RCU Review: Multiplex Fun Jet

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    Contributed by: Chuck Doud | Published: September 2007 | Views: 123328 | email icon Email this Article | PDFpdf icon

    Building Skill:
    Flying Skill:
    Advanced Intermediate

    Building the 5s Funjet seemed
    to be the easy part for Chuck.
    In this short story, read more
    about the pleasures and perils Chuck faced trying to log the maiden flight on one of the fastest FunJets on the planet...

    Making the 5s Multiplex FunJet


    For building and setup,
    the following were used:
    ZAP 15 Minute Epoxy
    6 inch Servo Extensions
    220 Grit Wet/Dry Sandpaper
    Small hobby/paint brushes
    #11 Hobby Blades
    Velcro and Velcro Straps
    1/16" Hobby Plywood

    The following vendors provided products or materials for testing or support in this article:


    ZAP Adhesives
    (CA and Epoxy)

    "Awaken the mad-scientist within..."

    Over the nearly past one year, I have spent a great amount of time (and personal finance) with the FunJet from Multiplex USA. I spent weeks between my workshop, the phone, and on the message boards at Wattflyer.com. I talked with the 'experimental contingent' of innovators about this plane's modification process. From those mediums, and my own personal process, I built countless versions of the Multiplex FunJet. Together, myself and others have built these unique aircraft to be fast-flyers, slow-flyers, 3D-Hybrid flyers...we have added fully functioning rudders, dual power systems, etc, etc, etc,...

    However, throughout my journey swapping ideas with gifted mod-flyers like Julian Meyers (WingTips24), Darryl Melton (Crash Test Dummy), Bill Mims (Twizter68), and others. Our pursuit of the ultimate 'buzz' with the FunJet, invariably kept returning to a common result...BLISTERING SPEED! There were successes, failures, and adrenaline filled moments of light with the FunJet. Through it all, we never stopped having a blast with these airplanes.

    The compelling thing about this plane is that one can fly it stock and hit a very controllable 100 miles an hour with minimal out of pocket investment. You can also build it 'light' and 'inexpensive' to create a phenomenal school yard flyer that handles like a dream. Also, if you wish to toss down a 'coupla-hundred'...I have personally verified these planes at speeds just over 150 miles an hour (real miles an hour...not scale). The FunJet truly is a foam plane that breaks the rules by letting each flyer seek an experience that is as casual or as extreme as they wish; while performing wonderfully at either end of the envelope.

    Though in order to attain excessive speeds on the FunJet, it is advisable to reinforce the airframe, the process of doing so is quite simple. This 'process', I will add, is constantly being innovated with new manners of strengthening the frame, and hitting the number each flyer dreams of posting on the message boards.

    In this example, I went with the most simplistic manner of reinforcement I could find in order to yield the lightest weight and heaviest payoff in watts to mass for level-flight. I hope you enjoy reading, listening, and learning from my journey with the FunJet...and I hope to hear what fete you have achieved with yours in the near future.

    While you are checking out the build, be sure to click through to the story of how difficult it was to actually maiden this hop-up. For me, the building was almost the easy part. Plus, I have assembled a behind the scenes video and media section, which, are both also available on the list to the left of this article.

    Also, if you decide to build one of these FunJets and find yourself with questions or concerns...I urge you to check out the message boards at Wattflyer.com (the sister site of RCUniverse.com). There you will find countless flyers that have built and flown mods such as the one featured in this article. Each of them are happy to offer a wealth of support and guidance. Of course, you may always reach me at the email link below.

    Fly hard and have FUN!!!

    Yours in Brotherhood,

    Chuck Doud
    Rc's Best Friend


    Email me: chuck@rcuniverse.com


    Kit Name: Multiplex FunJet
    Price: $69.99 retail price
    Wingspan: 32.29 "
    Wing Area: 232 sq. in.
    Stock flying weight: 21oz
    Airfoil: Semi-Symmetrical Mid-Wing

    Motor: Mega 16/25/3
    ESC: Castle Creations HV45
    Battery: MaxAmps 5s 3100HV *
    BEC: Ultimate BEC (
    Servos: JRSPORT MC35 (X2)
    Prop: Graupner Cam 5.9X5.9 (

    * 5s attainted using MaxAmps 2s and MaxAmps 3s 3100HV packs in series

    Hey, Nice Box!
    Top Notch Molded Parts
    Water & 220 Grit Sandpaper
    The Funjet comes in packaged a wonderfully attractive box...a 'big one' for me. LOOKS ARE EVERYTHING in today's saturated RC market...much time and love were put into this plane's appearance on the shelf, which, is something a company as committed to excellence as Multiplex would not do unless they knew they had a winner. That said...LETS TEAR 'ER OPEN AND GIT ER DONE!!!

