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Jun 26, 2019, 02:00 PM
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Gameengineer's Avatar
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Originally Posted by viva_peru
Full disclosure: I am somewhat of a pattern snob, but I also have built quite a few sport planes for fun. I would stay away from Golden rods or their Sig equivalent; they do expand and shrink with temperature and humidity and they also have a fair amount of built in friction, especially if curved. I used to have a LT-25 which used them and the plane needed to be trimmed and re-trimmed as it came in and out of the basement onto the flying field.

For the elevator I would put the servo in the tail and use a short pushrod rod to drive it. Using pull-pull for the rudder works well. For the wings, I would ditch the single servo and use dual servos.

Good luck,

Teo
Thanks Teo! The kit is fairly new-ish since it has laser cut parts rather than die-cut and it includes dual aileron servos already so I don't have to design that but yeah, I would have if the kit had single servo.
I was sort of going back and forth in my mind as to whether or not use pull-pull for the rudder or just use a metal pushrod and keep it simple. I have not done pull pull. Looks simple enough but I noticed there were no spring tensioners aded to the wires that took up slack at least in the Dubro set I was considering. You basically just tighten them some amount making sure not to crush the rudder horns. I'm guessing you need to be vigilant and re-check tension from time to time.

Re: re-position elev servo in tail near the horz stab. That's interesting. I'll consider that.
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Jun 26, 2019, 02:28 PM
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The pull pull wire will stretch with time and they need to be re-adjusted from time to time but it is not a big deal. The hardest thing about pull pull is getting the pass through holes in the right spot, other than that, it is pretty straight forward. Moving the elevator servo to the tail would allow you to put the rudder servo along the fuselage center line as well. I built a Star 4*20 for fun and I placed the servos in the tail to avoid a nose heavy condition. Just putting the elevator servo back there should be fairly simple.

Teo
Jun 26, 2019, 03:00 PM
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Quote:
Originally Posted by viva_peru
The pull pull wire will stretch with time and they need to be re-adjusted from time to time but it is not a big deal. The hardest thing about pull pull is getting the pass through holes in the right spot, other than that, it is pretty straight forward. Moving the elevator servo to the tail would allow you to put the rudder servo along the fuselage center line as well. I built a Star 4*20 for fun and I placed the servos in the tail to avoid a nose heavy condition. Just putting the elevator servo back there should be fairly simple.

Teo
I was looking at the 4-40 version of this Dubro pull pull system.
https://www.dubro.com/products/2-56-...nt=27880506759

Now I need the dual horn rudder. I understand that you need to keep the distances between the servo link and horn widths the same, basically making a rectangle, or crossed rectangle.
Jun 26, 2019, 03:56 PM
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Dude, it seems you just keep adding weight to that plane... LOL. 4-40 pull-pull is way overkill for that little guy. I use that on my 100cc gas planes. That plane is fine with all 2-56 hardware. I use a coated-kevlar, no stretch whatsoever... also no steel or weight in it. Those Dubro pull-pull kits are fine, but don't go with the 4-40.

