RE: SkyMaster MB339 Build Thread
 

To be honest I hadn't a clue when they turned up either, they ended up being a hydraulic system for running the gear. Now although there are a few parts to fit - not an issue with a big plane, it seems to work well and gives a very scale like working.

marc

RE: SkyMaster MB339 Build Thread
 

If I would have had the cockpit earlier I would have planned to not put items in the center of the tray's. A plane this big I would not have thought that something like that would come into play but it certainly does!

RE: SkyMaster MB339 Build Thread
 

Thats a lot of balast in the nose....I am still in build, any suggestions toget weight down? I am going full C/P so that will add weight....

RE: SkyMaster MB339 Build Thread
 

I have a full cockpit kit too, doesn't add much weight though. The problem is that there is not a lot of room to mount the batteries up front. In the nose gear well there is no room for the batts and I had originally moved the turbine all the way forward but the pipe was too short so I had to move it an inch backwards cause the heat was blistering the rear, so that added nose weight.

RE: SkyMaster MB339 Build Thread
 

Marc,

Based upon Yr findings I took a long shot on my CG... DARN !! (counts as YIKES...)
With most equipment and engine temporarily installed but less tanks I had to hook up already 900 grams to the nose... I think the killer is the double sided thrust tube.

For those who need a tip on CG-ing big airplanes, here's how I do it.

Long time ago I made two wooden beams which can be bolted together by means of 3 (who translates draadeind for me....pieces of threaded metal rods), with winged nuts (vleugelmoeren) at both ends.
For each big model I make a two dedicated plates that can be clamped in between the two beams at any location. The plates need to be high enough to be able to cycle the gear.
Topside of the plates have to be made conform the underside of the wing near the CG point. Normally a flat or slightly canted topside (to fit the dihedral) will do, but for the MB I had to do some contouring to suit the underside. This forms an effective seesaw.

Come to speak of it, due to the swept back wing I might have to reduce the contact area to a single point (mabe a screw that fits in the wing retaining hole) as my setup in this case gives a false reading due to that sweepback.
Anyways, for straight wings the CG seesaw works great, to get even preciser readings on some planes I modified the contact topside with a half side of a wooden dowel.

Here are some pics, the tempex blocks are of course only there for safety during the weighing.

RE: SkyMaster MB339 Build Thread
 

Hallo.

I'd like to install smoke in my 339, and I like to use the subwing-tank as real smoke tank.

But I have some problem to fix the pylons under the wing... I don't understand the istruction very well.

Any ideas ??

Thanks

RE: SkyMaster MB339 Build Thread
 

Richard

I calculated the CG at 25% of MAC at 10mm behind the wing tube. First flight was slightly tail heavy so I reverted to the reccomended CG which is on the centre of the wing tube, the model flys perfectly at this setting. To get the nose weight as far forward as possible I made up a lead weight and put a screw through the nose into the weight and filled the screw hole, I then glued lead strips to the inside of the fuselage above the nose gear, I placed both of my rx batteries to one side of the nose gear and the ecu battery on the other side. You will not need any elevator mixing with flap, I started with about 4mm down but this caused the model to dive so I removed all of it. My dry weight was 19.95Kg just 50 grams under the limit for WJM models.

John

RE: SkyMaster MB339 Build Thread
 

Hi John,

Tks for the tip on mixing, I tend to do this only after actually flying and testing flap.

Btw did you install the speedbrake as well?
If have two ideas for the control of it:
A/ Make a separate channel for it. Nice, but will You use it during normal flight?
B/ Make it extend in the last part of the flap selection. I guess they come in handy to slow down for landing. Also easy when making touch and goes, just one lever to operate to get flaps all the way(or partly) up and air brake in.

I have heard rumours that the 1/1 MB can crank the airbrake out inflight to a more steep position, but it retracts partly as the gear is lowered to have enought ground clearance. Nice challenge to get this done in the model, but is too complex for my wishes.

I dunno if those modern transmitters have a feature that provides a CONDITION for the airbrake: suppose You make a go-around or baulked landing, you want to get rid of the airbrake as soon as possible. So as soon as you get about let's say 95% of throttle, the brake will retract. So airbrake only with flap >90% AND throttle is <95%.
My FC28 cannot handle this, a workaround would be however to change the modelcondition past 95% throttle into one with airbrake retracted always. I tried this before however on another model, but as the airbrake was assigned to channel 9 or 10, it does not work, as these channels are not changed by changing model condition. Maybe with the MB plus weatronic I can assign the airbrake to one of the first 8 channels and get this trick done.

