Sig Four Star 20 EP Kit Review - RC Groups

Sig Four Star 20 EP Kit Review

Sig has released an update to the highly popular sport planes, the Four Star 20 made specifically for electric power, and Mike Llewellyn puts it to the test!



Wingspan:48" 1219mm
Wing Area:430 sq/in
Wing type:Built up balsa: Semi-symmetrical
AUW weight:Advertised - 40oz Actual - 37.1oz (1052g)
Wing loading:~12.4 oz/sq. ft.
Transmitter:Hitec Aurora 9
Servos:Micro MG BB and Naro BB
Receiver:Hitec Optima 6 channel
Battery:Subsonic 2200 3s 25c LiPo
Motor:Motrolfly DM-2810 1200Kv Brushless Motor
ESC:Motrolfly 40 AMP OPTO ESC
BEC:Motrolfly U-BEC
US distributor:SIG Manufacturing
SIG Four Star 20 EP Kit:Sig Four Star 20 EP Kit
ARF Price:$79.99

SIG has release an all new, but familiar, RC kit to market. This is a smaller variant of their wildly popular Four-Star line of kits and ARFs. SIG has been in the RC kit business for some time, and over the years they have established themselves as a premier kit and ARF maker. Those of us with a bit of time in the hobby have long recognized them as a leader in the industry. While they have branched out in recent years with ARF models of their popular kits, I think of them fondly as a provider of a box-o-balsa!

I have built many SIG kits, and several of their planes hold cherished spots in my memory. I have built SIG Kavaliers, Kougars, Colts, a 1/4 scale Cub and others. These models bring me back to the roots of my RC days, well before the days of laser cut wood.

I suspect that if we were brutally honest, many of us would admit we had not opened a kit box in a good long time, but with the introduction of the Four-Star 20 designed for electric power, it is now time for you to do that again. For those who have never built a kit, have no fear. The all new Four-Star 20 is laser cut and has an excellent step-by-step instruction manual with pictures!

It is time to start a nice winter build project and for those who have never built a kit this would be a great start. This SIG Four-Star 20 makes a perfect, quick build offering for even the first time builder.

This is a high quality kit with laser-cut parts and exceptional parts fit. The fine workmanship and laser cutting allow for the time tested Four-Star sport model heritage to shine though in this ultra quick build!

Kit Contents

The review kit shipped from SIG Manufacturing, and it arrived in perfect condition. It was well packaged to protect the parts and double-boxed.

Kit includes:

  • All the balsa and lite-ply parts necessary to build the kit
  • Clear canopy (pilot not included)
  • Nose cowl
  • Generous hardware package (push rods, aluminum landing gear and axles, nuts/bolts, SIG easy hinges, clevis, keepers and control horns)
  • Classic SIG Four-Star markings
  • Clear well-written picture assembly guide
  • Full sized plans

Kit requires:

  • 250w-350w brushless motor
  • 30-40 AMP ESC
  • 3s LiPoly battery (2200 mAh recommended)
  • 4 Micro/Mini servos
  • 4 channel receiver
  • 4 channel transmitter
  • Servo extensions for aileron servos
  • 2 1/4" tires
  • 1 roll of covering
  • Paint for cowl
  • 1.5"-2.25" spinner or prop nut


  • Pilot figure

Included for this review:

<font size=-2>Motrolfly DM-2810 Brushless Motor</font>
Motrolfly DM-2810 Brushless Motor
Type:Brushless Outrunner
Output shaft size:5mm
Cells:3S–4S Li-Po
RPM/Volt (kv):1240
Continuous Current:40A

<font size=-2>Motrolfly FM-40 AMP Opto ESC</font>
Motrolfly FM-40 AMP Opto ESC
Continuous maximum current:40 amps
Input Voltage:11V - 25.2V
Input connector type:Deans "T" connector
Output Input connector type:3.5mm female gold bullet connectors

<font size=-2>Sonic Power 2200mAh LiPo battery</font>
Sonic Power 2200mAh LiPo battery
Number of cells:3
C Rating:25C
Max. Continuous Current:55A

