Sig 1/6 Scale Cub - RC Groups
Thread Tools
Jul 15, 2003, 10:57 AM
Registered User

Sig 1/6 Scale Cub

I've run a few searches, but did not find much info on this plane. I picked up a kit for a very good price from a friend who decided he didn't have time to build it. Having looked over the plans and instructions, it looks like a nice light weight kit. I'm sure it will fly very well as an electric.

I'm planning to build this kit as a light weight floater, using 1950FAUP NIMH cells and a brushless motor, with the intention of flying it in a scale like way on days with little wind. I have other planes for aerobatics.

Now for the questions:

The plans suggest that if you are going to cover the wing with a "plastic film" rather then "silk and dope," that you add cross braces between the ribs. Is this necessary if the wing is covered with monocote or does mc add enough strength?

Also, how much should I expect the completed airframe to weigh? I'm looking for a number I can feed into Motocalc to help me choose cell count, motor, prop, etc.
Sign up now
to remove ads between posts
Jul 15, 2003, 02:08 PM
EDF Head
Haldor's Avatar
A friend of mine flies a GP .40 Cub on a Astro15G (2,38:1) and 14cells. 13x7 prop gives pull. With 3000mAh NiHM cells it will fly on a calm day for 14mins which will give you an idea on what power is needed.
Jul 15, 2003, 02:24 PM
Registered User
Thanks Haldor,

The instructions for the Sig 1/6 Cub say it flies well on a .25 size nitro engine, and it appears to be very lightly built, mostly sticks. I'm hoping I can run it on a much lighter power system then what your friend is using, but that is a good reference point for comparison.
Jul 15, 2003, 07:18 PM
EDF Head
Haldor's Avatar
BTW his Cub is a around 7,5pounds
Jul 15, 2003, 07:45 PM
Registered User
The nitro version of the kit I have is supposed to come out around 5 or 5.5 pounds. I'm assuming that includes motor, fuel tank, flight pack, 4 standard servos, full size receiver, etc.

I'm going to try is make it lighter then that as an electric.
Jul 15, 2003, 09:40 PM
Visitor from Reality
I've not come across the smaller Sig Cub, but would bet you can reduce weight with a lighter firewall, looking at where it's beefed up around the glow engine and so on. Smaller servos will help and there's plenty of ESCs around that will save you hauling a RX pack, even if you go to ten cells.

Having flown the similarly sized LT25 on a geared Mag Mayhem and ten cells, I'd reckon something like that would do you unless you fancy a smaller BL motor. I'd reckon you could sneak her in under 5lb with those cells you suggest.

What sort of wing structure is used? If its got a D box LE, it will be strong enough. If fully open, a good trick is to cover with film, tighten it up, then iron down onto every rib and spar. This means you have a whole bunch of small areas of film rather than a wing's surface area worth - makes it a lot stiffer. If you weren't too fussed over being see-through, you could use Micafilm - this can be a pain to apply, but is very strong and light, plus really stiffens up the frame. I used it on my Four Star 40 for a couple of years with no problems, and it has a fully openwork wing frame.

Good luck

Jul 15, 2003, 10:43 PM
Registered User

The wing is sheeted for about an inch at the leading edge, on top and bottom. Also, there is sheeting on about 1/4 inch at the trailing edge. Sounds like I won't need to add the additional bracing suggested on the plans.

I like the idea of ironing the covering to the individual ribs. I can see how that would add stiffness.

10 cells sounds good. I was thinking one of the LT-25 power systems might work. The structure looks similar to the pics I've seen of LT-25's in the forums, and it is about the same size.

This should be a fun project.
Jul 16, 2003, 02:09 PM
Senile Member
Lnagel's Avatar
I have a 1/6 Sig Cub I built about 10 or 12 years ago. It is powered with an OS .40 four cycle and a 12-6 prop. This is a first generation four cycle so the power output is equivalent to about a .28 two cycle. It flys very "cub like" with this power setup. In other words, it just kind of floats around a little above stall speed. With a 12-8 prop it flies faster, losing that scale speed look, but it keeps you out of trouble.

This plane is designed very light. I don't think you will find too much room for any lightening. About the only thing that comes to mind is the firewall. The AUW of my Cub with very heavy 21st Century fabric covering is about 5 1/2 pounds. This is great considering that other brands in the same scale are usually in the 7 1/2 to 8 pound range. You can save a few ounces over mine by using a film covering like Monocote.

As far as the wing structure goes, I don't think the cross bracing is necessary if you attach the covering to the ribs as suggested earlier. What I do is initially attach the covering to just the edges so I get an even overall shrink, and after I shrink the covering I seal it to the ribs with an iron. The wing struts are a must though. The wings will not support the airplane without the struts. That's one of the things that adds to the lightness.

The truth is, I actually have only 3/4 of a Cub. That flying just above stall speed on landing kind of destroyed the front half of the fuselage. I am planning on rebuilding the fuse in L4 Grasshopper form and electifying it. This time I will use a lighter covering. So I am interested in how yours comes out.

