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Nov 26, 2015, 06:04 PM
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Build Log

Aermacchi MB339 - FlyFly 90mm EDF


I have had the FlyFly MB229 for many years, in a box...... so it was time to get it out and build it finally! Especially with the demise of the Lander RC F9F Panther, though I had started the MB339 the week before that crashed - hmmm, maybe the F9F was not happy about that!

At approx 1.4m wingspan by 1.4m long, the FlyFly MB339 is quite a big "90mm" plane. It has a TON of internal space. This is all because the full scale one is not a 'big' plane and when you keep dimensions at "1.4m" across all the planes you make (FlyFly) then a smaller full scale plane makes for a lower scale number compared to other larger full scale jets they make. This then means the overall 'volume' of the plane is large, versus the lower scaled plane of the same span/length dimensions. (eg a Lancaster bomber of this same scale will have a pencil thin fuselage).

Everything about the MB339 is "Typical FlyFly" - nothing better, nothing worse. A great blank canvas to work on, though many have been built just as they came - and probably had short lifespans due to all those typical FlyFly inadequacies in their stock form. One common thing is the wings folding up = crash.

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Last edited by PeterVRC; Nov 26, 2015 at 07:16 PM.
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Nov 26, 2015, 06:08 PM
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First assessments/task - Main gear and Wing Spars


One of the first things I look at for aircraft now is the landing gear setup - the mountings and sizes etc. If you want landing gear that operates properly and reliably, it needs to all be robust! Far more robust than foamies typically come with! Any brands!

For a 90mm aircraft to operate from grass - even very good grass - it needs to be even more robust. But even hard runways can be very harsh on landing gear if you have a bad landing! The impact is far worse than on grass then!
This means you really want to be using the "Large" size 44mmx41mm retract systems on any 90mm aircraft. Not the commonly supplied/used 33mmx31mm "Medium" size!
The Large use 5mmm pins, not 4mm, and are a LOT stronger in total.
You also need to make mounts suited to the task - not use the stock paltry (weak) rubbish mounting systems!

I modded the foam of the stock retract areas to fit some large 4mm plywood plates for the large type retracts. These will be supported and 'bridged' across the wing by a carbon fiber spar also.

The oleo/wheel set I chose was the hobbyking:
https://www.hobbyking.com/hobbyking/s...Class_Jet.html
I wanted all three oleos to be Trailing link design so that it is far better for grass use - but really, they are the best system for landing gear used anywhere anyway.

The next thing to check was the wing joint and strength - especially seeing it is a known VERY weak point of this MB339.
It didn't take too long to work out what carbon fiber spar/s to add, and where. I decided on a 6mm spar and a 5mm spar. The 6mm is more forwards and bridges the two main landing gear mounts to form a subframe across the wing. The 5mm spar is more rearwards and much longer, thus both the 6mm and 5mm do the main wing section strengthening and the 5mm keeps going to give strength further out along the wing.

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Last edited by PeterVRC; Nov 26, 2015 at 07:08 PM.
Nov 29, 2015, 08:59 PM
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Aileron servos


I used my 'new' Print-Rite 3D printer to make up Servo Boxes to mount all the MB339 servo into. This makes them easily removable in future for maintenance. It is also far better - more robust and reliable - than just being glued into the foam!

Servo covers, that hold the servos into the box, will be 0.8mm alloy plates. I will make them later on.

The servo lead, right at the servo, is also coiled and stored in a foam gap to allow removing the servo with lead to 'spare' so you can cut and solder a new servo in if ever required.
I use the LEAST servo connectors possible in any aircraft. eg no servo extension sockets - all joins are soldered to be reliable!

Aileron Servos are Hobbyking HK15178B 13.5g Digital Metal Gear.

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Last edited by PeterVRC; May 29, 2016 at 09:09 AM.
Nov 29, 2015, 09:03 PM
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Elevator and Rudder servos


I cut/modded the Fin to have a Rudder - but I did not follow the sale lines as they are a complex shape. It is easier, and better really, to just be a straight line cut at the Rudder/Fin join.
I used 4 nylon pin type hinges.

All three servos (1 Rudder, 2 Elevators) are in 3D Printed servo boxes, as per the Ailerons. Again with the servo wiring 'coil' to allow future maintenance.

Once the Tailplanes and Fin are added to the Fuselage the servo leads will be extended to reach the RX area via soldering extension onto them.

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Nov 29, 2015, 09:05 PM
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Main landing gear connectors


Seeing you occasionally need to change a retract, I made an embedded servo socket for the retract lead. I don't like connectors, but a retract is not as critical as a flight surface, plus they fail more often than servos, so in this case it is worth using a socket for the extension run.

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May 28, 2016, 09:22 AM
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EDF setup


After some tossing up over the MB339 power system (EDF) I decided to run it on 8S - though 7S will also be possible and fine - using an ExtremeRC HET GRP housed Jetfan and a HET 650-1600kv motor. These are highly efficient and high power output from 8S.

Because of using 7S and 8S batteries, of 5000mAH capacity which are very heavy in total, I decided to move the fan rearwards to help balance it all out easier. I also did not like where the fan goes as it comes, plus it also gives more room up ahead to mount the ESC.
Moving it rearwards means it needs some extra work done.... but the stuff that that it needs is what I would rather have 'around' the EDF anyway!

I cut an underside hatch for EDF access and made some slots for 4mm thick plywood rails.
To make it somewhat easy to interface the rear of the EDF onto a thrust tube, I made a Basswood ply and Balsawood 'bulkhead'. This is about 14mm thick and is epoxied onto the internal foam bulkhead that is there. Thus the EDF butts up onto that, and the thrust tube butts up against the rear end of that bulkhead. This means the fan is a simple fit/remove setup and is independent of the thrust tube.

I have not decided exactly where the ESC is going yet....

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Last edited by PeterVRC; May 04, 2018 at 07:47 AM.
May 29, 2016, 09:08 AM
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Flaps


The Flap servos also use a 3D printed servo box.
Hobbyking HK15148B 19g Digital Metal Gear servos.

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May 29, 2016, 09:16 AM
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Aileron hinging change


I always hate the FlyFly stock idea of TAPE hinges. More so because all they do is bevel a control surface from ONE edge, which is still workable but just looks lousy. The main issue is the TAPE is truly lousy and dangerous to use really!

To alter the "Bevel from one edge" stock foam pieces you need to cut the bevel away and add balsawood 'faces' to the two meeting hinge faces. In this case on the Wing and the Aileron.
it is handy that the balsawood thickness required to 'replace' the foam bevel that needs to be cut off, also means you have material to put a "centered bevel" onto the Aileron, plus two nice robust faces for the pinned hinges to be glued into also.

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