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Aug 31, 2020, 11:14 AM
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Question

Electric winch for wooden scale glider (2.2m, 1.2 Kg)


Hello,

I have a couple of wooden scale gliders (Grunau Baby, Go-1 Wolf) that I usually fly from the slope or bungee launch using an F3 RES system. Models are 1/6 scale (2.2 m wingspan, 1.2 Kg RTF) and I'm considering winch launching. I have experience with the method as I'm also flying F3J/F3B with full composite gliders and I also own a dedicated winch, an equipment obviously not suitable for delicate wooden structure.

Looking forward for community feedback on two directions:
- I'm considering buying a Graupner 807 winch (if I can locate a second-hand one) but I'm not sure is the right tool for the job;
or
- a DIY winch out of a battery powered drilling machine/ screwdriver or similar.

Thank you for sharing your experience.

Best regards,
Iulian
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Aug 31, 2020, 12:53 PM
a.k.a. Bob Parks
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https://www.rcgroups.com/forums/show...y-Graupner-USA
Aug 31, 2020, 01:29 PM
B for Bruce
BMatthews's Avatar
We used to launch weaker and smaller models on the winches by simply pulsing the foot pedal to control the line tension. Meanwhile the guys with the bigger and stronger models would stomp and hold.

So it is likely that you could use your present winch if you learn to pulse the pedal to limit the tension. The model doesn't see the pulses since the line is typically fairly stretchy. With a bit of care you can zip them up and they'll never see any more tension than you get with the F3RES high start.

Hold the line when it's all laid out and pulse the switch to where you build some tension and then hold it there as the winch pulls in then lets out the line and you feel a light and pretty well even tension suitable for the lighter models. When you can do this for a good 30 seconds at a time and are used to the pedal frequency and duty cycle to get that sort of tension and can hear the sort of sound it makes you'll be ready to tow up the models with your winch.

Or perhaps your winch uses a low stretch line and is simply way too powerful? Perhaps run it with a lower voltage battery and a drum loaded with line that is a little more stretchy?

A cordless hand drill would likely do the job if you want to make such a winch. But you need the line to come in at some suitable rate of speed so you might find that you need to work out the proper drum size for the job.
Aug 31, 2020, 09:51 PM
Registered User
I suspect that if Iulian is serious about F3B/F3J, the line is very stretchy. It's probably monofilament, though, which gives a very strong zoom at the end. Unless they've changed
the rules, F3B winches are actually weaker than the usual American FLS winches, but the monofilament makes up for it. A light, braided nylon line would have enough stretch without so much zoom.
------
Iulian:
Can you describe the structure in those wings? Even a Gentle Lady can be winch launched if you tap gently. I've never broken one that way, though I prefer. slightly more robust spar. 6mm X 3mm spruce spar caps with shear webs are suitable for a 2 meter glider of normal proportions. If the struts on your gliders are functional, and the airfoils aren't too thin, then that might be enough for you, particularly if the structure or covering provides a reasonable amount of torsional stiffness. The famous Olympic II has a fairly robust spar, but if the covering gets slack, it flutters easily when,winch launched.

A very effective way to make a winch gentler is to use 6 volts instead of 12. You might need to use lower voltage solenoid, though. If you want to go back to 12 volts, you can hook up the coils in series instead of parallel. That worked fine when I ran my winch on 24V instead of 12. (The motor is wound for a higher voltage than most American winches.) In fact, I've sometimes hooked a battery charger on my wonch motor when installing new line. That way, it's much slower and more relaxed, and I don't need much space.
Aug 31, 2020, 09:59 PM
Registered User
BTW. I've read about people using a long coil of wire as a resistor to slow down winches. The coil is kept in a container of water so it won't overheat. I don't know where the articles were, or any of the details, but I'd guess you can find an article on line. Make sure the resistor wire is completely submerged or things might get exciting in a hurry.
Aug 31, 2020, 10:28 PM
B for Bruce
BMatthews's Avatar
Stainless aircraft safety wire would work nicely for something like that. It's cheap and has a good amount of resistance per meter compared to copper wire. And a ceramic tile could be notched using a diamond tile blade and the notches smoothed with a diamond burr in a rotary grinder as the non burning, non melting core for the wire wound resistor.

Mind you I think running it off a lower voltage battery would do the job. Pehaps even a 10,000mah 2S lipo?
Aug 31, 2020, 11:05 PM
Registered User
I wonder if the safety wire would have enough surface area to keep it cool? Copper would have much more area if it was the same gauge and resistance, since it would be much longer. I wonder how carbon fiber tow would work? It would have to be fairly thick to allow enough area, at least when water cooled. The stuff can handle very high temperatures*, though whatever it's connected to might melt. I would guess there is usually some surface treatment to make it compatible with epoxy. That might stink until it burned off. The carbon would have to be inside a ventilated box to avoid fires. Or one could skip a lot of trial and error by finding an article by someone who's already made the wire in water trick work.

