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ST Model's Arcus M Electric Sailplane Review: A Tower Hobbies Exclusive

ST Model's Arcus M is an exclusive in North America for Tower Hobbies. The electric motor comes in and out of the fuselage to power this sailplane which also features spoilers and a retracting main landing wheel.

Splash

Introduction


Wingspan: 87.5"
Wing Area: 444 sq in
Weight: 32.6-33 oz.
Length: 39.4"
Wing Loading: 10.6-11.7 oz sq ft
Transmitter: Tactic 650 6Ch
Receiver: Tactic
Battery: 3S 1300mAh
Propeller: 7 x 5
ESC: 20A
Manufacturer: ST Models
Available From: A Tower Hobby Exclusive
Price: $149.97 Receiver Ready

The Arcus in full scale is a two seat powered sailplane manufactured by Schempp-Hirth. It is available as a pure glider that can be towed aloft and as a self-launching glider using a motor that retracts into the fuselage. This ST Model is the motorized version and the motor, mount and propeller retracts and disappears into the fuselage where it is covered by plastic doors. The wings have spoilers which work as air brakes and can help bring the sailplane down from thermals and also serve as a landing aid. The model like the full size version has a retractable main landing wheel with smaller wheels in front and back to protect the fuselage. For tall grass just slide to a landing or with a runway roll to a stop.

ST Models has previous made the smaller DG-1000 sailplane that had a retractable motor/propeller but it had a shorter wingspan and no retractable main wheel. I was previously able to review the DG-1000 and along with many other pilots found the ST Models DG-1000 to be an excellent RC sailplane. I have found the Arcus M to be slightly faster in its glide than the DG-1000 and that is probably due to the extra weight of the spoilers and retractable main landing wheel. The retract motor system has been improved in the Arcus M but it is located inside the fuselage so I can't fully review this. I can report no problems with this review plane in lifting and lowering the motor. As mentioned in the title I have been told the Arcus M will be a Tower Hobbies exclusive here in the United States. It is a CAD designed model and constructed with EPO foam and hidden reinforcement. I am excited to have the chance to put the Arcus M through her paces and report how she stacks up to the DG-1000. On first blush there appears to be a lot for the money and there is! The electronics include 8 servos (seven micro and one mini), an ESC and a brushless motor as well as a controller for the motor mount and the starting and stopping of the motor/propeller. Mechanically there is the motor mount pylon that rises and lowers along with doors that open and close. The main wheel is retractable and includes retract doors that open and close. Finally, there are spoilers mounted in the wings and controlled by two of the servos. Having read the instruction manual the assembly should be quick and then we get to see how she flies.

Kit Contents

  • Fuselage
  • Vertical stabilizer/rudder
  • Retractable motor & propeller
  • ESC
  • Wheel retract and four servos installed
  • Hatch/Canopy for fuselage
  • Left and right wings with spoilers and aileron servos installed
  • Horizontal stabilizer with elevator
  • Wing connector rod
  • Two mounting screws and hook and loop material
  • Instructional Manuals

Additional items needed:

  • 6 Channel transmitter
  • 6 Channel receiver
  • 3-cell 1300mAp LiPo battery pack
  • Balanced Li-Po pack Charger

Tools Needed:

  • Phillips screwdriver

Assembly

The plane arrives with the individual parts assembled. There is a minimal amount of final assembly needed to get the plane ready to fly and I will cover that here.

Wing

The wing comes in two completed halves and there is no assembly to perform on the wing. The wing has a high aspect ratio to give excellent forward penetration with limited vertical drop. It has an excellent glide ratio. The aileron servos came installed and connected to the ailerons. The spoilers came installed and connected to their servos. Even the decal number under one of the wing sections came already installed. The wing just needs to be installed through the wing saddle in the fuselage and that will be discussed below.