    The FunJet's airframe consists of seven molded 'elapor' pieces. In testing, I found no reinforcement was needed at speeds of 100 miles an hour in the air. However, once you start going faster than 120 and plan on doing some aggressive turns at post '120' speeds, I lean towards reinforcement. To reinforce with lightweight fiberglass only requires some quick and easy steps.

    First you will need to sand off the casting pimples and do some simple filling on the mold injection points with lightweight spackling compound. Later, when the plane is semi-assembled, you should fill the wing seams with lightweight spackling as well. If you are cruising along, it is quite possible to knock out the sanding and filling in a night. I advise sanding and filling BEFORE assembling the plane as it is easier to complete this task a step at a time with smaller parts.

    Begin with some water and 220 grit wet/dry sand paper. Dunk your paper in the water, pick a part, mist the part with with a spay bottle of water, and begin sanding lightly in one direction to keep abrasion consistent. The water reduces friction and inhibits tearing of the elapor. Be sure to rinse your sandpaper frequently and then mist and wipe off each part occasionally as buildup starts to accumulate. You'll know its time to rinse when the buildup begins to look like 'skim milk' on your sandpaper and surfaces.
    Wet the sandpaper before and during sanding!!!
    Spray your surfaces with water as well for less friction

    Fill all injection points using lightweight spackle.
    Once all of your parts are sanded consistently smooth and uniform (top and bottom), fill in the injection points on the wings, fuse, and vert fins with lightweight spackle and let the spackle dry hard. Then sand the spackle to contour the airframe.

    (hint) take your time during sanding and you will be rewarded with a beautiful smooth surface, which, is now ready for assembly and glassing.
    Semi-assembled fuse
    Hatch modified
    test fit and mod servo bays
    After all of your parts are sanded and filled, assemble the plane as specified in your construction manual supplied with the plane. However, for high cell counts, (meaning more than 3 cells) DO NOT GLUE IN THE CANOPY AND "TURTLE BACK" PART OF THE FUSE AS YOU WILL WANT TO MODIFY THE HATCH AS SHOWN IN THE PICTURE ABOVE. . I extended my electronics hatch to 1/2 inch behind the horizontal wing spar to give plenty of room for balancing the plane to the specified CG. ALSO...DO NOT INSTALL THE MOTOR MOUNT OR VERT FINS UNTIL AFTER GLASSING. Fill the wing spar with lightweight spackle and sand them flush when dry as well.

    Also, before final filling of the wing seams, test fit (do not glue them in yet) your servos to make sure they fit into the pre-cast servo bays. Using the JRSport MC35 servos, I did have to cut out a small amount of the servo bays.

    I highly recommend using micro servos with 30+ ounces of torque if you plan on flying faster than 100 MPH. Sure, I have heard of people using smaller servos with less torque at high speeds...but I wouldn't want to be the one who found out the hard way that 15oz of torque was not enough at 120 miles an hour. eeeeek!!!

    Remove your servos, flip the plane upright, and fill in the wing join areas with lightweight spackle and let it dry up. When dry, sand the seams, make em pretty, wipe off the excess powder, and get ready for glassing.

    NOTE: Some flyers choose to replace the stock wing spar with a high strength carbon fiber tube for extra rigidity. Though I have done this on other FunJets, I used the stock spar with this build in an effort to make the strongest and lightest FunJet I could. If you plan on really getting 'crazy' with your flying...you can use a carbon fiber tube and take the weight penalty as a minimal loss compared to the increased structural strength of the FunJet...it all depends on your flying style and personal preference.

    Fill wing join areas with lightweight spackle and sand
    Glass the bottom of your FunJet first
    Use poly on centerlines working fore and aft
    For glassing, I apply the 1/2 oz glass with Minwax Polycrylic, a water-based polyurethane product available at most home improvement centers and hardware stores. I like using small hobby brushes to apply the polyurethane and glass to the fuse. In essence, the polyurethane is your adhesive for the glass.

    For simplicity, it is advised to glass the plane in sections (wings, fuse, etc) starting with the bottom of the aircraft. It is also advised that you wrap the glass 1/4 to 1/2 over the leading edge and trailing edge of the elevons, fuse, etc. This 'wrapping' technique will ensure maximum strength later when you lay on the top layer of glass.

    Glassing is easily done in panels by laying your plane on the glass and cutting the glass to the approximate size while leaving enough extra for wrapping around the LE and TE of the plane.

    I apply the poly from the centerline going outward in order to 'lock' the piece of glass in place. Then apply poly going forward and rearward in nice even strokes, working out any bubbles that may appear.