<font size=-2>Motrolfly U-BEC </font>
Motrolfly U-BEC
Input Voltage:5.5 - 42v
Output Voltage:5v or 6v
Output current:3 AMPs

<font size=-2>GWS Naro Servos</font>
GWS Naro Servos
Torque:25 oz/in at 4.8V
Speed:.12 sec/60 degrees at 4.8V
Gear type:Nylon

<font size=-2>GWS Micro Metal BB</font>
GWS Micro Metal BB
Torque:75 oz/in at 4.8V
Speed:.17 sec/60 degrees at 4.8V
Gear type:Metal

I have used the Motrolfly motors and ESCs on review models before. I can assure you the Motrolfly quality far exceeds the typical budget motors and ESCs. The 2810 brushless motor provided stunning power for the Four-Star and gets a top nod from me.

GWS was gracious enough to provide servos for the review as well. I have long used GWS servos, and they simply rock. They are also available at great prices, just a few dollars more than the very budget servos some use. They offer top quality, centering and torque well above those super cheap alternatives. Quality is worth a few dollars more.


It has been a while, too long in fact, since I have built a kit. I suspect many of you find yourself in the same boat. With the introduction of the new SIG Four-Star now is the time for a kit build. It is advisable to read the manual once or twice before starting the build as that helps avoid mistakes and parts mis-use. Since the key parts are all laser cut there was no question this would be a quick build. The feeling of accomplishment is great - build a kit!


Work began with the wing as per the instruction manual. Starting with the spars, some measuring and quick laminating had those ready as the starting point for the wing.

The laser cutting was impeccable with excellent parts fit. Even the spar webbing was laser cut with proper rib placement making the wing assembly a snap.

The wing progressed with the addition of center sheeting to the top of the wing. 1/16" balsa sheeting was provided for this purpose.

Tail Assembly

The SIG Four-Star included laser cut parts to assemble the horizontal, vertical stabilizers and control surfaces, rudder and elevator. All the parts were laser cut, including the stringers. The plans and parts key showed what went where, and the fit of all parts was excellent.


The fuselage of the Four-Star was also all laser cut. This made the kit build easy, accurate and fast. Identification of the parts was simple with the plans and parts guide in the manual.

The balsa fuselage sides were laser cut and they required a doubler to be added. Again, assure you are building a right and a left fuselage side. I use the top and bottom mirror method of building to assure that.

Now that the parts have their associated doublers it was time to move to the fuselage structure build. I appreciated the laser-cut top provided. In my past years I have tended to build banana shaped fuselages, building using this top plate as a template made that nearly impossible.

Steps have you progress from the tail to the front of the fuselage, gluing only when indicated.

The battery hatch was laser cut from 1/8" lite-ply. It keyed in between the firewall and the landing gear plate. The battery tray installation was one area where I should have deviated from the plans. The tray placement just allows my 2200 mAh packs to fit. Installing that more towards the top of the fuse would have allowed more battery space and I highly recommend moving the tray toward the top of the fuselage.

The turtle deck also has lite-ply formers that were keyed into the fuselage top for proper alignment.

The front deck shaping was done. The laser cut parts allow the pleasant rounded shape to be created. The balsa sheeting must be cut prior to installation. I soaked my sheeting in water as it was very hard stock. This allowed the balsa to bend and conform to the rounded shape in the nose. Make sure you bevel the fuse sides as the instructions called out.

It was necessary to build out from the firewall on the Four-Star allowing the proper placement of the motor and propeller. I used the included laser cut plywood stand-offs and then glued a sub firewall assembly with blind nuts (not included) for mounting the brushless Motrolfly 2810 motor.


SIG provided a molded clear canopy for use on the Four-Star. The canopy provides an attractive cabin area.


New to this SIG Four-Star 20 EP was a molded cowl. The glow equivalent Four-Star models just had fuse sides and open motor area. The cowl added a great finished detail for the EP version.

