| John
Duxbury tells us about his Multiplex Twin-Jet
Last Saturday, my son
Kestell and I went along for a day out at Sandown Park. We sat and had a
coffee with some club mates, one of whom informed me that he had bought
a Twin-Jet from Multiplex. I had a look in his box and half an hour
later was watching four of them flying in the extremely windy conditions
and was bitten.
I just had to have one.
For those that have not
yet seen the Twin Jet, it is a moulded foam (elapor) delta design model,
39" wingspan and powered by two 400 size pusher motors which are
included in the kit, together with props and motor wiring and lots of
fittings and bits and pieces. The instructions list everything that you
require to finish the model which is not in the kit.
So on to building, or
should that be assembling. Basically follow the instructions and you
cannot go far wrong, although it should be pointed out that a degree of
experience in model making is still required. I'm sure Multiplex would
counter this by saying that this model is far from suitable for
beginners anyway.
 The
first job is to join the main wing & fuselage section to the nose
section & then trim the abs radio tray to fit inside. Personally I
hate abs, this tray is too thin to sand and tears if you tried cutting
it with scissors; you just need patience to make a reasonable job of it
(which I don't think I did, see photo) Suddenly within approx 10 minutes
you have what looks like a 90% complete aeroplane.
It comes together
fairly quickly, but there a couple of bits that threw me. Firstly the
elevon horns stood proud of the moulded recesses, do you a) make the
recess deeper? or b) reduce the depth of the horn? I went for a) and the
horn came through the top of the elevon! Secondly, when assembling the
pushrod connector to the horns, I assumed that when the nut was
tightened, the connector should still be able to swivel, mine didn't so
I replaced the connectors with others I had in the spares box.
The wing has moulded
recesses in the underside to allow 2 Multiplex MS-X2 micros to slot
straight in. I had 2 JR 331 micros with extension leads soldered on
already so pressed those into service instead - it just meant that I had
to trim some of the foam away to allow the JR servos to fit. I secured
mine by wrapping in masking tape & holding in place with a blob of
epoxy.
Having servos with
extension leads already fitted, I thought I would save some time - wrong
. . . ! Due to the length of the servo and motor wires, Multiplex
recommend that you wrap the servo leads round ferrite rings near the
receiver to reduce the likelihood of interference. No problem here,
except that the servo leads will not go through the rings with the plugs
attached, ugh!!! These are the little purple rings you can see at the
bottom of the radio tray.
 Once
these little hurdles were overcame I had an airframe ready to go in
around 10 hours; not bad really considering that I am not exactly a fast
builder. The battery pack I used was a 1700 mAh 8.4v sub 'C' pack as
used in my Early Bird and I used a 40 amp Kontronic speed controller (35
amp will do) and a GWS 8 channel receiver ( I have 5 channels spare).
All I need to do now is fly the thing.
I went up to my local
flying field, nobody was there and it was pretty windy. My head said, Go
home and wait until it is a calmer day and somebody else is there to
give me a throw. My heart said, Go for it, so I went for it! A good
chuck into wind and wow . . . it just climbed and climbed. I
reduced the throttle to about 1/3 and it leveled out but still made
headway into a strong wind. Turning downwind, it sped up a great deal
but was still fairly easy to control. After about five minutes of fairly
leisurely flying, I decided to bring it in whilst I still had some power
left - with no power this plane loses height rapidly and I did not fancy
a walk. It came in with no problem except you need quite bit of down
trim. The controls, whilst responsive, also felt twitchy, so I put
exponential on my transmitter of 30% for both elevator & aileron
ready for the next flight.
I was happy as Larry,
put it back in the car and drove home. The next day, same wind but
other people down at the strip, so a launcher was selected. Again no
problem, this time I tried rolls (very fast), loops (very big), and
inverted flight (very scary - lots of down needed to keep to keep it
level). Everything certainly felt a lot smoother with the exponential.
 Next
flight, disaster! The plane climbed well from launch, I went into a
vertical climb and then turned it to bring it back downwind.
Unfortunately, on the point of turning it was virtually stalled and the
wind strong enough that coming back downwind it was moving quickly over
the ground but had little flying speed, to the point that I did not have
the elevator authority to pull out of the ensuing dive. It landed very,
very heavily. The battery pack flew out of the canopy, one prop was
broken and both motors had come adrift, together with the moulded foam
mounting pods. The damage can be seen in the photo. Ouch!
 I
have since cyanoed everything back in place but think that maybe there
are a couple of lessons to be learned. Firstly, this aeroplane needs
flying speed; lose it and there is little authority to either aileron or
elevator. Into wind this is no problem, but downwind it can be difficult
to judge. Secondly, use only a little epoxy to hold the motors in; too
much, as I did, and when it lands heavily the foam is ripped out. It
might even be worth looking at holding them in with silicon. It can be
easily repaired, provided you have all the bits of foam and cyano it all
back together like a 3D jigsaw. This photo of the rear of the plane was
taken after the repair was carried out.
As with 99% of
'incidents' it was pilot error. I just hope I have learned a few lessons
so that I don't do it again. I may wait for a calmer day as well, before
flying it again. Incidentally, the nice multi- colour stickers you see
on the box and in all the magazines are not included in the kit - they
should be available from where you by your kit for £2.95.
Would I recommend it?
Absolutely, in the short time mine has flown, it has been a lot of fun.
Just bear in mind that it is a fast delta and try not to take liberties.
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