Getting lead into the nose isn't the problem, I fly large gliders with which we do the following trick:
I press the nose of the plane into sand, a little humid so that is does not collapse into the hole.
Then heat up lead in an old pan, and pour it into the hole.
After cooling this block fits the nose area almost perfectly, the difference in form (because You have a copy of the outside and not the inside) is easily filled with silicon kit, which is a great glue and also forms a barrier so that the lead does not touch the fuse directly. In the end and with some patience the lead still can be removed with a curved knife.

The quantity of the lead should be slightly less than required. If theconical block is too heavy, a slice can be sawed off with an iron saw, but do use petroleum as e greasing medium, otherwise it will take a long time....

A slight mod can be, before You pour in the lead, place a long screw into the sand, which will then later be embedded in the lead form. It can be used to attach lead circular plates to adjust CG.

As the weather is nice, I might make one today and post pics.

Anyways, SM should take care:
A/ Try to get the tail lighter. I think a single wall thrusttube will improve things a lot CG wise, the fuse is wide enough to have sufficient cooling.
B/ Warn customers to get all items a fwd as possible. If I would have known this beforehand, I would have chosen NC cells iso Lipo.
Heavier(in this case a benefit), cheaper and easier to charge, less danger. Now I have 2 lipos for the Weatronic and one lipo engine bat. For lighting systemI will install therefore a good old NC.

RE: SkyMaster MB339 Build Thread
 

For those of you that are already flying the MB-339, how are you storing the wings after flying ? I was thinking of a Wing Tote bag but I don't know the size I would need (42" or 50")

RE: SkyMaster MB339 Build Thread
 

Hola sr Gonzalo,
If transportation is not an issue, You can make a wooden transport box for it.
You can make one in less than one day, see pics.
I use light, cheap plywood for the sides and about 12mm thick wood for the sideframe.
I use it for transportation and storage. It has a handle on it and rollers at the underside
IUt open like a book.
The inside I covered with foam plus some velcro tape to hold the wings.

Alternatively You can make bags Yourself, we do it all the time for lighter wings.
I wrote a thread on a dutch forum, You cannot read it, but pics are enough I guess.
http://www.modelbouwforum.nl/forums/...gelzakken.html

RE: SkyMaster MB339 Build Thread
 

Richard

I am not running with the airbrake at the moment, I think I will install it as the model does tend to glide on a bit. I will configure it to operate with the flaps and use a throttle mix to raise it automatically in the event of a go-round. This is no problem to assign with the 14MZ tx.

John

RE: SkyMaster MB339 Build Thread
 

Richard:

Thanks for the tip Richard and great looking box, but the truth is that I prefer a bag that I can hang from my shoulder. Do you have the length and width of each of the wings ? With that info I can search for the bag. My plane should arrive the first days of October and I want to have everything I need on hand ;)

RE: SkyMaster MB339 Build Thread
 

John, I have the 339....no airbrake....I did mix about 5/8" to 3/4" up aileron deflection (crow) with full flaps......it's also on a switch on my 12Z so I can turn it off....use the "offset" mix in your 14MZ and the limits screen to prevent the servo from binding when crow is active and u need to use aileron......a definate improvement in the drag config on the 339....aileron effectiveness doesn't seem to be degraded at all while on final and the crow acts as additional washout in the wing......works very wel and took less than 5 minutes to program the 12Z....

RE: SkyMaster MB339 Build Thread
 

Love your cammo scheme! Makes a nice change from the Italian display team.

John

RE: SkyMaster MB339 Build Thread
 

Was at JetPower in Ahrweiler (Germany) this weekend, and saw the MB fly, although that is the Airworld version, bigger als the SM one. Built VERY lightly and it made some incredible low speed, full flap passes at an AWESOME low speed for such a big airplane. I gues my MB will not go that slow due to a heavier wing loading, especially with all that lead up front!!

I am looking at building myself a smoke tank in the area just above the speedbrake. It will feature a "donut hole" in the middle to allow the airbrake cylinder to pass through.
Does anyone know a thread on the subject how to make (Kevlar)fueltanks?