Power system

SIG recommended a 250w to 350w motor to power the Four-Star. There are so many motor choices, so I consulted my friends at Subsonic Planes to discuss power options. With all of the statistics of the Four-Star and completed weight, Ken from Subsonic Planes recommended the Motrolfly DM-2810 1200 brushless motor to power this model. To be honest I was heading in a bit of a different direction kV wise and I really appreciated the free consultation and advice I received from Ken. You certainly do not receive this level of attention from all vendors. The recommendation proved to be spot on and I was very happy with the power provided by the high quality Motrolfly DM-2810. Thanks Ken!

Amp draws

The Motrolfly brushless motor was perfect for use with 3s 2200mAh packs recommended by SIG. With the Sonic Power 2200 mAh 3s pack and this powerful motor produced the following results:

Motor statistics on 3s
Propeller Amps Watts Voltage
APC e 9x6 30 333 11.1v
APC e 10x5 33.2 365 11v
APC e 10x7 36.7 400 10.9v
EMP 9 x 7.5 41.2 445 10.8v

These power levels gave the SIG Four-Star 20 model stunning power. With the 10x7 propeller and 173 watts per pound performance for the sport model was very impressive indeed.

The Motrolfly ESCs have provided me with consistent, impressive performance. I highly recommend them and where else can you get the personal service I did while selecting the power for this plane? Excellent free advice so hats off to Subsonic planes and Ken for all his help.


A single 3s 2200mAh Sonic Power 3s LiPo 25c battery to provide power. This pack weighs in right at 151g. Performance of this pack was stellar as can be seen it provided great voltage under at the ~37 amp load.

Final Assembly and Covering

Some naked shots of the SIG Four-Star.

Finish is always a personal preference, and for some reason I really struggled with a color scheme. I elected to use the yellow version right on the box. So much for originality, but the all yellow and all red schemes really fit the Four-Star models well. With the plane now built it was time cover. I choose the new Ultra Cote ParkLite covering from Horizon. This light weight covering worked fine for this model while helping to keep the overall weight down. I debated on color for a good long time, but decided on the classic Four-Star all yellow setup. One roll will do it, if you are careful!

Tail surfaces

After the surfaces were covered and hinged the final assembly began.

The work on the pushrods was completed. A sharp bend and solder had the brass threaded ends attached.

The rudder was glued to the fin and then the control horns were added to the surfaces. The servos were added to the fuselage and everything was setup.

The SIG Four-Star included a steerable tail wheel assembly.

The wing proceeded to the final steps. I know from past models it was easier to add the small lite-ply wing retention area after it was covered.


Here are some final shots of the SIG Four-Star just before first flight.


With the 3s 2200MAh pack placed as far back in the tray as possible, the SIG Four-Star was nose heavy. I was worried about this in assembly. A top hatch with larger tray would be welcome to balance the plane without adding additional weight.

After adding 7g of tail weight the Four-Star was able to be balanced at the recommended CG range from 2-3/8" to 2-3/4" from the leading edge of the wing. It would have been nice to achieve the balance without added weight by having a larger battery tray area for adjustment. A top hatch would have been welcome for this purpose.

Rates and transmitter setup

The Four-Star would receive guidance from my Hitec Aurora 9 system. Rates were set as recommended in the manual with ailerons at 5/16" up/down and elevator at 7/16" in each direction. Rudder was set to 7/8" on both sides. Exponential rates were set at 20% for the primary flight controls.

Those aileron control recommendations were a bit light in flight, great for sport flying but I added more control authority to swing that large wing around a bit quicker. Rudder was also a bit light on control, so I added more throw there as well. Elevator rates were fine for me. Control surface throws are a very personal preference, so please adjust your accordingly.

The flight timer was set to count down from 5 minutes of mixed flying giving an audible warning to land before the battery was depleted. The Sonic Power 2200 LiPo was able to supply the Four-Star with the power needed for the powerful Motrolfly 2810 motor.


The SIG Four-Star is a sport model, with excellent flight characteristics. It can comfortably be flown at a large park location or at the club field.

This SIG Four-Star 20, just as its larger brothers just floats along forever. The model was comfortable doing sport aerobatics, especially with higher rate throws. Loops, rolls, inverted, split-S, stall turn all are performed with ease. The Four-Star was gentle in flight as well, slowing very well for flybys.

