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New Aermacchi MB339 2.5m from CModels Italy - minireview & build

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New Aermacchi MB339 2.5m from CModels Italy - minireview & build

Old 11-26-2020, 07:10 AM
  #1  
Edhamp
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Default New Aermacchi MB339 2.5m from CModels Italy - minireview & build

Introduction

The Aermacchi MB339 has for me always been a great subject for a RC scale Jet. Developed in the 1970s in Italy as a military jet trainer and light attack aircraft, the MB339 entered service with the Italian Air Force as well as many other countries, and is probably best known as the aircraft of choice for the Frecce Tricolori aerobatic display team. This classic looking aeroplane has all the right attributes as a possible choice for a first scale jet, ticking all the boxes. A large straight wing should mean a reasonable wing loading and predictable behaviour. Check!. A wide undercarriage with trailing legs promises good ground handling and potential grass field operation. Check!. Conventional layout with plenty of space inside promises easy installation and maintenance. Check! Plenty of scope for adding scale details according to preference. Check! A wide choice of full-size colour schemes from military workhorses to aerobatic stars. Check that box too!

If you are in the market for an MB339 then you may find yourself spoilt for choice. You will find examples in all scales and prices to suit just about any engine size from 20N upwards. You choice is further determined by the level of detail and materials used in the construction of your model and how much work you want to do yourself before heading out to the flying field.

There has always been a place in my hanger for a MB339. A favourite for some time was an example from Fei Bao which flew really nicely despite rolling out at some 19.5kg dry with all the bells and whistles (what can I say, I have a knack of building heavy!). This was followed by the smaller (and lighter!) 2x2m MB339 from C&C models in Italy, which incidentally is a distant relative of the Fei Bao MB339. C&C models has been responsible for giving us some really great, high quality RC jets over the years (Aermacchi types being a favourite subject). Recently there has been a change of name to Cmodels Italy and at the same time the introduction of a newly designed range of models built mostly in-house. The new 2.5m MB 339A is one of the first and spans, er, 2.5m. Cmodels claim a weight of 14-16kg for this model with turbines ranging from 120-160N (these days the turbine choice makes less of a difference to final flying weight as the latest generation engines in this thrust range are mostly similar in size and weight).

If my old Fei Bao MB339, which is slightly smaller than the new offerring from Cmodels, could shed 3 or 4kg to match then I am sure it would have positively floated away and certainly made landings a breeze.

In this day and age, it does not take very long for the first flying videos of any new RC model to appear on-line. if you seek out these videos in the usual places, as I guess you will have already done so if you have an interest in this jet, you will already know that it flies great (which is the least to be expected these days from any new model that enters this overcrowded market if it is to succeed).

So having convinced myself this was a model I needed in the hanger, and seeing that it was a reality with a prototype on display at the Cmodels stand at Jetpower 2019, I placed my order soon after that event and joined the waiting list. The model arrived this year and is now built but as yet unflown (thanks to you know what!). The chosen powerplant is the new KingTech 142G4. For me this was a leap of faith as normally I would be thinking maybe a 160-200 for a model of this size but I was assured by Bruno, the owner, designer and manufacturer that a 140 would be a great choice for comfortable scale flight. So who am I to argue!

Everything in the photos (apart from the turbine of course) came with the model as ordered, together with Electron retracts and scale legs/wheels plus lightweight pipe.
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Old 11-26-2020, 07:46 AM
  #2  
Edhamp
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Default A closer look and build options

As we all know the world became a different place in 2020 and despite everything, the model arrived safely, understandingly delayed but worth the wait. First impressions were beyond expectations, certainly the main components on unpacking felt very light yet rigid despite the size. Everything was neatly put together and finished with strong and neat glue fillets. There was evidence of useful reinforcement in all areas that would take the most stress and even the internal fuselage surfaces were painted in a textured stone effect paint finish popular with many builders. Certainly Cmodels have a great deal of expertise in making lightweight models and this is no exception. I am no muscle man but I have no problems picking up the completed model fully assembled on my own!