Tail

The vertical stab is part of the fuselage and the rudder comes hinged to the fuselage and connected to the servo that controls it. No assembly needed there. The horizontal stabilizer and elevator come as one unit ready to install on the top of the rudder for the T-tail. The elevator control horn has a plastic circle and that goes over the elevator control rod and makes one bend on the rod as it slides down to be in proper position. The horizontal stabilizer is rotated from vertical to a horizontal position ready to be installed. It has two small plastic pins in the plastic mount in the bottom center of the stabilizer. These pins fit into the top of the rudder to align the stabilizer. The stabilizer is secured to the top of the rudder with one supplied bolt that mounts between the two alignment pins. The control rod was already connected to the elevator servo up in the cockpit area. That should have been all there was to complete the tail assembly, but it wasn't.

The mounting bolt on mine did not make a tight fit on top of the stabilizer and I wasn't going to force it. I had a bolt just slightly too long and that left the horizontal stabilizer too loose. (I haven't read about anyone else having this problem so it may be exclusive to my plane.) I thought about the problem for a while and I came up with two possible solutions. The first was to grind off a bit of the bottom of the mounting bolt so it could tighten and be flush with the top of the horizontal stabilizer. The second would be to use a small washer on the bolt above the stabilizer. This could serve two purposes: allow the screw to tighten as I expanded the distance with the washer and the washer might help keep the stabilizer level as it broadened the contact surface over that of the screw head. I decided to use the second option and looked and found a small brass washer in my can of spare hardware parts.

Since I am discussing the tail; The mounting of the horizontal stabilizer at the top of the vertical stabilizer on this T-tail looks like a potential weak spot just as it did on the DG-1000. However, with good flying both have held up very well for me with no problems at all! However, keeping the thin EPO foam stabilizer level is the main reason I recommend this sailplane only for experienced pilots.

Fuselage

Landing Gear

The Arcus M has three landing gear wheels. There is one mounted in the front to protect the nose of the fuselage and it comes into contact with the ground as the plane is slowing down and tips forward. Under the wing is a retractable main wheel and the plane touches down on this wheel when landing and it bears the most weight. In flight this wheel is retracted into the fuselage to reduce drag. The smallest wheel is mounted in the back of the fuselage. These three wheels all came installed and there was no assembly work connected with them. I have the retract on channel five.

Installed Electronics in the Fuselage

In the cockpit there are three servos and there is a fourth servo in the fuselage under the wing saddle. The servo under the wing saddle raises and lowers the motor mount pod out of and back into the fuselage. The servo is wired to a controller to allow the pod to raise. The motor then runs from the throttle control. The ESC is also wired to the controller. There are two connectors for possible use with the receiver. The other three servos in the cockpit area control the rudder, elevator and the main landing wheel and the doors to the landing gear bay.

The fuselage came fully assembled with the above components installed. The receiver is not included in the kit. I am using my Tactic receiver and transmitter. After binding the receiver to the transmitter and connecting the wires and programming the transmitter; the receiver was installed into the cockpit just in front of the servos using hook and loop material to secure it in place. In the nose of the cockpit there was some hook and loop material secured to the floor and that is where I installed the 3-cell 1300mAH LiPo battery pack.

Radio Installation

Most six channel radio systems can be used with this receiver ready plane. The instructions for set up included with the kit are perfect for a Futaba or Tactic Radio system. I used my Tactic 650 transmitter with a Tactic 6 channel receiver. My channel set up on the receiver was as posted below.

Receiver Channels Tactic 650

  • 1) I plugged in a Y-connector supplied in the kit for the ailerons
  • 2) I plugged in the elevator servo connector
  • 3) I plugged in the throttle connector from the special controller
  • 4) Next I plugged in the rudder connector
  • 5) I plugged in the main gear retract for the doors and main wheel
  • 6) I plugged in the second supplied Y-connector and this one is for the spoilers.

Per the instruction manual on the transmitter I reversed the servo control for channels 3 and 5. I followed the programming instructions concerning travel for the throttle. Don't skip this step! It is important for the proper rising and lowering of the motor mount pod with the motor off. Per the instruction manual I am using the automatic sequencing of the raising and lowering of the motor mount and that left one connector from the controller unplugged.

