Bumpy Green Model Aerodrome: Mupltiplex Pico-Jet Combat

Used in original review

Pico-Jet Combat (PJC)
Permax 400 6v motor
Gunther prop
8.4v 1100mAh battery
35A BEC Speed controller
Mini 4ch 35Mhz R/x
Micro servos X2.
All up 700g ready to fly.

In brief

An EPP (expanded poly propyleen) delta wing for speed 400/480 motor & suitable r/x & s/c requiring 2 servos & elevon mixing.
Cyno-acrylate (superglue) used entirely during construction.

Building

Construction is simple with 3 main parts.
The wing and lower fuselage body are a moulded single piece.
The tail fin which is superglued to the back of the fus' between the wings above the motor housing.
The canopy top cover is held on by a strip of ply hooked under the glued on tail and clever rubber band hooks to hold the nose together.
Motor fitted (thrust line is moulded into the mounting area) wiring is routed through the grooves under the tail. R/C-Line 35amp BEC speed controller hard wired to the motor loom before fitting to ease installation. 35A is a little overkill, but the R/C-Line item is very small and was spare.
Internal tray glued into place and velcro added for r/x. Jeti mini 4 channel reciever installed. Ariel lead fits into a pre cut channel along the wing. Wiring secured with cyno drips at intervals.

Mods on the fly

Motor mount lined with 1/64th beech venier and small blocks glued to underside of tail to hold motor for glueing. This allows epoxy to be used to secure the motor. Make sure the motor air vents align with the ducts built into the fuselage sides.
Speed controller wrapped in Flair alu-clad to reduce interference. R/x fitted and wrapped with protective foam & ariel routed though fus' side using control snake inner.

2 hardwood strips (1/4") are glued into the aileron slots for the 2 horns to attach to. 2 MS-X2 servos fitted into the wing cutouts with double sided tape. Wiring needs to be extended to reach r/x along very neat channels in the wings. 2 supplied pushrods fitted and attached to the horns via barrel fittings. Glass tape fitted to tops of wings as directed to protect the hinge area of the elevons. Control surfaces cut out of main moulding using sharp knife or slim fine toothed saw.
Aileron pushrods aligned and secured. Transmitter used has Delta/Elevon mixing and was also set up and trimmed at this point. Servo slots covered with glass tape to minimise dust & water ingress.

Wiring tip

When cutting the servo connectors off to fit extensions, cut the wire 3 different lengths at 1cm intervals. When soldered neatly and shrink wrapped this will not cause a bulge in the wiring channel.

Connecting the speed controller to the battery, the propeller was fitted and the motor was tested.
Initial checks looked like everything was fine.
A glide test on the local slope over a large patch of long -impact absorbing- nettles proved the centre of gravity needed adjusting back.Thank the maker for nettles & long live the Velcro strip.
A quick shuffle of ni-cad and foam and another test throw. It still dropped quickly. Balance and C of G checked again ~ OK.
New tactic - a much harder throw. The Pico-Jet glided off into the field.
Powered flight was the next test. Full throttle was making some good wind from the rear, a hefty chuck and the Pico-Jet sank into the nettles like I had fitted a flight box battery to it. ( ~ see the mods ~)
A quick turn coat for the prop and a few laughs later the Pico-Jet was launched from the slope and the nettles were just a memory. It flew in a stable shallow climb, slight trimming to the left required to straighten the flight.

Mods on the fly

Gunther props are supplied as tractor props. When fitted as supplied they are facing the wrong way. Pull out the black section, reverse the white blade section and re-fit. A reversed prop appears to be working but is highly inefficient.

Additional notes

With flights of around 6 minutes at full throttle getting some good altitude, gliding can be used to extend flight times.
The first casualty was the Gunther propeller, a dodgey launch and a sudden gust of wind caught the Pico-Jet and as it hit the floor it spun around it's nose and snapped one of the blades off.
How many people asked 'how did you break one of those?' ~ I lost count but eventually found a source of new props.
Put off by a 3 day wait, I picked up a free flight rubber power one piece prop. Pitch unknown but it worked well enough to fly.
After a second Gunther prop departed ~ this time simply detaching from the motor under thrust and whirling away into the long grass ~ a spun aluminium prop adapter was found and an FK 6x3 prop used to replace the 5x4.5 Gunther.
Another concern was the rubber band holding the top on. This was replaced by a single bolt at the rear of the Canopy section, passed thru some snake outer to prevent the foam crushing. A small captive nut was secured to a balsa block and glued above the speed controller. The front is now held down with 2 strips of velcro.