I chose a simpler RS45 colour scheme based on the MB339A full size prototype, which is a bright orange and white. Certainly this orange look would be nicely visible in flight and yet, despite the simplicity of this scheme compared, say to probably the more popular Frecce Tricolori scheme on offer from Cmodels (amongst other choices available to special order), it does work very well on this model. Compared to some factory painted models I have owned, the in house painting by Cmodels was nicely done, without being too heavily coated or over lacquered with sealer, thus keeping weight down. In addition to the normal markings, it came as a nice surprise to see various service nomenclature markings as standard on some of the hatches and maintenance points. A further nice touch is the incorporation of 3D printed parts within the fuselage moulding to replicate the various engine air intake louvers, grills, ducts as well has the various flush door handles. These details really looks sharp, much better than if simply moulded in. You also get various scale parts, including several hundred 3D printed dummy rivets, a distinct feature of the full size where the wings and tailplane meet the fuselage. If you do not fancy fitting these yourself (there are around five hundred so I am told!) then according to the Cmodels web site you can specify that they come factory fitted, with the option to upgrade to aluminium rivets (allthough bear in mind these large essentially engine panel bolts and washers are sometimes shown as painted in photos).

As standard, the model comes with the two large opening doors on the fuselage side for access to the engine bay, the engine and thrust tube being fitted into place before the two fuselage sections come together, the tail pipe being attached to the rear section. The fuselage is in two parts and the four fixing bolts are accessed through the same doors. You can specify which other doors and hatches, all located in scale positions, you want to open. It is better if this work is done before the model is factory painted (you can also order an unpainted model). It is useful having the large access panel hatch just behind the cockpit opening, and one of the forward nose doors, making for easier access to the nose gear and door servos. Incidentally, all the gear doors and access panels feature internal moulded scale panel detail, again it appears using 3D printed parts, something that is often omitted by other manufacturers. Also supplied are various useful bits and pieces of hardware including hatch magnets, control horns, M3 control rods and ball links of good enough quality for a model of this size as well as wooden servo mounting cradles the aileron servos which make installation easy.

Some of the other many available factory options include a working scale air brake under the fuselage (not specified for my model), and a scale cockpit. I also understand underwing and wing tip fuel tanks, will be available in the future. The vertical surfaces are moulded as part of the rear section so installing a rudder servo would require either a side hatch on the rudder to be opened out or small, double jointed hands and fingers to install the servo and linkages from inside! Not having the latter, it was much easier to specify a servo to be fitted during the manufacturing process (for which you could send in one of your own for Cmodels to install if you wished). The disadvantage of course is that should the servo fail it will be harder to replace without taking everything apart or cutting out a suitable hatch.
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Last edited by Edhamp; 11-26-2020 at 05:02 PM.
Old 11-26-2020, 08:33 AM
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Edhamp
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Default Ideal first scale jet?

A question I wanted to explore is would this MB339 make a good first scale jet or even, for that matter, a good all round jet, satisfying the same role in our RC jet world as it does in the real world, namely a good first step up from a basic RC jet trainer to an advanced trainer/scale jet! To do this we need to check a few more boxes. Ceretainly at a weight of around 16kg or less a model of this size with a large wing should have light wing loading for a scale jet making it nicer to fly and land. The all airex sandwich and composite materials used in construction also results in a light but strong model. Other design features such as single fuel tank, thanks to smaller engines (compared with three tanks in my old MB339) also help save weight, as does the surface skin hinged horizontal control surfaces. A first scale model should also be practical and easy to maintain and transport.

This MB339 is designed around electric retracts (actuators by Electron of Spain) but having said that there is no compromise as regards scale appearance with the nicely machined legs and wheels on offer as part of the UC package. A unique feature are the specially machined aluminium UC cradle mounts fitted outboard of the air intakes on the end of the wing root stubs. This means the fuselage section can stand on its wheels for ease of transport and assembly at the field. A further advantage is no visible UC fixings under the wing. So we can check a few more boxes for scale fans. So far so good but one box that remains unchecked relates to the the complexity of the retracts because the full size MB339 undercarriage has seven UC doors in total, five of which will need to be sequenced and to work reliably. Perhaps not ideal when it comes to choosing a first scale jet, but then who said this was going to be easy and messing about with retract systems goes with the territory if you are into scale RC models. More of this later.

