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Need advice about servos

Old 02-19-2019, 12:37 PM
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Real2You
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Default Need advice about servos

Hello all,
First time on the airplane side of these forums. I'm building a Sig J-3 Cub 71" wingspan(first build of an airplane of this size).
The build is going good and as I get closer to completion I am wondering what are good servos to use. As a beginner I will just be doing basic flying.
I have been trying to read information about different servos but I thought I would get some real life advice. I think I will need 5 servos...any advice?
Thanks.
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Old 02-19-2019, 01:44 PM
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Just about any standard size servo with over 50oz should work just fine. I suggest a ball bearing servo as centering is a bit better. Of course your planned engine could change the requirement. I also run 6.6V LiFe batteries in just about everything. Any servo is only as good as the power you provide for it.
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Old 02-19-2019, 03:33 PM
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Thanks! I was looking at the Futaba S3010's.....the price seems kind of cheap to me for a servo so I need to make sure I get something that is adequate.
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Old 02-19-2019, 03:40 PM
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Those servos are more than adequate for that cub. You can use better servos but you probably won't notice any difference given the way cubs fly. Looks like 4 servos if you use an aileron bell crank or 5 if you use separate aileron servos (highly preferred). Get at least a 6V battery. Whether its NiMH, LIFE or LIPO is personal preference and what your charger is capable of handling.
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Old 02-19-2019, 04:10 PM
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Thanks for the good information...I'll probably go with the 5 servos. Been using Lipos with my helicopters so I'll probably stick with those.
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Old 02-19-2019, 05:20 PM
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52larry52
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The Futaba S3010 servos are really overkill for that size Cub. Futaba S3004 servos are more than powerful enough for that size J-3 Cub especially with a 6.0 volt on board battery. Give or take, you will pay about $25 ea. for the 3010 servo and $15 ea. for the 3004 servo. That will save you about $50 on this plane. As a long time Cub flyer in all sizes I would use the 3004's in this plane and spend that extra $50 somewhere else.
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Old 02-19-2019, 08:19 PM
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Thanks everyone for all the advice...it's exactly what I was looking for! I saw the S3004's and didn't know if they would be good for this plane....but I will definitely take your advice and look at those. Heck, that extra 50 I save can buy more servos for the Kadet I'm going to build after the Cub.
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Old 02-19-2019, 08:48 PM
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52larry52
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If the Kadet you're going to build after the Cub is a Kadet Senior I would use the 3010's on it everywhere except the throttle where the 3004 is fine. The size of the surface area being moved into the airstream and the potential speed of the model is the guide for what servo to use. I have used 3004's on a 71" J-3 Cub and 3010's on a Kadet Senior, a Rascal 110, and many 81"-90" Cubs with success. Good luck with your Cub.
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Old 02-20-2019, 11:03 AM
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Thanks Larry...good information for me to remember.
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Old 02-20-2019, 02:04 PM
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Thanks all....being that I'm getting all this good information I might as well ask...How about a good receiver and battery? Any thoughts? I plan to go nitro instead of electric.
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Old 02-20-2019, 08:19 PM
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Are you planning the Cub to be your first plane? If so, I will strongly urge you to get the Kadet finished first and learn on that. Cubs are pure joy to fly, but they aren't forgiving of poor piloting. They will ground loop in a second if you don't know how to take off well, and they have some odd quirks in the wind. A purpose built trainer is a lot better choice.
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Old 02-21-2019, 07:26 AM
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To be honest I am building the Cub and Kadet because I love to tinker in the shop and build things. I do plan on flying them both but not until I am ready and have the skill level to fly them.
I have UMX Timber and a T-28 Trojan that I plan to learn on first. I have a few helicopters I have flown for a while and a drone so I hope between the SIM and helicopter and drone experience I'll be able to learn airplanes pretty quickly(at least the beginner planes). All the time it takes to build these balsa planes gosh I would hate to crash it my first flight. Good to know though that the Kadet is easier for a beginner than the Cub. Thanks.
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Old 02-21-2019, 05:43 PM
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jester s1 is dead on 100% correct. In fact, to be a bit more blunt...A SCALE MODEL PIPER CUB IS NOT A TRAINER PLANE. I am referring to a built up balsa wood scale or near scale model like you are building (either glow/gas or electric) not the RTF foamies that weigh nothing, are not scale correct having had all the quirks removed, and have an on board pilot assist system. My dog can fly one of those. Build the Kadet Senior as a taildragger and when you are really good flying it then you can transition to the Cub. Fly the Kadet first, then the Cub and you won't be sorry. And BTY a Kadet is a fun airplane to fly. Enjoy.....
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Old 02-22-2019, 07:57 AM
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Hi!
I have been in this hobby/sport now since 1975 and a good way to become a better flier is to go from a high winged trainer to some low winged sport planes to learn some aerobatics and to experience more speed ...and then go too a scale type airplane like a CUB.
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Old 02-22-2019, 08:19 AM
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I agree that a Cub is not a beginners airplane, mainly because of the ground handling. I suspect this is due to the gear being a bit forward. I do not feel it is as bad as described however. IMO it is made worse by a poor setup. Most do not take the time to add the correct amount of right thrust so the airplane will want to veer left on take off. Couple this with too much rudder throw that is there for good turning radius while taxiing but too much for flight and the airplane gets difficult to manage on the take off run. With the correct setup a Cub shouldn't be much more difficult to fly then most tail draggers.
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Old 02-23-2019, 12:36 PM
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Also, don't over-power your Cub. It's best kept light, especially for a beginner. A 26 four stroke is a good engine on that plane. Many like a 40 four stroke, but unless you build heavy, it's more than you need. And building a Cub heavy is a sure way to keep it from flying like a Cub, and for a beginner, it will be harder. Note that the fuselage is very short compared to the wingspan, and the wing chord is small compared to the span. Put it up against your Kadet and you will see. Don't judge power for a plane by the wingspan.

