Sig Four-Star 20EP Kit Build

[Marc]

Power and Electronics:

Motor: Turnigy 35-42B outrunner, 1250kv
I thought "20EP" meant .20 glow equivalent Electric Plane.
This motor is Turnigy's sweet spot for use with 3S LiPos.

Props: APC 9x6 (38 amps), APC 10x5 (43 amps)

LiPo: Blue Lipo, 3000mAh, 11.1v, 20C
Flat pack, light weight for its size.

Esc: Hobbyking SS Series 50-60A
Often gets bad reviews, but I have two that work perfectly.
Just don't power them up w/o the motor and/or Rx connected.
Used with Hobbywing 3A UBEC.

Rx: Corona RP8D1 synthesized, dual-conversion, 9ch, 72mHz

Servos: 4 Power HD HD1160A, 16 gram mini-servos

Four-Star 20EP Kit Modifications:

Top Battery Hatch: The kit is designed for an 1800-2400mAh LiPo to be inserted through the bottom hatch between the firewall and the leading edge of the wing. This space now houses the ESC and UBEC. A magnetic top hatch was fabricated and the rudder and elevator servos were moved back an inch or so to accommodate the larger battery.

Skid on Bottom of Wing: This was fabricated in lieu of landing gear to protect the aileron servos and linkages for grass landings. Standard landing gear can be added later if needed.

Substitute .047" Pushrods: The kit contains 1/32" (.031") music wire for the rudder and elevator pushrods and a pair of 12" 2-56 threaded rods for aileron pushrods. I substituted .047 music wire all around.

Four-Star 20EP

[smokejohnson]

Nice video Marc, the plane looks great. Have you flown it yet? How did it balance out and what is your weight?

[rcers]

Great top hatch! Excellent job at getting the pack back where it needs to be. Sig should have done this.

You are going to miss one of the best features of the plane IMHO, the touch and go's. I am really enjoying mine.

Mike

[Marc]

Originally Posted by smokejohnson

Nice video Marc, the plane looks great. Have you flown it yet? How did it balance out and what is your weight?

Hi Smoke,

No, I haven't flown it yet, but I hope to soon. With the back of the battery touching the hardwood servo mount, it balances on the front edge of the main spar with the spinner mounted. It balances at the back edge of the main spar without the spinner. I didn't need to add any lead, but it's a good thing I moved the servos back. I don't know what the model weighs since I only have a 16 oz. food scale, but you can bet it will have unlimited vertical with the setup I have.

Marc

[smokejohnson]

Originally Posted by Marc

Hi Smoke,

No, I haven't flown it yet, but I hope to soon. With the back of the battery touching the hardwood servo mount, it balances on the front edge of the main spar with the spinner mounted. It balances at the back edge of the main spar without the spinner. I didn't need to add any lead, but it's a good thing I moved the servos back. I don't know what the model weighs since I only have a 16 oz. food scale, but you can bet it will have unlimited vertical with the setup I have.

Marc

I bet it's going to be a fun ride . Good luck on the maiden and be sure to let us know how it goes.

[Marc]

Flies great. Only needed a couple of clicks on the elevator. Good axial rolls. Goes where you point it. No tendency to tip stall or any other adverse characteristics. Skid works great for pasture landings. I think I'll keep it for a while (I hope ).

[smokejohnson]

Congrats Marc. It sounds like the 20 is going to live up to the 4* reputation...nothing but smiles . I can't wait to fly mine.

[Dereck]

Hi Marc
Good job - can see why you altered the UC to allow for hand toss/belly landings if that's your regular patch!

Why Sig didn't put in a top hatch beats me. Every Four Star 40 I've heard of, bar one and you don't really want to know he fit the battery in, had a top hatch of some sort. I saw my first one at an e-fly meet in PA back around 1996, put one in my dear old Four Star 40 and have never used anything else in low wingers since.

All they had to do was drop by here and ask!

Whatever, they've turned out a great little electric sports aerobatic model. Here's to yours having a long and full-filled life.

Regards

Dereck

[ChrisW]

was looking at getting a .60 four star... this might be the ticket to get me into electric flight yet!

thanks for posting the build video
-Chris

[drummaker]

Originally Posted by Marc

Power and Electronics:

Motor: Turnigy 35-42B outrunner, 1250kv
I thought "20EP" meant .20 glow equivalent Electric Plane.
This motor is Turnigy's sweet spot for use with 3S LiPos.

Props: APC 9x6 (38 amps), APC 10x5 (43 amps)

LiPo: Blue Lipo, 3000mAh, 11.1v, 20C
Flat pack, light weight for its size.

Esc: Hobbyking SS Series 50-60A
Often gets bad reviews, but I have two that work perfectly.
Just don't power them up w/o the motor and/or Rx connected.
Used with Hobbywing 3A UBEC.

Rx: Corona RP8D1 synthesized, dual-conversion, 9ch, 72mHz

Servos: 4 Power HD HD1160A, 16 gram mini-servos

Four-Star 20EP Kit Modifications:

Top Battery Hatch: The kit is designed for an 1800-2400mAh LiPo to be inserted through the bottom hatch between the firewall and the leading edge of the wing. This space now houses the ESC and UBEC. A magnetic top hatch was fabricated and the rudder and elevator servos were moved back an inch or so to accommodate the larger battery.