A further plus for scale fans in that the control linkages for the ailerons, flaps and rudder are all mostly concealed with the aileron servos hidden behind scale access panels. So no unsightly, non-scale servo hatches, control horns, pushrods and screws visible externally. Check! In fact, as far as I can tell, this model does not require any additional non-scale openings or large hatches for access to the engine and radio and, as we shall see later, there are plenty of options for the installation of hidden switches, catches, dispaly panels etc. as well as other equipment which can be easily accessed without the inconvenience of having to remove the canopy and cockpit during start-up for instance.
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Last edited by Edhamp; 11-27-2020 at 02:17 AM.
Old 11-26-2020, 10:05 AM
  #4  
Airforce7
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Default

I think you are going to really like this model. I like the fact that they designed the main retract units to stay with the fuselage. I had a small version of the MB339 and the gear stayed with the wing when I removed it. Made it a little tricky to assemble it at the field as the model became unbalanced as you added one half of the wing. Your model looks really great and thanks for sharing your experience ordering the jet from this manufacturer.
Old 11-26-2020, 10:58 AM
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Default Putting it all together

Assembly and installation for a model of this size is fairly straightforward with nothing that would be out of the ordinary. The pre-cut mounts supplied for the aileron servos make for easy installation and removal. Similarly, provision has been made to fit standard sizes servos for the elevator, flaps and main gear door operation (the flaps are huge so use powerful servos here). The single, large fuel tank is mounted high in the fuselage supported on two formers supplied that need to be glued in. A couple of right-angle aluminium brackets were epoxied to the tank to secure it to the former. There is plenty of room in the fuselage, thanks to a minimal use of ducting, to mount the tank directly over the CG, which is just behind the wing tube, and thus in the ideal location.

The clear moulded canopy was cut and glued to the glass fibre frame and reinforced with epoxy. If you want a nice scale look, it helps if you run a thin fillet of black silicone sealant between the frame and canopy when the glue has set. Mask off the canopy and frame completely, leaving just a small gap between the solid frame edge and clear canopy. Next apply the sealant getting, it into any gaps and the smooth off with your finger to create a neat fillet. Remove the masking tape (it helps to use a quality tape with a smooth sharp edge) before the sealant has completely set to leave a sharp edge (a sharp scalpel blade can be used to tidy up any ragged edges. This looks just like the rubber seal on a real canopy. Take your time. It does not pay to rush this sort of work.

The canopy hatch is a simple home made rod and tube affair and is mounted behind the top access panel, which itself is held closed with magnets. The wings are secured from within the wheel wells using the supplied cap head bolts and mounts that are glued against the wing tube sleeve. I glued some knurled plastic threaded hand nuts onto the bolts to make them easy to tighten by hand and simplify wing installation in this confined space.

The forward nose hatch provides good access to this area so is really a must have option. The UC ply hard mounting plate for the Electron actuator is pre-installed, the whole assembly appears very solid and there appears to be carbon fibre cloth strengthening of the fuselage in this area. On my model the UC doors came pre cut and hinged. A set of wooden servo mounts for midi sized servos to operate the three nose leg doors are provided in the hardware pack. Again, a purely personal preference, but I decided to use small low profile wing type servos with side mounting lugs for this instead, being easily mounted in a confined location relative to the gear doors for a direct connection and taking up less room, as everything needs to fit in it’s own space without interference. The nose leg as supplied looks extremely well made and strong. Make sure that movement of the damper in the oleo is free from packing grease so that the leg fully extends on the suspension springs during retraction, otherwise the front door will be prevented from closing by the proud tyre.

