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Multiplex Gemini Biplane Review

Multiplex, the company that gave us great models like the Easystar, Magister and FunJet introduces their first biplane!

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Introduction

Wingspan:36" (1095mm)
Wing Area:557.27 sq in (36.6 sq dm)
Wing type:Multiplex Elapor foam, semi-symmetrical
AUW weight:Advertised – 32 oz to 36 oz Actual - 34.8 oz
Length:36" (1150mm)
Wing loading:8.19 oz/sq ft (25 g/sq dm)
Servos:4 – Hitec HS-55s for ailerons, rudder and elevator
Transmitter:Spektrum DX7:Available from Hobby Lobby
Receiver:Spektrum AR6100:Available from Hobby Lobby
Battery:Polyquest 3S1P 2150 LiPoly:Available from Hobby Lobby
Motor:Atlas 2902/20 Outrunner:Available from Hobby Lobby
ESC:Atlas 35 amp Brushless:Available from Hobby Lobby
US distributor:Multiplex USA
Available From:Multiplex USA
Retail Price:$109.99

As I've mentioned in previous reviews of Multiplex products, I'm a BIG fan of their airplanes, and I've flown just about all of them. Made of an extremely tough foam called Elapor, Multiplex planes can stand up to a lot of less than perfect flights. I'm also a longtime fan of biplanes, so not long ago when I heard that Multiplex was planning to release their first biplane, I knew I had to review it!

Kit Contents

The review package shipped from Multiplex USA, and it arrived double boxed with no damage. The Gemini parts are secured in a unique foam cradle that fits neatly in the ARF box and which prevents the parts from shifting during shipment. The Gemini has an average parts count for a Multiplex model. Because it is made from Multiplex Elapor, it assembles using ordinary CA glue. Having built several Multiplex planes before, I knew the build would go quickly.

Kit includes:

  • Two-piece fuselage
  • One-piece upper and lower wing panels
  • Removable canopy and battery hatch
  • Hardware (EZ type connectors, pushrods, clevis and horns)
  • Landing gear, mount and wheels
  • Foam wheel spats
  • Tail group with steerable tail wheel assembly
  • Well illustrated assembly guide and instructions

Kit requires:

  • Motor
  • 10x5.5 Propeller
  • 3s LiPoly battery
  • 4 servos
  • Receiver
  • 4 channel minimum transmitter

Included for this review:

  • Atlas 2909/20 outrunner brushless motor
  • Atlas 35amp Brushless ESC
  • Polyquest 3s1p 2150 LiPo battery
  • 4 - Hitec HS-55 servos (rudder/elevator)

Assembly

As is always the case with Multiplex planes, the assembly went very quickly! The control surfaces have molded-in hinges and only need to be cut free at each end. The wings are a one-piece design with a fiberglass spar on the bottom wing. I would allow 4-5 hours to complete the build of this plane. Although the airframe parts on Multiplex models are typically excellent, I was simply amazed at how well the individual parts fit together. The Gemini has the best fit and finish of any Multiplex model I've seen yet, and that's saying a lot!

The instruction manual was very easy to follow and understand. It has two corresponding sections, one written and the other pictorial. Anyone with even basic building experience will have no issues. Multiplex does recommend using CA accelerator during construction.

Fuselage

The fuselage assembles first, and the two halves key together. Although the manual recommends using CA accelerator, I did not use it on this step to allow time for alignment of the joint. Multiplex has again used their unique "flow through design" ventilation system that allows maximum cooling over the motor, battery and ESC. The fuselage houses two wing screw supports, which are simple in design yet very effective.

Wing

The upper and lower wings are molded in one piece. IMPORTANT: Before assembling the cabane and interplane struts, Multiplex recommends adding the self-adhesive decals to the wings first. Otherwise, it would have been very difficult to install the decals later around the struts. The lower wing houses the servos and the dual ailerons connect via pushrods. Both wings and cabane struts were straight and true, and the entire assembly fit perfectly. The HS-55 aileron servos installed in precut openings perfectly, and no servo extensions were needed. Two nylon bolts threaded into the fuselage and held the wing assembly in place.

Tail assembly

The elevator is molded in one piece. It and the rudder simply glue into the fuselage. The control horns are then attached, again using regular CA. I checked the alignment of the horizontal and vertical stab, and they were perfect. The steerable tail wheel assembly installs using CA as well.