Self Launching Motor Glider: Deploying the Motor

There are two ways to set up the motor system for deployment as there are two receiver connectors from the speed controller. I used the simplest method which allows the use of a six channel transmitter. I used the throttle only connector and plugged it into the throttle channel on my Tactic receiver. I followed the instructions exactly for programming my transmitter. They are spelled out clearly in the instructions, easy and don't skip this step. With the transmitter on and receiver powered with the flight battery I move the transmitter stick up and the motor mount pushes through the cover doors on the top of the fuselage to the straight and upright position. If I continue to push the throttle up the motor will turn on and I launch the plane normally with a straight forward hand toss. If I stop advancing the throttle after just a little movement the motor doesn't turn on, the motor mount drops back into the fuselage.

After reaching altitude I reduce power and a stopper deploys to stop the propeller in the straight, upright and locked position and the motor mount with motor and prop drops back into the fuselage and the doors in the top of the fuselage close. The motor can be deployed and operated multiple times during a flight with the power in the battery being the limiting factor.

Completion

The wings plug into the wing saddle and there is a wing joiner box that is used to secure the wing in place. I ran the aileron and spoiler servo wires forward in the cockpit as I slid the wings into place. With the plane upside down a pair of holes are visible on both sides of the underside of the wing near the fuselage. Using a small Phillips screwdriver I tightened the screws in the mounting box to clamp onto the carbon fiber wing rods that were already mounted into the wing sections. There is also a bolt that goes into a hole in the side of the fuselage, under the wing and secures the wing in place. This holds the wing halves in place. When done flying for the day the process is reversed and the screws loosened to remove the wing. Total assembly involved no glue and only the screws in the wing mount and the one bolt.

With the wing installed the battery is moved until the plane is properly balanced on the recommended Center of Gravity, the C/G.

Flying

Basics

The planes main controls are throttle, ailerons, elevator and rudder. The plane can be flown just using the throttle, ailerons and elevator but there is yaw in turns just using the ailerons. Mixing in 25% rudder with the ailerons helps make the turns much smoother. The mixing control is on a switch on the transmitter so it can be turned on and off. I normally fly with the mix on and controlled by the aileron stick. If on takeoff or landing a need more rudder due to a cross wind I can do that without using the ailerons by simply using the left/rudder stick on my mode 2 transmitter. My flying of the Arcus M is as an electric sailplane. I used the motor to get up to about 400 feet. I level off and slowly reduce power. At some point a rubber covered pin moves into position to stop the propeller's spin and it is lined up with the fuselage. The motor retracts into the fuselage and the doors close to cover the motor mechanism and reduce drag. I have my plane trimmed and the C/G set for this condition to get maximum glide from the plane and to be most responsive when encountering lift. The basics of flying a sailplane will be discussed below. Eventually as the plane comes down closer to the ground and I have to decide if I want to power up and climb back up to 400 feet up or to bring her in for a landing.

If I decide to climb and search for more lift I advance the throttle. The mechanical mechanism operated by a servo under the wing saddle starts to raise the motor and its pod and the covering doors are pushed open. After the propeller has cleared the storage bay and is upright the motor turns on and I control the speed of the motor/propeller. Back up at altitude I can slowly turn off the motor and it retracts into the fuselage as it did the first time. During this review I limited myself to four full climbs per battery.

The spoilers half a half up and a full up position using a three position switch. When deployed they work as an air brake and slow the plane down and also cause the plane to drop while deployed. They deploy evenly and work very well to bring her down from high in the sky as well as a landing aid to touch down where desired on the runway.

Wind Limitation

Per the instruction manual they recommend only flying in winds of 10 miles per hour or less. I have obeyed this limitation both at the thermal field and the slope. The wing span is 87 inches and the foam gets pretty thin out at the tips. I think the recommendation is appropriate and I have no plans to challenge the recommendation and trying to fly her in a high wind. Do so at your own risk but I strongly recommend against it!

Taking Off and Landing

At the slope takeoffs can be made with the motor retracted and just tossing the plane forward into the wind hitting the slope. At a thermal site the motor should be raised out of the fuselage and running with about 60% throttle and given a firm toss forward into any prevailing breeze, level with the ground. When I get my tossing hand back on the transmitter I usually advance the throttle for a faster climb up to about 400 feet. When at altitude I slowly lower the throttle and the motor propeller slows down and stops. A stopper stops the propeller so that it is lines up with the fuselage. With my radio set up with the throttle down the motor pod with the motor and propeller retracts into the fuselage and the cover doors close to reduce drag. She now looks and flies like a pure glider and I soar off looking for lift.

