Piper Super Cub Question - RC Groups
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Feb 17, 2013, 01:22 AM
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Piper Super Cub Question


I posted this in another forum, and someone suggested I put it here. I built and flew RC floaters and slope planes in years past, but for fun, (with a broken leg), I'm going to build a 24"Guillows Cub. I now have learned about the heavy wood and weight issues for great free flight, but I really just wanted to build it for fun.

My questions have to do with removing aft weight without jeopardizing the strength for the rubber motor and torque. I've seen build posts of removing wood from the formers, using smaller wood for the tail surfaces, and also of ommitting some of the wing ribs.

I'd rather avoid re-cutting parts from lighter wood if I can.

Any advice is welcome. Obviously lots to learn.

Thank you,

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Feb 17, 2013, 01:57 AM
B for Bruce
BMatthews's Avatar
Not ALL Guillows kits use the heavier ersatz balsa. I've had a couple that were done with rather excellent wood. The newer series seem to be that way. So get the kit first and evaluate the wood before you panic.
Feb 17, 2013, 04:25 AM
Registered User
Thanks for the advice.

I should get it in a day or two. I''ll look at it before any panic sets in.

When you come up with a figure for balsa weight, are you just weighng one or two sheets and then doing the math to get to a cubic foot?

Feb 17, 2013, 08:19 AM
Balsa Flies Better!
If that airplane is anything like the Cessna 180 in the series- get ready to change a lot of stuff including incidence, thrust lines, cg, airfoil...

Why not get something that's got decent wood and a better design to start with? I think the Herr kits are very nice- cost about the same- and the only tweak I did to their Cessna 180 was maybe add a little dihedral- and maybe not even that. OK- different prop too- but the airplane flew off the board fine. The fuse frames are a little harder to build, but not much. The Peck Polymer Baby Ace is also a bit trickier to build but will fly well too.

And if you want something easy to build- the BMJR Ranger 28 gets my vote- it's a joy to assemble- I'm helping an 11 y.o. girl build one and she's not needing much assistance.

Feb 17, 2013, 08:48 AM
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Yak 52's Avatar
Originally Posted by swift4me
When you come up with a figure for balsa weight, are you just weighng one or two sheets and then doing the math to get to a cubic foot?
Yes, if you know the volume of the piece then you can work it out.

You might find this calculator helpful.
Feb 17, 2013, 11:21 AM
Registered User

I live in France and have virtually no hobby resources around me, and I found an outfit in the UK that could ship the Guillows kit to me, so I went with it. Afterwards, I started surfing around and found sites that talked about the wood, props, thrust, etc., and this site.

For my goals, (mainly enjoying the build with my busted leg), it will probably be fine. I'm trying very hard to not get back into the RC thing. My glider addiction fifteen years ago was great fun, but I sold everything before moving.

I'll try to lighten things up if the wood is heavy, but like a gentleman above said, I'll wait til I get it and go from there. There will always be time for another kit tht is better. Also, where I will be flying this thing, it needs to be tough. If I can get it in the air so my neighbor's kids, (who've never been within a mile of any airplane in their lives), can watch and giggle, I will be happy.

Thank you Yak 52 for the link. It will be alot easier this way.

Thanks for all the help.

Last edited by swift4me; Feb 17, 2013 at 11:50 AM.
Feb 17, 2013, 11:51 AM
B for Bruce
BMatthews's Avatar
If it's this one;


then it's one of their older designs which uses a LOT of wood.

The funny thing is that this particular kit design has been around literally for decades. I built one back in the later 1960's with a Cox .049 in the nose for a control line model. It crashed on the first flight and busted into many, many pieces because at the time I didn't realise that the wing to stabilizer angles were so extreme.... But that's another story.

If it turns out that they use a lighter sort of stock thanks to being laser cut now then it may well build up to actually fly. It won't be a great flyer, it simply uses far too much wood and even with light wood will require far too much nose weight.