Landing gear

First, the wheel spats are assembled, then the wheels inserted and the landing gear wire fed through the spats and then the wheels, with two wheel collars holding everything together. The landing gear mount glues to the underside of the fuselage with CA. The landing gear wire is held in place with one screw. The entire assembly felt rock-solid!

Motor mount

Multiplex again uses their famous thrust-adjustable motor mount in the Gemini. The mount itself is held in place with two screws, and there are four more screws that allow for fine tuning of the thrust angle. A model of simplicity that works great!

Battery hatch and canopy

The battery hatch has a tab that is inserted into a slot in the fuselage. It is then held in place with some unique retaining clips that are different from the ones usually included with Multiplex models, so maybe they are trying something new. Also in this kit, they included two different designs of retainer clips, the familiar Multiplex one for the canopy hatch and the new design for the battery hatch. As usual, the included pushrod wires, control horns and clevis connections installed easily. Multiplex uses high quality hardware throughout the kit. The canopy uses the familiar latching I've seen in the Gemini, Fun Jet and others. I placed my receiver in the area beneath the canopy. Both latches worked great!

ESC and battery installation

The ESC is held in place with velcro placed on the side of the battery compartment, along with the battery itself. There was adequate room in the battery compartment for both the ESC and battery.

Finish

Finally, I installed the spinner adapter and the foam spinner. Although the spinner is foam, it installed snugly and spun very true, so there is no worries about it coming off.

Power system

Motor - Atlas 2909/20 Outrunner

  • Motor statistics:
  • Diameter – 1-3/8")
  • Length – 1-1/4"
  • Weight - 3-1/3oz
  • Shaft – 4.0mm
  • Peak current – 20 amps
  • KV (rpm/v) - 1240
  • Max Power: 350W

The Atlas 2909/20 motor provided by Hobby Lobby: The Atlas brushless outrunner motors are a new line from Hobby Lobby and offer excellent power for their price. They are reliable, maintenance free and include the motor and ESC connectors as well as several mounting options. The Atlas 2909/20 motor was very strong and provided more than enough power for the Gemini. The amp draw at full throttle using the recommended APC 10 X 5 prop was well within the limits of this motor. I flew the Gemini at half to three-quarter throttle most of the time, and the Polyquest 3S1P 2150 pack was barely warm upon landing.

ESC - Atlas 35 AMP ESC

  • Size – 1-7/8" x 15/16" x 1/2",
  • Weight 31 grams (1-1/8 oz.)
  • Battery recommendations 5 to 10 NiCd or NiMH, 2 to 3 Lithium cells, BEC can run 4 servos on 6 cell battery, 3 servos on 10 cells. Connectors are included.

The Atlas 35amp Brushless ESC provided by Hobby Lobby: The Atlas brand is a new line from Hobby Lobby. The Atlas motor controllers will work with all types of brushless motors, and come preprogrammed and ready to use right out of the package. Additional controller adjustments are available and most can be accessed and adjusted with your transmitter, but for easier programming, the included program card can be used to set all options and takes only a few seconds. Settings can easily be changed at the flying field without the need for additional instructions or a computer.

Polyquest 3S1P 2150 LiPo pack

  • Cells - 3s
  • Capacity - 2150 mAh total
  • Weight – 6.3oz
  • Size – 4 x 1-3/8 x 1-1/8"

Battery - Polyquest 3S1P 2150 LiPo pack provided by Hobby Lobby:I've used Polyquest packs in my smaller planes for some time now and have been very impressed with them. They are very light packs for their size and have excellent amp draw capability. They are a true 20C pack, and can be discharged at a rate 20 times their capacity.

Weight

The Gemini is not a particularly light park flyer at 27.8 oz, but its light wing loading allows it to fly very well at much slower speeds than comparable aircraft.

Flying

The CG range is stated as 75-85 mm from the front-edge of the upper wing. I decided to set mine at 85 mm by moving the battery as far forward as it would go. No additional nose weight was needed.

Rates were set as recommended in the manual with ailerons at 12 mm up and down for low rates and 16 mm for high rates. The elevator was set at the recommended 10 mm for low rates and 12 mm for high rates, and the rudder was set at 20 mm. I used 35% expo for ailerons and elevator.