Turbine installation is straight forward with the supplied mounts fitting neatly into the pre-installed engine formers. The KG142 has a diameter just over 95mm so fits easily with plenty of room. Make sure you pre-drill the mounts for the engine bolts before gluing them in. The best way is to attach the mounts to the engine first and then glue this as a single assembly and ensure that everything is properly lined up before the glue sets. Then when you remove the engine, the engine bolt holes will line up accurately with the mount. I did note that the engine sits high in the fuselage and as such the trust pipe has to angle down slightly to line up at the exit. Cmodels confirmed that this is correct and that test flying has proved this to be the best setup. The photos show the correct relative position of the pipe in the fuselage at the turbine end (centrally with the turbine) and at the exit, where it mounted on the former supplied so that it sits low at the outlet. The pipe supplied is a very nice lightweight affair. It is only about 50% double walled so make sure all components are well protected against radiant heat allthough I do not expect a problem as long as all wires etc are well clear and protected.
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Last edited by Edhamp; 11-26-2020 at 05:10 PM.
Old 11-26-2020, 02:16 PM
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Default Electronics installation

I decided not to use the large ply equipment tray provided. Instead I used two smaller trays, one up front mostly for the radio electronics, and one at the rear of the cockpit area for bubble trap and fuel and engine ancillaries. For me, a favourite choice of material for this is using lightweight 3mm foam PVC signage board. This is available in many colours and sizes, easy to cut, drill, takes small screws and glue with cyano and is generally fuelproof. Really there is so much room available in this model with easy access that you will little problem finding a home for everything but do not forget to allow room for the scale cockpit if you want one. It makes sense to put all the heavy stuff up front where possible. It is very likely that the model will require some weight in the nose to balance.

Equipment choice is a matter of personal preference but a model like this deserves a good quality electronics system to handle everything . I prefer to use Powerbox Powerbus systems wiring on larger models with or without SBus servos. One thing to bear in mind is that with five gear doors, you are likely to need some sort of gear sequencer if your radio does not have enough channels and/or built in sequencer mix. Having a Powerbox Royal available I decided this would be ideal. This would provide standard servo outputs including HV outputs, for direct connection as well Sbus outputs going to the tail section and wings. Plus the sequencer would take care of the door system. A good alternative if you do not want Sbus would be a Powerbox Mercury or the newer Powerbox Pioneer. The Electron GS200 control is also a good choice to go with these if you run out of channels as this will take care of all your gear sequencing needs with other benefits.

All wiring (with some important exceptions) from the Royal to the rear section and hidden in the central duct which is section of ordinary electrical cable mini-trunking connecting the front and rear trays. The turbine power supply cable as well as receiver and throttle cable to ECU are all routed separately and away from other wiring just in case. The model was also fitted with a Unilight 4 channel light system. All the wing Sbus servos, included the gear door, are connected using a single Powerbus SBus multiplex connector on the wing root. A second connector takes care of the lights.

Radio and turbine batteries are mounted on the front bulkhead and easily accessed as the instrument panel coving is easily removable. The powerbox sensor switch and readout are under the front hatch. The top hatch is ideal for a fuel tap and somewhere to plug in and mount turbine GSU if required on board.
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Last edited by Edhamp; 11-26-2020 at 05:13 PM.
Old 11-26-2020, 02:32 PM
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Originally Posted by Airforce7 View Post
I think you are going to really like this model. I like the fact that they designed the main retract units to stay with the fuselage. I had a small version of the MB339 and the gear stayed with the wing when I removed it. Made it a little tricky to assemble it at the field as the model became unbalanced as you added one half of the wing. Your model looks really great and thanks for sharing your experience ordering the jet from this manufacturer.
Yes, thank you, there are some nice models coming out of CModels. I agree having the retracts mounted on the fuselage does make assembly easier and safer on the ground. However, in some repects it does make transporting the model easy but it is not practical to retract the gear for transport as the gear legs and door could get damaged and take up a lot of space sticking out . I also did not like the idea of the model bouncing about on its springs in the back of the car on longer trips so have made a support cradle that also means I can assemble the model on the ground and retract the legs to test.
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Old 11-26-2020, 03:31 PM
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Default Retract installation - the tricky bit!

The gear system fitted easily on the pre-installed wood and metal mounts but there are a couple of considerations to watch out for. The nose gear Electron Evo40 actuator sits on TOP of the mount and, as already mentioned, the oleo needs to fully extended when retracting. There is little room for error but it is not a difficult install and is well thought out, including the steering servo installation.

I was worried that the Electron Actuators would have their work cut out as the scale legs, wheels and tyres, beautifully made as they are especially for the Cmodels MB339, may have been on the heavy side but certainly I have had no problems at all on the ground (using a 2S 25C lipo). I am confident they will also work as well in the air.