Between your adding wing sheeting, metal push rods, and now 4-40 stuff, man you really should take a look at how much weight that will add up to.... and where it's going comparative to where you want the CG to end up. Up to you though. Carry on.
Last edited by DGrant; Jun 26, 2019 at 05:43 PM.
Jun 26, 2019, 04:38 PM
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Quote:
Originally Posted by DGrant
Dude, it seems you just keep adding weight to that plane... LOL. 4-40 pull-pull is way overkill for that little guy. I use that on my 100cc gas planes. That plane is fine with all 2-56 hardware. I use a coated-kevlar, no stretch whatsoever... also no steel or weight in it. Those Dubro pull-pull kits are fine, but go with the 4-40.
Point taken.
Jun 26, 2019, 08:49 PM
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I rarely build exactly to plans and find that "re-engineering" things can be part of the fun of the build. I'm not sure if it was mentioned as the chatter got going pretty quick in this thread, but considering you are using a four stroke, you may want to wait on radio installation to see if you are nose or tail heavy. If nose heavy, you can always put either or both of the elevator and/ or rudder servos in the tail. Also as stated above, all these changes to the design usually end up adding weight. The four star series is meant to be low wing loading floaters that fly on the wing. I have flown some four stars with lots of repairs that added considerable weight and I will say they are definitely not as fun to fly as when light and floaty. Also while making changes to design and using "better" hardware, you also have to realize the Four Star planes have been around for 30 years for a reason...it's an amazing design, builds easy and flies great! Sig has been around a LONG time and put quality hardware in their kits. They arent like Chinese ARF's where most hardware is cheap junk and almost a necessity to replace with better hardware.
One thing I've always found in build discussions is people always feel there's something better; whether it's hardware, type of glue, building methods...list goes on and on. It comes down to whatever makes you feel good about your plane and what makes the build fun and enjoyable!
Don't take this as me trying to discourage "re-engineering " or making changes to the original plan. Quite the opposite! I love seeing how people make a plane their own. I'm just saying that you can build a Sig kit exactly as designed and with the included hardware and you'll have a quality aircraft.
Last edited by kimchiyuk; Jun 26, 2019 at 08:55 PM.
Jun 26, 2019, 10:05 PM
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Quote:
Originally Posted by kimchiyuk
I rarely build exactly to plans and find that "re-engineering" things can be part of the fun of the build. I'm not sure if it was mentioned as the chatter got going pretty quick in this thread, but considering you are using a four stroke, you may want to wait on radio installation to see if you are nose or tail heavy. If nose heavy, you can always put either or both of the elevator and/ or rudder servos in the tail. Also as stated above, all these changes to the design usually end up adding weight. The four star series is meant to be low wing loading floaters that fly on the wing. I have flown some four stars with lots of repairs that added considerable weight and I will say they are definitely not as fun to fly as when light and floaty. Also while making changes to design and using "better" hardware, you also have to realize the Four Star planes have been around for 30 years for a reason...it's an amazing design, builds easy and flies great! Sig has been around a LONG time and put quality hardware in their kits. They arent like Chinese ARF's where most hardware is cheap junk and almost a necessity to replace with better hardware.
One thing I've always found in build discussions is people always feel there's something better; whether it's hardware, type of glue, building methods...list goes on and on. It comes down to whatever makes you feel good about your plane and what makes the build fun and enjoyable!
Don't take this as me trying to discourage "re-engineering " or making changes to the original plan. Quite the opposite! I love seeing how people make a plane their own. I'm just saying that you can build a Sig kit exactly as designed and with the included hardware and you'll have a quality aircraft.
That's great insight right there. Especially the last area I high-lighted. I always say if you want to get very proficient, build kits from several manufacturers... just as they design them, and use their techniques described in their manuals, and you will come away with a library of different styles and techniques, and take that into your next realm... when you get into the more custom aspect. Above all as mentioned enjoy it, and use what feels good... That's what matters.
Jun 27, 2019, 06:52 AM
Registered User
I would not worry too much about making changes as long as you keep an eye on the model's weight. Light airplanes will always fly better. I do not think that I have truly ever built a kit where I did not deviate from the design in one way or another. I built a BUSA 1.20 sized Citabria Pro a few years ago which I modified extensively. I was told that the plane would come in at 12 lbs RTF and my electric version came in at 9.5 lbs, RTF. The power system is modest so it flies in a very scale like manner. It was a fun process and so far the wings have not folded. Even on that plane I used 2-56 hardware, just kept the connections nice and short. I also built a slightly modified Sig Something Extra a few years ago....Moved the tail 3 inches back, gave the stab anhedral, moved the canopy forward and used strip ailerons. It is nice little sport plane. Don't be afraid to change things a little.
Jun 28, 2019, 10:16 PM
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Was busy this week so I didn't get to the build table as I would have liked. I didn't get a lot done but some.

I added the remaining 1/4"×1/4" spars to the top and bottom. I cut and sanded flat the end ribs. The inner end has the 2 degree angle for the dihedral which is still true.

I decided to add wing tips carved from these massive 2x3x12 balsa blocks from Sig. After being epoxied to the tip rib it will be whittled down by at least 2/3 leaving a nice rounded tip.

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The next up is adding 3/32 planks to the inner center area. The center and LE will ultimately be covered. with 1/16 sheeting. I eliminated the cross bracing the kit plans called for. The sheeted LE will supply ample cross strength.
Last edited by Gameengineer; Jun 28, 2019 at 10:54 PM.
Jun 29, 2019, 03:53 AM
What could possibly go wrong?
Hi, just wanted to sub this thread and wish you well with it, sounds like a nice project. My last was a BTE Venture 60 which has some points in common with the 4*. Bruce Tharpe designed the 4* 40, 90 and 120 but not the 60. He says in his site that the Venture 60 is his idea of an evolved 4* 60 and it is another great model. Like the Sig it's got top hardware and well chosen wood. He also stresses keeping it light, it's a low loaded floaty model, the one issue that presents is it can keep on floating when you want it to come on down to the deck but otherwise the light loading is a blessing worth keeping.