As you can see from the photos, the plane looks fantastic on the ground and in the air.

The Basics

From the minute it left the ground, I knew the Gemini was a winner. It felt extremely responsive yet was solid as a rock in the air. It tracked extremely well.

The Atlas 3516-1130 Outrunner is an excellent performer. As is shown in the video, it provided terrific power while drawing a little less than 35 amps static at full throttle, and it likely unloaded a bit in the air. Upon landing, the motor was still cool, and the battery pack just slightly warm, even after several full throttle climbs. I did not even try another propeller.

The Gemini stalled very gently, with just a slight drop of the nose. It recovered very quickly when full power was applied, with no hint of a wingtip dropping. Superb inside and outside loops could be made as tight or big as you like from level flight, with no hint of a snap detected. The rolls were nice and very axial; on high rates the Gemini can do 2-3 per second, and slower rolls were easily accomplished by simply setting the ailerons at low rates.

Takeoff and Landing

The Gemini is extremely well powered with the Atlas Outrunner and Atlas ESC. The APC 10 x 5 propeller seems to be the perfect choice for it. The takeoff roll was very short with no hint of a ground loop, and once I applied full power the Gemini lifted off easily and climbed at a nice, shallow angle, gaining altitude quickly. If your flying field is grass, you may wish to leave off the wheel spats or simply opt for a hand launch. At 3/4 throttle, the Gemini will fly from your hand easily with just a light toss.

With an all-up weight of 27.8 oz you would expect that the Gemini would land fairly fast, but the plane slows down amazingly well. In fact, I was amazed at how slowly this plane landed and how well it behaved. All my landings were smooth and short with very little power applied.

Aerobatics/Special Flight Characteristics

Split-S turns were a beautiful maneuver that was made easy with the Gemini. Immelman a nice-looking turnaround maneuver for the plane. It did these with ease and tracked perfectly each time.

Spins are not particularly fast, but are slow and graceful in both upright and inverted positions. They were fun to perform, with a predictable and easy recovery at the bottom. Thanks to its big control surfaces, snap rolls were very fast and dramatic, especially on high rates. The Gemini performs knife edge very well with just a slight amount of pull to the gear, which is easily mixed out with a computer radio. It remains locked in until commanded to roll out of it.

Is this plane for a beginner?

While not a first-timers plane, the Gemini would make an excellent first biplane for someone with even a little bit of four channel experience. Its tough construction, stable flight characteristics and gentle landing abilities will bring a smile to your face every time you fly it.

Flight Video

Downloads

Conclusion

The Multiplex Gemini is an instant attention-grabber at my club field. It assembled quickly and required a minimum amount of time to set up. The power and performance were fantastic, and it flew exactly as a sport biplane should. Its stable flight characteristics and superb handling made me look like an expert pilot, and the tough Elapor foam definitely ensures that it will survive many less than perfect flights.

Pluses::

Excellent design and great looks

  • Parts fit together beautifully
  • Stable and solid flight performance
  • Fast assembly
  • Tough Elapor construction
  • Excellent instructions
  • Complete hardware kit

Minuses::

Wheel spats can make takeoffs from grass difficult

The Multiplex Gemini is an excellent value and a joy to fly. It is a true sport biplane and looks fantastic in flight. It has quickly become one of my favorite fliers, and it will be yours too! Check out the Gemini at your local hobby shop or at Multiplex USA.

Last edited by Angela H; Dec 27, 2007 at 08:16 PM..

Discussion

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Old Jan 03, 2008, 06:28 PM
Always room for improvement...
der Oberflügel's Avatar
Schertz, TX
Joined Jun 2004
847 Posts
Nice review!

What kind of flight times are you getting with that setup?
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Old Jan 03, 2008, 06:31 PM
"Have Glue - Will Travel"
dawnron1's Avatar
Ft. Worth, Texas
Joined Jan 2004
2,428 Posts
Thanks, glad you liked the review! With the 3S 2150 Polyquest pack I'm averaging 9-13 minutes, depending on throttle management.

Ronnie

Quote:
Originally Posted by der Oberflügel
Nice review!