You'll probably need some rudder on the turns, like the full scale does. Whereas the Kadet will turn quite well with just the ailerons.

Jim
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Old 02-23-2019, 07:42 PM
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A .26 four stroke in a 71 inch Cub? I can't get behind that. I have a Saito .72 4 stroke in my H9 .40 size Cub that's about the same size. I did cover it in fabric which added some weight, but I love how the plane performs with that engine. I tried a Magnum .52 4 stroke first and it was underpowered. It would fly, but I was at full throttle for the whole flight and didn't have any reserve power to get through windy days or abort a bad landing attempt.

It sounds like the OP has his head together about these planes. I think it's always good advice to get with an instructor for your first day of flying at least, but that's up to you. Remember that planes need a lot more space than it looks like they should.
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Old 02-24-2019, 04:51 AM
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Originally Posted by jester_s1 View Post
A .26 four stroke in a 71 inch Cub? I can't get behind that. I have a Saito .72 4 stroke in my H9 .40 size Cub that's about the same size. I did cover it in fabric which added some weight, but I love how the plane performs with that engine. I tried a Magnum .52 4 stroke first and it was underpowered. It would fly, but I was at full throttle for the whole flight and didn't have any reserve power to get through windy days or abort a bad landing attempt.

It sounds like the OP has his head together about these planes. I think it's always good advice to get with an instructor for your first day of flying at least, but that's up to you. Remember that planes need a lot more space than it looks like they should.
I agree the .26 is not the engine for this Cub. It might fly a very lightly built one but it would be marginal. But on the flip side, too much engine is just as bad for a variety of reasons. But for some people, like their cars and motorcycles, the HP under the hood is all that matters!
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Old 02-24-2019, 07:49 AM
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I would tend to think something along the lines of the OS 70 4 stroke would be ideal for a 71" Cub. Better to leave the overpowering to the guys who are capable of it. That is a whole differnt topic
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Old 02-24-2019, 01:53 PM
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Agreed. a .70ish 4 stroke is perfect. I love mine.
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Old 02-25-2019, 09:44 AM
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How about this engine for the Cub or Kadet? OS 46AXII ABL .46 Airplane Glow Engine with Muffler
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Old 02-25-2019, 09:52 AM
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That would most likely work well on the Kadet with an 11x5 prop but a bit low on power for the Cub. The 70 size 4 strokes do well with a 13x6 prop. Easy to see the useful power difference between the two although the 4 stroke will spin at less RPM. We are finding that larger props at lower RPM are more efficient.
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Old 02-25-2019, 10:05 AM
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Thanks for the advice...I think most are in agreement that the 70 size 4 stroke is a good engine for the Cub so that's what I'll go with. Thanks again everyone!
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Old 02-26-2019, 04:35 AM
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Originally Posted by speedracerntrixie View Post
......................................... We are finding that larger props at lower RPM are more efficient.
Known that for over 50 years. But available power plants also narrow choices of props.
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Old 02-27-2019, 05:49 AM
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There are plenty of Cubs in that size range flying on a ball bearing .46 like the OS. If you go that route, you'll want a low pitch, large diameter prop, probably an 11x5 or 12x4. I'm a fan of 4 strokes in Cubs for 2 reasons- the large amount of drag in these planes benefits from big props that create a lot of static thrust, and 4 strokes sound much more like a real aircraft engine. But I disagree that you won't get a good flying airplane by going with a .46 2 stroke.
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