Now if you were to build it up with the tail surfaces and nose modifications to convert it to a small electric RC package it could be a great little park flyer style RC model. But as a rubber powered model it's more or less doomed to short flights even by rubber scale standards. And that's pretty short by sport rubber model standards.

By all means build it up either as a rubber model or as an electric RC conversion. Because you're looking to fill in some healing time it'll be very successful either way. But if you actually fancy some quality rubber model flying time then perhaps give us the link to the supplier and we can suggest some kits that would make better flying models.
Feb 17, 2013, 12:53 PM
Balsa Flies Better!
If Bruce has the correct airplane (I was thinking of the 20" build by number series)- then my comments aren't valid.

However- one point to add if I may...

I find it harder to trim a heavy model intended to fly for a short period of time than a lighter model. In FF its really hard to build rugged-you often wind up with something that just hits the ground harder.

With all that being said- George Perryman's Mini Maxer is a robust design- yet flies like a champ with a decent prop/rubber combo. I've built one from a Sig kit and had it fly away- and a buddy built one as pretty much his first FF airplane (he was a good builder- meticulous)- used Balsa Rite to apply the tissue- and still had something that flew very well.

Feb 20, 2013, 12:22 PM
Registered User

finally got my kit

Hello again

I got my kit today and of course started right in on it. After reading the comments here and elsewhere about the Guillows kit, I was surprised at a couple things. It still has the 5"propeller, but the laser cutting seemed perfect. I had read about sanding the backsides of the sheets to facilitate removal of the parts and take out some weight, but these sheets were cut completely through, and the pieces just about fell out. I've rough built one wing and alot of the fuseleage, and haven't had to sand one groove.

I thought I had access to a scale, but I didn't and I wasn't going to wait. I'm doing some of the things suggested here and wait until I get a better free flight kit to worry about really getting light.

I just thought I'd share what I saw in the kit.

Feb 20, 2013, 05:50 PM
B for Bruce
BMatthews's Avatar
That hint on sanding the back side of the sheets comes from the days if the die cut (AKA "die CRUSHED") kits. When the dies got dull they often didn't cut all the way through the wood and sanding the back worked as you read to both free the parts and lighten things up.

The trick simply isn't valid with laser cut sheets.

And this IS the same design that I did back as a teen. Mine had the die crunched sheets which meant I had to smoothen up the parts before use. Do whatever you are comfortable with to lighten up everything aft of the wing's main spar if you are serious about the rubber power option.

To help things along get a bigger 7 inch prop and move the rear rubber anchor forward by one former. It will cut down on the amount of rubber you carry but the reduction in rubber will be offset by the reduction in nose weight. So you'll get a better flying model in the end.
Feb 21, 2013, 12:44 AM
Registered User
Thanks for the clarification. I thought even some of the laser cut kits required the sanding.

I'll take your advice on the rubber anchor, but is there any particular prop I should buy? Also any change in the rubber?

Thank you,

Feb 21, 2013, 09:39 AM
Balsa Flies Better!

Permit me to disagree with Bruce (who is a whizzbang free flighter by the way) and throw in a different point of view.

1) The biggest problem with heavy airplanes is not that flights are short- it's that they're harder to trim. It often takes a fair amount of tweaking to get that graceful circling flight that FF guys seem to do so effortlessly on You Tube- but the reality is that there's often a lot of trim flights, regluing, and $#%#$@% that happens before hand. Often the learning steps have happened in the dozens of airplanes built before. Very few people are rewarded with an airplane that "flew off the boards" on its first flight- even after building for awhile.
2) This airplane ISN'T designed to fly- it's really designed for static purposes. Far more have been flown successfully using RC gear than ever flew with rubber power. That's because the RC versions are probably lighter- with the motor and battery up front, the noseweight is doing something useful. Airplanes with short noses like this Super Cub often do better this way.
3) Since you flew RC- here's the challenge- think about building this airplane- and then setting the throttle on the Tx- tossing it- and then not touching anything! Most of the park flyer versions I've seen are anything but hands off.
4) Us FF guys build in trimming as we build. It's a knack to figure out what can be successfully lightened in a design, and what needs beefing up. It's not easy to do- and we often build by feel although the really serious guys weigh every piece.
5) Given your thoughts that you'd like to see the neighbor's kids chasing this airplane- I think you're going to be cruelly disappointed. My educated guess is that you'll be lucky to get a short hop of 10 seconds or less with no climb.
6) I suspect that the prop in the airplane is 6" and that they gave you a loop of 3/16" rubber- maybe 1/4". This is probably not a bad power combination for the airplane. It's easier to trim something with a smaller prop than a larger prop. With a decent airframe- Bruce's suggestion of a 7" prop is probably fine- heck, some guys might go to an 8" prop- but since you're going to be heavy- stick with a smaller prop. Don't be afraid to reduce the blade area either!
7) I'll reiterate- if you want a nice flying scale ship out of the box- go get a Herr kit. Penn Valley in the US will ship internationally- at least they used to, and I'll bet they stock them. Then your dream of having the neighboring kids chasing the airplane will have a shot at reality.