Takeoff and Landing

Just as you would expect with the power of the Motrolfly motor, take off distances were very short. The rudder was effective so it was simple to keep the Four-Star tracking straight down the runway. Power was abundant and kept the roll out on grass fields short as well.

Landings were a thing of beauty and simplicity. Plan for a long approach; remember, it floats even with no power! I enjoyed the increased rudder authority I added to keep the roll out straight.

Special Flight Characteristics

The Four-Star 20 was comfortable in flight a true sport model in every way. It was very predictable, and I found it to be one of the most stable low wing airplanes I have ever flown. It did not exhibit any bad behavior at all.

The plane stalled very predictably for a model with a low 12's in/oz wing loading. Recover is almost instant with zero wing drop or tendency to enter a snap. That was all with the CG at the very rear of the recommended range.

The Four-Star was able to perform huge round loops and rolls that were surprisingly axial. This model was very aerobatically capable yet gentle at the same time. This plane is an absolute joy to fly, just as one would expect. The touch and gos were especially fun. The all around flight performance with the stunning power the motor produced was a thrill to say the least.

Recommended power system

Power on 3s voltages was perfect for this model. The Motrolfly power system was perfectly matched to the Four-Star. It had excellent power, far more than needed for sport flight. T power was stuffing giving this 37oz model excellent performance for aerobatics. That coupled with the personal attention from Subsonic Planes and their expert advice and recommendations make them highly recommended.

Is this plane for a beginner?

The SIG Four-Star not a great first time plane for a first time pilot. While the build is very appropriate for a first time builder the model does take a bit of skill and does not exhibit the self-correcting characteristics a beginner needs. That said it would make a perfect 2nd plane!

Flight Video



When first opening the box it was great to see all of that wonderful balsa and ply, nearly all of it laser cut. Building The Sig Four-Star was exceptionally quick and completely straightforward. The parts fit was impeccable, and the full sized plans and excellent instructions make this an excellent choice for a first time build.

I only ran across one small issue during the build: the cloth coming off of the Sig Easy Hinges. I have used the SIG Easy Hinges many times in the past with zero issues, so I know this was out of the ordinary.

Another recommendation would have been the use of a top hatch incorporated in the Four-Star, as that would really aid the battery swaps at the field. I was thinking of the excellent top hatch in the SIG Somethin’ Extra and wish this model had that. The battery tray when positioned as plans indicated leave just enough room for a standard ~2200 3s pack. Allowing another half an inch would be easy to do, so when you build yours consider lifting that tray toward the top of the fuse as it will aid in battery swaps.

The SIG Four-Star 20 EP is also a sharp looking plane. It has classic sport ship lines that any modeler will recognize in an instant. The classic stickers allow it to fit in the classic Sig Four-Star family with ease. In flight the Four-Star really shines. Sport aerobatics are possible, yet it is a calm and gentle airframe. I am loving this airplane in flight. The performance of the model, and it long heritage of being stellar in flight are well deserved. The Four Star 20 lives up to what many modelers worldwide have found, you will be hard pressed to find a more admired sport ship on the planet. It is just a pure pleasure to fly the Four Star.

The Subsonic Planes Motrolfly power system provided stunning power, pulling the 37oz model through all the maneuvers with ease. The quality of the motor is far above many of offerings today in the brushless market. The GWS servos are more than abundant for this model and have performed very well.

I have thoroughly enjoyed building the Four-Star. All of the parts all fit, due largely to the laser cutting. Everything almost fell together so for those who have never tacked a build, try this one! You may find an element of the hobby that you had previously missed! Showing the heritage of a fantastic design, this model also performs flawlessly in flight. Zero bad habits and an easy build what more could you ask for?


  • Excellent flying characteristics of the Four-Star heritage
  • Instruction manual is detailed and in plain English full of helpful details
  • Superb flight performance
  • Excellent parts fit and easy build
  • Stunning performance on the Motrolfly power system


  • Magnet secured top battery hatch would be welcome
  • Hinges came apart (felt separated from the plastic sub structure)

Check it out the hobby shop or buy direct at SIG Manufacturing.