RE: SkyMaster MB339 Build Thread
 

Richard

The wing loading on the big Airworld MB339 must be very low as it is designed to be under the 20KG dry weight limit for WJM models. I don't know how they have managed this as the Skymaster / Feibao 339's are right on the limit, must be very thin glass layups.

John

RE: SkyMaster MB339 Build Thread
 

Richard,

I made a smoke tank for the MB I built recently (build thread on this forum) did not use kevlar, just glass cloth and resin, works fine and quite simple to make (a little time consuming though!)

marc.

RE: SkyMaster MB339 Build Thread
 

John.
The only way to achieve this is to reduce glass/epoxy. But wel all know that this comes at a price, indeed I did not see the Airworld Macchi's do anything at high-G, like flickrolls, square loops etc. (no Dave Shulman/Ultra Bandit style flying with these I guess)
Looking at my SM MB it gives me a sturdy impression, a plane that can handle a beating.

Very contradictionary, heavier airplanes take agressive stalls better as lighter ones because they outstall before buidling up too much G's. Or as they say: heavier planes outstall before they outbreak.
Most planes I witnessed folding wings were light trainer types! The combo of a light plane with an obviously weaker construction is a bad one.

Stalls have a bad name in aviation, but they do have a good side, they are a kind of "relief valve" for high-G manouvres...Any fullsize airplane is certified with different Va speeds (manouvring speed), the heavier you are loaded, the higher the speed You can use full and abrupt control forces.

Anyhow, I repeat my advise to SM to make the tail section lighter. I did talk to Anton at JetPower, he also needed some 600 grams extra nose weight, wonders how he got there...lead receiver batteries? :) And we all know there is sometimes a huge difference in the pre-production models the company flies, and the ones we get....
Also the building instructions (or whatever You'd call the scantily directives that come with it) should warn for a heavy tail.

RE: SkyMaster MB339 Build Thread
 

marc s, what's the red heat shield wrapped around your wires and where'd u get it?

RE: SkyMaster MB339 Build Thread
 

Its a glass fiber silicone treated heat sleeving which I get from a hobby shop although have found it on a google search from a company in the UK so should be available in your neck of the woods too. Have attached a link for product reference etc - its great stuff and works a treat too, you can 'clip' it to fuselage sides with a small drop of Cyano which bonds very well...

[link]http://www.sleeveit.co.uk/productcat.php?menu_id=15[/link]

marc

RE: SkyMaster MB339 Build Thread
 

Thanks....:)

RE: SkyMaster MB339 Build Thread
 

Finally found time again to continue the build, almost completed the tail section now, pics will come.
Weight does not look good, over 3 kgs fully installed plus thrusttube for the tail section alone....

Did look through the internet to find drawings on the 339, I did find and order a book though, but will take a while before I get it.
In the meantime anybody has a good 3-view available?
I like to know the angle at which the "strakes" (the flat plates below the stabiliser) are bolted to the fuselage. Ideally they would be 90 degress, but sometimes they "flatten" them in order to have sufficient ground clearance.
Studying pics I also noted a "bump" in between those strakes. Might be a "tail bumper" to protect for too high rotation or landing attitudes. Might be wise to add a functional scale one too...
Am also interested in the axact location of the wing fences. Looks like the big one is lined up with the flap/aileron split, but also need to know the location of the smaller ones

RE: SkyMaster MB339 Build Thread
 

Richard

PM me your e-mail address and I will send you a three view, unfortunately I don't have a tail view but you can see the angle of the ventral fins in the front view. There is a tail bumper between the fins. I made mine up with 1/16" glass board sandwiched between 1/8" hard balsa.

John

RE: SkyMaster MB339 Build Thread
 

Richard these might help although the measurements will need to be 'worked out', these items were pre-fitted by the fuselage builder.

There is a 'bump' in between the two strakes for that purpose, one of the pics shows the item on the full sized MB339.

marc.

RE: SkyMaster MB339 Build Thread
 

Marc,

does sleeveit have any adverse effect on servo cables that you are aware of? I have got a tech sheet from the company and it mentions something called "" Dielectric Strength"" - which beats me, and Wikipedia leaves me more confused. In short, does its use mess with the signal to servos?

Thanks

Sperx