The main legs alligned and retracted nicely into the well wheels and there was no adjustment necessary with the mounts as supplied so clearly this had been checked in the factory before shipping. With the wheels retracted, space can be tight as regards the linkage for the flaps and main gear door, as these servos are also side mounted in the wheel wheel, which is great for access, but could interfere with the tyre when retracted. The servo mounts are precut for you making installation easier. You may have a problem if your chpoice of servo, servo arm and pushrod connectors results in the linkage extending the servo profile much beyond the surface mounting location . I decided that the gear door servo should be a little further back then the mount would allow so I modified this to recess the servo by a few mm for that vital extra clearance. I could have also sourced some alternative servos with a smaller profile above the mounts, but my solution was cheaper!

Again, there is not a lot of clearance when the main legs are fully extended between the wheel and the gear door (see photo). Check that you will not have a problem here. I understand that this may only be a problem with legs sent out with the first batch of models and it is simple enough to restrict their movement a little if necessary to prevent full extension when unloaded.

Probably the most frustrating part of this build so far was getting the main gear door and leg linkage correctly alligned so that the door, mounted on the wing root, opens and closes with the leg as well as sits flush with the wing, which is a separate fit. No doubt there are other solutions but mine is as shown using a short linkage which rotates through almost 180 degrees as the gear moves. The door has to be tight to the leg when down. A lot of trial and error is involved and to get the door to sit flush. There is little margin for error if you want to avoid any resistance during operation. The photos will help get you on the right track and Cmodels supply a really really neat carbon fibre based clamp to connect a small link to the main le . Make sure this is orientated correctly. Without this little device the job would be much harder.
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Last edited by Edhamp; 11-26-2020 at 05:19 PM.
Old 11-26-2020, 04:24 PM
  #9  
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Default Final jobs and some detailing - the fun bits!

I ordered a cockpit from Cmodels. This is mostly made up of 3d printed parts in a glass fibre tub. Whilst the ejection seats were nicely made and detailed with warning nomenclature and seat belts etc , the instrument panels and controls where not that great for the price of the unit. However a little extra work detailing and painting produded a better if not 100% scale result. A lightweight pilot was sourced from Premier Pilots and sutably attired in Frecce Tricolori aerobatic display team flying suit.

CModels have put a lot of work into detailing all the panels and rivets on the original master moulding (see their Facebook page), some of this detail can be lost with painting and over time moulds can wear. I used some micro screws, sourced from a well know auction site, to enhance the canopy frame bolts, various inspection and maintenance panel screws, as well as other detail. I gave up counting after the first five hundred! The large distinctive panel fastners you can see on an MB339 at the wing and tail roots are supplied as 3d printed parts which is a nice touch, but I think these are a little too thick so I painstakingly sanded each on down a little and used a small countersunk screw to fix just as on the full size to represent the cup washers. On pictures I have seen of the prototype, these fastners are mostly painted but in service this paint is easily worn away and the fastners soon weathered and dirty. At the time the pictures were taken this work was still incomplete. There are several hundred! Before anyone points it out, also missing are the fuselage fin strakes still to fitted! This model really should have the tip tanks as fitted to the original but these were not available at the time of writing.

The model is lightly weathered with appropriate streaks and the panel and rivet detailed was futher highlighted with a dark grey wash and some of the techniques detailed in my article in RCJI Aug/SEP 2020. Being mostly white, it really helps the detail to stand out without looking to heavy. Remember less is more!
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Last edited by Edhamp; 11-26-2020 at 05:25 PM.
Old 11-26-2020, 04:41 PM
  #10  
Edhamp
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Default Conclusions

So in the end what is the all important final weight! Well I am very pleased to report about 16.5 kg dry (including some 700g lead in the nose to balance), cockpit and pilot.

Overall I am very impressed with the thought and attention to detail that has gone into producing this model, the lightness of construction without compromise in weight, the quality of manufacture, scale details, accurate shape, lovely retracts all electric, practical features and ease of access and maintenance. Yes there are a couple fo small niggles but compared to some other jets I have built, this one is top of the class. Well done CModels!