Good luck on your build and keep us informed.

Jul 16, 2003, 02:32 PM
Registered User
Thanks Larry,

It's nice to hear from someone who's built and flown one that the wing is strong enough as is. After playing with motocalc for a while, I came up with a workable electric power system that will weigh in the area of 24 ounces. I don't think that's much more then a nitro engine+standard servo+fuel tank+fuel would weigh. It's a Jeti 30/3 motor, 2:1 gearbox, 40 Amp ESC, 10 cell FAUP battery pack, 15x10 prop. Motocalc says it should have enough thrust to do continuous loops. I don't plan to test that theory, but having a little extra power for emergencies is nice.

Looking at the cowel and landing gear, I'm guessing that there is enough clearance for the 15 inch prop. What do you think?

I'm a slow builder, and I have another plane on the workbench right now so it may be a while before I have anything significant to report, but I just ordered a digital camera so I should be able to provide lots of pics as the build progresses.
Jul 17, 2003, 12:32 AM
Senile Member
Lnagel's Avatar
I really can't comment on the clearance for a 15" prop as my landing gear is no longer attached. There's nothing to attach it to. The largest prop I used was 12". However, on mine I used scale cub wheels. But the only ones I could find were 1/5 scale so they were a little over-sized. I figured it just looked like a bush plane in Alaska. You could go that route if needed.

I did weigh the components (motor, fuel tank, servos, battery and receiver) and it came up to 31.1 ounces. That's less than your proposed power system. As such, you could probably use 35 to 40 ounces as your empty airframe weight for calculations. This should get you pretty close.

With my .40 four cycle I had to start a loop from a shallow dive just like the full size. I did see a full size loop once.

One thing I would reccomend is that you use two aileron servos. The central servo-pushrod-bellcrank system on the plans is a real hassle to set up.

Good luck, and if you have any more questions, just ask.

Jul 17, 2003, 12:39 AM
Senile Member
Lnagel's Avatar
Correction on that last post. The weight I gave you is everything. The power system weight is 17.8 ounces for the engine and fuel tank, probably 8 ounces for fuel, and 1.7 ounces for the throttle servo. For a total of 27.5 ounces. I think I weighed some fuel once and found that a liquid ounce weighed about 1 ounce.

Jul 17, 2003, 06:56 AM
Registered User
Thanks for weighing your components Larry. Looks like this will make a really nice electric conversion. The dual servo wing sounds like a good idea. The bellcrank setup does look like it would be difficult to configure.
Jul 17, 2003, 08:15 AM
Registered User

Someone in our club recently flew a Goldberg Cub on an 2810 (is that an Axi outrunner?) with 8 cells and it flew well. I think this model is about the same size as the Sig, but heavier.

Funny, after seeing it fly I thought of the Sig cub myself as I had one years ago, film covered and Enya 35 powered. I fitted a 12x6 prop, which was a bit big for the Enya, but performance was good.

I've got a Mega 22-30-3 which is very similar to the Jeti 30-3 that Larry mentions, and I reckon on 8 cells this has similar power to the original OS40 FS that Larry also mentions - it turns an 11x6 at over 8000 rpm.

Larry's right - it is a light structure, and the struts are functional. I think it would be a winner with a modest brushless setup like a 30-3 and 8 - 10 cells.
Jul 17, 2003, 10:20 AM
Registered User
Thanks TrevC,

If it has enough clearance, I am thinking of running a Jeti 30/3 with a 2:1 gearbox, 15x10 prop, and 10 FAUP cells. If there is not enough clearance, I'll probably use the same motor direct drive with a 10x6 prop and the same batteries. Motocalc says the geared solution will climb at about 1000 feet per minute and be able to do continuous loops, while the direct drive version will climb at 600 feet per minute and fly like a trainer. Either one should make for a nice plane. I suppose the direct drive version would fly in a more scale like manner.
Jul 18, 2003, 04:58 AM
Registered User
Helge Sondresen's Avatar

I have a World Models Cub. 71 inch wing span.
I just checked with a 15inch propeller.

It clears the floor but if it nose down a little it touch.So I don't
think that will work well.
12 to 13 inch should be sufficient with the geared solution.

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Sold SIG 1/6 SCALE PIPER J-3 CUB KIT w/DUBRO CUB WHEELS hobbyfun100 Aircraft - Fuel - Airplanes (FS/W) 2 Jan 11, 2017 12:31 PM
For Sale Sig 1/6 scale Clipped Wing Cub Balsa Kit NIB Luscombe1940 Aircraft - Fuel - Airplanes (FS/W) 0 Jan 20, 2016 05:21 PM
For Sale Sig 1/6 scale Clipped Wing Cub Balsa Kit RC-26 NIB Luscombe1940 Aircraft - Fuel - Airplanes (FS/W) 4 Jan 17, 2016 05:27 PM
Sold Sig 1/6 scale Cub kit - unstarted. propjok1944 Aircraft - Fuel - Airplanes (FS/W) 0 Sep 13, 2015 09:35 PM