What kind of flight times are you getting with that setup?
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Old Jan 03, 2008, 07:41 PM
We shall serve the Lord
kingsflyer's Avatar
United States, TX, Kingsland
Joined Sep 2005
4,966 Posts
Great Review Ronnie. The Gemini looks stable and smooth in the air. I like the real tailwheel instead of a skid and the removeable hatches.

If you were to classify the Gemini, would it be more of an "FAI Pattern" plane than a "3-D" plane? It looks like a great all-around Sport airplane to me.

Mike McD
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Old Jan 03, 2008, 07:45 PM
"Have Glue - Will Travel"
dawnron1's Avatar
Ft. Worth, Texas
Joined Jan 2004
2,428 Posts
Thanks Mike!!

Yes sir, definitely more of a pattern-type than 3D, the control surfaces are too small. It's perhaps the best sport biplane I've ever flown!

Ronnie

Quote:
Originally Posted by kingsflyer
Great Review Ronnie. The Gemini looks stable and smooth in the air. I like the real tailwheel instead of a skid and the removalbe hatches.

If you were to classify the Gemini, would it be more of an "FAI Pattern" plane than a "3-D" plane? It looks like a great all-around Sport airplane to me.

Mike McD
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Old Jan 03, 2008, 09:05 PM
Hooper, full throttle!
Tommy D's Avatar
USA, NY, East Islip
Joined Feb 2004
11,048 Posts
Very well done review!

There is just something that instills confidence in you when you fly the Gemini. On a modest 250W my model does everything I can ask of it and it comes back begging for more.

If you’re on the fence on the Gemini go buy one!

Tommy D
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Old Jan 03, 2008, 11:43 PM
KK6MQJ
Bajora's Avatar
Joined Sep 2004
13,598 Posts
Nice action shots!

I have to be careful reading this review or I'll have ANOTHER plane on my list of planes I think I need! I like the Multiplex Elapor and this is a clean looking bipe.
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Old Jan 04, 2008, 03:51 AM
Registered User
Atlanta, GA
Joined Sep 2003
78 Posts
Thanks for taking the time to do such a great review with wonderful photos! Makes me want to order one right now!

Jim
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Old Jan 04, 2008, 07:50 AM
"Have Glue - Will Travel"
dawnron1's Avatar
Ft. Worth, Texas
Joined Jan 2004
2,428 Posts
Thanks Tommy, Jon and Jim! Glad you liked the review!
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Old Jan 04, 2008, 08:07 AM
War Eagle!
Spackles94's Avatar
Birmingham, Alabama
Joined Feb 2007
7,876 Posts
Nice review Ronnie!

I especially liked the video — nice flying!

It's funny, though: I just finished reviewing another biplane (Phase 3 Double Time), and I also found myself doing hammerheads with it all the time, like you did in the video. For some reason, stall turns are great with biplanes — they're very clean and straight.

Very nice plane, and it seems to be very stable.

Keep up the great work!
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Old Jan 04, 2008, 09:57 AM
Test your skills....fly IMAC!!
sun.flyer's Avatar
Swanton, Ohio
Joined Feb 2005
7,990 Posts
Excellent write-up Ronnie!! Definately a cool looking bipe. I thought a friend of mine to fly on a Magistar and I can surely attest to the strength and resiliance of the elapor foam. Very, very, tough.

Nice work my friend!!

Tim

BTW - Thanks to the robustness of the elapor foam (several accidents) my friend is now truly enjoying this hobby. In which he is still flying his Magistar 2yrs later.
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Old Jan 04, 2008, 12:37 PM
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USA, TX, Trophy Club
Joined May 2002
14,473 Posts
Great review- fun little plane...
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Old Jan 04, 2008, 02:02 PM
"Have Glue - Will Travel"
dawnron1's Avatar
Ft. Worth, Texas
Joined Jan 2004
2,428 Posts
Thanks guys!
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Old Jan 04, 2008, 02:37 PM
Registered User
Chalfont St Giles, Bucks, UK
Joined Jan 2007
3,180 Posts
Excellent review Ronnie.
Great in flight pictures and superb video.
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Old Jan 04, 2008, 02:53 PM
"Have Glue - Will Travel"
dawnron1's Avatar
Ft. Worth, Texas
Joined Jan 2004
2,428 Posts
Quote:
Originally Posted by Paul@SCC
Excellent review Ronnie.
Great in flight pictures and superb video.
Thank you sir!
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