Feb 21, 2013, 10:32 AM
Registered User

I think Guillow's recognized this when they came out with a Pilatus Porter recently. I talked with a rep from there at the RC Expo a couple years back when it was in prototype. They were trying to make a scale plane that would take more advantage of the laser cutting to fly on rubber.

I don't know if they succeeded. I've got a Cessna 140 from Dare built up that's about 26 inch span and weighs 47 g with a bit of nose ballast and a 8 inch Peck silver prop, which is working ballast. It's got 4 strands of 1/8 rubber 14.5 inches long and will make a minute in fair air on about 900 turns. It's not slow, but will climb. Pictures are on my Blog.

I hope Pete can get access to a scale, even a kitchen one, to get an idea of his problem.

Feb 21, 2013, 12:27 PM
Registered User
Thanks again for the comments.

No doubt that this plane will likely get chalked up to building experience and entertainment while my bones heal. I have a very basic understanding of what you guys speak when it comes to trimming and controling thrust, (although I have no experience in the thrust department), but I remember trimming the different gliders I flew and seeing the reactions.

I will try to get a scale, but after your comments, I'm expecting a big number. Fortunately my farm is on a hillside, so maybe the Cub will go a bit further. God help me if it gets out of the prairie. To be honest, the biggest reason I bought this kit was because it was a Super Cub. I've spent a fair amount of time in Cubs and Super Cubs, mostly in Alaska on hunts, but it always seemed to me to be a no-nonsense working plane whether on floats or tundra tires.

If I still want to pursue this after I'm ambulatory, among my other crazy hobbies, I will no doubt start with the right sort of kit.

Feb 21, 2013, 01:18 PM
B for Bruce
BMatthews's Avatar
Megowcoupe, I don't see anything in your reply that is wildly off what I'd have said myself. Unless perhaps it was my final comment about my suggestions that said "So you'll get a better flying model in the end.". If that's the part that made you chuckle then I agree that it should have read something more along the line of "With such mods you'll have a better chance of it flying to some degree".

Adding RC provides for a much higher degree of success not because it makes the model come out lighter in the end but rather because the electric power source provides more useable power which is located in a better placement to aid in getting the balance point right and hauling these "lumberyards" into the sky.

Still, all this woe might be misplaced if by some chance the wood used in the kit is of medium or lighter density. If that's the case and if the heavy hardwood wheels so often found in these kits were replaced with a light balsa with aluminium tube hub then it's possible that the nose weight needed will be moderate, by Guillows standards, and that the model might just be able to fly for up to around 30 to 40 seconds with suitable power.

Speaking of suitable power the single strip of rubber so often found in these kits won't do more than simply spin the prop around on the ground or pull it along a polished floor. To get this thing to fly you're looking at something along the lines of a double loop (4 strands) of 3/16 rubber or a triple (6 strands) of 1/8. To get a little more duration from such a motor and avoid a strong power burst you want to make up the motor so it's roughly 1.3 to 1.5 times as long as the prop hook to rear anchor distance.

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