Mods on the fly

6 different props have been aquired for testing and a crude thrust measuring device has been found.
A table of these findings along with flight times and percieved speed differences is reported on in the Thrust Test under Articles. (or click here)
Props in list are:
5x4 Gunther (standard)
5x3 Thimble Drome (cut down)
5x??, Bow Tie (band power)
5.5x4.3 Cam speed prop
6x3.5 Windsor prop
6x3 FK (yellow bendy) prop

	To Recap It all started when I bought my Pico-Jet Combat ~ ''Indestructable'' they said. And for the most part they were right. Having assembled the required parts to complete my PJC I set about the clogged up superglue and got to work. The following day Choddy and I went to test fly it. Nice day, mild wind, a hearty throw and the PJC sailed effortlessly into the long nettles. After the laughter had died away we decided the propellor was actually the wrong way round and a quick swap around and another hefty chuck and away it went. Some trim and all was well. A few further flights returned about 6 - 7 minutes of stick time. A few days later, hardly able to wait to show my new toy off, a few mates visited and we headed for Bumpy Green site-2 (electric only) A swift control surface check and a blast from the motor and I was ready to astonish. A reasonable launch suddenly turned bad and the Pico-Jet hit the dirt in a dying spin .... .... .... and broke the Gunther Prop.
	Yes, they all said it when I tried to buy replacements ''How did you break one of those'' Normally this is a very valid statement and Gunther props are usually very bendy. For some reason mine was not. Having ordered 5 new props (none in stock) from the local model store I was about to leave and wait 3 days for any more Pico-Fun, when I spotted a propellor that bore a striking resemblence to a Gunther. It was a rubber band powered model prop. By all descriptions (including that it looks like a comical bow-tie) this propellor should not fly this model. Well I was determined not to be grounded for 3 days. A small drill later and the bow-tie was ready. It fitted tightly to the motor shaft, it did not slip when held still, it did not fly off (see above & Topic 400 review) and it appeared to work. It needed to be fitted with the built in spinner facing forward.
	Once again to the test slope, with the long cushioning grass and a harder then needed throw the PJC was away and flying. It was a little sluggish but it was working sufficiently to fly the model. I actually kept this prop for a few weeks having just bought two 9.6V 1300mAh battery packs from Overlander and they seemed to make quite a difference. Being the same size as a transmiter pack and weighing just 200g (the 8.4v 1100NiCad weighs the same) the effect was good, over 10 minutes of powered flight if kept tame and so far my best is about 20mins with use of half power.

I have now been flying the Pico-Jet for some 8 months, and in that time there have only been a few weeks where I didn't get at least one flight in (some weeks it was just one flight in a day because it was so cold) I even tried to fly it when the gound was covered in snow. It was a freezing cold but clear blue day and the sun was just begining to reach a warming height. I had left the Pico-Jet in my car overnight. Big Mistake. The frozen batteries did not want to play. About half thrust from the NiCads and even less from the Ni-mh cell packs. Having buried the PJC in the snow twice, with just it's tail tip showing (good job it wasn't white) I called it a day and went home, cold and miserable. It did however demonstrate the need for battery packs to be at a reasonable temperature before flying.
More tales of joy and horror to follow.
A movie of the Pico-Jet in flight and doing some of the mad things you would only try with an EPP plane will be made soon.

I can now conclude my studies of 'indestructable' ~ It is, almost.
So far I have managed to snap the nose off the Pico-Jet twice. Each time I just grabbed the superglue and fixed it back on
The 3rd occaision (which just reopend the old war wound) I used a small diameter dowel, about 3 inches long pushed into the foam each side of the break and cyno'd into place. A sheet of balsa about 30mm x 100mm x 2mm has now been laid into the bottom of the battery bay as the internal plastic tray had lost all ability to stay back together. It also now weight about 725g after all the glue and mods were added.
The tail and wings have both lost the tiny pointed tips but have suffered no other damage at all. Several full power strikes from playing too close to the ground have done nothing to the model. The funniest but so far the softest crash was recently. Flying inverted at fairly high speed, pushed the elevators forward to do an outside loop and the battery fell prey to gravity and overcame the sticking resistance of the velcro holding the lid on.
The battery plummeted to earth and the Pico-Jet floated down spinning like a sycamore seed. The canopy ejection was almost realistic.
Superglue saves the day each time.
I would not have had much flying at all recently except for the PJC, what with a bitterly cold winter and then the foot & mouth disaster.
Glad there are some places I can get a good session from the Pico-Jet at.
My most flown plane this year.