Skid on Bottom of Wing: This was fabricated in lieu of landing gear to protect the aileron servos and linkages for grass landings. Standard landing gear can be added later if needed.

Substitute .047" Pushrods: The kit contains 1/32" (.031") music wire for the rudder and elevator pushrods and a pair of 12" 2-56 threaded rods for aileron pushrods. I substituted .047 music wire all around.

Four-Star 20EP

Can anyone on here tell me how much Dihedral is in the wings? I want to make sure it is right and don't want to rely Entirely on the angle cut into the spar

[Dereck]

Originally Posted by drummaker

Can anyone on here tell me how much Dihedral is in the wings? I want to make sure it is right and don't want to rely Entirely on the angle cut into the spar

By the technical method of holding one wing panel of mine down onto my table and measuring the gap under the other tip - 1 - 3/8" total, or 11/16" under each tip if you prefer that.

Flew mine today. Thankfully, an micro camera I bought way back wasn't working, so all are spared a video of my feet, tranny, bits of the model and, eventually, some sky with perhaps a small, fast moving dot in it...

It took off into around 10 - 15MPH wind ('Chicago breezy') with ease, in a straight line, albeit straight into wind. Climbout was very spirited with a 3S 2200mA battery giving a slightly forward of design range CG, E Flite Power 15 and 11 x 7 APC-E prop. Roll rate, both ways, proved good - I may up it a little later on to see what gives, but it is fine as stated in the kit. Pitch and yaw were equally solid as spec'd. Inverted required a slight push of down to hold level flight, knife edge was good considering the model was getting bounced around. Rudder does not cause noticeable yaw-roll coupling.

Stall and spin - stall was barely noticeable, spinning was hard to enter - as before, the CG is slightly forward. Think I need more rudder for stall turns, though again, really need to try her in calmer weather. Not that Chicago offers that luxury.

Landing, despite the wind, turbulence and direction, was uneventful. The kit UC offers good clearance on an 11" prop on our not so smooth grass field and the shallow ground angle makes touchdown into a non-event.

Have a range of 3S packs from 2200, 2400 and 2650. Only the first would fit in the kit's underside battery hatch/bay, all three fit in my top hatch modification.

I also moved the aileron servos inside the wings, rather than the ugly 'hanging out in the breeze' method employed in the kit.

Had my electrocuted Four Star 40 for eleven years. Suspect this little puppy will be around for a long while too.

Regards

Dereck

[Marc]

Originally Posted by drummaker

Can anyone on here tell me how much Dihedral is in the wings? I want to make sure it is right and don't want to rely Entirely on the angle cut into the spar

Yup, my dihedral turned out to be right at 1 - 1/2" total.

[drummaker]

Originally Posted by Marc

Yup, my dihedral turned out to be right at 1 - 1/2" total.

Thanks guys I appreciate it.

I am a beginner builder, this is my third. I have a question to ask

on all 3 of the wings I have build (all around 48" span)

eve though I glued with the wing down very tight on a very flat board, and I waited for the glue to dry, when I picked the wing up off the board there was a slight twist which would be considered washout if it was intentional. this is about 1/8 inch end to end at the back of the wing.

I know that I can fix this when I cover, But why is this happening. is it cause I am using CA?

Advice would definately be appreciated.

[Dereck]

Your wing warp. When I built mine, I did note that the mainspar protruded very slightly above the rib when it was placed in its slot - I built the main wing structure as per the kit manual. If that was the case with your model, pinning the wing down may be forced that wash-out in due to spar protrustion.

Before you get into covering, you could try lightly misting the wing framework with water from a spray bottle, then pinning it down with packing to warp it the same, but into wash-in. Leave for 24 hours, with luck it should settle down to 'flat'.

Snag with twisting the wing and heating the covering is that while it may be a temporary fix, the warp could creep back in. CA glues make a very solid joint - wood glues maintain a little flexibility for many years after assembly.

This open frame multi spar framework is very light, but sometimes wanders into a warp for no apparent reason. My Four Star 40, with a heavier version of the same structure, developed a warp to washout after 7 or 8 years. I had to check it before every flying session as the warp creeping back in was varied in time taken to happen. It was alright for the first years of its service life.

[drummaker]

Thanks for the info. I experienced the same issue with the main spar.

I did wet this thing down pretty thoroughly and it was still warped as soon as I unpinned. I am going to see if the other wing is identical... If it is. I will not worry and just call it wash out

is that ok you think?

[Dereck]

Equal washout won't ruin your Sundays, if it's the same both sides, probably better to leave it and live with it.

D

[Al_M]

One of the members of our club built his version just before the kit came out. It is a little smaller. He built in a terrible warp that is visible from a distance! It still flies ok enough with suitable trim, but he isn't one who does much aerobatics.

[Dereck]

Great thing about the Four Star is that once you've hacked that neat trick called 'landing', they are about as easy to fly as a trainer. Never mind the wing being on the bottom, they'll cruise around easy going like any of the Kadets.

Okay, we'll ignore overpowering, clipwings and suchlike behaviour...

D