Mine runs a Saito 82 glow 4-stroke which is a good match. Great power to weight. I'm another 4-stroke devotee, I still like glow too. That OS 91 should do a great job. I haven't seen it mentioned but one way to balance a model if it's nose heavy is to move the engine back a little. 4 strokes have the carby to the rear so the forward cylinder puts the weight forward. When I crashed and rebuilt my trainer I set it 30mm or so back and that was just right, it made it balance easily without ballast or reworking everything. You could consider trimming an inch or so from your fuselage sides to allow that move if you wish, but you'd have to decide if it seems worth it.

FWIW I only use digital Hitec servos, now I'm buying all D-series as their current line. They have been improving all the time and I don't find current draw or centring issues with the modern ones, I can't speak for older designs. Good servos at a good price. I tried super cheap no name units and rapidly decided it was a bad idea, you definitely get what you pay for.

Minor wing warps aren't a huge problem. Wait till it's covered anyway and thee will be different warps, either more or less than now. With heat shrink film it's easy to correct. You bend the wing straight which will make little wrinkles somewhere new on the covering, then just iron those out smooth and that should straighten the wing up pretty good. But I agree with your getting it as straight as possible now, I'm just saying after covering that might add different tensions so check it again at the time.

They have a rep as a nice flying model which you'll enjoy very much, and with that sweet engine on it that's some nice equipment. Enjoy the build and I look forward to seeing the results.
Jun 29, 2019, 04:01 AM
What could possibly go wrong?
Also I agree it's cool to modify things to your own preferences on the fly, but just be clear in your head exactly what you want to do, don't corner yourself and not be sure how to finish what you start. My current build is nominally an Ugly Stik but it's a complete mutant, all I'm keeping is the silhouette. Other than that I'm totally ignoring the plans and using all my own structures, it's a different scale and I've changed all but the shape. Which is fin and educational but a couple of times I've started a section then realised I hadn't fully designed that section to completion. It doesn't hurt to break out the sketch pad first, it's easier than cutting away finished wood.

Looks like a nice job so far, have fun
Jun 29, 2019, 04:44 PM
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Thanks for watching Bernard.

The mods I'm planning are not too many and I'm being weight conscious.

I decided against the pull pull rudder just to keep it simple but I am for certain going to replace the nyrods. I'll also be using hitec 485BB servoes. They have worked well for me so far and analog is perfectly fine for this plane. I was just curious on whether digital was worth the money for a plane like this given how I am going to fly it.

Another club member past on recently and his stash was donated to the club. I picked up his old CG Eagle 2. Needs some work and it has airtronics servoes. I'll solder on new hitec types and flip the power and ground wires. It's nice to have a beater plane that I wont be concerned about hard landings.
Last edited by Gameengineer; Jun 29, 2019 at 05:55 PM.
Jun 30, 2019, 03:21 AM
Registered User
RTL has some really nice servo mounting screws that have socket heads and straight threads.

https://www.rtlfasteners.com/

I use them for mounting control horns too. With the socket head you’re unlikely to slip off and punch through the covering. A hobby shop where I used to go carried some nice servo beams. They were 1/2” square balsa with a strip of 1/2” lite ply glued to the top. The combination made for a very strong and light beam that held screws really well. They came with lite ply saddles to notched out glue to the fuselage sides so they were very secure. To this day I still fabricate them for my builds.
Jul 01, 2019, 09:18 AM
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Quote:
Originally Posted by David2011
RTL has some really nice servo mounting screws that have socket heads and straight threads.

https://www.rtlfasteners.com/

I use them for mounting control horns too. With the socket head you’re unlikely to slip off and punch through the covering. A hobby shop where I used to go carried some nice servo beams. They were 1/2” square balsa with a strip of 1/2” lite ply glued to the top. The combination made for a very strong and light beam that held screws really well. They came with lite ply saddles to notched out glue to the fuselage sides so they were very secure. To this day I still fabricate them for my builds.
Thanks for the link. I'm adding it to my list of suppliers.
Jul 08, 2019, 10:03 AM
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Not much activity to post. I did do some to the wing but not enough to post. My attention has been diverted to more low hanging fruit which is the CG Eagle 2 I recently got and am restoring to be able to fly soon.
Its a beater plane for sure. Lots of hangar rash.

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Picked up a new OS 40 LA. Old, sleeved but should work fine for the life of a trainer.
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Hmmm, old servos, plastic gears, possible failure point. I soldered on hitec style connectors swapping + and - wires and they work but probably not going to trust them. I have some replacement servos.
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Wing patch job. Ugly but will fly.
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