RCU Review: Multiplex Fun Jet

 RCU Review: Multiplex Fun Jet More On This Product
Discussions on this Product Show user ratings Check for Retailers Contributed by: Chuck Doud | Published: September 2007 | Views: 122225 |
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"Awaken the mad-scientist within..."
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
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,
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. Making the 5s Multiplex
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. For building and setup,
the following were used:
1/2 oz Fiberglass Cloth
Minwax Polycrylic
ZAP Medium Thick CA
ZAP Super Thin CA
ZAP CA Accelerator
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:
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
Fly hard and have FUN!!!
Yours in Brotherhood,
Chuck Doud
Rc's Best Friend
ZAP Adhesives
(CA and Epoxy)
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 (KFS001)
Servos: JRSPORT MC35 (X2)
Prop: Graupner Cam 5.9X5.9 (GPF06060)
* 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
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
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
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
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. IMPORTANT:
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
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
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
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
Install Velcro, ply supports,
straps, add flare to paint Prepare Your Motor:
The Mega 16/25/3
Install Motor, and electronics
to pre-balance the plane. 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
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. Strike a pose
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
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)
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 ?
Profile 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!!!
Profile Posted by: SigMan on 05/27/2008
just maidend mine today and all i can say is....WOW ! i love it !
Profile Posted by: cloudancer03 on 06/22/2008
Profile 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?
Profile Posted by: littlephoenix on 03/26/2012
Here is my 10oz multiplex funjet, so light you can hover it...
Profile Posted by: littlephoenix on 03/26/2012
Profile 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. EMAIL THIS ARTICLE OR CHECK OUT THESE OTHER GREAT REVIEWS!
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