Last edited by Angela H; Jan 04, 2011 at 10:04 AM..
Thread Tools
Jan 04, 2011, 05:13 PM
Registered User
Nice review there. My 4*20 is nearing completion as I write this; have yet to decide on a motor. I'm thinking Turnigy 3536-1100, but it's probably more weight and power than I need.

I would add to the + column a very excellent manual, probably the best I've seen for a balsa kit.

In the - column, it's still not in a league with Mountain Models or Stevens Aero for ease or simplicity of construction. There's a good deal of pinning to do on the wings. The wing center sheeting step is quite tedious and time consuming -- a grand total of 20 pieces of balsa that need to be precisely hand-cut and then glued onto curved surfaces.

I too have noticed SIG hinges de-laminating. I anticipate some issues slotting the aileron hinges, as the 1/4" square balsa stock for the main wing trailing edge was extremely hard and dense.
Jan 04, 2011, 07:33 PM
Airliner Builder
WAGliderGuy's Avatar
Awesome review pda4you! I have to agree its a great plane

I had the same issue with the stock easy hinges that came with my kit. I have been buying seperate packs of Sig easy-hinges for along time with no problems.
Jan 04, 2011, 08:07 PM
Registered User
pda4you's Avatar
Thanks guys!

Rafe you are right it is not the jigsaw puzzle construction like MM or Stephens, this is much more typical of model construction.

The manual is excellent a long SIG tradition.

Interesting that both of you had issues with the hinges as well.

Jan 04, 2011, 09:59 PM
Build more, websurf less
FlyingW's Avatar
Thanks for the review Mike. Nice job. Makes me want one.

Any chance of the manual having a 3-view drawing (like the original did for working on paint schemes) that you could post - I'm interested whether Sig have made any subtle changes to the Four Star shape.

Jan 04, 2011, 10:32 PM
Visitor from Reality
Funny you should mention that Paul.

Oddly enough, I have a 70% IMAA legal large scale model plan of the 4*40...

Am dreading walking into a hobby shop and seeing a 4*20 kit. Wouldn't have got that BARF triplane if they'd had one.

Jan 05, 2011, 01:52 AM
Registered User
Dear Mike, Good review and a great price from SIG for this kit. That issue with the cloth coming off the hinge material is one I've encountered several times recently. To be honest I now ditch these and go back to the slightly heavier but very reliable "furry" fully cloth hinges.
Jan 05, 2011, 07:27 AM
Registered User
Ken Myers's Avatar
Very nice review Mike. Thanks for all the great information and data on this one. I would have liked some RPM values for the APC 10x7E, since it appears to be the prop you've settled on using.

Overall, a very, very nice review!
Jan 05, 2011, 09:24 AM
Registered User
pda4you's Avatar
Guys I am away from home, but will look at the RPM's on the 10x7 and see if the manual has the 3-views when I return home.

Ken as you can see from the video - the takeoff power is stunning with the 10x7 prop. I wish the wind was cooperating that day, the low power takeoffs are smooth and straight. In fact it is quite the excellent touch and go machine. Puts a big smile on my face every time I fly it.

It is a fantastic airplane!
Jan 05, 2011, 10:20 AM
Registered User
Mike... please tell us more about the CG situation. As I understand it you've got a 4.1 oz motor, mounted maybe an inch (?) or so in front of the firewall. You have a 5.4 oz (151 gram) battery pushed to the back of the tray. Plus another oz. or two for ESC and UBEC up there somewhere.

And you've used 1/4 oz. of weight in the tail to get the CG "in range," which I presume to mean the forward end of that range.

So maybe a lighter motor is called for, or mounting the motor closer to the firewall (shorter standoffs.) What do you think?

I've modified the tray so that the battery can extend aft of the tray, through the former if need be. The tray is also deeper so that I can use a larger battery if need be (eg. 3S/2350 or 3S/2650.)