The model is ready for test flight but this will have to wait the end of another lockdown and possibly not until next year with better weather.

The following recomendations for the various control throws etc are direct from CModels as a good starting point. It may be the CG could be further back by up to 10mm with less weight in the nose depending on preference which I will decide once flown. The model should need little or no elevator compensation with flaps at landing speeds and depending on CG.

CG Rear of wing tube
Elevators +25-20mm
Aileron +- 22mm
Flaps at take off 30mm
Flap landing 90mm
Aibrake 65


Thanks for looking. To be continued!
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Last edited by Edhamp; 11-27-2020 at 06:08 AM.
Old 11-29-2020, 10:12 AM
  #11  
martin.lees1
 
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Looking Good Ed,
Look forward to seeing it in the flesh,

Rgds Martin.
Old 12-06-2020, 05:35 AM
  #12  
JohnMac
 
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You're the man for MB339's Ed. Love the colour scheme. Looking good ED.
John
Old 12-15-2020, 05:32 AM
  #13  
Edhamp
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Smile

Thanks for your comments guys. Model is 95% complete and ready for final checks . Had a problem with the rear fin strakes and waiting for replacements which are delayed waiting production of new mould so they should be better.
Old 12-15-2020, 06:10 AM
  #14  
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Default Door Magnets

One thing I forgot to mention but you may consider the fitting of some main gear door magnets. Whilst all electric retracts are great, when it comes to servo operated large doors on scale models, it is not always possible to set up your servo/door linkage with a good moment arm for opening and closing in comparson with say using air cylinders on an air operated system. So even with high torque servos, large doors could be sucked open in flight and the short linkage arms provide little resistance and tends to amplify any play in the system. So rather then relying on the servo to keep the door closed which essentially means loading the servo with consequences on reliability and current draw, a couple of small powerfull magents help to keep things together when the door is closed.

I had a problem with my smaller 2x2 MB 339 doors coming open in flight with essentially similar servo operated setup (see photos) solved by fitting magnets and taking the load of the servos. One thing is that the doors on this MB339 are nice and sturdy and the internal moulding makes then thick ennough to fit the magnets out of sight on the edge. For the little effort involved worth doing this now for the extra security even if they may not be needed on this model.

I did consider fitting electric door actuators like the type produced by Electron but note that these operate at 6V only (so if you are HV you will need separate power supply) and it looked there would be issues with limited space and geometry options not to mention quite a high price!. I would be interested to see if anyone else has used these in a similar situation.
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Old 12-19-2020, 01:02 AM
  #15  
BashaBolla
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Great looking plane Ed.....fingers crossed you can get it in the air soon !...but I guess the 27th will be all about final fiddling and faffing ?
Richard
( as it will be for my new Hunter by the way.....all ready to go...fingers twitching in anticipation !! )
Old 12-19-2020, 05:55 AM
  #16  
Dansy
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The Linear actuators which are 6v operates quite fine as well on the MKS SBEC 2A that take 8.4v to 5.0v, Im using these in a current build for the speed brake, Drag Chute, canopy and gear doors.....

MKS Servos USA :: Servo Horns and Other Products :: SBEC - 2
Old 12-20-2020, 03:06 PM
  #17  
Edhamp
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Thanks Daniel. That would be another option. I have used these linear actuators from Actuonix in the past for air brakes also . The L6 works just like a standard 3 wire servo ( 6V operation) so unlike the Electron actuators they are fully proportional.

https://jettstreamuk.co.uk/l16/l16-r...-linear-servos

Ok if you have the space as they are quite bulky but have longer stroke lengths from 50- 140mm (20-30mm for the slimmer Electrons) ideal for sliding cockpits.
Ed
Old 12-25-2020, 04:17 AM
  #18  
stempi12
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Hi,
I am looking to purchase this mb339 and I am very curious what its his ready to fly weight.

Oskar
Old 12-26-2020, 04:43 AM
  #19  
Edhamp
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Hi Oskar

As mentioned mine came out at approx 16.5Kg dry which is very good for a scale model this size. Much will depend on your chosen equipment, battery locations and cg but you will probably always need some weight on the nose.

Ed

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