Diameter of wire lines: (about 30 thou) 0.8 mm.
Thicker insulation would have more air drag and be heavier; thinner might be a hazard to children unless the copper were also thinner.
Weight of lines: about 13 grams
Length of lines: (11.5 ') 3.5 meters
The copper of the lines is stranded, but I don't have the diameter. It looks like maybe 7 filaments, more would be better.
Jun 05, 2017, 10:42 PM
Design is everything.
Hi David

I really hope you succeed with this project. Controlled RTP is my final goal as well, but I have limited time and resources, so it will be a little time until I achieve my goal. I believe many an R/C airplane flight could be performed in the same way with a control line or tethered arrangement, at least indoor RC flight.

Thanks for calculating the voltage drop, that is indeed substantial, however if you use AC current ( dangerous at low voltages even) you may be able to get more power to the motor. There are several options that I have considered over the years but never built, although I have read of examples of these.

But first have a look at these indoor fliers in these videos and ask yourself if these flights could not have been flown by an RTP system? The planes flying in a circle certainly could, and as for figure eights, a system that allows for a slack wire should make this possible.

Rc Mirage III 3 indoor flight shot with a GoPro from a quadcopter (2 min 58 sec)

Airbus A310 by MM - indoor airshow Leipzig [HD] (5 min 19 sec)

Also check out Picasim, the RC simulator where the developer has included control line airplanes in the sim, actually any plane can be configured as control line with the option to control the airplane with slack wires as well as the traditional control line arrangement.

Jun 05, 2017, 10:50 PM
Design is everything.
I would think that you could run the power lines plus wires for the elevator and aileron servos from a central location, thereby achieving three channel control. The other option is to use an RC system but this is costly. I read of one account where the model was powered and controlled by a long wire, sort of like the TOW missile.

Also, check out Flyline RC.

If you make the central attachement point movable, at least in one dimension, you will be able to fly an elongated pattern, like an oval racetrack pattern. As I explained this is my next project. I have not found any information on this on the net, some have suggested the wings will tear off, but nothing like trying.

edit: former thread:
Last edited by Designer2010; Jun 05, 2017 at 10:53 PM. Reason: edit added former thread
Jun 06, 2017, 10:39 AM
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david.ingham's Avatar
Originally Posted by knlever
Thanks for calculating the voltage drop, that is indeed substantial, however if you use AC current ( dangerous at low voltages even) you may be able to get more power to the motor. There are several options that I have considered over the years but never built, although I have read of examples of these.
I am not aware that Lionel trains ever caused electrical harm. They were 12 V AC. I could feel mine tingle, but that was all. But I don't see any advantage to using AC. The loss would be slightly higher than with DC.

I don't think the one Ohm resistance of the lines is really a problem, even with longer thinner lines. It is easy to increase the voltage by using lithium ion cells. I think up to about 24 volts is still safe, or at least 12 volts with children around. It is now nominally 6 x 1.2 = 7.2 V, so there is a lot of room for more wire loss.
Jun 06, 2017, 04:34 PM
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david.ingham's Avatar
One of the nice things about a simple rubber powered airplane, in this day and age, is that you can see how it works by looking at it, unlike electronics that has components too small to see, even if you would understand it if you could see it.
It turns out that my line powered control line will have the same advantage, for the 5 1/2 year old I am watching. His father is an electrical engineer, so he has been playing with an electric kit with batteries, a motor, a switch and wires. So he understands and can recognize all the components of this simple electric airplane, just like the rubber powered one we played with today.
Jun 06, 2017, 08:51 PM
Registered User
If ? memory serves Powering an Electric CL model thru the Flying lines has been tried and discarded repeatedlly.
possibly you are using low power low/no performance motors ? and are merely wanting the model to fly flat level circles.. slowly?
Onboard batteries are a massive improvement powr wise Light and unconstrained by flying wires with their Very! high resistance.
Hell I use damaged control lines as Heat wire on my Foam cutting rig. .. as example 24 v heats it up to a red glow if inept
RC control is laughably simple to use /fit and buy! A Car type RC unit Tx and Receiver can be had Brand new for ~20$.. true
Here is a 23$ one that includes an ESC :-)

there is also a 19.99$ one as well
Jun 06, 2017, 10:41 PM
Design is everything.
The model I used and shown in the pictures ("J3 Cub") is actually a radio controlled model with a 60 metre or so range. I found it quicker and cheaper to purchase one of these for $20 plus shipping and tether it to a pole than either building a model or purchasing a control line or RTP model with all its hardware. These could be expensive, costing much more than the cheaper RC models.

There is a proper 3 channel RC model on one of these online sites, may be a than the twin motor set up for RTP.

The disadvantage of on-board power is the battery pack, but if you use capacitors you could get a fast recharging time. I have tested a super capacitor and found that it gives a really short running time with a large motor, but with the micro motors featured in these models, and with two or more supercapacitors in series there could be a chance.

Don't motors get overheated if they are run hours on end?

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