This plane is ROG (Rool Off Ground) capable from a runway, hard surface or short grass such as on a golf course runway. Some pilots make all launches takeoffs. I have also seen touch and goes with the Argus M. This ability is one of the perks of having the motor and prop above the wing. I haven't done either of these yet but the plane is certainly capable of it. Just remember to use the rudder to steer the plane while on or close to the ground. It does nothing for the wheels it is just you don't want to bank the wings with the ailerons.

Landings are also made into any prevailing breeze. If flying at a grass field I can leave the landing gear in the fuselage with the doors closed. With a runway I always lower the main wheel and land after making a three leg approach: down wind, cross wind and into the wind on final. Because of the landing gear doors I don't like to land with the gear down on grass unless it is very short grass. I don't want there to be a chance for the doors to catch. During this review all landings were quite ordinary. I don't make turns near the ground when landing. Because there is a delay in raising the motor and the propeller turning when I commit to the landing I stay committed.

Aerobatics/Special Flight Performance

The special performance for this plane is to seek and catch thermals for maximum duration or fly for extended periods at the slope when the wind is ten miles per hour or less. I have performed a loop with her and did so with the motor off after a short dive and then a hard climb. The Arcus M has a very nice glide ratio and travels a long time while slowly dropping even if no lift is encountered. She gives good tells when lift is encountered and lifts her tail and starts to climb in lift even though appearing to be in a slight dive position. If she goes too high in a thermal the spoilers cab be deployed and they smoothly help to bring her down. If you are an experienced sailplane pilot you can skip the next part of this review.

How to Fly Thermal Duration

As discussed above at a thermal field I climb to about 400 feet above the field and turn off the motor and have it retract. I then fly a search pattern in front of me into any existing wind. I fly forward and then back and forth in front of me looking for a thermal in the fresh air that is blowing towards me. I carefully watch the Arcus M and if she flies straight into a thermal she will drop her nose and lift her tail and yet in this apparent diving position she will actually go up in the thermal. I start turning to keep in the thermal. Remember that if there is a breeze the thermal will drift with the breeze at the same speed of the wind. If the breeze is 5 mph the thermal is traveling downwind at 5 mph. I remember that and keep circling as I fly the Arcus M down wind at the same rate. If I loose the thermal I will try to find it or fly back in front of myself back into the wind depending on where the plane is in relationship to me when the thermal is lost. I fly into the wind in front of myself so I encounter new air with room to drift down wind when a thermal is encountered. This lets me stay with the thermal longer and still be able to fly back to the field.

Another way to encounter a thermal is to hit the edge of it. In this situation the thermal may turn the Arcus M away from it. If my plane gets pushed to the left I will make a 270 degree turn to the left to try and fly straight into the thermal and look for the nose to go down and the tail to go up. With experience I got better at spotting thermals but I have friends that are much better than I am as they are able to detect the weakest of thermals and climb when I sometimes fly right through them.

A lot of things may change my standard search pattern and these are things learned with experience. If I see hawks or eagles circling as well as a number of other types birds and if they are going up I will fly over to try and share the thermal with them. If I feel a breeze blowing to my left and I know the wind is into my face I will fly to my right as that "Breeze" is actually a thermal drawing in air to my right. I also look for dust moving in the air, small insects moving in a flock in one specific direction, movement on the ground of grass or paper can all be signs of thermals. Flying and search for and finding lift is the special flying I do with my Arcus M ... and occasionally I will do a loop just for the fun of it.

Is This For a Beginner?

No! This is not a plane for a beginner. It would not in my opinion hold up well to the abuse most beginners give to a plane when first learning. This is a very nice plane for experienced pilots!

Flight Video/Photo Gallery

Arcus M R/C Electric Sailplane (4 min 10 sec)

Conclusion

This plane is a really nice sailplane and is an excellent bargain for the intermediate and better pilot who wants to try soaring or flying at the slope in light wind. She has a good glide ratio and allows the pilot to cover a lot of ground while searching for lift. When lift is encountered she gives good tells so the lift can be used to climb and have extended flights. The motor works well and easily comes out of and returns to the fuselage using the simple set-up programming they give in the instruction manual. I easily get four full climbs to 400 feet per battery charge and have lots of spare juice for a long flight if lift is found after the fourth climb.

