os120s-e overkill ????/ - RCCanada - Canada Radio Controlled Hobby Forum
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Old 08-20-2013, 08:27 AM   #1
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os120s-e overkill ????/

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Hi guys

I am fairly new to this site,so any help would be great.

I recently picked up a sig 1/5 scale cub with an 84" wingspan.

I have a chance at purchasing a os120s-e 4 stroke that is brand new for a really good price.

Would this motor be total overkill?? or could I make it work without hacking the cowl all to crap??

I will also be float flying sooner or later as well.

I would love to make this combo work.

Thanks guys

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Old 08-20-2013, 10:45 AM   #2
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Re: os120s-e overkill ????/

For a Cub, lots of engines are too much.

The Cub was designed for low power and gentle flight Long ago... it will fly with almost anything.

If you want to put the 120 in it - no problems. However; You will need to learn 'Throttle Control' - which is a polite way to say BACK OFF ON THE POWER! before the wings get torn off!

That being said, if you NEED the power -it is available.

Extra power is needed for Floats, Skiis, Wind etc.

Your call, but rarely do people complain about too much power.

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Old 08-20-2013, 01:06 PM   #3
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Re: os120s-e overkill ????/

The Sig cub was designed for a 25 to a 40 size engine. I have a Saito 50 in mine and it is great power. that being said, a 60 4 stroke would be plenty of power to fly with floats. any more and you would have way way too much power and rip the airframe into pieces. it is a stick construction and built light. A 120 will fly the Sig 1/4 scale cub with ease. Way, way too much power and weight for the little cub, not to mention you wouldn't have much left of the cowl by time you got done fitting it in there and the firewall would have to be beefed up as would the fuse and the wings. It just isn't designed for that much power or torque.
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Old 08-20-2013, 04:12 PM   #4
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Re: os120s-e overkill ????/

There are two major problems that you will encounter with that engine aircraft combination:

1. the engine is physically much to large to fit inot the plane. There won't be much if any cowl left once you finish

2. the engine is much too heavy compared to the suggested and preferred engine sizes. This will result in the need for considerable ballast to compensate which will further increase your problems.

There is absolutely no advantage to this. Much better to stick within the size recommendation ro go just a tad higher in engine size and make it a clipped wing bird if you want snappy performance, even on floats.

How do I know? I've done at least half a dozen Cubs in all configurations and flown several more, in numerous sizes, both clipped and full span wings versions, with both 4 and 2 stroke engines.

If you insist on using a 120 engine, either 2 or 4 stroke, go with a 1/4 size Cub on wheels or floats.
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Old 08-20-2013, 06:28 PM   #5
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Re: os120s-e overkill ????/

I have a Goldberg Anniversary Cub Kit build clipped wing at 67.5" on floats and burned out My 35 year old YS45 so I put a Saito 90 four stroke in it, had to tag 2 2oz lead wheel leads under the stab to balance it. NOT a good match! any take off attempt over half throttle and it will torque roll very severely. Same in level flight from 1/4 to 1/2 throttle, it is NOT a fun plane to fly. I have always over powered My airplanes but this one is just stoopid and I will be putting a much smaller engine in it.
Cubs do not need or like over power.

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Old 08-22-2013, 08:00 AM   #6
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Re: os120s-e overkill ????/

I see comments above for .25 to .40 engine being recommended... On a 84" 1/5 scale cub??!!! No way!!! Maybe the poster was thinking of the smaller 40 size cub, but on a 1/5 cub, a 120 is perfect IMHO. I have flown a lot of dogs over the years. The last thing you want is not enough power. If properly installed, the 120 will make the plane look "sexy" with the engine sticking out.
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Old 08-23-2013, 10:24 AM   #7
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Re: os120s-e overkill ????/

Leeann, my spouse, built and flies a 1/4 scale Sig Cub with a Saito 130 Twin. It's still a bit overpowered for true scale flying, but not so overpowered that it's an issue at full throttle. Another club member has a Hangar 9, 1/4 scale, with a big gas engine. His sounds like he should be tearing past our Cub, even at 1/2 throttle, but it doesn't, simply due to all the drag. You can only go so fast in a Cub. I've seen the Goldberg Anniversary Cub with the old Saito 90 twin, and that was plenty of power as well. I think you'd have an excess of power.
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Old 08-23-2013, 10:28 AM   #8
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Re: os120s-e overkill ????/

Engines .40 - .46 in³ (6.5 - 7.5 cm³) 2-Stroke
.45 - .65 in³ (7.5 - 10.7 cm³) 4-stroke

That's what Sig recommends. A 120 is twice the recommended power!!! I've got an 8 foot span telemaster, that's got insane rate of climb with an OS 91 four stroke. If you want a bit of reserve power, then I'd recommend a 72-90 Four Stroke. Going with a clipped wing? Then the 90-91 is plenty. Over power it, as our club in Germany did, with the four club Cubs that we built, and you'll tear the airplane apart. We had to rebuild and beef up all the tail feathers on our four Anniversary Cubs, to handle the ST 61s we'd installed.
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Old 08-23-2013, 05:53 PM   #9
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Re: os120s-e overkill ????/

I'm chipping in too. A 120 4 stroke is just waayyy too much for this cub. Flew one with a 90 4s and it even felt over powered. I agree with Rellic, they dont like or need to be over powered. Its a cub. Meant to fly slow and scale like.

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Old 08-25-2013, 05:30 PM   #10
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Re: os120s-e overkill ????/

There were two other 1/4 scale Cubs at the field this weekend, both with 26CC gassers, and then ours, with the Saito 130 Twin. While they are flown by great pilots, they don't sound or fly like cubs. I kept waiting for the wings to tear off. We putted around the sky, lots of stall turns, canyon turns, wingovers, and loops that were done the old-fashioned way, lower the nose, gain airspeed, than pull. Me, I prefer flying a scale aircraft in a scale manner.
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