    While glassing the elevon area (using the same piece of glass you are using on the wing), take extra care to ensure there are no bubbles while you lay the glass into the elevon elapor-hinge point. If you do get any pesky bubbles in hinge area, I found that using a 2-56 pushrod to 'tuck' the glass in snug to the elapor hinge area worked very well. Once this dries, you will have a super-strong hinge worthy of post 100 MPH speeds.

    Note: Do not 'free' your elevons at the wingtips until after the complete glassing process is finished and dried on both the top and bottom of the aircraft.

    Lightly sand any rough edges with the 220 grit sandpaper and also sand the areas where the glass was wrapped at the end of the fiberglass to make a sooth area for the top layer of glass to matte against. As you sand the dried glass, you will notice it sands quite easily and any hangs or rough edges just powder away leaving a nice end surface.

    Glass the top of the plane in the same manner, wrapping the glass 1/4 to 1/4 inch over the leading edge and trailing edge of the elevons. Double check that no bubbles have popped up. If they have, simply work them out with your brush that is wetted with the water based poly. After it has dried, lightly buff sand the structure to remove any imperfections. Some people like to now add a second layer of poly for luster and strength. I did not do this on this model; the choice is yours.

    Glass your vert fins on both sides (letting one side dry completely before doing the second side of each vertical fin). Then, glass your canopy and set it aside to dry as well.


    You will need to glass your motor mount area heavily for high cell count applications. This strengthening process is necessary in order to prepare it to handle tremendous amounts of thrust. Do this before installing the black mount ring.

    I found that using 2oz fiberglass and applying it to the mount area with super-thin CA worked excellently. Lay up two layers of 2oz glass on the round mount area, folding the glass with a series of cuts to lay 1/2 inch inside the motor mount area (as shown below). Brush the glass on with with your hobby brushes, changing brushes as the CA hardens. When dried, the mount area will feel extremely rigid. If you do not have 2oz glass, use 4 or 5 layers of the 1/2 oz glass to essentially give the same result.

    Again, do not apply the black mounting ring until you have reinforced the motor mount area...otherwise the extreme thrust generated will start to weaken the surrounding airframe, causing poor flying attributes.

    Take your time on elevons to eliminate hinge bubbles
    Glass vert fins before installing them to the fuse
    Glass the top of the plane, paint and install fins
    Once the plane is fully glassed and dried, free the elevons at the wingtips as described in the Multiplex FunJet assembly manual. Then, flex the elevons in their full range of motion 5-10 times to 'break in' the glass seam. You will hear a mild 'crunching sound' as you move the elevons with your hand...this is normal. It is important to 'break in' your hinges in this manner so that they will move freely once you install and attach your servos, horns, and linkages as specified in the instruction manual.

    At this time, paint the aircraft as you wish. I went very light on the paint to keep my weight as low as possible; just a flew blazes of neon-yellow at the wingtips and a mild pinstripe down the canopy. My vert fins were painted black.

    Paint (if desired) and install your vert fins at this time. Check the elevons range of motion in accordance with the manual. If needed, trim 1mm off the innermost (root) portion of the elevon. I had to trim my elevons just under 1mm on this build for them to achieve full range of motion.

    Glass reinforce the motor mount area for BIG thrust
    Prepare Your Motor:
    The Mega 16/25/3
    Install Motor, and electronics
    to pre-balance the plane.

    Install Velcro, ply supports, straps, add flare to paint

    Convince wife that your plane belongs near the bed
    Install the motor mount ring on your funJet with CA as shown above. Also, cut out the overlaying glass on the servo points and install the servos as specified in the Muliplex FunJet instruction manual. You will need to use a razor to re-open the channel for your servo leads. I used a straight-head screw driver to recess them into the pre-cast channels. There is no need to re-glass these channels after you install the servo leads; though I know some folks that do so. Add the servo hardware and fairings as shown in your Multiplex FunJet manual at this time. Note: Be sure to center your servos before installing them!!!


    For the canopy mod (extension) that was made, 2lb hold rare earth magnets were used at the canopy mid-section and end section (4 magnets total for top and bottom). These were used in tandem with the Multiplex Funjet 'snap lock' canopy latches to keep the extended portions of the canopy in place. If installed correctly, the magnets and clips should lock in with an audible 'click'.

    Install your your electronics, motor, batteries, BEC circuit, and related materials. Now, balance the plane. Once you have found the balance point, mark the battery position in the fuselage with a ballpoint pen and remove the batteries.