*I once saw a model which had an unfortunate encounter with some power lines. The carbon fiber canopy was undamaged, except that all the epoxy was missing. In other places, fiber was hanging out of the wings like hair. There was also an unpleasant smell. I don't recommend experimenting with this.
Sep 01, 2020, 12:32 AM
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Thread OP
Quote:
Originally Posted by lincoln View Post
I suspect that if Iulian is serious about F3B/F3J, the line is very stretchy. It's probably monofilament, though, which gives a very strong zoom at the end.
...
Iulian:
Can you describe the structure in those wings?
....
Thank you all for the reactions, I'll try to clarify the picture a little bit.

Indeed, I'm using monofilament (nylon, most of the time 1.32 mm diam.) as most European flyers.
The winch is "almost FAI compliant" as I do not have the power resistor allowing me to adjust the overall resistance of the system. The motor is the usual (on this continent) Bosch 1.1kW, direct drive. Winch construction is DIY and from the F3J/F3B experience it does not tolerate "pulsing" very well, most probably due to high drum inertia causing line tangling.

As for the models, one is the Krick Grunau Baby, 1:6 scale. In original form the model was without spar between the LH and RH wing panel, supported by wing struts only. I've slightly altered the construction by adding a 200mm long 4 mm diam. steel connecting bar in brass sleeves. The Go-1 Wolf is quite similar.
Right now the only images I have are the ones below; I'll make relevant ones latter in the day and post them if needed.

I somehow like more the idea of having a compact winch (e.g. Graupner 807 size) instead of using the F3J/ F3B one.

Best regards,
Iulian
Sep 02, 2020, 09:47 AM
Registered User
I'd bet the joiner rod won't do much until the struts fail, unless the struts are stretchy. After the struts failed, the 4mm rod would be too weak. I'd suggest at least a 6 mm music wire rod if you want it strong enough to handle the load without the struts.

You still haven't told us about the structure of the wings.

You might check out the Little Big Winch, which woukd probably fit your needs.
Sep 02, 2020, 11:15 AM
B for Bruce
BMatthews's Avatar
You mentioned flying these off a F3RES high start. Then asked about using the big winch. So I was thinking that the goal here was to allow flying both types of models on the same session using the F3B/F3J winch instead of needing to lay out two launch systems.

If you're going to buy a second winch then I'm wondering why you simply would not continue to use the F3RES high start for the lighter models. After all a high start is a lot more compact and lighter than any winch I've ever seen. And a lot less costly too.
Sep 02, 2020, 04:12 PM
Registered User
Isn't an F3-RES hi start too weak for a 1.2 kg model?
Sep 03, 2020, 01:04 AM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by lincoln View Post
Isn't an F3-RES hi start too weak for a 1.2 kg model?
Perhaps on a calm day it would not give a great launch. But even a little wind will perk things up by adding the wind speed to the power of the high start. At least I'm thinking it would be enough to "get by".
Sep 03, 2020, 11:40 AM
Registered User
Thread OP
I'll try to cover all raised questions in one post:

- indeed, launching those models with the RES hi-start is marginal even with some headwind help; it only allows for a decent circuit;
- I would prefer a winch for launching in order to avoid the stress on the balsa fuselage while building-up the tension in the bungee (or holding just before launch); it also helps in those days when you're alone on the field;
- the vegetation on our field is very harsh on the bare rubber (unbraided ?) bungee (as the case with the RES type), one more reason to look for alternatives;
- as for the wing structure details: balsa ribs 2 mm thick, 5x2 (mm x mm) pine spars - upper and lower - with balsa webbing and 2 mm balsa sheets from leading edge down to the spars (attached an image during wing construction).

Best regards,
Iulian
Sep 05, 2020, 06:03 AM
Registered User
That construction seems like it would be enough for a careful winch launch, assuming the rest of the model is in proportion. However, it sounds like the fuselage might be weak if you're worried about damage from pulling out a hi start.

I only have two hands, but I don't have much trouble flying with a hi start by myself, even with a 3.4 meter thermal duration model. Then again, our field isn't abrasive.

BTW, I've heard of supporting the line from the turnaround to the winch so there's less friction with the ground. I think they ran the line through ceramic telephone wire insulators on posts, or something like that. A friend of mine had a turnaround that was 4 or 5 feet high for the same reason.


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