What sort of motor weight would be ideal? What sort of motor weights have folks been using? I would guess nothing much lighter than 3 oz., since we want 300+ watts or so, right?
Jan 05, 2011, 10:38 AM
Registered User
pda4you's Avatar
The motor must be placed where it was in order to provide the necessary propeller clearance off the cowl. So the standoffs are needed for proper prop clearance. I LOVE the power of this Motrolfly motor, but you are correct a lighter one would help there at the cost of power. To me that might be a mistake. When I was doing test flights the 10x5 propeller at 365w just seemed a bit ho hum. The 10x7 woke it up nicely. Granted some of that was the pitch gain.

In the CG range the 7g tail weight added took me to the forward most CG recommended and the plane flies just fine there.

The best plan might be to change the plans and build a top hatch and larger battery tray that would allow the battery to be placed closer to the CG.

To be honest I am 3 full ounces below the recommended weight, and adding a tiny bit of tail weight was a non issue, even though all of us hate to do that.

My battery is placed through the former into the wing area a bit. That was needed to help the CG as well.

I HIGHLY recommend this motor by the way, as you can tell from the takeoff it pulls it with authority. I would not go below 350w for power, at least IMHO.

It is all a bit of give an take, had it not been a review model, the top hatch would have been my first mod. That would have solved any CG issues with no added weight.

Jan 05, 2011, 11:00 AM
Visitor from Reality
Hi Mike
Have to agree with your last comment, though the 4*20 will have its bottom hatch from now until balsa trees become extinct, I fear. Shame really, all that Sig had to do was ask any one of dozens of folk hereabouts how to fit a top hatch. With laser cutting, it would be easy and it would have made the equipment/CG placing a lesser issue.

Know what you mean - haven't used any ballast to nail a CG since electric models were invented

Not sure about their reasoning regarding the UC. A little more ground clearance wouldn't have broken the 'price point' or whatever the present jargon is. Your findings of a steeper pitch echo how my Four Star 40 lit up on a 15 x 10 - RPM figures will be interesting here.

Having done the odd kit review over the years, your feelings of having to do it by the manual are appreciated - reckon you did a good job all round. Incidentally - I might be one of the very few reviewers around who does know what happens to a less than favourable kit review It's a fun side to our hobby, but I need some serious talking to before I do them nowadays.

Looking over your results, numbers etc - I'd suggest that you've come up with the basics for a solid replacement for the old '20 - 25' range of models in slimey terms. These weren't as popular as the 40 and 60 sizes - they didn't involve buying as much fuel, for one - but done right, they could blow away any sports model at your average flying patch for much less financial involvement.

Idly thinking - when my models first made it over 300W, their flying weights were around 48 - 54oz and the battery packs - 10 nicads, 1700mA - weighed around 22 ounces. That was all of ten years ago... You've given everyone a real demo of how progress can actually be good.


Jan 05, 2011, 11:07 AM
Registered User
It's all good. I always struggle with this phase of construction, trying to match motor to airframe, not just in power but looking after CG as well. Trouble is, you can't finalize this stuff until the very end of the build process and by then it may be too late...

I have a couple of Turnigy 3536 motors on hand, and wondering if it's worth trying to go lighter. I'm certain this motor suffice as far as power is concerned.
Jan 05, 2011, 11:19 AM
Registered User
pda4you's Avatar
Rafe - I have that exact motor, on a much lighter plane, and to be honest I could not be less impressed. It was really not comfy over about 250w and that would be very light power for the EP 20. Now it would fly but sport aerobatics would suffer.

Jan 05, 2011, 12:01 PM
Registered User
Regarding the 3536 motor, my experience is quite positive. Reviews of the motor on the HC site are overwhelmingly (almost unanimously) positive.

I originally used it on a Formosa II with 10x7 prop and 3S power, and it was terrific. The Formosa II has about the same AUW as the 4*20 -- a bit over two pounds. My second Formosa II uses this motor, rated 38 A, 350W, 113 grams; I use it with 10x10 prop and it zooms.

I've searched high and low for motors that can deliver about the same power in a lighter package. The lightest 400 W motor I've found is the Hyperion ZS 3009-20 at 98 grams. Max power 450 W, max current 34A.

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