Since they recommend not flying her in winds above 10 mph I intentionally limit myself to very short dives and I have had no problems with control or with the control surfaces. If I feel a need for speed or rapid high speed turns I will fly one of my other planes. She is an excellent flyer with spoilers and a retract main wheel and can be stored and transported in her original box. The experienced intermediate to expert pilot should really enjoy this sailplane and with the built in motor there is no need for a High Start or a winch to get up and start searching for thermals. There is even the capability to aerotow this plane with a release in the nose with a little work. My friend Jeff Hunter has made one ready for aerotowing. For the experienced smooth flying pilot I give this sailplane two big thumbs up. Sailplane flying experience is not necessary to enjoy this plane and the joy of soaring.

Pluses & Minuses

Pluses

  • No building, final assembly only
  • Can be stored and transported in the original box
  • Quick assembly at the field for flying
  • Easy access to change the battery
  • Wheels come installed for landing on a runway
  • After climb to altitude the motor retracts into fuselage
  • Spoilers come installed and they are effective in slowing down the plane
  • The plane gives good tells when medium to moderate lift is encountered.
  • Parts will be available at Tower Hobbies
  • A very good bang for the buck

Minuses

  • Plane is limited to flying in winds at or below 10 mph
Last edited by Michael Heer; Nov 11, 2014 at 11:28 AM..

Discussion

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Old Nov 10, 2014, 07:12 PM
Registered User
Joined Mar 2012
100 Posts
you need some elevator compensation with the deployment of spoilers it seems. easy to program in. smooth flyer!
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Old Nov 10, 2014, 08:04 PM
Registered User
United States, MO, Fenton
Joined Jan 2012
2,964 Posts
I am waiting for them to come back in stock. I had one but it had a mis manufactured wing. Ailerons had to be deflected about 3/16 of an inch to keep her flying level at thermal speed. Also added some carbon to the ailerons as they deformed easily with aileron input. A heck of a lot of airplane for the money but I wish they had put a little more effort into fit, function, and finish.

I also never hand launched. Very cool to be able to rog!
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Old Nov 11, 2014, 12:52 PM
Registered User
pete914's Avatar
United States, VA, Richmond
Joined Jan 2010
142 Posts
Been flying this glider around my house for about 3 weeks. I had the SLS servo strip the first time I attempted to raise the SLS. I replaced it with a Hitec servo and pulled out the SLS programmer and instead control that with my radio. My left airbrake servo and landing gear servo stripped soon thereafter but have worked without problem since replacing them with better servos.

So, the servos strip easily, but aside from that this is a quality scale glider! The pricetag is worth the airframe and SLS/motor/esc alone.

Awesome addition to ST's lineup and I hope they don't stop with the Arcus. How about the JS-1 or the Diana 2 SLS?
They would sell just as well! Come on ST Models
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Old Nov 16, 2014, 04:37 PM
No substitute for span
L over D's Avatar
Sweden, Dalarna County, Leksand
Joined Mar 2008
66 Posts
It's a fantastic little glider! Not 100% static scale but 110% "action" scale", just makes you smile when flying it. Wings could be more rigid and have better finish ( not too much work to fix yourself) but otherwise it's a gem. Flown it for 2 summers with out any problems, always started it from the runway though. I have a mix for rudder to follow ailerons that I switch on at altitude when thermaling, although I do not recommend taking off or landing with it. It requires proper use of rudder just like the full scale plane.
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Old Jan 07, 2015, 07:23 AM
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Joined Jan 2015
11 Posts
good aerobatic
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Old Feb 10, 2015, 05:56 PM
Chuck it and see!
Wing-span's Avatar
UK, Cambridgeshire, Huntingdonshire
Joined Sep 2006
1,436 Posts
To adjust the motor mechanism refer to RCGroups thread, post #518

This plane does fly really well. No problems with the quality of the airframe or components. Its actually really good and fun to fly in a scale manner.
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