    Using hobby plywood, create 2 1/16th inch thick plywood mounting areas for your batteries with your Velcro straps running underneath the plywood. Install these mounts 2mm behind the balance marks that you made in the battery area during the previous step. Using epoxy or medium thick CA, affix the mounts and straps (creating a channel for the strap in the elapor to keep the plywood flush against the foam). Let the epoxy or CA setup and then reinstall the cells, canopy, and check your balance again. Using your ballpoint pen, make a very dark mark on the elapor inside the bay for a balance reference point to be used in the future as a 'starting point' for CG balancing of your aircraft.

    Hint: Apply Velcro to both your lipos and plywood supports to work in tandem with the velcro battery strap for extra support.

    Now its time to get ready to fly your FunJet. Charge your batteries, prepare your transmitter settings, and get a good nights sleep.

    Flying this 5s FunJet is no easy joyride around the park. From the second it leaves your hand, 830 screaming watts send the FunJet off like a falcon with its tail feathers on fire. Within nanoseconds you are at 100 miles an hour and your mind jumps to recall if put on clean underwear before leaving for the field.

    The beachfront where I maidened the plane was roughly 150 yards wide at low tide. After getting the plane 'up' and trimmed I punched the throttle a few times to test my CG and thrust alignment. I did notice the nose would dip slightly when I gave it full power. I landed quickly, gave the mount thrust alignment screw 1/4 turn to give it just a touch of 'up'.

    I also noticed my elevons had about 1mm of reflex (up). Therefore, the CG was also adjusted about 3mm aft. Then, I topped off my MaxAmps 3100mAh lipos which only needed 10 minutes to replace about 280mAh from my first quick flight.

    As I launched the plane this time...I could tell from the second it left my hand that the CG and thrust were spot-on. The JunJet just has this 'locking in' feeling when you have it dialed properly. There is nothing skittish or uneasy about it's flight characteristics. I went down to the end of my flying space, turned the corner, and kocked the throttle full forward.

    I banged a level pass past the microphone which dopplered out to 137 miles an hour in level flight....no tail wind, either. EUREKA!

    The performance of the FunJet can best be likened to a performance motor cycle; tight turns, super crisp handling, and damn scary if you don't stay on your toes!

    This plane small to begin with; be ready for it to go out of sight in a hurry. It literally gets 'small' within about 2-3 seconds at these speeds. On one 40 degree dive pass I did, the doppler registered 172 and I nearly lost the plane as it is quite difficult to keep the low profile in sight if you are not locked on the plane....DO NOT LOOK AWAY FOR EVEN A SECOND.

    Don't expect to be doing wild aerobatics at post 130 mile an hour speeds...just some nice smooth 110-120 mile and hour rolls around the field and then slamming it wide open across the deck for a true 135MPH + adrenaline pass.

    The FunJet handles like a dream at these speeds...but be sure you are ready for the performance it will give you on a 5s lipo setup.

    Personally, my favorite speed on the FunJet is about 100-110. At those speeds I can still do nice tight rolling circles, hot split-s maneuvers, and some really awesome loops. However, once you take a plane this small at 137 miles an hour...its pretty much like watching a NASCAR race. TURN LEFT! TURN LEFT! TURN LEFT!

    For its size, price, and cost to get it there, I love my super fast FunJet...So, if it's speed you want...and ya don't want a pylon or hotliner ship...GET A FUNJET. You will not be sorry!

    The 5s 830-Watt FunJet in action!
    Full-Length Review Video (3:30)


    Strike a pose

    Comments on RCU Review: Multiplex Fun Jet

    Posted by: djp_9494 on 03/02/2008
    that is sooo cool did you find the funjet was had to launch and quiet heavy ?
    Posted by: geh3 on 05/01/2008
    I built one, flying it on 6s... totally AWSOME I just launch it straight up and VERY SOON it is in the clouds!!!
    Posted by: SigMan on 05/27/2008
    just maidend mine today and all i can say is....WOW ! i love it !
    Posted by: cloudancer03 on 06/22/2008
    I am blown away by this!I just picked up the mpx pico twinjet.is there a set up that will give me say 80 to 100 mph ..do you need to fiberglass for that level of performance and what motors can I use and do I need 2 esc.I want to use a 3 cell2100lipo. what a awesome jet.
    Posted by: dic181 on 01/23/2009
    How do you mount an outrunner to the funjet?
    Posted by: littlephoenix on 03/26/2012
    Here is my 10oz multiplex funjet, so light you can hover it... http://www.youtube.com/watch?v=eFTg-qEVTkc&list=UU5-npdMgGS4psDghZFQX68w&index=1&feature=plcp
    Posted by: littlephoenix on 03/26/2012
    Page: 1
    The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply generally to similar products by the manufacturer. We cannot be responsible for any manufacturer defects in workmanship or other deficiencies in products like the one featured in the review.

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