The following vendors provided
products or materials for testing or support in this article:
(CA and Epoxy)
"Awaken the mad-scientist within..."
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
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,
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
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
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
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
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.
WARNING...THE BEST THING YOU
CAN DO FOR THE SAFETY OF YOURSELF AND OTHERS IS TO FLY WITHIN
YOUR SKILL LEVEL...WHEN FLYING HIGH POWERED RC AIRCRAFT...USE A
SPOTTER...THEY CAN SAVE YOUR PLANE AND SAVE A LIFE BY HELPING
YOU KEEP A CLEAR AND SAFE FLIGHT PATH.
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
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
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
Fill all injection points using lightweight spackle.
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.
take your time during sanding and you will be rewarded with a
beautiful smooth surface, which, is now ready for assembly and
test fit and mod servo bays
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
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
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
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
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
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
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
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
specified in the instruction manual.
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.
(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.
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
running underneath the plywood. Install these mounts 2mm behind
the balance marks that you made in the battery area during the
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.
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.
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
banged a level pass past the microphone which dopplered out to
137 miles an hour in level flight....no tail wind, either.
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
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
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
The 5s 830-Watt FunJet in action! Full-Length Review Video (3:30)
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.